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4HTTPbis Working Group                                          M. Belshe
5Internet-Draft                                                     Twist
6Expires: July 26, 2013                                           R. Peon
7                                                             Google, Inc
8                                                         M. Thomson, Ed.
9                                                               Microsoft
10                                                        A. Melnikov, Ed.
11                                                               Isode Ltd
12                                                        January 22, 2013
13
14
15                Hypertext Transfer Protocol version 2.0
16                      draft-ietf-httpbis-http2-01
17
18Abstract
19
20   This document describes an optimised expression of the semantics of
21   the HTTP protocol.  The HTTP/2.0 encapsulation enables more efficient
22   transfer of resources over HTTP by providing compressed headers,
23   simultaneous requests, and unsolicited push of resources from server
24   to client.
25
26   This document is an alternative to, but does not obsolete
27   RFC{http-p1}.  The HTTP protocol semantics described in RFC{http-
28   p2..p7} are unmodified.
29
30Editorial Note (To be removed by RFC Editor)
31
32   This draft is a work-in-progress, and does not yet reflect Working
33   Group consensus.
34
35   This draft contains features from the SPDY Protocol as a starting
36   point, as per the Working Group's charter.  Future drafts will add,
37   remove and change text, based upon the Working Group's decisions.
38
39   Discussion of this draft takes place on the HTTPBIS working group
40   mailing list (ietf-http-wg@w3.org), which is archived at
41   <http://lists.w3.org/Archives/Public/ietf-http-wg/>.
42
43   The current issues list is at
44   <http://tools.ietf.org/wg/httpbis/trac/report/21> and related
45   documents (including fancy diffs) can be found at
46   <http://tools.ietf.org/wg/httpbis/>.
47
48   The changes in this draft are summarized in Appendix A.1.
49
50Status of This Memo
51
52
53
54
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59
60   This Internet-Draft is submitted in full conformance with the
61   provisions of BCP 78 and BCP 79.
62
63   Internet-Drafts are working documents of the Internet Engineering
64   Task Force (IETF).  Note that other groups may also distribute
65   working documents as Internet-Drafts.  The list of current Internet-
66   Drafts is at http://datatracker.ietf.org/drafts/current/.
67
68   Internet-Drafts are draft documents valid for a maximum of six months
69   and may be updated, replaced, or obsoleted by other documents at any
70   time.  It is inappropriate to use Internet-Drafts as reference
71   material or to cite them other than as "work in progress."
72
73   This Internet-Draft will expire on July 26, 2013.
74
75Copyright Notice
76
77   Copyright (c) 2013 IETF Trust and the persons identified as the
78   document authors.  All rights reserved.
79
80   This document is subject to BCP 78 and the IETF Trust's Legal
81   Provisions Relating to IETF Documents
82   (http://trustee.ietf.org/license-info) in effect on the date of
83   publication of this document.  Please review these documents
84   carefully, as they describe your rights and restrictions with respect
85   to this document.  Code Components extracted from this document must
86   include Simplified BSD License text as described in Section 4.e of
87   the Trust Legal Provisions and are provided without warranty as
88   described in the Simplified BSD License.
89
90Table of Contents
91
92   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
93     1.1.  Document Organization  . . . . . . . . . . . . . . . . . .  5
94     1.2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . .  6
95   2.  Starting HTTP/2.0  . . . . . . . . . . . . . . . . . . . . . .  6
96     2.1.  HTTP/2.0 Version Identification  . . . . . . . . . . . . .  6
97     2.2.  Starting HTTP/2.0 for "http:" URIs . . . . . . . . . . . .  7
98     2.3.  Starting HTTP/2.0 for "https:" URIs  . . . . . . . . . . .  8
99   3.  HTTP/2.0 Framing Layer . . . . . . . . . . . . . . . . . . . .  8
100     3.1.  Session (Connections)  . . . . . . . . . . . . . . . . . .  8
101     3.2.  Framing  . . . . . . . . . . . . . . . . . . . . . . . . .  8
102       3.2.1.  Control frames . . . . . . . . . . . . . . . . . . . .  9
103       3.2.2.  Data frames  . . . . . . . . . . . . . . . . . . . . . 10
104     3.3.  Streams  . . . . . . . . . . . . . . . . . . . . . . . . . 11
105       3.3.1.  Stream frames  . . . . . . . . . . . . . . . . . . . . 11
