HTTPbis Working Group                                   R. Fielding, Ed.
Internet-Draft                                                     Adobe
Obsoletes: 2145,2616 (if approved)                             J. Gettys                         Y. Lafon, Ed.
Updates: 2817 (if approved)                               Alcatel-Lucent                                          W3C
Intended status: Standards Track                         J. Mogul
Expires: July 7, 2012                                                 HP
                                                              H. Frystyk
                                                               Microsoft
                                                             L. Masinter
                                                                   Adobe
                                                                P. Leach
                                                               Microsoft
                                                          T. Berners-Lee
                                                                 W3C/MIT
                                                           Y. Lafon, Ed.
                                                                     W3C
                                                         J. Reschke, Ed.
Expires: September 13, 2012                                   greenbytes
                                                         January 4,
                                                          March 12, 2012

        HTTP/1.1, part 1: URIs, Connections, and Message Parsing
                   draft-ietf-httpbis-p1-messaging-18
                   draft-ietf-httpbis-p1-messaging-19

Abstract

   The Hypertext Transfer Protocol (HTTP) is an application-level
   protocol for distributed, collaborative, hypertext information
   systems.  HTTP has been in use by the World Wide Web global
   information initiative since 1990.  This document is Part 1 of the
   seven-part specification that defines the protocol referred to as
   "HTTP/1.1" and, taken together, obsoletes RFC 2616 and moves it to
   historic status, along with its predecessor RFC 2068.

   Part 1 provides an overview of HTTP and its associated terminology,
   defines the "http" and "https" Uniform Resource Identifier (URI)
   schemes, defines the generic message syntax and parsing requirements
   for HTTP message frames, and describes general security concerns for
   implementations.

   This part also obsoletes RFCs 2145 (on HTTP version numbers) and 2817
   (on using CONNECT for TLS upgrades) and moves them to historic
   status.

Editorial Note (To be removed by RFC Editor)

   Discussion of this draft should take place on the HTTPBIS working
   group mailing list (ietf-http-wg@w3.org), which is archived at
   <http://lists.w3.org/Archives/Public/ietf-http-wg/>.

   The current issues list is at
   <http://tools.ietf.org/wg/httpbis/trac/report/3> and related
   documents (including fancy diffs) can be found at
   <http://tools.ietf.org/wg/httpbis/>.

   The changes in this draft are summarized in Appendix C.19. C.20.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on July 7, September 13, 2012.

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   document authors.  All rights reserved.

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   Contributions published or made publicly available before November
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   than English.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  6
     1.1.  Conformance and Error Handling . . . . . . . . . . . . . .  7
     1.2.  Syntax  Requirement Notation . . . . . . . . . . . . . . . . . . . . .  7
       1.2.1.  ABNF Extension: #rule  . . . . . . . . . . . . . . . .  8
       1.2.2.  Basic Rules
     1.2.  Syntax Notation  . . . . . . . . . . . . . . . . . . . . .  9  7
   2.  Architecture . . . . . . . . . . . . . . . . . . . . . . . . .  9  7
     2.1.  Client/Server Messaging  . . . . . . . . . . . . . . . . . 10  7
     2.2.  Message Orientation  Connections and Buffering Transport Independence . . . . . . . . . .  9
     2.3.  Intermediaries . . 11
     2.3.  Connections and Transport Independence . . . . . . . . . . 12
     2.4.  Intermediaries . . . . . . . . . .  9
     2.4.  Caches . . . . . . . . . . . . 12
     2.5.  Caches . . . . . . . . . . . . . . 12
     2.5.  Conformance and Error Handling . . . . . . . . . . . . 14 . . 12
     2.6.  Protocol Versioning  . . . . . . . . . . . . . . . . . . . 15 13
     2.7.  Uniform Resource Identifiers . . . . . . . . . . . . . . . 17 15
       2.7.1.  http URI scheme  . . . . . . . . . . . . . . . . . . . 18 16
       2.7.2.  https URI scheme . . . . . . . . . . . . . . . . . . . 19 17
       2.7.3.  http and https URI Normalization and Comparison  . . . 20 18
   3.  Message Format . . . . . . . . . . . . . . . . . . . . . . . . 21 19
     3.1.  Start Line . . . . . . . . . . . . . . . . . . . . . . . . 21 19
       3.1.1.  Request-Line  Request Line . . . . . . . . . . . . . . . . . . . . . 22 20
       3.1.2.  Response Status-Line  Status Line  . . . . . . . . . . . . . . . . . 23 . . . . 21
     3.2.  Header Fields  . . . . . . . . . . . . . . . . . . . . . . 23 21
       3.2.1.  Field Parsing  Whitespace . . . . . . . . . . . . . . . . . . . . 25 . . 23
       3.2.2.  Field Length . Parsing  . . . . . . . . . . . . . . . . . . . . 25 23
       3.2.3.  Common  Field ABNF Rules Length . . . . . . . . . . . . . . . 26
     3.3.  Message Body . . . . . . 24
       3.2.4.  Field value components . . . . . . . . . . . . . . . . 25
       3.2.5.  ABNF list extension: #rule . 27
     3.4.  Handling Incomplete Messages . . . . . . . . . . . . . 26
     3.3.  Message Body . . 30
     3.5.  Message Parsing Robustness . . . . . . . . . . . . . . . . 31
   4.  Message Routing . . . . . 27
       3.3.1.  Transfer-Encoding  . . . . . . . . . . . . . . . . . . 31
     4.1.  Types of Request Target 27
       3.3.2.  Content-Length . . . . . . . . . . . . . . . . . 31
     4.2.  The Resource Identified by a Request . . . 29
       3.3.3.  Message Body Length  . . . . . . . . 33
     4.3.  Effective Request URI . . . . . . . . . 30
     3.4.  Handling Incomplete Messages . . . . . . . . . . 34
   5.  Protocol Parameters . . . . . 32
     3.5.  Message Parsing Robustness . . . . . . . . . . . . . . . . 35
     5.1. 33
   4.  Transfer Codings . . . . . . . . . . . . . . . . . . . . . 35
       5.1.1. . . 33
     4.1.  Chunked Transfer Coding  . . . . . . . . . . . . . . . 36
       5.1.2. . . 34
     4.2.  Compression Codings  . . . . . . . . . . . . . . . . . 38
       5.1.3.  Transfer . . 36
       4.2.1.  Compress Coding Registry  . . . . . . . . . . . . . . . 39
     5.2.  Product Tokens . . . . 36
       4.2.2.  Deflate Coding . . . . . . . . . . . . . . . . . . 39
     5.3.  Quality Values . . 36
       4.2.3.  Gzip Coding  . . . . . . . . . . . . . . . . . . . . 40
   6.  Connections . 36
     4.3.  TE . . . . . . . . . . . . . . . . . . . . . . . . 40
     6.1.  Persistent Connections . . . . 36
       4.3.1.  Quality Values . . . . . . . . . . . . . . 40
       6.1.1.  Purpose . . . . . . 38
     4.4.  Trailer  . . . . . . . . . . . . . . . . . 40
       6.1.2.  Overall Operation . . . . . . . . 38
   5.  Message Routing  . . . . . . . . . . 41
       6.1.3.  Proxy Servers . . . . . . . . . . . . . 39
     5.1.  Identifying a Target Resource  . . . . . . . 42
       6.1.4.  Practical Considerations . . . . . . . 39
     5.2.  Connecting Inbound . . . . . . . . 45
       6.1.5.  Retrying Requests . . . . . . . . . . . . 39
     5.3.  Request Target . . . . . . 46
     6.2.  Message Transmission Requirements . . . . . . . . . . . . 46
       6.2.1.  Persistent Connections and Flow Control . . . . 40
     5.4.  Host . . . 46
       6.2.2.  Monitoring Connections for Error Status Messages . . . 46
       6.2.3.  Use of the 100 (Continue) Status . . . . . . . . . . . 46
   7.  Miscellaneous notes that might disappear . . . . . . . . . . 42
     5.5.  Effective Request URI  . 48
     7.1.  Scheme aliases considered harmful . . . . . . . . . . . . 48
     7.2.  Use of HTTP for proxy communication . . . . . 43
     5.6.  Intermediary Forwarding  . . . . . . 49
     7.3.  Interception of HTTP for access control . . . . . . . . . 49
     7.4.  Use of HTTP by other protocols . . 44
       5.6.1.  End-to-end and Hop-by-hop Header Fields  . . . . . . . 45
       5.6.2.  Non-modifiable Header Fields . . . . . . . . . . 49
     7.5.  Use of HTTP by media type specification . . . 46
     5.7.  Associating a Response to a Request  . . . . . . 49
   8.  Header Field Definitions . . . . . 47
   6.  Connection Management  . . . . . . . . . . . . . . . 49
     8.1. . . . . . 47
     6.1.  Connection . . . . . . . . . . . . . . . . . . . . . . . . 49
     8.2.  Content-Length 47
     6.2.  Via  . . . . . . . . . . . . . . . . . . . . . . 51
     8.3.  Host . . . . . 49
     6.3.  Persistent Connections . . . . . . . . . . . . . . . . . . 50
       6.3.1.  Purpose  . . . . 51
     8.4.  TE . . . . . . . . . . . . . . . . . . . 50
       6.3.2.  Overall Operation  . . . . . . . . . 53
     8.5.  Trailer . . . . . . . . . 51
       6.3.3.  Practical Considerations . . . . . . . . . . . . . . . 52
       6.3.4.  Retrying Requests  . 54
     8.6.  Transfer-Encoding . . . . . . . . . . . . . . . . . 53
     6.4.  Message Transmission Requirements  . . . 54
     8.7.  Upgrade . . . . . . . . . 54
       6.4.1.  Persistent Connections and Flow Control  . . . . . . . 54
       6.4.2.  Monitoring Connections for Error Status Messages . . . 54
       6.4.3.  Use of the 100 (Continue) Status . . . . . . 55
       8.7.1.  Upgrade Token Registry . . . . . 54
       6.4.4.  Closing Connections on Error . . . . . . . . . . . 56
     8.8.  Via . . 56
     6.5.  Upgrade  . . . . . . . . . . . . . . . . . . . . . . . . . 57
   9. 56
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 58
     9.1.
     7.1.  Header Field Registration  . . . . . . . . . . . . . . . . 58
     9.2.
     7.2.  URI Scheme Registration  . . . . . . . . . . . . . . . . . 59
     9.3. 58
     7.3.  Internet Media Type Registrations  . . . . . . . . . . . . 59
       9.3.1.
       7.3.1.  Internet Media Type message/http . . . . . . . . . . . 59
       9.3.2.
       7.3.2.  Internet Media Type application/http . . . . . . . . . 61
     9.4. 60
     7.4.  Transfer Coding Registry . . . . . . . . . . . . . . . . . 62
     9.5.  Upgrade Token Registration . . 61
     7.5.  Transfer Coding Registrations  . . . . . . . . . . . . . . 62
   10. Security Considerations  .
     7.6.  Upgrade Token Registry . . . . . . . . . . . . . . . . . . 62
     10.1. Personal Information
     7.7.  Upgrade Token Registration . . . . . . . . . . . . . . . . 63
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 63
     10.2.
     8.1.  Personal Information . . . . . . . . . . . . . . . . . . . 63
     8.2.  Abuse of Server Log Information  . . . . . . . . . . . . . 63
     10.3.
     8.3.  Attacks Based On File and Path Names . . . . . . . . . . . 63
     10.4. 64
     8.4.  DNS-related Attacks  . . . . . . . . . . . . . . . . . . . 63
     10.5. Proxies 64
     8.5.  Intermediaries and Caching . . . . . . . . . . . . . . . . . . . 64
     10.6.
     8.6.  Protocol Element Size Overflows  . . . . . . . . . . . . . 64
     10.7. Denial of Service Attacks on Proxies . . . . . . . . . . . 65
   11.
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 65
   12. 66
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 66
     12.1. 67
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 66
     12.2. 67
     10.2. Informative References . . . . . . . . . . . . . . . . . . 67 68
   Appendix A.  HTTP Version History  . . . . . . . . . . . . . . . . 69 70
     A.1.  Changes from HTTP/1.0  . . . . . . . . . . . . . . . . . . 70 71
       A.1.1.  Multi-homed Web Servers  . . . . . . . . . . . . . . . 70 71
       A.1.2.  Keep-Alive Connections . . . . . . . . . . . . . . . . 71
     A.2.  Changes from RFC 2616  . . . . . . . . . . . . . . . . . . 71 72
     A.3.  Changes from RFC 2817  . . . . . . . . . . . . . . . . . . 73
   Appendix B.  Collected ABNF  . . . . . . . . . . . . . . . . . . . 72 73
   Appendix C.  Change Log (to be removed by RFC Editor before
                publication)  . . . . . . . . . . . . . . . . . . . . 75 76
     C.1.  Since RFC 2616 . . . . . . . . . . . . . . . . . . . . . . 75 76
     C.2.  Since draft-ietf-httpbis-p1-messaging-00 . . . . . . . . . 75 76
     C.3.  Since draft-ietf-httpbis-p1-messaging-01 . . . . . . . . . 77 78
     C.4.  Since draft-ietf-httpbis-p1-messaging-02 . . . . . . . . . 78 79
     C.5.  Since draft-ietf-httpbis-p1-messaging-03 . . . . . . . . . 78 79
     C.6.  Since draft-ietf-httpbis-p1-messaging-04 . . . . . . . . . 79 80
     C.7.  Since draft-ietf-httpbis-p1-messaging-05 . . . . . . . . . 79 80
     C.8.  Since draft-ietf-httpbis-p1-messaging-06 . . . . . . . . . 80 81
     C.9.  Since draft-ietf-httpbis-p1-messaging-07 . . . . . . . . . 81 82
     C.10. Since draft-ietf-httpbis-p1-messaging-08 . . . . . . . . . 82
     C.11. Since draft-ietf-httpbis-p1-messaging-09 . . . . . . . . . 82 83
     C.12. Since draft-ietf-httpbis-p1-messaging-10 . . . . . . . . . 82 83
     C.13. Since draft-ietf-httpbis-p1-messaging-11 . . . . . . . . . 83 84
     C.14. Since draft-ietf-httpbis-p1-messaging-12 . . . . . . . . . 83 84
     C.15. Since draft-ietf-httpbis-p1-messaging-13 . . . . . . . . . 84 85
     C.16. Since draft-ietf-httpbis-p1-messaging-14 . . . . . . . . . 84 85
     C.17. Since draft-ietf-httpbis-p1-messaging-15 . . . . . . . . . 85
     C.18. Since draft-ietf-httpbis-p1-messaging-16 . . . . . . . . . 85 86
     C.19. Since draft-ietf-httpbis-p1-messaging-17 . . . . . . . . . 85 86
     C.20. Since draft-ietf-httpbis-p1-messaging-18 . . . . . . . . . 87
   Index  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 87

1.  Introduction

   The Hypertext Transfer Protocol (HTTP) is an application-level
   request/response protocol that uses extensible semantics and MIME-
   like message payloads for flexible interaction with network-based
   hypertext information systems.  HTTP relies upon the Uniform Resource
   Identifier (URI) standard [RFC3986] to indicate the target resource
   (Section 5.1) and relationships between resources.  Messages are
   passed in a format similar to that used by Internet mail [RFC5322]
   and the Multipurpose Internet Mail Extensions (MIME) [RFC2045] (see
   Appendix A of [Part3] for the differences between HTTP and MIME
   messages).

   HTTP is a generic interface protocol for information systems.  It is
   designed to hide the details of how a service is implemented by
   presenting a uniform interface to clients that is independent of the
   types of resources provided.  Likewise, servers do not need to be
   aware of each client's purpose: an HTTP request can be considered in
   isolation rather than being associated with a specific type of client
   or a predetermined sequence of application steps.  The result is a
   protocol that can be used effectively in many different contexts and
   for which implementations can evolve independently over time.

   HTTP is also designed for use as an intermediation protocol for
   translating communication to and from non-HTTP information systems.
   HTTP proxies and gateways can provide access to alternative
   information services by translating their diverse protocols into a
   hypertext format that can be viewed and manipulated by clients in the
   same way as HTTP services.

   One consequence of HTTP flexibility is that the protocol cannot be
   defined in terms of what occurs behind the interface.  Instead, we
   are limited to defining the syntax of communication, the intent of
   received communication, and the expected behavior of recipients.  If
   the communication is considered in isolation, then successful actions
   ought to be reflected in corresponding changes to the observable
   interface provided by servers.  However, since multiple clients might
   act in parallel and perhaps at cross-purposes, we cannot require that
   such changes be observable beyond the scope of a single response.

   This document is Part 1 of the seven-part specification of HTTP,
   defining the protocol referred to as "HTTP/1.1", obsoleting [RFC2616]
   and [RFC2145].  Part 1 describes the architectural elements that are
   used or referred to in HTTP, defines the "http" and "https" URI
   schemes, describes overall network operation and connection
   management, and defines HTTP message framing and forwarding
   requirements.  Our goal is to define all of the mechanisms necessary
   for HTTP message handling that are independent of message semantics,
   thereby defining the complete set of requirements for message parsers
   and message-forwarding intermediaries.

1.1.  Conformance and Error Handling  Requirement Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

1.2.  Syntax Notation

   This document defines conformance criteria for several roles in HTTP
   communication, including Senders, Recipients, Clients, Servers, User-
   Agents, Origin Servers, Intermediaries, Proxies and Gateways.  See
   Section 2 for definitions specification uses the Augmented Backus-Naur Form (ABNF)
   notation of these terms.

   An implementation is considered conformant if it complies [RFC5234] with all of the requirements associated with its role(s).  Note that SHOULD-level
   requirements are relevant here, unless one of list rule extension defined in
   Section 3.2.5.  Appendix B shows the documented
   exceptions is applicable.

   This document also uses collected ABNF to define valid protocol elements
   (Section 1.2).  In addition to with the prose requirements placed upon
   them, Senders MUST NOT generate protocol elements that are invalid.

   Unless noted otherwise, Recipients MAY take steps to recover a usable
   protocol element from an invalid construct.  However, HTTP does not
   define specific error handling mechanisms, except in cases where it
   has direct impact on security.  This is because different uses of the
   protocol require different error handling strategies; for example, a
   Web browser may wish to transparently recover from a response where
   the Location header field doesn't parse according to the ABNF,
   whereby in a systems control protocol using HTTP, this type of error
   recovery could lead to dangerous consequences.

1.2.  Syntax Notation

   This specification uses the Augmented Backus-Naur Form (ABNF)
   notation of [RFC5234].

   The following core rules list
   rule expanded.

   The following core rules are included by reference, as defined in
   [RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF
   (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line
   feed), OCTET (any 8-bit sequence of data), SP (space), and VCHAR (any
   visible [USASCII] character).

   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
   "obsolete" grammar rules that appear for historical reasons.

1.2.1.  ABNF Extension: #rule

   The #rule extension

2.  Architecture

   HTTP was created for the World Wide Web architecture and has evolved
   over time to support the ABNF rules scalability needs of [RFC5234] a worldwide hypertext
   system.  Much of that architecture is reflected in the terminology
   and syntax productions used to improve
   readability.

   A construct "#" define HTTP.

2.1.  Client/Server Messaging

   HTTP is defined, similar a stateless request/response protocol that operates by
   exchanging messages (Section 3) across a reliable transport or
   session-layer "connection".  An HTTP "client" is a program that
   establishes a connection to "*", a server for defining comma-
   delimited lists the purpose of elements.  The full form sending one
   or more HTTP requests.  An HTTP "server" is "<n>#<m>element"
   indicating at least <n> and at most <m> elements, each separated by a
   single comma (",") program that accepts
   connections in order to service HTTP requests by sending HTTP
   responses.

   Note that the terms client and optional whitespace (OWS, Section 1.2.2).

   Thus,

     1#element => element *( OWS "," OWS element )

   and:

     #element => [ 1#element ]

   and for n >= 1 and m > 1:

     <n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )

   For compatibility with legacy list rules, recipients SHOULD accept
   empty list elements.  In other words, consumers would follow the list
   productions:

     #element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]

     1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )

   Note that empty elements do not contribute server refer only to the count of elements
   present, though.

   For example, given these ABNF productions:

     example-list      = 1#example-list-elmt
     example-list-elmt = token ; see Section 3.2.3

   Then roles that
   these are valid values for example-list (not including the
   double quotes, which are present programs perform for delimitation only):

     "foo,bar"
     "foo ,bar,"
     "foo , ,bar,charlie   "

   But these values would be invalid, a particular connection.  The same program
   might act as at least one non-empty element
   is required:

     ""
     ","
     ",   ,"

   Appendix B shows a client on some connections and a server on others.  We
   use the collected ABNF, with term "user agent" to refer to the list rules expanded program that initiates a
   request, such as
   explained above.

1.2.2.  Basic Rules

   This specification uses three rules a WWW browser, editor, or spider (web-traversing
   robot), and the term "origin server" to refer to denote the program that can
   originate authoritative responses to a request.  For general
   requirements, we use of linear
   whitespace: OWS (optional whitespace), RWS (required whitespace), the term "sender" to refer to whichever
   component sent a given message and
   BWS ("bad" whitespace).

   The OWS rule is used the term "recipient" to refer to
   any component that receives the message.

      Note: The term 'user agent' covers both those situations where zero
      there is a user (human) interacting with the software agent (and
      for which user interface or more linear whitespace octets interactive suggestions might appear.  OWS SHOULD either not be produced made,
      e.g., warning the user or be produced as given the user an option in the case of
      security or privacy options) and also those where the software
      agent may act autonomously.

   Most HTTP communication consists of a
   single SP.  Multiple OWS octets that occur within field-content
   SHOULD either retrieval request (GET) for a
   representation of some resource identified by a URI.  In the simplest
   case, this might be replaced with accomplished via a single SP or transformed to all SP
   octets (each octet other than SP replaced with SP) before
   interpreting bidirectional
   connection (===) between the field value or forwarding user agent (UA) and the message downstream.

   RWS is used when at least one linear whitespace octet is required origin server
   (O).

            request   >
       UA ======================================= O
                                   <   response

   A client sends an HTTP request to
   separate field tokens.  RWS SHOULD be produced as the server in the form of a single SP.
   Multiple RWS octets that occur within field-content SHOULD either be
   replaced request
   message, beginning with a single SP or transformed request-line that includes a method, URI,
   and protocol version (Section 3.1.1), followed by MIME-like header
   fields containing request modifiers, client information, and
   representation metadata (Section 3.2), an empty line to all SP octets before
   interpreting indicate the field value or forwarding
   end of the message downstream.

   BWS is used where the grammar allows optional whitespace for
   historical reasons but senders SHOULD NOT produce it in messages.
   HTTP/1.1 recipients MUST accept such bad optional whitespace header section, and
   remove it before interpreting the field value or forwarding the finally a message downstream.

     OWS            = *( SP / HTAB / obs-fold )
                    ; "optional" whitespace
     RWS            = 1*( SP / HTAB / obs-fold )
                    ; "required" whitespace
     BWS            = OWS
                    ; "bad" whitespace
     obs-fold       = CRLF ( SP / HTAB )
                    ; obsolete line folding
                    ; see Section 3.2.1

2.  Architecture

   HTTP was created for body containing the World Wide Web architecture and has evolved
   over time
   payload body (if any, Section 3.3).

   A server responds to support the scalability needs of a worldwide hypertext
   system.  Much of that architecture is reflected in the terminology
   and syntax productions used to define HTTP.

2.1.  Client/Server Messaging

   HTTP is a stateless request/response protocol that operates client's request by
   exchanging messages (Section 3) across a reliable transport or
   session-layer "connection".  An HTTP "client" is a program that
   establishes a connection to a server for the purpose of sending one or more HTTP requests.  An HTTP "server" is
   response messages, each beginning with a program that accepts
   connections in order to service HTTP requests by sending HTTP
   responses.

   Note status line that includes
   the terms client protocol version, a success or error code, and textual reason
   phrase (Section 3.1.2), possibly followed by MIME-like header fields
   containing server refer only information, resource metadata, and representation
   metadata (Section 3.2), an empty line to indicate the roles that
   these programs perform for end of the
   header section, and finally a particular connection. message body containing the payload
   body (if any, Section 3.3).

   The same program
   might act as following example illustrates a client on some connections and typical message exchange for a server
   GET request on others.  We
   use the term "user agent" to refer to URI "http://www.example.com/hello.txt":

   client request:

     GET /hello.txt HTTP/1.1
     User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
     Host: www.example.com
     Accept: */*

   server response:

     HTTP/1.1 200 OK
     Date: Mon, 27 Jul 2009 12:28:53 GMT
     Server: Apache
     Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
     ETag: "34aa387-d-1568eb00"
     Accept-Ranges: bytes
     Content-Length: 14
     Vary: Accept-Encoding
     Content-Type: text/plain

     Hello World!

2.2.  Connections and Transport Independence

   HTTP messaging is independent of the program that initiates a
   request, such as a WWW browser, editor, underlying transport or spider (web-traversing
   robot), session-
   layer connection protocol(s).  HTTP only presumes a reliable
   transport with in-order delivery of requests and the term "origin server" to refer to corresponding
   in-order delivery of responses.  The mapping of HTTP request and
   response structures onto the program that can
   originate authoritative responses to a request.  For general
   requirements, we use data units of the term "sender" to refer underlying transport
   protocol is outside the scope of this specification.

   The specific connection protocols to whichever
   component sent a given message be used for an interaction are
   determined by client configuration and the term "recipient" to refer to
   any component that receives target URI (Section 5.1).
   For example, the message.

      Note: The term 'user agent' covers both those situations where
      there is "http" URI scheme (Section 2.7.1) indicates a user (human) interacting
   default connection of TCP over IP, with a default TCP port of 80, but
   the software agent (and
      for which user interface or interactive suggestions client might be made,
      e.g., warning the user configured to use a proxy via some other
   connection port or given the user an option in the case protocol instead of
      security or privacy options) and also those where using the software
      agent may act autonomously.

   Most defaults.

   A connection might be used for multiple HTTP communication consists request/response
   exchanges, as defined in Section 6.3.

2.3.  Intermediaries

   HTTP enables the use of intermediaries to satisfy requests through a retrieval request (GET) for a
   representation
   chain of some resource identified by a URI. connections.  There are three common forms of HTTP
   intermediary: proxy, gateway, and tunnel.  In the simplest
   case, this might be accomplished via some cases, a single bidirectional
   connection (===)
   intermediary might act as an origin server, proxy, gateway, or
   tunnel, switching behavior based on the nature of each request.

            >             >             >             >
       UA =========== A =========== B =========== C =========== O
                  <             <             <             <

   The figure above shows three intermediaries (A, B, and C) between the
   user agent (UA) and the origin server
   (O). server.  A request   >
       UA ======================================= O
                                   < or response

   A client sends an message that
   travels the whole chain will pass through four separate connections.
   Some HTTP request communication options might apply only to the server in the form of a request
   message, beginning connection
   with a request-line that includes a method, URI,
   and protocol version (Section 3.1.1), followed by MIME-like header
   fields containing request modifiers, client information, and payload
   metadata (Section 3.2), an empty line the nearest, non-tunnel neighbor, only to indicate the end end-points of the
   header section, and finally a message body containing
   chain, or to all connections along the payload
   body (if any, Section 3.3).

   A server responds chain.  Although the diagram
   is linear, each participant might be engaged in multiple,
   simultaneous communications.  For example, B might be receiving
   requests from many clients other than A, and/or forwarding requests
   to servers other than C, at the client's request by sending an HTTP response
   message, beginning with a status line same time that includes it is handling A's
   request.

   We use the protocol
   version, a success or error code, and textual reason phrase
   (Section 3.1.2), followed by MIME-like header fields containing
   server information, resource metadata, terms "upstream" and payload metadata
   (Section 3.2), an empty line "downstream" to describe various
   requirements in relation to indicate the end directional flow of a message: all
   messages flow from upstream to downstream.  Likewise, we use the header
   section,
   terms inbound and finally a message body containing outbound to refer to directions in relation to the payload body (if
   any, Section 3.3).

   Note that 1xx responses (Section 7.1 of [Part2]) are not final;
   therefore, a server can send zero or more 1xx responses, followed by
   exactly one final response (with any other status code).

   The following example illustrates a typical message exchange for a
   GET
   request on path: "inbound" means toward the URI "http://www.example.com/hello.txt":

   client request:

     GET /hello.txt HTTP/1.1
     User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
     Host: www.example.com
     Accept: */* origin server response:

     HTTP/1.1 200 OK
     Date: Mon, 27 Jul 2009 12:28:53 GMT
     Server: Apache
     Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
     ETag: "34aa387-d-1568eb00"
     Accept-Ranges: bytes
     Content-Length: 14
     Vary: Accept-Encoding
     Content-Type: text/plain

     Hello World!

2.2.  Message Orientation and Buffering

   Fundamentally, HTTP "outbound"
   means toward the user agent.

