HTTPbis Working Group                                          M. Belshe
Internet-Draft                                                     Twist
Expires: July 26, 2013
Intended status: Standards Track                                 R. Peon
Expires: October 5, 2013                                     Google, Inc
                                                         M. Thomson, Ed.
                                                               Microsoft
                                                        A. Melnikov, Ed.
                                                               Isode Ltd
                                                        January 22,
                                                           April 3, 2013

                Hypertext Transfer Protocol version 2.0
                      draft-ietf-httpbis-http2-01
                      draft-ietf-httpbis-http2-02

Abstract

   This document specification describes an optimised expression of the semantics syntax of
   the HTTP protocol. Hypertext Transfer Protocol (HTTP).  The HTTP/2.0 encapsulation
   enables more efficient transfer of resources over HTTP representations by providing
   compressed headers, header fields, simultaneous requests, and also introduces
   unsolicited push of resources representations from server to client.

   This document is an alternative to, but does not obsolete
   RFC{http-p1}.  The the HTTP
   message format.  HTTP protocol semantics described in RFC{http-
   p2..p7} are unmodified. remain unchanged.

Editorial Note (To be removed by RFC Editor)

   This draft is a work-in-progress, and does not yet reflect Working
   Group consensus.

   This draft contains features from the SPDY Protocol as a starting
   point, as per the Working Group's charter.  Future drafts will add,
   remove and change text, based upon the Working Group's decisions.

   Discussion of this draft takes 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/21>

   Working Group information and related documents (including fancy diffs) can be found at
   <http://tools.ietf.org/wg/httpbis/>.
   <http://tools.ietf.org/wg/httpbis/> (Wiki) and
   <https://github.com/http2/http2-spec> (source code and issues
   tracker).

   The changes in this draft are summarized in Appendix A.1.

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 26, October 5, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.1.  Document Organization  . . . . . . . . . . . . . . . . . .  5
     1.2.  Definitions  . . . . . . . .  Conventions and Terminology  . . . . . . . . . . . . . . .  6
   2.  Starting HTTP/2.0  . . . . . . . . . . . . . . . . . . . . . .  6  7
     2.1.  HTTP/2.0 Version Identification  . . . . . . . . . . . . .  6  7
     2.2.  Starting HTTP/2.0 for "http:" URIs . . . . . . . . . . . .  7  8
     2.3.  Starting HTTP/2.0 for "https:" URIs  . . . . . . . . . . .  8
     2.4.  Starting HTTP/2.0 with Prior Knowledge . . . . . . . . . .  9
   3.  HTTP/2.0 Framing Layer . . . . . . . . . . . . . . . . . . . .  8  9
     3.1.  Session (Connections)  . . . . . . . . . . . . . . . . . .  8
     3.2.  Framing . . . . . . .  9
     3.2.  Session Header . . . . . . . . . . . . . . . . . .  8
       3.2.1.  Control frames . . . .  9
     3.3.  Framing  . . . . . . . . . . . . . . . .  9
       3.2.2.  Data frames . . . . . . . . . 10
       3.3.1.  Frame Header . . . . . . . . . . . . 10
     3.3.  Streams . . . . . . . . . 10
       3.3.2.  Frame Processing . . . . . . . . . . . . . . . . . . . 11
       3.3.1.  Stream frames
     3.4.  Streams  . . . . . . . . . . . . . . . . . . . . . . . . . 11
       3.3.2.
       3.4.1.  Stream creation Creation  . . . . . . . . . . . . . . . . . . . 11
       3.3.3. 12
       3.4.2.  Stream priority  . . . . . . . . . . . . . . . . . . . 12
       3.3.4.
       3.4.3.  Stream headers . . . . . . . . . . . . . . . . . . . . 12
       3.3.5. 13
       3.4.4.  Stream data exchange . . . . . . . . . . . . . . . . . 13
       3.3.6.
       3.4.5.  Stream half-close  . . . . . . . . . . . . . . . . . . 13
       3.3.7.
       3.4.6.  Stream close . . . . . . . . . . . . . . . . . . . . . 13
     3.4.
     3.5.  Error Handling . . . . . . . . . . . . . . . . . . . . . . 14
       3.4.1.
       3.5.1.  Session Error Handling . . . . . . . . . . . . . . . . 14
       3.4.2.
       3.5.2.  Stream Error Handling  . . . . . . . . . . . . . . . . 14
     3.5.  Stream Flow Control 15
       3.5.3.  Error Codes  . . . . . . . . . . . . . . . . . . . . . 15
       3.5.1.
     3.6.  Stream Flow Control Principles  . . . . . . . . . . . . . . . 15
       3.5.2.  Basic . . . . 16
       3.6.1.  Flow Control Algorithm Principles  . . . . . . . . . . . . . . . 16
     3.6.
       3.6.2.  Appropriate Use of Flow Control frame types  . . . . . . . . . . . 17
     3.7.  Frame Types  . . . . . . . . . 16
       3.6.1.  SYN_STREAM . . . . . . . . . . . . . . 18
       3.7.1.  DATA Frames  . . . . . . . . . 16
       3.6.2.  SYN_REPLY . . . . . . . . . . . . 18
       3.7.2.  HEADERS+PRIORITY . . . . . . . . . . . . . . . . . . . 18
       3.6.3.
       3.7.3.  RST_STREAM . . . . . . . . . . . . . . . . . . . . . . 19
       3.6.4. 18
       3.7.4.  SETTINGS . . . . . . . . . . . . . . . . . . . . . . . 20
       3.6.5.  PING . 19
       3.7.5.  PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . 22
       3.7.6.  PING . . . 23
       3.6.6.  GOAWAY . . . . . . . . . . . . . . . . . . . . . . 23
       3.7.7.  GOAWAY . . 24
       3.6.7.  HEADERS . . . . . . . . . . . . . . . . . . . . . . 23
       3.7.8.  HEADERS  . 25
       3.6.8.  WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . 26
       3.6.9.  CREDENTIAL . . 24
       3.7.9.  WINDOW_UPDATE  . . . . . . . . . . . . . . . . . . . . 28
       3.6.10. Name/Value 25
       3.7.10. Header Block . . . . . . . . . . . . . . . 30 . . . . . . 28
   4.  HTTP Layering over HTTP/2.0 Message Exchanges . . . . . . . . . . . . . . . . . 36 . . . 28
     4.1.  Connection Management  . . . . . . . . . . . . . . . . . . 36 28
       4.1.1.  Use of GOAWAY  . . . . . . . . . . . . . . . . . . . . 36 29
     4.2.  HTTP Request/Response  . . . . . . . . . . . . . . . . . . 37 29
       4.2.1.  Request  . . . . . . . . . . . . .  HTTP Header Fields and HTTP/2.0 Headers  . . . . . . . 29
       4.2.2.  Request  . . . 37
       4.2.2.  Response . . . . . . . . . . . . . . . . . . . . 29
       4.2.3.  Response . . . 39
       4.2.3.  Authentication . . . . . . . . . . . . . . . . . . . . 39 31
     4.3.  Server Push Transactions . . . . . . . . . . . . . . . . . 40 32
       4.3.1.  Server implementation  . . . . . . . . . . . . . . . . 41 33
       4.3.2.  Client implementation  . . . . . . . . . . . . . . . . 42 34
   5.  Design Rationale and Notes . . . . . . . . . . . . . . . . . . 43 35
     5.1.  Separation of Framing Layer and Application Layer  . . . . 43 35
     5.2.  Error handling - Framing Layer . . . . . . . . . . . . . . 43 35
     5.3.  One Connection Per Domain  . . . . . . . . . . . . . . . . 44 36
     5.4.  Fixed vs Variable Length Fields  . . . . . . . . . . . . . 44 36
     5.5.  Compression Context(s)  Server Push  . . . . . . . . . . . . . . . . . . . 45
     5.6.  Unidirectional streams . . . . 36
   6.  Security Considerations  . . . . . . . . . . . . . . 45
     5.7.  Data Compression . . . . . 37
     6.1.  Use of Same-origin constraints . . . . . . . . . . . . . . 37
     6.2.  Cross-Protocol Attacks . . 45
     5.8.  Server Push . . . . . . . . . . . . . . . . 37
     6.3.  Cacheability of Pushed Resources . . . . . . . 46
   6.  Security . . . . . . 37
   7.  Privacy Considerations . . . . . . . . . . . . . . . . . . . 46
     6.1.  Use of Same-origin constraints . 37
     7.1.  Long Lived Connections . . . . . . . . . . . . . 46
     6.2.  HTTP Headers and HTTP/2.0 Headers . . . . . 38
     7.2.  SETTINGS frame . . . . . . . 46
     6.3.  Cross-Protocol Attacks . . . . . . . . . . . . . . . 38
   8.  IANA Considerations  . . . 46
     6.4.  Server Push Implicit Headers . . . . . . . . . . . . . . . 46
   7.  Privacy Considerations . . . 38
     8.1.  Frame Type Registry  . . . . . . . . . . . . . . . . . 47
     7.1.  Long Lived Connections . . 38
     8.2.  Error Code Registry  . . . . . . . . . . . . . . . . . 47
     7.2.  SETTINGS frame . . 39
     8.3.  Settings Registry  . . . . . . . . . . . . . . . . . . . . 47

   8.  Requirements Notation 39
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . 47
   9.  Acknowledgements . . 40
   10. References . . . . . . . . . . . . . . . . . . . . . 47
   10. . . . . . 41
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 41
     10.2. Informative References . . . . . . . . . . . . . . 48 . . . . 42
   Appendix A.  Change Log (to be removed by RFC Editor before
                publication)  . . . . . . . . . . . . . . . . . . . . 49 42

     A.1.  Since draft-ietf-httpbis-http2-00 draft-ietf-httpbis-http2-01  . . . . . . . . . . . . 49 42
     A.2.  Since draft-ietf-httpbis-http2-00  . . . . . . . . . . . . 43
     A.3.  Since draft-mbelshe-httpbis-spdy-00  . . . . . . . . . . . 49 43

1.  Introduction

   HTTP

   The Hypertext Transfer Protocol (HTTP) is a wildly successful
   protocol.  The HTTP/1.1 message encapsulation
   [HTTP-p1] ([HTTP-p1], Section 3)
   is optimized for implementation simplicity and accessibility, not
   application performance.  As such it has several characteristics that
   have a negative overall effect on application performance.

   The HTTP/1.1 encapsulation ensures that only one request can be
   delivered at a time on a given connection.  HTTP/1.1 pipelining,
   which is not widely deployed, only partially addresses these
   concerns.  Clients that need to make multiple requests therefore use
   commonly multiple connections to a server or servers in order to
   reduce the overall latency of those requests. [[anchor1: Need to tune
   the anti-pipelining comments here.]]

   Furthermore, HTTP/1.1 headers header fields are represented in an inefficient
   fashion, which, in addition to generating more or larger network
   packets, can cause the small initial TCP window to fill more quickly
   than is ideal.  This results in excessive latency where multiple
   requests are made on a new TCP connection.

   This document defines an optimized mapping of the HTTP semantics to a
   TCP connection.  This optimization reduces the latency costs of HTTP
   by allowing parallel requests on the same connection and by using an
   efficient coding for HTTP headers. header fields.  Prioritization of requests
   lets more important requests complete faster, further improving
   application performance.

   HTTP/2.0 applications have an improved impact on network congestion
   due to the use of fewer TCP connections to achieve the same effect.
   Fewer TCP connections compete more fairly with other flows.  Long-
   lived connections are also more able to take better advantage of the
   available network capacity, rather than operating in the slow start
   phase of TCP.

   The HTTP/2.0 encapsulation also enables more efficient processing of
   messages by providing efficient message framing.  Processing of
   headers
   header fields in HTTP/2.0 messages is more efficient (for entities
   that process many messages).

1.1.  Document Organization

   The HTTP/2.0 Specification is split into three parts: starting
   HTTP/2.0 (Section 2), which covers how a HTTP/2.0 is started; a
   framing layer (Section 3), which multiplexes a TCP connection into
   independent, length-prefixed frames; and an HTTP layer (Section 4),
   which specifies the mechanism for overlaying HTTP request/response
   pairs on top of the framing layer.  While some of the framing layer
   concepts are isolated from the HTTP layer, building a generic framing
   layer has not been a goal.  The framing layer is tailored to the
   needs of the HTTP protocol and server push.

1.2.  Definitions  Conventions and Terminology

   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 RFC 2119 [RFC2119].

   All numeric values are in network byte order.  Values are unsigned
   unless otherwise indicated.  Literal values are provided in decimal
   or hexadecimal as appropriate.  Hexadecimal literals are prefixed
   with "0x" to distinguish them from decimal literals.

   The following terms are used:

   client:  The endpoint initiating the HTTP/2.0 session.

   connection:  A transport-level connection between two endpoints.

   endpoint:  Either the client or server of a connection.

   frame: A header-prefixed sequence  The smallest unit of bytes sent over communication, each containing a HTTP/2.0
      session. frame
      header.

   message:  A complete sequence of frames.

   receiver:  An endpoint that is receiving frames.

   sender:  An endpoint that is transmitting frames.

   server:  The endpoint which did not initiate the HTTP/2.0 session.

   session:  A synonym for a connection.

   session error:  An error on the HTTP/2.0 session.

   stream:  A bi-directional flow of bytes across a virtual channel
      within a HTTP/2.0 session.

   stream error:  An error on an individual HTTP/2.0 stream.

2.  Starting HTTP/2.0

   Just as HTTP/1.1 does, HTTP/2.0 uses the "http:" and "https:" URI
   schemes.  An HTTP/2.0-capable client is therefore required to
   discover whether a server (or intermediary) supports HTTP/2.0.

   Different discovery mechanisms are defined for "http:" and "https:"
   URIs.  Discovery for "http:" URIs is described in Section 2.2;
   discovery for "https:" URIs is described in Section 2.3.

2.1.  HTTP/2.0 Version Identification

   HTTP/2.0 is identified in using the string "HTTP/2.0".  This
   identification is used in the HTTP/1.1 Upgrade header, header field, in the
   TLS-NPN [TLSNPN] [[TBD]] [[anchor4: TBD]] field and other places where
   protocol identification is required.

   [[Editor's

   Negotiating "HTTP/2.0" implies the use of the transport, security,
   framing and message semantics described in this document.

   [[anchor5: Editor's Note: please remove the following text prior to
   the publication of a final version of this document.]]

   Only implementations of the final, published RFC can identify
   themselves as "HTTP/2.0".  Until such an RFC exists, implementations
   MUST NOT identify themselves using "HTTP/2.0".

   Examples and text throughout the rest of this document use "HTTP/2.0"
   as a matter of editorial convenience only.  Implementations of draft
   versions MUST NOT identify using this string.

   Implementations of draft versions of the protocol MUST add the string
   "-draft-" and the corresponding draft number to the identifier before
   the separator ('/').  For example, draft-ietf-httpbis-http2-03 is
   identified using the string "HTTP-03/2.0". "HTTP-draft-03/2.0".

   Non-compatible experiments that are based on these draft versions
   MUST include instead replace the string "draft" with a further different identifier.
   For example, an experimental implementation of packet mood-based
   encoding based on draft-ietf-httpbis-http2-07 might identify itself
   as "HTTP-07-
   emo/2.0". "HTTP-emo-07/2.0".  Note that any label MUST conform with the
   "token" syntax defined in Section 3.2.4 3.2.6 of [HTTP-p1].  Experimenters
   are encouraged to coordinate their experiments on the
   ietf-http-wg@w3.org mailing list.

2.2.  Starting HTTP/2.0 for "http:" URIs

   A client that makes a request to an "http:" URI without prior
   knowledge about support for HTTP/2.0 uses the HTTP Upgrade mechanism
   [HTTP-p2].
   (Section 6.7 of [HTTP-p1]).  The client makes an HTTP/1.1 request
   that includes an Upgrade header field identifying HTTP/2.0.

   For example:

     GET /default.htm HTTP/1.1
     Host: server.example.com
     Connection: Upgrade
     Upgrade: HTTP/2.0

   A server that does not support HTTP/2.0 can respond to the request as
   though the Upgrade header field were absent:

     HTTP/1.1 200 OK
     Content-length: 243
     Content-type: text/html
           ...

   A server that supports HTTP/2.0 can accept the upgrade with a 101
   (Switching Protocols) status code.  After the empty line that
   terminates the 101 response, the server can begin sending HTTP/2.0
   frames.  These frames MUST include a response to the request that
   initiated the Upgrade.

     HTTP/1.1 101 Switching Protocols
     Connection: Upgrade
     Upgrade: HTTP/2.0

     [ HTTP/2.0 frames session ...

   Once the server returns the 101 response, both the client and the
   server send a session header (Section 3.2).

2.3.  Starting HTTP/2.0 for "https:" URIs

   A client that makes a request to an "https:" URI without prior
   knowledge about support for HTTP/2.0 uses TLS [RFC5246] with TLS-NPN
   [TLSNPN] extension. [[anchor6: TBD, maybe ALPN]]

   Once TLS negotiation is complete, both the client and the server send
   a session header (Section 3.2).