106       3.3.2.  Stream creation  . . . . . . . . . . . . . . . . . . . 11
107       3.3.3.  Stream priority  . . . . . . . . . . . . . . . . . . . 12
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116       3.3.4.  Stream headers . . . . . . . . . . . . . . . . . . . . 12
117       3.3.5.  Stream data exchange . . . . . . . . . . . . . . . . . 13
118       3.3.6.  Stream half-close  . . . . . . . . . . . . . . . . . . 13
119       3.3.7.  Stream close . . . . . . . . . . . . . . . . . . . . . 13
120     3.4.  Error Handling . . . . . . . . . . . . . . . . . . . . . . 14
121       3.4.1.  Session Error Handling . . . . . . . . . . . . . . . . 14
122       3.4.2.  Stream Error Handling  . . . . . . . . . . . . . . . . 14
123     3.5.  Stream Flow Control  . . . . . . . . . . . . . . . . . . . 15
124       3.5.1.  Flow Control Principles  . . . . . . . . . . . . . . . 15
125       3.5.2.  Basic Flow Control Algorithm . . . . . . . . . . . . . 16
126     3.6.  Control frame types  . . . . . . . . . . . . . . . . . . . 16
127       3.6.1.  SYN_STREAM . . . . . . . . . . . . . . . . . . . . . . 16
128       3.6.2.  SYN_REPLY  . . . . . . . . . . . . . . . . . . . . . . 18
129       3.6.3.  RST_STREAM . . . . . . . . . . . . . . . . . . . . . . 19
130       3.6.4.  SETTINGS . . . . . . . . . . . . . . . . . . . . . . . 20
131       3.6.5.  PING . . . . . . . . . . . . . . . . . . . . . . . . . 23
132       3.6.6.  GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . 24
133       3.6.7.  HEADERS  . . . . . . . . . . . . . . . . . . . . . . . 25
134       3.6.8.  WINDOW_UPDATE  . . . . . . . . . . . . . . . . . . . . 26
135       3.6.9.  CREDENTIAL . . . . . . . . . . . . . . . . . . . . . . 28
136       3.6.10. Name/Value Header Block  . . . . . . . . . . . . . . . 30
137   4.  HTTP Layering over HTTP/2.0  . . . . . . . . . . . . . . . . . 36
138     4.1.  Connection Management  . . . . . . . . . . . . . . . . . . 36
139       4.1.1.  Use of GOAWAY  . . . . . . . . . . . . . . . . . . . . 36
140     4.2.  HTTP Request/Response  . . . . . . . . . . . . . . . . . . 37
141       4.2.1.  Request  . . . . . . . . . . . . . . . . . . . . . . . 37
142       4.2.2.  Response . . . . . . . . . . . . . . . . . . . . . . . 39
143       4.2.3.  Authentication . . . . . . . . . . . . . . . . . . . . 39
144     4.3.  Server Push Transactions . . . . . . . . . . . . . . . . . 40
145       4.3.1.  Server implementation  . . . . . . . . . . . . . . . . 41
146       4.3.2.  Client implementation  . . . . . . . . . . . . . . . . 42
147   5.  Design Rationale and Notes . . . . . . . . . . . . . . . . . . 43
148     5.1.  Separation of Framing Layer and Application Layer  . . . . 43
149     5.2.  Error handling - Framing Layer . . . . . . . . . . . . . . 43
150     5.3.  One Connection Per Domain  . . . . . . . . . . . . . . . . 44
151     5.4.  Fixed vs Variable Length Fields  . . . . . . . . . . . . . 44
152     5.5.  Compression Context(s) . . . . . . . . . . . . . . . . . . 45
153     5.6.  Unidirectional streams . . . . . . . . . . . . . . . . . . 45
154     5.7.  Data Compression . . . . . . . . . . . . . . . . . . . . . 45
155     5.8.  Server Push  . . . . . . . . . . . . . . . . . . . . . . . 46
156   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 46
157     6.1.  Use of Same-origin constraints . . . . . . . . . . . . . . 46
158     6.2.  HTTP Headers and HTTP/2.0 Headers  . . . . . . . . . . . . 46
159     6.3.  Cross-Protocol Attacks . . . . . . . . . . . . . . . . . . 46
160     6.4.  Server Push Implicit Headers . . . . . . . . . . . . . . . 46
161   7.  Privacy Considerations . . . . . . . . . . . . . . . . . . . . 47
162     7.1.  Long Lived Connections . . . . . . . . . . . . . . . . . . 47
163     7.2.  SETTINGS frame . . . . . . . . . . . . . . . . . . . . . . 47
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172   8.  Requirements Notation  . . . . . . . . . . . . . . . . . . . . 47
173   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 47
174   10. Normative References . . . . . . . . . . . . . . . . . . . . . 48
175   Appendix A.  Change Log (to be removed by RFC Editor before
176                publication)  . . . . . . . . . . . . . . . . . . . . 49
177     A.1.  Since draft-ietf-httpbis-http2-00  . . . . . . . . . . . . 49
178     A.2.  Since draft-mbelshe-httpbis-spdy-00  . . . . . . . . . . . 49
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2281.  Introduction
229
230   HTTP is a wildly successful protocol.  HTTP/1.1 message encapsulation
231   [HTTP-p1] is optimized for implementation simplicity and
232   accessibility, not application performance.  As such it has several
233   characteristics that have a negative overall effect on application
234   performance.