   A "proxy" is a message-based protocol.  Although message
   bodies can be chunked (Section 5.1.1) and implementations often make
   parts of a message available progressively, this is not required, and
   some widely-used implementations only make a message available when
   it forwarding agent that is complete.  Furthermore, while most proxies will progressively
   stream messages, selected by the
   client, usually via local configuration rules, to receive requests
   for some amount type(s) of buffering will take place, absolute URI and some
   proxies might buffer messages attempt to perform transformations, check
   content or provide satisfy those
   requests via translation through the HTTP interface.  Some
   translations are minimal, such as for proxy requests for "http" URIs,
   whereas other services.

   Therefore, extensions requests might require translation to and uses of from entirely
   different application-layer protocols.  Proxies are often used to
   group an organization's HTTP cannot rely on requests through a common intermediary
   for the
   availability sake of security, annotation services, or shared caching.

   An HTTP-to-HTTP proxy is called a partial message, "transforming proxy" if it is
   designed or assume that messages will not
   be buffered.  There are strategies that can be used configured to test for
   buffering modify request or response messages in a given connection, but it should be understood
   semantically meaningful way (i.e., modifications, beyond those
   required by normal HTTP processing, that
   behaviors can differ across connections, and between requests and
   responses.

   Recipients MUST consider every change the message in a connection in isolation;
   because HTTP is a stateless protocol, it cannot be assumed way
   that two
   requests on the same connection are from would be significant to the same client original sender or share any
   other common attributes.  In particular, intermediaries potentially
   significant to downstream recipients).  For example, a transforming
   proxy might mix
   requests from different clients into be acting as a single shared annotation server connection.
   Note that some existing HTTP extensions (e.g., [RFC4559]) violate
   this requirement, thereby potentially causing interoperability and
   security problems.

2.3.  Connections and Transport Independence

   HTTP messaging is independent of the underlying transport or session-
   layer connection protocol(s).  HTTP only presumes (modifying
   responses to include references to a reliable
   transport with in-order delivery of requests and the corresponding
   in-order delivery of responses.  The mapping of HTTP request and
   response structures onto local annotation database), a
   malware filter, a format transcoder, or an intranet-to-Internet
   privacy filter.  Such transformations are presumed to be desired by
   the data units of client (or client organization) that selected the underlying transport
   protocol is outside proxy and are
   beyond the scope of this specification.

   The specific connection protocols  However, when a proxy is not
   intended to be used for an interaction are
   determined by client configuration and transform a given message, we use the term "non-
   transforming proxy" to target resource's URI.
   For example, the "http" URI scheme (Section 2.7.1) indicates a
   default connection requirements that preserve HTTP message
   semantics.  See Section 7.2.4 of TCP over IP, with a default TCP port [Part2] and Section 3.6 of 80, but
   the client might be configured [Part6]
   for status and warning codes related to use transformations.

   A "gateway" (a.k.a., "reverse proxy") is a proxy via receiving agent that acts
   as a layer above some other
   connection port or protocol instead of using server(s) and translates the defaults.

   A connection might be used for multiple HTTP request/response
   exchanges, as defined in Section 6.1.

2.4.  Intermediaries

   HTTP enables received
   requests to the use of intermediaries underlying server's protocol.  Gateways are often
   used to satisfy requests encapsulate legacy or untrusted information services, to
   improve server performance through a
   chain of connections.  There are three common forms "accelerator" caching, and to
   enable partitioning or load-balancing of HTTP
   intermediary: proxy, gateway, and tunnel.  In some cases, a single
   intermediary might act services across
   multiple machines.

   A gateway behaves as an origin server, proxy, gateway, or
   tunnel, switching behavior based server on the nature of each request.

            >             >             >             >
       UA =========== A =========== B =========== C =========== O
                  <             <             <             <

   The figure above shows three intermediaries (A, B, its outbound connection and C) between the
   as a user agent and origin server.  A request or response message that
   travels the whole chain will pass through four separate connections.
   Some on its inbound connection.  All HTTP communication options might apply only requirements
   applicable to the connection
   with the nearest, non-tunnel neighbor, only an origin server also apply to the end-points outbound
   communication of the
   chain, or to all connections along the chain.  Although the diagram
   is linear, each participant might be engaged in multiple,
   simultaneous communications.  For example, B might be receiving
   requests from many clients other than A, and/or forwarding requests
   to a gateway.  A gateway communicates with inbound
   servers other than C, at the same time using any protocol that it is handling A's
   request.

   We use the terms "upstream" and "downstream" to describe various
   requirements in relation desires, including private
   extensions to HTTP that are outside the directional flow scope of a message: all
   messages flow from upstream this specification.
   However, an HTTP-to-HTTP gateway that wishes to downstream.  Likewise, we use interoperate with
   third-party HTTP servers MUST conform to HTTP user agent requirements
   on the
   terms gateway's inbound connection and outbound to refer to directions in relation to the
   request path: "inbound" means toward MUST implement the origin server Connection
   (Section 6.1) and "outbound"
   means toward the user agent. Via (Section 6.2) header fields for both
   connections.

   A "proxy" is "tunnel" acts as a message forwarding agent that is selected by blind relay between two connections without
   changing the
   client, usually via local configuration rules, to receive requests
   for some type(s) of absolute URI and attempt messages.  Once active, a tunnel is not considered a
   party to satisfy those
   requests via translation through the HTTP interface.  Some
   translations are minimal, such as for proxy requests for "http" URIs,
   whereas other requests communication, though the tunnel might require translation have been
   initiated by an HTTP request.  A tunnel ceases to and from entirely
   different application-layer protocols.  Proxies exist when both
   ends of the relayed connection are closed.  Tunnels are often used to
   group
   extend a virtual connection through an organization's HTTP requests intermediary, such as when
   transport-layer security is used to establish private communication
   through a common intermediary
   for the sake shared firewall proxy.

   In addition, there may exist network intermediaries that are not
   considered part of security, annotation services, the HTTP communication but nevertheless act as
   filters or shared caching.

   An HTTP-to-HTTP proxy is called redirecting agents (usually violating HTTP semantics,
   causing security problems, and otherwise making a "transforming proxy" if it is
   designed or configured mess of things).
   Such a network intermediary, often referred to modify request as an "interception
   proxy" [RFC3040], "transparent proxy" [RFC1919], or response messages in a
   semantically meaningful way (i.e., modifications, beyond those
   required by normal "captive portal",
   differs from an HTTP processing, that change the message in a way
   that would be significant to proxy because it has not been selected by the original sender or potentially
   significant
   client.  Instead, the network intermediary redirects outgoing TCP
   port 80 packets (and occasionally other common port traffic) to downstream recipients).  For example, a transforming
   proxy might be acting an
   internal HTTP server.  Interception proxies are commonly found on
   public network access points, as a shared annotation server (modifying
   responses means of enforcing account
   subscription prior to include references allowing use of non-local Internet services,
   and within corporate firewalls to enforce network usage policies.
   They are indistinguishable from a local annotation database), a
   malware filter, man-in-the-middle attack.

   HTTP is defined as a format transcoder, or an intranet-to-Internet
   privacy filter.  Such transformations are presumed to stateless protocol, meaning that each request
   message can be desired by
   the client (or client organization) understood in isolation.  Many implementations depend
   on HTTP's stateless design in order to reuse proxied connections or
   dynamically load balance requests across multiple servers.  Hence,
   servers MUST NOT assume that selected two requests on the proxy and same connection are
   beyond
   from the scope of this specification.  However, when a proxy is not
   intended to transform a given message, we use same user agent unless the term "non-
   transforming proxy" connection is secured and
   specific to target requirements that preserve agent.  Some non-standard HTTP message
   semantics.  See Section 7.2.4 of [Part2] and Section 3.6 of [Part6]
   for status and warning codes related extensions (e.g.,
   [RFC4559]) have been known to transformations. violate this requirement, resulting in
   security and interoperability problems.

2.4.  Caches

   A "gateway" (a.k.a., "reverse proxy") "cache" is a receiving agent local store of previous response messages and the
   subsystem that acts
   as a layer above some other server(s) controls its message storage, retrieval, and translates the received
   requests deletion.
   A cache stores cacheable responses in order to reduce the underlying server's protocol.  Gateways are often
   used to encapsulate legacy or untrusted information services, to
   improve server performance through "accelerator" caching, response
   time and to
   enable partitioning network bandwidth consumption on future, equivalent
   requests.  Any client or load-balancing of HTTP services across
   multiple machines.

   A gateway behaves as an origin server on its outbound connection and
   as MAY employ a cache, though a cache
   cannot be used by a user agent on its inbound connection.  All HTTP requirements
   applicable to an origin server also apply to the outbound
   communication while it is acting as a tunnel.

   The effect of a gateway.  A gateway communicates with inbound
   servers using any protocol that it desires, including private
   extensions to HTTP cache is that are outside the scope request/response chain is shortened
   if one of this specification.
   However, an HTTP-to-HTTP gateway that wishes to interoperate with
   third-party HTTP servers MUST comply with HTTP user agent
   requirements on the gateway's inbound connection and MUST implement participants along the Connection (Section 8.1) and Via (Section 8.8) header fields for
   both connections.

   A "tunnel" acts as chain has a blind relay between two connections without
   changing cached response
   applicable to that request.  The following illustrates the messages.  Once active, resulting
   chain if B has a tunnel is not considered cached copy of an earlier response from O (via C)
   for a
   party to the HTTP communication, though the tunnel might have request which has not been
   initiated cached by an HTTP request.  A tunnel ceases to exist when both
   ends of the relayed connection are closed.  Tunnels are used to
   extend UA or A.

               >             >
          UA =========== A =========== B - - - - - - C - - - - - - O
                     <             <

   A response is "cacheable" if a virtual connection through an intermediary, such as when
   transport-layer security cache is used allowed to establish private communication
   through store a shared firewall proxy.

   In addition, there may exist network intermediaries that are not
   considered part copy of
   the HTTP communication but nevertheless act as
   filters or redirecting agents (usually violating HTTP semantics,
   causing security problems, and otherwise making a mess of things).
   Such response message for use in answering subsequent requests.  Even
   when a network intermediary, often referred to as an "interception
   proxy" [RFC3040], "transparent proxy" [RFC1919], or "captive portal",
   differs from an HTTP proxy because it has not been selected response is cacheable, there might be additional constraints
   placed by the
   client.  Instead, client or by the network intermediary redirects outgoing TCP
   port 80 packets (and occasionally other common port traffic) to an
   internal HTTP server.  Interception proxies are commonly found origin server on
   public network access points, as when that cached
   response can be used for a means of enforcing account
   subscription prior to allowing use of non-local Internet services, particular request.  HTTP requirements for
   cache behavior and within corporate firewalls to enforce network usage policies.
   They cacheable responses are defined in Section 2 of
   [Part6].

   There are indistinguishable from a man-in-the-middle attack.

2.5.  Caches

   A "cache" is a local store wide variety of previous response messages and the
   subsystem that controls its message storage, retrieval, and deletion.
   A cache stores cacheable responses in order to reduce the response
   time and network bandwidth consumption on future, equivalent
   requests.  Any client or server MAY employ a cache, though a cache
   cannot be used by a server while it is acting as a tunnel.

   The effect of a cache is that the request/response chain is shortened
   if one of the participants along the chain has a cached response
   applicable to that request.  The following illustrates the resulting
   chain if B has a cached copy of an earlier response from O (via C)
   for a request which has not been cached by UA or A.

               >             >
          UA =========== A =========== B - - - - - - C - - - - - - O
                     <             <

   A response is "cacheable" if a cache is allowed to store a copy of
   the response message for use in answering subsequent requests.  Even
   when a response is cacheable, there might be additional constraints
   placed by the client or by the origin server on when that cached
   response can be used for a particular request.  HTTP requirements for
   cache behavior and cacheable responses are defined in Section 2 of
   [Part6].

   There are a wide variety of architectures architectures and configurations of
   caches and proxies deployed across the World Wide Web and inside
   large organizations.  These systems include national hierarchies of
   proxy caches to save transoceanic bandwidth, systems that broadcast
   or multicast cache entries, organizations that distribute subsets of
   cached data via optical media, and so on.

2.6.  Protocol Versioning

   HTTP uses a "<major>.<minor>" numbering scheme to indicate versions
   of the protocol.

2.5.  Conformance and Error Handling

   This specification defines version "1.1".  The
   protocol version as a whole indicates the sender's compliance with targets conformance criteria according to the set role
   of requirements laid out a participant in that version's corresponding HTTP communication.  Hence, HTTP requirements are
   placed on senders, recipients, clients, servers, user agents,
   intermediaries, origin servers, proxies, gateways, or caches,
   depending on what behavior is being constrained by the requirement.

   An implementation is considered conformant if it complies with all of
   the requirements associated with the roles it partakes in HTTP.

   Senders MUST NOT generate protocol elements that do not match the
   grammar defined by the ABNF rules for those protocol elements.

   Unless otherwise noted, recipients MAY attempt to recover a usable
   protocol element from an invalid construct.  HTTP does not define
   specific error handling mechanisms except when they have a direct
   impact on security, since different applications of the protocol
   require different error handling strategies.  For example, a Web
   browser might wish to transparently recover from a response where the
   Location header field doesn't parse according to the ABNF, whereas a
   systems control client might consider any form of error recovery to
   be dangerous.

2.6.  Protocol Versioning

   HTTP uses a "<major>.<minor>" numbering scheme to indicate versions
   of the protocol.  This specification defines version "1.1".  The
   protocol version as a whole indicates the sender's conformance with
   the set of requirements laid out in that version's corresponding
   specification of HTTP.

   The version of an HTTP message is indicated by an HTTP-Version HTTP-version field
   in the first line of the message.  HTTP-Version  HTTP-version is case-sensitive.

     HTTP-Version

     HTTP-version  = HTTP-Prot-Name HTTP-name "/" DIGIT "." DIGIT
     HTTP-Prot-Name
     HTTP-name     = %x48.54.54.50 ; "HTTP", case-sensitive

   The HTTP version number consists of two decimal digits separated by a
   "." (period or decimal point).  The first digit ("major version")
   indicates the HTTP messaging syntax, whereas the second digit ("minor
   version") indicates the highest minor version to which the sender is
   at least conditionally compliant
   conformant and able to understand for future communication.  The
   minor version advertises the sender's communication capabilities even
   when the sender is only using a backwards-compatible subset of the
   protocol, thereby letting the recipient know that more advanced
   features can be used in response (by servers) or in future requests
   (by clients).

   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient [RFC1945]
   or a recipient whose version is unknown, the HTTP/1.1 message is
   constructed such that it can be interpreted as a valid HTTP/1.0
   message if all of the newer features are ignored.  This specification
   places recipient-version requirements on some new features so that a
   compliant
   conformant sender will only use compatible features until it has
   determined, through configuration or the receipt of a message, that
   the recipient supports HTTP/1.1.

   The interpretation of an HTTP a header field does not change between minor
   versions of the same major HTTP version, though the default behavior
   of a recipient in the absence of such a field can change.  Unless
   specified otherwise, header fields defined in HTTP/1.1 are defined
   for all versions of HTTP/1.x.  In particular, the Host and Connection
   header fields ought to be implemented by all HTTP/1.x implementations
   whether or not they advertise compliance conformance with HTTP/1.1.

   New header fields can be defined such that, when they are understood
   by a recipient, they might override or enhance the interpretation of
   previously defined header fields.  When an implementation receives an
   unrecognized header field, the recipient MUST ignore that header
   field for local processing regardless of the message's HTTP version.
   An unrecognized header field received by a proxy MUST be forwarded
   downstream unless the header field's field-name is listed in the
   message's Connection header-field (see Section 8.1). 6.1).  These
   requirements allow HTTP's functionality to be enhanced without
   requiring prior update of all compliant deployed intermediaries.

   Intermediaries that process HTTP messages (i.e., all intermediaries
   other than those acting as a tunnel) tunnels) MUST send their own HTTP-Version HTTP-version
   in forwarded messages.  In other words, they MUST NOT blindly forward
   the first line of an HTTP message without ensuring that the protocol
   version in that message matches what the a version to which that intermediary understands, and
   is at least
   conditionally compliant to, conformant for both the receiving and sending of messages.
   Forwarding an HTTP message without rewriting the HTTP-
   Version HTTP-version might
   result in communication errors when downstream recipients use the
   message sender's version to determine what features are safe to use
   for later communication with that sender.

   An HTTP client SHOULD send a request version equal to the highest
   version for to which the client is at least conditionally compliant conformant and whose major version is
   no higher than the highest version supported by the server, if this
   is known.  An HTTP client MUST NOT send a version for to which it is not at least conditionally compliant.
   conformant.

   An HTTP client MAY send a lower request version if it is known that
   the server incorrectly implements the HTTP specification, but only
   after the client has attempted at least one normal request and
   determined from the response status or header fields (e.g., Server)
   that the server improperly handles higher request versions.

   An HTTP server SHOULD send a response version equal to the highest
   version for to which the server is at least conditionally compliant conformant and whose major version is
   less than or equal to the one received in the request.  An HTTP
   server MUST NOT send a version for to which it is not
   at least conditionally compliant. conformant.  A
   server MAY send a 505 (HTTP Version Not Supported) response if it
   cannot send a response using the major version used in the client's
   request.

   An HTTP server MAY send an HTTP/1.0 response to an HTTP/1.0 request
   if it is known or suspected that the client incorrectly implements
   the HTTP specification and is incapable of correctly processing later
   version responses, such as when a client fails to parse the version
   number correctly or when an intermediary is known to blindly forward
   the HTTP-Version HTTP-version even when it doesn't comply with conform to the given minor
   version of the protocol.  Such protocol downgrades SHOULD NOT be
   performed unless triggered by specific client attributes, such as
   when one or more of the request header fields (e.g., User-Agent)
   uniquely match the values sent by a client known to be in error.

   The intention of HTTP's versioning design is that the major number
   will only be incremented if an incompatible message syntax is
   introduced, and that the minor number will only be incremented when
   changes made to the protocol have the effect of adding to the message
   semantics or implying additional capabilities of the sender.
   However, the minor version was not incremented for the changes
   introduced between [RFC2068] and [RFC2616], and this revision is
   specifically avoiding any such changes to the protocol.

2.7.  Uniform Resource Identifiers

   Uniform Resource Identifiers (URIs) [RFC3986] are used throughout
   HTTP as the means for identifying resources.  URI references are used
   to target requests, indicate redirects, and define relationships.
   HTTP does not limit what a resource might be; it merely defines an
   interface that can be used to interact with a resource via HTTP.
   More information on the scope of URIs and resources can be found in
   [RFC3986].

   This specification adopts the definitions of "URI-reference",
   "absolute-URI", "relative-part", "port", "host", "path-abempty",
   "path-absolute", "query", and "authority" from the URI generic syntax
   [RFC3986].  In addition, we define a partial-URI rule for protocol
   elements that allow a relative URI but not a fragment.

     URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
     absolute-URI  = <absolute-URI, defined in [RFC3986], Section 4.3>
     relative-part = <relative-part, defined in [RFC3986], Section 4.2>
     authority     = <authority, defined in [RFC3986], Section 3.2>
     path-abempty  = <path-abempty, defined in [RFC3986], Section 3.3>
     path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
     port          = <port, defined in [RFC3986], Section 3.2.3>
     query         = <query, defined in [RFC3986], Section 3.4>
     uri-host      = <host, defined in [RFC3986], Section 3.2.2>

     partial-URI   = relative-part [ "?" query ]

   Each protocol element in HTTP that allows a URI reference will
   indicate in its ABNF production whether the element allows any form
   of reference (URI-reference), only a URI in absolute form (absolute-
   URI), only the path and optional query components, or some
   combination of the above.  Unless otherwise indicated, URI references
   are parsed relative to the effective request URI, which defines the
   default base URI for references in both the request and its
   corresponding response. (Section 5.5).

2.7.1.  http URI scheme

   The "http" URI scheme is hereby defined for the purpose of minting
   identifiers according to their association with the hierarchical
   namespace governed by a potential HTTP origin server listening for
   TCP connections on a given port.

     http-URI = "http:" "//" authority path-abempty [ "?" query ]

   The HTTP origin server is identified by the generic syntax's
   authority component, which includes a host identifier and optional
   TCP port ([RFC3986], Section 3.2.2).  The remainder of the URI,
   consisting of both the hierarchical path component and optional query
   component, serves as an identifier for a potential resource within
   that origin server's name space.

   If the host identifier is provided as an IP literal or IPv4 address,
   then the origin server is any listener on the indicated TCP port at
   that IP address.  If host is a registered name, then that name is
   considered an indirect identifier and the recipient might use a name
   resolution service, such as DNS, to find the address of a listener
   for that host.  The host MUST NOT be empty; if an "http" URI is
   received with an empty host, then it MUST be rejected as invalid.  If
   the port subcomponent is empty or not given, then TCP port 80 is
   assumed (the default reserved port for WWW services).

   Regardless of the form of host identifier, access to that host is not
   implied by the mere presence of its name or address.  The host might
   or might not exist and, even when it does exist, might or might not
   be running an HTTP server or listening to the indicated port.  The
   "http" URI scheme makes use of the delegated nature of Internet names
   and addresses to establish a naming authority (whatever entity has
   the ability to place an HTTP server at that Internet name or address)
   and allows that authority to determine which names are valid and how
   they might be used.

   When an "http" URI is used within a context that calls for access to
   the indicated resource, a client MAY attempt access by resolving the
   host to an IP address, establishing a TCP connection to that address
   on the indicated port, and sending an HTTP request message
   (Section 3) containing the URI's identifying data (Section 4) 5) to the
   server.  If the server responds to that request with a non-interim
   HTTP response message, as described in Section 4 of [Part2], then
   that response is considered an authoritative answer to the client's
   request.

   Although HTTP is independent of the transport protocol, the "http"
   scheme is specific to TCP-based services because the name delegation
   process depends on TCP for establishing authority.  An HTTP service
   based on some other underlying connection protocol would presumably
   be identified using a different URI scheme, just as the "https"
   scheme (below) is used for servers that require an SSL/TLS transport
   layer on a connection.  Other protocols might also be used to provide
   access to "http" identified resources -- it is only the authoritative
   interface used for mapping the namespace that is specific to TCP.

   The URI generic syntax for authority also includes a deprecated
   userinfo subcomponent ([RFC3986], Section 3.2.1) for including user
   authentication information in the URI.  Some implementations make use
   of the userinfo component for internal configuration of
   authentication information, such as within command invocation
   options, configuration files, or bookmark lists, even though such
   usage might expose a user identifier or password.  Senders MUST NOT
   include a userinfo subcomponent (and its "@" delimiter) when
   transmitting an "http" URI in a message.  Recipients of HTTP messages
   that contain a URI reference SHOULD parse for the existence of
   userinfo and treat its presence as an error, likely indicating that
   the deprecated subcomponent is being used to obscure the authority
   for the sake of phishing attacks.

2.7.2.  https URI scheme

   The "https" URI scheme is hereby defined for the purpose of minting
   identifiers according to their association with the hierarchical
   namespace governed by a potential HTTP origin server listening for
   SSL/TLS-secured connections on a given TCP port.

   All of the requirements listed above for the "http" scheme are also
   requirements for the "https" scheme, except that a default TCP port
   of 443 is assumed if the port subcomponent is empty or not given, and
   the TCP connection MUST be secured for privacy through the use of
   strong encryption prior to sending the first HTTP request.

     https-URI = "https:" "//" authority path-abempty [ "?" query ]

   Unlike the "http" scheme, responses to "https" identified requests
   are never "public" and thus MUST NOT be reused for shared caching.
   They can, however, be reused in a private cache if the message is
   cacheable by default in HTTP or specifically indicated as such by the
   Cache-Control header field (Section 3.2 of [Part6]).

   Resources made available via the "https" scheme have no shared
   identity with the "http" scheme even if their resource identifiers
   indicate the same authority (the same host listening to the same TCP
   port).  They are distinct name spaces and are considered to be
   distinct origin servers.  However, an extension to HTTP that is
   defined to apply to entire host domains, such as the Cookie protocol
   [RFC6265], can allow information set by one service to impact
   communication with other services within a matching group of host
   domains.

   The process for authoritative access to an "https" identified
   resource is defined in [RFC2818].

2.7.3.  http and https URI Normalization and Comparison

   Since the "http" and "https" schemes conform to the URI generic
   syntax, such URIs are normalized and compared according to the
   algorithm defined in [RFC3986], Section 6, using the defaults
   described above for each scheme.

   If the port is equal to the default port for a scheme, the normal
   form is to elide the port subcomponent.  Likewise, an empty path
   component is equivalent to an absolute path of "/", so the normal
   form is to provide a path of "/" instead.  The scheme and host are
   case-insensitive and normally provided in lowercase; all other
   components are compared in a case-sensitive manner.  Characters other
   than those in the "reserved" set are equivalent to their percent-
   encoded octets (see [RFC3986], Section 2.1): the normal form is to
   not encode them.

   For example, the following three URIs are equivalent:

      http://example.com:80/~smith/home.html
      http://EXAMPLE.com/%7Esmith/home.html
      http://EXAMPLE.com:/%7esmith/home.html

3.  Message Format

   All HTTP/1.1 messages consist of a start-line followed by a sequence
   of octets in a format similar to the Internet Message Format
   [RFC5322]: zero or more header fields (collectively referred to as
   the "headers" or the "header section"), an empty line indicating the
   end of the header section, and an optional message-body. message body.

     HTTP-message   = start-line
                      *( header-field CRLF )
                      CRLF
                      [ message-body ]

   The normal procedure for parsing an HTTP message is to read the
   start-line into a structure, read each header field into a hash table
   by field name until the empty line, and then use the parsed data to
   determine if a message-body message body is expected.  If a message-body message body has been
   indicated, then it is read as a stream until an amount of octets
   equal to the message-body message body length is read or the connection is closed.

   Recipients MUST parse an HTTP message as a sequence of octets in an
   encoding that is a superset of US-ASCII [USASCII].  Parsing an HTTP
   message as a stream of Unicode characters, without regard for the
   specific encoding, creates security vulnerabilities due to the
   varying ways that string processing libraries handle invalid
   multibyte character sequences that contain the octet LF (%x0A).
   String-based parsers can only be safely used within protocol elements
   after the element has been extracted from the message, such as within
   a header field-value after message parsing has delineated the
   individual fields.

   An HTTP message can be parsed as a stream for incremental processing
   or forwarding downstream.  However, recipients cannot rely on
   incremental delivery of partial messages, since some implementations
   will buffer or delay message forwarding for the sake of network
   efficiency, security checks, or payload transformations.

3.1.  Start Line

   An HTTP message can either be a request from client to server or a
   response from server to client.  Syntactically, the two types of
   message differ only in the start-line, which is either a Request-Line request-line
   (for requests) or a Status-Line status-line (for responses), and in the algorithm
   for determining the length of the message-body message body (Section 3.3).  In
   theory, a client could receive requests and a server could receive
   responses, distinguishing them by their different start-line formats,
   but in practice servers are implemented to only expect a request (a
   response is interpreted as an unknown or invalid request method) and
   clients are implemented to only expect a response.

     start-line     = Request-Line request-line / Status-Line status-line

   Implementations MUST NOT send whitespace between the start-line and
   the first header field.  The presence of such whitespace in a request
   might be an attempt to trick a server into ignoring that field or
   processing the line after it as a new request, either of which might
   result in a security vulnerability if other implementations within
   the request chain interpret the same message differently.  Likewise,
   the presence of such whitespace in a response might be ignored by
   some clients or cause others to cease parsing.

3.1.1.  Request-Line

   The Request-Line  Request Line

   A request-line begins with a method token, followed by a single space
   (SP), the request-target, another single space (SP), the protocol
   version, and ending with CRLF.

     Request-Line

     request-line   = Method method SP request-target SP HTTP-Version HTTP-version CRLF

3.1.1.1.  Method

   The Method method token indicates the request method to be performed on the
   target resource.  The request method is case-sensitive.

     Method

     method         = token

   See Section 2 of [Part2] for further information, such as the list of

   The methods defined by this specification, specification can be found in Section 2
   of [Part2], along with information regarding the IANA registry, HTTP method registry
   and considerations for defining new methods.

3.1.1.2.  request-target

   The request-target identifies the target resource upon which to apply
   the request.  The four options for request-target are described request, as defined in Section 4.1. 5.3.

   No whitespace is allowed inside the method, request-target, and
   protocol version.  Hence, recipients typically parse the request-line
   into its component parts by splitting on the SP characters.

   Unfortunately, some user agents fail to properly encode hypertext
   references that have embedded whitespace, sending the characters
   directly instead of properly percent-encoding the disallowed
   characters.  Recipients of an invalid request-line SHOULD respond
   with either a 400 (Bad Request) error or a 301 (Moved Permanently)
   redirect with the request-target = "*"
                    / absolute-URI
                    / ( path-absolute [ "?" query ] )
                    / authority properly encoded.  Recipients SHOULD
   NOT attempt to autocorrect and then process the request without a
   redirect, since the invalid request-line might be deliberately
   crafted to bypass security filters along the request chain.