2.4.  Starting HTTP/2.0 with Prior Knowledge

   A client can learn that a particular server supports HTTP/2.0 by
   other means.  A client MAY immediately send HTTP/2.0 frames to a
   server that is known to support HTTP/2.0.  [[Open Issue:  This is not
   definite.  We may yet choose only affects the
   resolution of "http:" URIs, servers supporting HTTP/2.0 are required
   to perform support protocol negotiation in TLS [TLSNPN].

   Prior support for every
   connection.  Reasons include intermediaries; phased upgrade of load-
   balanced HTTP/2.0 is not a strong signal that a given server farms; etc...]]  [[Open Issue: We need
   will support HTTP/2.0 for future sessions.  It is possible for server
   configurations to enumerate
   the ways change or for configurations to differ between
   instances in clustered server.  Different "transparent"
   intermediaries - intermediaries that clients can learn are not explicitly selected by
   either client or server - are another source of HTTP/2.0 support.]]

2.3.  Starting HTTP/2.0 for "https:" URIs

   [[TBD, maybe NPN]] variability.

3.  HTTP/2.0 Framing Layer

3.1.  Session (Connections)

   The HTTP/2.0 framing layer (or "session") session runs atop a reliable
   transport layer such as TCP [RFC0793]. ([RFC0793]).  The client is the
   TCP connection initiator.

   HTTP/2.0 connections are persistent connections.  For best
   performance, it is expected that clients will not close open
   connections until the user navigates away from all web pages
   referencing a connection, or until the server closes the connection.
   Servers are encouraged to leave connections open for as long as
   possible, but can terminate idle connections if necessary.  When
   either endpoint closes the transport-level connection, it MUST first
   send a GOAWAY (Section 3.6.6) 3.7.7) frame so that the endpoints can
   reliably determine if requests finished before the close.

3.2.  Framing

   Once the  Session Header

   After opening a TCP connection is established, clients and servers exchange
   framed messages.  There are two types of frames: control frames
   (Section 3.2.1) and data frames (Section 3.2.2).  Frames always have performing either an HTTP/1.1
   Upgrade or TLS handshake, the client sends the client session header.
   The server replies with a common header which is 8 bytes in length. server session header.

   The first bit is a control bit indicating whether a frame is session header provides a
   control final confirmation that both peers
   agree to use the HTTP/2.0 protocol.  The SETTINGS frame ensures that
   client or data frame.  Control frames carry a version number, server configuration is known as quickly as possible.

   The client session header is the 25 byte sequence
   0x464f4f202a20485454502f322e300d0a0d0a4241520d0a0d0a (the string "FOO
   * HTTP/2.0\r\n\r\nBAR\r\n\r\n") followed by a SETTINGS frame type, flags, and a length.  Data frames contain the stream
   ID, flags, and the length for
   (Section 3.7.4).  The client sends the payload carried client session header
   immediately after receiving an HTTP/1.1 Upgrade, or after receiving a
   TLS Finished message from the common
   header. server.

      The simple client session header is designed to make reading and writing selected so that a large proportion
      of
   frames easy.

   All integer values, including length, version, HTTP/1.1 or HTTP/1.0 servers and type, are in
   network byte order.  HTTP/2.0 does intermediaries do not enforce alignment of types in
   dynamically sized attempt
      to process further frames.

3.2.1.  Control frames

   +----------------------------------+
   |C| Version(15bits) | Type(16bits) |
   +----------------------------------+
   | Flags (8)  |  Length (24 bits)   |
   +----------------------------------+
   |               Data               |
   +----------------------------------+

   Control bit:  This doesn't address the concerns
      raised in [TALKING].

   The 'C' bit is a single bit indicating if this server session header is a
   control message.  For control frames this value is always 1.

   Version: The version number of the HTTP/2.0 protocol.  This document
   describes HTTP/2.0 version 3.

   Type: SETTINGS frame (Section 3.7.4).  The type of control frame.  See Control Frames for
   server sends the complete
   list of control frames.

   Flags: Flags related to this frame.  Flags for control frames server session header immediately after receiving
   and
   data frames are different.

   Length: An unsigned 24-bit value representing validating the number of bytes client session header.

   The client sends requests immediately after sending the length field.

   Data: data associated with this control frame.  The format session
   header, without waiting to receive a server session header.  This
   ensures that confirming session headers does not add latency.

   Both client and length
   of this data is controlled by server MUST close the control frame type.

   Control connection if it does not begin
   with a valid session header.  A GOAWAY frame processing requirements:

      Note that full length control frames (16MB) can be large for
      implementations running on resource-limited hardware.  In such
      cases, implementations (Section 3.7.7) MAY limit the maximum length frame
      supported.  However, all implementations MUST be able to receive
      control frames
   omitted if it is clear that the peer is not using HTTP/2.0.

3.3.  Framing

   Once the connection is established, clients and servers exchange
   HTTP/2.0 frames.  Frames are the basic unit of at least 8192 octets in length.

3.2.2.  Data communication.

3.3.1.  Frame Header

   HTTP/2.0 frames

   +----------------------------------+
   |C|       Stream-ID (31bits) share a common header format.  Frames have an 8 byte
   header with between 0 and 65535 bytes of data.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |
   +----------------------------------+         Length (16)           |   Type (8)    |   Flags (8)   |  Length (24 bits)
   +-+-------------+---------------+-------------------------------+
   |R|                 Stream Identifier (31)                      |
   +----------------------------------+
   +-+-------------------------------------------------------------+
   |                     Frame Data               |
   +----------------------------------+

   Control bit: For data frames this value is always 0.

   Stream-ID: A 31-bit value identifying the stream.

   Flags: Flags related to this frame.  Valid flags are:

      0x01 = FLAG_FIN - signifies that this frame represents the last
      frame to be transmitted on this stream.  See Stream Close
      (Section 3.3.7) below.

      0x02 = FLAG_COMPRESS - indicates that (0...)                       ...
   +---------------------------------------------------------------+

                               Frame Header

   The fields of the data in this frame has
      been compressed. header are defined as:

   Length: An unsigned 24-bit value representing the number  The 16-bit length of bytes
   after the length field. frame payload in bytes.  The total size length
      of a data the frame header is 8 bytes +
   length.  It is valid to have a zero-length data not included in this sum.

   Type:  The 8-bit type of the frame.

   Data:  The variable-length data payload; frame type determines how
      the length was defined in remainder of the
   length field.

   Data frame processing requirements:

      If an endpoint receives a data frame for a stream-id which is not
      open header and the endpoint has not sent a GOAWAY (Section 3.6.6) frame,
      it payload are interpreted.
      Implementations MUST send issue a stream error (Section 3.4.2) with the error
      code INVALID_STREAM ignore frames that use types that they do not
      support.

   Flags:  An 8-bit field reserved for the stream-id.

      If the endpoint which created the stream receives a data flags.  Bits that have undefined
      semantics are reserved.  The following flags are defined for all
      frame
      before receiving a SYN_REPLY on types:

      FINAL (0x1):  Bit 1 (the least significant bit) indicates that stream, it
         this is a protocol
      error, and the recipient MUST issue last frame in a stream.  This places the stream error
         into a half-closed state (Section 3.4.2)
      with 3.4.5).  No further frames
         follow in the status code PROTOCOL_ERROR for direction of the stream-id.

      Implementors note: If an endpoint receives multiple data frames carrying frame.

      Frame types can define semantics for invalid stream-ids, it MAY close the session.

      All HTTP/2.0 endpoints MUST accept compressed data frames.
      Compression frame-specific flags.

   R: A reserved 1-bit field.  The semantics of data frames is always done using zlib compression.
      Each stream initializes and uses its own compression context
      dedicated to use within that stream.  Endpoints this bit are encouraged to
      use application level compression rather than HTTP/2.0 stream
      level compression.

      Each HTTP/2.0 not
      defined.

   Stream Identifier:  A 31-bit stream sending compressed frames creates its own
      zlib context identifier (see Section 3.4.1).
      A value 0 is reserved for frames that stream, and these compression contexts MUST
      be distinct from are directed at the compression contexts used with SYN_STREAM/
      SYN_REPLY/HEADER compression.  (Thus, if both endpoints of session
      as a
      stream are compressing data on whole instead of a single stream.

   Frame Data:  Frames contain between 0 and 65535 bytes of data.

   Reserved bits in the stream, there will frame header MUST be two zlib
      contexts, one for set to zero when sending
   and one MUST be ignored when receiving frames, unless the semantics of
   the bit are known.

3.3.2.  Frame Processing

   A frame of the maximum size might be too large for receiving).

3.3. implementations
   with limited resources to process.  Implementations MAY choose to
   support frames smaller than the maximum possible size.  However,
   implementations MUST be able to receive frames containing at least
   8192 octets of payload.

   An implementation MUST immediately close a stream if it is unable to
   process a frame related to that stream due to it exceeding a size
   limit.  The implementation MUST send a RST_STREAM frame
   (Section 3.7.3) containing FRAME_TOO_LARGE error code if the frame
   size limit is exceeded.

   [[anchor9: <https://github.com/http2/http2-spec/issues/28>: Need a
   way to signal the maximum frame size; no way to RST_STREAM on non-
   stream-related frames.]]

3.4.  Streams

   Streams are independent sequences of bi-directional data divided into
   frames with several properties:

   o  Streams may can be created by either the client or server.

   o  Streams optionally carry a set of name/value name-value header pairs.

   o  Streams can concurrently send data interleaved with other streams.

   o  Streams may can be established and used unilaterally.

   o  Streams can be cancelled.

3.3.1.

3.4.1.  Stream frames

   HTTP/2.0 defines 3 control frames to manage the lifecycle of a
   stream:

      SYN_STREAM - Open a new stream

      SYN_REPLY - Remote acknowledgement Creation

   Use of a new, open stream

      RST_STREAM - Close a stream

3.3.2.  Stream creation streams does not require negotiation.  A stream is created not
   created, streams are used by sending a control frame with the type set to
   SYN_STREAM (Section 3.6.1).  If the server is initiating the stream,
   the Stream-ID must be even.  If on the stream.

   Streams are identified by a 31-bit numeric identifier.  Streams
   initiated by a client is initiating the stream, use odd numbered stream identifiers.  Streams
   initiated by the Stream-ID must server use odd numbered stream identifiers.  A
   stream identifier of zero MUST NOT be odd. 0 is not used to create a valid Stream-ID.  Stream-IDs
   from each side of the connection must increase monotonically as new
   streams are created.  E.g.  Stream 2 may be created after stream 3,
   but stream 7 must not be created after stream.

   The stream 9.  Stream IDs do not
   wrap: when a client or server cannot create identifier of a new stream id without
   exceeding a 31 bit value, it MUST NOT create be greater than all other
   streams from that endpoint, unless the stream identifier was
   previously reserved (such as the promised stream identifier in a new stream.

   The stream-id MUST increase with each new stream.  If an
   PUSH_PROMISE (Section 3.7.5) frame).  An endpoint that receives a SYN_STREAM with a an
   unexpected stream id which is less than any
   previously received SYN_STREAM, it identifier MUST issue treat this as a session error
   (Section 3.4.1) with the status 3.5.1) of type PROTOCOL_ERROR.

   It

   A long-lived session can result in available stream identifiers being
   exhausted.  An endpoint that is a protocol error unable to send two SYN_STREAMs with the same
   stream-id.  If create a recipient receives new stream
   identifier can establish a second SYN_STREAM new session for any new streams.

   An endpoint cannot prevent the same creation of a new stream, but it MUST issue a stream error (Section 3.4.2) with can
   request the status
   code PROTOCOL_ERROR. early termination of an unwanted stream.  Upon receipt of
   a SYN_STREAM, frame, the recipient can reject terminate the corresponding stream by
   sending a stream error (Section 3.4.2) with the error code 3.5.2) of type REFUSED_STREAM.  Note, however, that  This
   cannot prevent the creating initiating endpoint may have
   already sent additional from sending frames for that
   stream which cannot be
   immediately stopped.

   Once the stream is created, the creator may immediately send HEADERS
   or DATA frames for that stream, without needing to wait for the
   recipient prior to acknowledge.

3.3.2.1.  Unidirectional streams

   When an endpoint creates receiving this request.

3.4.2.  Stream priority

   The creator of a stream with the FLAG_UNIDIRECTIONAL flag
   set, it creates a unidirectional stream which the creating endpoint
   can use to send frames, but the receiving endpoint cannot.  The
   receiving endpoint is implicitly already in the half-closed
   (Section 3.3.6) state.

3.3.2.2.  Bidirectional streams

   SYN_STREAM frames which do not use the FLAG_UNIDIRECTIONAL flag are
   bidirectional streams.  Both endpoints can send data on a bi-
   directional stream.

3.3.3.  Stream priority

   The creator of a stream assigns assigns a priority for that stream.  Priority
   is represented as an integer from 0 to 7. a 31 bit integer. 0 represents the highest priority
   and 7 2^31-1 represents the lowest priority.

   The sender and recipient SHOULD use best-effort to process streams in
   the order of highest priority to lowest priority.

3.3.4. [[anchor11: ED:
   toothless, useless "SHOULD": reword]]

3.4.3.  Stream headers

   Streams carry optional sets of name/value pair headers header fields which carry metadata
   about the stream.  After the stream has been created, and as long as
   the sender is not closed (Section 3.3.7) 3.4.6) or half-closed
   (Section 3.3.6), 3.4.5), each side may send HEADERS frame(s) containing the
   header data.  Header data can be sent in multiple HEADERS frames, and
   HEADERS frames may be interleaved with data frames.

3.3.5.

3.4.4.  Stream data exchange

   Once a stream is created, it can be used to send arbitrary amounts of
   data.  Generally this means that a series of data frames will be sent
   on the stream until a frame containing the FLAG_FIN FINAL flag (Section 3.3.1)
   is set.  The
   FLAG_FIN can be set on a SYN_STREAM (Section 3.6.1), SYN_REPLY
   (Section 3.6.2), HEADERS (Section 3.6.7) or a DATA (Section 3.2.2)
   frame.  Once the FLAG_FIN FINAL flag has been sent, set on any frame, the stream is
   considered to be half-closed.

3.3.6.

3.4.5.  Stream half-close

   When one side of the stream sends a frame with the FLAG_FIN FINAL flag set,
   the stream is half-closed from that endpoint.  The sender of the
   FLAG_FIN
   FINAL flag MUST NOT send further frames on that stream.  When both
   sides have half-closed, the stream is closed.

   If an

   An endpoint receives MUST treat the receipt of a data frame after the stream is half-closed
   from the sender (e.g. the endpoint has already received on a prior frame
   for the half-closed
   stream with the FIN flag set), it MUST send as a RST_STREAM stream error (Section 3.5.2) of type STREAM_CLOSED.

   Streams that have never received packets can be considered to be
   half-closed in the sender with direction that is silent.  This allows either peer
   to create a unidirectional stream, which does not require an explicit
   close from the status STREAM_ALREADY_CLOSED.

3.3.7. peer that does not transmit frames.

3.4.6.  Stream close

   There are 3 ways that streams

   Streams can be terminated: terminated in the following ways:

   Normal termination:  Normal stream termination occurs when both
      sender and recipient have half-closed the stream by sending a
      FLAG_FIN.
      frame containing a FINAL flag (Section 3.3.1).

   Half-close on unidirectional stream:  A stream that only has frames
      sent in one direction can be tentatively considered to be closed
      once a frame containing a FINAL flag is sent.  The active sender
      on the stream MUST be prepared to receive frames after closing the
      stream.

   Abrupt termination:  Either the client or server peer can send a RST_STREAM control
      frame at any time.  A time to terminate an active stream.  RST_STREAM
      contains an error code to indicate the reason for failure.  When a termination.  A
      RST_STREAM
      is sent from the stream originator, it indicates a failure to
      complete the stream and that the sender will transmit no further data will be sent on the
      stream.  When a RST_STREAM is sent from the stream recipient, the
      sender, upon receipt, should stop sending any data
      on the stream.
      The stream recipient should be aware and that there the receiver is requested to cease
      transmission.

      The sender of a race between
      data RST_STREAM frame MUST allow for frames that have
      already in transit from the sender and been sent by the time peer prior to the RST_STREAM is received. being
      processed.  If in-transit frames alter session state, these frames
      cannot be safely discarded.  See Stream Error Handling
      (Section 3.4.2) 3.5.2) for more details.

   TCP connection teardown:  If the TCP connection is torn down while
      un-closed streams exist, then the endpoint must assume that the
      stream was abnormally interrupted and may be incomplete.

   If an endpoint receives a data frame after the stream is closed, it
   must
   MAY send a RST_STREAM to the sender with the status PROTOCOL_ERROR.

3.4.

3.5.  Error Handling

   The

   HTTP/2.0 framing layer has only permits two types classes of errors, and they are
   always handled consistently.  Any reference in this specification to
   "issue error:

   o  An error condition that renders the entire session unusable is a
      session error" refers to Section 3.4.1.  Any reference to
   "issue error.

   o  An error in an individual stream is a stream error" refers to Section 3.4.2.

