HTTPbis Working Group                                          M. Belshe
Internet-Draft                                                     Twist
Intended status: Standards Track                                 R. Peon
Expires: November 30, 2013 January 9, 2014                                     Google, Inc
                                                         M. Thomson, Ed.
                                                               Microsoft
                                                        A. Melnikov, Ed.
                                                               Isode Ltd
                                                            May 29,
                                                            July 8, 2013

                Hypertext Transfer Protocol version 2.0
                      draft-ietf-httpbis-http2-03
                      draft-ietf-httpbis-http2-04

Abstract

   This specification describes an optimized expression of the syntax of
   the Hypertext Transfer Protocol (HTTP).  The HTTP/2.0 encapsulation
   enables more efficient use of network resources and reduced
   perception of latency by allowing header field compression and
   multiple concurrent messages on the same connection.  It also
   introduces unsolicited push of representations from servers to
   clients.

   This document is an alternative to, but does not obsolete the
   HTTP/1.1 message format or protocol.  HTTP's existing semantics
   remain unchanged.

   This version of the draft has been marked for implementation.
   Interoperability testing will occur in the HTTP/2.0 interim in
   Hamburg, DE, starting 2013-08-05.

Editorial Note (To be removed by RFC Editor)

   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/>.

   Working Group information and related documents can be found at
   <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 November 30, 2013. January 9, 2014.

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.  Conventions and Terminology  . . . . . . . . . . . . . . .  6
   2.  Starting  HTTP/2.0 Protocol Overview . . . . . . . . . . . . . . . . . .  6
     2.1.  HTTP Frames  . . . . . . . . . .  6
     2.1.  HTTP/2.0 Version Identification . . . . . . . . . . . . .  7
     2.2.  Starting HTTP/2.0 for "http:" URIs  HTTP Multiplexing  . . . . . . . . . . . .  8
     2.3.  Starting HTTP/2.0 for "https:" URIs . . . . . . . .  7
     2.3.  HTTP Semantics . . .  8
     2.4.  Starting HTTP/2.0 with Prior Knowledge . . . . . . . . . .  9
   3.  HTTP/2.0 Framing Layer . . . . . . . . .  7
   3.  Starting HTTP/2.0  . . . . . . . . . . .  9
     3.1.  Connection . . . . . . . . . . .  7
     3.1.  HTTP/2.0 Version Identification  . . . . . . . . . . . . .  9  8
     3.2.  Connection Header  Starting HTTP/2.0 for "http" URIs  . . . . . . . . . . . .  8
       3.2.1.  HTTP2-Settings Header Field  . . . . . . . . .  9
     3.3.  Framing . . . . 10
     3.3.  Starting HTTP/2.0 for "https" URIs . . . . . . . . . . . . 10
     3.4.  Starting HTTP/2.0 with Prior Knowledge . . . . . . . . . . 10
       3.3.1.  Frame
     3.5.  Connection Header  . . . . . . . . . . . . . . . . . . . . 11
   4.  HTTP Frames  . 10
       3.3.2.  Frame Size . . . . . . . . . . . . . . . . . . . . . . 12
     3.4.  Streams . . 12
     4.1.  Frame Header . . . . . . . . . . . . . . . . . . . . . . . 12
       3.4.1.  Stream Creation  . . .
     4.2.  Frame Size . . . . . . . . . . . . . . . . 13
       3.4.2.  Stream priority . . . . . . . . 13
     4.3.  Header Compression and Decompression . . . . . . . . . . . 13
       3.4.3.  Stream half-close
   5.  Streams and Multiplexing . . . . . . . . . . . . . . . . . . . 14
       3.4.4.
     5.1.  Stream close States  . . . . . . . . . . . . . . . . . . . . . . 14
     3.5.  Error Handling
       5.1.1.  Stream Identifiers . . . . . . . . . . . . . . . . . . 18
       5.1.2.  Stream Concurrency . . . . 15
       3.5.1.  Connection Error Handling . . . . . . . . . . . . . . 15
       3.5.2.  Stream Error Handling 18
     5.2.  Flow Control . . . . . . . . . . . . . . . . 16
       3.5.3.  Error Codes . . . . . . . 18
       5.2.1.  Flow Control Principles  . . . . . . . . . . . . . . 16
     3.6.  Stream . 19
       5.2.2.  Appropriate Use of Flow Control  . . . . . . . . . . . 20
     5.3.  Stream priority  . . . . . . . . 17
       3.6.1.  Flow Control Principles . . . . . . . . . . . . . 20
     5.4.  Error Handling . . 17
       3.6.2.  Appropriate Use of Flow Control . . . . . . . . . . . 18
     3.7.  Header Blocks . . . . . . . . . 21
       5.4.1.  Connection Error Handling  . . . . . . . . . . . . . 19
     3.8.  Frame Types . 21
       5.4.2.  Stream Error Handling  . . . . . . . . . . . . . . . . 22
       5.4.3.  Connection Termination . . . . . . 19
       3.8.1.  DATA Frames . . . . . . . . . . 22
   6.  Frame Definitions  . . . . . . . . . . . 20
       3.8.2.  HEADERS+PRIORITY . . . . . . . . . . . 22
     6.1.  DATA . . . . . . . . 20
       3.8.3.  RST_STREAM . . . . . . . . . . . . . . . . . . . 23
     6.2.  HEADERS  . . . 21
       3.8.4.  SETTINGS . . . . . . . . . . . . . . . . . . . . . . 23
     6.3.  PRIORITY . 21
       3.8.5.  PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . 25
       3.8.6.  PING . . . 24
     6.4.  RST_STREAM . . . . . . . . . . . . . . . . . . . . . . 26
       3.8.7.  GOAWAY . . 25
     6.5.  SETTINGS . . . . . . . . . . . . . . . . . . . . . . 26
       3.8.8.  HEADERS . . . 26
       6.5.1.  Setting Format . . . . . . . . . . . . . . . . . . . . 28
       3.8.9.  WINDOW_UPDATE 26
       6.5.2.  Defined Settings . . . . . . . . . . . . . . . . . . . 27
     6.6.  PUSH_PROMISE . 29
   4.  HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . . 32
     4.1.  Connection Management . . 27
     6.7.  PING . . . . . . . . . . . . . . . . 32
     4.2.  HTTP Request/Response . . . . . . . . . . . 29
     6.8.  GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . . 29
     6.9.  WINDOW_UPDATE  . . . . . . . . . 33
       4.2.1.  HTTP Header Fields and HTTP/2.0 Headers . . . . . . . 33
       4.2.2.  Request . . . . . . 31
       6.9.1.  The Flow Control Window  . . . . . . . . . . . . . . . 32
       6.9.2.  Initial Flow Control Window Size . . . . . . . . . . . 33
       4.2.3.  Response
       6.9.3.  Reducing the Stream Window Size  . . . . . . . . . . . 34
       6.9.4.  Ending Flow Control  . . . . . . . . . . . . . . . . . 34
     4.3.  Server Push Transactions
   7.  Error Codes  . . . . . . . . . . . . . . . . . . . . . . . . . 35
       4.3.1.  Server implementation
   8.  HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . . 36
       4.3.2.  Client implementation
     8.1.  HTTP Request/Response Exchange . . . . . . . . . . . . . . 36
       8.1.1.  Examples . . . 37
   5.  Design Rationale and Notes . . . . . . . . . . . . . . . . . . 38
     5.1.  Separation of Framing Layer and Application Layer . . 37
       8.1.2.  Request Header Fields  . . 38
     5.2.  Error handling - Framing Layer . . . . . . . . . . . . . . 39
     5.3.  One Connection per Domain 38
       8.1.3.  Response Header Fields . . . . . . . . . . . . . . . . 39
     5.4.  Fixed vs Variable Length Fields
       8.1.4.  GZip Content-Encoding  . . . . . . . . . . . . . 39
     5.5. . . . 40
       8.1.5.  Request Reliability Mechanisms in HTTP/2.0 . . . . . . 40
     8.2.  Server Push  . . . . . . . . . . . . . . . . . . . . . . . 40
   6.  Security Considerations 41
   9.  Additional HTTP Requirements/Considerations  . . . . . . . . . 43
     9.1.  Frame Size Limits for HTTP . . . . . . . . . . 40
     6.1.  Server Authority and Same-Origin . . . . . . 43
     9.2.  Connection Management  . . . . . . . 40
     6.2.  Cross-Protocol Attacks . . . . . . . . . . . 43
   10. Security Considerations  . . . . . . . . 40
     6.3.  Cacheability of Pushed Resources . . . . . . . . . . . 43
     10.1. Server Authority and Same-Origin . . 41
   7.  Privacy Considerations . . . . . . . . . . . 43
     10.2. Cross-Protocol Attacks . . . . . . . . . . . 41
     7.1.  Long Lived Connections . . . . . . . 44
     10.3. Cacheability of Pushed Resources . . . . . . . . . . . 41
     7.2.  SETTINGS frame . . 44
   11. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 41
   8. 45
   12. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 42
     8.1. 45
     12.1. Frame Type Registry  . . . . . . . . . . . . . . . . . . . 42
     8.2. 45
     12.2. Error Code Registry  . . . . . . . . . . . . . . . . . . . 43
     8.3. 46
     12.3. Settings Registry  . . . . . . . . . . . . . . . . . . . . 43
   9. 47
     12.4. HTTP2-Settings Header Field Registration . . . . . . . . . 47
   13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 44
   10. 48
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 44
     10.1. 48
     14.1. Normative References . . . . . . . . . . . . . . . . . . . 44
     10.2. 48
     14.2. Informative References . . . . . . . . . . . . . . . . . . 45 50
   Appendix A.  Change Log (to be removed by RFC Editor before
                publication)  . . . . . . . . . . . . . . . . . . . . 46 50
     A.1.  Since draft-ietf-httpbis-http2-02 draft-ietf-httpbis-http2-03  . . . . . . . . . . . . 46 50
     A.2.  Since draft-ietf-httpbis-http2-01 draft-ietf-httpbis-http2-02  . . . . . . . . . . . . 46 50
     A.3.  Since draft-ietf-httpbis-http2-00 draft-ietf-httpbis-http2-01  . . . . . . . . . . . . 47 50
     A.4.  Since draft-mbelshe-httpbis-spdy-00 draft-ietf-httpbis-http2-00  . . . . . . . . . . . 47

1.  Introduction . 51
     A.5.  Since draft-mbelshe-httpbis-spdy-00  . . . . . . . . . . . 51

1.  Introduction

   The Hypertext Transfer Protocol (HTTP) is a wildly successful
   protocol.  However, the HTTP/1.1 message encapsulation format ([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.

   In particular, HTTP/1.0 only allows one request to be delivered at a
   time on a given connection.  HTTP/1.1 pipelining only partially
   addressed request concurrency, and is not widely deployed.
   Therefore, clients that need to make many requests (as is common on
   the Web) typically use multiple connections to a server in order to
   reduce perceived latency.

   Furthermore, HTTP/1.1 header fields are often repetitive and verbose,
   which, in addition to generating more or larger network packets, can
   cause the small initial TCP congestion window to quickly fill.  This
   can result in excessive latency when multiple requests are made on a
   single new TCP connection.

   This document addresses these issues by defining an optimized mapping
   of HTTP's semantics to an underlying connection.  Specifically, it
   allows interleaving of request and response messages on the same
   connection and uses an efficient coding for HTTP header fields.  It
   also allows prioritization of requests, letting more important
   requests complete more quickly, further improving perceived
   performance.

   The resulting protocol is designed to have be more friendly to the
   network, because fewer TCP connections can be used, in comparison to
   HTTP/1.x.  This means less competition with other flows, and longer-
   lived connections, which in turn leads to better utilization of
   available network capacity.

   Finally, this encapsulation also enables more scalable processing of
   messages through use of binary message framing.

1.1.  Document Organization

   The HTTP/2.0 Specification is split into three parts: starting
   HTTP/2.0 (Section 2), 3), which covers how a HTTP/2.0 connection is
   initiated; a framing layer (Section 3), 4), which multiplexes a single
   TCP connection into independent frames of various types; and an HTTP
   layer (Section 4), 8), which specifies the mechanism for expressing HTTP
   interactions using the framing layer.  While some of the framing
   layer concepts are isolated from HTTP, 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.  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 connection.

   connection:  A transport-level connection between two endpoints.

   endpoint:  Either the client or server of the connection.

   frame:  The smallest unit of communication within an HTTP/2.0
      connection, consisting of a header and a variable-length sequence
      of bytes structured according to the frame type.

   peer:  An endpoint.  When discussing a particular endpoint, "peer"
      refers to the endpoint that is remote to the primary subject of
      discussion.

   receiver:  An endpoint that is receiving frames.

   sender:  An endpoint that is transmitting frames.

   server:  The endpoint which did not initiate the HTTP connection.

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

   stream:  A bi-directional flow of frames across a virtual channel
      within the HTTP/2.0 connection.

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

2.  HTTP/2.0 Protocol Overview

   HTTP/2.0 provides an optimized transport for HTTP semantics.

   An HTTP/2.0 connection is an application level protocol running on
   top of a TCP connection ([RFC0793]).  The client is the TCP
   connection initiator.

   This document describes the HTTP/2.0 protocol using a logical
   structure that is formed of three parts: framing, streams, and
   application mapping.  This structure is provided primarily as an aid
   to specification, implementations are free to diverge from this
   structure as necessary.

2.1.  HTTP Frames

   HTTP/2.0 provides an efficient serialization of HTTP semantics.  HTTP
   requests and responses are encoded into length-prefixed frames (see
   Section 4.1).

   HTTP headers are compressed into a series of frames that contain
   header block fragments (see Section 4.3).

2.2.  HTTP Multiplexing

   HTTP/2.0 provides the ability to multiplex multiple HTTP requests and
   responses onto a single connection.  Multiple requests or responses
   can be sent concurrently on a connection using streams (Section 5).
   In order to maintain independent streams, flow control and
   prioritization are necessary.

2.3.  HTTP Semantics

   HTTP/2.0 defines how HTTP requests and responses are mapped to
   streams (see Section 8) and introduces a new interaction model,
   server push (Section 8.2).

3.  Starting HTTP/2.0

   HTTP/2.0 uses the same "http:" "http" and "https:" "https" URI schemes used by
   HTTP/1.1.  HTTP/2.0 shares the same default port numbers: 80 for
   "http" URIs and 443 for "https" URIs.  As a result, implementations
   processing requests for target resource URIs like
   "http://example.org/foo" or "https://example.com/bar" are required to
   first discover whether the upstream server (the immediate peer to
   which the client wishes to establish a connection) supports HTTP/2.0.