   HTTP does not place a pre-defined limit on the length of a request-
   target.
   line.  A server that receives a method longer than any that it
   implements SHOULD respond with either a 404 (Not Allowed), if it is
   an origin server, or a 501 (Not Implemented) status code.  A server
   MUST be prepared to receive URIs of unbounded length and respond with
   the 414 (URI Too Long) status code if the received request-target
   would be longer than the server wishes to handle (see Section 7.4.15 7.4.12
   of [Part2]).

   Various ad-hoc limitations on request-target request-line length are found in
   practice.  It is RECOMMENDED that all HTTP senders and recipients
   support request-target
   support, at a minimum, request-line lengths of up to 8000 or more octets.

      Note: Fragments ([RFC3986], Section 3.5) are not part of the
      request-target and thus will not be transmitted in an HTTP
      request.

3.1.2.  Response Status-Line  Status Line

   The first line of a Response response message is the Status-Line, status-line, consisting
   of the protocol version, a space (SP), the status code, another
   space, a possibly-empty textual phrase describing the status code,
   and ending with CRLF.

     Status-Line

     status-line = HTTP-Version HTTP-version SP Status-Code status-code SP Reason-Phrase reason-phrase CRLF

3.1.2.1.  Status Code

   The Status-Code status-code element is a 3-digit integer result code of the
   attempt to understand and satisfy the request.  See Section 4 of
   [Part2] for further information, such as the list of status codes
   defined by this specification, the IANA registry, and considerations
   for new status codes.

     Status-Code

     status-code    = 3DIGIT

3.1.2.2.  Reason Phrase

   The Reason Phrase reason-phrase element exists for the sole purpose of providing a
   textual description associated with the numeric status code, mostly
   out of deference to earlier Internet application protocols that were
   more frequently used with interactive text clients.  A client SHOULD ignore the
   content of the Reason Phrase.

     Reason-Phrase  = *( HTAB / SP / VCHAR / obs-text )

3.2.  Header Fields

   Each HTTP header field consists of a case-insensitive field name
   followed by a colon (":"), optional whitespace, and the field value.

     header-field   = field-name ":" OWS field-value BWS
     field-name     = token
     field-value    = *( field-content / obs-fold )
     field-content  = *( HTAB / SP / VCHAR / obs-text )

   The field-name token labels the corresponding field-value as having
   the semantics defined by that header field.  For example, the Date
   header field is defined in Section 9.2 of [Part2] as containing the
   origination timestamp for the message in which it appears.

   HTTP header fields are fully extensible: there is no limit on the
   introduction of new field names, each presumably defining new
   semantics, or on the number of header fields used in a given message.
   Existing fields are defined in each part of this specification and in
   many other specifications outside the standards process.  New header
   fields can be introduced without changing the protocol version if
   their defined semantics allow them to be safely ignored by recipients
   that do not recognize them.

   New HTTP header fields SHOULD be registered with IANA according to
   the procedures in Section 3.1 of [Part2].  Unrecognized header fields
   MUST be forwarded by a proxy unless the field-name is listed in the
   Connection header field (Section 8.1) or the proxy is specifically
   configured to block or otherwise transform such fields.  Unrecognized
   header fields SHOULD be ignored by other recipients.

   The order in which header fields with differing field names are
   received is not significant.  However, it is "good practice" to send
   header fields that contain control data first, such as Host on
   requests and Date on responses, so that implementations can decide
   when not to handle a message as early as possible.  A server MUST
   wait until the entire header section is received before interpreting
   a request message, since later header fields might include
   conditionals, authentication credentials, or deliberately misleading
   duplicate header fields that would impact request processing.

   Multiple header fields with the same field name MUST NOT be sent in a
   message unless the entire field value for that header field is
   defined as a comma-separated list [i.e., #(values)].  Multiple header
   fields with the same field name can be combined into one "field-name:
   field-value" pair, without changing the semantics of the message, by
   appending each subsequent field value to the combined field value in
   order, separated by a comma.  The order in which header fields with
   the same field name are received is therefore significant to the
   interpretation of the combined field value; a proxy MUST NOT change
   the order of these field values when forwarding a message.

      Note: The "Set-Cookie" header field as implemented in practice can
      occur multiple times, but does not use the list syntax, and thus
      cannot be combined into a single line ([RFC6265]).  (See Appendix
      A.2.3 of [Kri2001] for details.)  Also note that the Set-Cookie2
      header field specified in [RFC2965] does not share this problem.

3.2.1.  Field Parsing

   No whitespace is allowed between the header field-name and colon.  In
   the past, differences in the handling of such whitespace have led to
   security vulnerabilities in request routing and response handling.
   Any received request message that contains whitespace between a
   header field-name and colon MUST be rejected with a response code of
   400 (Bad Request).  A proxy MUST remove any such whitespace from a
   response message before forwarding the message downstream.

   A field value MAY be preceded by optional whitespace (OWS); a single
   SP is preferred.  The field value does not include any leading or
   trailing white space: OWS occurring before the first non-whitespace
   octet of the field value or after the last non-whitespace octet of
   the field value is ignored and SHOULD be removed before further
   processing (as this does not change the meaning of the header field).

   Historically, HTTP header field values could be extended over
   multiple lines by preceding each extra line with at least one space
   or horizontal tab (obs-fold).  This specification deprecates such
   line folding except within the message/http media type
   (Section 9.3.1).  HTTP senders MUST NOT produce messages that include
   line folding (i.e., that contain any field-content that matches the
   obs-fold rule) unless the message is intended for packaging within
   the message/http media type.  HTTP recipients SHOULD accept line
   folding and replace any embedded obs-fold whitespace with either a
   single SP or a matching number of SP octets (to avoid buffer copying)
   prior to interpreting the field value or forwarding the message
   downstream.

   Historically, HTTP has allowed field content with text in the ISO-
   8859-1 [ISO-8859-1] character encoding and supported other character
   sets only through use of [RFC2047] encoding.  In practice, most HTTP
   header field values use only a subset of the US-ASCII character
   encoding [USASCII].  Newly defined header fields SHOULD limit their
   field values to US-ASCII octets.  Recipients SHOULD treat other (obs-
   text) octets in field content as opaque data.

3.2.2.  Field Length

   HTTP does not place a pre-defined limit on the length of header
   fields, either in isolation or as a set.  A server MUST be prepared
   to receive request header fields of unbounded length and respond with
   a 4xx status code if the received header field(s) would be longer
   than the server wishes to handle.

   A client that receives response headers that are longer than it
   wishes to handle can only treat it as a server error.

   Various ad-hoc limitations on header length are found in practice.
   It is RECOMMENDED that all HTTP senders and recipients support
   messages whose combined header fields have 4000 or more octets.

3.2.3.  Common Field ABNF Rules

   Many HTTP/1.1 header field values consist of words (token or quoted-
   string) separated by whitespace or special characters.  These special
   characters MUST be in a quoted string to be used within a parameter
   value (as defined in Section 5.1).

     word           = token / quoted-string

     token          = 1*tchar

     tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "*"
                    / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
                    / DIGIT / ALPHA
                    ; any VCHAR, except special

     special        = "(" / ")" / "<" / ">" / "@" / ","
                    / ";" / ":" / "\" / DQUOTE / "/" / "["
                    / "]" / "?" / "=" / "{" / "}"

   A string of text is parsed as a single word if it is quoted using
   double-quote marks.

     quoted-string  = DQUOTE *( qdtext / quoted-pair ) DQUOTE
     qdtext         = OWS / %x21 / %x23-5B / %x5D-7E / obs-text
     obs-text       = %x80-FF

   The backslash octet ("\") can be used as a single-octet quoting
   mechanism within quoted-string constructs:

     quoted-pair clients.  A client SHOULD
   ignore the reason-phrase content.

     reason-phrase  = "\" ( *( HTAB / SP / VCHAR / obs-text )

   Recipients that process the value

3.2.  Header Fields

   Each HTTP header field consists of the quoted-string MUST handle a
   quoted-pair as if it were replaced case-insensitive field name
   followed by the octet following the
   backslash.

   Senders SHOULD NOT escape octets in quoted-strings that do not
   require escaping (i.e., other than DQUOTE a colon (":"), optional whitespace, and the backslash octet).

   Comments can be included in some HTTP header fields by surrounding
   the comment text with parentheses.  Comments are only allowed in
   fields containing "comment" as part of their field value definition.

     comment value.

     header-field   = field-name ":" OWS field-value BWS
     field-name     = token
     field-value    = "(" *( ctext / quoted-cpair field-content / comment obs-fold ) ")"
     ctext
     field-content  = OWS / %x21-27 *( HTAB / %x2A-5B SP / %x5D-7E VCHAR / obs-text

   The backslash octet ("\") can be used as a single-octet quoting
   mechanism within comment constructs:

     quoted-cpair )
     obs-fold       = "\" CRLF ( HTAB / SP / VCHAR / obs-text HTAB )

   Senders SHOULD NOT escape octets in comments that do not require
   escaping (i.e., other than the backslash octet "\" and the
   parentheses "(" and ")").

3.3.  Message Body
                    ; obsolete line folding
                    ; see Section 3.2.2

   The message-body (if any) of an HTTP message is used to carry field-name token labels the
   payload body associated with corresponding field-value as having
   the request or response.

     message-body = *OCTET

   The message-body differs from semantics defined by that header field.  For example, the payload body only when a transfer-
   coding has been applied, Date
   header field is defined in Section 10.2 of [Part2] as indicated by containing the Transfer-Encoding
   origination timestamp for the message in which it appears.

   HTTP header fields are fully extensible: there is no limit on the
   introduction of new field (Section 8.6).  If more than one Transfer-Encoding names, each presumably defining new
   semantics, or on the number of header field
   is present fields used in a message, given message.
   Existing fields are defined in each part of this specification and in
   many other specifications outside the multiple field-values MUST standards process.  New header
   fields can be combined
   into one field-value, introduced without changing the protocol version if
   their defined semantics allow them to be safely ignored by recipients
   that do not recognize them.

   New HTTP header fields SHOULD be registered with IANA according to
   the algorithm defined procedures in Section 3.2, before determining the message-body length.

   When one or more transfer-codings are applied to 3.1 of [Part2].  Unrecognized header fields
   MUST be forwarded by a payload in order
   to form proxy unless the message-body, field-name is listed in the Transfer-Encoding
   Connection header field MUST
   contain (Section 6.1) or the list of transfer-codings applied.  Transfer-Encoding proxy is a
   property of the message, not of the payload, and thus MAY be added specifically
   configured to block or
   removed otherwise transform such fields.  Unrecognized
   header fields SHOULD be ignored by any implementation along the request/response chain under
   the constraints found other recipients.

   The order in Section 5.1.

   If which header fields with differing field names are
   received is not significant.  However, it is "good practice" to send
   header fields that contain control data first, such as Host on
   requests and Date on responses, so that implementations can decide
   when not to handle a message as early as possible.  A server MUST
   wait until the entire header section is received before interpreting
   a request message, since later header fields might include
   conditionals, authentication credentials, or deliberately misleading
   duplicate header fields that has multiple Content-Length would impact request processing.

   Multiple header fields (Section 8.2) with field-values consisting of the same decimal
   value, or a single Content-Length header field with name MUST NOT be sent in a
   message unless the entire field value
   containing for that header field is
   defined as a comma-separated list of identical decimal values (e.g., "Content-Length:
   42, 42"), indicating that duplicate Content-Length [i.e., #(values)].  Multiple header
   fields have
   been generated or combined by an upstream message processor, then with the
   recipient MUST either reject same field name can be combined into one "field-name:
   field-value" pair, without changing the message as invalid or replace semantics of the
   duplicated field-values with a single valid Content-Length message, by
   appending each subsequent field
   containing that decimal value prior to determining the message-body
   length.

   The rules for when a message-body is allowed combined field value in
   order, separated by a message differ for
   requests and responses. comma.  The presence of a message-body order in a request which header fields with
   the same field name are received is signaled by therefore significant to the
   inclusion
   interpretation of the combined field value; a Content-Length or Transfer-Encoding proxy MUST NOT change
   the order of these field values when forwarding a message.

      Note: The "Set-Cookie" header field as implemented in
   the request's header fields, even if the request method practice can
      occur multiple times, but does not
   define any use for the list syntax, and thus
      cannot be combined into a message-body.  This allows single line ([RFC6265]).  (See Appendix
      A.2.3 of [Kri2001] for details.)  Also note that the request message
   framing algorithm Set-Cookie2
      header field specified in [RFC2965] does not share this problem.

3.2.1.  Whitespace

   This specification uses three rules to be independent denote the use of method semantics.

   For response messages, whether linear
   whitespace: OWS (optional whitespace), RWS (required whitespace), and
   BWS ("bad" whitespace).

   The OWS rule is used where zero or more linear whitespace octets
   might appear.  OWS SHOULD either not be produced or be produced as a message-body is included
   single SP.  Multiple OWS octets that occur within field-content
   SHOULD either be replaced with a message is dependent on both the request method and the response
   status code (Section 3.1.2.1).  Responses single SP or transformed to all SP
   octets (each octet other than SP replaced with SP) before
   interpreting the HEAD request method
   never include a message-body because the associated response header
   fields (e.g., Transfer-Encoding, Content-Length, etc.) only indicate
   what their values would have been if field value or forwarding the request method had been GET.
   All 1xx (Informational), 204 (No Content), and 304 (Not Modified)
   responses MUST NOT include message downstream.

   RWS is used when at least one linear whitespace octet is required to
   separate field tokens.  RWS SHOULD be produced as a message-body.  All other responses do
   include single SP.
   Multiple RWS octets that occur within field-content SHOULD either be
   replaced with a message-body, although single SP or transformed to all SP octets before
   interpreting the body MAY be of zero length.

   The length of field value or forwarding the message-body message downstream.

   BWS is determined by one of used where the following
   (in order of precedence):

   1.  Any response to a HEAD request grammar allows optional whitespace for
   historical reasons but senders SHOULD NOT produce it in messages.
   HTTP/1.1 recipients MUST accept such bad optional whitespace and any response with a status
       code of 100-199, 204,
   remove it before interpreting the field value or 304 is always terminated by forwarding the first
       empty line after
   message downstream.

     OWS            = *( SP / HTAB )
                    ; "optional" whitespace
     RWS            = 1*( SP / HTAB )
                    ; "required" whitespace
     BWS            = OWS
                    ; "bad" whitespace

3.2.2.  Field Parsing

   No whitespace is allowed between the header fields, regardless of field-name and colon.  In
   the header
       fields present past, differences in the message, handling of such whitespace have led to
   security vulnerabilities in request routing and thus cannot contain a message-
       body.

   2.  If response handling.
   Any received request message that contains whitespace between a Transfer-Encoding
   header field is present and the "chunked"
       transfer-coding (Section 5.1) is the final encoding, the message-
       body length is determined by reading field-name and decoding the chunked
       data until the transfer-coding indicates the data is complete.

       If colon MUST be rejected with a Transfer-Encoding header field is present in response code of
   400 (Bad Request).  A proxy MUST remove any such whitespace from a
   response and message before forwarding the "chunked" transfer-coding message downstream.

   A field value MAY be preceded by optional whitespace (OWS); a single
   SP is preferred.  The field value does not include any leading or
   trailing white space: OWS occurring before the final encoding, first non-whitespace
   octet of the
       message-body length is determined by reading field value or after the connection until
       it is closed by last non-whitespace octet of
   the server.  If a Transfer-Encoding header field value is present in a request ignored and the "chunked" transfer-coding is SHOULD be removed before further
   processing (as this does not change the final encoding, meaning of the message-body length cannot header field).

   Historically, HTTP header field values could be determined
       reliably; extended over
   multiple lines by preceding each extra line with at least one space
   or horizontal tab (obs-fold).  This specification deprecates such
   line folding except within the server message/http media type
   (Section 7.3.1).  HTTP senders MUST respond with NOT produce messages that include
   line folding (i.e., that contain any field-value that matches the 400 (Bad Request)
       status code and then close
   obs-fold rule) unless the connection.

       If a message is received with both a Transfer-Encoding header
       field and a Content-Length header field, the Transfer-Encoding
       overrides intended for packaging within
   the Content-Length.  Such message/http media type.  HTTP recipients SHOULD accept line
   folding and replace any embedded obs-fold whitespace with either a message might indicate an
       attempt to perform request
   single SP or response smuggling (bypass a matching number of
       security-related checks on message routing or content) and thus
       ought to be handled as an error.  The provided Content-Length
       MUST be removed, SP octets (to avoid buffer copying)
   prior to interpreting the field value or forwarding the message downstream, or
       replaced
   downstream.

   Historically, HTTP has allowed field content with text in the real message-body length after the transfer-
       coding is decoded.

   3.  If a message is received without Transfer-Encoding ISO-
   8859-1 [ISO-8859-1] character encoding and with
       either multiple Content-Length supported other character
   sets only through use of [RFC2047] encoding.  In practice, most HTTP
   header field values use only a subset of the US-ASCII character
   encoding [USASCII].  Newly defined header fields SHOULD limit their
   field values to US-ASCII octets.  Recipients SHOULD treat other (obs-
   text) octets in field content as opaque data.

3.2.3.  Field Length

   HTTP does not place a pre-defined limit on the length of header fields having differing
       field-values
   fields, either in isolation or as a single Content-Length header field having an
       invalid value, then the message framing is invalid and set.  A server MUST be
       treated as an error prepared
   to prevent request or response smuggling.  If
       this is a receive request message, the server MUST header fields of unbounded length and respond with
   a 400
       (Bad Request) 4xx status code and then close the connection.  If this
       is a response message received by a proxy, the proxy MUST discard if the received response, send a 502 (Bad Gateway) status code as
       its downstream response, and then close header field(s) would be longer
   than the connection.  If this
       is a server wishes to handle.

   A client that receives response message received by a user-agent, headers that are longer than it
   wishes to handle can only treat it MUST be
       treated as an error by discarding the message and closing the
       connection.

   4.  If a valid Content-Length server error.

   Various ad-hoc limitations on header field is present without
       Transfer-Encoding, its decimal value defines the message-body length are found in octets.  If the actual number of octets sent in the
       message practice.
   It is less than the indicated Content-Length, the recipient
       MUST consider the message to be incomplete RECOMMENDED that all HTTP senders and treat the
       connection as no longer usable.  If the actual number of octets
       sent in the message is recipients support
   messages whose combined header fields have 4000 or more than the indicated Content-Length,
       the recipient MUST only process the message-body up to the octets.

3.2.4.  Field value components

   Many HTTP/1.1 header field
       value's number of octets; the remainder values consist of the message words (token or quoted-
   string) separated by whitespace or special characters.  These special
   characters MUST
       either be discarded or treated as the next message in a pipeline.
       For the sake of robustness, a user-agent MAY attempt to detect
       and correct such an error in message framing if it is parsing the
       response quoted string to the last request on a connection and the connection
       has been closed by the server.

   5.  If this is be used within a request message and none parameter
   value (as defined in Section 4).

     word           = token / quoted-string

     token          = 1*tchar

     tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "*"
                    / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
                    / DIGIT / ALPHA
                    ; any VCHAR, except special

     special        = "(" / ")" / "<" / ">" / "@" / ","
                    / ";" / ":" / "\" / DQUOTE / "/" / "["
                    / "]" / "?" / "=" / "{" / "}"

   A string of the above are true, then
       the message-body length is zero (no message-body is present).

   6.  Otherwise, this text is parsed as a response message without a declared message-
       body length, so the message-body length single word if it is determined by quoted using
   double-quote marks.

     quoted-string  = DQUOTE *( qdtext / quoted-pair ) DQUOTE
     qdtext         = OWS / %x21 / %x23-5B / %x5D-7E / obs-text
     obs-text       = %x80-FF

   The backslash octet ("\") can be used as a single-octet quoting
   mechanism within quoted-string constructs:

     quoted-pair    = "\" ( HTAB / SP / VCHAR / obs-text )

   Recipients that process the
       number value of octets received prior to the server closing the
       connection.

   Since there is no way to distinguish a successfully completed, close-
   delimited message from quoted-string MUST handle a partially-received message interrupted
   quoted-pair as if it were replaced by
   network failure, implementations the octet following the
   backslash.

   Senders SHOULD use encoding or length-
   delimited messages whenever possible.  The close-delimiting feature
   exists primarily for backwards compatibility with HTTP/1.0.

   A server MAY reject a request NOT escape octets in quoted-strings that contains a message-body but do not a
   Content-Length by responding with 411 (Length Required).

   Unless a transfer-coding
   require escaping (i.e., other than "chunked" has been applied, a
   client that sends a request containing a message-body SHOULD use a
   valid Content-Length header field if DQUOTE and the message-body length is known backslash octet).

   Comments can be included in advance, rather than the "chunked" encoding, since some existing
   services respond to "chunked" with a 411 (Length Required) status
   code even though they understand HTTP header fields by surrounding
   the chunked encoding.  This is
   typically because such services comment text with parentheses.  Comments are implemented via a gateway that
   requires a content-length only allowed in advance of being called and the server
   is unable or unwilling to buffer the entire request before
   processing.

   A client that sends a request
   fields containing a message-body MUST include
   a valid Content-Length header "comment" as part of their field if it does not know the server
   will handle HTTP/1.1 (or later) requests; such knowledge value definition.

     comment        = "(" *( ctext / quoted-cpair / comment ) ")"
     ctext          = OWS / %x21-27 / %x2A-5B / %x5D-7E / obs-text

   The backslash octet ("\") can be in
   the form of specific user configuration or by remembering the version
   of a prior received response.

3.4.  Handling Incomplete Messages

   Request messages that are prematurely terminated, possibly due to a
   cancelled connection or used as a server-imposed time-out exception, MUST
   result single-octet quoting
   mechanism within comment constructs:

     quoted-cpair   = "\" ( HTAB / SP / VCHAR / obs-text )

   Senders SHOULD NOT escape octets in closure of the connection; sending an HTTP/1.1 error
   response prior to closing the connection is OPTIONAL.

   Response messages comments that are prematurely terminated, usually by closure
   of do not require
   escaping (i.e., other than the connection prior backslash octet "\" and the
   parentheses "(" and ")").

3.2.5.  ABNF list extension: #rule

   A #rule extension to receiving the expected number ABNF rules of octets or
   by failure [RFC5234] is used to decode a transfer-encoded message-body, MUST be
   recorded as incomplete.  A response that terminates improve
   readability in the middle definitions of
   the some header block (before field values.

   A construct "#" is defined, similar to "*", for defining comma-
   delimited lists of elements.  The full form is "<n>#<m>element"
   indicating at least <n> and at most <m> elements, each separated by a
   single comma (",") and optional whitespace (OWS).

   Thus,

     1#element => element *( OWS "," OWS element )

   and:

     #element => [ 1#element ]

   and for n >= 1 and m > 1:

     <n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )

   For compatibility with legacy list rules, recipients SHOULD accept
   empty list elements.  In other words, consumers would follow the list
   productions:

     #element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]

     1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )

   Note that empty line is received) cannot be
   assumed elements do not contribute to convey the full semantics count of elements
   present, though.

   For example, given these ABNF productions:

     example-list      = 1#example-list-elmt
     example-list-elmt = token ; see Section 3.2.4

   Then these are valid values for example-list (not including the response and MUST
   double quotes, which are present for delimitation only):

     "foo,bar"
     "foo ,bar,"
     "foo , ,bar,charlie   "

   But these values would be
   treated invalid, as an error.

   A message-body that uses the chunked transfer encoding is incomplete
   if the zero-sized chunk that terminates the encoding has not been
   received.  A message that uses a valid Content-Length is incomplete
   if the size of the message-body received (in octets) is less than the
   value given by Content-Length.  A response that has neither chunked
   transfer encoding nor Content-Length is terminated by closure of the
   connection, and thus at least one non-empty element
   is considered complete regardless of required:

     ""
     ","
     ",   ,"

   Appendix B shows the number
   of message-body octets received, provided that collected ABNF, with the header block was
   received intact.

   A user agent MUST NOT render an incomplete response message-body list rules expanded as
   if it were complete (i.e., some indication must be given to the user
   that an error occurred).  Cache requirements for incomplete responses
   are defined in Section 2.1 of [Part6].

   A server MUST read
   explained above.

3.3.  Message Body

   The message body (if any) of an HTTP message is used to carry the entire
   payload body of that request message-body or close the
   connection after sending its response, since otherwise response.  The message body is
   identical to the remaining
   data on payload body unless a persistent connection would be misinterpreted transfer coding has been
   applied, as the next
   request.  Likewise, described in Section 3.3.1.

     message-body = *OCTET

   The rules for when a client MUST read the entire response message- message body is allowed in a message differ for
   requests and responses.

   The presence of a message body in a request is signaled by a a
   Content-Length or Transfer-Encoding header field.  Request message
   framing is independent of method semantics, even if it intends to reuse the same connection method does
   not define any use for a subsequent
   request.  Pipelining multiple requests on message body.

   The presence of a connection is described message body in Section 6.1.2.2.

3.5.  Message Parsing Robustness

   Older HTTP/1.0 client implementations might send an extra CRLF after a POST response depends on both the
   request as method to which it is responding and the response status code
   (Paragraph 2).  Responses to the HEAD request method never include a lame workaround for some early server
   applications that failed
   message body because the associated response header fields (e.g.,
   Transfer-Encoding, Content-Length, etc.) only indicate what their
   values would have been if the request method had been GET.
   Successful (2xx) responses to read message-body content that was not
   terminated by CONNECT switch to tunnel mode instead
   of having a line-ending.  An HTTP/1.1 client message body.  All 1xx (Informational), 204 (No Content),
   and 304 (Not Modified) responses MUST NOT preface include a message body.
   All other responses do include a message body, although the body MAY
   be of zero length.

3.3.1.  Transfer-Encoding

   When one or
   follow more transfer codings are applied to a request with an extra CRLF.  If terminating payload body in
   order to form the request
   message-body with message body, a line-ending is desired, then Transfer-Encoding header field MUST
   be sent in the client message and MUST
   include contain the terminating CRLF octets as part list of corresponding
   transfer-coding names in the message-body
   length.

   In same order that they were applied.
   Transfer codings are defined in Section 4.

     Transfer-Encoding = 1#transfer-coding

   Transfer-Encoding is analogous to the interest Content-Transfer-Encoding field
   of robustness, servers SHOULD ignore at least one
   empty line received where MIME, which was designed to enable safe transport of binary data
   over a Request-Line is expected. 7-bit transport service ([RFC2045], Section 6).  However, safe
   transport has a different focus for an 8bit-clean transfer protocol.
   In other
   words, if the server HTTP's case, Transfer-Encoding is reading the protocol stream at the beginning
   of primarily intended to accurately
   delimit a message dynamically generated payload and receives a CRLF first, it SHOULD ignore to distinguish payload
   encodings that are only applied for transport efficiency or security
   from those that are characteristics of the CRLF.
   Likewise, although target resource.

   The "chunked" transfer-coding (Section 4.1) MUST be implemented by
   all HTTP/1.1 recipients because it plays a crucial role in delimiting
   messages when the line terminator for payload body size is not known in advance.  When
   the start-line and header
   fields "chunked" transfer-coding is used, it MUST be the sequence CRLF, we recommend that recipients recognize a
   single LF as last transfer-
   coding applied to form the message body and MUST NOT be applied more
   than once in a line terminator and ignore message body.  If any CR.

   When transfer-coding is applied to a server listening only for HTTP
   request messages, or processing
   what appears from payload body, the start-line to final transfer-coding applied MUST be an HTTP request message,
   receives
   "chunked".  If any transfer-coding is applied to a sequence of octets response payload
   body, then either the final transfer-coding applied MUST be "chunked"
   or the message MUST be terminated by closing the connection.

   For example,

     Transfer-Encoding: gzip, chunked

   indicates that does not match the HTTP-message
   grammar aside from payload body has been compressed using the robustness exceptions listed above, gzip
   coding and then chunked using the server
   MUST respond with an HTTP/1.1 400 (Bad Request) response.

4.  Message Routing

   In most cases, chunked coding while forming the user agent
   message body.

   If more than one Transfer-Encoding header field is provided present in a URI reference from which
   it determines an absolute URI for identifying
   message, the target resource.
   When a request multiple field-values MUST be combined into one field-
   value, according to the resource is initiated, all or part algorithm defined in Section 3.2, before
   determining the message body length.

   Unlike Content-Encoding (Section 2.2 of that URI [Part3]), Transfer-Encoding
   is used to construct the HTTP request-target.

4.1.  Types a property of Request Target

   The four options for request-target are dependent on the nature message, not of the request.

   The asterisk "*" form of request-target, which MUST NOT payload, and thus MAY be used with
   added or removed by any request method other than OPTIONS, means that implementation along the request applies
   to request/response
   chain.  Additional information about the server as encoding parameters MAY be
   provided by other header fields not defined by this specification.