235
236   The HTTP/1.1 encapsulation ensures that only one request can be
237   delivered at a time on a given connection.  HTTP/1.1 pipelining,
238   which is not widely deployed, only partially addresses these
239   concerns.  Clients that need to make multiple requests therefore use
240   commonly multiple connections to a server or servers in order to
241   reduce the overall latency of those requests.
242
243   Furthermore, HTTP/1.1 headers are represented in an inefficient
244   fashion, which, in addition to generating more or larger network
245   packets, can cause the small initial TCP window to fill more quickly
246   than is ideal.  This results in excessive latency where multiple
247   requests are made on a new TCP connection.
248
249   This document defines an optimized mapping of the HTTP semantics to a
250   TCP connection.  This optimization reduces the latency costs of HTTP
251   by allowing parallel requests on the same connection and by using an
252   efficient coding for HTTP headers.  Prioritization of requests lets
253   more important requests complete faster, further improving
254   application performance.
255
256   HTTP/2.0 applications have an improved impact on network congestion
257   due to the use of fewer TCP connections to achieve the same effect.
258   Fewer TCP connections compete more fairly with other flows.  Long-
259   lived connections are also more able to take better advantage of the
260   available network capacity, rather than operating in the slow start
261   phase of TCP.
262
263   The HTTP/2.0 encapsulation also enables more efficient processing of
264   messages by providing efficient message framing.  Processing of
265   headers in HTTP/2.0 messages is more efficient (for entities that
266   process many messages).
267
2681.1.  Document Organization
269
270   The HTTP/2.0 Specification is split into three parts: starting
271   HTTP/2.0 (Section 2), which covers how a HTTP/2.0 is started; a
272   framing layer (Section 3), which multiplexes a TCP connection into
273   independent, length-prefixed frames; and an HTTP layer (Section 4),
274   which specifies the mechanism for overlaying HTTP request/response
275   pairs on top of the framing layer.  While some of the framing layer
276
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283
284   concepts are isolated from the HTTP layer, building a generic framing
285   layer has not been a goal.  The framing layer is tailored to the
286   needs of the HTTP protocol and server push.
287
2881.2.  Definitions
289
290      client: The endpoint initiating the HTTP/2.0 session.
291
292      connection: A transport-level connection between two endpoints.
293
294      endpoint: Either the client or server of a connection.
295
296      frame: A header-prefixed sequence of bytes sent over a HTTP/2.0
297      session.
298
299      server: The endpoint which did not initiate the HTTP/2.0 session.
300
301      session: A synonym for a connection.
302
303      session error: An error on the HTTP/2.0 session.
304
305      stream: A bi-directional flow of bytes across a virtual channel
306      within a HTTP/2.0 session.
307
308      stream error: An error on an individual HTTP/2.0 stream.
309
3102.  Starting HTTP/2.0
311
312   Just as HTTP/1.1 does, HTTP/2.0 uses the "http:" and "https:" URI
313   schemes.  An HTTP/2.0-capable client is therefore required to
314   discover whether a server (or intermediary) supports HTTP/2.0.
315
316   Different discovery mechanisms are defined for "http:" and "https:"
317   URIs.  Discovery for "http:" URIs is described in Section 2.2;
318   discovery for "https:" URIs is described in Section 2.3.
319
3202.1.  HTTP/2.0 Version Identification
321
322   HTTP/2.0 is identified in using the string "HTTP/2.0".  This
323   identification is used in the HTTP/1.1 Upgrade header, in the TLS-NPN
324   [TLSNPN] [[TBD]] field and other places where protocol identification
325   is required.
326
327   [[Editor's Note: please remove the following text prior to the
328   publication of a final version of this document.]]
329
330   Only implementations of the final, published RFC can identify
331   themselves as "HTTP/2.0".  Until such an RFC exists, implementations
332
333
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339
340   MUST NOT identify themselves using "HTTP/2.0".
341
342   Examples and text throughout the rest of this document use "HTTP/2.0"
343   as a matter of editorial convenience only.  Implementations of draft
344   versions MUST NOT identify using this string.