   The means by which support for HTTP/2.0 is determined is different
   for "http" and "https" URIs.  Discovery for "https:" "http" URIs is described
   in Section 2.3. 3.2.  Discovery for "http" "https" URIs is described
   here.

2.1. in
   Section 3.3.

3.1.  HTTP/2.0 Version Identification

   The protocol defined in this document is identified using the string
   "HTTP/2.0".  This identification is used in the HTTP/1.1 Upgrade
   header field, in the TLS application layer protocol negotiation
   extension [TLSALPN] field field, and other places where protocol
   identification is required.

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

   [[anchor3:

   [[anchor6: 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-draft-03/2.0".

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

2.2.

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

   A client that makes a request to an "http:" "http" URI without prior
   knowledge about support for HTTP/2.0 uses the HTTP Upgrade mechanism
   (Section 6.7 of [HTTP-p1]).  The client makes an HTTP/1.1 request
   that includes an Upgrade header field identifying HTTP/2.0.  The
   HTTP/1.1 request MUST include an HTTP2-Settings (Section 3.2.1)
   header field.

   For example:

     GET /default.htm HTTP/1.1
     Host: server.example.com
     Connection: Upgrade Upgrade, HTTP2-Settings
     Upgrade: HTTP/2.0

   A server that does not support
     HTTP2-Settings: <base64url encoding of HTTP/2.0 can respond to the SETTINGS payload>

   Requests that contain a request as
   though entity body MUST be sent in their
   entirety before the Upgrade client can send HTTP/2.0 frames.  This means that
   a large request entity can block the use of the connection until it
   is completely sent.

      If concurrency of an initial request with subsequent requests is
      important, a small request can be used to perform the upgrade to
      HTTP/2.0, at the cost of an additional round trip.

   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 accepts 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 connection ...

   The first HTTP/2.0 frame sent by the server is a SETTINGS frame
   (Section 3.8.4). 6.5).  Upon receiving the 101 response, the client sends a
   connection header (Section 3.2), 3.5), which includes a SETTINGS frame.

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

   A client that makes a

   The HTTP/1.1 request to an "https:" URI without that is sent prior
   knowledge about support for HTTP/2.0 uses TLS [RFC5246] to upgrade is associated with
   stream 1 and is assigned the
   application layer protocol negotiation extension [TLSALPN].

   Once TLS negotiation highest possible priority.  Stream 1 is complete, both
   implicitly half closed from the client and toward the server, since the
   request is completed as an HTTP/1.1 request.  After commencing the server send
   a connection header (Section 3.2).

2.4.  Starting
   HTTP/2.0 with Prior Knowledge connection, stream 1 is used for the response.

3.2.1.  HTTP2-Settings Header Field

   A client can learn that a particular server supports HTTP/2.0 by
   other means.  A client MAY immediately send HTTP/2.0 frames upgrades from HTTP/1.1 to HTTP/2.0 MUST include an
   "HTTP2-Settings" header field.  The "HTTP2-Settings" header field is
   a
   server hop-by-hop header field that is known to support HTTP/2.0.  This only affects includes settings that govern the
   resolution of "http:" URIs, servers supporting
   HTTP/2.0 are required
   to support protocol negotiation connection, provided in TLS [TLSALPN] for "https:" URIs.

   Prior support for HTTP/2.0 anticipation of the server accepting
   the request to upgrade.  A server MUST reject an attempt to upgrade
   if this header is not present.

     HTTP2-Settings    = token68

   The content of the "HTTP2-Settings" header field is the payload of a strong signal that
   SETTINGS frame (Section 6.5), encoded as a base64url string (that is,
   the URL- and filename-safe Base64 encoding described in Section 5 of
   [RFC4648], with any trailing '=' characters omitted).  The ABNF
   [RFC5234] production for "token68" is defined in Section 2.1 of
   [HTTP-p7].

   The client MUST include values for the following settings
   (Section 6.5.1):

   o  SETTINGS_MAX_CONCURRENT_STREAMS

   o  SETTINGS_INITIAL_WINDOW_SIZE

   As a hop-by-hop header field, the "Connection" header field MUST
   include a value of "HTTP2-Settings" in addition to "Upgrade" when
   upgrading to HTTP/2.0.

   A server decodes and interprets these values as it would any other
   SETTINGS frame.  Providing these values in the Upgrade request
   ensures that the protocol does not require default values for the
   above settings, and gives a client an opportunity to provide other
   settings prior to receiving any frames from the server.

3.3.  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 the
   application layer protocol negotiation extension [TLSALPN].

   Once TLS negotiation is complete, both the client and the server send
   a connection header (Section 3.5).

3.4.  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, after the connection header
   (Section 3.5).  This only affects the resolution of "http" URIs;
   servers supporting HTTP/2.0 are required to support protocol
   negotiation in TLS [TLSALPN] for "https" URIs.

   Prior support for HTTP/2.0 is not a strong signal that a given server
   will support HTTP/2.0 for future connections.  It is possible for
   server configurations to change or for configurations to differ
   between instances in clustered server.  Interception proxies (a.k.a.
   "transparent" proxies) are another source of variability.

3.  HTTP/2.0 Framing Layer

3.1.

3.5.  Connection

   The HTTP/2.0 connection is an Application Level protocol running on
   top Header

   Upon establishment of a TCP connection ([RFC0793]).  The client is the TCP
   connection initiator.

   HTTP/2.0 connections are persistent.  That is, for best performance,
   it is expected a clients will not close connections until it is
   determined that no further communication with a server is necessary
   (for example, when a user navigates away from a particular web page),
   or until the server closes the connection.

   Servers are encouraged to maintain open connections for as long as
   possible, but are permitted to terminate idle connections if
   necessary.  When either endpoint chooses to close the transport-level
   TCP connection, the terminating endpoint MUST first send a GOAWAY
   (Section 3.8.7) frame so that both endpoints can reliably determine
   whether previously sent frames have been processed and gracefully
   complete or terminate any necessary remaining tasks.

3.2.  Connection Header

   Upon establishment of a TCP connection and determination that and determination that
   HTTP/2.0 will be used by both peers to communicate, peers, each endpoint MUST send a
   connection header as a final confirmation and to establish the default parameters
   initial settings for the HTTP/2.0 connection.

   The client connection header is a sequence of 24 octets (in octets, which in hex
   notation)

   464f4f202a20485454502f322e300d0a0d0a42410d0a0d0a
   notation are:

     505249202a20485454502f322e300d0a0d0a534d0d0a0d0a

   (the string "FOO "PRI * HTTP/2.0\r\n\r\nBA\r\n\r\n") HTTP/2.0\r\n\r\nSM\r\n\r\n") followed by a
   SETTINGS frame (Section 3.8.4). 6.5).  The client sends the client connection
   header immediately upon receipt of a 101 Switching Protocols response
   (indicating a successful upgrade), or after receiving a TLS Finished
   message from the server.  If starting an HTTP/2.0 connection with
   prior knowledge of server support for the protocol, the client
   connection header is sent upon connection establishment.

      The client connection header is selected so that a large
      proportion of HTTP/1.1 or HTTP/1.0 servers and intermediaries do
      not attempt to process further frames.  Note that this does not
      address the concerns raised in [TALKING].

   The server connection header consists of just a SETTINGS frame
   (Section 3.8.4) 6.5) that MUST be the first frame the server sends in the
   HTTP/2.0 connection.

   To avoid unnecessary latency, clients are permitted to send
   additional frames to the server immediately after sending the client
   connection header, without waiting to receive the server connection
   header.  It is important to note, however, that the server connection
   header SETTINGS frame might include parameters that necessarily alter
   how a client is expected to communicate with the server.  Upon
   receiving the SETTINGS frame, the client is expected to honor any
   parameters established.

   Clients and servers MUST terminate the TCP connection if either peer
   does not begin with a valid connection header.  A GOAWAY frame
   (Section 3.8.7) 6.8) MAY be omitted if it is clear that the peer is not
   using HTTP/2.0.

3.3.  Framing

4.  HTTP Frames

   Once the HTTP/2.0 connection is established, clients and servers endpoints can begin
   exchanging frames.

3.3.1.

4.1.  Frame Header

   HTTP/2.0

   All frames share a common base format consisting of begin with an 8-byte 8-octet header followed by 0 to 65535 bytes a payload of data.
   between 0 and 65,535 octets.

     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)   |
    +-+-------------+---------------+-------------------------------+
    |R|                 Stream Identifier (31)                      |
    +-+-------------------------------------------------------------+
    |                   Frame Data Payload (0...)                      ...
    +---------------------------------------------------------------+

                               Frame Header

   The fields of the frame header are defined as:

   Length:  The length of the frame data payload expressed as an unsigned 16-bit 16-
      bit integer.  The 8 bytes octets of the frame header are not included in
      this value.

   Type:  The 8-bit type of the frame.  The frame type determines how
      the remainder of the frame header and data payload are interpreted.
      Implementations MUST ignore unsupported and unrecognized frame
      types.

   Flags:  An 8-bit field reserved for frame-type specific boolean
      flags.

      The least significant bit (0x1) - the FINAL bit - is defined for
      all frame types as an indication that this frame is the last the
      endpoint will send for the identified stream.  Setting this flag
      causes the stream to enter the half-closed state (Section 3.4.3).
      Implementations MUST process the FINAL bit for all frames whose
      stream identifier field is not 0x0.  The FINAL bit MUST NOT be set
      on frames that use a stream identifier of 0.

      The remaining flags can be

      Flags are assigned semantics specific to the indicated frame type.
      Flags that have no defined semantics for a particular frame type
      MUST be ignored, and MUST be left unset (0) when sending.

   R: A reserved 1-bit field.  The semantics of this bit are undefined
      and the bit MUST remain unset (0) when sending and MUST be ignored
      when receiving.

   Stream Identifier:  A 31-bit stream identifier (see Section 3.4.1). 5.1.1).
      A value 0 is reserved for frames that are associated with the
      connection as a whole as opposed to an individual stream.

   The structure and content of the remaining frame data payload is dependent entirely
   on the frame type.

3.3.2.

4.2.  Frame Size

   Implementations with limited resources might not be capable

   The maximum size of
   processing large a frame sizes.  Such implementations MAY choose to
   place additional limits on the maximum payload varies by frame size.  However, all type and use.
   The absolute maximum size is 65,535 octets.  All implementations MUST
   SHOULD be capable of receiving and minimally processing frames
   containing at least 8192 octets of data. [[anchor6: Ed.  Question:
   Does this minimum include the 8-byte header or just the frame data?]]

   An implementation MUST terminate a stream immediately if it is unable up to process a frame due it's
   this size.  This is done by sending an
   RST_STREAM frame (Section 3.8.3) containing the FRAME_TOO_LARGE error
   code.

   [[anchor7: <https://github.com/http2/http2-spec/issues/28>: Need a
   way to signal the maximum

   Certain frame size; no way to RST_STREAM types, such as PING (see Section 6.7), impose
   additional limits on non-
   stream-related frames.]]

3.4.  Streams

   A "stream" is an independent, bi-directional sequence of frames
   exchanged between the client and server within an HTTP/2.0
   connection.  Streams have several important characteristics:

   o  Streams can be established and used unilaterally or shared by
      either the client or server.

   o  Streams can be rejected or cancelled by either endpoint.

   o  Multiple types amount of frames payload data allowed.  Likewise,
   additional size limits can be sent set by either specific application uses (see
   Section 9).

   If a frame size exceeds any defined limit, or is too small to contain
   mandatory frame data, the endpoint within MUST send a
      single stream.

   o  The order FRAME_TOO_LARGE error.
   Frame size errors in which frames are sent within that affect connection-level state MUST
   be treated as a stream is significant.
      Recipients are required to process frames connection error (Section 5.4.1).

4.3.  Header Compression and Decompression

   A header in the order they are
      received.

   o  Streams optionally carry HTTP/2.0 is a set of name-value header pairs that pair with one or more associated
   values.  They are
      expressed used within the headers block of HEADERS+PRIORITY, HEADERS,
      or PUSH_PROMISE frames.

   o  A single HTTP/2.0 connection can contain multiple concurrently
      active streams, with either endpoint interleaving frames from
      multiple streams.

3.4.1.  Stream Creation

   There is no coordination or shared action between the client HTTP request and response messages as
   well as server required to create a stream.  Rather, new streams are
   established by sending a frame whose stream identifier field
   references a previously unused stream identifier.

   All streams push operations (see Section 8.2).

   Header sets are identified by an unsigned 31-bit integer.  Streams
   initiated by a client use odd numbered stream identifiers; those
   initiated by the server use even numbered stream identifiers.  A
   stream identifier logical collections of zero MUST NOT be used to establish a new stream.

   The identifier of a newly established stream MUST be numerically
   greater than all previously established streams from that endpoint
   within or more header fields
   arranged at the HTTP/2.0 application layer.  When transmitted over a
   connection, unless the identifier has been
   reserved using a PUSH_PROMISE (Section 3.8.5) frame.  An endpoint
   that receives an unexpected stream identifier MUST respond with header set is serialized into a
   connection error (Section 3.5.1) of type PROTOCOL_ERROR.

   A peer can limit the total number of concurrently active streams header block using the SETTINGS_MAX_CONCURRENT_STREAMS parameters within a
   SETTINGS frame.
   HTTP Header Compression [COMPRESSION].  The maximum concurrent streams setting serialized header block
   is specific
   to each endpoint then divided into one or more octet sequences, called header block
   fragments, and applies only to the peer.  That is, clients
   specify transmitted within the maximum number payload of concurrent streams HEADERS
   (Section 6.2) or PUSH_PROMISE (Section 6.6) frames.  The receiving
   endpoint reassembles the server can
   initiate, and servers specify header block by concatenating the maximum number of concurrent
   streams individual
   fragments, then decompresses the client block to reconstruct the header set.

   Header block fragments can initiate.  Peer endpoints MUST NOT exceed this
   limit.  All concurrently active streams initiated by an endpoint,
   including streams that are half-open (Section 3.4.3) in any
   direction, count toward that endpoint's limit.

   Stream identifiers cannot only be reused within a connection.  Long-lived
   connections can cause an endpoint to exhaust sent as the available range payload of
   stream identifiers. HEADERS or
   PUSH_PROMISE frames.

   A client that compressed and encoded header block is unable to establish a new
   stream identifier can establish a new connection for new streams.