   Transfer-Encoding MAY be sent in a whole (the listening process) rather than response to a
   specific named resource at that server.  For example,

     OPTIONS * HTTP/1.1

   The "absolute-URI" form is REQUIRED when the HEAD request is being made or in a
   304 response to a proxy.  The proxy is requested GET request, neither of which includes a message
   body, to either forward indicate that the request or
   service it from origin server would have applied a valid cache, and then return the response.  Note
   that
   transfer coding to the proxy MAY forward message body if the request had been an
   unconditional GET.  This indication is not required, however, because
   any recipient on to another proxy or
   directly to the server specified by response chain (including the absolute-URI.  In order to
   avoid request loops, a proxy origin server) can
   remove transfer codings when they are not needed.

   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed
   that forwards requests implementations advertising only HTTP/1.0 support will not
   understand how to other proxies process a transfer-encoded payload.  A client MUST be able to recognize and exclude all of its own server names,
   including any aliases, local variations, and
   NOT send a request containing Transfer-Encoding unless it knows the numeric IP address.
   An example Request-Line would be:

     GET http://www.example.org/pub/WWW/TheProject.html
   server will handle HTTP/1.1

   To allow for transition to absolute-URIs in all requests (or later) requests; such knowledge might
   be in future
   versions the form of HTTP, all HTTP/1.1 servers specific user configuration or by remembering the
   version of a prior received response.  A server MUST accept NOT send a
   response containing Transfer-Encoding unless the absolute-URI
   form in requests, even though corresponding
   request indicates HTTP/1.1 clients will only generate
   them in requests to proxies.

   If a proxy (or later).

   A server that receives a host name that is not request message with a fully qualified domain
   name, transfer-coding it MAY add its domain to
   does not understand SHOULD respond with 501 (Not Implemented) and
   then close the host name it received.  If connection.

3.3.2.  Content-Length

   When a proxy
   receives message does not have a fully qualified domain name, Transfer-Encoding header field and the proxy MUST NOT change
   payload body length can be determined prior to being transferred, a
   Content-Length header field SHOULD be sent to indicate the
   host name.

   The "authority form" length of
   the payload body that is only used by either present as the message body, for
   requests and non-HEAD responses other than 304, or would have been
   present had the CONNECT request method
   (Section 6.9 of [Part2]). been an unconditional GET.  The most common form length is
   expressed as a decimal number of request-target octets.

     Content-Length = 1*DIGIT

   An example is that used when making

     Content-Length: 3495

   In the case of a
   request response to an origin server ("origin form"). a HEAD request, Content-Length indicates
   the size of the payload body (without any potential transfer-coding)
   that would have been sent had the request been a GET.  In this case, the
   absolute path and query components case of
   a 304 (Not Modified) response to a GET request, Content-Length
   indicates the URI MUST be transmitted as size of the payload body (without any potential
   transfer-coding) that would have been sent in a 200 (OK) response.

   HTTP's use of Content-Length is significantly different from how it
   is used in MIME, where it is an optional field used only within the
   "message/external-body" media-type.

   Any Content-Length field value greater than or equal to zero is
   valid.  Since there is no predefined limit to the request-target, length of an HTTP
   payload, recipients SHOULD anticipate potentially large decimal
   numerals and prevent parsing errors due to integer conversion
   overflows (Section 8.6).

   If a message is received that has multiple Content-Length header
   fields (Section 3.3.2) with field-values consisting of the authority component MUST be transmitted
   in same
   decimal value, or a Host single Content-Length header field.  For example, field with a client wishing to retrieve field
   value containing a
   representation list of identical decimal values (e.g., "Content-
   Length: 42, 42"), indicating that duplicate Content-Length header
   fields have been generated or combined by an upstream message
   processor, then the resource, recipient MUST either reject the message as identified above, directly from
   invalid or replace the origin server would open (or reuse) duplicated field-values with a TCP connection to port 80
   of the host "www.example.org" and send the lines:

     GET /pub/WWW/TheProject.html HTTP/1.1
     Host: www.example.org

   followed by the remainder of the Request.  Note single valid
   Content-Length field containing that decimal value prior to
   determining the origin form message body length.

3.3.3.  Message Body Length

   The length of request-target always starts with an absolute path; if the target
   resource's URI path a message body is empty, then an absolute path determined by one of "/" MUST be
   provided in the request-target.

   If following
   (in order of precedence):

   1.  Any response to a proxy receives an OPTIONS HEAD request with an absolute-URI form of
   request-target in which the URI has an empty path and no query
   component, then the last proxy on the request chain MUST use any response with a
   request-target status
       code of "*" when it forwards the request to the indicated
   origin server.

   For example, the request

     OPTIONS http://www.example.org:8001 HTTP/1.1

   would be forwarded 100-199, 204, or 304 is always terminated by the final proxy as

     OPTIONS * HTTP/1.1
     Host: www.example.org:8001 first
       empty line after connecting to port 8001 the header fields, regardless of host "www.example.org".

   The request-target is transmitted in the format specified header
       fields present in
   Section 2.7.1.  If the request-target is percent-encoded ([RFC3986],
   Section 2.1), message, and thus cannot contain a message
       body.

   2.  Any successful (2xx) response to a CONNECT request implies that
       the origin server MUST decode connection will become a tunnel immediately after the request-target in
   order to properly interpret empty
       line that concludes the request.  Servers SHOULD respond to
   invalid request-targets with an appropriate status code. header fields.  A non-transforming proxy client MUST NOT rewrite the "path-absolute" ignore any
       Content-Length or Transfer-Encoding header fields received in
       such a message.

   3.  If a Transfer-Encoding header field is present and
   "query" parts of the received request-target when forwarding it to "chunked"
       transfer-coding (Section 4.1) is the next inbound server, except as noted above to replace a null
   path-absolute with "/" or "*".

      Note: The "no rewrite" rule prevents final encoding, the proxy from changing message
       body length is determined by reading and decoding the
      meaning of chunked
       data until the request when transfer-coding indicates the origin server data is improperly using complete.

       If a non-reserved URI character for Transfer-Encoding header field is present in a reserved purpose.  Implementors
      need to be aware that some pre-HTTP/1.1 proxies have been known to
      rewrite response and
       the request-target.

4.2.  The Resource Identified "chunked" transfer-coding is not the final encoding, the
       message body length is determined by a Request

   The exact resource identified reading the connection until
       it is closed by an Internet the server.  If a Transfer-Encoding header field
       is present in a request and the "chunked" transfer-coding is determined by
   examining both not
       the request-target and final encoding, the message body length cannot be determined
       reliably; the Host header field.

   An origin server that does not allow resources to differ by MUST respond with the
   requested host MAY ignore 400 (Bad Request)
       status code and then close the Host connection.

       If a message is received with both a Transfer-Encoding header
       field value when
   determining and a Content-Length header field, the resource identified by Transfer-Encoding
       overrides the Content-Length.  Such a message might indicate an HTTP/1.1 request.  (But see
   Appendix A.1.1 for other requirements on Host support in HTTP/1.1.)

   An origin server that does differentiate resources based
       attempt to perform request or response smuggling (bypass of
       security-related checks on the host
   requested (sometimes referred message routing or content) and thus
       ought to be handled as virtual hosts or vanity host
   names) an error.  The provided Content-Length
       MUST use be removed, prior to forwarding the following rules for determining message downstream, or
       replaced with the requested
   resource on an HTTP/1.1 request:

   1.  If request-target is an absolute-URI, real message body length after the host transfer-
       coding is part of the
       request-target.  Any Host decoded.

   4.  If a message is received without Transfer-Encoding and with
       either multiple Content-Length header fields having differing
       field-values or a single Content-Length header field value in having an
       invalid value, then the request message framing is invalid and MUST be ignored.

   2.
       treated as an error to prevent request or response smuggling.  If the request-target
       this is not an absolute-URI, and the a request
       includes message, the server MUST respond with a Host header field, 400
       (Bad Request) status code and then close the host connection.  If this
       is determined a response message received by a proxy, the Host
       header field value.

   3.  If proxy MUST discard
       the host received response, send a 502 (Bad Gateway) status code as determined by rule 1 or 2
       its downstream response, and then close the connection.  If this
       is not a valid host on
       the server, the response message received by a user-agent, it MUST be a 400 (Bad Request) error
       message.

   Recipients of
       treated as an HTTP/1.0 request that lacks error by discarding the message and closing the
       connection.

   5.  If a Host valid Content-Length header field MAY
   attempt to use heuristics (e.g., examination of is present without
       Transfer-Encoding, its decimal value defines the URI path for
   something unique to a particular host) message body
       length in order to determine what
   exact resource octets.  If the actual number of octets sent in the
       message is being requested.

4.3.  Effective Request URI

   HTTP requests often do not carry less than the absolute URI ([RFC3986], Section
   4.3) for indicated Content-Length, the target resource; instead, recipient
       MUST consider the URI needs message to be inferred
   from the request-target, Host header field, incomplete and connection context.
   The result of this process is called the "effective request URI".
   The "target resource" is the resource identified by treat the effective
   request URI.
       connection as no longer usable.  If the request-target is an absolute-URI, then actual number of octets
       sent in the effective request
   URI message is more than the request-target.

   If the request-target uses indicated Content-Length,
       the origin form or recipient MUST only process the asterisk form, and message body up to the Host header field is present, then the effective request URI is
   constructed by concatenating

   o  the scheme name: "http" if the request was received over an
      insecure TCP connection, or "https" when received over a SSL/
      TLS-secured TCP connection,

   o
       value's number of octets; the octet sequence "://",

   o remainder of the authority component, message MUST
       either be discarded or treated as specified the next message in a pipeline.
       For the Host header field
      (Section 8.3), sake of robustness, a user-agent MAY attempt to detect
       and

   o  the request-target obtained from the Request-Line, unless the
      request-target correct such an error in message framing if it is just parsing the asterisk "*".

   If
       response to the request-target uses last request on a connection and the origin form or connection
       has been closed by the asterisk form, server.

   6.  If this is a request message and none of the Host header field is not present, above are true, then
       the effective request URI message body length is zero (no message body is undefined. present).

   7.  Otherwise, when request-target uses the authority form, the effective
   request URI this is undefined.

   Example 1: the effective request URI for a response message without a declared message
       body length, so the message

     GET /pub/WWW/TheProject.html HTTP/1.1
     Host: www.example.org:8080

   (received over an insecure TCP connection) body length is "http", plus "://",
   plus the authority component "www.example.org:8080", plus determined by the
   request-target "/pub/WWW/TheProject.html", thus
   "http://www.example.org:8080/pub/WWW/TheProject.html".

   Example 2:
       number of octets received prior to the effective request URI for server closing the message

     OPTIONS * HTTP/1.1
     Host: www.example.org

   (received over an SSL/TLS secured TCP connection)
       connection.

   Since there is "https", plus
   "://", plus the authority component "www.example.org", thus
   "https://www.example.org".

   Effective request URIs are compared using the rules described in
   Section 2.7.3, except that empty path components MUST NOT be treated
   as equivalent to an absolute path of "/".

5.  Protocol Parameters

5.1.  Transfer Codings

   Transfer-coding values are used no way to indicate an distinguish a successfully completed, close-
   delimited message from a partially-received message interrupted by
   network failure, implementations SHOULD use encoding
   transformation or length-
   delimited messages whenever possible.  The close-delimiting feature
   exists primarily for backwards compatibility with HTTP/1.0.

   A server MAY reject a request that has been, can be, or might need to be applied to contains a payload message body in order to ensure "safe transport" through the
   network.  This differs from but not a content coding in
   Content-Length by responding with 411 (Length Required).

   Unless a transfer-coding other than "chunked" has been applied, a
   client that the transfer-
   coding is sends a property of request containing a message body SHOULD use a
   valid Content-Length header field if the message body length is known
   in advance, rather than the "chunked" encoding, since some existing
   services respond to "chunked" with a property of 411 (Length Required) status
   code even though they understand the
   representation that chunked encoding.  This is being transferred.

     transfer-coding         = "chunked" ; Section 5.1.1
                             / "compress" ; Section 5.1.2.1
                             / "deflate" ; Section 5.1.2.2
                             / "gzip" ; Section 5.1.2.3
                             / transfer-extension
     transfer-extension      = token *( OWS ";" OWS transfer-parameter )

   Parameters
   typically because such services are implemented via a gateway that
   requires a content-length in the form advance of attribute/value pairs.

     transfer-parameter      = attribute BWS "=" BWS value
     attribute               = token
     value                   = word

   All transfer-coding values are case-insensitive.  HTTP/1.1 uses
   transfer-coding values in the TE header field (Section 8.4) being called and in
   the Transfer-Encoding header field (Section 8.6).

   Transfer-codings are analogous to the Content-Transfer-Encoding
   values of MIME, which were designed to enable safe transport of
   binary data over a 7-bit transport service ([RFC2045], Section 6).
   However, safe transport has a different focus for an 8bit-clean
   transfer protocol.  In HTTP, the only unsafe characteristic of
   message-bodies server
   is the difficulty in determining the exact message
   body length (Section 3.3), unable or the desire unwilling to encrypt data over a
   shared transport. buffer the entire request before
   processing.

   A server client that receives sends a request containing a message with body MUST include
   a transfer-coding valid Content-Length header field if it does not understand SHOULD respond with 501 (Not Implemented) and
   then close know the connection.  A server MUST NOT send transfer-codings
   to an HTTP/1.0 client.

5.1.1.  Chunked Transfer Coding

   The chunked encoding modifies the body of a message
   will handle HTTP/1.1 (or later) requests; such knowledge can be in order to
   transfer it as a series
   the form of chunks, each with its own size indicator,
   followed specific user configuration or by an OPTIONAL trailer containing header fields.  This
   allows dynamically produced content to be transferred along with the
   information necessary for the recipient to verify that it has
   received remembering the full message.

     Chunked-Body   = *chunk
                      last-chunk
                      trailer-part
                      CRLF

     chunk          = chunk-size [ chunk-ext ] CRLF
                      chunk-data CRLF
     chunk-size     = 1*HEXDIG
     last-chunk     = 1*("0") [ chunk-ext ] CRLF

     chunk-ext      = *( ";" chunk-ext-name
                         [ "=" chunk-ext-val ] )
     chunk-ext-name = token
     chunk-ext-val  = token / quoted-str-nf
     chunk-data     = 1*OCTET ; a sequence version
   of chunk-size octets
     trailer-part   = *( header-field CRLF )

     quoted-str-nf  = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
                    ; like quoted-string, but disallowing line folding
     qdtext-nf      = HTAB / SP / %x21 / %x23-5B / %x5D-7E / obs-text

   The chunk-size field is a string of hex digits indicating the size of
   the chunk-data in octets.  The chunked encoding is ended by any chunk
   whose size is zero, followed by prior received response.

3.4.  Handling Incomplete Messages

   Request messages that are prematurely terminated, possibly due to a
   cancelled connection or a server-imposed time-out exception, MUST
   result in closure of the trailer, which connection; sending an HTTP/1.1 error
   response prior to closing the connection is terminated OPTIONAL.

   Response messages that are prematurely terminated, usually by
   an empty line.

   The trailer allows closure
   of the sender connection prior to include additional HTTP header
   fields at receiving the end expected number of the message.  The Trailer header field can be
   used octets or
   by failure to indicate which header fields are included in decode a trailer (see
   Section 8.5). transfer-encoded message body, MUST be
   recorded as incomplete.  A server using chunked transfer-coding in a response MUST NOT use that terminates in the
   trailer for any header fields unless at least one middle of
   the following is
   true:

   1.  the request included a TE header field that indicates "trailers" block (before the empty line is acceptable in received) cannot be
   assumed to convey the transfer-coding full semantics of the response, response and MUST be
   treated as
       described in Section 8.4; or,

   2. an error.

   A message body that uses the trailer fields consist entirely of optional metadata, and chunked transfer encoding is incomplete
   if the
       recipient could use zero-sized chunk that terminates the encoding has not been
   received.  A message (in that uses a manner acceptable to valid Content-Length is incomplete
   if the
       server where size of the field originated) without receiving it.  In
       other words, message body received (in octets) is less than the server
   value given by Content-Length.  A response that generated the header (often but not
       always has neither chunked
   transfer encoding nor Content-Length is terminated by closure of the origin server)
   connection, and thus is willing to accept considered complete regardless of the possibility number
   of message body octets received, provided that the trailer fields might header block was
   received intact.

   A user agent MUST NOT render an incomplete response message body as
   if it were complete (i.e., some indication must be silently discarded along the
       path given to the client.

   This requirement prevents user
   that an interoperability failure when error occurred).  Cache requirements for incomplete responses
   are defined in Section 2.1 of [Part6].

   A server MUST read the entire request message is being received by an HTTP/1.1 (or later) proxy and
   forwarded to an HTTP/1.0 recipient.  It avoids a situation where
   compliance with the protocol would have necessitated a possibly
   infinite buffer on body or close the proxy.

   A process for decoding
   connection after sending its response, since otherwise the "chunked" transfer-coding can be
   represented in pseudo-code as:

     length := 0
     read chunk-size, chunk-ext (if any) and CRLF
     while (chunk-size > 0) {
        read chunk-data and CRLF
        append chunk-data to decoded-body
        length := length + chunk-size
        read chunk-size and CRLF
     }
     read header-field
     while (header-field not empty) {
        append header-field to existing header fields
        read header-field
     }
     Content-Length := length
     Remove "chunked" from Transfer-Encoding

   All HTTP/1.1 applications MUST remaining
   data on a persistent connection would be able to receive and decode misinterpreted as the
   "chunked" transfer-coding and next
   request.  Likewise, a client MUST ignore chunk-ext extensions they
   do not understand.

   Since "chunked" is read the only transfer-coding required to be understood
   by HTTP/1.1 recipients, entire response message
   body if it plays intends to reuse the same connection for a crucial role in delimiting
   messages subsequent
   request.  Pipelining multiple requests on a persistent connection.  Whenever connection is described
   in Section 6.3.2.2.

3.5.  Message Parsing Robustness

   Older HTTP/1.0 client implementations might send an extra CRLF after
   a POST request as a transfer-coding is
   applied lame workaround for some early server
   applications that failed to a payload read message body in content that was not
   terminated by a request, the final transfer-coding
   applied line-ending.  An HTTP/1.1 client MUST be "chunked". NOT preface or
   follow a request with an extra CRLF.  If terminating the request
   message body with a transfer-coding line-ending is applied to a
   response payload body, desired, then either the final transfer-coding applied client MUST be "chunked" or
   include the message MUST be terminated by closing terminating CRLF octets as part of the
   connection.  When message body
   length.

   In the "chunked" transfer-coding interest of robustness, servers SHOULD ignore at least one
   empty line received where a request-line is used, it MUST be expected.  In other
   words, if the last transfer-coding applied to form server is reading the message-body.  The
   "chunked" transfer-coding MUST NOT be applied more than once in a
   message-body.

5.1.2.  Compression Codings

   The codings defined below can be used to compress protocol stream at the payload beginning
   of a
   message.

      Note: Use of program names message and receives a CRLF first, it SHOULD ignore the CRLF.
   Likewise, although the line terminator for the identification of encoding
      formats is not desirable start-line and header
   fields is discouraged the sequence CRLF, we recommend that recipients recognize a
   single LF as a line terminator and ignore any CR.

   When a server listening only for future encodings.
      Their use here is representative of historical practice, not good
      design.

      Note: For compatibility with previous implementations HTTP request messages, or processing
   what appears from the start-line to be an HTTP request message,
   receives a sequence of HTTP,
      applications SHOULD consider "x-gzip" and "x-compress" octets that does not match the HTTP-message
   grammar aside from the robustness exceptions listed above, the server
   MUST respond with an HTTP/1.1 400 (Bad Request) response.

4.  Transfer Codings

   Transfer-coding values are used to indicate an encoding
   transformation that has been, can be, or might need to be
      equivalent applied to "gzip" and "compress" respectively.

5.1.2.1.  Compress Coding

   The "compress" format is produced by
   a payload body in order to ensure "safe transport" through the common UNIX file compression
   program "compress".
   network.  This format is an adaptive Lempel-Ziv-Welch differs from a content coding (LZW).

5.1.2.2.  Deflate Coding

   The "deflate" format is defined as the "deflate" compression
   mechanism (described in [RFC1951]) used inside that the "zlib" data format
   ([RFC1950]).

      Note: Some incorrect implementations send transfer-
   coding is a property of the "deflate" compressed
      data without message rather than a property of the zlib wrapper.

5.1.2.3.  Gzip Coding

   The "gzip" format
   representation that is produced by the file compression program being transferred.

     transfer-coding    = "chunked" ; Section 4.1
                        / "compress" ; Section 4.2.1
                        / "deflate" ; Section 4.2.2
                        / "gzip"
   (GNU zip), as described ; Section 4.2.3
                        / transfer-extension
     transfer-extension = token *( OWS ";" OWS transfer-parameter )

   Parameters are in [RFC1952].  This format is a Lempel-Ziv
   coding (LZ77) with a 32 bit CRC.

5.1.3.  Transfer Coding Registry the form of attribute/value pairs.

     transfer-parameter = attribute BWS "=" BWS value
     attribute          = token
     value              = word

   All transfer-coding values are case-insensitive.  The HTTP Transfer
   Coding Registry defines the name space for the
   transfer registry is defined in Section 7.4.  HTTP/1.1 uses transfer-
   coding names.

   Registrations MUST include values in the TE header field (Section 4.3) and in the following fields:

   o  Name

   o  Description

   o  Pointer to specification text

   Names
   Transfer-Encoding header field (Section 3.3.1).

4.1.  Chunked Transfer Coding

   The chunked encoding modifies the body of a message in order to
   transfer codings MUST NOT overlap with names it as a series of chunks, each with its own size indicator,
   followed by an OPTIONAL trailer containing header fields.  This
   allows dynamically produced content
   codings (Section 2.2 of [Part3]), unless the encoding transformation
   is identical (as it is to be transferred along with the case
   information necessary for the compression codings defined
   in Section 5.1.2).

   Values to be added recipient to this name space require verify that it has
   received the full message.

     chunked-body   = *chunk
                      last-chunk
                      trailer-part
                      CRLF

     chunk          = chunk-size [ chunk-ext ] CRLF
                      chunk-data CRLF
     chunk-size     = 1*HEXDIG
     last-chunk     = 1*("0") [ chunk-ext ] CRLF

     chunk-ext      = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
     chunk-ext-name = token
     chunk-ext-val  = token / quoted-str-nf
     chunk-data     = 1*OCTET ; a specification (see
   "Specification Required" in Section 4.1 sequence of [RFC5226]), and MUST
   conform to chunk-size octets
     trailer-part   = *( header-field CRLF )

     quoted-str-nf  = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
                    ; like quoted-string, but disallowing line folding
     qdtext-nf      = HTAB / SP / %x21 / %x23-5B / %x5D-7E / obs-text

   The chunk-size field is a string of hex digits indicating the purpose size of transfer coding defined
   the chunk-data in this section. octets.  The registry itself chunked encoding is maintained at
   <http://www.iana.org/assignments/http-parameters>.

5.2.  Product Tokens

   Product tokens are used to allow communicating applications to
   identify themselves ended by software name and version.  Most fields using
   product tokens also allow sub-products any chunk
   whose size is zero, followed by the trailer, which form a significant part
   of is terminated by
   an empty line.

   The trailer allows the application sender to be listed, separated by whitespace.  By
   convention, include additional HTTP header
   fields at the products are listed in order end of their significance
   for identifying the application.

     product         = token ["/" product-version]
     product-version = token

   Examples:

     User-Agent: CERN-LineMode/2.15 libwww/2.17b3
     Server: Apache/0.8.4

   Product tokens SHOULD message.  The Trailer header field can be short and
   used to the point.  They indicate which header fields are included in a trailer (see
   Section 4.4).

   A server using chunked transfer-coding in a response MUST NOT be
   used use the
   trailer for advertising or other non-essential information.  Although any token octet MAY appear in a product-version, this token SHOULD
   only be used for a version identifier (i.e., successive versions header fields unless at least one of the same product SHOULD only differ following is
   true:

   1.  the request included a TE header field that indicates "trailers"
       is acceptable in the product-version portion transfer-coding of the product value).

5.3.  Quality Values

   Both transfer codings (TE request header field, response, as
       described in Section 8.4) and
   content negotiation (Section 5 4.3; or,

   2.  the trailer fields consist entirely of [Part3]) optional metadata, and the
       recipient could use short "floating point"
   numbers the message (in a manner acceptable to indicate the relative importance ("weight") of various
   negotiable parameters.  A weight
       server where the field originated) without receiving it.  In
       other words, the server that generated the header (often but not
       always the origin server) is normalized willing to accept the possibility
       that the trailer fields might be silently discarded along the
       path to the client.

   This requirement prevents an interoperability failure when the
   message is being received by an HTTP/1.1 (or later) proxy and
   forwarded to an HTTP/1.0 recipient.  It avoids a real number in
   the range 0 through 1, situation where 0 is the minimum and 1
   conformance with the maximum
   value.  If a parameter has protocol would have necessitated a quality value of 0, then content with
   this parameter is "not acceptable" possibly
   infinite buffer on the proxy.

   A process for decoding the client. "chunked" transfer-coding can be
   represented in pseudo-code as:

     length := 0
     read chunk-size, chunk-ext (if any) and CRLF
     while (chunk-size > 0) {
        read chunk-data and CRLF
        append chunk-data to decoded-body
        length := length + chunk-size
        read chunk-size and CRLF
     }
     read header-field
     while (header-field not empty) {
        append header-field to existing header fields
        read header-field
     }
     Content-Length := length
     Remove "chunked" from Transfer-Encoding

   All HTTP/1.1 applications MUST NOT generate more than three digits after the
   decimal point.  User configuration of these values SHOULD also be
   limited in this fashion.

     qvalue         = ( "0" [ "." 0*3DIGIT ] )
                    / ( "1" [ "." 0*3("0") ] )

      Note: "Quality values" is a misnomer, since these values merely
      represent relative degradation in desired quality.

6.  Connections

6.1.  Persistent Connections

6.1.1.  Purpose

   Prior able to persistent connections, a separate TCP connection was
   established for each request, increasing the load on HTTP servers receive and
   causing congestion on decode the Internet.  The use
   "chunked" transfer-coding and MUST ignore chunk-ext extensions they
   do not understand.

   Use of inline images chunk-ext extensions by senders is deprecated; they SHOULD NOT
   be sent and
   other associated data often requires a client to make multiple
   requests definition of new chunk-extensions is discouraged.

4.2.  Compression Codings

   The codings defined below can be used to compress the same server in payload of a short amount
   message.

      Note: Use of time.  Analysis program names for the identification of
   these performance problems and results from a prototype
   implementation are available [Pad1995] [Spe].  Implementation
   experience encoding
      formats is not desirable and measurements is discouraged for future encodings.
      Their use here is representative of actual HTTP/1.1 implementations show historical practice, not good results [Nie1997].  Alternatives have also been explored, for
   example, T/TCP [Tou1998].

   Persistent HTTP connections have a number
      design.

      Note: For compatibility with previous implementations of advantages:

   o  By opening HTTP,
      applications SHOULD consider "x-gzip" and closing fewer TCP connections, CPU time "x-compress" to be
      equivalent to "gzip" and "compress" respectively.

4.2.1.  Compress Coding

   The "compress" format is saved produced by the common UNIX file compression
   program "compress".  This format is an adaptive Lempel-Ziv-Welch
   coding (LZW).

4.2.2.  Deflate Coding

   The "deflate" format is defined as the "deflate" compression
   mechanism (described in
      routers and hosts (clients, servers, proxies, gateways, tunnels,
      or caches), and memory [RFC1951]) used for TCP protocol control blocks can be
      saved inside the "zlib" data format
   ([RFC1950]).

      Note: Some incorrect implementations send the "deflate" compressed
      data without the zlib wrapper.

4.2.3.  Gzip Coding

   The "gzip" format is produced by the file compression program "gzip"
   (GNU zip), as described in hosts.

   o  HTTP requests and responses can be pipelined on [RFC1952].  This format is a connection.
      Pipelining allows Lempel-Ziv
   coding (LZ77) with a 32 bit CRC.

4.3.  TE

   The "TE" header field indicates what extension transfer-codings the
   client to make multiple requests without
      waiting for each response, allowing a single TCP connection to be
      used much more efficiently, with much lower elapsed time.

   o  Network congestion is reduced by reducing willing to accept in the number of packets
      caused by TCP opens, response, and by allowing TCP sufficient time whether or not it is
   willing to
      determine accept trailer fields in a chunked transfer-coding.

   Its value consists of the congestion state keyword "trailers" and/or a comma-separated
   list of extension transfer-coding names with optional accept
   parameters (as described in Section 4).