345
346   Implementations of draft versions of the protocol MUST add the
347   corresponding draft number to the identifier before the separator
348   ('/').  For example, draft-ietf-httpbis-http2-03 is identified using
349   the string "HTTP-03/2.0".
350
351   Non-compatible experiments that are based on these draft versions
352   MUST include a further identifier.  For example, an experimental
353   implementation of packet mood-based encoding based on
354   draft-ietf-httpbis-http2-07 might identify itself as "HTTP-07-
355   emo/2.0".  Note that any label MUST conform with the "token" syntax
356   defined in Section 3.2.4 of [HTTP-p1].  Experimenters are encouraged
357   to coordinate their experiments on the ietf-http-wg@w3.org mailing
358   list.
359
3602.2.  Starting HTTP/2.0 for "http:" URIs
361
362   A client that makes a request to an "http:" URI without prior
363   knowledge about support for HTTP/2.0 uses the HTTP Upgrade mechanism
364   [HTTP-p2].  The client makes an HTTP/1.1 request that includes an
365   Upgrade header field identifying HTTP/2.0.
366
367   For example:
368
369      GET /default.htm HTTP/1.1
370      Host: server.example.com
371      Connection: Upgrade
372      Upgrade: HTTP/2.0
373
374   A server that does not support HTTP/2.0 can respond to the request as
375   though the Upgrade header field were absent:
376
377      HTTP/1.1 200 OK
378      Content-length: 243
379      Content-type: text/html
380         ...
381
382   A server that supports HTTP/2.0 can accept the upgrade with a 101
383   (Switching Protocols) status code.  After the empty line that
384   terminates the 101 response, the server can begin sending HTTP/2.0
385   frames.  These frames MUST include a response to the request that
386   initiated the Upgrade.
387
388
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395
396      HTTP/1.1 101 Switching Protocols
397      Connection: Upgrade
398      Upgrade: HTTP/2.0
399
400      [ HTTP/2.0 frames ...
401
402   A client can learn that a particular server supports HTTP/2.0 by
403   other means.  A client MAY immediately send HTTP/2.0 frames to a
404   server that is known to support HTTP/2.0.  [[Open Issue: This is not
405   definite.  We may yet choose to perform negotiation for every
406   connection.  Reasons include intermediaries; phased upgrade of load-
407   balanced server farms; etc...]]  [[Open Issue: We need to enumerate
408   the ways that clients can learn of HTTP/2.0 support.]]
409
4102.3.  Starting HTTP/2.0 for "https:" URIs
411
412   [[TBD, maybe NPN]]
413
4143.  HTTP/2.0 Framing Layer
415
4163.1.  Session (Connections)
417
418   The HTTP/2.0 framing layer (or "session") runs atop a reliable
419   transport layer such as TCP [RFC0793].  The client is the TCP
420   connection initiator.  HTTP/2.0 connections are persistent
421   connections.
422
423   For best performance, it is expected that clients will not close open
424   connections until the user navigates away from all web pages
425   referencing a connection, or until the server closes the connection.
426   Servers are encouraged to leave connections open for as long as
427   possible, but can terminate idle connections if necessary.  When
428   either endpoint closes the transport-level connection, it MUST first
429   send a GOAWAY (Section 3.6.6) frame so that the endpoints can
430   reliably determine if requests finished before the close.
431
4323.2.  Framing
433
434   Once the connection is established, clients and servers exchange
435   framed messages.  There are two types of frames: control frames
436   (Section 3.2.1) and data frames (Section 3.2.2).  Frames always have
437   a common header which is 8 bytes in length.
438
439   The first bit is a control bit indicating whether a frame is a
440   control frame or data frame.  Control frames carry a version number,
441   a frame type, flags, and a length.  Data frames contain the stream
442   ID, flags, and the length for the payload carried after the common
443   header.  The simple header is designed to make reading and writing of
444
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451
452   frames easy.
453
454   All integer values, including length, version, and type, are in
455   network byte order.  HTTP/2.0 does not enforce alignment of types in
456   dynamically sized frames.
457
4583.2.1.  Control frames
459
460   +----------------------------------+
461   |C| Version(15bits) | Type(16bits) |
462   +----------------------------------+
463   | Flags (8)  |  Length (24 bits)   |
464   +----------------------------------+
465   |               Data               |
466   +----------------------------------+
467
468   Control bit: The 'C' bit is a single bit indicating if this is a
469   control message.  For control frames this value is always 1.