   Either endpoint can request transmitted in one or more
   HEADERS or PUSH_PROMISE frames.  If the early termination number of an unwanted
   stream by sending an RST_STREAM frame (Section 3.5.2) with an error
   code octets in the block
   is greater than the space remaining in the frame, the block is
   divided into multiple fragments, which are then transmitted in
   multiple frames.

   Header blocks MUST be transmitted as a contiguous sequence of either REFUSED_STREAM (if frames,
   with no interleaved frames have been processed) of any other type, or
   CANCEL (if at least one from any other
   stream.  The last frame has been processed).  Such termination
   might not take effect immediately as the peer might have sent
   additional in a sequence of HEADERS frames on the stream prior to receiving MUST have the termination
   request.

3.4.2.  Stream priority
   END_HEADERS flag set.  The endpoint establishing a new stream can assign last frame in a priority for sequence of PUSH_PROMISE
   frames MUST have the
   stream.  Priority is represented as an unsigned 31-bit integer. 0
   represents END_PUSH_PROMISE flag set.

   HEADERS and PUSH_PROMISE frames carry data that can modify the highest priority
   compression context maintained by a receiver.  An endpoint receiving
   HEADERS or PUSH_PROMISE frames MUST reassemble header blocks and 2^31-1 represents
   perform decompression even if the lowest
   priority.

   The purpose of this value frames are to be discarded, which
   is likely to allow the initiating endpoint to
   request that frames for the occur after a stream be processed is reset.  A receiver MUST
   terminate the connection with higher priority
   relative to any other concurrently active streams.  That is, a connection error (Section 5.4.1) of
   type COMPRESSION_ERROR, if it does not decompress a header block.

5.  Streams and Multiplexing

   A "stream" is an
   endpoint receives interleaved independent, bi-directional sequence of HEADER and
   DATA frames for exchanged between the client and server within an
   HTTP/2.0 connection.  Streams have several important characteristics:

   o  A single HTTP/2.0 connection can contain multiple concurrently
      active streams, the with either endpoint ought to make a best-effort attempt at processing interleaving frames for
   higher priority streams before processing those for lower priority from
      multiple streams.

   Explicitly setting the priority for a stream does not guarantee any
   particular processing order for

   o  Streams can be established and used unilaterally or shared by
      either the stream relative to any other
   stream.  Nor is there is any mechanism provided client or server.

   o  Streams can be closed by either endpoint.

   o  The order in which the
   initiator of frames are sent within a stream can force or require a receiving endpoint to is significant.
      Recipients process frames from one stream before processing frames from another.

3.4.3.  Stream half-close

   When in the order they are received.

   o  Streams are identified by an integer.  Stream identifiers are
      assigned to streams by the endpoint sends that initiates a frame for stream.

5.1.  Stream States

   The lifecycle of a stream with the FINAL flag set,
   the stream is considered to be half-closed for that endpoint.
   Subsequent frames MUST NOT be sent by that endpoint for the half
   closed stream for the remaining duration of the HTTP/2.0 connection.
   When both endpoints shown in Figure 1.

                          +--------+
                    PP    |        |    PP
                 ,--------|  idle  |--------.
                /         |        |         \
               v          +--------+          v
        +----------+          |           +----------+
        |          |          | H         |          |
    ,---| reserved |          |           | reserved |---.
    |   | (local)  |          v           | (remote) |   |
    |   +----------+      +--------+      +----------+   |
    |      |          ES  |        |  ES          |      |
    |      | H    ,-------|  open  |-------.      | H    |
    |      |     /        |        |        \     |      |
    |      v    v         +--------+         v    v      |
    |   +----------+          |           +----------+   |
    |   |   half   |          |           |   half   |   |
    |   |  closed  |          | R         |  closed  |   |
    |   | (remote) |          |           | (local)  |   |
    |   +----------+          |           +----------+   |
    |        |                v                 |        |
    |        |  ES / R    +--------+  ES / R    |        |
    |        `----------->|        |<-----------'        |
    |  R                  | closed |                  R  |
    `-------------------->|        |<--------------------'
                          +--------+

                          Figure 1: Stream States

   Both endpoints have sent frames with the FINAL flag set, the
   stream is considered to be fully closed.

   If an endpoint receives additional frames for a stream that was
   previously half-closed by the sending peer, subjective view of the recipient MUST
   respond with state of a stream error (Section 3.5.2) of type STREAM_CLOSED.

   An endpoint that has
   could be different when frames are in transit.  Endpoints do not yet half-closed a stream
   coordinate the creation of streams, they are created unilaterally by sending
   either endpoint.  The negative consequences of a mismatch in states
   are limited to the
   FINAL flag can continue "closed" state after sending RST_STREAM, where
   frames on the stream.

   It is not necessary for an endpoint to half-close a stream might be received for which
   it has not sent any frames.  This allows endpoints to use fully
   unidirectional streams that do not require explicit action or
   acknowledgement from the receiver.

3.4.4.  Stream close some time after closing.

   Streams can be terminated in have the following ways:

   Normal termination:  Normal stream termination occurs when both
      client and server have half-closed states:

   idle:
      All streams start in the stream by sending "idle" state.  In this state, no frames
      have been exchanged.

      The following transitions are valid from this state:

      *  Sending or receiving a HEADERS frame
      containing a FINAL flag (Section 3.3.1).

   Half-close on unidirectional stream:  A causes the stream that only has frames
      sent in one direction can be tentatively considered to be closed
      once
         become "open".  The stream identifier is selected as described
         in Section 5.1.1.

      *  Sending a PUSH_PROMISE frame containing a FINAL flag is sent. marks the associated stream for
         later use.  The active sender
      on stream state for the reserved stream MUST be prepared
         transitions to receive frames after closing the
      stream.

   Abrupt termination:  Either peer can send "reserved (local)".

      *  Receiving a RST_STREAM control PUSH_PROMISE frame
      at any time to terminate an active stream.  RST_STREAM contains an
      error code to indicate marks the reason for termination.  A RST_STREAM
      indicates that associated stream as
         reserved by the sender will transmit no further data on remote peer.  The state of the stream and that becomes
         "reserved (remote)".

   reserved (local):
      A stream in the receiver "reserved (local)" state is advised to cease transmission on
      it.

      The sender of one that has been
      promised by sending a RST_STREAM PUSH_PROMISE frame.  A PUSH_PROMISE frame MUST allow for frames
      reserves an idle stream by associating the stream with an open
      stream that have
      already been sent was initiated by the remote peer prior to the RST_STREAM being
      processed.  If in-transit frames alter connection (see Section 8.2).

      In this state, these
      frames cannot be safely discarded.  See Stream Error Handling
      (Section 3.5.2) for more details.

   TCP connection teardown:  If the TCP connection is torn down while
      un-closed streams exist, then only the following transitions are possible:

      *  The endpoint MUST assume that can send a HEADERS frame.  This causes the stream was abnormally interrupted and may be incomplete.

3.5.  Error Handling

   HTTP/2.0 framing permits two classes of error:

   o  An error condition that renders the entire connection unusable is
      a connection error.

   o  An error
         to open in an individual stream is a stream error.

3.5.1.  Connection Error Handling

   A connection error is any error which prevents further processing of
   the framing layer or which corrupts any connection "half closed (remote)" state.

   An

      *  Either endpoint that encounters a connection error MUST first can send a
   GOAWAY (Section 3.8.7) RST_STREAM frame with to cause the stream identifier of
         to become "closed".  This releases the last stream that it successfully received from its peer.  The GOAWAY frame
   includes an error code that indicates why the connection is
   terminating.  After sending the GOAWAY frame, the reservation.

      An endpoint MUST close
   the TCP connection.

   It is possible that NOT send any other type of frame in this state.

   reserved (remote):
      A stream in the GOAWAY will not be reliably received "reserved (remote)" state has been reserved by the
   receiving endpoint. a
      remote peer.

      In this state, only the event of following transitions are possible:

      *  Receiving a connection error, GOAWAY only
   provides HEADERS frame causes the stream to transition to
         "half closed (local)".

      *  Either endpoint can send a best-effort attempt RST_STREAM frame to communicate with cause the peer about why stream
         to become "closed".  This releases the connection stream reservation.

      Receiving any other type of frame MUST be treated as a stream
      error (Section 5.4.2) of type PROTOCOL_ERROR.

   open:
      The "open" state is being terminated.

   An where both peers can send frames.  In this
      state, sending peers observe advertised stream level flow control
      limits (Section 5.2).

      From this state either endpoint can end send a connection at any time.  In particular, frame with a END_STREAM
      flag set, which causes the stream to transition into one of the
      "half closed" states: an endpoint MAY choose to treat sending a END_STREAM flag causes
      the stream error as state to become "half closed (local)"; an endpoint
      receiving a connection error if END_STREAM flag causes the error is recurrent.  Endpoints SHOULD stream state to become
      "half closed (remote)".

      Either endpoint can send a GOAWAY RST_STREAM frame from this state,
      causing it to transition immediately to "closed".

   half closed (local):
      A stream that is "half closed (local)" cannot be used for sending
      frames.

      A stream transitions from this state to "closed" when a frame that
      contains a END_STREAM flag is received, or when
   ending either peer sends
      a connection, as long as circumstances permit it.

3.5.2.  Stream Error Handling RST_STREAM frame.

   half closed (remote):
      A stream error that is "half closed (remote)" is no longer being used by
      the peer to send frames.  In this state, an error related endpoint is no longer
      obligated to maintain a specific stream identifier
   that does not affect processing of other streams at the framing
   layer.

   An receiver flow control window if it
      performs flow control.

      If an endpoint receives additional frames for a stream that detects is in
      this state it MUST respond with a stream error sends a RST_STREAM (Section 3.8.3) frame that contains the stream identifier 5.4.2) of the
      type STREAM_CLOSED.

      A stream where the error occurred.  The RST_STREAM can transition from this state to "closed" by sending a
      frame includes an
   error code that indicates the type of error.

   A contains a END_STREAM flag, or when either peer sends a
      RST_STREAM frame.

   closed:
      The "closed" state is the last frame that an terminal state.

      An endpoint can MUST NOT send frames on a closed stream.
   The peer  An endpoint
      that sends the receives a frame after receiving a RST_STREAM or a frame
      containing a END_STREAM flag on that stream MUST be prepared to receive
   any frames treat that were as a
      stream error (Section 5.4.2) of type STREAM_CLOSED.

      If this state is reached as a result of sending a RST_STREAM
      frame, the peer that receives the RST_STREAM might have already
      sent - or enqueued for sending by the remote peer.
   These - frames can be ignored, except where they modify connection
   state (such as on the state maintained for header compression
   (Section 3.7)).

   Normally, an endpoint SHOULD NOT send more than one RST_STREAM frame
   for any stream.  However, an stream that cannot
      be withdrawn.  An endpoint MAY send additional that sends a RST_STREAM frame MUST
      ignore frames if that it receives frames on a closed stream streams after more than it has sent
      a
   round trip time.  This behavior is permitted to deal with misbehaving
   implementations. RST_STREAM frame.  An endpoint MUST NOT send a RST_STREAM in response to an RST_STREAM
   frame, MAY choose to avoid looping.

3.5.3.  Error Codes

   Error codes are 32-bit fields that are used in RST_STREAM limit the period
      over which it ignores frames and GOAWAY treat frames to convey the reasons for the stream or connection that arrive after
      this time as being in error.

   Error codes share

      An endpoint might receive a common code space.  Some error codes only apply
   to specific conditions and have no defined semantics in certain PUSH_PROMISE frame
   types.

   The following error codes after it sends
      RST_STREAM.  PUSH_PROMISE causes a stream to become "reserved".
      If promised streams are defined:

   NO_ERROR (0):  The associated condition is not as desired, a result RST_STREAM can be used to
      close any of those streams.

5.1.1.  Stream Identifiers

   Streams are identified with an
      error.  For example, unsigned 31-bit integer.  Streams
   initiated by a GOAWAY might include this code to indicate
      graceful shutdown client MUST use odd-numbered stream identifiers; those
   initiated by the server MUST use even-numbered stream identifiers.  A
   stream identifier of a connection.

   PROTOCOL_ERROR (1):  The endpoint detected an unspecific protocol
      error.  This error zero (0x0) is used for use when connection control
   message; the stream identifier zero MUST NOT be used to establish a more specific error code is
      not available.

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

   FLOW_CONTROL_ERROR (3):
   new stream.

   The endpoint detected that its peer violated identifier of a newly established stream MUST be numerically
   greater than all streams that the flow control protocol.

   INVALID_STREAM (4):  The initiating endpoint received has opened or
   reserved.  This governs streams that are opened using a HEADERS frame for an inactive
      stream.

   STREAM_CLOSED (5):  The
   and streams that are reserved using PUSH_PROMISE.  An endpoint received that
   receives an unexpected stream identifier MUST respond with a frame after
   connection error (Section 5.4.1) of type PROTOCOL_ERROR.

   Stream identifiers cannot be reused.  Long-lived connections can
   result in endpoint exhausting the available range of stream
   identifiers.  A client that is unable to establish a new stream was
      half-closed.

   FRAME_TOO_LARGE (6):
   identifier can establish a new connection for new streams.

5.1.2.  Stream Concurrency

   A peer can limit the number of concurrently active streams using the
   SETTINGS_MAX_CONCURRENT_STREAMS parameters within a SETTINGS frame.
   The maximum concurrent streams setting is specific to each endpoint received a frame
   and applies only to the peer that was larger
      than receives the setting.  That is,
   clients specify the maximum size number of concurrent streams the server
   can initiate, and servers specify the maximum number of concurrent
   streams the client can initiate.  Endpoints MUST NOT exceed the limit
   set by their peer.

   Streams that it supports.

   REFUSED_STREAM (7):  The are in the "open" state, or either of the "half closed"
   states count toward the maximum number of streams that an endpoint is refusing
   permitted to open.  Streams in any of these three states count toward
   the stream before
      processing its payload.

   CANCEL (8):  Used by limit advertised in the creator SETTINGS_MAX_CONCURRENT_STREAMS setting
   (see Section 6.5.2).

   Streams in either of the "reserved" states do not count as open, even
   if a stream small amount of application state is retained to indicate ensure that the
   promised stream is no longer needed.

   COMPRESSION_ERROR (9):  The endpoint is unable to maintain the
      compression context for the connection.

3.6.  Stream can be successfully used.

5.2.  Flow Control

   Using streams for multiplexing introduces contention over use of the
   TCP connection, resulting in blocked streams.  A flow control scheme
   ensures that streams on the same connection do not destructively
   interfere with each other.  Flow control is used for both individual
   streams and for the connection as a whole.