     TE        = #t-codings
     t-codings = "trailers" / ( transfer-extension [ te-params ] )
     te-params = OWS ";" OWS "q=" qvalue *( te-ext )
     te-ext    = OWS ";" OWS token [ "=" word ]

   The presence of the network.

   o  Latency on subsequent requests is reduced since there keyword "trailers" indicates that the client is no time
      spent
   willing to accept trailer fields in TCP's connection opening handshake.

   o  HTTP can evolve more gracefully, since errors can be reported
      without the penalty a chunked transfer-coding, as
   defined in Section 4.1.  This keyword is reserved for use with
   transfer-coding values even though it does not itself represent a
   transfer-coding.

   Examples of closing its use are:

     TE: deflate
     TE:
     TE: trailers, deflate;q=0.5

   The TE header field only applies to the TCP immediate connection.  Clients using
      future versions of HTTP might optimistically try
   Therefore, the keyword MUST be supplied within a new feature,
      but if communicating with an older server, retry with old
      semantics after an error Connection header
   field (Section 6.1) whenever TE is reported.

   HTTP implementations SHOULD implement persistent connections.

6.1.2.  Overall Operation

   A significant difference between present in an HTTP/1.1 and earlier versions of
   HTTP message.

   A server tests whether a transfer-coding is acceptable, according to
   a TE field, using these rules:

   1.  The "chunked" transfer-coding is always acceptable.  If the
       keyword "trailers" is listed, the client indicates that persistent connections are it is
       willing to accept trailer fields in the default behavior chunked response on
       behalf of itself and any
   HTTP connection.  That is, unless otherwise indicated, downstream clients.  The implication is
       that, if given, the client
   SHOULD assume is stating that either all downstream
       clients are willing to accept trailer fields in the server forwarded
       response, or that it will maintain a persistent connection,
   even after error responses from attempt to buffer the server.

   Persistent connections provide response on
       behalf of downstream recipients.

       Note: HTTP/1.1 does not define any means to limit the size of a mechanism by which
       chunked response such that a client and a
   server can signal be assured of buffering
       the close entire response.

   2.  If the transfer-coding being tested is one of the transfer-
       codings listed in the TE field, then it is acceptable unless it
       is accompanied by a qvalue of 0.  (As defined in Section 4.3.1, a
       qvalue of 0 means "not acceptable".)

   3.  If multiple transfer-codings are acceptable, then the acceptable
       transfer-coding with the highest non-zero qvalue is preferred.
       The "chunked" transfer-coding always has a qvalue of 1.

   If the TE field-value is empty or if no TE field is present, the only
   acceptable transfer-coding is "chunked".  A message with no transfer-
   coding is always acceptable.

4.3.1.  Quality Values

   Both transfer codings (TE request header field, Section 4.3) and
   content negotiation (Section 5 of [Part3]) use short "floating point"
   numbers to indicate the relative importance ("weight") of various
   negotiable parameters.  A weight is normalized to a TCP connection.  This signaling
   takes place using real number in
   the Connection header field (Section 8.1).  Once range 0 through 1, where 0 is the minimum and 1 the maximum
   value.  If a
   close parameter has been signaled, a quality value of 0, then content with
   this parameter is "not acceptable" for the client client.  HTTP/1.1
   applications MUST NOT send any generate more requests
   on that connection.

6.1.2.1.  Negotiation

   An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
   maintain a persistent connection unless a Connection header field
   including the connection-token "close" was sent in the request.  If
   the server chooses to close the connection immediately than three digits after sending the response, it
   decimal point.  User configuration of these values SHOULD send also be
   limited in this fashion.

     qvalue         = ( "0" [ "." 0*3DIGIT ] )
                    / ( "1" [ "." 0*3("0") ] )

      Note: "Quality values" is a Connection misnomer, since these values merely
      represent relative degradation in desired quality.

4.4.  Trailer

   The "Trailer" header field including the
   connection-token "close".

   An HTTP/1.1 client MAY expect a connection to remain open, but would
   decide to keep it open based on whether indicates that the response from a server
   contains a Connection given set of header field with the connection-token close.

   In case
   fields is present in the client does not want to maintain trailer of a connection for more
   than that request, it message encoded with chunked
   transfer-coding.

     Trailer = 1#field-name

   An HTTP/1.1 message SHOULD send include a Connection Trailer header field including
   the connection-token close.

   If either the client or the server sends in a
   message using chunked transfer-coding with a non-empty trailer.
   Doing so allows the close token recipient to know which header fields to expect
   in the
   Connection trailer.

   If no Trailer header field, that request becomes the last one for field is present, the
   connection.

   Clients and servers trailer SHOULD NOT assume that a persistent connection is
   maintained for HTTP versions less than 1.1 unless it is explicitly
   signaled. include
   any header fields.  See Appendix A.1.2 Section 4.1 for more information on backward
   compatibility with HTTP/1.0 clients.

   In order to remain persistent, all messages restrictions on the connection MUST
   have a self-defined message length (i.e., one not defined by closure use of the connection), as described
   trailer fields in Section 3.3.

6.1.2.2.  Pipelining

   A client that supports persistent connections MAY "pipeline" its
   requests (i.e., send multiple requests without waiting for each
   response).  A server MUST send its responses to those requests a "chunked" transfer-coding.

   Message header fields listed in the
   same order that the requests were received.

   Clients which assume persistent connections and pipeline immediately
   after connection establishment SHOULD be prepared to retry their
   connection if the first pipelined attempt fails.  If a client does
   such a retry, it Trailer header field MUST NOT pipeline before it knows
   include the connection following header fields:

   o  Transfer-Encoding

   o  Content-Length

   o  Trailer

5.  Message Routing

   HTTP request message routing is
   persistent.  Clients MUST also be prepared to resend their requests
   if the server closes determined by each client based on
   the connection before sending all of target resource, the
   corresponding responses.

   Clients SHOULD NOT pipeline requests using non-idempotent request
   methods client's proxy configuration, and
   establishment or non-idempotent sequences of request methods (see Section
   6.1.2 of [Part2]).  Otherwise, a premature termination reuse of an inbound connection.  The corresponding
   response routing follows the
   transport same connection could lead to indeterminate results.  A client
   wishing chain back to send the
   client.

5.1.  Identifying a non-idempotent request SHOULD wait Target Resource

   HTTP is used in a wide variety of applications, ranging from general-
   purpose computers to send that
   request until it has received home appliances.  In some cases, communication
   options are hard-coded in a client's configuration.  However, most
   HTTP clients rely on the response status line same resource identification mechanism and
   configuration techniques as general-purpose Web browsers.

   HTTP communication is initiated by a user agent for the
   previous request.

6.1.3.  Proxy Servers

   It some purpose.
   The purpose is especially important that proxies correctly implement the
   properties a combination of the Connection header field as specified request semantics, which are defined
   in
   Section 8.1.

   The proxy server MUST signal persistent connections separately with
   its clients [Part2], and the origin servers (or other proxy servers) that it
   connects to.  Each persistent connection applies a target resource upon which to only one
   transport link. apply those
   semantics.  A proxy server MUST NOT establish a HTTP/1.1 persistent connection
   with URI reference (Section 2.7) is typically used as an HTTP/1.0 client (but see Section 19.7.1 of [RFC2068]
   identifier for
   information and discussion of the problems with "target resource", which a user agent would
   resolve to its absolute form in order to obtain the Keep-Alive header
   field implemented by many HTTP/1.0 clients).

6.1.3.1.  End-to-end and Hop-by-hop Header Fields

   For "target URI".
   The target URI excludes the purpose of defining reference's fragment identifier
   component, if any, since fragment identifiers are reserved for
   client-side processing ([RFC3986], Section 3.5).

   HTTP intermediaries obtain the behavior of caches request semantics and non-caching
   proxies, we divide HTTP header fields into two categories:

   o  End-to-end header fields, which are transmitted to target URI from
   the ultimate
      recipient request-line of an incoming request message.

5.2.  Connecting Inbound

   Once the target URI is determined, a client needs to decide whether a
   network request or response.  End-to-end header fields in
      responses MUST is necessary to accomplish the desired semantics and,
   if so, where that request is to be stored as part of directed.

   If the client has a response cache entry and MUST the request semantics can be
      transmitted in any response formed from
   satisfied by a cache entry.

   o  Hop-by-hop header fields, which are meaningful only for ([Part6]), then the request is usually directed
   to the cache first.

   If the request is not satisfied by a single
      transport-level connection, cache, then a typical client
   will check its configuration to determine whether a proxy is to be
   used to satisfy the request.  Proxy configuration is implementation-
   dependent, but is often based on URI prefix matching, selective
   authority matching, or both, and are not stored the proxy itself is usually
   identified by caches an "http" or
      forwarded "https" URI.  If a proxy is applicable,
   the client connects inbound by proxies.

   The following HTTP/1.1 header fields are hop-by-hop header fields:

   o  Connection

   o  Keep-Alive

   o  Proxy-Authenticate

   o  Proxy-Authorization

   o  TE

   o  Trailer

   o  Transfer-Encoding

   o  Upgrade

   All other header fields establishing (or reusing) a connection
   to that proxy.

   If no proxy is applicable, a typical client will invoke a handler
   routine, usually specific to the target URI's scheme, to connect
   directly to an authority for the target resource.  How that is
   accomplished is dependent on the target URI scheme and defined by HTTP/1.1 are end-to-end header
   fields.

   Other hop-by-hop header fields MUST be listed in a Connection header
   field (Section 8.1).

6.1.3.2.  Non-modifiable Header Fields

   Some features its
   associated specification, similar to how this specification defines
   origin server access for resolution of HTTP/1.1, such as Digest Authentication, depend on the value of certain end-to-end header fields.  A non-transforming
   proxy SHOULD NOT modify "http" (Section 2.7.1) and
   "https" (Section 2.7.2) schemes.

5.3.  Request Target

   Once an end-to-end header field unless inbound connection is obtained (Section 6), the
   definition of that header field requires or specifically allows that.

   A non-transforming proxy MUST NOT modify any client sends
   an HTTP request message (Section 3) with a request-target derived
   from the target URI.  There are four distinct formats for the
   request-target, depending on both the method being requested and
   whether the request is to a proxy.

     request-target = origin-form
                    / absolute-form
                    / authority-form
                    / asterisk-form

     origin-form    = path-absolute [ "?" query ]
     absolute-form  = absolute-URI
     authority-form = authority
     asterisk-form  = "*"

   The most common form of request-target is the following fields
   in origin-form.  When
   making a request directly to an origin server, other than a CONNECT
   or response, and it server-wide OPTIONS request (as detailed below), a client MUST NOT add any
   send only the absolute path and query components of these fields if
   not already present:

   o  Allow

   o  Content-Location

   o  Content-MD5

   o  ETag

   o  Last-Modified

   o  Server

   A non-transforming proxy the target URI as
   the request-target.  If the target URI's path component is empty,
   then the client MUST NOT modify any of send "/" as the following fields
   in a response:

   o  Expires

   but it MAY add any path within the origin-form of these fields if not already present.  If an
   Expires
   request-target.  A Host header field is added, it MUST be given also sent, as defined in
   Section 5.4, containing the target URI's authority component
   (excluding any userinfo).

   For example, a client wishing to retrieve a representation of the
   resource identified as

     http://www.example.org/where?q=now

   directly from the origin server would open (or reuse) a field-value
   identical TCP
   connection to that port 80 of the Date header field in that response.

   A proxy MUST NOT modify or add any host "www.example.org" and send the
   lines:

     GET /where?q=now HTTP/1.1
     Host: www.example.org

   followed by the remainder of the following fields in request message.

   When making a
   message that contains the no-transform cache-control directive, request to a proxy, other than a CONNECT or server-wide
   OPTIONS request (as detailed below), a client MUST send the target
   URI in
   any request:

   o  Content-Encoding

   o  Content-Range

   o  Content-Type

   A transforming absolute-form as the request-target.  The proxy MAY modify or add these fields is requested
   to a message either service that
   does not include no-transform, but if it does so, it MUST add request from a
   Warning 214 (Transformation applied) valid cache, if one does not already appear
   in possible, or
   make the message (see Section 3.6 of [Part6]).

      Warning: Unnecessary modification of end-to-end header fields
      might cause authentication failures if stronger authentication
      mechanisms are introduced in later versions of HTTP.  Such
      authentication mechanisms MAY rely same request on the values of header fields
      not listed here.

   A non-transforming client's behalf to either the next
   inbound proxy MUST preserve server or directly to the message payload ([Part3]),
   though it MAY change origin server indicated by
   the message-body through application or removal request-target.  Requirements on such "forwarding" of a transfer-coding (Section 5.1).

6.1.4.  Practical Considerations

   Servers will usually have messages
   are defined in Section 5.6.

   An example absolute-form of request-line would be:

     GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1

   To allow for transition to the absolute-form for all requests in some time-out value beyond which they will
   no longer maintain an inactive connection.  Proxy
   future version of HTTP, HTTP/1.1 servers might make
   this a higher value since it is likely that MUST accept the client absolute-
   form in requests, even though HTTP/1.1 clients will be only send them in
   requests to proxies.

   The authority-form of request-target is only used for CONNECT
   requests (Section 6.9 of [Part2]).  When making
   more connections a CONNECT request to
   establish a tunnel through one or more proxies, a client MUST send
   only the same server.  The use of persistent
   connections places no requirements on target URI's authority component (excluding any userinfo) as
   the length (or existence) request-target.  For example,

     CONNECT www.example.com:80 HTTP/1.1

   The asterisk-form of
   this time-out request-target is only used for either the client or the server. a server-wide
   OPTIONS request (Section 6.2 of [Part2]).  When a client or server wishes to time-out it SHOULD issue a graceful
   close on the transport connection.  Clients and servers SHOULD both
   constantly watch
   request OPTIONS for the other side server as a whole, as opposed to a specific
   named resource of that server, the transport close, and
   respond to it client MUST send only "*" (%x2A)
   as appropriate. the request-target.  For example,

     OPTIONS * HTTP/1.1

   If a client or server does not detect proxy receives an OPTIONS request with an absolute-form of
   request-target in which the other side's close promptly it could cause unnecessary resource
   drain on URI has an empty path and no query
   component, then the network.

   A client, server, or last proxy MAY close on the transport connection at any
   time.  For example, a client might have started to request chain MUST send a new request
   at the same time that
   request-target of "*" when it forwards the server has decided request to close the "idle"
   connection.  From indicated
   origin server.

   For example, the request

     OPTIONS http://www.example.org:8001 HTTP/1.1

   would be forwarded by the server's point final proxy as

     OPTIONS * HTTP/1.1
     Host: www.example.org:8001

   after connecting to port 8001 of view, host "www.example.org".

5.4.  Host

   The "Host" header field in a request provides the connection is being
   closed while it was idle, but host and port
   information from the client's point of view, a
   request is in progress.

   Clients (including proxies) SHOULD limit target URI, enabling the number of simultaneous
   connections that they maintain to a given origin server (including proxies).

   Previous revisions of HTTP gave a specific number of connections as a
   ceiling, but this was found to be impractical
   distinguish among resources while servicing requests for many applications.
   As multiple
   host names on a result, this specification does not mandate single IP address.  Since the Host field-value is
   critical information for handling a particular maximum
   number of connections, but instead encourages clients to request, it SHOULD be
   conservative when opening multiple connections.

   In particular, while using multiple connections avoids sent as the "head-of-
   line blocking" problem (whereby a request that takes significant
   server-side processing and/or has a large payload can block
   subsequent requests on
   first header field following the same connection), each connection used
   consumes server resources (sometimes significantly), and furthermore
   using multiple connections can cause undesirable side effects in
   congested networks.

   Note that servers might reject traffic that they deem abusive,
   including an excessive number of connections from request-line.

     Host = uri-host [ ":" port ] ; Section 2.7.1

   A client MUST send a client.

6.1.5.  Retrying Requests

   Senders can close the transport connection at any time.  Therefore,
   clients, servers, and proxies Host header field in all HTTP/1.1 request
   messages.  If the target URI includes an authority component, then
   the Host field-value MUST be able identical to recover from
   asynchronous close events.  Client software MAY reopen the transport
   connection and retransmit the aborted sequence of requests without
   user interaction so long as that authority component
   after excluding any userinfo (Section 2.7.1).  If the request sequence authority
   component is idempotent (see
   Section 6.1.2 of [Part2]).  Non-idempotent request methods missing or
   sequences MUST NOT be automatically retried, although user agents MAY
   offer a human operator undefined for the choice of retrying target URI, then the request(s).
   Confirmation by user-agent software Host
   header field MUST be sent with semantic understanding of an empty field-value.

   For example, a GET request to the application MAY substitute origin server for user confirmation.
   <http://www.example.org/pub/WWW/> would begin with:

     GET /pub/WWW/ HTTP/1.1
     Host: www.example.org

   The automatic
   retry SHOULD NOT Host header field MUST be repeated sent in an HTTP/1.1 request even if the second sequence of requests
   fails.

6.2.  Message Transmission Requirements

6.2.1.  Persistent Connections and Flow Control

   HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
   flow control mechanisms to resolve temporary overloads, rather than
   terminating connections with
   request-target is in the expectation absolute-form, since this allows the Host
   information to be forwarded through ancient HTTP/1.0 proxies that clients will retry.
   The latter technique can exacerbate network congestion.

6.2.2.  Monitoring Connections for Error Status Messages

   An
   might not have implemented Host.

   When an HTTP/1.1 (or later) client sending proxy receives a message-body SHOULD monitor
   the network connection for request with an error status code while absolute-form of
   request-target, the proxy MUST ignore the received Host header field
   (if any) and instead replace it is
   transmitting with the host information of the request.
   request-target.  If the client sees an error status code, proxy forwards the request, it SHOULD immediately cease transmitting MUST generate
   a new Host field-value based on the body.  If received request-target rather
   than forward the body received Host field-value.

   Since the Host header field acts as an application-level routing
   mechanism, it is
   being sent using a "chunked" encoding (Section 5.1), frequent target for malware seeking to poison a zero length
   chunk and empty trailer MAY be used
   shared cache or redirect a request to prematurely mark the end of
   the message.  If an unintended server.  An
   interception proxy is particularly vulnerable if it relies on the body was preceded by
   Host field-value for redirecting requests to internal servers, or for
   use as a Content-Length header
   field, cache key in a shared cache, without first verifying that
   the client intercepted connection is targeting a valid IP address for that
   host.

   A server MUST close the connection.

6.2.3.  Use of the 100 (Continue) Status

   The purpose of the 100 (Continue) respond with a 400 (Bad Request) status code (see Section 7.1.1 of
   [Part2]) is to allow a client any
   HTTP/1.1 request message that is sending lacks a Host header field and to any
   request message with that contains more than one Host header field or a
   Host header field with an invalid field-value.

5.5.  Effective Request URI

   A server that receives an HTTP request body message MUST reconstruct the
   user agent's original target URI, based on the pieces of information
   learned from the request-target, Host, and connection context, in
   order to determine if identify the origin server intended target resource and properly service
   the request.  The URI derived from this reconstruction process is willing
   referred to accept as the "effective request URI".

   For a user agent, the effective request (based on URI is the request header fields) before target URI.

   If the client
   sends request-target is in absolute-form, then the effective request body.  In some cases, it might either be
   inappropriate or highly inefficient for the client to send the body
   if
   URI is the server will reject same as the message without looking at request-target.  Otherwise, the body.

   Requirements for HTTP/1.1 clients:

   o effective
   request URI is constructed as follows.

   If a client will wait for a 100 (Continue) response before sending the request body, it MUST send an Expect header field (Section 9.3
      of [Part2]) with the "100-continue" expectation.

   o  A client MUST NOT send is received over an Expect header field (Section 9.3 of
      [Part2]) with SSL/TLS-secured TCP connection,
   then the "100-continue" expectation if it does not intend
      to send a effective request body.

   Because of URI's scheme is "https"; otherwise, the presence of older implementations,
   scheme is "http".

   If the protocol allows
   ambiguous situations request-target is in which a client might send "Expect: 100-
   continue" without receiving either a 417 (Expectation Failed) or a
   100 (Continue) status code.  Therefore, when a client sends this
   header field to an origin server (possibly via a proxy) from which it
   has never seen a 100 (Continue) status code, the client SHOULD NOT
   wait for an indefinite period before sending authority-form, then the effective
   request body.

   Requirements for HTTP/1.1 origin servers:

   o  Upon receiving URI's authority component is the same as the request-target.
   Otherwise, if a request which includes an Expect Host header field
      with the "100-continue" expectation, an origin server MUST either
      respond with 100 (Continue) status code and continue to read from
      the input stream, or respond is supplied with a final status code.  The origin
      server MUST NOT wait non-empty field-
   value, then the authority component is the same as the Host field-
   value.  Otherwise, the authority component is the concatenation of
   the default hostname configured for the request body before sending server, a colon (":"), and
   the 100
      (Continue) response. connection's incoming TCP port number in decimal form.

   If it responds with a final status code, it
      MAY close the transport connection request-target is in authority-form or it MAY continue to read asterisk-form, then the
   effective request URI's combined path and
      discard query component is empty.
   Otherwise, the rest combined path and query component is the same as the
   request-target.

   The components of the request.  It MUST NOT perform effective request URI, once determined as
   above, can be combined into absolute-URI form by concatenating the
   scheme, "://", authority, and combined path and query component.

   Example 1: the following message received over an insecure TCP
   connection

     GET /pub/WWW/TheProject.html HTTP/1.1
     Host: www.example.org:8080

   has an effective request URI of

     http://www.example.org:8080/pub/WWW/TheProject.html

   Example 2: the following message received over an SSL/TLS-secured TCP
   connection

     OPTIONS * HTTP/1.1
     Host: www.example.org

   has an effective request
      method if it returns a final status code.

   o URI of

     https://www.example.org

   An origin server SHOULD NOT send a 100 (Continue) response if the
      request message that does not include an Expect header field with allow resources to differ by requested
   host MAY ignore the
      "100-continue" expectation, Host field-value and MUST NOT send a 100 (Continue)
      response if such a request comes from an HTTP/1.0 (or earlier)
      client.  There is an exception to this rule: for compatibility instead replace it with [RFC2068], a
   configured server MAY send a 100 (Continue) status code in
      response to name when constructing the effective request URI.

   Recipients of an HTTP/1.1 PUT or POST HTTP/1.0 request that does not include
      an Expect lacks a Host header field with MAY
   attempt to use heuristics (e.g., examination of the "100-continue" expectation.  This
      exception, URI path for
   something unique to a particular host) in order to guess the purpose
   effective request URI's authority component.

5.6.  Intermediary Forwarding

   As described in Section 2.3, intermediaries can serve a variety of which is to minimize any client
   roles in the processing delays associated with an undeclared wait of HTTP requests and responses.  Some
   intermediaries are used to improve performance or availability.
   Others are used for 100
      (Continue) status code, applies only access control or to HTTP/1.1 requests, and not filter content.  Since an
   HTTP stream has characteristics similar to requests a pipe-and-filter
   architecture, there are no inherent limits to the extent an
   intermediary can enhance (or interfere) with any either direction of the
   stream.

   In order to avoid request loops, a proxy that forwards requests to
   other HTTP-version value.

   o  An origin proxies MUST be able to recognize and exclude all of its own
   server MAY omit names, including any aliases, local variations, or literal IP
   addresses.

   If a 100 (Continue) response if proxy receives a request-target with a host name that is not a
   fully qualified domain name, it has
      already received some or all of MAY add its domain to the request body for host name
   it received when forwarding the
      corresponding request.

   o  An origin server that sends a 100 (Continue) response  A proxy MUST
      ultimately send a final status code, once NOT change the request body
   host name if it is
      received a fully qualified domain name.

   A non-transforming proxy MUST NOT rewrite the "path-absolute" and processed, unless
   "query" parts of the received request-target when forwarding it terminates to
   the transport
      connection prematurely.

   o  If next inbound server, except as noted above to replace an origin server receives a request empty
   path with "/" or "*".

   Intermediaries that does not include an
      Expect forward a message MUST implement the Connection
   header field with as specified in Section 6.1.

5.6.1.  End-to-end and Hop-by-hop Header Fields

   For the "100-continue" expectation, purpose of defining the
      request includes a request body, behavior of caches and non-caching
   proxies, we divide HTTP header fields into two categories:

   o  End-to-end header fields, which are transmitted to the server responds with ultimate
      recipient of a
      final status code before reading the entire request body from the
      transport connection, then the server SHOULD NOT close the
      transport connection until it has read the entire request, or
      until the client closes the connection.  Otherwise, the client
      might not reliably receive the response message.  However, this
      requirement is not response.  End-to-end header fields in
      responses MUST be construed stored as preventing part of a server from
      defending itself against denial-of-service attacks, or cache entry and MUST be
      transmitted in any response formed from badly
      broken client implementations.

   Requirements a cache entry.

   o  Hop-by-hop header fields, which are meaningful only for a single
      transport-level connection, and are not stored by caches or
      forwarded by proxies.

   The following HTTP/1.1 proxies: header fields are hop-by-hop header fields:

   o  If  Connection

   o  Keep-Alive

   o  Proxy-Authenticate

   o  Proxy-Authorization

   o  TE

   o  Trailer

   o  Transfer-Encoding

   o  Upgrade

   All other header fields defined by HTTP/1.1 are end-to-end header
   fields.

   Other hop-by-hop header fields MUST be listed in a Connection header
   field (Section 6.1).

5.6.2.  Non-modifiable Header Fields

   Some features of HTTP/1.1, such as Digest Authentication, depend on
   the value of certain end-to-end header fields.  A non-transforming
   proxy receives a request that includes SHOULD NOT modify an Expect end-to-end header field
      with the "100-continue" expectation, and unless the proxy either knows
   definition of that the next-hop server complies with HTTP/1.1 or higher, header field requires or does
      not know the HTTP version specifically allows that.

   A non-transforming proxy MUST NOT modify any of the next-hop server, following fields
   in a request or response, and it MUST forward
      the request, including the Expect header field. NOT add any of these fields if
   not already present:

   o  If the  Allow

   o  Content-Location

   o  Content-MD5

   o  ETag

   o  Last-Modified

   o  Server

   A non-transforming proxy knows that the version MUST NOT modify any of the next-hop server following fields
   in a response:

   o  Expires

   but it MAY add any of these fields if not already present.  If an
   Expires header field is
      HTTP/1.0 or lower, added, it MUST NOT forward be given a field-value
   identical to that of the request, and it Date header field in that response.

   A proxy MUST
      respond with NOT modify or add any of the following fields in a 417 (Expectation Failed) status code.
   message that contains the no-transform cache-control directive, or in
   any request:

   o  Proxies SHOULD maintain  Content-Encoding

   o  Content-Range

   o  Content-Type

   A transforming proxy MAY modify or add these fields to a record message that
   does not include no-transform, but if it does so, it MUST add a
   Warning 214 (Transformation applied) if one does not already appear
   in the message (see Section 3.6 of [Part6]).

      Warning: Unnecessary modification of end-to-end header fields
      might cause authentication failures if stronger authentication
      mechanisms are introduced in later versions of HTTP.  Such
      authentication mechanisms MAY rely on the HTTP version numbers
      received from recently-referenced next-hop servers.

   o values of header fields
      not listed here.

   A non-transforming proxy MUST NOT forward a 100 (Continue) response if preserve the request message was received from an HTTP/1.0 (or earlier) client and did payload ([Part3]),
   though it MAY change the message body through application or removal
   of a transfer-coding (Section 4).

5.7.  Associating a Response to a Request

   HTTP does not include an Expect header field a request identifier for associating a given
   request message with its corresponding one or more response messages.
   Hence, it relies on the "100-continue"
      expectation.  This requirement overrides the general rule for
      forwarding order of 1xx response arrival to correspond
   exactly to the order in which requests are made on the same
   connection.  More than one response message per request only occurs
   when one or more informational responses (see (1xx, see Section 7.1 of [Part2]).

7.  Miscellaneous notes that might disappear

7.1.  Scheme aliases considered harmful

   [[TBD-aliases-harmful: describe why aliases like webcal are
   harmful.]]

7.2.  Use of HTTP for proxy communication

   [[TBD-proxy-other: Configured to use HTTP
   [Part2]) precede a final response to proxy HTTP or other
   protocols.]]

7.3.  Interception of HTTP for access control

   [[TBD-intercept: Interception of HTTP traffic for initiating access
   control.]]

7.4.  Use of HTTP by other protocols

   [[TBD-profiles: Profiles of HTTP defined by other protocol.
   Extensions of HTTP like WebDAV.]]

7.5.  Use of HTTP by media type specification

   [[TBD-hypertext: Instructions on composing HTTP requests via
   hypertext formats.]]

8.  Header Field Definitions

   This section defines the syntax same request.

   A client that uses persistent connections and semantics sends more than one
   request per connection MUST maintain a list of HTTP header fields
   related to message origination, framing, and routing.

   +-------------------+---------------+
   | Header Field Name | Defined in... |
   +-------------------+---------------+
   | outstanding requests
   in the order sent on that connection and MUST associate each received
   response message to the highest ordered request that has not yet
   received a final (non-1xx) response.