3.4.1. error.

3.5.1.  Session Error Handling

   A session error is any error which prevents further processing of the
   framing layer or which corrupts the any session compression state.  When

   An endpoint that encounters a session error occurs, the endpoint encountering the error MUST first send a GOAWAY
   (Section 3.6.6) 3.7.7) frame with the stream id identifier of most
   recently received the last stream
   that it successfully received from the remote endpoint, and the its peer.  The GOAWAY frame
   includes an error code
   for that indicates why the session is terminating.
   After sending the GOAWAY frame, the endpoint MUST close the TCP
   connection.

   Note that the session compression state is dependent upon both
   endpoints always processing all compressed data.  If an endpoint
   partially processes a frame containing compressed data without
   updating compression state properly, future control frames which use
   compression will be always be errored.  Implementations SHOULD always
   try to process compressed data so that errors which could be handled
   as stream errors do not become session errors.

   Note that because this GOAWAY is sent during a session error case, it

   It is possible that the GOAWAY will not be reliably received by the
   receiving endpoint.  It is  In the event of a session error, GOAWAY only
   provides a best-effort attempt to communicate with the remote peer about why
   the session is going down.

3.4.2.  Stream Error Handling

   A stream error is an error related to

   An endpoint can end a session at any time.  In particular, an
   endpoint MAY choose to treat a stream error as a session error if the
   error is recurrent.  Endpoints SHOULD send a GOAWAY frame when ending
   a session, as long as circumstances permit it.

3.5.2.  Stream Error Handling

   A stream error is an error related to a specific stream-id which stream identifier
   that does not affect processing of other streams at the framing
   layer.  Upon

   An endpoint that detects a stream error, the endpoint MUST send error sends a RST_STREAM
   (Section 3.6.3) 3.7.3) frame which that contains the stream id identifier of the
   stream where the error
   occurred and the occurred.  The RST_STREAM frame includes an
   error status which caused code that indicates the type of error.  After sending

   A RST_STREAM is the RST_STREAM, last frame that an endpoint can send on a stream.
   The peer that sends the stream is closed RST_STREAM frame MUST be prepared to the sending endpoint.  After receive
   any frames that were sent or enqueued for sending by the RST_STREAM, if the sender receives any remote peer.
   These frames other can be ignored, except where they modify session state
   (such as the header compression state).

   An endpoint SHOULD NOT send more than
   a one RST_STREAM frame for that stream id, it will result in sending any
   stream.  An endpoint MAY send additional RST_STREAM frames. frames if it
   receives frames on a closed stream after more than a round trip time.
   This behaviour is permitted to deal with misbehaving implementations
   where treating this as a session error is inappropriate.

   An endpoint MUST NOT send a RST_STREAM in response to an RST_STREAM, as doing so would lead to RST_STREAM
   loops.  Sending a
   frame.  This could trigger infinite loops of RST_STREAM does not cause the HTTP/2.0 session to
   be closed.

   If an endpoint has multiple frames.

3.5.3.  Error Codes

   Error codes are 32-bit fields that are used in RST_STREAM and GOAWAY
   frames to send in succession
   for convey the same stream-id and reasons for the same error code, it MAY coalesce them
   into stream or session error.

   Error codes share a single RST_STREAM frame.  (This can happen if a stream is
   closed, but the remote sends multiple data frames.  There is common code space.  Some error codes only apply
   to specific conditions and have no
   reason defined semantics in certain frame
   types.

   The following error codes are defined:

   NO_ERROR (0):  The associated condition is not as a result of an
      error.  For example, a GOAWAY might include this code to send indicate
      graceful shutdown of a RST_STREAM session.

   PROTOCOL_ERROR (1):  An unspecific protocol error was detected.  This
      error is for each use when a more specific error code is not available.

   INTERNAL_ERROR (2):  The implementation encountered an unexpected
      internal error.

   FLOW_CONTROL_ERROR (3):  The endpoint detected that its peer violated
      the flow control protocol.

   INVALID_STREAM (4):  A frame in succession).

3.5. was received for an inactive stream.

   STREAM_CLOSED (5):  The endpoint received a frame after a stream was
      half-closed.

   FRAME_TOO_LARGE (6):  The endpoint received a frame that was larger
      than the maximum size that it supports.

   REFUSED_STREAM (7):  Indicates that the stream was refused before any
      processing has been done on the stream.

   CANCEL (8):  Used by the creator of a stream to indicate that the
      stream is no longer needed.

3.6.  Stream Flow Control

   Multiplexing streams introduces contention for access to the shared
   TCP connection.  Stream contention can result in streams being
   blocked by other streams.  A flow control scheme ensures that streams
   do not destructively interfere with other streams on the same TCP
   connection.

3.5.1.

3.6.1.  Flow Control Principles

   Experience with TCP congestion control has shown that algorithms can
   evolve over time to become more sophisticated without requiring
   protocol changes.  TCP congestion control and its evolution is
   clearly different from HTTP/2.0 flow control, though the evolution of
   TCP congestion control algorithms shows that a similar approach could
   be feasible for HTTP/2.0 flow control.

   HTTP/2.0 stream flow control aims to allow for future improvements to
   flow control algorithms without requiring protocol changes.  The
   following principles guide the  Flow
   control in HTTP/2.0 design: has the following characteristics:

   1.  Flow control is hop-by-hop, not end-to-end.

   2.  Flow control is based on window update messages.  Receivers
       advertise how many octets they are prepared to receive on a
       stream.  This is a credit-based scheme.

   3.  Flow control is directional with overall control provided by the
       receiver.  A receiver MAY choose to set any window size that it
       desires for each stream [[TBD: ... and for the overall
       connection]]. entire connection.  A sender
       MUST respect flow control limits imposed by a receiver.  Clients,
       servers and intermediaries all independently advertise their flow
       control preferences as a receiver and abide by the flow control
       limits set by their peer when sending.

   4.  The initial value for the flow control window is 65536 bytes for
       both new streams and the overall connection.

   5.  The frame type determines whether flow control applies to a
       frame.  Of the frames specified in this document, only data
       frames are subject to flow control; all other frame types do not
       consume space in the advertised flow control window.  This
       ensures that important control frames are not blocked by flow
       control.

   6.  Flow control can be disabled by a receiver.  A receiver can
       choose to either disable flow control, control for a stream or to declare connection
       by declaring an infinite flow control limit.  [[TBD: determine whether just one mechanism
       is sufficient, and then which alternative]]

   5.

   7.  HTTP/2.0 standardizes only the format of the window update
       message (Section 3.6.8). 3.7.9).  This does not stipulate how a receiver
       decides when to send this message or the value that it sends.
       Nor does it specify how a sender chooses to send packets.
       Implementations are able to select any algorithm that suits their
       needs.  An example flow control algorithm is described in
       Section 3.5.2.

   Implementations are also responsible for managing how requests and
   responses are sent based on priority; choosing how to avoid head of
   line blocking for requests; and managing the creation of new streams.
   Algorithm choices for these could interact with any flow control
   algorithm.

3.5.2.  Basic

3.6.2.  Appropriate Use of Flow Control Algorithm

   This section describes

   Flow control is defined to protect deployments (client, server or
   intermediary) that are operating under constraints.  For example, a basic
   proxy must share memory between many connections.  Flow control
   addresses cases where the receiver is unable process data on one
   stream, yet wants to be continue to process other streams.

   Deployments that do not rely on this capability SHOULD disable flow
   control algorithm.  This
   algorithm for data that is provided as an being received.  Note that flow control
   cannot be disabled for sending.  Sending data is always subject to
   the flow control window advertised by the receiver.

   Deployments with constrained resources (for example, implementations memory), MAY
   employ flow control to limit the amount of memory a peer can consume.
   This can lead to suboptimal use any
   algorithm that complies with of available network resources if
   flow control requirements.

   [[Algorithm TBD]]

3.6.  Control is enabled without knowledge of the bandwidth-delay
   product (see [RFC1323]).

   Implementation of flow control in full awareness of the current
   bandwidth-delay product is difficult, but it can ensure that
   constrained resources are protected without any reduction in
   connection utilization.

3.7.  Frame Types

3.7.1.  DATA Frames

   DATA frames (type=0) are used to convey HTTP message bodies.  The
   payload of a data frame types

3.6.1.  SYN_STREAM contains either a request or response body.

   No frame-specific flags are defined for DATA frames.

3.7.2.  HEADERS+PRIORITY

   The SYN_STREAM control HEADERS+PRIORITY frame (type=1) allows the sender to asynchronously
   create a set header
   fields and stream between priority at the endpoints.  See Stream Creation
   (Section 3.3.2)
   +------------------------------------+
   |1|    version    |         1        |
   +------------------------------------+
   |  Flags (8)  |  Length (24 bits)    |
   +------------------------------------+
   |X|           Stream-ID (31bits)     |
   +------------------------------------+
   |X| Associated-To-Stream-ID (31bits) |
   +------------------------------------+
   | Pri|Unused | Slot |                |
   +-------------------+                |
   | Number of Name/Value pairs (int32) |   <+
   +------------------------------------+    |
   |     Length of name (int32)         |    | same time.  This section is the
   +------------------------------------+    | "Name/Value Header
   |           Name (string)            |    | Block", and MUST be used for
   each stream that is
   +------------------------------------+    | compressed.
   |     Length of value  (int32)       |    |
   +------------------------------------+    |
   |          Value   (string)          |    |
   +------------------------------------+    | created.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |X|                   Priority (31)                             |           (repeats)
   +-+-------------------------------------------------------------+
   |   <+

   Flags: Flags related to this frame.  Valid flags are:

      0x01 = FLAG_FIN - marks this frame as the last                    Header Block (*)                         ...
   +---------------------------------------------------------------+

                      HEADERS+PRIORITY Frame Payload

   The HEADERS+PRIORITY frame is identical to be
      transmitted on this stream and puts the sender in the half-closed HEADERS frame
   (Section 3.3.6) state.

      0x02 = FLAG_UNIDIRECTIONAL - a stream created 3.7.8), with this flag puts
      the recipient in a 32-bit field containing priority included
   before the half-closed (Section 3.3.6) state.

   Length: header block.

   The length is the number most significant bit of bytes which follow the length
   field in the frame.  For SYN_STREAM frames, this priority is 10 bytes plus the
   length of the compressed Name/Value block.

   Stream-ID: reserved.  The 31-bit identifier
   priority indicates the priority for this stream.  This stream-id
   will be used in frames which are part of this stream.

   Associated-To-Stream-ID: the stream, as assigned by the
   sender, see Section 3.4.2.

3.7.3.  RST_STREAM

   The 31-bit identifier RST_STREAM frame (type=3) allows for abnormal termination of a stream which
   this stream is associated to.  If this stream is independent
   stream.  When sent by the creator of all
   other streams, a stream, it should be 0.

   Priority: A 3-bit priority (Section 3.3.3) field.

   Unused: 5 bits of unused space, reserved for future use.

   Slot: An 8 bit unsigned integer specifying indicates the index in
   creator wishes to cancel the stream.  When sent by the server's
   CREDENTIAL vector recipient of a
   stream, it indicates an error or that the client certificate recipient did not want to be used for this
   request. see CREDENTIAL frame (Section 3.6.9).  The value 0 means no
   client certificate should be associated with this stream.

   Name/Value Header Block: A set of name/value pairs carried as part of
   accept the SYN_STREAM. see Name/Value Header Block (Section 3.6.10).

   If an endpoint receives a SYN_STREAM which is larger than stream, so the
   implementation supports, it MAY send a stream should be closed.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Error Code (32)                       |
   +---------------------------------------------------------------+

                         RST_STREAM with Frame Payload

   The RST_STREAM frame does not define any valid flags.

   The RST_STREAM frame contains a single 32-bit error code
   FRAME_TOO_LARGE.  All implementations MUST support the minimum size
   limits defined in the Control Frames section
   (Section 3.2.1).

3.6.2.  SYN_REPLY

   SYN_REPLY 3.5.3).  The error code indicates why the acceptance of a stream creation by is being
   terminated.

   After receiving a RST_STREAM on a stream, the recipient of must not send
   additional frames for that stream, and the stream moves into the
   closed state.

3.7.4.  SETTINGS

   A SETTINGS frame (type=4) contains a SYN_STREAM frame.

   +------------------------------------+
   |1|    version    |         2        |
   +------------------------------------+
   |  Flags (8)  |  Length (24 bits)    |
   +------------------------------------+
   |X|           Stream-ID (31bits)     |
   +------------------------------------+
   | Number set of Name/Value id/value pairs (int32) |   <+
   +------------------------------------+    |
   |     Length for
   communicating configuration data about how the two endpoints may
   communicate.  SETTINGS frames MUST be sent at the start of name (int32)         |    | This section a session,
   but they can be sent at any other time by either endpoint.  Settings
   are declarative, not negotiated, each peer indicates their own
   configuration.

   [[anchor17: Note that persistence of settings is under discussion in
   the
   +------------------------------------+    | "Name/Value Header
   |           Name (string)            |    | Block", WG and is
   +------------------------------------+    | compressed.
   |     Length might be removed in a future version of value  (int32)       |    |
   +------------------------------------+    |
   |          Value   (string)          |    |
   +------------------------------------+    |
   |           (repeats)                |   <+

   Flags: Flags related to this frame.  Valid flags are:

      0x01 = FLAG_FIN - marks this frame as document.]]

   When the last frame to be
      transmitted on this stream and puts server is the sender, the sender in can request that
   configuration data be persisted by the half-closed
      (Section 3.3.6) state.

   Length: The length is client across HTTP/2.0
   sessions and returned to the number server in future communications.

   Clients persist settings on a per origin basis (see [RFC6454] for a
   definition of bytes which follow web origins).  That is, when a client connects to a
   server, and the length
   field in server persists settings within the frame.  For SYN_REPLY frames, this is 4 bytes plus client, the
   length of
   client SHOULD return the compressed Name/Value block.

   Stream-ID: The 31-bit identifier for this stream.

   If an endpoint receives multiple SYN_REPLY frames for persisted settings on future connections to
   the same active
   stream ID, it origin AND IP address and TCP port.  Clients MUST issue a stream error (Section 3.4.2) with NOT
   request servers to use the
   error code STREAM_IN_USE.

   Name/Value Header Block: A set of name/value pairs carried as part persistence features of the SYN_STREAM. see Name/Value Header Block (Section 3.6.10).

   If an endpoint receives a SYN_REPLY which is larger than the
   implementation supports, it MAY send a RST_STREAM with error code
   FRAME_TOO_LARGE.  All implementations SETTINGS
   frames, and servers MUST support the minimum size
   limits defined in the Control Frames section (Section 3.2.1).

3.6.3.  RST_STREAM

   The RST_STREAM frame allows for abnormal termination of a stream.
   When ignore persistence related flags sent by the creator of a stream, it indicates
   client.

   Valid frame-specific flags for the creator wishes SETTINGS frame are:

   CLEAR_PERSISTED (0x2):  Bit 2 being set indicates a request to cancel the stream.  When sent by clear
      any previously persisted settings before processing the recipient of a stream, it
   indicates an error or that the recipient did not want settings.
      Clients MUST NOT set this flag.

   SETTINGS frames always apply to accept the
   stream, so the a session, never a single stream.
   The stream should identifier for a settings frame MUST be closed.

   +----------------------------------+
   |1|   version    | zero.

    0                   1                   2                   3       |
   +----------------------------------+
   | Flags (8)  |
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |SettingFlags(8)|             Setting Identifier (24)           |
   +----------------------------------+
   |X|          Stream-ID (31bits)    |
   +----------------------------------+
   +---------------+-----------------------------------------------+
   |          Status code                        Value (32)                             |
   +----------------------------------+
   +---------------------------------------------------------------+

                          SETTINGS ID/Value Pair

   The payload of a SETTINGS frame contains zero or more settings.  Each
   setting is comprised of the following

   Settings Flags: Flags related to this frame.  RST_STREAM does not define any
   flags.  This value must be 0.

   Length:  An unsigned 24-bit value representing 8-bit flags field containing per-setting
      instructions.  The following flags are valid:

      PERSIST_VALUE (0x1):  Bit 1 (the least significant bit) being set
         indicates a request from the number of bytes
   after server to the length field.  For RST_STREAM control frames, client to persist
         this value is
   always 8.

   Stream-ID: The 31-bit identifier for setting.  A client MUST NOT set this stream.

   Status code: (32 bits) An indicator for why the stream is flag.

      PERSISTED (0x2):  Bit 2 being
   terminated.The following status codes are defined:

      1 - PROTOCOL_ERROR.  This set indicates that this setting is a generic error, and should only be
      used if a more specific error is not available.

      2 - INVALID_STREAM.
         persisted setting being returned by the client to the server.
         This also indicates that this setting is returned when not a frame is received for client setting,
         but a stream which is not active.