   HTTP/2.0 provides for flow control through use of the WINDOW_UPDATE
   (Section 3.8.9) 6.9) frame type.

3.6.1.

5.2.1.  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.  Flow
   control in HTTP/2.0 has the following characteristics:

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

   2.  Flow control is based on window update frames.  Receivers
       advertise how many octets bytes they are prepared to receive on a
       stream. stream
       and for the entire connection.  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 each stream and for the 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 for a stream or connection
       by sending a window update frame with a specific flag.  See
       Ending Flow Control (Section 6.9.4) for more details.

   7.  HTTP/2.0 standardizes only the format of the WINDOW_UPDATE frame
       (Section 6.9).  This does not stipulate how a receiver decides
       when to send this frame 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.

   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 for managing the entire connection.  A sender
       MUST respect creation of new streams.
   Algorithm choices for these could interact with any flow control limits imposed by
   algorithm.

5.2.2.  Appropriate Use of Flow Control

   Flow control is defined to protect endpoints that are operating under
   resource constraints.  For example, a receiver.  Clients,
       servers proxy needs to share memory
   between many connections, and intermediaries all independently advertise their flow
       control preferences as also might have a receiver slow upstream
   connection and abide by the flow a fast downstream one.  Flow control
       limits set by their peer when sending.

   4.  The initial value for addresses cases
   where the flow control window receiver is 65536 bytes for
       both new unable process data on one stream, yet wants to
   continue to process other streams and in the overall same connection.

   5.  The frame type determines whether

   Deployments that do not require this capability SHOULD disable flow
   control applies to a
       frame.  Of the frames specified in this document, only for data
       frames are that is being received.  Note that flow control
   cannot be disabled for sending.  Sending data is always 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 window advertised by the receiver.

   Deployments with constrained resources (for example, memory) MAY
   employ flow
       control.

   6.  Flow control can be disabled by to limit the amount of memory a receiver.  A receiver peer can
       choose consume.
   Note, however, that this can lead to either disable suboptimal use of available
   network resources if flow control is enabled without knowledge of the
   bandwidth-delay product (see [RFC1323]).

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

5.3.  Stream priority

   The endpoint establishing a new stream or connection
       by declaring can assign a priority for the
   stream.  Priority is represented as an infinite flow control limit.

   7.  HTTP/2.0 standardizes only unsigned 31-bit integer. 0
   represents the format of highest priority and 2^31-1 represents the window update frame
       (Section 3.8.9).  This does not stipulate how a receiver decides
       when to send lowest
   priority.

   The purpose of this frame or the value that it sends.  Nor does it
       specify how a sender chooses is to send packets.  Implementations
       are able allow the initiating endpoint to select any algorithm
   request that suits their needs.

   Implementations are also responsible frames for managing how requests and
   responses are sent based on priority; choosing how the stream be processed with a specified
   priority relative to avoid head of
   line blocking other concurrently active streams.  That is, if
   an endpoint receives interleaved frames for requests; and managing multiple streams, the creation of new
   endpoint ought to make a best-effort attempt at processing frames for
   higher priority streams before processing those for lower priority
   streams.
   Algorithm choices

   Explicitly setting the priority for these could interact with a stream does not guarantee any flow control
   algorithm.

3.6.2.  Appropriate Use
   particular processing order for the stream relative to any other
   stream.  Nor is there any mechanism provided by which the initiator
   of Flow Control

   Flow control a stream can force or require a receiving endpoint to process
   frames from one stream before processing frames from another.

   Unless explicitly specified in the HEADERS frame (Section 6.2) during
   stream creation, the default stream priority is defined to protect endpoints (client, server or
   intermediary) that 2^30.  Pushed streams
   (Section 8.2) are operating under resource constraints.  For
   example, a proxy needs assumed to share memory between many connections, and
   also might inherit the priority of the associated
   stream plus one (or 2^31-1 if the the associated stream priority is
   2^31-1), i.e. they have priority one lower than the associated
   stream.

5.4.  Error Handling

   HTTP/2.0 framing permits two classes of error:

   o  An error condition that renders the entire connection unusable is
      a slow upstream connection and error.

   o  An error in an individual stream is a fast downstream one.
   Flow control addresses cases where the receiver stream error.

   A list of error codes is unable process
   data on one stream, yet wants to continue to process other streams included in Section 7.

5.4.1.  Connection Error Handling

   A connection error is any error which prevents further processing of
   the same connection.

   Deployments framing layer or which corrupts any connection state.

   An endpoint that do not require this capability encounters a connection error SHOULD disable flow
   control for data first send a
   GOAWAY (Section 6.8) frame with the stream identifier of the last
   stream that is being received.  Note it successfully received from its peer.  The GOAWAY frame
   includes an error code that flow control
   cannot be disabled for sending.  Sending data indicates why the connection is always subject to
   terminating.  After sending the flow control window advertised by GOAWAY frame, the receiver.

   Deployments with constrained resources (for example, memory) MAY
   employ flow control to limit endpoint MUST close
   the TCP connection.

   It is possible that the GOAWAY will not be reliably received by the amount
   receiving endpoint.  In the event of memory a connection error, GOAWAY only
   provides a best-effort attempt to communicate with the peer about why
   the connection is being terminated.

   An endpoint can consume.
   Note, however, that this can lead end a connection at any time.  In particular, an
   endpoint MAY choose to suboptimal use of available
   network resources treat a stream error as a connection error if flow control
   the error is enabled without knowledge recurrent.  Endpoints SHOULD send a GOAWAY frame when
   ending a connection, as long as circumstances permit it.

5.4.2.  Stream Error Handling

   A stream error is an error related to a specific stream identifier
   that does not affect processing of other streams.

   An endpoint that detects a stream error sends a RST_STREAM
   (Section 6.4) frame that contains the
   bandwidth-delay product (see [RFC1323]).

   Even with full awareness stream identifier of the current bandwidth-delay product,
   implementation stream
   where the error occurred.  The RST_STREAM frame includes an error
   code that indicates the type of flow control error.

   A RST_STREAM is difficult.  However, it the last frame that an endpoint can ensure send on a stream.
   The peer that constrained resources are protected without sends the RST_STREAM frame MUST be prepared to receive
   any reduction in frames that were sent or enqueued for sending by the remote peer.
   These frames can be ignored, except where they modify connection utilization.

3.7.  Header Blocks

   The header block is found in
   state (such as the HEADERS, HEADERS+PRIORITY and
   PUSH_PROMISE frames.  The state maintained for header block consists of compression
   (Section 4.3)).

   Normally, an endpoint SHOULD NOT send more than one RST_STREAM frame
   for any stream.  However, an endpoint MAY send additional RST_STREAM
   frames if it receives frames on a set of header
   fields, which are name-value pairs.  Headers are compressed using
   black magic.

   Compression of header fields closed stream after more than a
   round trip time.  This behavior is permitted to deal with misbehaving
   implementations.

   An endpoint MUST NOT send a work RST_STREAM in progress, as response to an RST_STREAM
   frame, to avoid looping.

5.4.3.  Connection Termination

   If the TCP connection is torn down while streams remain in open or
   half closed states, then the format
   of this block.

   The contents of header blocks endpoint MUST be processed by assume that the compression
   context, even if stream has been reset or the frame is discarded.  If
   header blocks cannot was
   abnormally interrupted and could be processed, the receiver MUST treat the
   connection with a connection error (Section 3.5.1) of type
   COMPRESSION_ERROR.

3.8. incomplete.

6.  Frame Types Definitions

   This specification defines a number of frame types, each identified
   by a unique 8-bit type code.  Each frame type serves a distinct
   purpose either in the establishment and management of the connection
   as a whole, or of individual streams.

   The transmission of specific frame types can alter the state of a
   connection.  If endpoints fail to maintain a synchronized view of the
   connection state, successful communication within the connection will
   no longer be possible.  Therefore, it is important that endpoints
   have a shared comprehension of how the state is affected by the use
   any given frame.  Accordingly, while it is expected that new frame
   types will be introduced by extensions to this protocol, only frames
   defined by this document are permitted to alter the connection state.

3.8.1.

6.1.  DATA Frames

   DATA frames (type=0x0) convey arbitrary, variable-length sequences of
   octets associated with a stream.  One or more DATA frames are used,
   for instance, to carry HTTP request or response payloads.

   The DATA frame does not define any type-specific flags.

   DATA frames MUST be associated with a stream.  If a DATA frame is
   received whose stream identifier field is 0x0, the recipient MUST
   respond with a connection error (Section 3.5.1) of type
   PROTOCOL_ERROR.

3.8.2.  HEADERS+PRIORITY

   The HEADERS+PRIORITY frame (type=0x1) allows the sender to set header
   fields and stream priority at the same time.

    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)                             |
   +-+-------------------------------------------------------------+
   |                    Header Block (*)                         ...
   +---------------------------------------------------------------+

                      HEADERS+PRIORITY Frame Payload

   The HEADERS+PRIORITY frame is identical to the HEADERS frame
   (Section 3.8.8), preceded by a single reserved bit and a 31-bit
   priority; see Section 3.4.2.

   HEADERS+PRIORITY uses the same flags as the HEADERS frame, except defines the following flags:

   END_STREAM (0x1):  Bit 1 being set indicates that a HEADERS+PRIORITY this frame with is the
      last that the endpoint will send for the identified stream.
      Setting this flag causes the stream to enter a CONTINUES bit MUST be followed
   by another HEADERS+PRIORITY frame.  See HEADERS frame "half closed" state
      (Section 3.8.8) 5.1).

   RESERVED (0x2):  Bit 2 is reserved for any flags.

   HEADERS+PRIORITY future use.

   DATA frames MUST be associated with a stream.  If a
   HEADERS+PRIORITY DATA frame is
   received whose stream identifier field is 0x0, the recipient MUST
   respond with a connection error (Section 3.5.1) 5.4.1) of type
   PROTOCOL_ERROR.

6.2.  HEADERS

   The HEADERS+PRIORITY HEADERS frame modifies the connection state as defined
   in Section 3.7.

3.8.3.  RST_STREAM (type=0x1) carries name-value pairs.  The RST_STREAM frame (type=0x3) allows for abnormal termination of a
   stream.  When sent by the initiator of a stream, it indicates that
   they wish HEADERS
   is used to cancel the stream.  When sent by the receiver of open a
   stream, it indicates that either the receiver is rejecting the
   stream, requesting that the stream (Section 5.1).  Any number of HEADERS frames
   can be cancelled or that sent on an error
   condition has occurred. existing stream at any time.

    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)                        |                         Error Code (32)
    +-+-------------------------------------------------------------+
    |                   Header Block Fragment (*)                 ...
    +---------------------------------------------------------------+

                         RST_STREAM

                           HEADERS Frame Payload

   The RST_STREAM HEADERS frame contains a single unsigned, 32-bit integer
   identifying the error code (Section 3.5.3).  The error code indicates
   why defines the stream is following flags:

   END_STREAM (0x1):  Bit 1 being terminated.

   No type-flags are defined.

   The RST_STREAM set indicates that this frame fully terminates the referenced stream and
   causes it to enter is the closed state.  After receiving a RST_STREAM on
   a stream,
      last that the receiver MUST NOT endpoint will send additional frames for that
   stream.  However, after sending the RST_STREAM, the sending endpoint
   MUST be prepared to receive and process additional frames sent on identified stream.
      Setting this flag causes the stream to enter a "half closed" state
      (Section 5.1).

   RESERVED (0x2):  Bit 2 is reserved for future use.

   END_HEADERS (0x4):  The END_HEADERS bit indicates that might have been sent by this frame
      ends the peer prior sequence of header block fragments necessary to the arrival provide a
      complete set of headers.

      The payload for a complete header block is provided by a sequence
      of HEADERS frames, terminated by a HEADERS frame with the RST_STREAM.

   RST_STREAM
      END_HEADERS flag set.  Once the sequence terminates, the payload
      of all HEADERS frames are concatenated and interpreted as a single
      block.

      A HEADERS frame without the END_HEADERS flag set MUST be associated with followed
      by a HEADERS frame for the same stream.  If  A receiver MUST treat the
      receipt of any other type of frame or a RST_STREAM frame is received whose on a different
      stream identifier field is 0x0 the recipient
   MUST respond with as a connection error (Section 3.5.1) 5.4.1) of type
      PROTOCOL_ERROR.

3.8.4.  SETTINGS

   The SETTINGS frame (type=0x4) conveys configuration parameters

   PRIORITY (0x8):  Bit 4 being set indicates that
   affect how endpoints communicate.  The parameters are either
   constraints on peer behavior or preferences.

   SETTINGS frames MUST be sent at the start of a connection, and MAY be
   sent at any other time by either endpoint over the lifetime of the
   connection.

   Implementations MUST support all first four octets
      of the settings defined by this
   specification frame contain a single reserved bit and MAY support additional settings defined by
   extensions.  Unsupported or unrecognized settings MUST be ignored.
   New settings MUST NOT be defined or implemented in a way that
   requires endpoints to understand then in order to communicate
   successfully.

   A SETTINGS frame 31-bit priority;
      see Section 5.3.  If this bit is not required to include every defined setting;
   senders can include only those parameters for which it has accurate
   values set, the four bytes do not
      appear and the frame only contains a need to convey.  When multiple parameters are sent, they
   SHOULD be sent in order header block fragment.

   The payload of numerically lowest ID to highest ID.  A
   single SETTINGS a HEADERS frame contains a header block fragment
   (Section 4.3).

   HEADERS frames MUST NOT contain multiple values for the same
   ID. be associated with a stream.  If the receiver of a SETTINGS HEADERS frame discovers multiple values
   for
   is received whose stream identifier field is 0x0, the same ID, it recipient MUST ignore all values for that ID except the
   first one.

   Over the lifetime of
   respond with a connection, an endpoint MAY send multiple
   SETTINGS frames containing previously unspecified parameters or new
   values for parameters whose values have already been established.
   Only connection error (Section 5.4.1) of type
   PROTOCOL_ERROR.

   The HEADERS frame changes the most recent value provided setting value applies. connection state as defined in
   Section 4.3.

6.3.  PRIORITY

   The SETTINGS PRIORITY frame defines (type=0x2) specifies the following flag:

   CLEAR_PERSISTED (0x2):  Bit 2 being set indicates sender-advised priority
   of a request to clear stream.  It can be sent at any previously persisted settings before processing the settings.
      Clients MUST NOT set this flag.

   SETTINGS frames always apply to time for an existing stream.
   This enables reprioritisation of existing streams.