6.  Connection        | Section 8.1   |
   | Content-Length    | Section 8.2   |
   | Host              | Section 8.3   |
   | TE                | Section 8.4   |
   | Trailer           | Section 8.5   |
   | Transfer-Encoding | Section 8.6   |
   | Upgrade           | Section 8.7   |
   | Via               | Section 8.8   |
   +-------------------+---------------+

8.1. Management

6.1.  Connection

   The "Connection" header field allows the sender to specify options
   that are desired only for that particular connection.  Such
   connection options MUST be removed or replaced before the message can
   be forwarded downstream by a proxy or gateway.  This mechanism also
   allows the sender to indicate which HTTP header fields used in the
   message are only intended for the immediate recipient ("hop-by-hop"),
   as opposed to all recipients on the chain ("end-to-end"), enabling
   the message to be self-descriptive and allowing future connection-
   specific extensions to be deployed in HTTP without fear that they
   will be blindly forwarded by previously deployed intermediaries.

   The Connection header field's value has the following grammar:

     Connection       = 1#connection-token
     connection-token = token

   A proxy or gateway MUST parse a received Connection header field
   before a message is forwarded and, for each connection-token in this
   field, remove any header field(s) from the message with the same name
   as the connection-token, and then remove the Connection header field
   itself or replace it with the sender's own connection options for the
   forwarded message.

   A sender MUST NOT include field-names in the Connection header field-
   value for fields that are defined as expressing constraints for all
   recipients in the request or response chain, such as the Cache-
   Control header field (Section 3.2 of [Part6]).

   The connection options do not have to correspond to a header field
   present in the message, since a connection-specific header field
   might not be needed if there are no parameters associated with that
   connection option.  Recipients that trigger certain connection
   behavior based on trigger certain connection
   behavior based on the presence of connection options MUST do so based
   on the presence of the connection-token rather than only the presence
   of the optional header field.  In other words, if the connection
   option is received as a header field but not indicated within the
   Connection field-value, then the recipient MUST ignore the
   connection-specific header field because it has likely been forwarded
   by an intermediary that is only partially conformant.

   When defining new connection options, specifications ought to
   carefully consider existing deployed header fields and ensure that
   the new connection-token does not share the same name as an unrelated
   header field that might already be deployed.  Defining a new
   connection-token essentially reserves that potential field-name for
   carrying additional information related to the connection option,
   since it would be unwise for senders to use that field-name for
   anything else.

   HTTP/1.1 defines the "close" connection option for the sender to
   signal that the connection will be closed after completion of the
   response.  For example,

     Connection: close

   in either the request or the response header fields indicates that
   the connection SHOULD NOT be considered "persistent" (Section 6.3)
   after the current request/response is complete.

   An HTTP/1.1 client that does not support persistent connections MUST
   include the presence of "close" connection options option in every request message.

   An HTTP/1.1 server that does not support persistent connections MUST do so based
   on the presence of the connection-token rather than only the presence
   of the optional header field.  In other words, if
   include the "close" connection option is received as in every response message that
   does not have a 1xx (Informational) status code.

6.2.  Via

   The "Via" header field but not indicated within MUST be sent by a proxy or gateway to indicate
   the
   Connection field-value, then intermediate protocols and recipients between the recipient MUST ignore user agent and
   the
   connection-specific header server on requests, and between the origin server and the client
   on responses.  It is analogous to the "Received" field because it has likely been forwarded used by an intermediary that email
   systems (Section 3.6.7 of [RFC5322]) and is only partially compliant.

   When defining new connection options, specifications ought intended to
   carefully consider existing deployed header fields be used for
   tracking message forwards, avoiding request loops, and ensure that identifying
   the new connection-token does not share protocol capabilities of all senders along the same name as an unrelated
   header field that might already be deployed.  Defining a new
   connection-token essentially reserves request/response
   chain.

     Via               = 1#( received-protocol RWS received-by
                             [ RWS comment ] )
     received-protocol = [ protocol-name "/" ] protocol-version
     received-by       = ( uri-host [ ":" port ] ) / pseudonym
     pseudonym         = token

   The received-protocol indicates the protocol version of the message
   received by the server or client along each segment of the request/
   response chain.  The received-protocol version is appended to the Via
   field value when the message is forwarded so that potential field-name for
   carrying additional information related to about
   the connection option,
   since protocol capabilities of upstream applications remains visible to
   all recipients.

   The protocol-name is excluded if and only if it would be unwise for senders to use "HTTP".  The
   received-by field is normally the host and optional port number of a
   recipient server or client that field-name for
   anything else.

   HTTP/1.1 defines subsequently forwarded the "close" connection option for message.
   However, if the sender real host is considered to
   signal that be sensitive information,
   it MAY be replaced by a pseudonym.  If the connection will port is not given, it MAY
   be assumed to be closed after completion of the
   response.  For example,

     Connection: close

   in either default port of the request received-protocol.

   Multiple Via field values represent each proxy or the response header fields indicates gateway that has
   forwarded the connection SHOULD NOT be considered "persistent" (Section 6.1)
   after message.  Each recipient MUST append its information
   such that the current request/response end result is complete.

   An HTTP/1.1 client that does not support persistent connections MUST
   include ordered according to the "close" connection option sequence of
   forwarding applications.

   Comments MAY be used in every request message.

   An HTTP/1.1 server that does not support persistent connections MUST
   include the "close" connection option in every response message that
   does not have a 1xx (Informational) status code.

8.2.  Content-Length

   The "Content-Length" Via header field indicates the size of the message-
   body, in decimal number of octets, for any message other than a
   response to a HEAD request or a response with a status code of 304.
   In identify the case software
   of a response each recipient, analogous to a HEAD request, Content-Length indicates the size of User-Agent and Server header
   fields.  However, all comments in the payload body (not including Via field are optional and MAY
   be removed by any potential transfer-
   coding) that would have been sent had recipient prior to forwarding the request been message.

   For example, a GET.  In request message could be sent from an HTTP/1.0 user
   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
   forward the
   case of a 304 (Not Modified) response request to a GET request, Content-
   Length indicates public proxy at p.example.net, which
   completes the size of request by forwarding it to the payload body (not including any
   potential transfer-coding) that origin server at
   www.example.com.  The request received by www.example.com would then
   have been sent in the following Via header field:

     Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)

   A proxy or gateway used as a 200 (OK)
   response.

     Content-Length = 1*DIGIT

   An example is

     Content-Length: 3495

   Implementations portal through a network firewall SHOULD use this field to indicate
   NOT forward the message-body
   length when no transfer-coding is being applied names and the payload's
   body length can be determined prior to being transferred.
   Section 3.3 describes how recipients determine the length ports of a
   message-body.

   Any Content-Length greater than or equal to zero hosts within the firewall region
   unless it is a valid value.

   Note that explicitly enabled to do so.  If not enabled, the use
   received-by host of this field in HTTP is significantly different
   from any host behind the corresponding definition in MIME, where it is firewall SHOULD be replaced
   by an appropriate pseudonym for that host.

   For organizations that have strong privacy requirements for hiding
   internal structures, a proxy or gateway MAY combine an optional
   field used within the "message/external-body" content-type.

8.3.  Host

   The "Host" ordered
   subsequence of Via header field in entries with identical received-
   protocol values into a request provides single such entry.  For example,

     Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy

   could be collapsed to

     Via: 1.0 ricky, 1.1 mertz, 1.0 lucy

   Senders SHOULD NOT combine multiple entries unless they are all under
   the host same organizational control and port
   information from the target resource's URI, enabling the origin
   server hosts have already been
   replaced by pseudonyms.  Senders MUST NOT combine entries which have
   different received-protocol values.

6.3.  Persistent Connections

6.3.1.  Purpose

   Prior to distinguish between resources while servicing requests for
   multiple host names on persistent connections, a single IP address.  Since the Host field-
   value is critical information separate TCP connection was
   established for handling a each request, it SHOULD be
   sent as increasing the first header field following load on HTTP servers and
   causing congestion on the Request-Line.

     Host = uri-host [ ":" port ] ; Section 2.7.1

   A client MUST send Internet.  The use of inline images and
   other associated data often requires a Host header field in all HTTP/1.1 request
   messages.  If the target resource's URI includes an authority
   component, then the Host field-value MUST be identical client to that
   authority component after excluding any userinfo (Section 2.7.1).  If make multiple
   requests of the authority component same server in a short amount of time.  Analysis of
   these performance problems and results from a prototype
   implementation are available [Pad1995] [Spe].  Implementation
   experience and measurements of actual HTTP/1.1 implementations show
   good results [Nie1997].  Alternatives have also been explored, for
   example, T/TCP [Tou1998].

   Persistent HTTP connections have a number of advantages:

   o  By opening and closing fewer TCP connections, CPU time is missing saved in
      routers and hosts (clients, servers, proxies, gateways, tunnels,
      or undefined caches), and memory used for the target
   resource's URI, then the Host header field MUST TCP protocol control blocks can be sent with an empty
   field-value.

   For example,
      saved in hosts.

   o  HTTP requests and responses can be pipelined on a GET request connection.
      Pipelining allows a client to the origin server make multiple requests without
      waiting for
   <http://www.example.org/pub/WWW/> would begin with:

     GET /pub/WWW/ HTTP/1.1
     Host: www.example.org

   The Host header field MUST each response, allowing a single TCP connection to be sent in an HTTP/1.1 request even if
      used much more efficiently, with much lower elapsed time.

   o  Network congestion is reduced by reducing the
   request-target number of packets
      caused by TCP opens, and by allowing TCP sufficient time to
      determine the congestion state of the network.

   o  Latency on subsequent requests is reduced since there is no time
      spent in TCP's connection opening handshake.

   o  HTTP can evolve more gracefully, since errors can be reported
      without the form penalty of an absolute-URI, since this allows closing the Host information to be forwarded through ancient HTTP/1.0 proxies
   that TCP connection.  Clients using
      future versions of HTTP might not have implemented Host.

   When an HTTP/1.1 proxy receives optimistically try a request new feature,
      but if communicating with a request-target in an older server, retry with old
      semantics after an error is reported.

   HTTP implementations SHOULD implement persistent connections.

6.3.2.  Overall Operation

   A significant difference between HTTP/1.1 and earlier versions of
   HTTP is that persistent connections are the form default behavior of an absolute-URI, any
   HTTP connection.  That is, unless otherwise indicated, the proxy MUST ignore client
   SHOULD assume that the received Host
   header field (if any) server will maintain a persistent connection,
   even after error responses from the server.

   Persistent connections provide a mechanism by which a client and instead replace it with a
   server can signal the host
   information close of the request-target.  When a proxy forwards a request,
   it MUST generate TCP connection.  This signaling
   takes place using the Host Connection header field based on the received
   absolute-URI rather than the received Host.

   Since (Section 6.1).  Once a
   close has been signaled, the Host header field acts as an application-level routing
   mechanism, it is client MUST NOT send any more requests
   on that connection.

6.3.2.1.  Negotiation

   An HTTP/1.1 server MAY assume that a frequent target for malware seeking HTTP/1.1 client intends to poison
   maintain a
   shared cache or redirect persistent connection unless a request to an unintended server.  An
   interception proxy is particularly vulnerable if it relies on the
   Host Connection header field value for redirecting requests to internal servers,
   or for use as a cache key
   including the connection-token "close" was sent in a shared cache, without first verifying
   that the intercepted connection is targeting a valid IP address for
   that host.

   A request.  If
   the server MUST respond with a 400 (Bad Request) status code chooses to any
   HTTP/1.1 request message that lacks close the connection immediately after sending
   the response, it SHOULD send a Host Connection header field and including the
   connection-token "close".

   An HTTP/1.1 client MAY expect a connection to remain open, but would
   decide to any
   request message that keep it open based on whether the response from a server
   contains more than one Host header field or a
   Host Connection header field with an invalid field-value.

   See Sections 4.2 and A.1.1 for other requirements relating the connection-token close.
   In case the client does not want to Host.

8.4.  TE

   The "TE" maintain a connection for more
   than that request, it SHOULD send a Connection header field indicates what extension transfer-codings it is
   willing to accept in including
   the response, and whether connection-token close.

   If either the client or not it is willing
   to accept trailer fields in a chunked transfer-coding.

   Its value consists of the keyword "trailers" and/or a comma-separated
   list of extension transfer-coding names with optional accept
   parameters (as described in Section 5.1).

     TE        = #t-codings
     t-codings = "trailers" / ( transfer-extension [ te-params ] )
     te-params = OWS ";" OWS "q=" qvalue *( te-ext )
     te-ext    = OWS ";" OWS server sends the close token [ "=" word ]

   The presence of in the keyword "trailers" indicates
   Connection header field, that request becomes the client is
   willing to accept trailer fields in last one for the
   connection.

   Clients and servers SHOULD NOT assume that a chunked transfer-coding, as
   defined in Section 5.1.1.  This keyword persistent connection is reserved
   maintained for use with
   transfer-coding values even though HTTP versions less than 1.1 unless it does not itself represent is explicitly
   signaled.  See Appendix A.1.2 for more information on backward
   compatibility with HTTP/1.0 clients.

   Each persistent connection applies to only one transport link.

   A proxy server MUST NOT establish a
   transfer-coding.

   Examples HTTP/1.1 persistent connection
   with an HTTP/1.0 client (but see Section 19.7.1 of its use are:

     TE: deflate
     TE:
     TE: trailers, deflate;q=0.5

   The TE [RFC2068] for
   information and discussion of the problems with the Keep-Alive header
   field only applies implemented by many HTTP/1.0 clients).

   In order to remain persistent, all messages on the immediate connection.
   Therefore, the keyword connection MUST be supplied within
   have a Connection header
   field (Section 8.1) whenever TE is present self-defined message length (i.e., one not defined by closure
   of the connection), as described in an HTTP/1.1 message. Section 3.3.

6.3.2.2.  Pipelining

   A client that supports persistent connections MAY "pipeline" its
   requests (i.e., send multiple requests without waiting for each
   response).  A server tests whether a transfer-coding is acceptable, according MUST send its responses to
   a TE field, using these rules:

   1.  The "chunked" transfer-coding is always acceptable.  If those requests in the
       keyword "trailers" is listed,
   same order that the requests were received.

   Clients which assume persistent connections and pipeline immediately
   after connection establishment SHOULD be prepared to retry their
   connection if the first pipelined attempt fails.  If a client indicates that does
   such a retry, it MUST NOT pipeline before it knows the connection is
       willing
   persistent.  Clients MUST also be prepared to accept trailer fields in resend their requests
   if the chunked response on
       behalf server closes the connection before sending all of the
   corresponding responses.

   Clients SHOULD NOT pipeline requests using non-idempotent request
   methods or non-idempotent sequences of request methods (see Section
   6.1.2 of [Part2]).  Otherwise, a premature termination of itself and any downstream clients.  The implication is
       that, if given, the
   transport connection could lead to indeterminate results.  A client is stating that either all downstream
       clients are willing
   wishing to accept trailer fields in the forwarded
       response, or send a non-idempotent request SHOULD wait to send that
   request until it will attempt to buffer has received the response on
       behalf of downstream recipients.

       Note: HTTP/1.1 does not define any means to limit status line for the size of
   previous request.

6.3.3.  Practical Considerations

   Servers will usually have some time-out value beyond which they will
   no longer maintain an inactive connection.  Proxy servers might make
   this a
       chunked response such higher value since it is likely that a the client can will be assured of buffering making
   more connections through the entire response.

   2.  If same server.  The use of persistent
   connections places no requirements on the transfer-coding being tested is one length (or existence) of
   this time-out for either the transfer-
       codings listed in client or the TE field, then it is acceptable unless it
       is accompanied by server.

   When a qvalue of 0.  (As defined in Section 5.3, client or server wishes to time-out it SHOULD issue a
       qvalue of 0 means "not acceptable".)

   3.  If multiple transfer-codings are acceptable, then graceful
   close on the acceptable
       transfer-coding with transport connection.  Clients and servers SHOULD both
   constantly watch for the highest non-zero qvalue is preferred.
       The "chunked" transfer-coding always has a qvalue other side of 1. the transport close, and
   respond to it as appropriate.  If a client or server does not detect
   the TE field-value is empty other side's close promptly it could cause unnecessary resource
   drain on the network.

   A client, server, or if no TE field is present, proxy MAY close the transport connection at any
   time.  For example, a client might have started to send a new request
   at the only
   transfer-coding is "chunked".  A message with no transfer-coding is
   always acceptable.

8.5.  Trailer

   The "Trailer" header field indicates same time that the given set server has decided to close the "idle"
   connection.  From the server's point of header
   fields view, the connection is present in being
   closed while it was idle, but from the trailer client's point of view, a message encoded with chunked
   transfer-coding.

     Trailer = 1#field-name

   An HTTP/1.1 message
   request is in progress.

   Clients (including proxies) SHOULD include limit the number of simultaneous
   connections that they maintain to a Trailer header field in given server (including proxies).

   Previous revisions of HTTP gave a
   message using chunked transfer-coding with specific number of connections as a non-empty trailer.
   Doing so allows the recipient to know which header fields
   ceiling, but this was found to expect
   in the trailer.

   If no Trailer header field is present, the trailer SHOULD NOT include
   any header fields.  See Section 5.1.1 be impractical for restrictions on the use of
   trailer fields in many applications.
   As a "chunked" transfer-coding.

   Message header fields listed in the Trailer header field MUST NOT
   include the following header fields:

   o  Transfer-Encoding

   o  Content-Length

   o  Trailer

8.6.  Transfer-Encoding

   The "Transfer-Encoding" header field indicates what transfer-codings
   (if any) have been applied result, this specification does not mandate a particular maximum
   number of connections, but instead encourages clients to be
   conservative when opening multiple connections.

   In particular, while using multiple connections avoids the message body.  It differs from
   Content-Encoding (Section 2.2 of [Part3]) "head-of-
   line blocking" problem (whereby a request that takes significant
   server-side processing and/or has a large payload can block
   subsequent requests on the same connection), each connection used
   consumes server resources (sometimes significantly), and furthermore
   using multiple connections can cause undesirable side effects in
   congested networks.

   Note that transfer-codings
   are a property servers might reject traffic that they deem abusive,
   including an excessive number of the message (and therefore are removed by
   intermediaries), whereas content-codings are not.

     Transfer-Encoding = 1#transfer-coding

   Transfer-codings are defined in Section 5.1.  An example is:

     Transfer-Encoding: chunked

   If multiple encodings have been applied to connections from a representation, client.

6.3.4.  Retrying Requests

   Senders can close the
   transfer-codings transport connection at any time.  Therefore,
   clients, servers, and proxies MUST be listed in the order in which they were
   applied.  Additional information about the encoding parameters able to recover from
   asynchronous close events.  Client software MAY be
   provided by other header fields not defined by this specification.

   Many older HTTP/1.0 applications do not understand the Transfer-
   Encoding header field.

8.7.  Upgrade

   The "Upgrade" header field allows reopen the client to specify what
   additional communication protocols it would like to use, if transport
   connection and retransmit the
   server chooses to switch protocols.  Servers can use it to indicate
   what protocols they are willing to switch to.

     Upgrade = 1#product

   For example,

     Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11

   The Upgrade header field is intended to provide a simple mechanism
   for transition from HTTP/1.1 to some other, incompatible protocol.
   It does aborted sequence of requests without
   user interaction so by allowing the client to advertise its desire to use
   another protocol, such long as the request sequence is idempotent (see
   Section 6.1.2 of [Part2]).  Non-idempotent request methods or
   sequences MUST NOT be automatically retried, although user agents MAY
   offer a later version human operator the choice of HTTP retrying the request(s).

   Confirmation by user-agent software with a higher major
   version number, even though semantic understanding of
   the current request has been made using
   HTTP/1.1.  This eases application MAY substitute for user confirmation.  The automatic
   retry SHOULD NOT be repeated if the difficult transition between incompatible
   protocols by allowing second sequence of requests
   fails.

6.4.  Message Transmission Requirements

6.4.1.  Persistent Connections and Flow Control

   HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
   flow control mechanisms to resolve temporary overloads, rather than
   terminating connections with the expectation that clients will retry.
   The latter technique can exacerbate network congestion.

6.4.2.  Monitoring Connections for Error Status Messages

   An HTTP/1.1 (or later) client to initiate sending a request in message body SHOULD monitor
   the more
   commonly supported protocol network connection for an error status code while indicating to the server that it
   would like to use a "better" protocol if available (where "better" is
   determined by
   transmitting the server, possibly according request.  If the client sees an error status code,
   it SHOULD immediately cease transmitting the body.  If the body is
   being sent using a "chunked" encoding (Section 4), a zero length
   chunk and empty trailer MAY be used to prematurely mark the nature end of
   the
   request method or target resource).

   The Upgrade message.  If the body was preceded by a Content-Length header field only applies to switching application-layer
   protocols upon
   field, the client MUST close the existing transport-layer connection.  Upgrade
   cannot be used

6.4.3.  Use of the 100 (Continue) Status

   The purpose of the 100 (Continue) status code (see Section 7.1.1 of
   [Part2]) is to insist on allow a client that is sending a protocol change; its acceptance and use
   by request message with
   a request body to determine if the origin server is optional.  The capabilities and nature of the
   application-layer communication after willing to accept
   the protocol change is entirely
   dependent upon request (based on the new protocol chosen, although request header fields) before the first action
   after changing client
   sends the protocol MUST request body.  In some cases, it might either be a response
   inappropriate or highly inefficient for the client to send the initial HTTP
   request containing body
   if the Upgrade header field.

   The Upgrade header field only applies to server will reject the immediate connection.
   Therefore, message without looking at the upgrade keyword MUST be supplied within body.

   Requirements for HTTP/1.1 clients:

   o  If a Connection client will wait for a 100 (Continue) response before sending
      the request body, it MUST send an Expect header field (Section 8.1) whenever Upgrade is present in
      10.3 of [Part2]) with the "100-continue" expectation.

   o  A client MUST NOT send an HTTP/1.1
   message.

   The Upgrade Expect header field cannot be used to indicate a switch to a
   protocol on a different connection.  For that purpose, (Section 10.3 of
      [Part2]) with the "100-continue" expectation if it is more
   appropriate does not intend
      to use send a 3xx redirection response (Section 7.3 request body.

   Because of
   [Part2]).

   Servers MUST include the "Upgrade" header field presence of older implementations, the protocol allows
   ambiguous situations in 101 (Switching
   Protocols) responses to indicate which protocol(s) are being switched
   to, and MUST include it in 426 (Upgrade Required) responses to
   indicate acceptable protocols a client might send "Expect: 100-
   continue" without receiving either a 417 (Expectation Failed) or a
   100 (Continue) status code.  Therefore, when a client sends this
   header field to upgrade to.  Servers MAY include an origin server (possibly via a proxy) from which it
   in any other response to indicate that they are willing to upgrade to
   one of the specified protocols.

   This specification only defines
   has never seen a 100 (Continue) status code, the protocol name "HTTP" client SHOULD NOT
   wait for use by an indefinite period before sending the family of Hypertext Transfer Protocols, as defined by request body.

   Requirements for HTTP/1.1 origin servers:

   o  Upon receiving a request which includes an Expect header field
      with the HTTP
   version rules of Section 2.6 "100-continue" expectation, an origin server MUST either
      respond with 100 (Continue) status code and future updates continue to this
   specification.  Additional tokens can be registered with IANA using read from
      the registration procedure defined below.

8.7.1.  Upgrade Token Registry input stream, or respond with a final status code.  The HTTP Upgrade Token Registry defines the name space origin
      server MUST NOT wait for product
   tokens used to identify protocols in the Upgrade header field.  Each
   registered token is associated request body before sending the 100
      (Continue) response.  If it responds with contact information a final status code, it
      MAY close the transport connection or it MAY continue to read and an
   optional set
      discard the rest of specifications that details how the connection will
   be processed after request.  It MUST NOT perform the request
      method if it has been upgraded.

   Registrations are allowed on returns a First Come First Served basis as
   described in Section 4.1 of [RFC5226].  The specifications need final status code.

   o  An origin server SHOULD NOT send a 100 (Continue) response if the
      request message does not
   be IETF documents or be subject to IESG review.  Registrations are
   subject to include an Expect header field with the following rules:

   1.  A token, once registered, stays registered forever.

   2.  The registration
      "100-continue" expectation, and MUST name NOT send a responsible party 100 (Continue)
      response if such a request comes from an HTTP/1.0 (or earlier)
      client.  There is an exception to this rule: for the
       registration.

   3.  The registration MUST name compatibility
      with [RFC2068], a point of contact.

   4.  The registration server MAY name send a set 100 (Continue) status code in
      response to an HTTP/1.1 PUT or POST request that does not include
      an Expect header field with the "100-continue" expectation.  This
      exception, the purpose of specifications which is to minimize any client
      processing delays associated with
       that token.  Such specifications need an undeclared wait for 100
      (Continue) status code, applies only to HTTP/1.1 requests, and not be publicly available.

   5.  The responsible party MAY change the registration at
      to requests with any time.
       The IANA will keep other HTTP-version value.

   o  An origin server MAY omit a record of 100 (Continue) response if it has
      already received some or all such changes, and make them
       available upon request.

   6.  The responsible party of the request body for the first registration of
      corresponding request.

   o  An origin server that sends a "product"
       token 100 (Continue) response MUST approve later registrations of a "version" token
       together with that "product" token before they can be registered.

   7.  If absolutely required, the IESG MAY reassign the responsibility
       for
      ultimately send a token.  This will normally only be used in final status code, once the case when request body is
      received and processed, unless it terminates the transport
      connection prematurely.

   o  If an origin server receives a
       responsible party cannot be contacted.

8.8.  Via

   The "Via" request that does not include an
      Expect header field MUST be sent by a proxy or gateway to indicate with the intermediate protocols and recipients between "100-continue" expectation, the user agent
      request includes a request body, and the server on requests, and between responds with a
      final status code before reading the entire request body from the
      transport connection, then the origin server and SHOULD NOT close the
      transport connection until it has read the entire request, or
      until the client
   on responses.  It is analogous to closes the "Received" field used by email
   systems (Section 3.6.7 of [RFC5322]) and is intended to connection.  Otherwise, the client
      might not reliably receive the response message.  However, this
      requirement ought not be used construed as preventing a server from
      defending itself against denial-of-service attacks, or from badly
      broken client implementations.

   Requirements for
   tracking message forwards, avoiding HTTP/1.1 proxies:

   o  If a proxy receives a request loops, and identifying
   the protocol capabilities of all senders along the request/response
   chain.

     Via               = 1#( received-protocol RWS received-by
                             [ RWS comment ] )
     received-protocol = [ protocol-name "/" ] protocol-version
     protocol-name     = token
     protocol-version  = token
     received-by       = ( uri-host [ ":" port ] ) / pseudonym
     pseudonym         = token

   The received-protocol indicates that includes an Expect header field
      with the protocol version of "100-continue" expectation, and the message
   received by proxy either knows
      that the next-hop server complies with HTTP/1.1 or client along each segment of higher, or does
      not know the request/
   response chain.  The received-protocol HTTP version is appended to of the next-hop server, it MUST forward
      the Via
   field value when request, including the message is forwarded so Expect header field.

   o  If the proxy knows that information about the protocol capabilities version of upstream applications remains visible to
   all recipients.

   The protocol-name the next-hop server is excluded if and only if
      HTTP/1.0 or lower, it would be "HTTP".  The
   received-by field is normally MUST NOT forward the host request, and optional port number it MUST
      respond with a 417 (Expectation Failed) status code.

   o  Proxies SHOULD maintain a record of the HTTP version numbers
      received from recently-referenced next-hop servers.

   o  A proxy MUST NOT forward a
   recipient server or 100 (Continue) response if the request
      message was received from an HTTP/1.0 (or earlier) client that subsequently forwarded and did
      not include an Expect header field with the message.
   However, if "100-continue"
      expectation.  This requirement overrides the real host is considered to be sensitive information,
   it MAY be replaced by a pseudonym. general rule for
      forwarding of 1xx responses (see Section 7.1 of [Part2]).

6.4.4.  Closing Connections on Error

   If the port client is not given, it MAY sending data, a server implementation using TCP
   SHOULD be assumed careful to be ensure that the default port client acknowledges receipt of
   the received-protocol.

   Multiple Via field values represent each proxy or gateway that has
   forwarded packet(s) containing the message.  Each recipient MUST append its information
   such that response, before the end result is ordered according server closes the
   input connection.  If the client continues sending data to the sequence of
   forwarding applications.

   Comments MAY server
   after the close, the server's TCP stack will send a reset packet to
   the client, which might erase the client's unacknowledged input
   buffers before they can be used in read and interpreted by the Via HTTP
   application.

6.5.  Upgrade

   The "Upgrade" header field to identify allows the software
   of each recipient, analogous client to specify what
   additional communication protocols it would like to use, if the User-Agent and Server header
   fields.  However, all comments in the Via field
   server chooses to switch protocols.  Servers can use it to indicate
   what protocols they are optional and MAY
   be removed by any recipient prior willing to forwarding the message. switch to.