      3 - REFUSED_STREAM.  Indicates that value previously set by the stream was refused before
      any processing has been done on the stream.

      4 - UNSUPPORTED_VERSION.  Indicates server.  A server MUST NOT
         set this flag.

      All other settings flags are reserved.

   Setting Identifier:  A 24-bit field that identifies the recipient of a stream
      does not support setting.

   Value:  A 32-bit value for the HTTP/2.0 version requested.

      5 - CANCEL.  Used by setting.

   The following settings are defined:

   SETTINGS_UPLOAD_BANDWIDTH (1):  allows the creator of a stream sender to indicate that the
      stream is no longer needed.

      6 - INTERNAL_ERROR. send its
      expected upload bandwidth on this channel.  This number is a generic error which can an
      estimate.  The value should be used
      when the implementation has internally failed, not due to anything
      in integral number of kilobytes
      per second that the protocol.

      7 - FLOW_CONTROL_ERROR. sender predicts as an expected maximum upload
      channel capacity.

   SETTINGS_DOWNLOAD_BANDWIDTH (2):  allows the sender to send its
      expected download bandwidth on this channel.  This number is an
      estimate.  The endpoint detected value should be the integral number of kilobytes
      per second that its peer
      violated the flow control protocol.

      8 - STREAM_IN_USE.  The endpoint received a SYN_REPLY for a stream
      already open.

      9 - STREAM_ALREADY_CLOSED. sender predicts as an expected maximum
      download channel capacity.

   SETTINGS_ROUND_TRIP_TIME (3):  allows the sender to send its expected
      round-trip-time on this channel.  The endpoint received round trip time is defined
      as the minimum amount of time to send a data or
      SYN_REPLY control frame for from this
      client to the remote and receive a stream which is half closed.

      10 - INVALID_CREDENTIALS. response.  The server received a request for a
      resource whose origin does not have valid credentials value is
      represented in milliseconds.

   SETTINGS_MAX_CONCURRENT_STREAMS (4):  allows the
      client certificate vector.

      11 - FRAME_TOO_LARGE.  The sender to inform the
      remote endpoint received a frame which this
      implementation could not support.  If FRAME_TOO_LARGE is sent for
      a SYN_STREAM, HEADERS, or SYN_REPLY frame without fully processing the compressed portion maximum number of those frames, then the compression state concurrent streams which it
      will be out-of-sync with the other endpoint.  In this case,
      senders of FRAME_TOO_LARGE MUST close the session.

      Note: 0 allow.  This limit is not a valid status code for a RST_STREAM.

   After receiving a RST_STREAM on a stream, the recipient must not send
   additional frames for that stream, and the stream moves into directional: it applies to the
   closed state.

3.6.4.  SETTINGS

   A SETTINGS frame contains a set number
      of id/value pairs for communicating
   configuration data about how streams that the two endpoints may communicate.
   SETTINGS frames can be sent at any time by either endpoint, are
   optionally sent, and are fully asynchronous.  When sender permits the server receiver to create.  By
      default there is the
   sender, the sender can request no limit.  For implementers it is recommended
      that configuration data this value be persisted
   by no smaller than 100, so as to not unnecessarily
      limit parallelism.

   SETTINGS_CURRENT_CWND (5):  allows the client across HTTP/2.0 sessions and returned sender to inform the server in
   future communications.

   Persistence remote
      endpoint of SETTINGS ID/Value pairs is done on a per origin/IP
   pair (the "origin" is the set of scheme, host, and port from current TCP CWND value.

   SETTINGS_DOWNLOAD_RETRANS_RATE (6):  allows the URI.
   See [RFC6454]).  That is, when a client connects sender to a server, and the
   server persists settings within the client, inform the client SHOULD return
      remote endpoint the persisted settings on future connections to retransmission rate (bytes retransmitted /
      total bytes transmitted).

   SETTINGS_INITIAL_WINDOW_SIZE (7):  allows the same origin AND
   IP address and TCP port.  Clients MUST NOT request servers sender to use inform the
   persistence features of
      remote endpoint the SETTINGS frames, and servers MUST ignore
   persistence related flags sent by a client.

   +----------------------------------+
   |1|   version    |         4       |
   +----------------------------------+
   | Flags (8)  |  Length (24 bits)   |
   +----------------------------------+
   |         Number of entries        |
   +----------------------------------+
   |          ID/Value Pairs          |
   |             ...                  |

   Control bit: initial window size (in bytes) for new
      streams.

   SETTINGS_FLOW_CONTROL_OPTIONS (10):  This setting allows an endpoint
      to indicate that streams directed to them will not be subject to
      flow control.  The control least significant bit (0x1) is always 1 for this message.

   Version: The HTTP/2.0 version number.

   Type: set to indicate
      that new streams are not flow controlled.  Bit 2 (0x2) is set to
      indicate that the session is not flow controlled.  All other bits
      are reserved.

      This setting applies to all streams, including existing streams.

      These bits cannot be cleared once set, see Section 3.7.9.4.

   The message is intentionally extensible for future information which
   may improve client-server communications.  The sender does not need
   to send every type of ID/value.  It must only send those for which it
   has accurate values to convey.  When multiple ID/value pairs are
   sent, they should be sent in order of lowest id to highest id.  A
   single SETTINGS frame MUST not contain multiple values for the same
   ID.  If the recipient of a SETTINGS message is 4.

   Flags: FLAG_SETTINGS_CLEAR_SETTINGS (0x1): frame discovers multiple values
   for the same ID, it MUST ignore all values except the first one.

   A server may send multiple SETTINGS frames containing different ID/
   Value pairs.  When set, the client
   should clear same ID/Value is sent twice, the most recent
   value overrides any previously persisted SETTINGS ID/Value pairs. sent values.  If
   this frame contains ID/Value pairs the server sends IDs
   1, 2, and 3 with the FLAG_SETTINGS_PERSIST_VALUE set, then the client will in a first clear its
   existing, persisted settings, SETTINGS
   frame, and then persist the values sends IDs 4 and 5 with the
   flag set which are contained within this frame.  Because persistence
   is only implemented on the client, this flag can only be used
   FLAG_SETTINGS_PERSIST_VALUE, when the sender is the server.

   Length: An unsigned 24-bit value representing the number of bytes
   after the length field.  The total size of a SETTINGS frame is 8
   bytes + length.

   Number of entries: A 32-bit value representing the number of ID/value
   pairs in this message.

   ID: A 32-bit ID number, comprised of 8 bits of flags and 24 bits of
   unique ID.

      ID.flags:

         FLAG_SETTINGS_PERSIST_VALUE (0x1): When set, client returns the sender of this persisted
   state on its next SETTINGS frame is requesting that the recipient persist the ID/
         Value and return frame, it SHOULD send all 5 settings (1,
   2, 3, 4, and 5 in future SETTINGS frames sent from the
         sender to this recipient.  Because persistence is only
         implemented on the client, this flag is only sent by example) to the server.

         FLAG_SETTINGS_PERSISTED (0x2): When set,

3.7.5.  PUSH_PROMISE

   The PUSH_PROMISE frame (type=5) allows the sender is
         notifying the recipient that this ID/Value pair was previously
         sent to the sender by the recipient with the
         FLAG_SETTINGS_PERSIST_VALUE, signal a promise
   to create a stream and serve the sender is returning it.
         Because persistence is only implemented on the client, this
         flag is only sent by the client.

      Defined IDs:

         1 - SETTINGS_UPLOAD_BANDWIDTH allows referenced resource.  Minimal data
   allowing the sender receiver to send its
         expected upload bandwidth understand which resource(s) are to be
   pushed are to be included.

   PUSH_PROMISE frames are sent on this channel.  This number is an
         estimate.  The value should be existing stream.  They declare the integral number
   intent to use another stream for the pushing of kilobytes
         per second that a resource.  The
   PUSH_PROMISE allows the sender predicts as client an expected maximum
         upload channel capacity. opportunity to reject pushed
   resources.

    0                   1                   2 - SETTINGS_DOWNLOAD_BANDWIDTH allows                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |X|                Promised-Stream-ID (31)                      |
   +-+-------------------------------------------------------------+
   |                    Header Block (*)                         ...
   +---------------------------------------------------------------+

                        PUSH_PROMISE Payload Format

   There are no frame-specific flags for the sender to send its
         expected download bandwidth on this channel. PUSH_PROMISE frame.

   The body of a PUSH_PROMISE includes a "Promised-Stream-ID".  This number is an
         estimate. 31-
   bit identifier indicates the stream on which the resource will be
   pushed.  The value should promised stream identifier MUST be a valid choice for
   the integral number of kilobytes
         per second that next stream sent by the sender predicts as an expected maximum
         download channel capacity.

         3 - SETTINGS_ROUND_TRIP_TIME allows (see new stream identifier
   (Section 3.4.1)).

   There is no requirement that the sender streams referred to send its
         expected round-trip-time on by this channel. frame
   are created in the order referenced.  The round trip time
         is defined PUSH_PROMISE reserves
   stream identifiers for later use; these reserved identifiers can be
   used as the minimum amount of time to send prioritization needs dictate.

   The PUSH_PROMISE also includes a control
         frame from this client to header block (Section 3.7.10), which
   describes the remote and receive a response. resource that will be pushed.

3.7.6.  PING

   The value PING frame (type=6) is represented in milliseconds.

         4 - SETTINGS_MAX_CONCURRENT_STREAMS allows a mechanism for measuring a minimal round-
   trip time from the sender to inform sender.  PING frames can be sent from the remote endpoint client
   or the maximum number server.

   Recipients of concurrent streams
         which it will allow.  By default a PING frame send an identical frame to the sender as
   soon as possible.  PING should take highest priority if there is no limit.  For
         implementors it is recommended
   other data waiting to be sent.

   The PING frame defines a frame-specific flag:

   PONG (0x2):  Bit 2 being set indicates that this value be no smaller
         than 100.

         5 - SETTINGS_CURRENT_CWND allows the sender to inform the
         remote ping frame is a ping
      response.  An endpoint MUST set this flag in ping responses.  An
      endpoint MUST NOT respond to ping frames containing this flag.

   The payload of the current TCP CWND a PING frame contains any value.

         6 - SETTINGS_DOWNLOAD_RETRANS_RATE allows the sender to inform
         the remote endpoint  A PING response MUST
   contain the retransmission rate (bytes
         retransmitted / total bytes transmitted).

         7 - SETTINGS_INITIAL_WINDOW_SIZE allows contents of the sender to inform PING request.

3.7.7.  GOAWAY

   The GOAWAY frame (type=7) informs the remote endpoint the initial window size (in bytes) for new
         streams.

         8 - SETTINGS_CLIENT_CERTIFICATE_VECTOR_SIZE allows side of the server connection
   to inform stop creating streams on this session.  It can be sent from the
   client of or the new size of server.  Once sent, the client certificate
         vector.

   Value: A 32-bit value.

   The message is intentionally extensible for future information which
   may improve client-server communications.  The sender does not need
   to send every type of ID/value.  It must only send those for which it
   has accurate values to convey.  When multiple ID/value pairs are
   sent, they should be will ignore frames sent in order of lowest id to highest id.  A
   single SETTINGS frame MUST not contain multiple values
   on new streams for the same
   ID.  If remainder of the recipient session.  Recipients of a SETTINGS
   GOAWAY frame discovers multiple values
   for the same ID, it MUST ignore all values except NOT open additional streams on the first one.

   A server may send multiple SETTINGS frames containing different ID/
   Value pairs.  When the same ID/Value session,
   although a new session can be established for new streams.  The
   purpose of this message is sent twice, the most recent
   value overrides any to allow an endpoint to gracefully stop
   accepting new streams (perhaps for a reboot or maintenance), while
   still finishing processing of previously sent values.  If the server sends IDs
   1, 2, established streams.

   There is an inherent race condition between an endpoint starting new
   streams and 3 with the FLAG_SETTINGS_PERSIST_VALUE in remote sending a first SETTINGS
   frame, and then sends IDs 4 and 5 GOAWAY message.  To deal with this
   case, the
   FLAG_SETTINGS_PERSIST_VALUE, when GOAWAY contains the client returns stream identifier of the persisted
   state last stream
   which was processed on its next SETTINGS frame, it SHOULD send all 5 settings (1,
   2, 3, 4, and 5 the sending endpoint in this example) to the server.

3.6.5.  PING

   The PING control frame is a mechanism for measuring a minimal round-
   trip time from session.  If the sender.  It can be sent from
   receiver of the client or GOAWAY used streams that are newer than the
   server.  Recipients of a PING frame should send an identical frame to indicated
   stream identifier, they were not processed by the sender and the
   receiver may treat the streams as soon as possible (if there is other pending data
   waiting though they had never been created
   at all (hence the receiver may want to be sent, PING should take highest priority).  Each ping
   sent by re-create the streams later on
   a sender new session).

   Endpoints should use a unique ID.

   +----------------------------------+
   |1|   version    |         6       |
   +----------------------------------+
   | 0 (flags) |     4 (length)       |
   +----------------------------------|
   |            32-bit ID             |
   +----------------------------------+

   Control bit: The control bit is always 1 for this message.

   Version: The HTTP/2.0 version number.

   Type: The message type for send a PING GOAWAY message is 6.

   Length: This frame is always 4 bytes long.

   ID: A unique ID for this ping, represented as an unsigned 32 bit
   value.  When the client initiates before closing a ping, it must use an odd numbered
   ID.  When
   connection so that the server initiates remote can know whether a ping, it must use an even numbered
   ping.  Use of odd/even IDs is required in order to avoid accidental
   looping on PINGs (where each side initiates stream has been
   partially processed or not.  (For example, if an identical PING HTTP client sends a
   POST at the same time).

   Note: If a sender uses all possible PING ids (e.g. has sent all 2^31
   possible IDs), it can wrap and start re-using IDs.

   If time that a server receives an even numbered PING which it did not initiate,
   it must ignore the PING.  If a client receives an odd numbered PING
   which it did not initiate, it must ignore the PING.

3.6.6.  GOAWAY

   The GOAWAY control frame is closes a mechanism to tell the remote side of
   the connection to stop creating streams on this session.  It can be
   sent from connection, the client or
   cannot know if the server.  Once sent, server started to process that POST request if the sender will
   server does not
   respond to any new SYN_STREAMs on this session.  Recipients of send a GOAWAY frame must not send additional streams on this session,
   although to indicate where it stopped
   working).

   After sending a new session GOAWAY message, the sender can be established ignore frames for new
   streams.  The
   purpose of this message

   [[anchor18: Issue: session state that is to allow an endpoint to gracefully stop
   accepting new streams (perhaps for a reboot or maintenance), while
   still finishing processing of previously established streams.

   There is an inherent race condition between an endpoint sending
   SYN_STREAMs and by those
   "ignored" messages cannot be ignored without the remote sending a state in the two
   peers becoming unsynchronized.]]

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |X|                  Last-Stream-ID (31)                        |
   +-+-------------------------------------------------------------+
   |                      Error Code (32)                          |
   +---------------------------------------------------------------+

                           GOAWAY message.  To deal with
   this case, Payload Format

   The GOAWAY frame does not define any valid flags.

   The GOAWAY frame applies to the session, not a specific stream.  The
   stream identifier MUST be zero.

   The GOAWAY frame contains a last-stream-id indicating the
   stream-id an identifier of the last stream which was created on the sending
   endpoint in this session.  If that the receiver
   sender of the GOAWAY sent new
   SYN_STREAMs for sessions after this last-stream-id, they were not
   processed by the server is prepared to act upon, which can include
   processing and the receiver may treat the stream as
   though it replies.  This allows an endpoint to discover what
   streams might have had never been created at all (hence the receiver may want some effect or what might be safe to re-create
   automatically retry.  If no streams were acted upon, the last stream later on a new session).

   Endpoints should always send a
   ID MUST be 0.

   The GOAWAY message before closing frame contains a
   connection so 32-bit error code (Section 3.5.3) that
   contains the remote can know whether reason for closing the session.

3.7.8.  HEADERS

   The HEADERS frame (type=8) provides header fields for a stream has been
   partially processed or not.  (For example, if stream.  It
   may be optionally sent on an HTTP client sends a
   POST existing stream at any time.  Specific
   application of the same time that a server closes a connection, the client
   cannot know if the server started to process that POST request if the
   server does not send a GOAWAY headers in this frame to indicate where it stopped
   working).

   After sending a GOAWAY message, the sender must ignore all SYN_STREAM
   frames for new streams.

   +----------------------------------+
   |1|   version    |         7       |
   +----------------------------------+
   | 0 (flags) |     8 (length)       |
   +----------------------------------|
   |X|  Last-good-stream-ID (31 bits) |
   +----------------------------------+
   |          Status code             |
   +----------------------------------+

   Control bit: The control bit is always 1 application-dependent.

   No frame-specific flags are defined for this message.

   Version: The HTTP/2.0 version number.

   Type: the HEADERS frame.

   The message type for body of a GOAWAY message is 7.

   Length: This HEADERS frame is always 8 bytes long.