470
471   Version: The version number of the HTTP/2.0 protocol.  This document
472   describes HTTP/2.0 version 3.
473
474   Type: The type of control frame.  See Control Frames for the complete
475   list of control frames.
476
477   Flags: Flags related to this frame.  Flags for control frames and
478   data frames are different.
479
480   Length: An unsigned 24-bit value representing the number of bytes
481   after the length field.
482
483   Data: data associated with this control frame.  The format and length
484   of this data is controlled by the control frame type.
485
486   Control frame processing requirements:
487
488      Note that full length control frames (16MB) can be large for
489      implementations running on resource-limited hardware.  In such
490      cases, implementations MAY limit the maximum length frame
491      supported.  However, all implementations MUST be able to receive
492      control frames of at least 8192 octets in length.
493
494
495
496
497
498
499
500
501
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507
5083.2.2.  Data frames
509
510   +----------------------------------+
511   |C|       Stream-ID (31bits)       |
512   +----------------------------------+
513   | Flags (8)  |  Length (24 bits)   |
514   +----------------------------------+
515   |               Data               |
516   +----------------------------------+
517
518   Control bit: For data frames this value is always 0.
519
520   Stream-ID: A 31-bit value identifying the stream.
521
522   Flags: Flags related to this frame.  Valid flags are:
523
524      0x01 = FLAG_FIN - signifies that this frame represents the last
525      frame to be transmitted on this stream.  See Stream Close
526      (Section 3.3.7) below.
527
528      0x02 = FLAG_COMPRESS - indicates that the data in this frame has
529      been compressed.
530
531   Length: An unsigned 24-bit value representing the number of bytes
532   after the length field.  The total size of a data frame is 8 bytes +
533   length.  It is valid to have a zero-length data frame.
534
535   Data: The variable-length data payload; the length was defined in the
536   length field.
537
538   Data frame processing requirements:
539
540      If an endpoint receives a data frame for a stream-id which is not
541      open and the endpoint has not sent a GOAWAY (Section 3.6.6) frame,
542      it MUST send issue a stream error (Section 3.4.2) with the error
543      code INVALID_STREAM for the stream-id.
544
545      If the endpoint which created the stream receives a data frame
546      before receiving a SYN_REPLY on that stream, it is a protocol
547      error, and the recipient MUST issue a stream error (Section 3.4.2)
548      with the status code PROTOCOL_ERROR for the stream-id.
549
550      Implementors note: If an endpoint receives multiple data frames
551      for invalid stream-ids, it MAY close the session.
552
553      All HTTP/2.0 endpoints MUST accept compressed data frames.
554      Compression of data frames is always done using zlib compression.
555      Each stream initializes and uses its own compression context
556
557
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563
564      dedicated to use within that stream.  Endpoints are encouraged to
565      use application level compression rather than HTTP/2.0 stream
566      level compression.
567
568      Each HTTP/2.0 stream sending compressed frames creates its own
569      zlib context for that stream, and these compression contexts MUST
570      be distinct from the compression contexts used with SYN_STREAM/
571      SYN_REPLY/HEADER compression.  (Thus, if both endpoints of a
572      stream are compressing data on the stream, there will be two zlib
573      contexts, one for sending and one for receiving).
574
5753.3.  Streams
576
577   Streams are independent sequences of bi-directional data divided into
578   frames with several properties:
579
580      Streams may be created by either the client or server.
581
582      Streams optionally carry a set of name/value header pairs.
583
584      Streams can concurrently send data interleaved with other streams.
585
586      Streams may be cancelled.
587
5883.3.1.  Stream frames
589
590   HTTP/2.0 defines 3 control frames to manage the lifecycle of a
591   stream:
592
593      SYN_STREAM - Open a new stream
594
595      SYN_REPLY - Remote acknowledgement of a new, open stream
596
597      RST_STREAM - Close a stream
598
5993.3.2.  Stream creation
600
601   A stream is created by sending a control frame with the type set to
602   SYN_STREAM (Section 3.6.1).  If the server is initiating the stream,
603   the Stream-ID must be even.  If the client is initiating the stream,
604   the Stream-ID must be odd. 0 is not a valid Stream-ID.  Stream-IDs
605   from each side of the connection must increase monotonically as new
606   streams are created.  E.g.  Stream 2 may be created after stream 3,
607   but stream 7 must not be created after stream 9.  Stream IDs do not
608   wrap: when a client or server cannot create a new stream id without
609   exceeding a 31 bit value, it MUST NOT create a new stream.