     Upgrade          = 1#protocol

     protocol         = protocol-name ["/" protocol-version]
     protocol-name    = token
     protocol-version = token

   For example,

     Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11

   The Upgrade header field is intended to provide a request message could be sent simple mechanism
   for transitioning from an HTTP/1.0 user
   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
   forward some other, incompatible protocol.
   It does so by allowing the request client to advertise its desire to use
   another protocol, such as a public proxy at p.example.net, which
   completes later version of HTTP with a higher major
   version number, even though the current request has been made using
   HTTP/1.1.  This eases the difficult transition between incompatible
   protocols by forwarding it allowing the client to initiate a request in the more
   commonly supported protocol while indicating to the origin server at
   www.example.com.  The request received by www.example.com that it
   would then
   have like to use a "better" protocol if available (where "better" is
   determined by the following Via header field:

     Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)

   A proxy server, possibly according to the nature of the
   request method or gateway used as a portal through target resource).

   The Upgrade header field only applies to switching application-layer
   protocols upon the existing transport-layer connection.  Upgrade
   cannot be used to insist on a network firewall SHOULD
   NOT forward protocol change; its acceptance and use
   by the names server is optional.  The capabilities and ports nature of hosts within the firewall region
   unless it
   application-layer communication after the protocol change is explicitly enabled entirely
   dependent upon the new protocol chosen, although the first action
   after changing the protocol MUST be a response to do so.  If not enabled, the
   received-by host of any host behind initial HTTP
   request containing the firewall SHOULD Upgrade header field.

   The Upgrade header field only applies to the immediate connection.
   Therefore, the upgrade keyword MUST be replaced
   by an appropriate pseudonym for that host.

   For organizations that have strong privacy requirements for hiding
   internal structures, supplied within a proxy or gateway MAY combine Connection
   header field (Section 6.1) whenever Upgrade is present in an ordered
   subsequence of Via HTTP/1.1
   message.

   The Upgrade header field entries with identical received- cannot be used to indicate a switch to a
   protocol values into on a single such entry. different connection.  For example,

     Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy

   could be collapsed that purpose, it is more
   appropriate to

     Via: 1.0 ricky, 1.1 mertz, 1.0 lucy

   Senders SHOULD NOT combine multiple entries unless use a 3xx redirection response (Section 7.3 of
   [Part2]).

   Servers MUST include the "Upgrade" header field in 101 (Switching
   Protocols) responses to indicate which protocol(s) are being switched
   to, and MUST include it in 426 (Upgrade Required) responses to
   indicate acceptable protocols to upgrade to.  Servers MAY include it
   in any other response to indicate that they are all under willing to upgrade to
   one of the specified protocols.

   This specification only defines the same organizational control and protocol name "HTTP" for use by
   the hosts have already been
   replaced family of Hypertext Transfer Protocols, as defined by pseudonyms.  Senders MUST NOT combine entries which have
   different received-protocol values.

9. the HTTP
   version rules of Section 2.6 and future updates to this
   specification.  Additional tokens can be registered with IANA using
   the registration procedure defined in Section 7.6.

7.  IANA Considerations

9.1.

7.1.  Header Field Registration

   The

   HTTP header fields are registered within the Message Header Field
   Registry located [RFC3864] maintained by IANA at <http://www.iana.org/
   assignments/message-headers/message-header-index.html>
   assignments/message-headers/message-header-index.html>.

   This document defines the following HTTP header fields, so their
   associated registry entries shall be updated with according to the
   permanent registrations below (see [RFC3864]):

   +-------------------+----------+----------+-------------+ below:

   +-------------------+----------+----------+---------------+
   | Header Field Name | Protocol | Status   | Reference     |
   +-------------------+----------+----------+-------------+
   +-------------------+----------+----------+---------------+
   | Connection        | http     | standard | Section 8.1 6.1   |
   | Content-Length    | http     | standard | Section 8.2 3.3.2 |
   | Host              | http     | standard | Section 8.3 5.4   |
   | TE                | http     | standard | Section 8.4 4.3   |
   | Trailer           | http     | standard | Section 8.5 4.4   |
   | Transfer-Encoding | http     | standard | Section 8.6 3.3.1 |
   | Upgrade           | http     | standard | Section 8.7 6.5   |
   | Via               | http     | standard | Section 8.8 6.2   |
   +-------------------+----------+----------+-------------+
   +-------------------+----------+----------+---------------+

   Furthermore, the header field name field-name "Close" shall be registered as
   "reserved", since using that name as its use as an HTTP header field would be in might
   conflict with the use of the "close" connection option for of the "Connection"
   header field (Section 8.1). 6.1).

   +-------------------+----------+----------+-------------+
   | Header Field Name | Protocol | Status   | Reference   |
   +-------------------+----------+----------+-------------+
   | Close             | http     | reserved | Section 9.1 7.1 |
   +-------------------+----------+----------+-------------+

   The change controller is: "IETF (iesg@ietf.org) - Internet
   Engineering Task Force".

9.2.

7.2.  URI Scheme Registration

   The entries for

   IANA maintains the "http" and "https" registry of URI Schemes in [RFC4395] at
   <http://www.iana.org/assignments/uri-schemes.html>.

   This document defines the following URI schemes, so their associated
   registry
   located at <http://www.iana.org/assignments/uri-schemes.html> entries shall be updated according to point to Sections the permanent
   registrations below:

   +------------+------------------------------------+---------------+
   | URI Scheme | Description                        | Reference     |
   +------------+------------------------------------+---------------+
   | http       | Hypertext Transfer Protocol        | Section 2.7.1 and |
   | https      | Hypertext Transfer Protocol Secure | Section 2.7.2 of this document (see
   [RFC4395]).

9.3. |
   +------------+------------------------------------+---------------+

7.3.  Internet Media Type Registrations

   This document serves as the specification for the Internet media
   types "message/http" and "application/http".  The following is to be
   registered with IANA (see [RFC4288]).

9.3.1.

7.3.1.  Internet Media Type message/http

   The message/http type can be used to enclose a single HTTP request or
   response message, provided that it obeys the MIME restrictions for
   all "message" types regarding line length and encodings.

   Type name:  message

   Subtype name:  http

   Required parameters:  none

   Optional parameters:  version, msgtype

      version:  The HTTP-Version HTTP-version number of the enclosed message (e.g.,
         "1.1").  If not present, the version can be determined from the
         first line of the body.

      msgtype:  The message type -- "request" or "response".  If not
         present, the type can be determined from the first line of the
         body.

   Encoding considerations:  only "7bit", "8bit", or "binary" are
      permitted

   Security considerations:  none

   Interoperability considerations:  none

   Published specification:  This specification (see Section 9.3.1). 7.3.1).

   Applications that use this media type:

   Additional information:

      Magic number(s):  none

      File extension(s):  none

      Macintosh file type code(s):  none

   Person and email address to contact for further information:  See
      Authors Section.

   Intended usage:  COMMON

   Restrictions on usage:  none

   Author/Change controller:  IESG

9.3.2.

7.3.2.  Internet Media Type application/http

   The application/http type can be used to enclose a pipeline of one or
   more HTTP request or response messages (not intermixed).

   Type name:  application

   Subtype name:  http

   Required parameters:  none

   Optional parameters:  version, msgtype

      version:  The HTTP-Version HTTP-version number of the enclosed messages (e.g.,
         "1.1").  If not present, the version can be determined from the
         first line of the body.

      msgtype:  The message type -- "request" or "response".  If not
         present, the type can be determined from the first line of the
         body.

   Encoding considerations:  HTTP messages enclosed by this type are in
      "binary" format; use of an appropriate Content-Transfer-Encoding
      is required when transmitted via E-mail.

   Security considerations:  none

   Interoperability considerations:  none
   Published specification:  This specification (see Section 9.3.2). 7.3.2).

   Applications that use this media type:

   Additional information:

      Magic number(s):  none

      File extension(s):  none

      Macintosh file type code(s):  none

   Person and email address to contact for further information:  See
      Authors Section.

   Intended usage:  COMMON

   Restrictions on usage:  none

   Author/Change controller:  IESG

9.4.

7.4.  Transfer Coding Registry

   The registration procedure for HTTP Transfer Codings Coding Registry defines the name space for transfer
   coding names.

   Registrations MUST include the following fields:

   o  Name

   o  Description

   o  Pointer to specification text

   Names of transfer codings MUST NOT overlap with names of content
   codings (Section 2.2 of [Part3]) unless the encoding transformation
   is now identical, as it is the case for the compression codings defined
   by
   in Section 4.2.

   Values to be added to this name space require IETF Review (see
   Section 5.1.3 4.1 of [RFC5226]), and MUST conform to the purpose of
   transfer coding defined in this document. section.

   The registry itself is maintained at
   <http://www.iana.org/assignments/http-parameters>.

7.5.  Transfer Coding Registrations

   The HTTP Transfer Codings Coding Registry located at
   <http://www.iana.org/assignments/http-parameters> shall be updated with the
   registrations below:

   +----------+--------------------------------------+-----------------+

   +----------+----------------------------------------+---------------+
   | Name     | Description                            | Reference     |
   +----------+--------------------------------------+-----------------+
   +----------+----------------------------------------+---------------+
   | chunked  | Transfer in a series of chunks         | Section 5.1.1 4.1   |
   | compress | UNIX "compress" program method         | Section 5.1.2.1 4.2.1 |
   | deflate  | "deflate" compression mechanism        | Section 5.1.2.2 4.2.2 |
   |          | ([RFC1951]) used inside the "zlib"     |               |
   |          | data format ([RFC1950])                |               |
   | gzip     | Same as GNU zip [RFC1952]              | Section 5.1.2.3 4.2.3 |
   +----------+--------------------------------------+-----------------+

9.5.
   +----------+----------------------------------------+---------------+

7.6.  Upgrade Token Registration Registry

   The HTTP Upgrade Token Registry defines the name space for protocol-
   name tokens used to identify protocols in the Upgrade header field.
   Each registered protocol-name is associated with contact information
   and an optional set of specifications that details how the connection
   will be processed after it has been upgraded.

   Registrations require IETF Review (see Section 4.1 of [RFC5226]) and
   are subject to the following rules:

   1.  A protocol-name token, once registered, stays registered forever.

   2.  The registration MUST name a responsible party for the
       registration.

   3.  The registration MUST name a point of contact.

   4.  The registration MAY name a set of specifications associated with
       that token.  Such specifications need not be publicly available.

   5.  The registration SHOULD name a set of expected "protocol-version"
       tokens associated with that token at the time of registration.

   6.  The responsible party MAY change the registration at any time.
       The IANA will keep a record of all such changes, and make them
       available upon request.

   7.  The IESG MAY reassign responsibility for a protocol token.  This
       will normally only be used in the case when a responsible party
       cannot be contacted.

   This registration procedure for HTTP Upgrade Tokens -- replaces that
   previously defined in Section 7.2 of [RFC2817] -- is now defined by
   Section 8.7.1 of this document. [RFC2817].

7.7.  Upgrade Token Registration

   The HTTP Status Code Upgrade Token Registry located at
   <http://www.iana.org/assignments/http-upgrade-tokens/> shall be updated with the
   registration below:

   +-------+---------------------------+-------------------------------+

   +-------+----------------------+----------------------+-------------+
   | Value | Description          | Expected Version     | Reference   |
   +-------+---------------------------+-------------------------------+
   |       |                      | Tokens               |             |
   +-------+----------------------+----------------------+-------------+
   | HTTP  | Hypertext Transfer   | any DIGIT.DIGIT      | Section 2.6 of this |
   |       | Protocol             | specification (e.g, "2.0")         |             |
   +-------+---------------------------+-------------------------------+

10.
   +-------+----------------------+----------------------+-------------+

   The responsible party is: "IETF (iesg@ietf.org) - Internet
   Engineering Task Force".

8.  Security Considerations

   This section is meant to inform application developers, information
   providers, and users of the security limitations in HTTP/1.1 as
   described by this document.  The discussion does not include
   definitive solutions to the problems revealed, though it does make
   some suggestions for reducing security risks.

10.1.

8.1.  Personal Information

   HTTP clients are often privy to large amounts of personal information
   (e.g., the user's name, location, mail address, passwords, encryption
   keys, etc.), and SHOULD be very careful to prevent unintentional
   leakage of this information.  We very strongly recommend that a
   convenient interface be provided for the user to control
   dissemination of such information, and that designers and
   implementors be particularly careful in this area.  History shows
   that errors in this area often create serious security and/or privacy
   problems and generate highly adverse publicity for the implementor's
   company.

10.2.

8.2.  Abuse of Server Log Information

   A server is in the position to save personal data about a user's
   requests which might identify their reading patterns or subjects of
   interest.  This  In particular, log information gathered at an intermediary
   often contains a history of user agent interaction, across a
   multitude of sites, that can be traced to individual users.

   HTTP log information is clearly confidential in nature and nature; its handling can be is often
   constrained by law in certain countries.  People
   using HTTP laws and regulations.  Log information needs to provide data are responsible be
   securely stored and appropriate guidelines followed for ensuring that such
   material its analysis.
   Anonymization of personal information within individual entries
   helps, but is generally not distributed without the permission of any individuals sufficient to prevent real log traces
   from being re-identified based on correlation with other access
   characteristics.  As such, access traces that are identifiable by the keyed to a specific
   client should not be published results.

10.3. even if the key is pseudonymous.

   To minimize the risk of theft or accidental publication, log
   information should be purged of personally identifiable information,
   including user identifiers, IP addresses, and user-provided query
   parameters, as soon as that information is no longer necessary to
   support operational needs for security, auditing, or fraud control.

8.3.  Attacks Based On File and Path Names

   Implementations of HTTP origin servers SHOULD be careful to restrict
   the documents returned by HTTP requests to be only those that were
   intended by the server administrators.  If an HTTP server translates
   HTTP URIs directly into file system calls, the server MUST take
   special care not to serve files that were not intended to be
   delivered to HTTP clients.  For example, UNIX, Microsoft Windows, and
   other operating systems use ".." as a path component to indicate a
   directory level above the current one.  On such a system, an HTTP
   server MUST disallow any such construct in the request-target if it
   would otherwise allow access to a resource outside those intended to
   be accessible via the HTTP server.  Similarly, files intended for
   reference only internally to the server (such as access control
   files, configuration files, and script code) MUST be protected from
   inappropriate retrieval, since they might contain sensitive
   information.  Experience has shown that minor bugs in such HTTP
   server implementations have turned into security risks.

10.4.

8.4.  DNS-related Attacks

   HTTP clients rely heavily on the Domain Name Service (DNS), and are
   thus generally prone to security attacks based on the deliberate
   misassociation of IP addresses and DNS names not protected by DNSSec.
   Clients need to be cautious in assuming the validity of an IP number/
   DNS name association unless the response is protected by DNSSec
   ([RFC4033]).

10.5.  Proxies

8.5.  Intermediaries and Caching

   By their very nature, HTTP proxies intermediaries are men-in-the-middle, and
   represent an opportunity for man-in-the-middle attacks.  Compromise
   of the systems on which the proxies intermediaries run can result in serious
   security and privacy problems.  Proxies  Intermediaries have access to security-
   related
   security-related information, personal information about individual
   users and organizations, and proprietary information belonging to
   users and content providers.  A compromised proxy, intermediary, or a proxy an
   intermediary implemented or configured without regard to security and
   privacy considerations, might be used in the commission of a wide
   range of potential attacks.

   Proxy operators need to protect the systems on which proxies run as
   they would protect any system

   Intermediaries that contains or transports sensitive
   information.  In particular, log information gathered at proxies
   often contains highly sensitive personal information, and/or
   information about organizations.  Log information needs to be
   carefully guarded, and appropriate guidelines for use need contain a shared cache are especially vulnerable
   to be
   developed and followed.  (Section 10.2).

   Proxy implementors cache poisoning attacks.

   Implementors need to consider the privacy and security implications
   of their design and coding decisions, and of the configuration
   options they provide to proxy operators (especially the default
   configuration).

   Users of a proxy need to be aware that proxies intermediaries are no trustworthier more trustworthy
   than the people who run them; HTTP itself cannot solve this problem.

   The judicious use of cryptography, when appropriate, might suffice to
   protect against a broad range of security and privacy attacks.  Such
   cryptography is beyond the scope of the HTTP/1.1 specification.

10.6.

8.6.  Protocol Element Size Overflows

   Because HTTP uses mostly textual, character-delimited fields,
   attackers can overflow buffers in implementations, and/or perform a
   Denial of Service against implementations that accept fields with
   unlimited lengths.

   To promote interoperability, this specification makes specific
   recommendations for minimum size limits on request-targets request-line
   (Section 3.1.1.2) 3.1.1) and blocks of header fields (Section 3.2).  These are
   minimum recommendations, chosen to be supportable even by
   implementations with limited resources; it is expected that most
   implementations will choose substantially higher limits.

   This specification also provides a way for servers to reject messages
   that have request-targets that are too long (Section 7.4.15 7.4.12 of
   [Part2]) or request entities that are too large (Section 7.4 of
   [Part2]).

   Other fields (including but not limited to request methods, response
   status phrases, header field-names, and body chunks) SHOULD be
   limited by implementations carefully, so as to not impede
   interoperability.

10.7.  Denial of Service Attacks on Proxies

   They exist.  They are hard to defend against.  Research continues.
   Beware.

11.

9.  Acknowledgments

   This document revision edition of HTTP builds on the work many contributions that went into
   RFC 2616 1945, RFC 2068, RFC 2145, and
   its predecessors. RFC 2616, including substantial
   contributions made by the previous authors, editors, and working
   group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding, Henrik
   Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter, Paul
   J. Leach, and Mark Nottingham.  See Section 16 of [RFC2616] for detailed
   acknowledgements.
   additional acknowledgements from prior revisions.

   Since 1999, many the following contributors have helped improve the HTTP
   specification by reporting bugs, asking smart questions, drafting and or
   reviewing text, and discussing evaluating open issues:

   Adam Barth, Adam Roach, Addison Phillips, Adrian Chadd, Adrien de
   Croy, Alan Ford, Alan Ruttenberg, Albert Lunde, Alex Rousskov, Alexey
   Melnikov, Alisha Smith, Amichai Rothman, Amit Klein, Amos Jeffries,
   Andreas Maier, Andreas Petersson, Anne van Kesteren, Anthony Bryan,
   Asbjorn Ulsberg, Balachander Krishnamurthy, Barry Leiba, Ben Laurie,
   Benjamin Niven-Jenkins, Bil Corry, Bill Burke, Bjoern Hoehrmann, Bob
   Scheifler, Boris Zbarsky, Brett Slatkin, Brian Kell, Brian McBarron,
   Brian Pane, Brian Smith, Bryce Nesbitt, Cameron Heavon-Jones, Carl
   Kugler, Carsten Bormann, Charles Fry, Chris Newman, Cyrus Daboo, Dale
   Robert Anderson, Dan Winship, Daniel Stenberg, Dave Cridland, Dave
   Crocker, Dave Kristol, David Booth, David Singer, David W. Morris,
   Diwakar Shetty, Dmitry Kurochkin, Drummond Reed, Duane Wessels,
   Edward Lee, Eliot Lear, Eran Hammer-Lahav, Eric D. Williams, Eric J.
   Bowman, Eric Lawrence, Eric Rescorla, Erik Aronesty, Florian Weimer,
   Frank Ellermann, Fred Bohle, Geoffrey Sneddon, Gervase Markham, Greg
   Wilkins, Harald Tveit Alvestrand, Harry Halpin, Helge Hess, Henrik
   Nordstrom, Henry S. Thompson, Henry Story, Herbert van de Sompel,
   Howard Melman, Hugo Haas, Ian Hickson, Ingo Struck, J. Ross Nicoll,
   James H. Manger, James Lacey, James M. Snell, Jamie Lokier, Jan
   Algermissen, Jeff Hodges (for coming up with the term 'effective
   Request-URI'), Jeff Walden, Jim Luther, Joe D. Williams, Joe
   Gregorio, Joe Orton, John C. Klensin, John C. Mallery, John Cowan,
   John Kemp, John Panzer, John Schneider, John Stracke, Jonas Sicking,
   Jonathan Billington, Jonathan Moore, Jonathan Rees, Jordi Ros, Joris
   Dobbelsteen, Josh Cohen, Julien Pierre, Jungshik Shin, Justin
   Chapweske, Justin Erenkrantz, Justin James, Kalvinder Singh, Karl
   Dubost, Keith Hoffman, Keith Moore, Koen Holtman, Konstantin
   Voronkov, Kris Zyp, Lisa Dusseault, Maciej Stachowiak, Marc
   Schneider, Marc Slemko, Mark Baker, Mark Nottingham
   (Working Group chair), Mark Pauley, Markus Lanthaler,
   Martin J. Duerst, Martin Thomson, Matt Lynch, Matthew Cox, Max Clark,
   Michael Burrows, Michael Hausenblas, Mike Amundsen, Mike Belshe, Mike
   Kelly, Mike Schinkel, Miles Sabin, Mykyta Yevstifeyev, Nathan Rixham,
   Nicholas Shanks, Nico Williams, Nicolas Alvarez, Nicolas Mailhot,
   Noah Slater, Pablo Castro, Pat Hayes, Patrick R. McManus, Paul E.

   Jones, Paul Hoffman, Paul Marquess, Peter Saint-
   Andre, Saint-Andre, Peter Watkins,
   Phil Archer, Phillip Hallam-Baker, Poul-Henning Kamp, Preethi
   Natarajan, Ray Polk, Reto Bachmann-Gmuer, Richard Cyganiak, Robert
   Brewer, Robert Collins, Robert O'Callahan, Robert Olofsson, Robert
   Sayre, Robert Siemer, Robert de Wilde, Roberto Javier Godoy, Ronny
   Widjaja, S. Mike Dierken, Salvatore Loreto, Sam Johnston, Sam Ruby,
   Scott Lawrence (for maintaining the original issues list), Sean B.
   Palmer, Shane McCarron, Stefan Eissing, Stefan Tilkov, Stefanos
   Harhalakis, Stephane Bortzmeyer, Stephen Farrell, Stuart Williams,
   Subbu Allamaraju, Sylvain Hellegouarch, Tapan Divekar, Ted Hardie,
   Thomas Broyer, Thomas Nordin, Thomas Roessler, Tim Morgan, Tim Olsen,
   Travis Snoozy, Tyler Close, Vincent Murphy, Wenbo Zhu, Werner
   Baumann, Wilbur Streett, Wilfredo Sanchez Vega, William A. Rowe Jr.,
   William Chan, Willy Tarreau, Xiaoshu Wang, Yaron Goland, Yngve
   Nysaeter Pettersen, Yogesh Bang, Yutaka Oiwa, and Zed A. Shaw.

12. Shaw, and Zhong
   Yu.

10.  References

12.1.

10.1.  Normative References

   [ISO-8859-1]  International Organization for Standardization,
                 "Information technology -- 8-bit single-byte coded
                 graphic character sets -- Part 1: Latin alphabet No.
                 1", ISO/IEC 8859-1:1998, 1998.

   [Part2]       Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
                 Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., and J. Reschke, Ed.,
                 "HTTP/1.1, part 2: Message Semantics", draft-ietf-httpbis-p2-semantics-18
                 draft-ietf-httpbis-p2-semantics-19 (work in progress), January
                 March 2012.

   [Part3]       Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
                 Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., and J. Reschke, Ed.,
                 "HTTP/1.1, part 3: Message Payload and Content
                 Negotiation",
                 draft-ietf-httpbis-p3-payload-18 draft-ietf-httpbis-p3-payload-19 (work in
                 progress),
                 January March 2012.

   [Part6]       Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
                 Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., Nottingham, M., Ed.,
                 and J. Reschke, Ed., "HTTP/1.1, part 6: Caching",
                 draft-ietf-httpbis-p6-cache-18
                 draft-ietf-httpbis-p6-cache-19 (work in progress),
                 January
                 March 2012.

   [RFC1950]     Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data
                 Format Specification version 3.3", RFC 1950, May 1996.

   [RFC1951]     Deutsch, P., "DEFLATE Compressed Data Format
                 Specification version 1.3", RFC 1951, May 1996.

   [RFC1952]     Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and
                 G. Randers-Pehrson, "GZIP file format specification
                 version 4.3", RFC 1952, May 1996.

   [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3986]     Berners-Lee, T., Fielding, R., and L. Masinter,
                 "Uniform Resource Identifier (URI): Generic Syntax",
                 STD 66, RFC 3986, January 2005.

   [RFC5234]     Crocker, D., Ed. and P. Overell, "Augmented BNF for
                 Syntax Specifications: ABNF", STD 68, RFC 5234,
                 January 2008.

   [USASCII]     American National Standards Institute, "Coded Character
                 Set -- 7-bit American Standard Code for Information
                 Interchange", ANSI X3.4, 1986.

12.2.

10.2.  Informative References

   [Kri2001]     Kristol, D., "HTTP Cookies: Standards, Privacy, and
                 Politics", ACM Transactions on Internet Technology Vol.
                 1, #2, November 2001,
                 <http://arxiv.org/abs/cs.SE/0105018>.

   [Nie1997]     Frystyk, H., Gettys, J., Prud'hommeaux, E., Lie, H.,
                 and C. Lilley, "Network Performance Effects of
                 HTTP/1.1, CSS1, and PNG", ACM Proceedings of the ACM
                 SIGCOMM '97 conference on Applications, technologies,
                 architectures, and protocols for computer communication
                 SIGCOMM '97, September 1997,
                 <http://doi.acm.org/10.1145/263105.263157>.

   [Pad1995]     Padmanabhan, V. and J. Mogul, "Improving HTTP Latency",
                 Computer Networks and ISDN Systems v. 28, pp. 25-35,
                 December 1995,
                 <http://portal.acm.org/citation.cfm?id=219094>.

   [RFC1919]     Chatel, M., "Classical versus Transparent IP Proxies",
                 RFC 1919, March 1996.

   [RFC1945]     Berners-Lee, T., Fielding, R., and H. Nielsen,
                 "Hypertext Transfer Protocol -- HTTP/1.0", RFC 1945,
                 May 1996.

   [RFC2045]     Freed, N. and N. Borenstein, "Multipurpose Internet
                 Mail Extensions (MIME) Part One: Format of Internet
                 Message Bodies", RFC 2045, November 1996.

   [RFC2047]     Moore, K., "MIME (Multipurpose Internet Mail
                 Extensions) Part Three: Message Header Extensions for
                 Non-ASCII Text", RFC 2047, November 1996.

   [RFC2068]     Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and
                 T. Berners-Lee, "Hypertext Transfer Protocol --
                 HTTP/1.1", RFC 2068, January 1997.

   [RFC2145]     Mogul, J., Fielding, R., Gettys, J., and H. Nielsen,
                 "Use and Interpretation of HTTP Version Numbers",
                 RFC 2145, May 1997.

   [RFC2616]     Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
                 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
                 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2817]     Khare, R. and S. Lawrence, "Upgrading to TLS Within
                 HTTP/1.1", RFC 2817, May 2000.

   [RFC2818]     Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC2965]     Kristol, D. and L. Montulli, "HTTP State Management
                 Mechanism", RFC 2965, October 2000.

   [RFC3040]     Cooper, I., Melve, I., and G. Tomlinson, "Internet Web
                 Replication and Caching Taxonomy", RFC 3040,
                 January 2001.

   [RFC3864]     Klyne, G., Nottingham, M., and J. Mogul, "Registration
                 Procedures for Message Header Fields", BCP 90,
                 RFC 3864, September 2004.

   [RFC4033]     Arends, R., Austein, R., Larson, M., Massey, D., and S.
                 Rose, "DNS Security Introduction and Requirements",
                 RFC 4033, March 2005.

   [RFC4288]     Freed, N. and J. Klensin, "Media Type Specifications
                 and Registration Procedures", BCP 13, RFC 4288,
                 December 2005.

   [RFC4395]     Hansen, T., Hardie, T., and L. Masinter, "Guidelines
                 and Registration Procedures for New URI Schemes",
                 BCP 115, RFC 4395, February 2006.

   [RFC4559]     Jaganathan, K., Zhu, L., and J. Brezak, "SPNEGO-based
                 Kerberos and NTLM HTTP Authentication in Microsoft
                 Windows", RFC 4559, June 2006.

   [RFC5226]     Narten, T. and H. Alvestrand, "Guidelines for Writing
                 an IANA Considerations Section in RFCs", BCP 26,
                 RFC 5226, May 2008.

   [RFC5322]     Resnick, P., "Internet Message Format", RFC 5322,
                 October 2008.

   [RFC6265]     Barth, A., "HTTP State Management Mechanism", RFC 6265,
                 April 2011.

   [Spe]         Spero, S., "Analysis of HTTP Performance Problems",
                 <http://sunsite.unc.edu/mdma-release/http-prob.html>.

   [Tou1998]     Touch, J., Heidemann, J., and K. Obraczka, "Analysis of
                 HTTP Performance", ISI Research Report ISI/RR-98-463,
                 Aug 1998, <http://www.isi.edu/touch/pubs/http-perf96/>.