   Last-good-stream-Id: contains a Headers Block
   (Section 3.7.10).

3.7.9.  WINDOW_UPDATE

   The last stream id which was replied WINDOW_UPDATE frame (type=9) is used to (with
   either implement flow control in
   HTTP/2.0.

   Flow control in HTTP/2.0 operates at two levels: on each individual
   stream and on the entire session.

   Flow control in HTTP/2.0 is hop by hop, that is, only between the two
   endpoints of a SYN_REPLY or RST_STREAM) HTTP/2.0 connection.  Intermediaries do not forward
   WINDOW_UPDATE messages between dependent sessions.  However,
   throttling of data transfer by any recipient can indirectly cause the sender
   propagation of flow control information toward the GOAWAY
   message.  If no streams were replied to, original sender.

   Flow control only applies to frames that are identified as being
   subject to flow control.  Of the frames defined in this value document,
   only data frames are subject to flow control.  Receivers MUST be 0.

   Status: The reason for closing either
   buffer or process all other frames, terminate the corresponding
   stream, or terminate the session.

      0 - OK.  This is a normal  The stream or session teardown.

      1 - PROTOCOL_ERROR.  This is
   terminated with a generic error, and should only be
      used if a more specific error is not available. FLOW_CONTROL_ERROR code.

   Valid flags for the WINDOW_UPDATE frame are:

   END_FLOW_CONTROL (0x2):  Bit 2 - INTERNAL_ERROR.  This is a generic error which can be used
      when being set indicates that flow control
      for the implementation has internally failed, identified stream or session is ended and subsequent
      frames do not due need to anything
      in the protocol.

3.6.7.  HEADERS be flow controlled.

   The HEADERS WINDOW_UPDATE frame augments a stream with additional headers.  It may can be optionally sent on an existing stream at any time.  Specific
   application of the headers related or session related.
   The stream identifier in this the WINDOW_UPDATE frame is application-dependent.
   The name/value header block within this frame is compressed.

   +------------------------------------+
   |1|   version     |          8       |
   +------------------------------------+
   | Flags (8)  |   Length (24 bits)    |
   +------------------------------------+
   |X|          Stream-ID (31bits)      |
   +------------------------------------+
   | Number of Name/Value pairs (int32) |   <+
   +------------------------------------+    |
   |     Length of name (int32)         |    | This section is identifies
   the
   +------------------------------------+    | "Name/Value Header
   |           Name (string)            |    | Block", and is
   +------------------------------------+    | compressed.
   |     Length of affected stream, or includes a value  (int32)       |    |
   +------------------------------------+    |
   |          Value   (string)          |    |
   +------------------------------------+    |
   |           (repeats)                |   <+

   Flags: Flags related of 0 to this frame.  Valid flags are:

      0x01 = FLAG_FIN - marks this frame as indicate that the last
   session flow control window is updated.

   The payload of a WINDOW_UPDATE frame to be
      transmitted on this stream and puts the sender in the half-closed
      (Section 3.3.6) state.

   Length: An unsigned 24 bit contains a 32-bit value.  This
   value representing is the additional number of bytes
   after that the length field.  The minimum length of sender can transmit
   in addition to the length existing flow control window.  The legal range for
   this field is 4
   (when 1 to 2^31 - 1 (0x7fffffff) bytes; the number most significant
   bit of name this value pairs is 0).

   Stream-ID: reserved.

3.7.9.1.  The stream this HEADERS block is associated with.

   Name/Value Header Block: A set of name/value pairs carried as part of
   the SYN_STREAM. see Name/Value Header Block (Section 3.6.10).

3.6.8.  WINDOW_UPDATE

   The WINDOW_UPDATE control frame is used to implement per stream flow
   control in HTTP/2.0.  Flow control in HTTP/2.0 is per hop, that is,
   only between the two endpoints of a HTTP/2.0 connection.  If there
   are one or more intermediaries between the client and the origin
   server, flow control signals are not explicitly forwarded by the
   intermediaries.  (However, throttling of data transfer by any
   recipient may have the effect of indirectly propagating flow control
   information upstream back to the original sender.)  Flow control only
   applies to the data portion of data frames.  Recipients must buffer
   all control frames.  If a recipient fails to buffer an entire control
   frame, it MUST issue a stream error (Section 3.4.2) with the status
   code FLOW_CONTROL_ERROR for the stream.

   Flow control in HTTP/2.0 Flow Control Window

   Flow control in HTTP/2.0 is implemented by a data transfer flow control window kept
   by the sender of each stream.  The data transfer flow control window is a simple uint32
   integer value that indicates how many bytes of data the sender can
   transmit.  After a stream is created, but before any data frames have
   been transmitted, the sender begins with the initial window size.
   This
   permitted to transmit.  The flow control window size is a measure of
   the buffering capability of the recipient.

   Two flow control windows apply to the sending of every message: the
   stream flow control window and the session flow control window.  The
   sender must not MUST NOT send a data flow controlled frame with data a length
   greater than that
   exceeds the transfer window size. space available in either of the flow control windows
   advertised by the receiver.  Frames with zero length with the FINAL
   flag set (for example, an empty data frame) MAY be sent if there is
   no available space in either flow control window.

   For flow control calculations, the 8 byte frame header is not
   counted.

   After sending each data a flow controlled frame, the sender decrements its transfer window size by reduces the amount
   of data transmitted.  When the window size becomes less than or equal
   to 0, the sender must pause transmitting data frames.  At space
   available in both windows by the other
   end length of the stream, the recipient transmitted frame.

   The receiver of a message sends a WINDOW_UPDATE control back
   to notify the sender that frame as it has consumed some consumes
   data and freed frees up
   buffer space to receive more data.

   +----------------------------------+
   |1|   version    |         9       |
   +----------------------------------+
   | 0 (flags) |     8 (length)       |
   +----------------------------------+
   |X|     Stream-ID (31-bits)        |
   +----------------------------------+
   |X|  Delta-Window-Size (31-bits)   |
   +----------------------------------+

   Control bit: The in flow control bit is always 1 for this message.

   Version: The HTTP/2.0 version number.

   Type: The message type for a windows.  Separate
   WINDOW_UPDATE message is 9.

   Length: The length field is always 8 for this frame (there messages are 8
   bytes after sent for the length field).

   Stream-ID: The stream ID and session level flow
   control windows.

   A sender that this receives a WINDOW_UPDATE control frame is
   for.

   Delta-Window-Size: The additional number of bytes that updates the sender can
   transmit
   corresponding window by the amount specified in addition to existing remaining the frame.

   A sender MUST NOT allow a flow control window size.  The legal
   range for this field is 1 to exceed 2^31 - 1 (0x7fffffff)
   bytes.

   The window size as kept by the sender must never exceed 2^31
   (although it can become negative in one special case).  If a sender receives a WINDOW_UPDATE that causes the its a flow
   control window size to exceed this limit, maximum it must send MUST terminate either the
   stream or the session, as appropriate.  For streams, the sender sends
   a RST_STREAM with status the error code of FLOW_CONTROL_ERROR to terminate code; for the stream.

   When
   session, a HTTP/2.0 connection is first established, GOAWAY message with a FLOW_CONTROL_ERROR code.

   Flow controlled frames from the default initial
   window size for all streams is 64KB.  An endpoint can use sender and WINDOW_UPDATE frames from
   the
   SETTINGS control frame receiver are completely asynchronous with respect to adjust the initial each other.
   This property allows a receiver to aggressively update the window
   size for the
   connection.  That is, its peer can start out using kept by the 64KB default sender to prevent streams from stalling.

3.7.9.2.  Initial Flow Control Window Size

   When a HTTP/2.0 connection is first established, new streams are
   created with an initial flow control window size when sending data frames before receiving the
   SETTINGS.  Because SETTINGS of 65535 bytes.  The
   session flow control window is asynchronous, there may be a race
   condition if the recipient wants to decrease 65536 bytes.  Both endpoints can
   adjust the initial window size,
   but its peer immediately sends 64KB on the creation of a size for new
   connection, before waiting streams by including a value
   for SETTINGS_INITIAL_WINDOW_SIZE in the SETTINGS frame that forms
   part of the session header.

   Prior to arrive.  This is one
   case where receiving a SETTINGS frame that sets a value for
   SETTINGS_INITIAL_WINDOW_SIZE, a client can only use the default
   initial window size kept by the sender will become negative.
   Once the sender detects this condition, it must stop when sending data
   frames and wait for the recipient to catch up.  The recipient has two
   choices:

      immediately send RST_STREAM with FLOW_CONTROL_ERROR status code.

      allow the head of line blocking (as there is only one stream for flow controlled frames.  Similarly,
   the session and the amount of data in flight flow control window is bounded by set to the default initial window size), and send WINDOW_UPDATE as it
      consumes data.

   In the case of option 2, both sides must compute the window
   size
   based on until a WINDOW_UPDATE message is received.

   A SETTINGS frame can alter the initial flow control window size in the SETTINGS.  For example, if for
   all current streams.  When the recipient sets value of SETTINGS_INITIAL_WINDOW_SIZE
   changes, a receiver MUST adjust the initial window size to be 16KB, and the of all flow control windows
   that it maintains by the difference between the new value and the old
   value.

   A change to SETTINGS_INITIAL_WINDOW_SIZE could cause the available
   space in a flow control window to become negative.  A sender MUST
   track the negative flow control window and not send new flow
   controlled frames until it receives WINDOW_UPDATE messages that cause
   the flow control window to become positive.

   For example, if the server sets the initial window size to be 16KB,
   and the client sends 64KB immediately on connection establishment,
   the sender client will
   discover its recalculate the available flow control window size is to be
   -48KB on receipt of the SETTINGS.  As the
   recipient consumes the first 16KB, it must send SETTINGS frame.  The client retains a WINDOW_UPDATE of
   16KB back to the sender.  This interaction continues
   negative flow control window until WINDOW_UPDATE frames restore the
   sender's
   window size becomes positive again, and it to being positive, after which the client can resume
   transmitting data frames.

   After sending.

3.7.9.3.  Reducing the recipient reads in a data frame with FLAG_FIN Stream Window Size

   A receiver that marks wishes to use a smaller flow control window than the end of
   current size sends a new SETTINGS frame.  However, the receiver MUST
   be prepared to receive data stream, it should not send WINDOW_UPDATE frames
   as it consumes that exceeds this window size, since the last data frame.  A
   sender should ignore all might send data that exceeds the
   WINDOW_UPDATE frames associated with lower limit prior to
   processing the stream after it SETTINGS frame.

   A receiver has two options for handling streams that exceed flow
   control limits:

   1.  The receiver can immediately send the
   last frame RST_STREAM with
       FLOW_CONTROL_ERROR error code for the stream. affected streams.

   2.  The data frames from receiver can accept the sender streams and tolerate the resulting
       head of line blocking, sending WINDOW_UPDATE frames from the
   recipient are completely asynchronous with respect to each other.
   This property allows messages as it
       consumes data.

   If a recipient receiver decides to aggressively update accept streams, both sides must recompute
   the available flow control window based on the initial window size kept by
   sent in the sender to prevent SETTINGS.

3.7.9.4.  Ending Flow Control

   After a recipient reads in a frame that marks the end of a stream from stalling.

3.6.9.  CREDENTIAL

   The CREDENTIAL control frame
   (for example, a data stream with a FINAL flag set), it ceases
   transmission of WINDOW_UPDATE frames.  A sender is used by the client to send additional
   client certificates not required to
   maintain the server.  A HTTP/2.0 client may decide to
   send requests available flow control window for resources from different origins on the same
   HTTP/2.0 session if it decides that streams that server handles both origins.
   For example if it is no
   longer sending on.

   Flow control can be disabled for all streams or the IP address associated with both hostnames matches
   and session using the SSL server certificate presented
   SETTINGS_FLOW_CONTROL_OPTIONS setting.  An implementation that does
   not wish to perform flow control can use this in the initial handshake is
   valid for both hostnames.  However, because the SSL connection SETTINGS
   exchange.

   Flow control can
   contain at most one client certificate, be disabled for an individual stream or the client needs overall
   session by sending a mechanism
   to send additional client certificates to WINDOW_UPDATE with the server. END_FLOW_CONTROL flag
   set.  The server is required to maintain a vector payload of client certificates
   associated with a HTTP/2.0 session.  When the client needs to send a
   client certificate to the server, it will send a CREDENTIAL WINDOW_UPDATE frame that specifies the index of has the slot in which
   END_FLOW_CONTROL flag set is ignored.

   Flow control cannot be enabled again once disabled.  Any attempt to store the
   certificate as well as proof that
   re-enable flow control - by sending a WINDOW_UPDATE or by clearing
   the client posesses bits on the
   corresponding private key.  The initial size of this vector must SETTINGS_FLOW_CONTROL_OPTIONS setting - MUST be
   8.  If the client provides
   rejected with a client certificate during FLOW_CONTROL_ERROR error code.

3.7.10.  Header Block

   The header block is found in the first TLS
   handshake, HEADERS, HEADERS+PRIORITY and
   PUSH_PROMISE frames.  The header block consists of a set of header
   fields, which are name-value pairs.  Headers are compressed using
   black magic.

   Compression of header fields is a work in progress, as is the contents format
   of this certificate must block.

4.  HTTP Message Exchanges

   HTTP/2.0 is intended to be copied into as compatible as possible with current
   web-based applications.  This means that, from the
   first slot (index 1) in perspective of the CREDENTIAL vector, though it may be
   overwritten by subsequent CREDENTIAL frames.  The
   server must
   exclusively use business logic or application API, the CREDENTIAL vector when evaluating features of HTTP are
   unchanged.  To achieve this, all of the client
   certificates associated with an origin.  The server may change application request and
   response header semantics are preserved, although the
   size syntax of this vector by sending a SETTINGS frame with
   conveying those semantics has changed.  Thus, the setting
   SETTINGS_CLIENT_CERTIFICATE_VECTOR_SIZE value specified.  In rules from HTTP/1.1
   ([HTTP-p1], [HTTP-p2], [HTTP-p4], [HTTP-p5], [HTTP-p6], and
   [HTTP-p7]) apply with the
   event that changes in the new size is smaller sections below.

4.1.  Connection Management

   Clients SHOULD NOT open more than the current size, truncation
   occurs preserving lower-index slots as possible.

   TLS renegotiation with client authentication is incompatible with one HTTP/2.0 session to a given the multiplexed nature of HTTP/2.0.  Specifically,
   imagine
   origin ([RFC6454]) concurrently.

   Note that it is possible for one HTTP/2.0 session to be finishing
   (e.g. a GOAWAY message has been sent, but not all streams have
   finished), while another HTTP/2.0 session is starting.

4.1.1.  Use of GOAWAY

   HTTP/2.0 provides a GOAWAY message which can be used when closing a
   connection from either the client or server.  Without a server GOAWAY
   message, HTTP has 2 requests outstanding to a race condition where the server for
   two different pages (in different tabs).  When the renegotiation + client certificate sends a request comes in,
   just as the browser server is unable to
   determine which resource triggered closing the connection, and the client certificate request, cannot
   know if the server received the stream or not.  By using the last-
   stream-id in
   order the GOAWAY, servers can indicate to prompt the user accordingly.

   +----------------------------------+
   |1|000000000000001|0000000000001011|
   +----------------------------------+
   | flags (8)  |  Length (24 bits)   |
   +----------------------------------+
   |  Slot (16 bits) |                |
   +-----------------+                |
   |      Proof Length (32 bits)      |
   +----------------------------------+
   |               Proof              |
   +----------------------------------+ <+
   |   Certificate Length (32 bits)   |  |
   +----------------------------------+  | Repeated until end of frame
   |            Certificate           |  |
   +----------------------------------+ <+

   Slot: The index in client if a
   request was processed or not.

   Note that some servers will choose to send the GOAWAY and immediately
   terminate the server's connection without waiting for active streams to
   finish.  The client certificate vector where this
   certificate should will be stored.  If there is already a certificate
   stored at able to determine this index, it because HTTP/2.0
   streams are deterministically closed.  This abrupt termination will be overwritten.  The index is one
   based, not zero based; zero is an invalid slot index.

   Proof: Cryptographic proof that
   force the client has possession of to heuristically decide whether to retry the
   private key associated pending
   requests.  Clients always need to be capable of dealing with the certificate.  The format is a TLS
   digitally-signed element ([RFC5246], Section 4.7).  The signature
   algorithm this
   case because they must be deal with accidental connection termination
   cases, which are the same as that used in the CertificateVerify
   message.  However, since the MD5+SHA1 signature type used in TLS 1.0
   connections can not be correctly encoded in server never having sent a digitally-signed
   element, SHA1 must be used when MD5+SHA1 was used in GOAWAY.