610
611   The stream-id MUST increase with each new stream.  If an endpoint
612
613
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619
620   receives a SYN_STREAM with a stream id which is less than any
621   previously received SYN_STREAM, it MUST issue a session error
622   (Section 3.4.1) with the status PROTOCOL_ERROR.
623
624   It is a protocol error to send two SYN_STREAMs with the same
625   stream-id.  If a recipient receives a second SYN_STREAM for the same
626   stream, it MUST issue a stream error (Section 3.4.2) with the status
627   code PROTOCOL_ERROR.
628
629   Upon receipt of a SYN_STREAM, the recipient can reject the stream by
630   sending a stream error (Section 3.4.2) with the error code
631   REFUSED_STREAM.  Note, however, that the creating endpoint may have
632   already sent additional frames for that stream which cannot be
633   immediately stopped.
634
635   Once the stream is created, the creator may immediately send HEADERS
636   or DATA frames for that stream, without needing to wait for the
637   recipient to acknowledge.
638
6393.3.2.1.  Unidirectional streams
640
641   When an endpoint creates a stream with the FLAG_UNIDIRECTIONAL flag
642   set, it creates a unidirectional stream which the creating endpoint
643   can use to send frames, but the receiving endpoint cannot.  The
644   receiving endpoint is implicitly already in the half-closed
645   (Section 3.3.6) state.
646
6473.3.2.2.  Bidirectional streams
648
649   SYN_STREAM frames which do not use the FLAG_UNIDIRECTIONAL flag are
650   bidirectional streams.  Both endpoints can send data on a bi-
651   directional stream.
652
6533.3.3.  Stream priority
654
655   The creator of a stream assigns a priority for that stream.  Priority
656   is represented as an integer from 0 to 7. 0 represents the highest
657   priority and 7 represents the lowest priority.
658
659   The sender and recipient SHOULD use best-effort to process streams in
660   the order of highest priority to lowest priority.
661
6623.3.4.  Stream headers
663
664   Streams carry optional sets of name/value pair headers which carry
665   metadata about the stream.  After the stream has been created, and as
666   long as the sender is not closed (Section 3.3.7) or half-closed
667   (Section 3.3.6), each side may send HEADERS frame(s) containing the
668
669
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675
676   header data.  Header data can be sent in multiple HEADERS frames, and
677   HEADERS frames may be interleaved with data frames.
678
6793.3.5.  Stream data exchange
680
681   Once a stream is created, it can be used to send arbitrary amounts of
682   data.  Generally this means that a series of data frames will be sent
683   on the stream until a frame containing the FLAG_FIN flag is set.  The
684   FLAG_FIN can be set on a SYN_STREAM (Section 3.6.1), SYN_REPLY
685   (Section 3.6.2), HEADERS (Section 3.6.7) or a DATA (Section 3.2.2)
686   frame.  Once the FLAG_FIN has been sent, the stream is considered to
687   be half-closed.
688
6893.3.6.  Stream half-close
690
691   When one side of the stream sends a frame with the FLAG_FIN flag set,
692   the stream is half-closed from that endpoint.  The sender of the
693   FLAG_FIN MUST NOT send further frames on that stream.  When both
694   sides have half-closed, the stream is closed.
695
696   If an endpoint receives a data frame after the stream is half-closed
697   from the sender (e.g. the endpoint has already received a prior frame
698   for the stream with the FIN flag set), it MUST send a RST_STREAM to
699   the sender with the status STREAM_ALREADY_CLOSED.
700
7013.3.7.  Stream close
702
703   There are 3 ways that streams can be terminated:
704
705      Normal termination: Normal stream termination occurs when both
706      sender and recipient have half-closed the stream by sending a
707      FLAG_FIN.
708
709      Abrupt termination: Either the client or server can send a
710      RST_STREAM control frame at any time.  A RST_STREAM contains an
711      error code to indicate the reason for failure.  When a RST_STREAM
712      is sent from the stream originator, it indicates a failure to
713      complete the stream and that no further data will be sent on the
714      stream.  When a RST_STREAM is sent from the stream recipient, the
715      sender, upon receipt, should stop sending any data on the stream.
716      The stream recipient should be aware that there is a race between
717      data already in transit from the sender and the time the
718      RST_STREAM is received.  See Stream Error Handling (Section 3.4.2)
719
720      TCP connection teardown: If the TCP connection is torn down while
721      un-closed streams exist, then the endpoint must assume that the
722      stream was abnormally interrupted and may be incomplete.
723
724
725
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731
732   If an endpoint receives a data frame after the stream is closed, it
733   must send a RST_STREAM to the sender with the status PROTOCOL_ERROR.