    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)                        |
    +-+-------------------------------------------------------------+

                          PRIORITY Frame Payload

   The payload of a connection, never PRIORITY frame contains a single stream.
   The stream identifier for reserved bit and a settings
   31-bit priority.

   The PRIORITY frame MUST be zero.  If does not define any flags.

   The PRIORITY frame is associated with an
   endpoint receives existing stream.  If a SETTINGS
   PRIORITY frame whose is received with a stream identifier field is
   anything other than of 0x0, the endpoint
   recipient MUST respond with a connection error (Section 3.5.1) 5.4.1) of
   type PROTOCOL_ERROR.

3.8.4.1.  Setting Format

6.4.  RST_STREAM

   The payload RST_STREAM frame (type=0x3) allows for abnormal termination of a SETTINGS frame consists
   stream.  When sent by the initiator of zero a stream, it indicates that
   they wish to cancel the stream or more settings.
   Each setting consists of an 8-bit flags field specifying per-item
   instructions, that an unsigned 24-bit setting identifier, and error condition has
   occurred.  When sent by the receiver of a stream, it indicates that
   either the receiver is rejecting the stream, requesting that the
   stream be cancelled or that an unsigned
   32-bit value. error condition has occurred.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |SettingFlags(8)|             Setting Identifier (24)           |
   +---------------+-----------------------------------------------+
    |                        Value                        Error Code (32)                        |
    +---------------------------------------------------------------+
                              Setting Format

   Two flags are defined for

                         RST_STREAM Frame Payload

   The RST_STREAM frame contains a single unsigned, 32-bit integer
   identifying the 8-bit flags field:

   PERSIST_VALUE (0x1):  Bit 1 (the least significant bit) being set error code (Section 7).  The error code indicates a request from why
   the server to stream is being terminated.

   The RST_STREAM frame does not define any flags.

   The RST_STREAM frame fully terminates the client referenced stream and
   causes it to persist this
      setting.  A client enter the closed state.  After receiving a RST_STREAM on
   a stream, the receiver MUST NOT set this flag.

   PERSISTED (0x2):  Bit 2 being set indicates send additional frames for that this setting is a
      persisted setting being returned by
   stream.  However, after sending the client RST_STREAM, the sending endpoint
   MUST be prepared to receive and process additional frames sent on the server.
      This also indicates
   stream that this setting is not a client setting, but
      a value previously set might have been sent by the server.  A server MUST NOT set this
      flag.

3.8.4.2.  Setting Persistence

   [[anchor12: Note that persistence peer prior to the arrival of settings is under discussion in
   the WG and might RST_STREAM.

   RST_STREAM frames MUST be removed in associated with a future version of this document.]]

   A server endpoint can request that configuration parameters sent to stream.  If a
   client in RST_STREAM
   frame is received whose stream identifier field is 0x0 the recipient
   MUST respond with a connection error (Section 5.4.1) of type
   PROTOCOL_ERROR.

6.5.  SETTINGS

   The SETTINGS frame (type=0x4) conveys configuration parameters that
   affect how endpoints communicate.  The parameters are to either
   constraints on peer behavior or preferences.

   SETTINGS frames MUST be persisted by sent at the client across
   HTTP/2.0 connections start of a connection, and returned to the server in MAY be
   sent at any new SETTINGS
   frame other time by either endpoint over the client sends to lifetime of the server in
   connection.

   Implementations MUST support all of the current connection settings defined by this
   specification and MAY support additional settings defined by
   extensions.  Unsupported or any
   future connections.

   Persistence is requested on unrecognized settings MUST be ignored.
   New settings MUST NOT be defined or implemented in a per-setting basis by setting the
   PERSIST_VALUE flag (0x1).

   Client way that
   requires endpoints are not permitted to make such requests.  Servers
   MUST ignore any attempt by clients understand them in order to request that a server persist
   configuration parameters.

   Persistence of configuration parameters communicate
   successfully.

   A SETTINGS frame is done on a per-origin basis
   (see [RFC6454]).  That is, when a client establishes a connection
   with a server, not required to include every defined setting;
   senders can include only those parameters for which it has accurate
   values and the server requests that the client maintain
   persistent settings, the client a need to convey.  When multiple parameters are sent, they
   SHOULD return the persisted settings
   on all future connections be sent in order of numerically lowest ID to highest ID.  A
   single SETTINGS frame MUST NOT contain multiple values for the same origin, IP address and TCP
   port.

   Whenever
   ID.  If the client sends receiver of a SETTINGS frame in discovers multiple values
   for the current same ID, it MUST ignore all values for that ID except the
   first one.

   Over the lifetime of a connection, an endpoint MAY send multiple
   SETTINGS frames containing previously unspecified parameters or establishes a new connection with the same origin, persisted
   configuration
   values for parameters are sent with whose values have already been established.
   Only the PERSISTED flag (0x2) set most recent provided setting value applies.

   The SETTINGS frame does not define any flags.

   SETTINGS frames always apply to a connection, never a single stream.
   The stream identifier for each persisted parameter.

   Persisted settings accumulate until the server requests that all
   previously persisted a settings are to frame MUST be cleared by setting the
   CLEAR_PERSISTED (0x2) flag on the zero.  If an
   endpoint receives a SETTINGS frame.

   For example, if frame whose stream identifier field is
   anything other than 0x0, the server sends IDs 1, 2, and 3 endpoint MUST respond with the
   FLAG_SETTINGS_PERSIST_VALUE in a first connection
   error (Section 5.4.1) of type PROTOCOL_ERROR.

   The SETTINGS frame, and then sends
   IDs 4 and 5 with the FLAG_SETTINGS_PERSIST_VALUE in frame affects connection state.  A badly formed or
   incomplete SETTINGS frame MUST be treated as a connection error
   (Section 5.4.1).

6.5.1.  Setting Format

   The payload of a subsequent SETTINGS frame, the client will return values for all frame consists of zero or more settings.
   Each setting consists of an 8-bit reserved field, an unsigned 24-bit
   setting identifier, and an unsigned 32-bit value.

    0                   1                   2                   3
    0 1 2 3 4 5 settings (1,
   2, 3, 4, and 6 7 8 9 0 1 2 3 4 5 in this example) to the server.

3.8.4.3. 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Reserved (8) |            Setting Identifier (24)            |
    +---------------+-----------------------------------------------+
    |                        Value (32)                             |
    +---------------------------------------------------------------+

                              Setting Format

6.5.2.  Defined Settings

   The following settings are defined:

   SETTINGS_UPLOAD_BANDWIDTH (1):  indicates the sender's estimated
      upload bandwidth for this connection.  The value is an the
      integral number of kilobytes per second that the sender predicts
      as an expected maximum upload channel capacity.

   SETTINGS_DOWNLOAD_BANDWIDTH (2):  indicates the sender's estimated
      download bandwidth for this connection.  The value is an integral
      number of kilobytes per second that the sender predicts as an
      expected maximum download channel capacity.

   SETTINGS_ROUND_TRIP_TIME (3):  indicates the sender's estimated
      round-trip-time for this connection.  The round trip time is
      defined as the minimum amount of time to send a control frame from
      this client to the remote and receive a response.  The value is
      represented in milliseconds.

   SETTINGS_MAX_CONCURRENT_STREAMS (4):  indicates the maximum number of
      concurrent streams that the sender will allow.  This limit is
      directional: it applies to the number of streams that the sender
      permits the receiver to create.  By default there is no limit.  It
      is recommended that this value be no smaller than 100, so as to
      not unnecessarily limit parallelism.

   SETTINGS_CURRENT_CWND (5):  indicates the sender's current TCP CWND
      value.

   SETTINGS_DOWNLOAD_RETRANS_RATE (6):  indicates the sender's
      retransmission rate (bytes retransmitted / total bytes
      transmitted).

   SETTINGS_INITIAL_WINDOW_SIZE (7):  indicates the sender's initial
      stream
      window size (in bytes) for new streams. stream level flow control.

      This settings affects the window size of all streams, including
      existing streams, see Section 6.9.2.

   SETTINGS_FLOW_CONTROL_OPTIONS (10):  indicates that streams directed
      to the sender will not be subject to flow control.  The least
      significant bit (0x1) of the value is set to indicate that new
      streams are 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 3.8.9.4.

3.8.5. 6.9.4.

6.6.  PUSH_PROMISE

   The PUSH_PROMISE frame (type=0x5) is used to notify the peer endpoint
   in advance of streams the sender intends to initiate.  The
   PUSH_PROMISE frame includes the unsigned 31-bit identifier of the
   stream the endpoint plans to create along with a minimal set of
   headers that provide additional context for the stream.  Section 4.3 8.2
   contains a thorough description of the use of PUSH_PROMISE frames.

    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|                Promised-Stream-ID (31)                      |
    +-+-------------------------------------------------------------+
    |                 Header Block Fragment (*)                   ...
    +---------------------------------------------------------------+

                        PUSH_PROMISE Payload Format

   The payload of a PUSH_PROMISE includes a "Promised-Stream-ID".  This
   unsigned 31-bit integer identifies the stream the endpoint intends to
   start sending frames for.  The promised stream identifier MUST be a
   valid choice for the next stream sent by the sender (see new stream
   identifier (Section 3.4.1)). 5.1.1)).

   Following the "Promised-Stream-ID" is a header block fragment
   (Section 4.3).

   PUSH_PROMISE frames MUST be associated with an existing existing, peer-
   initiated stream.  If the stream identifier field specifies the value
   0x0, a recipient MUST respond with a connection error (Section 3.5.1) 5.4.1)
   of type PROTOCOL_ERROR.

   The state of promised streams is bound to the state of the original
   associated stream on which the PUSH_PROMISE frame were sent.  If defines the
   originating stream state changes to fully closed, all associated
   promised streams fully close as well. [[anchor13: Ed.  Note: We need
   clarification on following flags:

   END_PUSH_PROMISE (0x1):  The END_PUSH_PROMISE bit indicates that this point.  How synchronized are
      frame ends the sequence of header block fragments necessary to
      provide a complete set of headers.

      The payload for a complete header block is provided by a sequence
      of PUSH_PROMISE frames, terminated by a PUSH_PROMISE frame with
      the END_PUSH_PROMISE flag set.  Once the sequence terminates, the lifecycles
      payload of
   streams and associated promised streams?]] all PUSH_PROMISE uses the same flags frames are concatenated and
      interpreted as the HEADERS frame, except that a single block.

      A PUSH_PROMISE frame with a CONTINUES bit without the END_PUSH_PROMISE flag set MUST be
      followed by another a PUSH_PROMISE frame.  See HEADERS frame (Section 3.8.8) for the same stream.  A receiver
      MUST treat the receipt of any flags. other type of frame or a frame on a
      different stream as a connection error (Section 5.4.1) of type
      PROTOCOL_ERROR.

   Promised streams are not required to be used in order promised.  The
   PUSH_PROMISE only reserves stream identifiers for later use.

   Recipients of PUSH_PROMISE frames can choose to reject promised
   streams by returning a RST_STREAM referencing the promised stream
   identifier back to the sender of the PUSH_PROMISE.

   The PUSH_PROMISE frame modifies the connection state as defined in
   Section 3.7.

3.8.6. 4.3.

6.7.  PING

   The PING frame (type=0x6) is a mechanism for measuring a minimal
   round-trip time from the sender, as well as determining whether an
   idle connection is still functional.  PING frames can be sent from
   any endpoint.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                      Opaque Data (64)                         |
    |                                                               |
    +---------------------------------------------------------------+

                            PING Payload Format

   In addition to the frame header, PING frames consist of an arbitrary, variable-length sequence MUST contain 8 octets of
   octets.
   data in the payload.  A sender can include any value it chooses and
   use those bytes in any fashion.

   Receivers of a PING frame that does not include a PONG flag MUST send
   a response PING frame with the PONG flag set and precisely the same sequence of octets back to the sender
   as soon as possible.

   Processing of in response, with an identical
   payload.  PING frames responses SHOULD be performed with the highest given higher priority if there are additional frames waiting to be processed. than any other
   frame.

   The PING frame defines one type-specific flag: the following flags:

   PONG (0x2): (0x1):  Bit 2 1 being set indicates that this 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.

   PING frames are not associated with any individual stream.  If a PING
   frame is received with a stream identifier field value other than
   0x0, the recipient MUST respond with a connection error
   (Section 3.5.1) 5.4.1) of type PROTOCOL_ERROR.

   Receipt of a PING frame with a length field value other than 8 MUST
   be treated as a connection error (Section 5.4.1) of type
   PROTOCOL_ERROR.

3.8.7.

6.8.  GOAWAY

   The GOAWAY frame (type=0x7) informs the remote peer to stop creating
   streams on this connection.  It can be sent from the client or the
   server.  Once sent, the sender will ignore frames sent on new streams
   for the remainder of the connection.  Receivers of a GOAWAY frame
   MUST NOT open additional streams on the connection, although a new
   connection can be established for new streams.  The purpose of this
   frame 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 starting new
   streams and the remote sending a GOAWAY frame.  To deal with this
   case, the GOAWAY contains the stream identifier of the last stream
   which was processed on the sending endpoint in this connection.  If
   the receiver of the GOAWAY used streams that are newer than the
   indicated stream identifier, they were not processed by the sender
   and the receiver may treat the streams as though they had never been
   created at all (hence the receiver may want to re-create the streams
   later on a new connection).

   Endpoints should SHOULD always send a GOAWAY frame before closing a
   connection so that the remote can know whether a stream has been
   partially processed or not.  (For  For example, if an HTTP client sends a
   POST at 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 frame to indicate where it stopped
   working).
   working.  An endpoint might choose to close a connection without
   sending GOAWAY for misbehaving peers.

   After sending a GOAWAY frame, the sender can ignore discard frames for new
   streams.

   [[anchor14: Issue:  However, any frames that alter connection state that is established by those
   "ignored" frames cannot be ignored without the
   completely ignored.  For instance, HEADERS and PUSH_PROMISE frames
   MUST be minimally processed to ensure a consistent compression state in the two peers
   becoming unsynchronized.]]
   (see Section 4.3).

    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)                          |
    +---------------------------------------------------------------+
    |                  Additional Debug Data (*)                    |
    +---------------------------------------------------------------+

                           GOAWAY Payload Format

   The GOAWAY frame does not define any type-specific flags.

   The GOAWAY frame applies to the connection, not a specific stream.

   The stream identifier MUST be zero.

   The last stream identifier in the GOAWAY frame contains the highest
   numbered stream identifier for which the sender of the GOAWAY frame
   has received frames on and might have taken some action on.  All
   streams up to and including the identified stream might have been
   processed in some way.  The last stream identifier is set to 0 if no
   streams were processed.