   More sophisticated servers will use GOAWAY to implement a graceful
   teardown.  They will send the GOAWAY and provide some time for the
   active streams to finish before terminating the SSL connection.  The signature is calculated over a 32 byte TLS extractor
   value (http://tools.ietf.org/html/rfc5705) with

   If a label of "EXPORTER HTTP/2.0 certificate proof" using the empty string as context.
   ForRSA certificates client closes the signature would be a PKCS#1 v1.5 signature.
   For ECDSA, connection, it would be an ECDSA-Sig-Value
   (http://tools.ietf.org/html/rfc5480#appendix-A).  For should also send a 1024-bit RSA
   key, the CREDENTIAL message would be ~500 bytes.

   Certificate: The certificate chain, starting with
   GOAWAY message.  This allows the leaf
   certificate.  Each certificate must be encoded as a 32 bit length,
   followed server to know if any server-push
   streams were received by a DER encoded certificate.  The certificate must be of the same type (RSA, ECDSA, etc) as client.

   If the client certificate associated
   with endpoint closing the SSL connection.

   If connection has not received frames on any
   stream, the server receives a request for GOAWAY will contain a resource with unacceptable
   credential (either missing or invalid), it must reply last-stream-id of 0.

4.2.  HTTP Request/Response

4.2.1.  HTTP Header Fields and HTTP/2.0 Headers

   At the application level, HTTP uses name-value pairs in its header
   fields.  Because HTTP/2.0 merges the existing HTTP header fields with
   HTTP/2.0 headers, there is a
   RST_STREAM frame with the status code INVALID_CREDENTIALS.  Upon
   receipt of possibility that some HTTP applications
   already use a RST_STREAM frame particular header field name.  To avoid any conflicts,
   all header fields introduced for layering HTTP over HTTP/2.0 are
   prefixed with INVALID_CREDENTIALS, the ":". ":" is not a valid sequence in HTTP/1.* header
   field naming, preventing any possible conflict.

4.2.2.  Request

   The client
   should initiate initiates a new stream directly to request by sending a HEADERS+PRIORITY frame.
   Requests that do not contain a body MUST set the requested origin and
   resend FINAL flag,
   indicating that the request.  Note, HTTP/2.0 does not allow client intends to send no further data on this
   stream, unless the server intends to
   request different client authentication for different push resources in
   the same origin.

   If the server receives an invalid CREDENTIAL frame, it MUST respond
   with a GOAWAY (see
   Section 4.3).  HEADERS+PRIORITY frame and shutdown does not contain the session.

3.6.10.  Name/Value Header Block FINAL flag
   for requests that contain a body.  The Name/Value Header Block is found in the SYN_STREAM, SYN_REPLY and
   HEADERS control frames, and shares a common format:

   +------------------------------------+
   | Number of Name/Value pairs (int32) |
   +------------------------------------+
   |     Length of name (int32)         |
   +------------------------------------+
   |           Name (string)            |
   +------------------------------------+
   |     Length body of value  (int32)       |
   +------------------------------------+
   |          Value   (string)          |
   +------------------------------------+
   |           (repeats)                |

   Number a request follows as a
   series of Name/Value pairs: DATA frames.  The number of repeating name/value pairs
   following this field.

   List of Name/Value pairs:

      Length of Name: a 32-bit value containing last DATA frame sets the number FINAL flag to
   indicate the end of octets in the name field.  Note that body.

   The header fields included in practice, this length must not
      exceed 2^24, as that is the maximum size of a HTTP/2.0 frame.

      Name: 0 or more octets, 8-bit sequences of data, excluding 0.

      Length HEADERS+PRIORITY frame contain all
   of Value: a 32-bit value containing the number of octets HTTP header fields that are associated with an HTTP request.
   The header block in HTTP/2.0 is mostly unchanged from today's HTTP
   header block, with the value field.  Note following differences:

      The following fields that are carried in practice, this length must not
      exceed 2^24, as that is the maximum size of a HTTP/2.0 frame.

      Value: 0 or more octets, 8-bit sequences of data, excluding 0.

   Each header name must have at least one value.  Header names request line in
      HTTP/1.1 ([HTTP-p1], Section 3.1.1) are
   encoded using defined as special-valued
      name-value pairs:

      ":method":  the US-ASCII character set [ASCII] and must be all
   lower case.  The length of each name must be greater than zero.  A
   recipient of a zero-length name MUST issue a stream error
   (Section 3.4.2) with HTTP method for this request (e.g.  "GET", "POST",
         "HEAD", etc) ([HTTP-p2], Section 4)

      ":path":  ":path" - the status code PROTOCOL_ERROR request-target for this URI with "/"
         prefixed (see [HTTP-p1], Section 3.1.1).  For example, for
         "http://www.google.com/search?q=dogs" the
   stream-id.

   Duplicate header names path would be
         "/search?q=dogs". [[anchor26: what forms of the HTTPbis
         request-target are not allowed.  To send two identically
   named headers, send a allowed here?]]

      These header with two values, where fields MUST be present in HTTP requests.

      In addition, the values are
   separated by a single NUL (0) byte.  A header value can either following two name-value pairs MUST be
   empty (e.g. present in
      every request:

      ":host":  the length is zero) or it can contain multiple, NUL-
   separated values, each with length greater than zero.  The value
   never starts nor ends with a NUL character.  Recipients host and optional port portions (see [RFC3986],
         Section 3.2) of illegal
   value fields MUST issue a stream error (Section 3.4.2) with the
   status code PROTOCOL_ERROR URI for the stream-id.

3.6.10.1.  Compression

   The Name/Value Header Block this request (e.g. "www.google.com:
         1234").  This header field is a section the same as the HTTP 'Host'
         header field ([HTTP-p1], Section 5.4).

      ":scheme":  the scheme portion of the SYN_STREAM,
   SYN_REPLY, and HEADERS frames used to carry URI for this request (e.g.
         "https")

      All header meta-data.  This
   block is always compressed using zlib compression.  Within field names starting with ":" (whether defined in this
   specification, any reference to 'zlib' is referring
      document or future extensions to the ZLIB
   Compressed Data Format Specification Version 3.3 as part this document) MUST appear before
      any other header fields.

      Header field names MUST be all lowercase.

      The Connection, Host, Keep-Alive, Proxy-Connection, and Transfer-
      Encoding header fields are not valid and MUST not be sent.

      User-agents MUST support gzip compression.  Regardless of RFC1950.
   [RFC1950]

   For each HEADERS compression instance, the initial state is
   initialized using
      Accept-Encoding sent by the following dictionary [UDELCOMPRESSION]:

   <CODE BEGINS>

   const unsigned char http2_dictionary_txt[] = {
     0x00, 0x00, 0x00, 0x07, 0x6f, 0x70, 0x74, 0x69,  \\ - - - - o p t i
     0x6f, 0x6e, 0x73, 0x00, 0x00, 0x00, 0x04, 0x68,  \\ o n s - - - - h
     0x65, 0x61, 0x64, 0x00, 0x00, 0x00, 0x04, 0x70,  \\ e user-agent, the server may always send
      content encoded with gzip or deflate encoding. [[anchor27: Still
      valid?]]

      If a d - - - - p
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     0x75, 0x74, 0x00, 0x00, 0x00, 0x06, 0x64, 0x65,  \\ u t - - - - d e
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     0x06, 0x61, 0x63, 0x63, 0x65, 0x70, 0x74, 0x00,  \\ - request where the sum of the data frame
      payload lengths does not equal the size of the Content-Length
      header field, the server MUST return a c c e p t -
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   };

   <CODE ENDS>

   The entire contents of the name/value header block is compressed
   using zlib.  There is a single zlib stream for all name value pairs
   in one direction on a connection.  HTTP/2.0 uses a SYNC_FLUSH between
   each compressed frame.

   Implementation notes: the compression engine can be tuned to favor
   speed or size.  Optimizing for size increases memory use and CPU
   consumption.  Because header blocks are generally small, implementors
   may want to reduce the window-size of the compression engine from the
   default 15bits (a 32KB window) to more like 11bits (a 2KB window).
   The exact setting is chosen by the compressor, the decompressor will
   work with any setting.

4.  HTTP Layering over HTTP/2.0

   HTTP/2.0 is intended to be as compatible as possible with current
   web-based applications.  This means that, from the perspective of the
   server business logic or application API, the features of HTTP are
   unchanged.  To achieve this, all of the application request and
   response header semantics are preserved, although the syntax of
   conveying those semantics has changed.  Thus, the rules from the
   HTTP/1.1 specification in RFC2616 [RFC2616] apply with the changes in
   the sections below.

4.1.  Connection Management

   Clients SHOULD NOT open more than one HTTP/2.0 session to a given
   origin [RFC6454] concurrently.

   Note that it is possible for one HTTP/2.0 session to be finishing
   (e.g. a GOAWAY message has been sent, but not all streams have
   finished), while another HTTP/2.0 session is starting.

4.1.1.  Use of GOAWAY

   HTTP/2.0 provides a GOAWAY message which can be used when closing a
   connection from either the client or server.  Without a server GOAWAY
   message, HTTP has a race condition where the client sends a request
   (a new SYN_STREAM) just as the server is closing the connection, and
   the client cannot know if the server received the stream or not.  By
   using the last-stream-id in the GOAWAY, servers can indicate to the
   client if a request was processed or not.

   Note that some servers will choose to send the GOAWAY and immediately
   terminate the connection without waiting for active streams to
   finish.  The client will be able to determine this because HTTP/2.0
   streams are determinstically closed.  This abrupt termination will
   force the client to heuristically decide whether to retry the pending
   requests.  Clients always need to be capable of dealing with this
   case because they must deal with accidental connection termination
   cases, which are the same as the server never having sent a GOAWAY.

   More sophisticated servers will use GOAWAY to implement a graceful
   teardown.  They will send the GOAWAY and provide some time for the
   active streams to finish before terminating the connection.

   If a HTTP/2.0 client closes the connection, it should also send a
   GOAWAY message.  This allows the server to know if any server-push
   streams were received by the client.

   If the endpoint closing the connection has not received any
   SYN_STREAMs from the remote, the GOAWAY will contain a last-stream-id
   of 0.

4.2.  HTTP Request/Response

4.2.1.  Request

   The client initiates a request by sending a SYN_STREAM frame.  For
   requests which do not contain a body, the SYN_STREAM frame MUST set
   the FLAG_FIN, indicating that the client intends to send no further
   data on this stream.  For requests which do contain a body, the
   SYN_STREAM will not contain the FLAG_FIN, and the body will follow
   the SYN_STREAM in a series of DATA frames.  The last DATA frame will
   set the FLAG_FIN to indicate the end of the body.

   The SYN_STREAM Name/Value section will contain all of the HTTP
   headers which are associated with an HTTP request.  The header block
   in HTTP/2.0 is mostly unchanged from today's HTTP header block, with
   the following differences:

      The first line of the request is unfolded into name/value pairs
      like other HTTP headers and MUST be present:

         ":method" - the HTTP method for this request (e.g.  "GET",
         "POST", "HEAD", etc)

         ":path" - the url-path for this url with "/" prefixed.  (See
         RFC1738 [RFC1738]).  For example, for
         "http://www.google.com/search?q=dogs" the path would be
         "/search?q=dogs".

         ":version" - the HTTP version of this request (e.g.
         "HTTP/1.1")

      In addition, the following two name/value pairs must also be
      present in every request:

         ":host" - the hostport (See RFC1738 [RFC1738]) portion of the
         URL for this request (e.g. "www.google.com:1234").  This header
         is the same as the HTTP 'Host' header.

         ":scheme" - the scheme portion of the URL for this request
         (e.g. "https"))

      Header names are all lowercase.

      The Connection, Host, Keep-Alive, Proxy-Connection, and Transfer-
      Encoding headers are not valid and MUST not be sent.

      User-agents MUST support gzip compression.  Regardless of the
      Accept-Encoding sent by the user-agent, the server may always send
      content encoded with gzip or deflate encoding.

      If a server receives a request where the sum of the data frame
      payload lengths does not equal the size of the Content-Length
      header, the server MUST return a 400 (Bad Request) error.

      POST-specific changes:

         Although POSTs are inherently chunked, POST requests SHOULD
         also be accompanied by a Content-Length header.  There are two
         reasons for this: First, it assists with upload progress meters
         for an improved user experience.  But second, we know from
         early versions of HTTP/2.0 that failure to send a content
         length header is incompatible with many existing HTTP server
         implementations.  Existing user-agents do not omit the Content-
         Length header, and server implementations have come to depend
         upon this.

   The user-agent is free to prioritize requests as it sees fit.  If the
   user-agent cannot make progress without receiving a resource, it
   should attempt to raise the priority of that resource.  Resources
   such as images, SHOULD generally use the lowest priority.

   If a client sends a SYN_STREAM without all of the method, host, path,
   scheme, and version headers, the server MUST reply with a HTTP 400
   Bad Request reply.

4.2.2.  Response

   The server responds to a client request with a SYN_REPLY frame.
   Symmetric to the client's upload stream, server will send data after
   the SYN_REPLY frame via a series of DATA frames, and the last data
   frame will contain the FLAG_FIN to indicate successful end-of-stream.
   If a response (like a 202 or 204 response) contains no body, the
   SYN_REPLY frame may contain the FLAG_FIN flag to indicate no further
   data will be sent on the stream.

      The response status line is unfolded into name/value pairs like
      other HTTP headers and must be present:

         ":status" - The HTTP response status code (e.g. "200" or "200
         OK")

         ":version" - The HTTP response version (e.g.  "HTTP/1.1")

      All header names must be lowercase.

      The Connection, Keep-Alive, Proxy-Connection, and Transfer-
      Encoding headers are not valid and MUST not be sent.

      Responses MAY be accompanied by a Content-Length header for
      advisory purposes. (e.g. for UI progress meters)

      If a client receives a response where the sum of the data frame
      payload lengths does not equal the size of the Content-Length
      header, the client MUST ignore the content length header.

   If a client receives a SYN_REPLY without a status or without a
   version header, the client must reply with a RST_STREAM frame
   indicating a PROTOCOL ERROR.

4.2.3.  Authentication

   When a client sends a request to an origin server that requires
   authentication, the server can reply with a "401 Unauthorized"
   response, and include a WWW-Authenticate challenge header that
   defines the authentication scheme to be used.  The client then
   retries the request with an Authorization header appropriate to the
   specified authentication scheme.

   There are four options for proxy authentication, Basic, Digest, NTLM
   and Negotiate (SPNEGO).  The first two options were defined in
   RFC2617 [RFC2617], and are stateless.  The second two options were
   developed by Microsoft and specified in RFC4559 [RFC4559], and are
   stateful; otherwise known as multi-round authentication, or
   connection authentication.

4.2.3.1.  Stateless Authentication

   Stateless Authentication over HTTP/2.0 is identical to how it is
   performed over HTTP.  If multiple HTTP/2.0 streams are concurrently
   sent to a single server, each will authenticate independently,
   similar to how two HTTP connections would independently authenticate
   to a proxy server.

4.2.3.2.  Stateful Authentication

   Unfortunately, the stateful authentication mechanisms were
   implemented and defined in a such a way that directly violates
   RFC2617 - they do not include a "realm" as part of the request.  This
   is problematic in HTTP/2.0 because it makes it impossible for a
   client to disambiguate two concurrent server authentication
   challenges.

   To deal with this case, HTTP/2.0 servers using Stateful
   Authentication MUST implement one of two changes:

      Servers can add a "realm=<desired realm>" header so that the two
      authentication requests can be disambiguated and run concurrently.
      Unfortunately, given how these mechanisms work, this is probably
      not practical.

      Upon sending the first stateful challenge response, the server
      MUST buffer and defer all further frames which are not part of
      completing the challenge until the challenge has completed.
      Completing the authentication challenge may take multiple round
      trips.  Once the client receives a "401 Authenticate" response for
      a stateful authentication type, it MUST stop sending new requests
      to the server until the authentication has completed by receiving
      a non-401 response on at least one stream.

4.3.  Server Push Transactions

   HTTP/2.0 enables a server to send multiple replies to a client for a
   single request.  The rationale for this feature is that sometimes a
   server knows that it will need to send multiple resources in response
   to a single request.  Without server push features, the client must
   first download the primary resource, then discover the secondary
   resource(s), and request them.  Pushing of resources avoids the
   round-trip delay, but 400 (Bad Request) error.

      Although POSTs are inherently chunked, POST requests SHOULD also creates a potential race where a server
   can
      be pushing content which accompanied by a user-agent is in Content-Length header field.  First, it
      informs the process server of
   requesting.  The following mechanics attempt how much data to prevent the race
   condition while enabling the performance benefit.

   Browsers receiving a pushed response MUST validate that expect, which the server is
   authorized
      can used to push the URL using track overall progress and provide appropriate user
      feedback.  More importantly, some HTTP server implementations fail
      to correctly process requests that omit the browser same-origin [RFC6454]
   policy.  For example, Content-Length header
      field.  Many existing clients send a HTTP/2.0 connection Content-Length header field,
      which caused server implementations have come to www.foo.com depend upon its
      presence.

   The user-agent is
   generally not permitted free to push a response for www.evil.com. prioritize requests as it sees fit.  If the browser accepts
   user-agent cannot make progress without receiving a pushed response (e.g. resource, it does not send a
   RST_STREAM), the browser MUST
   should attempt to cache the pushed response in
   same way that it would cache any other response.  This means
   validating the response headers and inserting into the disk cache.