                 (original report dated Aug. 1996)

Appendix A.  HTTP Version History

   HTTP has been in use by the World-Wide Web global information
   initiative since 1990.  The first version of HTTP, later referred to
   as HTTP/0.9, was a simple protocol for hypertext data transfer across
   the Internet with only a single request method (GET) and no metadata.
   HTTP/1.0, as defined by [RFC1945], added a range of request methods
   and MIME-like messaging that could include metadata about the data
   transferred and modifiers on the request/response semantics.
   However, HTTP/1.0 did not sufficiently take into consideration the
   effects of hierarchical proxies, caching, the need for persistent
   connections, or name-based virtual hosts.  The proliferation of
   incompletely-implemented applications calling themselves "HTTP/1.0"
   further necessitated a protocol version change in order for two
   communicating applications to determine each other's true
   capabilities.

   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
   requirements that enable reliable implementations, adding only those
   new features that will either be safely ignored by an HTTP/1.0
   recipient or only sent when communicating with a party advertising
   compliance
   conformance with HTTP/1.1.

   It is beyond the scope of a protocol specification to mandate
   compliance
   conformance with previous versions.  HTTP/1.1 was deliberately
   designed, however, to make supporting previous versions easy.  We
   would expect a general-purpose HTTP/1.1 server to understand any
   valid request in the format of HTTP/1.0 and respond appropriately
   with an HTTP/1.1 message that only uses features understood (or
   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect an
   HTTP/1.1 client to understand any valid HTTP/1.0 response.

   Since HTTP/0.9 did not support header fields in a request, there is
   no mechanism for it to support name-based virtual hosts (selection of
   resource by inspection of the Host header field).  Any server that
   implements name-based virtual hosts ought to disable support for
   HTTP/0.9.  Most requests that appear to be HTTP/0.9 are, in fact,
   badly constructed HTTP/1.x requests wherein a buggy client failed to
   properly encode linear whitespace found in a URI reference and placed
   in the request-target.

A.1.  Changes from HTTP/1.0

   This section summarizes major differences between versions HTTP/1.0
   and HTTP/1.1.

A.1.1.  Multi-homed Web Servers

   The requirements that clients and servers support the Host header
   field (Section 8.3), 5.4), report an error if it is missing from an
   HTTP/1.1 request, and accept absolute URIs (Section 3.1.1.2) 5.3) are among
   the most important changes defined by HTTP/1.1.

   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
   addresses and servers; there was no other established mechanism for
   distinguishing the intended server of a request than the IP address
   to which that request was directed.  The Host header field was
   introduced during the development of HTTP/1.1 and, though it was
   quickly implemented by most HTTP/1.0 browsers, additional
   requirements were placed on all HTTP/1.1 requests in order to ensure
   complete adoption.  At the time of this writing, most HTTP-based
   services are dependent upon the Host header field for targeting
   requests.

A.1.2.  Keep-Alive Connections

   In HTTP/1.0, each connection is established by the client prior to
   the request and closed by the server after sending the response.
   However, some implementations implement the explicitly negotiated
   ("Keep-Alive") version of persistent connections described in Section
   19.7.1 of [RFC2068].

   Some clients and servers might wish to be compatible with these
   previous approaches to persistent connections, by explicitly
   negotiating for them with a "Connection: keep-alive" request header
   field.  However, some experimental implementations of HTTP/1.0
   persistent connections are faulty; for example, if a HTTP/1.0 proxy
   server doesn't understand Connection, it will erroneously forward
   that header to the next inbound server, which would result in a hung
   connection.

   One attempted solution was the introduction of a Proxy-Connection
   header, targeted specifically at proxies.  In practice, this was also
   unworkable, because proxies are often deployed in multiple layers,
   bringing about the same problem discussed above.

   As a result, clients are encouraged not to send the Proxy-Connection
   header in any requests.

   Clients are also encouraged to consider the use of Connection: keep-
   alive in requests carefully; while they can enable persistent
   connections with HTTP/1.0 servers, clients using them need will need
   to monitor the connection for "hung" requests (which indicate that
   the client ought stop sending the header), and this mechanism ought
   not be used by clients at all when a proxy is being used.

A.2.  Changes from RFC 2616

   Empty list elements in list productions have been deprecated.
   (Section 1.2.1)

   Rules about implicit linear whitespace between certain grammar
   productions have been removed; now it's only allowed when
   specifically pointed out in the ABNF.  (Section 1.2.2)

   Clarify that the string "HTTP" in the HTTP-Version HTTP-version ABFN production is
   case sensitive.  Restrict the version numbers to be single digits due
   to the fact that implementations are known to handle multi-digit
   version numbers incorrectly.  (Section 2.6)

   Update use of abs_path production from RFC 1808 to the path-absolute
   + query components of RFC 3986.  State that the asterisk form is
   allowed for the OPTIONS request method only.  (Section 5.3)

   Require that invalid whitespace around field-names be rejected.
   (Section 3.2)

   Rules about implicit linear whitespace between certain grammar
   productions have been removed; now whitespace is only allowed where
   specifically defined in the ABNF.  (Section 3.2.1)

   The NUL octet is no longer allowed in comment and quoted-string text.
   The quoted-pair rule no longer allows escaping control characters
   other than HTAB.  Non-ASCII content in header fields and reason
   phrase has been obsoleted and made opaque (the TEXT rule was
   removed).  (Section 3.2.3) 3.2.4)

   Empty list elements in list productions have been deprecated.
   (Section 3.2.5)

   Require recipients to handle bogus Content-Length header fields as
   errors.  (Section 3.3)

   Remove reference to non-existent identity transfer-coding value
   tokens.  (Sections 3.3 and 5.1)

   Update use of abs_path production from RFC 1808 to the path-absolute
   + query components of RFC 3986.  State that the asterisk form is
   allowed for the OPTIONS request method only. fields as
   errors.  (Section 3.1.1.2) 3.3)
   Remove reference to non-existent identity transfer-coding value
   tokens.  (Sections 3.3 and 4)

   Clarification that the chunk length does not include the count of the
   octets in the chunk header and trailer.  Furthermore disallowed line
   folding in chunk extensions. extensions, and deprecate their use.  (Section 4.1)

   Registration of Transfer Codings now requires IETF Review
   (Section 5.1.1) 7.4)

   Remove hard limit of two connections per server.  Remove requirement
   to retry a sequence of requests as long it was idempotent.  Remove
   requirements about when servers are allowed to close connections
   prematurely.  (Section 6.1.4) 6.3.3)

   Remove requirement to retry requests under certain cirumstances when
   the server prematurely closes the connection.  (Section 6.2) 6.4)

   Change ABNF productions for header fields to only define the field
   value.  (Section 8)

   Clarify exactly when close connection options must be sent.
   (Section 8.1) 6.1)

   Define the semantics of the "Upgrade" header field in responses other
   than 101 (this was incorporated from [RFC2817]).  (Section 8.7) 6.5)

A.3.  Changes from RFC 2817

   Registration of Upgrade tokens now requires IETF Review (Section 7.6)

Appendix B.  Collected ABNF

   BWS = OWS

   Chunked-Body = *chunk last-chunk trailer-part CRLF

   Connection = *( "," OWS ) connection-token *( OWS "," [ OWS
    connection-token ] )
   Content-Length = 1*DIGIT
   HTTP-Prot-Name = %x48.54.54.50 ; HTTP
   HTTP-Version = HTTP-Prot-Name "/" DIGIT "." DIGIT

   HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body
    ]
   HTTP-name = %x48.54.54.50 ; HTTP
   HTTP-version = HTTP-name "/" DIGIT "." DIGIT
   Host = uri-host [ ":" port ]

   Method = token

   OWS = *( SP / HTAB / obs-fold )

   RWS = 1*( SP / HTAB / obs-fold )
   Reason-Phrase = *( HTAB / SP / VCHAR / obs-text )
   Request-Line = Method SP request-target SP HTTP-Version CRLF

   Status-Code = 3DIGIT
   Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
   TE = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
   Trailer = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
   Transfer-Encoding = *( "," OWS ) transfer-coding *( OWS "," [ OWS
    transfer-coding ] )

   URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
   Upgrade = *( "," OWS ) product protocol *( OWS "," [ OWS product protocol ] )

   Via = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
    *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
    )

   absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
   absolute-form = absolute-URI
   asterisk-form = "*"
   attribute = token
   authority = <authority, defined in [RFC3986], Section 3.2>
   authority-form = authority

   chunk = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
   chunk-data = 1*OCTET
   chunk-ext = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
   chunk-ext-name = token
   chunk-ext-val = token / quoted-str-nf
   chunk-size = 1*HEXDIG
   chunked-body = *chunk last-chunk trailer-part CRLF
   comment = "(" *( ctext / quoted-cpair / comment ) ")"
   connection-token = token
   ctext = OWS / %x21-27 ; '!'-'''
    / %x2A-5B ; '*'-'['
    / %x5D-7E ; ']'-'~'
    / obs-text

   field-content = *( HTAB / SP / VCHAR / obs-text )
   field-name = token
   field-value = *( field-content / obs-fold )

   header-field = field-name ":" OWS field-value BWS
   http-URI = "http://" authority path-abempty [ "?" query ]
   https-URI = "https://" authority path-abempty [ "?" query ]

   last-chunk = 1*"0" [ chunk-ext ] CRLF

   message-body = *OCTET
   method = token

   obs-fold = CRLF ( SP / HTAB )
   obs-text = %x80-FF
   origin-form = path-absolute [ "?" query ]

   partial-URI = relative-part [ "?" query ]
   path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
   path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
   port = <port, defined in [RFC3986], Section 3.2.3>
   product
   protocol = token protocol-name [ "/" product-version protocol-version ]
   product-version = token
   protocol-name = token
   protocol-version = token
   pseudonym = token

   qdtext = OWS / "!" / %x23-5B ; '#'-'['
    / %x5D-7E ; ']'-'~'
    / obs-text
   qdtext-nf = HTAB / SP / "!" / %x23-5B ; '#'-'['
    / %x5D-7E ; ']'-'~'
    / obs-text
   query = <query, defined in [RFC3986], Section 3.4>
   quoted-cpair = "\" ( HTAB / SP / VCHAR / obs-text )
   quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )
   quoted-str-nf = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
   quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
   qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )

   reason-phrase = *( HTAB / SP / VCHAR / obs-text )
   received-by = ( uri-host [ ":" port ] ) / pseudonym
   received-protocol = [ protocol-name "/" ] protocol-version
   relative-part = <relative-part, defined in [RFC3986], Section 4.2>
   request-line = method SP request-target SP HTTP-version CRLF
   request-target = "*" origin-form / absolute-URI absolute-form / ( path-absolute [ "?" query ] ) authority-form / authority
    asterisk-form

   special = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "\" /
    DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
   start-line = Request-Line request-line / Status-Line status-line
   status-code = 3DIGIT
   status-line = HTTP-version SP status-code SP reason-phrase CRLF

   t-codings = "trailers" / ( transfer-extension [ te-params ] )
   tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
    "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
   te-ext = OWS ";" OWS token [ "=" word ]
   te-params = OWS ";" OWS "q=" qvalue *te-ext
   token = 1*tchar
   trailer-part = *( header-field CRLF )
   transfer-coding = "chunked" / "compress" / "deflate" / "gzip" /
    transfer-extension
   transfer-extension = token *( OWS ";" OWS transfer-parameter )
   transfer-parameter = attribute BWS "=" BWS value

   uri-host = <host, defined in [RFC3986], Section 3.2.2>

   value = word

   word = token / quoted-string

   ABNF diagnostics:

   ; Chunked-Body defined but not used
   ; Connection defined but not used
   ; Content-Length defined but not used
   ; HTTP-message defined but not used
   ; Host defined but not used
   ; TE defined but not used
   ; Trailer defined but not used
   ; Transfer-Encoding defined but not used
   ; URI-reference defined but not used
   ; Upgrade defined but not used
   ; Via defined but not used
   ; chunked-body defined but not used
   ; http-URI defined but not used
   ; https-URI defined but not used
   ; partial-URI defined but not used
   ; special defined but not used

Appendix C.  Change Log (to be removed by RFC Editor before publication)

C.1.  Since RFC 2616

   Extracted relevant partitions from [RFC2616].

C.2.  Since draft-ietf-httpbis-p1-messaging-00

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/1>: "HTTP Version
      should be case sensitive"
      (<http://purl.org/NET/http-errata#verscase>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/2>: "'unsafe'
      characters" (<http://purl.org/NET/http-errata#unsafe-uri>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/3>: "Chunk Size
      Definition" (<http://purl.org/NET/http-errata#chunk-size>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/4>: "Message Length"
      (<http://purl.org/NET/http-errata#msg-len-chars>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/8>: "Media Type
      Registrations" (<http://purl.org/NET/http-errata#media-reg>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/11>: "URI includes
      query" (<http://purl.org/NET/http-errata#uriquery>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/15>: "No close on
      1xx responses" (<http://purl.org/NET/http-errata#noclose1xx>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/16>: "Remove
      'identity' token references"
      (<http://purl.org/NET/http-errata#identity>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/26>: "Import query
      BNF"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/31>: "qdtext BNF"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/35>: "Normative and
      Informative references"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/42>: "RFC2606
      Compliance"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/45>: "RFC977
      reference"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/46>: "RFC1700
      references"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/47>: "inconsistency
      in date format explanation"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/48>: "Date reference
      typo"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/65>: "Informative
      references"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/66>: "ISO-8859-1
      Reference"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/86>: "Normative up-
      to-date references"

   Other changes:

   o  Update media type registrations to use RFC4288 template.

   o  Use names of RFC4234 core rules DQUOTE and HTAB, fix broken ABNF
      for chunk-data (work in progress on
      <http://tools.ietf.org/wg/httpbis/trac/ticket/36>)

C.3.  Since draft-ietf-httpbis-p1-messaging-01

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/19>: "Bodies on GET
      (and other) requests"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/55>: "Updating to
      RFC4288"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/57>: "Status Code
      and Reason Phrase"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/82>: "rel_path not
      used"

   Ongoing work on ABNF conversion
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):

   o  Get rid of duplicate BNF rule names ("host" -> "uri-host",
      "trailer" -> "trailer-part").

   o  Avoid underscore character in rule names ("http_URL" -> "http-
      URL", "abs_path" -> "path-absolute").

   o  Add rules for terms imported from URI spec ("absoluteURI",
      "authority", "path-absolute", "port", "query", "relativeURI",
      "host) -- these will have to be updated when switching over to
      RFC3986.

   o  Synchronize core rules with RFC5234.

   o  Get rid of prose rules that span multiple lines.

   o  Get rid of unused rules LOALPHA and UPALPHA.

   o  Move "Product Tokens" section (back) into Part 1, as "token" is
      used in the definition of the Upgrade header field.

   o  Add explicit references to BNF syntax and rules imported from
      other parts of the specification.

   o  Rewrite prose rule "token" in terms of "tchar", rewrite prose rule
      "TEXT".

C.4.  Since draft-ietf-httpbis-p1-messaging-02

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/51>: "HTTP-date vs.
      rfc1123-date"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/64>: "WS in quoted-
      pair"

   Ongoing work on IANA Message Header Field Registration
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/40>):

   o  Reference RFC 3984, and update header field registrations for
      headers defined in this document.

   Ongoing work on ABNF conversion
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):

   o  Replace string literals when the string really is case-sensitive
      (HTTP-Version).
      (HTTP-version).

C.5.  Since draft-ietf-httpbis-p1-messaging-03

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/28>: "Connection
      closing"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/97>: "Move
      registrations and registry information to IANA Considerations"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/120>: "need new URL
      for PAD1995 reference"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/127>: "IANA
      Considerations: update HTTP URI scheme registration"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/128>: "Cite HTTPS
      URI scheme definition"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/129>: "List-type
      headers vs Set-Cookie"

   Ongoing work on ABNF conversion
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):

   o  Replace string literals when the string really is case-sensitive
      (HTTP-Date).

   o  Replace HEX by HEXDIG for future consistence with RFC 5234's core
      rules.

C.6.  Since draft-ietf-httpbis-p1-messaging-04

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/34>: "Out-of-date
      reference for URIs"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/132>: "RFC 2822 is
      updated by RFC 5322"

   Ongoing work on ABNF conversion
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):

   o  Use "/" instead of "|" for alternatives.

   o  Get rid of RFC822 dependency; use RFC5234 plus extensions instead.

   o  Only reference RFC 5234's core rules.

   o  Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
      whitespace ("OWS") and required whitespace ("RWS").

   o  Rewrite ABNFs to spell out whitespace rules, factor out header
      field value format definitions.

C.7.  Since draft-ietf-httpbis-p1-messaging-05

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/30>: "Header LWS"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/52>: "Sort 1.3
      Terminology"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/63>: "RFC2047
      encoded words"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/74>: "Character
      Encodings in TEXT"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/77>: "Line Folding"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/83>: "OPTIONS * and
      proxies"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/94>: "Reason-Phrase "reason-phrase
      BNF"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/111>: "Use of TEXT"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/118>: "Join
      "Differences Between HTTP Entities and RFC 2045 Entities"?"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/134>: "RFC822
      reference left in discussion of date formats"

   Final work on ABNF conversion
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):

   o  Rewrite definition of list rules, deprecate empty list elements.

   o  Add appendix containing collected and expanded ABNF.

   Other changes:

   o  Rewrite introduction; add mostly new Architecture Section.

   o  Move definition of quality values from Part 3 into Part 1; make TE
      request header field grammar independent of accept-params (defined
      in Part 3).

C.8.  Since draft-ietf-httpbis-p1-messaging-06

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/161>: "base for
      numeric protocol elements"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/162>: "comment ABNF"

   Partly resolved issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/88>: "205 Bodies"
      (took out language that implied that there might be methods for
      which a request body MUST NOT be included)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/163>: "editorial
      improvements around HTTP-date"

C.9.  Since draft-ietf-httpbis-p1-messaging-07

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/93>: "Repeating
      single-value headers"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/131>: "increase
      connection limit"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/157>: "IP addresses
      in URLs"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/172>: "take over
      HTTP Upgrade Token Registry"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/173>: "CR and LF in
      chunk extension values"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/184>: "HTTP/0.9
      support"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/188>: "pick IANA
      policy (RFC5226) for Transfer Coding / Content Coding"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/189>: "move
      definitions of gzip/deflate/compress to part 1"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/194>: "disallow
      control characters in quoted-pair"

   Partly resolved issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/148>: "update IANA
      requirements wrt Transfer-Coding values" (add the IANA
      Considerations subsection)

C.10.  Since draft-ietf-httpbis-p1-messaging-08

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/201>: "header
      parsing, treatment of leading and trailing OWS"

   Partly resolved issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/60>: "Placement of
      13.5.1 and 13.5.2"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/200>: "use of term
      "word" when talking about header structure"

C.11.  Since draft-ietf-httpbis-p1-messaging-09

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/73>: "Clarification
      of the term 'deflate'"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/83>: "OPTIONS * and
      proxies"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/122>: "MIME-Version
      not listed in P1, general header fields"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/143>: "IANA registry
      for content/transfer encodings"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/165>: "Case-
      sensitivity of HTTP-date"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/200>: "use of term
      "word" when talking about header structure"

   Partly resolved issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/196>: "Term for the
      requested resource's URI"

C.12.  Since draft-ietf-httpbis-p1-messaging-10

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/28>: "Connection
      Closing"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/90>: "Delimiting
      messages with multipart/byteranges"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/95>: "Handling
      multiple Content-Length headers"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/109>: "Clarify
      entity / representation / variant terminology"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/220>: "consider
      removing the 'changes from 2068' sections"

   Partly resolved issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/159>: "HTTP(s) URI
      scheme definitions"

C.13.  Since draft-ietf-httpbis-p1-messaging-11

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/193>: "Trailer
      requirements"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/204>: "Text about
      clock requirement for caches belongs in p6"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/221>: "effective
      request URI: handling of missing host in HTTP/1.0"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/248>: "confusing
      Date requirements for clients"

   Partly resolved issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/95>: "Handling
      multiple Content-Length headers"

C.14.  Since draft-ietf-httpbis-p1-messaging-12

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/75>: "RFC2145
      Normative"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/159>: "HTTP(s) URI
      scheme definitions" (tune the requirements on userinfo)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/210>: "define
      'transparent' proxy"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/224>: "Header
      Classification"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/233>: "Is * usable
      as a request-uri for new methods?"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/240>: "Migrate
      Upgrade details from RFC2817"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/276>: "untangle
      ABNFs for header fields"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/279>: "update RFC
      2109 reference"

C.15.  Since draft-ietf-httpbis-p1-messaging-13

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/53>: "Allow is not
      in 13.5.2"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/95>: "Handling
      multiple Content-Length headers"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/276>: "untangle
      ABNFs for header fields"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/286>: "Content-
      Length ABNF broken"

C.16.  Since draft-ietf-httpbis-p1-messaging-14

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/273>: "HTTP-Version "HTTP-version
      should be redefined as fixed length pair of DIGIT .  DIGIT"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/282>: "Recommend
      minimum sizes for protocol elements"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/283>: "Set
      expectations around buffering"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/288>: "Considering
      messages in isolation"

C.17.  Since draft-ietf-httpbis-p1-messaging-15

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/100>: "DNS Spoofing
      / DNS Binding advice"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/254>: "move RFCs
      2145, 2616, 2817 to Historic status"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/270>: "\-escaping in
      quoted strings"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/305>: "'Close'
      should be reserved in the HTTP header field registry"

C.18.  Since draft-ietf-httpbis-p1-messaging-16

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/186>: "Document
      HTTP's error-handling philosophy"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/215>: "Explain
      header registration"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/219>: "Revise
      Acknowledgements Sections"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/297>: "Retrying
      Requests"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/318>: "Closing the
      connection on server error"

C.19.  Since draft-ietf-httpbis-p1-messaging-17

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/166>: "Clarify 'User
      Agent'"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/300>: "Define non-
      final responses"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/323>: "intended
      maturity level vs normative references"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/324>: "Intermediary
      rewriting of queries"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/158>: "Proxy-
      Connection and Keep-Alive"

C.20.  Since draft-ietf-httpbis-p1-messaging-18

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/250>: "message-body
      in CONNECT response"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/302>: "Misplaced
      text on connection handling in p2"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/335>: "wording of
      line folding rule"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/343>: "chunk-
      extensions"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/346>: "make IANA
      policy definitions consistent"

Index

   A
      absolute-URI form
      absolute-form (of request-target)  32  41
      accelerator  13  11
      application/http Media Type  61
      asterisk form  60
      asterisk-form (of request-target)  31
      authority form  41
      authority-form (of request-target)  32  41

   B
      browser  10  7

   C
      cache  14  12
      cacheable  15  12
      captive portal  14  11
      chunked (Coding Format)  36  34
      client  10  7
      Coding Format
         chunked  36  34
         compress  38  36
         deflate  38  36
         gzip  39  36
      compress (Coding Format)  38  36
      connection  10  7
      Connection header field  49  47
      Content-Length header field  51  29

   D
      deflate (Coding Format)  38  36
      downstream  13  10

   E
      effective request URI  34  43

   G
      gateway  13  11
      Grammar
         absolute-form  40
         absolute-URI  18  16
         ALPHA  7
         asterisk-form  40
         attribute  35  34
         authority  18  16
         authority-form  40
         BWS  9  23
         chunk  36  34
         chunk-data  36  34
         chunk-ext  36  34
         chunk-ext-name  36  34
         chunk-ext-val  36  34
         chunk-size  36
         Chunked-Body  36  34
         chunked-body  34
         comment  26  25
         Connection  50  47
         connection-token  50  47
         Content-Length  51  29
         CR  7
         CRLF  7
         ctext  26  25
         CTL  7
         date2  35  34
         date3  35  34
         DIGIT  7
         DQUOTE  7
         field-content  23  22
         field-name  23  22
         field-value  23  22
         header-field  23  22
         HEXDIG  7
         Host  52  42
         HTAB  7
         HTTP-message  21
         HTTP-Prot-Name  15  19
         HTTP-name  13
         http-URI  18
         HTTP-Version  15  16
         HTTP-version  13
         https-URI  20  18
         last-chunk  36  34
         LF  7
         message-body  27
         Method
         method  20
         obs-fold  22
         obs-text  26  25
         OCTET  7
         origin-form  40
         OWS  9  23
         path-absolute  18  16
         port  18
         product  39
         product-version  39  16
         protocol-name  57  49
         protocol-version  57  49
         pseudonym  57  49
         qdtext  26  25
         qdtext-nf  36  34
         query  18  16
         quoted-cpair  27
         quoted-pair  26
         quoted-pair  25
         quoted-str-nf  36  34
         quoted-string  26  25
         qvalue  40
         Reason-Phrase  23  38
         reason-phrase  21
         received-by  57  49
         received-protocol  57
         Request-Line  22  49
         request-line  20
         request-target  22  40
         RWS  9  23
         SP  7
         special  26  25
         start-line  20
         status-code  21
         status-line  21
         Status-Code  23
         Status-Line  23
         t-codings  53  37
         tchar  26  25
         TE  53  37
         te-ext  53  37
         te-params  53  37
         token  26  25
         Trailer  54  38
         trailer-part  36  34
         transfer-coding  35  34
         Transfer-Encoding  54  28
         transfer-extension  35  34
         transfer-parameter  35  34
         Upgrade  55  56
         uri-host  18  16
         URI-reference  18  16
         value  35  34
         VCHAR  7
         Via  57  49
         word  26  25
      gzip (Coding Format)  39  36

   H
      header field  21  19
      Header Fields
         Connection  49  47
         Content-Length  51  29
         Host  51  42
         TE  53  36
         Trailer  54  38
         Transfer-Encoding  54  27
         Upgrade  55  56
         Via  57  49
      header section  21  19
      headers  21  19
      Host header field  51  42
      http URI scheme  18  16
      https URI scheme  19  17

   I
      inbound  13  10
      interception proxy  14  11
      intermediary  12  9

   M
      Media Type
         application/http  61  60
         message/http  59
      message  10  8
      message/http Media Type  59
      method  20

   N
      non-transforming proxy  13  10

   O
      origin form server  7
      origin-form (of request-target)  32
      origin server  10  40
      outbound  13  10

   P
      proxy  13  10

   R
      recipient  10  7
      request  10  8
      request-target  20
      resource  17  15
      response  10  8
      reverse proxy  13  11

   S
      sender  10  7
      server  10  7
      spider  10  7

   T
      target resource  34  39
      target URI  39
      TE header field  53  36
      Trailer header field  54  38
      Transfer-Encoding header field  54  27
      transforming proxy  13  10
      transparent proxy  14  11
      tunnel  14  11

   U
      Upgrade header field  55  56
      upstream  13  10
      URI scheme
         http  18  16
         https  19  17
      user agent  10  7

   V
      Via header field  57  49

Authors' Addresses

   Roy T. Fielding (editor)
   Adobe Systems Incorporated
   345 Park Ave
   San Jose, CA  95110
   USA

   EMail: fielding@gbiv.com
   URI:   http://roy.gbiv.com/

   Jim Gettys
   Alcatel-Lucent Bell Labs
   21 Oak Knoll Road
   Carlisle, MA  01741
   USA

   EMail: jg@freedesktop.org
   URI:   http://gettys.wordpress.com/

   Jeffrey C. Mogul
   Hewlett-Packard Company
   HP Labs, Large Scale Systems Group
   1501 Page Mill Road, MS 1177
   Palo Alto, CA  94304
   USA

   EMail: JeffMogul@acm.org
   Henrik Frystyk Nielsen
   Microsoft Corporation
   1 Microsoft Way
   Redmond, WA  98052
   USA

   EMail: henrikn@microsoft.com

   Larry Masinter
   Adobe Systems Incorporated
   345 Park Ave
   San Jose, CA  95110
   USA

   EMail: LMM@acm.org
   URI:   http://larry.masinter.net/

   Paul J. Leach
   Microsoft Corporation
   1 Microsoft Way
   Redmond, WA  98052

   EMail: paulle@microsoft.com

   Tim Berners-Lee
   World Wide Web Consortium
   MIT Computer Science and Artificial Intelligence Laboratory
   The Stata Center, Building 32
   32 Vassar Street
   Cambridge, MA  02139
   USA

   EMail: timbl@w3.org
   URI:   http://www.w3.org/People/Berners-Lee/
   Yves Lafon (editor)
   World Wide Web Consortium
   W3C / ERCIM
   2004, rte des Lucioles
   Sophia-Antipolis, AM  06902
   France

   EMail: ylafon@w3.org
   URI:   http://www.raubacapeu.net/people/yves/

   Julian F. Reschke (editor)
   greenbytes GmbH
   Hafenweg 16
   Muenster, NW  48155
   Germany

   Phone: +49 251 2807760
   Fax:   +49 251 2807761
   EMail: julian.reschke@greenbytes.de
   URI:   http://greenbytes.de/tech/webdav/