      Note: In this case, "processed" means that some data from the
      stream was passed to some higher layer of software that might have
      taken some action as a result.

   On streams with lower or equal numbered identifiers that do were not close
   closed completely prior to the connection being closed, re-attempting
   requests, transactions, or any protocol activity is not possible
   (with the exception of idempotent actions like HTTP GET, PUT, or
   DELETE).  Any protocol activity that uses higher numbered streams can
   be safely retried using a new connection.

   Activity on streams numbered lower or equal to the last stream
   identifier might still complete successfully.  The sender of a GOAWAY
   frame might gracefully shut down a connection by sending a GOAWAY
   frame, maintaining the connection in an open state until all in-progress
   streams complete.

   The last stream ID MUST be 0 if no streams were acted upon.

   The GOAWAY frame also contains a 32-bit error code (Section 3.5.3)
   that contains the reason for closing the connection.

3.8.8.  HEADERS

   The HEADERS frame (type=0x8) provides header fields for a stream.
   Any number of HEADERS frames can may be sent on an existing stream at
   any time.

   Additional type-specific flags for the HEADERS frame are:

   CONTINUES (0x2):  The CONTINUES bit indicates that this frame does
      not contain the entire payload necessary to provide a complete set
      of headers.

      The payload for a complete set of headers is provided by a
      sequence of HEADERS frames, terminated by a HEADERS frame without
      the CONTINUES bit.  Once the sequence terminates, the payload of
      all HEADERS frames are concatenated and interpreted as a single
      block.

      A HEADERS frame that includes a CONTINUES bit MUST be followed by
      a HEADERS frame for the same stream.  A receiver MUST treat the
      receipt of any other type of frame or a frame on a different
      stream as a connection error (Section 3.5.1) of type
      PROTOCOL_ERROR.

   The payload of a HEADERS frame contains a Headers Block
   (Section 3.7).

   The HEADERS frame is associated with an existing stream.  If a
   HEADERS frame is received with a in-
   progress streams complete.

   The last stream identifier of 0x0, the
   recipient ID MUST respond with be 0 if no streams were acted upon.

   The GOAWAY frame also contains a stream 32-bit error code (Section 3.5.2) of type
   PROTOCOL_ERROR.

   The HEADERS frame changes 7) that
   contains the connection state as defined in
   Section 3.7.

3.8.9. reason for closing the connection.

   Endpoints MAY append opaque data to the payload of any GOAWAY frame.
   Additional debug data is intended for diagnostic purposes only and
   carries no semantic value.  Debug data MUST NOT be persistently
   stored, since it could contain sensitive information.

6.9.  WINDOW_UPDATE

   The WINDOW_UPDATE frame (type=0x9) is used to implement flow control.

   Flow control operates at two levels: on each individual stream and on
   the entire connection.

   Both types of flow control are hop by hop; that is, only between the
   two endpoints.  Intermediaries do not forward WINDOW_UPDATE frames
   between dependent connections.  However, throttling of data transfer
   by any receiver can indirectly cause the propagation of flow control
   information toward the original sender.

   Flow control only applies to frames that are identified as being
   subject to flow control.  Of the frame types defined in this
   document, this includes only DATA frame.  Frames that are exempt from
   flow control MUST be accepted and processed, unless the receiver is
   unable to assign resources to handling the frame.  A receiver MAY
   respond with a stream error (Section 3.5.2) 5.4.2) or connection error
   (Section 3.5.1) 5.4.1) of type FLOW_CONTROL_ERROR if it is unable accept a
   frame.

    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|              Window Size Increment (31)                     |
    +-+-------------------------------------------------------------+

                       WINDOW_UPDATE Payload Format

   The following additional flags are defined payload of a WINDOW_UPDATE frame is one reserved bit, plus an
   unsigned 31-bit integer indicating the number of bytes that the
   sender can transmit in addition to the existing flow control window.
   The legal range for the increment to the flow control window is 1 to
   2^31 - 1 (0x7fffffff) bytes.

   The WINDOW_UPDATE
   frame: frame defines the following flags:

   END_FLOW_CONTROL (0x2): (0x1):  Bit 2 1 being set indicates that flow control
      for the identified stream or connection has been ended; subsequent
      frames do not need to be flow controlled.

   The WINDOW_UPDATE frame can be specific to a stream or to the entire
   connection.  In the former case, the frame's stream identifier
   indicates the affected stream; in the latter, the value "0" indicates
   that the entire connection is the subject of the frame.

   The payload of a WINDOW_UPDATE frame is a 32-bit value indicating the
   additional number of bytes that the sender can transmit in addition
   to the existing flow control window.  The legal range for this field
   is 1 to 2^31 - 1 (0x7fffffff) bytes; the most significant bit of this
   value is reserved.

3.8.9.1.

6.9.1.  The Flow Control Window

   Flow control in HTTP/2.0 is implemented using a window kept by each
   sender on every stream.  The flow control window is a simple integer
   value that indicates how many bytes of data the sender is permitted
   to transmit; as such, its size is a measure of the buffering
   capability of the receiver.

   Two flow control windows are applicable; the stream flow control
   window and the connection flow control window.  The sender MUST NOT
   send a flow controlled frame with a length that exceeds the space
   available in either of the flow control windows advertised by the
   receiver.  Frames with zero length with the FINAL END_STREAM 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 a flow controlled frame, the sender reduces the space
   available in both windows by the length of the transmitted frame.

   The receiver of a frame sends a WINDOW_UPDATE frame as it consumes
   data and frees up space in flow control windows.  Separate
   WINDOW_UPDATE frames are sent for the stream and connection level
   flow control windows.

   A sender that receives a WINDOW_UPDATE frame updates the
   corresponding window by the amount specified in the frame.

   A sender MUST NOT allow a flow control window to exceed 2^31 - 1
   bytes.  If a sender receives a WINDOW_UPDATE that causes a flow
   control window to exceed this maximum it MUST terminate either the
   stream or the connection, as appropriate.  For streams, the sender
   sends a RST_STREAM with the error code of FLOW_CONTROL_ERROR code;
   for the connection, a GOAWAY frame with a FLOW_CONTROL_ERROR code.

   Flow controlled frames from the sender and WINDOW_UPDATE frames from
   the receiver are completely asynchronous with respect to each other.
   This property allows a receiver to aggressively update the window
   size kept by the sender to prevent streams from stalling.

3.8.9.2.

6.9.2.  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 of 65535 bytes.  The
   connection flow control window is 65536 65535 bytes.  Both endpoints can
   adjust the initial window size for new streams by including a value
   for SETTINGS_INITIAL_WINDOW_SIZE in the SETTINGS frame that forms
   part of the connection header.

   Prior to receiving a SETTINGS frame that sets a value for
   SETTINGS_INITIAL_WINDOW_SIZE, a client an endpoint can only use the default
   initial window size when sending flow controlled frames.  Similarly,
   the connection flow control window is set to the default initial
   window size until a WINDOW_UPDATE frame is received.

   A SETTINGS frame can alter the initial flow control window size for
   all current streams.  When the value of SETTINGS_INITIAL_WINDOW_SIZE
   changes, a receiver MUST adjust the size of all stream flow control
   windows that it maintains by the difference between the new value and
   the old value.  A SETTINGS frame cannot alter the connection flow
   control window.

   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 MUST NOT send new flow
   controlled frames until it receives WINDOW_UPDATE frames that cause
   the flow control window to become positive.

   For example, if the client sends 64KB immediately on connection
   establishment, and the server sets the initial window size to be
   16KB,
   and the client sends 64KB immediately on connection establishment, the client will recalculate the available flow control window
   to be -48KB on receipt of the SETTINGS frame.  The client retains a
   negative flow control window until WINDOW_UPDATE frames restore the
   window to being positive, after which the client can resume sending.

3.8.9.3.

6.9.3.  Reducing the Stream Window Size

   A receiver that wishes to use a smaller flow control window than the
   current size can send a new SETTINGS frame.  However, the receiver
   MUST be prepared to receive data that exceeds this window size, since
   the sender might send data that exceeds the lower limit prior to
   processing the SETTINGS frame.

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

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

   2.  The receiver can accept the streams and tolerate the resulting
       head of line blocking, sending WINDOW_UPDATE frames as it
       consumes data.

   If a receiver decides to accept streams, both sides MUST recompute
   the available flow control window based on the initial window size
   sent in the SETTINGS.

3.8.9.4.

6.9.4.  Ending Flow Control

   After a receiver reads in a frame that marks the end of a stream (for
   example, a data stream with a FINAL END_STREAM flag set), it MUST cease
   transmission of WINDOW_UPDATE frames for that stream.  A sender is
   not obligated to maintain the available flow control window for
   streams that it is no longer sending on.

   Flow control can be disabled for all streams or on the connection using
   the SETTINGS_FLOW_CONTROL_OPTIONS setting.  An implementation that
   does not wish to perform flow control can use this in the initial
   SETTINGS exchange.

   Flow control can be disabled for an individual stream or the overall
   connection by sending a WINDOW_UPDATE with the END_FLOW_CONTROL flag
   set.  The payload of a WINDOW_UPDATE frame that has the
   END_FLOW_CONTROL flag set is ignored.

   Flow control cannot be enabled again once disabled.  Any attempt to
   re-enable flow control - by sending a WINDOW_UPDATE or by clearing
   the bits on the SETTINGS_FLOW_CONTROL_OPTIONS setting - MUST be
   rejected with a FLOW_CONTROL_ERROR error code.

4.  HTTP Message Exchanges

   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 HTTP/1.1
   ([HTTP-p1], [HTTP-p2], [HTTP-p4], [HTTP-p5], [HTTP-p6], and
   [HTTP-p7]) apply with the changes in the sections below.

4.1.  Connection Management

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

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

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 possibility that some HTTP applications
   already can use a particular header field name.  To avoid any conflicts,
   all header fields introduced this in the
   initial SETTINGS exchange.

   Flow control can be disabled for layering HTTP over HTTP/2.0 are
   prefixed with ":". ":" is not an individual stream or the overall
   connection by sending a valid sequence in HTTP/1.* header
   field naming, preventing any possible conflict.

4.2.2.  Request WINDOW_UPDATE with the END_FLOW_CONTROL flag
   set.  The client initiates payload of a request WINDOW_UPDATE frame that has the
   END_FLOW_CONTROL flag set is ignored.

   Flow control cannot be enabled again once disabled.  Any attempt to
   re-enable flow control - by sending a HEADERS+PRIORITY frame.
   Requests that do not contain a body MUST set WINDOW_UPDATE or by clearing
   the FINAL flag,
   indicating that bits on the client intends SETTINGS_FLOW_CONTROL_OPTIONS setting - MUST be
   rejected with a FLOW_CONTROL_ERROR error code.

7.  Error Codes

   Error codes are 32-bit fields that are used in RST_STREAM and GOAWAY
   frames to send no further data on this
   stream, unless convey the server intends reasons for the stream or connection error.

   Error codes share a common code space.  Some error codes only apply
   to push resources (see
   Section 4.3).  HEADERS+PRIORITY specific conditions and have no defined semantics in certain frame does
   types.

   The following error codes are defined:

   NO_ERROR (0):  The associated condition is not contain the FINAL flag as a result of an
      error.  For example, a GOAWAY might include this code to indicate
      graceful shutdown of a connection.

   PROTOCOL_ERROR (1):  The endpoint detected an unspecific protocol
      error.  This error is for requests that contain use when a body. more specific error code is
      not available.

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

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

   STREAM_CLOSED (5):  The body of endpoint received a request follows as frame after a
   series of DATA frames. stream was
      half closed.

   FRAME_TOO_LARGE (6):  The last DATA endpoint received a frame sets the FINAL flag to
   indicate the end of that was larger
      than the body. maximum size that it supports.

   REFUSED_STREAM (7):  The header fields included in the HEADERS+PRIORITY frame contain all
   of endpoint refuses the HTTP header fields associated with an HTTP request.  The
   definitions of these headers are largely unchanged relative stream prior to
   HTTP/1.1, with a few notable exceptions:

   o  The HTTP/1.1 request-line has been split into two separate header
      fields named :method and :path, whose values specify the HTTP
      method
      performing any application processing, see Section 8.1.5 for
      details.

   CANCEL (8):  Used by the request and endpoint to indicate that the request-target, respectively. stream is no
      longer needed.

   COMPRESSION_ERROR (9):  The
      HTTP-version component of the request-line endpoint is removed entirely
      from unable to maintain the headers.

   o  The host and optional port portions of
      compression context for the request URI (see
      [RFC3986], Section 3.2), connection.

8.  HTTP Message Exchanges

   HTTP/2.0 is specified using the new :host header
      field. [[anchor21: Ed.  Note: it needs intended to be clarified whether or
      not this replaces the existing HTTP/1.1 Host header.]]

   o  A new :scheme header field has been added to specify as compatible as possible with current
   web-based applications.  This means that, from the scheme
      portion perspective of the request-target (e.g. "https")

   o  All header field names MUST be lowercased, and
   server business logic or application API, the definitions features of
      all header field names defined by HTTP/1.1 HTTP are updated to be all
      lowercase.

   o  The Connection, Host, Keep-Alive, Proxy-Connection,
   unchanged.  To achieve this, all of the application request and Transfer-
      Encoding
   response header fields semantics are no longer valid and MUST not be sent.

   All HTTP Requests MUST include preserved, although the ":method", ":path", ":host", syntax of
   conveying those semantics has changed.  Thus, the rules from HTTP/1.1
   ([HTTP-p1], [HTTP-p2], [HTTP-p4], [HTTP-p5], [HTTP-p6], and
   ":scheme" header fields.

   Header fields whose names begin
   [HTTP-p7]) apply with ":" (whether defined the changes in this
   document or future extensions to this document) MUST appear before
   any other header fields.

   If a the sections below.

8.1.  HTTP Request/Response Exchange

   A client sends an HTTP request on a HEADERS+PRIORITY frame that omits new stream, using a mandatory
   header, the previously
   unused stream identifier (Section 5.1.1).  A server MUST reply with a sends an HTTP 400 Bad Request reply.
   [[anchor22: Ed: why PROTOCOL_ERROR
   response on missing ":status" in the
   response, but same stream as the request.

   An HTTP 400 here?]]

   If a server receives a request where the sum of the data frame
   payload lengths does not equal the size or response each consist of:

   o  one contiguous sequence of the Content-Length header
   field, the server MUST return a 400 (Bad Request) error.