   Because pushed responses have no request, they have no request
   headers associated with them.  At the framing layer, HTTP/2.0 pushed
   streams contain an "associated-stream-id" which indicates the
   requested stream for which the pushed stream is related.  The pushed
   stream inherits all of the headers from the associated-stream-id with raise the exception priority of ":host", ":scheme", and ":path", which are provided that resource.  Resources
   such as part of images, SHOULD generally use the lowest priority.

   If a client sends a HEADERS+PRIORITY frame that omits a mandatory
   header, the pushed response stream headers.  The browser server MUST
   store these inherited and implied request headers reply with a HTTP 400 Bad Request reply.
   [[anchor28: Ed: why PROTOCOL_ERROR on missing ":status" in the
   response, but HTTP 400 here?]]

   If the cached
   resource.

   Implementation note: With server push, it is theoretically possible
   for servers receives a data frame prior to push unreasonable amounts of content a HEADERS or resources to HEADERS+
   PRIORITY frame the user-agent.  Browsers server MUST implement throttles to protect against
   unreasonable push attacks.

4.3.1.  Server implementation

   When the treat this as a stream error
   (Section 3.5.2) of type PROTOCOL_ERROR.

4.2.3.  Response

   The server intends responds to push a resource client request with a HEADERS frame.
   Symmetric to the user-agent, it
   opens client's upload stream, server will send any
   response body in a new series of DATA frames.  The last data frame will
   contain the FINAL flag to indicate the end of the stream by sending and the end
   of the response.  A response that contains no body (such as a unidirectional SYN_STREAM. 204 or
   304 response) consists only of a HEADERS frame that contains the
   FINAL flag to indicate no further data will be sent on the stream.

      The
   SYN_STREAM MUST include an Associated-To-Stream-ID, response status line is unfolded into name-value pairs like
      other HTTP header fields and must be present:

      ":status":  The HTTP response status code (e.g. "200" or "200 OK")

      All header field names starting with ":" (whether defined in this
      document or future extensions to this document) MUST set the
   FLAG_UNIDIRECTIONAL flag. appear before
      any other header fields.

      All header field names MUST be all lowercase.

      The SYN_STREAM Connection, Keep-Alive, Proxy-Connection, and Transfer-
      Encoding header fields are not valid and MUST include headers not be sent.

      Responses MAY be accompanied by a Content-Length header field for
   ":scheme", ":host", ":path", which represent
      advisory purposes.  This allows clients to learn the URL for full size of
      an entity prior to receiving all the resource
   being pushed.  Subsequent headers may follow in HEADERS data frames.  The
   purpose  This can help
      in, for example, reporting progress.

      If a client receives a response where the sum of the association is so that data frame
      payload length does not equal the user-agent can
   differentiate which request induced size of the pushed stream; without it, if Content-Length
      header field, the user-agent had two tabs open to client MUST ignore the same page, each pushing
   unique content under length header
      field. [[anchor29: Ed: See
      <https://github.com/http2/http2-spec/issues/46>.]]

   If a fixed URL, the user-agent would not be able to
   differentiate the requests.

   The Associated-To-Stream-ID must be the ID of an existing, open
   stream.  The reason for this restriction is to have client receives a clear endpoint
   for pushed content.  If response with an absent or duplicated status
   header, the user-agent requested client MUST treat this as a resource on stream
   11, the server replies on stream 11.  It can push any number error (Section 3.5.2)
   of
   additional streams to type PROTOCOL_ERROR.

   If the client before sending receives a FLAG_FIN on stream
   11.  However, once the originating stream is closed no further push
   streams may be associated with it.  The pushed streams do not need to
   be closed (FIN set) before the originating stream is closed, they
   only need data frame prior to be created before a HEADERS or HEADERS+
   PRIORITY frame the originating client MUST treat this as a stream closes.

   It is illegal for error
   (Section 3.5.2) of type PROTOCOL_ERROR.

4.3.  Server Push Transactions

   HTTP/2.0 enables a server to push send multiple replies to a resource with the Associated-To-
   Stream-ID of 0.

   To minimize race conditions with the client, the SYN_STREAM client for the
   pushed a
   single request.  The rationale for this feature is that sometimes a
   server knows that it will need to send multiple resources MUST be sent prior in response
   to sending any content which
   could allow a single request.  Without server push features, the client to must
   first download the primary resource, then discover the pushed resource secondary
   resource(s), and request
   it.

   The server MUST only push them.  Pushing of resources avoids the
   round-trip delay, but also creates a potential race where a server
   can be pushing content which would have been returned
   from a GET request.

   Note: If user-agent is in the server does not have all process of
   requesting.  The following mechanics attempt to prevent the Name/Value Response
   headers available at the time it issues the HEADERS frame for race
   condition while enabling the
   pushed resource, it may later use performance benefit.

   Server push is an additional HEADERS frame optional feature.  Server push can be disabled by
   clients that do not wish to
   augment receive pushed resources by advertising a
   SETTINGS_MAX_CONCURRENT_STREAMS SETTING (Section 3.7.4) of zero.
   This prevents servers from creating the name/value pairs streams necessary to be associated with the pushed stream.
   The subsequent HEADERS frame(s) must not contain push
   resources.

   Browsers receiving a header for
   ':host', ':scheme', or ':path' (e.g. pushed response MUST validate that the server can't change the
   identity of is
   authorized to push the resource using the same-origin policy
   ([RFC6454], Section 3).  For example, a HTTP/2.0 connection to be pushed).  The HEADERS frame must
   "example.com" is generally [[anchor30: Ed: weaselly use of
   "generally", needs better definition]] not
   contain duplicate headers with a previously sent HEADERS frame.  The
   server must send permitted to push a HEADERS frame including the scheme/host/port
   headers before sending any data frames on the stream.

4.3.2.  Client implementation

   When fetching
   response for "www.example.org".

   A client that accepts pushed resources caches those resources as
   though they were responses to GET requests.

   Pushed responses are associated with a resource the client has 3 possibilities: request at the resource is not being HTTP/2.0
   framing layer.  The PUSH_PROMISE includes a stream identifier for an
   associated request/response exchange that supplies request header
   fields.  The pushed stream inherits all of the resource is being pushed, but request header fields
   from the data has not yet arrived associated stream with the exception of resource is being pushed, and the data has started to arrive

   When a SYN_STREAM
   identification header fields (":host", ":scheme", and HEADERS frame ":path"), which contains an Associated-To-
   Stream-ID is received, the client must not issue GET requests for the
   resource in
   are provided as part of the pushed stream, PUSH_PROMISE frame.  Pushed resources
   always have an associated ":method" of "GET".  A cache MUST store
   these inherited and instead wait for implied request header fields with the pushed stream
   to arrive.

   If a client receives a cached
   resource.

   Implementation note: With server push stream with stream-id 0, push, it is theoretically possible
   for servers to push unreasonable amounts of content or resources to
   the user-agent.  Browsers MUST
   issue a session error (Section 3.4.1) implement throttles to protect against
   unreasonable push attacks. [[anchor31: Ed: insufficiently specified
   to implement; would like to remove]]

4.3.1.  Server implementation

   A server pushes resources in association with the status code
   PROTOCOL_ERROR.

   When a client receives a SYN_STREAM request from the server without a
   client.  Prior to closing the
   ':host', ':scheme', and ':path' headers in response stream, the Name/Value section, it
   MUST reply with a RST_STREAM with error code HTTP_PROTOCOL_ERROR.

   To cancel individual server push streams, sends a
   PUSH_PROMISE for each resource that it intends to push.  The
   PUSH_PROMISE includes header fields that allow the client can issue a
   stream error (Section 3.4.2) with error code CANCEL.  Upon receipt, to identify
   the resource (":scheme", ":host", and ":port").

   A server MUST stop sending on this stream immediately (this is an
   Abrupt termination).

   To cancel all server can push streams related multiple resources in response to a request, but
   these can only be sent while the client
   may issue a response stream error (Section 3.4.2) with error code CANCEL on
   the associated-stream-id.  By cancelling that stream, the remains open.  A
   server MUST
   immediately stop sending frames for any streams with
   in-association-to for the original NOT send a PUSH_PROMISE on a half-closed stream.

   If the

   The server sends SHOULD include any header fields in a HEADER frame containing duplicate headers with PUSH_PROMISE that
   would allow a previous HEADERS frame for the same stream, cache to determine if the client must issue resource is already cached
   (see [HTTP-p6], Section 4).

   After sending a
   stream error (Section 3.4.2) with error code PROTOCOL ERROR.

   If PUSH_PROMISE, the server commences transmission of a
   pushed resource.  A pushed resource uses a server-initiated stream.
   The server sends frames on this stream in the same order as an HTTP
   response (Section 4.2.3): a HEADERS frame after sending followed by DATA frames.

   Many uses of server push are to send content that a data frame client is likely
   to discover a need for based on the same stream, content of a response
   representation.  To minimize the chances that a client MAY ignore the HEADERS frame.  Ignoring
   the HEADERS frame after will make a data frame prevents handling of HTTP's
   trailing headers
   (http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.40).

5.  Design Rationale and Notes

   Authors' notes: The notes in this section have no bearing on the
   HTTP/2.0 protocol as specified within this document, and none
   request for resources that are being pushed - causing duplicate
   copies of
   these notes should a resource to be considered authoritative about how sent by the protocol
   works.  However, these notes may prove useful in future debates about
   how to resolve protocol ambiguities or how server - a PUSH_PROMISE frame
   SHOULD be sent prior to evolve any content in the protocol
   going forward.  They may be removed before response representation
   that might allow a client to discover the final draft.

5.1.  Separation of Framing Layer pushed resource and Application Layer

   Readers may note request
   it.

   The server MUST only push resources that this specification sometimes blends could have been returned
   from a GET request.

   Note: A server does not need to have all response header fields
   available at the framing
   layer (Section 3) with requirements of time it issues a specific application - HTTP
   (Section 4).  This is reflected PUSH_PROMISE frame.  All remaining
   header fields are included in the request/response nature of HEADERS frame.  The HEADERS frame
   MUST NOT duplicate header fields from the
   streams, PUSH_PROMISE frames.

4.3.2.  Client implementation

   When fetching a resource the definition of client has 3 possibilities:

   1.  the HEADERS and compression contexts which
   are very similar to HTTP, and other areas as well.

   This blending resource is intentional - not being pushed

   2.  the primary goal of this protocol resource is
   to create a low-latency protocol for use with HTTP.  Isolating being pushed, but the
   two layers is convenient for description of data has not yet arrived

   3.  the protocol resource is being pushed, and how it
   relates to existing HTTP implementations.  However, the ability data has started to
   reuse the HTTP/2.0 framing layer is arrive

   When a non goal.

5.2.  Error handling - Framing Layer

   Error handling at the HTTP/2.0 layer splits errors into two groups:
   Those that affect an individual HTTP/2.0 stream, and those HEADERS+PRIORITY frame that do
   not.

   When contains an error is confined to a single stream, but general framing
   Associated-To-Stream-ID is received, the client MUST NOT[[anchor34:
   SHOULD NOT?]] issue GET requests for the resource in tact, HTTP/2.0 attempts to use the RST_STREAM pushed
   stream, and instead wait for the pushed stream to arrive.

   A server MUST NOT push a resource with an Associated-To-Stream-ID of
   0.  Clients MUST treat this as a mechanism to
   invalidate session error (Section 3.5.1) of
   type PROTOCOL_ERROR.

   When a client receives a PUSH_PROMISE frame from the stream but move forward server without aborting a
   the
   connection altogether.

   For errors occuring outside of ":host", ":scheme", and ":path" header fields, it MUST treat this
   as a single stream context, HTTP/2.0
   assumes error (Section 3.5.2) of type PROTOCOL_ERROR.

   To cancel individual server push streams, the entire session is hosed.  In this case, client can issue a
   stream error (Section 3.5.2) of type CANCEL.  Upon receipt, the endpoint
   detecting
   server ceases transmission of the error should initiate a connection close.

5.3.  One Connection Per Domain

   HTTP/2.0 attempts to use fewer connections than other protocols have
   traditionally used.  The rationale for this behavior is because it is
   very difficult pushed data.

   To cancel all server push streams related to provide a consistent level of service (e.g.  TCP
   slow-start), prioritization, or optimal compression when request, the client
   may issue a stream error (Section 3.5.2) of type CANCEL on the
   associated-stream-id.  By cancelling that stream, the server MUST
   immediately stop sending frames for any streams with
   in-association-to for the original stream. [[anchor35: Ed: Triggering
   side-effects on stream reset is connecting going to be problematic for the server through multiple channels.

   Through lab measurements, we have seen consistent latency benefits by
   using fewer connections
   framing layer.  Purely from a design perspective, it's a layering
   violation.  More practically speaking, the client.  The overall number of
   packets sent by HTTP/2.0 can base request stream might
   already be removed.  Special handling logic would be as much as 40% less than HTTP.
   Handling large numbers of concurrent connections on required.]]
   If the server also
   does become sends a scalability problem, and HTTP/2.0 reduces HEADERS frame containing header fields that
   duplicate values on a previous HEADERS or PUSH_PROMISE frames on the
   same stream, the client MUST treat this load.

   The use as a stream error
   (Section 3.5.2) of multiple connections is not without benefit, however.
   Because HTTP/2.0 multiplexes multiple, independent streams onto type PROTOCOL_ERROR.

   If the server sends a
   single stream, it creates HEADERS frame after sending a potential data frame for head-of-line blocking
   problems at
   the transport level.  In tests so far, same stream, the negative
   effects of head-of-line blocking (especially in client MAY ignore the presence of
   packet loss) is outweighed by HEADERS frame.  Ignoring
   the benefits HEADERS frame after a data frame prevents handling of compression HTTP's
   trailing header fields (Section 4.1.1 of [HTTP-p1]).

5.  Design Rationale and
   prioritization.

5.4.  Fixed vs Variable Length Fields Notes

   Authors' notes: The notes in this section have no bearing on the
   HTTP/2.0 favors use protocol as specified within this document, and none of fixed length 32bit fields
   these notes should be considered authoritative about how the protocol
   works.  However, these notes may prove useful in cases where
   smaller, variable length encodings could have been used.  To some, future debates about
   how to resolve protocol ambiguities or how to evolve the protocol
   going forward.  They may be removed before the final draft.

5.1.  Separation of Framing Layer and Application Layer

   Readers may note that this seems like specification sometimes blends the framing
   layer (Section 3) with requirements of a tragic waste specific application - HTTP
   (Section 4).  This is reflected in the request/response nature of bandwidth.  HTTP/2.0 choses the
   simple encoding for speed
   streams and simplicity.

   The goal of HTTP/2.0 is to reduce latency on the network.  The
   overhead definition of HTTP/2.0 frames is generally quite low.  Each data frame the HEADERS which are very similar to
   HTTP, and other areas as well.

   This blending is only an 8 byte overhead for a 1452 byte payload (~0.6%).  At intentional - the
   time primary goal of this writing, bandwidth is already plentiful, and there protocol is a
   strong trend indicating that bandwidth will continue
   to increase.
   With an average worldwide bandwidth of 1Mbps, and assuming that create a
   variable length encoding could reduce low-latency protocol for use with HTTP.  Isolating the overhead by 50%,
   two layers is convenient for description of the
   latency saved by using a variable length encoding would be less than
   100 nanoseconds.  More interesting are protocol and how it
   relates to existing HTTP implementations.  However, the effects when ability to
   reuse the larger
   encodings force a packet boundary, in which case HTTP/2.0 framing layer is a round-trip could
   be induced.  However, by addressing other aspects of non goal.

5.2.  Error handling - Framing Layer

   Error handling at the HTTP/2.0 layer splits errors into two groups:
   Those that affect an individual HTTP/2.0 stream, and TCP
   interactions, we believe this is completely mitigated.

5.5.  Compression Context(s) those that do
   not.

   When isolating the compression contexts used for communicating with
   multiple origins, we had a few choices an error is confined to make.  We could have
   maintained a map (or list) of compression contexts usable for each
   origin.  The basic case single stream, but general framing is easy - each HEADERS frame would need to
   identify the context
   in tact, HTTP/2.0 attempts to use for that frame.  However, compression
   contexts are not cheap, so the lifecycle of each context would need
   to be bounded.  For proxy servers, where we could churn through many
   contexts, this would be a concern.  We considered using RST_STREAM as a static set
   of contexts, say 16 of them, which would bound mechanism to
   invalidate the memory use.  We
   also considered dynamic contexts, which could be created on stream but move forward without aborting the fly,
   and would need to be subsequently destroyed.  All
   connection altogether.

   For errors occurring outside of these are
   complicated, and ultimately we decided that such a mechanism creates
   too many problems to solve.