734
7353.4.  Error Handling
736
737   The HTTP/2.0 framing layer has only two types of errors, and they are
738   always handled consistently.  Any reference in this specification to
739   "issue a session error" refers to Section 3.4.1.  Any reference to
740   "issue a stream error" refers to Section 3.4.2.
741
7423.4.1.  Session Error Handling
743
744   A session error is any error which prevents further processing of the
745   framing layer or which corrupts the session compression state.  When
746   a session error occurs, the endpoint encountering the error MUST
747   first send a GOAWAY (Section 3.6.6) frame with the stream id of most
748   recently received stream from the remote endpoint, and the error code
749   for why the session is terminating.  After sending the GOAWAY frame,
750   the endpoint MUST close the TCP connection.
751
752   Note that the session compression state is dependent upon both
753   endpoints always processing all compressed data.  If an endpoint
754   partially processes a frame containing compressed data without
755   updating compression state properly, future control frames which use
756   compression will be always be errored.  Implementations SHOULD always
757   try to process compressed data so that errors which could be handled
758   as stream errors do not become session errors.
759
760   Note that because this GOAWAY is sent during a session error case, it
761   is possible that the GOAWAY will not be reliably received by the
762   receiving endpoint.  It is a best-effort attempt to communicate with
763   the remote about why the session is going down.
764
7653.4.2.  Stream Error Handling
766
767   A stream error is an error related to a specific stream-id which does
768   not affect processing of other streams at the framing layer.  Upon a
769   stream error, the endpoint MUST send a RST_STREAM (Section 3.6.3)
770   frame which contains the stream id of the stream where the error
771   occurred and the error status which caused the error.  After sending
772   the RST_STREAM, the stream is closed to the sending endpoint.  After
773   sending the RST_STREAM, if the sender receives any frames other than
774   a RST_STREAM for that stream id, it will result in sending additional
775   RST_STREAM frames.  An endpoint MUST NOT send a RST_STREAM in
776   response to an RST_STREAM, as doing so would lead to RST_STREAM
777   loops.  Sending a RST_STREAM does not cause the HTTP/2.0 session to
778   be closed.
779
780
781
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787
788   If an endpoint has multiple RST_STREAM frames to send in succession
789   for the same stream-id and the same error code, it MAY coalesce them
790   into a single RST_STREAM frame.  (This can happen if a stream is
791   closed, but the remote sends multiple data frames.  There is no
792   reason to send a RST_STREAM for each frame in succession).
793
7943.5.  Stream Flow Control
795
796   Multiplexing streams introduces contention for access to the shared
797   TCP connection.  Stream contention can result in streams being
798   blocked by other streams.  A flow control scheme ensures that streams
799   do not destructively interfere with other streams on the same TCP
800   connection.
801
8023.5.1.  Flow Control Principles
803
804   Experience with TCP congestion control has shown that algorithms can
805   evolve over time to become more sophisticated without requiring
806   protocol changes.  TCP congestion control and its evolution is
807   clearly different from HTTP/2.0 flow control, though the evolution of
808   TCP congestion control algorithms shows that a similar approach could
809   be feasible for HTTP/2.0 flow control.
810
811   HTTP/2.0 stream flow control aims to allow for future improvements to
812   flow control algorithms without requiring protocol changes.  The
813   following principles guide the HTTP/2.0 design:
814
815   1.  Flow control is hop-by-hop, not end-to-end.
816
817   2.  Flow control is based on window update messages.  Receivers
818       advertise how many octets they are prepared to receive on a
819       stream.  This is a credit-based scheme.
820
821   3.  Flow control is directional with overall control provided by the
822       receiver.  A receiver MAY choose to set any window size that it
823       desires for each stream [[TBD: ... and for the overall
824       connection]].  A sender MUST respect flow control limits imposed
825       by a receiver.  Clients, servers and intermediaries all
826       independently advertise their flow control preferences as a
827       receiver and abide by the flow control limits set by their peer
828       when sending.
829
830   4.  Flow control can be disabled by a receiver.  A receiver can
831       choose to either disable flow control, or to declare an infinite
832       flow control limit.  [[TBD: determine whether just one mechanism
833       is sufficient, and then which alternative]]
834
835
836
837
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843
844   5.  HTTP/2.0 standardizes only the format of the window update
845       message (Section 3.6.8).  This does not stipulate how a receiver
846       decides when to send this message or the value that it sends.
847       Nor does it specify how a sender chooses to send packets.
848       Implementations are able to select any algorithm that suits their
849       needs.  An example flow control algorithm is described in
850       Section 3.5.2.
851
852   Implementations are also responsible for managing how requests and
853   responses are sent based on priority; choosing how to avoid head of
854   line blocking for requests; and managing the creation of new streams.