   Although POSTs are inherently chunked, POST requests SHOULD also be
   accompanied by HEADERS frames;

   o  zero or more DATA frames; and

   o  optionally, a Content-Length header field.  First, it informs the
   server contiguous sequence of how much data to expect, which the server can use to track
   overall progress and provide appropriate user feedback.  More
   importantly, some HTTP server implementations fail to correctly
   process requests that omit HEADERS frames

   The last frame in the Content-Length header field.  Many
   existing clients send a Content-Length header field, and some server
   implementations have come to depend upon its presence.

   A client provides priority sequence bears an END_STREAM flag.

   Other frames, including HEADERS, MAY be interspersed with these
   frames, but those frames do not carry HTTP semantics.

   Trailing header fields are carried in requests as a hint to header block that also
   terminates the server.  A
   server SHOULD attempt to provide responses to higher priority
   requests before lower priority requests.  A server could send lower
   priority responses during periods stream.  That is, a sequence of HEADERS frames that higher priority responses
   carries an END_STREAM flag on the last frame.  Header blocks after
   the first that do not terminate the stream are
   unavailable to ensure better utilization not part of an HTTP
   request or response.

   An HTTP request/response exchange fully consumes a connection.

   If single stream.  A
   request starts with the server receives HEADERS frame that puts the stream into an
   "open" state and ends with a data frame prior bearing END_STREAM, which causes
   the stream to become "half closed" for the client.  A response starts
   with a HEADERS frame and ends with a HEADERS+PRIORITY frame bearing END_STREAM, which
   places the server MUST treat this stream in the "closed" state.

8.1.1.  Examples

   For example, an HTTP GET request that includes request header fields
   and no body, is transmitted as a stream error (Section 3.5.2) single contiguous sequence of
   HEADERS frames containing the serialized block of type
   PROTOCOL_ERROR.

4.2.3.  Response

   The server responds to a client request using header
   fields.  The last HEADERS frame in the same stream
   identifier that was used by sequence has both the request.  An HTTP
   END_HEADERS and END_STREAM flag set:

     GET /resource HTTP/1.1         HEADERS
     Host: example.org        ==>     + END_STREAM
     Accept: image/jpeg               + END_HEADERS
                                        :method = get
                                        :scheme = https
                                        :host = example.org
                                        :path = /resource
                                        accept = image/jpeg

   Similarly, a response begins
   with that includes only response header fields is
   transmitted as a sequence of HEADERS frame. frames containing the serialized
   block of response header fields.  The last HEADERS frame in the
   sequence has both the END_HEADERS and END_STREAM flag set:

     HTTP/1.1 204 No Content       HEADERS
     Content-Length: 0        ===>   + END_STREAM
                                     + END_HEADERS
                                       :status = 204
                                       content-length: 0

   An HTTP response body consists of a series of POST request that includes request header fields and payload
   data is transmitted as one or more HEADERS frames containing the
   request headers followed by one or more DATA frames.  The frames, with the last data
   HEADERS frame contains a FINAL having the END_HEADERS flag to indicate set and the end of final DATA
   frame having the response. END_STREAM flag set:

     POST /resource HTTP/1.1        HEADERS
     Host: example.org         ==>    - END_STREAM
     Content-Type: image/jpeg         + END_HEADERS
     Content-Length: 123                :method = post
                                        :scheme = https
     {binary data}                      :host = example.org
                                        :path = /resource
                                        content-type = image/jpeg
                                        content-length = 123

                                    DATA
                                      + END_STREAM
                                        {binary data}

   A response that contains no body (such includes header fields and payload data is
   transmitted as one or more HEADERS frames followed by one or more
   DATA frames, with the last DATA frame in the sequence having the
   END_STREAM flag set:

     HTTP/1.1 200 OK                HEADERS
     Content-Type: image/jpeg  ==>    - END_STREAM
     Content-Length: 123              + END_HEADERS
                                        :status = 200
     {binary data}                      content-type = image/jpeg
                                        content-length = 123

                                    DATA
                                      + END_STREAM
                                        {binary data}

   Trailing header fields are sent as a
   204 header block after both the
   request or 304 response) consists only response header block and all the DATA frames have been
   sent.  The sequence of a HEADERS frames that bears the trailers
   includes a terminal frame that contains has both END_HEADERS and END_STREAM
   flags set.

     HTTP/1.1 200 OK               HEADERS
     Content-Type: image/jpeg ===>   - END_STREAM
     Content-Length: 123             + END_HEADERS
     TE: trailers                      :status        = 200
     123                               content-type   = image/jpeg
     {binary data}                     content-length = 123
     0
     Foo: bar                      DATA
                                     - END_STREAM
                                       {binary data}

                                   HEADERS
                                     + END_STREAM
                                     + END_HEADERS
                                       foo: bar

8.1.2.  Request Header Fields

   The definitions of the FINAL flag request header fields are largely unchanged
   relative to indicate no further data will be sent on the
   stream. HTTP/1.1, with a few notable exceptions:

   o  The response status line is unfolded HTTP/1.1 request-line has been split into name-value pairs like
      other HTTP two separate header
      fields named :method and must be present:

      ":status":  The :path, whose values specify the HTTP response status code
      method for the request and the request-target, respectively.  The
      HTTP-version component of the request-line is removed entirely
      from the headers.

   o  The host and optional port portions of the request URI (see
      [RFC3986], Section 3.2), are specified using the new :host header
      field. [[anchor13: Ed.  Note: it needs to be clarified whether or
      not this replaces the existing HTTP/1.1 Host header.]]

   o  A new :scheme header field has been added to specify the scheme
      portion of the request-target (e.g. "200" or "200 OK") "https")

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

      All be lowercased, and the definitions of
      all header field names MUST defined by HTTP/1.1 are updated to be all
      lowercase.

   o  The Connection, Host, Keep-Alive, Proxy-Connection, and Transfer-
      Encoding header fields are not no longer valid and MUST not NOT be sent.

      Responses MAY be accompanied by a Content-Length header field for
      advisory purposes.  This allows clients to learn the full size of
      an entity prior to receiving all the data frames.  This can help
      in, for example, reporting progress.

      If a client receives a response where the sum of the data frame
      payload length does not equal the size of the Content-Length
      header field, the client
      [[anchor14: Ed.  Note: And "TE" I presume?]]

   All HTTP Requests MUST ignore include the content length ":method", ":path", ":host", and
   ":scheme" header
      field. [[anchor23: Ed: See
      <https://github.com/http2/http2-spec/issues/46>.]]

   If a client receives a response fields.

   Header fields whose names begin with an absent or duplicated status
   header, the client MUST treat ":" (whether defined in this as a stream error (Section 3.5.2)
   of type PROTOCOL_ERROR.

   If the client receives a data frame prior
   document or future extensions to a HEADERS frame the
   client MUST treat this as a stream error (Section 3.5.2) of type
   PROTOCOL_ERROR.

   Clients MUST support gzip compression.  Regardless of the value of
   the Accept-Encoding header field, a server MAY send responses with
   gzip or deflate encoding.  A compressed response document) MUST still bear an
   appropriate Content-Encoding appear before
   any other header field.

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 fields. [[anchor15: Ed.  Note: This requirement is
   currently pending review.  Consider it "on hold" for the moment.]]

   All HTTP Requests that sometimes include a
   server knows that it will need to send multiple resources in response
   to body SHOULD include the "content-
   length" header field.  If a single request.  Without server push features, the client must
   first download the primary resource, then discover the secondary
   resource(s), and receives a request them.

   Server push is an optional feature.  The
   SETTINGS_MAX_CONCURRENT_STREAMS setting from the client limits where the
   number sum
   of resources that can be concurrently pushed by a server.
   Server push can be disabled by clients that do the DATA frame payload lengths does not wish to receive
   pushed resources by advertising a SETTINGS_MAX_CONCURRENT_STREAMS
   SETTING (Section 3.8.4) equal the value of zero.  This prevents servers from creating the streams necessary to push resources.

   Clients receiving a pushed response MUST validate that
   "content-length" header field, the server is
   authorized to push the resource using the same-origin policy
   ([RFC6454], Section 3).  For example, MUST return a HTTP/2.0 connection to
   "example.com" is generally [[anchor24: Ed: weaselly use of
   "generally", needs better definition]] not permitted to push 400 (Bad
   Request) error.

   If a
   response for "www.example.org".

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

   Pushing of resources avoids the round-trip delay, but also creates a
   potential race where a server can be pushing content which omits a client
   is in the process of requesting.  The PUSH_PROMISE frame reduces mandatory header field from the
   chances of this condition occurring, while retaining request, the performance
   benefit.

   Pushed responses are associated
   server MUST reply with a request at the HTTP/2.0
   framing layer. HTTP 400 Bad Request reply.

8.1.3.  Response Header Fields

   The PUSH_PROMISE is sent on the stream for definitions of the
   associated request, which allows a receiver response header fields are largely unchanged
   relative to correlate the pushed
   resource HTTP/1.1, with a request. few notable exceptions:

   o  The pushed stream inherits all response status line has been reduced to a single ":status"
      header field whose value specifies only the numeric response
      status code.  The status text component of the
   request HTTP/1.1 response
      has been dropped entirely.

   o  The response MUST contain exactly one :status header fields from the associated stream field with
      exactly one response status value.  If the exception client receives an HTTP
      response that does not include the :status field, or provides
      multiple response status code values, it MUST respond with a
      stream error (Section 5.4.2) of resource identification type PROTOCOL_ERROR.

   o  All header fields (":host", ":scheme", field names MUST be lowercased, and
   ":path"), which are provided as part of the PUSH_PROMISE frame.

   Pushed resources always have an associated ":method" definitions of "GET".  A
   cache MUST store these inherited
      all header field names defined by HTTP/1.1 are updated to be all
      lowercase.

   o  The Connection, Keep-Alive, Proxy-Connection, and implied request Transfer-
      Encoding header fields are not valid and MUST NOT be sent.

   Header fields whose names begin with the cached resource.

4.3.1.  Server implementation

   A server pushes resources ":" (whether defined in association with a request from the
   client.  Prior this
   document or future extensions to closing this document) MUST appear before
   any other header fields. [[anchor16: Ed.  Note: This requirement is
   currently pending review.  Consider it "on hold" for the moment.]]

8.1.4.  GZip Content-Encoding

   Clients MUST support gzip compression for HTTP response stream, bodies.
   Regardless of the value of the accept-encoding header field, a server sends
   MAY send responses with gzip or deflate encoding.  A compressed
   response MUST still bear an appropriate content-encoding header
   field.

8.1.5.  Request Reliability Mechanisms in HTTP/2.0

   In HTTP/1.1, an HTTP client is unable to retry a
   PUSH_PROMISE for each resource that it intends non-idempotent
   request when an error occurs, because there is no means to push.  The
   PUSH_PROMISE includes header fields that allow determine
   the client to identify nature of the resource (":scheme", ":host", and ":path").

   A error.  It is possible that some server can push multiple resources in response processing
   occurred prior to a request, but
   all pushed resources MUST be promised on the response stream for error, which could result in undesirable
   effects if the
   associated request.  A server cannot send request were reattempted.

   HTTP/2.0 provides two mechanisms for providing a PUSH_PROMISE on guarantee to a new
   stream or
   client that a half-closed stream. request has not been processed:

   o  The server SHOULD include any header fields in a PUSH_PROMISE GOAWAY frame indicates the highest stream number that
   would allow might
      have been processed.  Requests on streams with higher numbers are
      therefore guaranteed to be safe to retry.

   o  The REFUSED_STREAM error code can be included in a cache RST_STREAM
      frame to determine if indicate that the resource stream is already cached
   (see [HTTP-p6], Section 4).

   After sending a PUSH_PROMISE, being closed prior to any
      processing having occurred.  Any request that was sent on the server commences transmission of a
   pushed resource.
      reset stream can be safely retried.

   In both cases, clients MAY automatically retry all requests,
   including those with non-idempotent methods.

   A pushed resource uses a server-initiated stream.
   The server sends MUST NOT indicate that a stream has not been processed
   unless it can guarantee that fact.  If frames that are on this stream in the same order as an HTTP
   response (Section 4.2.3): a HEADERS frame followed by DATA frames.

   Many uses of server push stream
   are passed to send content the application layer for any stream, then
   REFUSED_STREAM MUST NOT be used for that stream, and a client GOAWAY frame
   MUST include a stream identifier that is likely greater than or equal to the
   given stream identifier.

   In addition to discover a need for based on these mechanisms, the content of PING frame provides a response
   representation.  To minimize the chances that way for a
   client will make to easily test a
   request for resources connection.  Connections that are being pushed - causing duplicate
   copies of remain idle can
   become broken as some middleboxes (for instance, network address
   translators, or load balancers) silently discard connection bindings.
   The PING frame allows a resource client to be sent by the server - safely test whether a PUSH_PROMISE frame
   SHOULD be sent prior connection is
   still active without sending a request.

8.2.  Server Push

   HTTP/2.0 enables a server to pre-emptively send (or "push") multiple
   associated resources to any content in the response representation
   that might allow a client in response to discover the pushed resource and request
   it.

   The server MUST only push resources that could have been returned
   from a GET single request.

   Note: A
   This feature becomes particularly helpful when the server does not knows the
   client will need to have all response header fields those resources available at the time it issues a PUSH_PROMISE frame.  All remaining
   header fields are included in order to fully
   process the HEADERS frame.  The HEADERS frame
   MUST NOT duplicate header fields from the PUSH_PROMISE frames.

4.3.2.  Client implementation

   When fetching a resource the client has 3 possibilities:

   1.  the resource originally requested resource.

   Pushing additional resources is not being optional, and is negotiated only
   between individual endpoints.  For instance, an intermediary could
   receive pushed

   2. resources from the resource is being pushed, server but the data has is not yet arrived

   3. required to
   forward those on to the resource is being pushed, and client.  How to make use of the data has started pushed
   resources is up to arrive

   A client SHOULD NOT issue GET requests for a resource that has been
   promised.  A client is instead advised intermediary.  Equally, the intermediary
   might choose to push additional resources to wait for the pushed
   resource client, without any
   action taken by the server.

   Server push is semantically equivalent to arrive.

   When a client receives server responding to a
   GET request for that resource.  The PUSH_PROMISE frame from frame, or frames,
   sent by the server without includes a
   the ":host", ":scheme", and ":path" header fields, it MUST treat this
   as a stream error (Section 3.5.2) of type PROTOCOL_ERROR.

   To cancel individual server push streams, block that contains the client can issue a
   stream error (Section 3.5.2) of type CANCEL.  After receiving request
   headers that the server has assumed.