   Alternatively, we've chosen single stream context, HTTP/2.0
   assumes the simple approach, which entire session is to simply
   provide a flag for resetting hosed.  In this case, the compression context.  For endpoint
   detecting the common
   case (no proxy), error should initiate a connection close.

5.3.  One Connection Per Domain

   HTTP/2.0 attempts to use fewer connections than other protocols have
   traditionally used.  The rationale for this fine behavior is because most requests are it is
   very difficult to provide a consistent level of service (e.g.  TCP
   slow-start), prioritization, or optimal compression when the same
   origin and we never need client
   is connecting to reset the context.  For cases where server through multiple channels.

   Through lab measurements, we
   are have seen consistent latency benefits by
   using two different origins over a single fewer connections from the client.  The overall number of
   packets sent by HTTP/2.0 session, we
   simply reset can be as much as 40% less than HTTP.
   Handling large numbers of concurrent connections on the compression state between each transition.

5.6.  Unidirectional streams

   Many readers notice that unidirectional streams are both server also
   does become a bit
   confusing in concept scalability problem, and also somewhat redundant.  If the recipient HTTP/2.0 reduces this load.

   The use of multiple connections is not without benefit, however.
   Because HTTP/2.0 multiplexes multiple, independent streams onto a stream doesn't wish to send data on a
   single stream, it could simply
   send creates a SYN_REPLY with the FLAG_FIN bit set.  The FLAG_UNIDIRECTIONAL
   is, therefore, not necessary.

   It is true that we don't need potential for head-of-line blocking
   problems at the UNIDIRECTIONAL markings.  It is
   added because it avoids transport level.  In tests so far, the recipient negative
   effects of pushed streams from needing
   to send a set head-of-line blocking (especially in the presence of empty frames (e.g.
   packet loss) is outweighed by the SYN_STREAM w/ FLAG_FIN) which
   otherwise serve no purpose.

5.7.  Data Compression

   Generic benefits of compression and
   prioritization.

5.4.  Fixed vs Variable Length Fields

   HTTP/2.0 favors use of data portion fixed length 32bit fields in cases where
   smaller, variable length encodings could have been used.  To some,
   this seems like a tragic waste of bandwidth.  HTTP/2.0 chooses the streams (as opposed to
   compression
   simple encoding for speed and simplicity.

   The goal of HTTP/2.0 is to reduce latency on the headers) without knowing the content network.  The
   overhead of the stream HTTP/2.0 frames is redundant.  There generally quite low.  Each data frame
   is no value in compressing only an 8 byte overhead for a stream which 1452 byte payload (~0.6%).  At the
   time of this writing, bandwidth is already compressed.  Because of this, HTTP/2.0 does allow data
   compression plentiful, and there is a
   strong trend indicating that bandwidth will continue to be optional.  We included it because study increase.
   With an average worldwide bandwidth of existing
   websites shows 1Mbps, and assuming that many sites are not a
   variable length encoding could reduce the overhead by 50%, the
   latency saved by using compression as they
   should, and users suffer because of it.  We wanted a mechanism where,
   at the HTTP/2.0 layer, site administrators variable length encoding would be less than
   100 nanoseconds.  More interesting are the effects when the larger
   encodings force a packet boundary, in which case a round-trip could simply force
   compression - it is better to compress twice than to not compress.

   Overall, however, with this feature being optional
   be induced.  However, by addressing other aspects of HTTP/2.0 and sometimes
   redundant, it is unclear if it TCP
   interactions, we believe this is useful at all.  We will likely
   remove it from the specification.

5.8. completely mitigated.

5.5.  Server Push

   A subtle but important point is that server push streams must be
   declared before the associated stream is closed.  The reason for this
   is so that proxies have a lifetime for which they can discard
   information about previous streams.  If a pushed stream could
   associate itself with an already-closed stream, then endpoints would
   not have a specific lifecycle for when they could disavow knowledge
   of the streams which went before.

6.  Security Considerations

6.1.  Use of Same-origin constraints

   This specification uses Same-origin constraints

   This specification uses the same-origin policy ([RFC6454], Section 3)
   in all cases where verification of content is required.

6.2.  Cross-Protocol Attacks

   By utilizing TLS, we believe that HTTP/2.0 introduces no new cross-
   protocol attacks.  TLS encrypts the contents of all transmission
   (except the handshake itself), making it difficult for attackers to
   control the data which could be used in a cross-protocol attack.
   [[anchor45: Issue: This is no longer true]]

6.3.  Cacheability of Pushed Resources

   Pushed resources do not have an associated request.  In order for
   existing HTTP cache control validations (such as the Vary header
   field) to work, all cached resources must have a set of request
   header fields.  For this reason, caches MUST be careful to inherit
   request header fields from the associated stream for the push.  This
   includes the Cookie header field.

   Caching resources that are pushed is possible, based on the guidance
   provided by the origin server in the Cache-Control header field.
   However, this can cause issues if a single server hosts more than one
   tenant.  For example, a server might offer multiple users each a
   small portion of its URI space.

   Where multiple tenants share space on the same server, that server
   MUST ensure that tenants are not able to push representations of
   resources that they do not have authority over.  Failure to enforce
   this would allow a tenant to provide a representation that would be
   served out of cache, overriding the same-origin policy [RFC6454] in all cases
   where verification of content actual representation that the
   authoritative tenant provides.

   Pushed resources for which an origin server is required.

6.2.  HTTP Headers and not authoritative are
   never cached or used.

7.  Privacy Considerations
7.1.  Long Lived Connections

   HTTP/2.0 Headers

   At the application level, HTTP uses name/value pairs aims to keep connections open longer between clients and
   servers in its headers.
   Because HTTP/2.0 merges order to reduce the existing HTTP headers with HTTP/2.0
   headers, there is latency when a possibility that some HTTP applications already
   use user makes a particular header name.  To avoid any conflicts, all headers
   introduced for layering HTTP request.
   The maintenance of these connections over HTTP/2.0 are prefixed with ":". ":" time could be used to
   expose private information.  For example, a user using a browser
   hours after the previous user stopped using that browser may be able
   to learn about what the previous user was doing.  This is not a valid sequence in problem
   with HTTP header naming, preventing any
   possible conflict.

6.3.  Cross-Protocol Attacks

   By utilizing TLS, we believe that HTTP/2.0 introduces no new cross-
   protocol attacks.  TLS encrypts in its current form as well, however the contents short lived
   connections make it less of all transmission
   (except a risk.

7.2.  SETTINGS frame

   The HTTP/2.0 SETTINGS frame allows servers to store out-of-band
   transmitted information about the handshake itself), making communication between client and
   server on the client.  Although this is intended only to be used to
   reduce latency, renegade servers could use it difficult for attackers as a mechanism to
   control store
   identifying information about the data which could be used client in future requests.

   Clients implementing privacy modes can disable client-persisted
   SETTINGS storage.

   Clients MUST clear persisted SETTINGS information when clearing the
   cookies.

8.  IANA Considerations

   This document establishes registries for frame types, error codes and
   settings.

8.1.  Frame Type Registry

   This document establishes a cross-protocol attack.

6.4.  Server Push Implicit Headers

   Pushed resources do not have registry for HTTP/2.0 frame types.  The
   "HTTP/2.0 Frame Type" registry operates under the "IETF Review"
   policy [RFC5226].

   Frame types are an associated request.  In order 8-bit value.  When reviewing new frame type
   registrations, special attention is advised for any frame type-
   specific flags that are defined.  Frame flags can interact with
   existing HTTP cache control validations (such as flags and could prevent the Vary header) to
   work, however, all cached resources must have a set creation of request
   headers.  For this reason, browsers MUST be careful to inherit
   request headers from the associated stream globally applicable
   flags.

   Initial values for the push.  This
   includes the 'Cookie' header.

7.  Privacy Considerations

7.1.  Long Lived Connections

   HTTP/2.0 aims to keep connections open longer between clients and
   servers "HTTP/2.0 Frame Type" registry are shown in order to reduce the latency when a user makes
   Table 1.

          +------------+------------------+---------------------+
          | Frame Type | Name             | Flags               |
          +------------+------------------+---------------------+
          | 0          | DATA             | -                   |
          | 1          | HEADERS+PRIORITY | -                   |
          | 3          | RST_STREAM       | -                   |
          | 4          | SETTINGS         | CLEAR_PERSISTED(2)  |
          | 5          | PUSH_PROMISE     | -                   |
          | 6          | PING             | PONG(2)             |
          | 7          | GOAWAY           | -                   |
          | 8          | HEADERS          | -                   |
          | 9          | WINDOW_UPDATE    | END_FLOW_CONTROL(2) |
          +------------+------------------+---------------------+

                                  Table 1

8.2.  Error Code Registry

   This document establishes a request. registry for HTTP/2.0 error codes.  The maintenance of these connections over time could be used to
   expose private information.  For example,
   "HTTP/2.0 Error Code" registry manages a user using 32-bit space.  The "HTTP/2.0
   Error Code" registry operates under the "Expert Review" policy
   [RFC5226].

   Registrations for error codes are required to include a browser
   hours after description
   of the previous user stopped using that browser may error code.  An expert reviewer is advised to examine new
   registrations for possible duplication with existing error codes.
   Use of existing registrations is to be able encouraged, but not mandated.

   New registrations are advised to learn about what provide the previous user was doing.  This following information:

   Error Code:  The 32-bit error code value.

   Name:  A name for the error code.  Specifying an error code name is
      optional.

   Description:  A description of the conditions where the error code is
      applicable.

   Specification:  An optional reference for a problem
   with HTTP in its current form as well, however specification that
      defines the short lived
   connections make it less error code.

   An initial set of error code registrations can be found in
   Section 3.5.3.

8.3.  Settings Registry

   This document establishes a risk.

7.2.  SETTINGS frame

   The registry for HTTP/2.0 SETTINGS frame allows servers to store out-of-band
   transmitted information about the communication between client and
   server on settings.  The
   "HTTP/2.0 Settings" registry manages a 24-bit space.  The "HTTP/2.0
   Settings" registry operates under the client.  Although this is intended only to be used "Expert Review" policy
   [RFC5226].

   Registrations for settings are required to
   reduce latency, renegade servers could use it as include a mechanism to store
   identifying information about description of
   the client in future requests.

   Clients implementing privacy modes, such as Google Chrome's
   "incognito mode", may wish setting.  An expert reviewer is advised to disable client-persisted SETTINGS
   storage.

   Clients MUST clear persisted SETTINGS information when clearing the
   cookies.

   TODO: Put range maximums on each type examine new
   registrations for possible duplication with existing settings.  Use
   of setting existing registrations is to limit
   inappropriate uses.

8.  Requirements Notation be encouraged, but not mandated.

   New registrations are advised to provide the following information:

   Setting:  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", 24-bit setting value.

   Name:  A name for the setting.  Specifying a name is optional.

   Flags:  Any setting-specific flags that apply, including their value
      and semantics.

   Description:  A description of the setting.  This might include the
      range of values, any applicable units and "OPTIONAL" in this
   document are how to act upon a value
      when it is provided.

   Specification:  An optional reference for a specification that
      defines the setting.

   An initial set of settings registrations can be interpreted as described found in RFC 2119 [RFC2119].
   Section 3.7.4.

9.  Acknowledgements

   This document includes substantial input from the following
   individuals:

   o  Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham, Alyssa
      Wilk, Costin Manolache, William Chan, Vitaliy Lvin, Joe Chan, Adam
      Barth, Ryan Hamilton, Gavin Peters, Kent Alstad, Kevin Lindsay,
      Paul Amer, Fan Yang, Jonathan Leighton (SPDY contributors).

   o  Gabriel Montenegro and Willy Tarreau (Upgrade mechanism)

   o  William Chan, Salvatore Loreto, Osama Mazahir, Gabriel Montenegro,
      Jitu Padhye, Roberto Peon, Rob Trace (Flow control principles) control)

   o  Mark Nottingham and Julian Reschke

10.  References
10.1.  Normative References

   [ASCII]            "US-ASCII. Coded Character Set - 7-Bit American
                      Standard Code for Information Interchange.
                      Standard ANSI X3.4-1986, ANSI, 1986.".

   [HTTP-p1]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Message Syntax and Routing",
                      draft-ietf-httpbis-p1-messaging-21
              draft-ietf-httpbis-p1-messaging-22 (work in progress), October 2012.
              February 2013.

   [HTTP-p2]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Semantics and Content",
                      draft-ietf-httpbis-p2-semantics-21
              draft-ietf-httpbis-p2-semantics-22 (work in progress), October 2012.
              February 2013.

   [HTTP-p4]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Conditional Requests",
              draft-ietf-httpbis-p4-conditional-22 (work in progress),
              February 2013.

   [HTTP-p5]  Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
              "Hypertext Transfer Protocol (HTTP/1.1): Range Requests",
              draft-ietf-httpbis-p5-range-22 (work in progress),
              February 2013.

   [HTTP-p6]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
              draft-ietf-httpbis-p6-cache-22 (work in progress),
              February 2013.

   [HTTP-p7]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Authentication",
              draft-ietf-httpbis-p7-auth-22 (work in progress),
              February 2013.

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, September 1981.

   [RFC1738]          Berners-Lee, T., Masinter, L., and M. McCahill,
                      "Uniform Resource Locators (URL)", RFC 1738,
                      December 1994.

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

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

   [RFC2616]

   [RFC3986]  Berners-Lee, T., 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.

   [RFC2617]          Franks, J., Hallam-Baker, P., Hostetler, J.,
                      Lawrence, S., Leach, P., Luotonen, A., and L.
                      Stewart, "HTTP Authentication: Basic and Digest
                      Access Authentication", Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 2617, June 1999.

   [RFC4559]          Jaganathan, K., Zhu, L., and J. Brezak, "SPNEGO-
                      based Kerberos 3986, January 2005.

   [RFC5226]  Narten, T. and NTLM HTTP Authentication H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in
                      Microsoft Windows", RFCs", BCP 26, RFC 4559, June 2006. 5226,
              May 2008.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC6454]  Barth, A., "The Web Origin Concept", RFC 6454,
              December 2011.

   [TLSNPN]   Langley, A., "TLS "Transport Layer Security (TLS) Next Protocol Negotiation",
                      draft-agl-tls-nextprotoneg-01
              Negotiation Extension", draft-agl-tls-nextprotoneg-04
              (work in progress),
                      August 2010.

   [UDELCOMPRESSION]  Yang, F., Amer, P., May 2012.

10.2.  Informative References

   [RFC1323]  Jacobson, V., Braden, B., and D. Borman, "TCP Extensions
              for High Performance", RFC 1323, May 1992.

   [TALKING]  Huang, L-S., Chen, E., Barth, A., Rescorla, E., and J. Leighton, "A
                      Methodology C.
              Jackson, "Talking to Derive SPDY's Initial Dictionary Yourself for Zlib Compression", <http://www.eecis.udel.edu/
                      ~amer/PEL/poc/pdf/SPDY-Fan.pdf>. Fun and Profit", 2011,
              <http://w2spconf.com/2011/papers/websocket.pdf>.

Appendix A.  Change Log (to be removed by RFC Editor before publication)

A.1.  Since draft-ietf-httpbis-http2-01

   Added IANA considerations section for frame types, error codes and
   settings.

   Removed data frame compression.

   Added PUSH_PROMISE.

   Added globally applicable flags to framing.

   Removed zlib-based header compression mechanism.

   Updated references.

   Clarified stream identifier reuse.

   Removed CREDENTIALS frame and associated mechanisms.

   Added advice against naive implementation of flow control.

   Added session header section.

   Restructured frame header.  Removed distinction between data and
   control frames.

   Altered flow control properties to include session-level limits.

   Added note on cacheability of pushed resources and multiple tenant
   servers.

   Changed protocol label form based on discussions.

A.2.  Since draft-ietf-httpbis-http2-00

   Changed title throughout.

   Removed section on Incompatibilities with SPDY draft#2.

   Changed INTERNAL_ERROR on GOAWAY to have a value of 2 <https://
   groups.google.com/forum/?fromgroups#!topic/spdy-dev/cfUef2gL3iU>.

   Replaced abstract and introduction.

   Added section on starting HTTP/2.0, including upgrade mechanism.

   Removed unused references.

   Added flow control principles (Section 3.5.1) 3.6.1) based on <http://
   tools.ietf.org/html/draft-montenegro-httpbis-http2-fc-principles-01>.

A.2.

A.3.  Since draft-mbelshe-httpbis-spdy-00

   Adopted as base for draft-ietf-httpbis-http2.

   Updated authors/editors list.

   Added status note.

Authors' Addresses

   Mike Belshe
   Twist

   EMail: mbelshe@chromium.org

   Roberto Peon
   Google, Inc

   EMail: fenix@google.com
   Martin Thomson (editor)
   Microsoft
   3210 Porter Drive
   Palo Alto  94043
   US

   EMail: martin.thomson@skype.net

   Alexey Melnikov (editor)
   Isode Ltd
   5 Castle Business Village
   36 Station Road
   Hampton, Middlesex  TW12 2BX
   UK

   EMail: Alexey.Melnikov@isode.com