   Pushed resources are always associated with an explicit request from
   a client.  The PUSH_PROMISE frame, the client is able to cancel the pushed resource
   before receiving any frames on sent by the promised stream.  The server
   ceases transmission of are sent on the pushed resource; if
   stream created for the server has not
   commenced transmission, it does not start.

   To cancel all server push streams related to original request.  The PUSH_PROMSE frame
   includes a request, promised stream identifier, chosen from the client
   may issue a stream error (Section 3.5.2) of type CANCEL on
   identifiers available to the
   associated-stream-id.  By cancelling server (see Section 5.1.1).  Any header
   fields that stream, are not specified in the server MUST
   immediately stop sending PUSH_PROMISE frames for any streams with
   in-association-to for the original stream. [[anchor27: Ed: Triggering
   side-effects on stream reset is going to be problematic for sent by the
   framing layer.  Purely
   server are inherited from a design perspective, it's a layering
   violation.  More practically speaking, the base original request stream might
   already be removed.  Special handling logic would be required.]] sent by the client.

   The header fields in PUSH_PROMISE MUST include the ":scheme", ":host"
   and ":path" header fields that identify the resource that is being
   pushed.  A PUSH_PROMISE always implies an HTTP method of GET.  If a
   client can choose to time out pushed streams if the server receives a PUSH_PROMISE that does not
   provide include these header
   fields, or a value for the resource in ":method" header field, it MUST respond
   with a timely fashion.  A stream error (Section 3.5.2) 5.4.2) of type CANCEL can be used to stop a timed out push.

   If PROTOCOL_ERROR.

   After sending the PUSH_PROMISE frame, the server sends a HEADERS frame containing header fields that
   duplicate values can begin delivering
   the pushed resource on a previous HEADERS or PUSH_PROMISE frames on new, server-initiated stream that uses the
   same stream,
   promised stream identifier.  This stream is already implicitly "half
   closed" to the client MUST treat (Section 5.1).  The server uses this as a stream error
   (Section 3.5.2) of type PROTOCOL_ERROR.

   If to
   transmit an HTTP response, using the server sends same sequence of frames as
   defined in Section 8.1.

   Once a HEADERS frame after sending client receives a data PUSH_PROMISE frame for and chooses to accept the same stream,
   pushed resource, the client MAY ignore the HEADERS frame.  Ignoring SHOULD NOT issue any subsequent GET
   requests for the HEADERS frame promised resource until after a data frame prevents handling of HTTP's
   trailing header fields (Section 4.1.1 of [HTTP-p1]).

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 of
   these notes should be considered authoritative about how the protocol
   works.  However, these notes may prove useful in future debates about
   how promised stream
   has closed.

   The server SHOULD send PUSH_PROMISE (Section 6.6) frames prior to resolve protocol ambiguities
   sending any HEADERS 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 DATA frames that this specification sometimes blends reference the framing
   layer (Section 3) with requirements of promised
   resources.  This avoids a race where clients issue requests for
   resources prior to receiving any PUSH_PROMISE frames.

   For example, if the server receives a specific application - HTTP
   (Section 4).  This is reflected in request for a document
   containing embedded links to multiple image files, and the request/response nature of server
   chooses to push those additional images to the
   streams and client, sending push
   promises before the definition of DATA frames that contain the HEADERS which are very similar to
   HTTP, and other areas as well.

   This blending is intentional - image links ensure
   that the primary goal of this protocol client is able to create a low-latency protocol for use with HTTP.  Isolating see the
   two layers is convenient for description of promises before discovering the protocol and how it
   relates to existing HTTP implementations.  However,
   resources.  Likewise, if the ability to
   reuse server pushes resources referenced by
   the HTTP/2.0 framing layer is a non goal.

5.2.  Error handling - Framing Layer

   Error handling at header block (for instance, in Link header fields), sending the HTTP/2.0 layer splits errors into two groups:
   Those that affect an individual HTTP/2.0 stream, and those
   push promises before sending the header block ensures that clients do
   not.

   When an error is confined to a single stream, but general framing is
   intact, HTTP/2.0 attempts to use
   not request those resources.

   PUSH_PROMISE frames MUST NOT be sent by the RST_STREAM as a mechanism to
   invalidate client.  PUSH_PROMISE
   frames can be sent by the server on any stream but move forward without aborting that was opened by the
   connection altogether.

   For errors occurring outside of
   client.  They MUST be sent on a single stream context, HTTP/2.0
   assumes the entire connection that is hosed.  In this case, the endpoint
   detecting in either 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 to provide a consistent level of service (e.g.  TCP
   slow-start), prioritization, "open"
   or optimal compression when "half closed (remote)" to the server.  PUSH_PROMISE frames can be
   interspersed within the frames that comprise response, with the
   exception that they cannot be interspersed with HEADERS frames that
   comprise a single header block.

   A client
   is connecting to can use the server through multiple channels.

   Through lab measurements, we have seen consistent latency benefits by
   using fewer connections from SETTINGS_MAX_CONCURRENT_STREAMS setting to limit
   the client.  The overall number of
   packets sent by HTTP/2.0 resources that can be as much as 40% less than HTTP.
   Handling large numbers concurrently pushed by a server.
   Advertising a SETTINGS_MAX_CONCURRENT_STREAMS value of concurrent connections on zero disables
   server push by preventing the server also
   does become a scalability problem, and HTTP/2.0 reduces this load. from creating the necessary
   streams.

   The use of multiple connections is not without benefit, however.
   Because HTTP/2.0 multiplexes multiple, independent streams onto request header fields provided in the PUSH_PROMISE frame SHOULD
   include enough information for a
   single stream, it creates client to determine whether a potential cached
   representation of the resource is already available.  If the client
   determines, for head-of-line blocking
   problems at any reason, that it does not wish to receive the transport level.  In tests so far,
   pushed resource from the negative
   effects of head-of-line blocking (especially in server, or if the presence of
   packet loss) is outweighed by server takes too long to
   begin sending the benefits of compression promised resource, the client can send an
   RST_STREAM frame, using either the CANCEL or REFUSED_STREAM codes,
   and
   prioritization.

5.4.  Fixed vs Variable Length Fields referencing the pushed stream's identifier.

   Clients receiving a pushed response MUST validate that the server is
   authorized to push the resource using the same-origin policy
   ([RFC6454], Section 3).  For example, a HTTP/2.0 favors connection to
   "example.com" is generally [[anchor17: Ed: weaselly use of fixed length 32bit fields in cases where
   smaller, variable length encodings could have been used.  To some,
   this seems like
   "generally", needs better definition]] not permitted to push a tragic waste of bandwidth.  HTTP/2.0 chooses the
   simple encoding
   response for speed "www.example.org".

9.  Additional HTTP Requirements/Considerations

   TODO: SNI, gzip and simplicity.

   The goal of HTTP/2.0 is to reduce latency on deflate Content-Encoding, etc..

9.1.  Frame Size Limits for HTTP

   Frames used for HTTP messages MUST NOT exceed 2^14-1 (16383) octets
   in length, not counting the network.  The
   overhead 8 octet frame header.  An endpoint MUST
   treat the receipt of a larger frame as a FRAME_TOO_LARGE error (see
   Section 4.2).

9.2.  Connection Management

   HTTP/2.0 frames connections are persistent.  For best performance, it is generally quite low.  Each data frame
   expected clients will not close connections until it is only an 8 byte overhead for determined
   that no further communication with a 1452 byte payload (~0.6%).  At the
   time of this writing, bandwidth is already plentiful, and there server is necessary (for
   example, when a
   strong trend indicating that bandwidth will continue to increase.
   With an average worldwide bandwidth of 1Mbps, and assuming that user navigates away from a
   variable length encoding could reduce particular web page), or
   until the overhead by 50%, server closes the
   latency saved by using a variable length encoding would be less connection.

   Clients SHOULD NOT open more than
   100 nanoseconds.  More interesting are the effects when the larger
   encodings force a packet boundary, in which case a round-trip could
   be induced.  However, by addressing other aspects of one HTTP/2.0 and TCP
   interactions, we believe this is completely mitigated.

5.5.  Server Push connection to a given
   origin ([RFC6454]) concurrently.  A subtle but important point is client can create additional
   connections as replacements, either to replace connections that server push streams must be
   declared before are
   near to exhausting the associated available stream is closed.  The reason for this
   is so identifiers (Section 5.1.1),
   or to replace connections that proxies have a lifetime encountered errors
   (Section 5.4.1).

   Servers are encouraged to maintain open connections for which they can discard
   information about previous streams.  If as long as
   possible, but are permitted to terminate idle connections if
   necessary.  When either endpoint chooses to close the transport-level
   TCP connection, the terminating endpoint MUST first send a pushed stream could
   associate itself with an already-closed stream, then endpoints would
   not GOAWAY
   (Section 6.8) frame so that both endpoints can reliably determine
   whether previously sent frames have a specific lifecycle for when they could disavow knowledge
   of the streams which went before.

6. been processed and gracefully
   complete or terminate any necessary remaining tasks.

10.  Security Considerations

6.1.

10.1.  Server Authority and Same-Origin

   This specification uses the same-origin policy ([RFC6454], Section 3)
   to determine whether an origin server is permitted to provide
   content.

   A server that is contacted using TLS is authenticated based on the
   certificate that it offers in the TLS handshake (see [RFC2818],
   Section 3).  A server is considered authoritative for an "https:" "https"
   resource if it has been successfully authenticated for the domain
   part of the origin of the resource that it is providing.

   A server is considered authoritative for an "http:" "http" resource if the
   connection is established to a resolved IP address for the domain in
   the origin of the resource.

   A client MUST NOT use, in any way, resources provided by a server
   that is not authoritative for those resources.

6.2.

10.2.  Cross-Protocol Attacks

   When using 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.

   [[anchor37:
   [[anchor23: Issue: This is no longer true]]

6.3.

10.3.  Cacheability of Pushed Resources

   Pushed resources are synthesized responses without an explicit request; the
   request for a pushed resource is synthesized from the request that
   triggered the push, plus resource identification information provided
   by the server.  Request header fields are necessary for HTTP cache
   control validations (such as the Vary header field) to work.  For
   this reason, caches MUST 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 actual representation that the
   authoritative tenant provides.

   Pushed resources for which an origin server is not authoritative are
   never cached or used.

7.

11.  Privacy Considerations

7.1.  Long Lived Connections

   HTTP/2.0 aims to keep connections open longer between clients and
   servers in order to reduce the latency when a user makes a request.
   The maintenance of these connections over 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 a problem
   with HTTP in its current form as well, however the short lived
   connections make it less of a risk.

7.2.  SETTINGS frame

   The HTTP/2.0 SETTINGS frame allows servers to store out-of-band
   transmitted information about the communication between client and
   server on the client.  Although this is intended only to be used to
   reduce latency, renegade servers could use it as a mechanism to store
   identifying information about the 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.

12.  IANA Considerations

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

8.1.  These new registries are entered in a new "Hypertext
   Transfer Protocol (HTTP) 2.0 Parameters" section.

   This document also registers the "HTTP2-Settings" header field for
   use in HTTP.

12.1.  Frame Type Registry

   This document establishes a 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 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 flags and could prevent the creation of globally applicable
   flags.

   Initial values for the "HTTP/2.0 Frame Type" registry are shown in
   Table 1.

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

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

                                  Table 1

8.2.

12.2.  Error Code Registry

   This document establishes a registry for HTTP/2.0 error codes.  The
   "HTTP/2.0 Error Code" registry manages a 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 description
   of the 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 encouraged, but not mandated.

   New registrations are advised to provide the 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 specification that
      defines the error code.

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

8.3. 7.

12.3.  Settings Registry

   This document establishes a registry for HTTP/2.0 settings.  The
   "HTTP/2.0 Settings" registry manages a 24-bit space.  The "HTTP/2.0
   Settings" registry operates under the "Expert Review" policy
   [RFC5226].

   Registrations for settings are required to include a description of
   the setting.  An expert reviewer is advised to examine new
   registrations for possible duplication with existing settings.  Use
   of existing registrations is to be encouraged, but not mandated.

   New registrations are advised to provide the following information:

   Setting:  The 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 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 found in
   Section 3.8.4.3.

9. 6.5.2.

12.4.  HTTP2-Settings Header Field Registration

   This section registers the "HTTP2-Settings" header field in the
   Permanent Message Header Field Registry [BCP90].

   Header field name:  HTTP2-Settings

   Applicable protocol:  http

   Status:  standard

   Author/Change controller:  IETF

   Specification document(s):  RFC XXXX (this document)
   Related information:  This header field is only used by an HTTP/2.0
      client for Upgrade-based negotiation.

13.  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)

   o  Mark Nottingham, Julian Reschke, James Snell (Editorial)

10. Snell, Jeff Pinner
      (Substantial editorial contributions)

14.  References

10.1.

14.1.  Normative References

   [COMPRESSION]  Ruellan, H. and R. Peon, "HTTP Header Compression",
                  draft-ietf-httpbis-header-compression-00 (work in
                  progress), June 2013.

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

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

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

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

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

   [RFC4648]      Josefsson, S., "The Base16, Base32, and Base64 Data
                  Encodings", RFC 4648, October 2006.

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

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

   [TLSALPN]      Friedl, S., Popov, A., Langley, A., and E. Stephan,
                  "Transport Layer Security (TLS) Application Layer
                  Protocol Negotiation Extension",
                  draft-ietf-tls-applayerprotoneg-01 (work in progress),
                  April 2013.

10.2.

14.2.  Informative References

   [BCP90]        Klyne, G., Nottingham, M., and J. Mogul, "Registration
                  Procedures for Message Header Fields", BCP 90,
                  RFC 3864, September 2004.

   [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 C.
                  Jackson, "Talking to Yourself for 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-http2-03

   Committed major restructuring atrocities.

   Added reference to first header compression draft.

   Added more formal description of frame lifecycle.

   Moved END_STREAM (renamed from FINAL) back to HEADERS/DATA.

   Removed HEADERS+PRIORITY, added optional priority to HEADERS frame.

   Added PRIORITY frame.

A.2.  Since draft-ietf-httpbis-http2-02

   Added continuations to frames carrying header blocks.

   Replaced use of "session" with "connection" to avoid confusion with
   other HTTP stateful concepts, like cookies.

   Removed "message".

   Switched to TLS ALPN from NPN.

   Editorial changes.

A.2.

A.3.  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.3.

A.4.  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 3.6.1) 5.2.1) based on <http://
   tools.ietf.org/html/draft-montenegro-httpbis-http2-fc-principles-01>.

A.4.

A.5.  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  94304
   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