855   Algorithm choices for these could interact with any flow control
856   algorithm.
857
8583.5.2.  Basic Flow Control Algorithm
859
860   This section describes a basic flow control algorithm.  This
861   algorithm is provided as an example, implementations can use any
862   algorithm that complies with flow control requirements.
863
864   [[Algorithm TBD]]
865
8663.6.  Control frame types
867
8683.6.1.  SYN_STREAM
869
870   The SYN_STREAM control frame allows the sender to asynchronously
871   create a stream between the endpoints.  See Stream Creation
872   (Section 3.3.2)
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
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899
900   +------------------------------------+
901   |1|    version    |         1        |
902   +------------------------------------+
903   |  Flags (8)  |  Length (24 bits)    |
904   +------------------------------------+
905   |X|           Stream-ID (31bits)     |
906   +------------------------------------+
907   |X| Associated-To-Stream-ID (31bits) |
908   +------------------------------------+
909   | Pri|Unused | Slot |                |
910   +-------------------+                |
911   | Number of Name/Value pairs (int32) |   <+
912   +------------------------------------+    |
913   |     Length of name (int32)         |    | This section is the
914   +------------------------------------+    | "Name/Value Header
915   |           Name (string)            |    | Block", and is
916   +------------------------------------+    | compressed.
917   |     Length of value  (int32)       |    |
918   +------------------------------------+    |
919   |          Value   (string)          |    |
920   +------------------------------------+    |
921   |           (repeats)                |   <+
922
923   Flags: Flags related to this frame.  Valid flags are:
924
925      0x01 = FLAG_FIN - marks this frame as the last frame to be
926      transmitted on this stream and puts the sender in the half-closed
927      (Section 3.3.6) state.
928
929      0x02 = FLAG_UNIDIRECTIONAL - a stream created with this flag puts
930      the recipient in the half-closed (Section 3.3.6) state.
931
932   Length: The length is the number of bytes which follow the length
933   field in the frame.  For SYN_STREAM frames, this is 10 bytes plus the
934   length of the compressed Name/Value block.
935
936   Stream-ID: The 31-bit identifier for this stream.  This stream-id
937   will be used in frames which are part of this stream.
938
939   Associated-To-Stream-ID: The 31-bit identifier for a stream which
940   this stream is associated to.  If this stream is independent of all
941   other streams, it should be 0.
942
943   Priority: A 3-bit priority (Section 3.3.3) field.
944
945   Unused: 5 bits of unused space, reserved for future use.
946
947   Slot: An 8 bit unsigned integer specifying the index in the server's
948
949
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955
956   CREDENTIAL vector of the client certificate to be used for this
957   request. see CREDENTIAL frame (Section 3.6.9).  The value 0 means no
958   client certificate should be associated with this stream.
959
960   Name/Value Header Block: A set of name/value pairs carried as part of
961   the SYN_STREAM. see Name/Value Header Block (Section 3.6.10).
962
963   If an endpoint receives a SYN_STREAM which is larger than the
964   implementation supports, it MAY send a RST_STREAM with error code
965   FRAME_TOO_LARGE.  All implementations MUST support the minimum size
966   limits defined in the Control Frames section (Section 3.2.1).
967
9683.6.2.  SYN_REPLY
969
970   SYN_REPLY indicates the acceptance of a stream creation by the
971   recipient of a SYN_STREAM frame.
972
973   +------------------------------------+
974   |1|    version    |         2        |
975   +------------------------------------+
976   |  Flags (8)  |  Length (24 bits)    |
977   +------------------------------------+
978   |X|           Stream-ID (31bits)     |
979   +------------------------------------+
980   | Number of Name/Value pairs (int32) |   <+
981   +------------------------------------+    |
982   |     Length of name (int32)         |    | This section is the
983   +------------------------------------+    | "Name/Value Header
984   |           Name (string)            |    | Block", and is
985   +------------------------------------+    | compressed.
986   |     Length of value  (int32)       |    |
987   +------------------------------------+    |
988   |          Value   (string)          |    |
989   +------------------------------------+    |
990   |           (repeats)                |   <+
991
992   Flags: Flags related to this frame.  Valid flags are:
993
994      0x01 = FLAG_FIN - marks this frame as the last frame to be
995      transmitted on this stream and puts the sender in the half-closed
996      (Section 3.3.6) state.
997
998   Length: The length is the number of bytes which follow the length
999   field in the frame.  For SYN_REPLY frames, this is 4 bytes plus the
1000   length of the compressed Name/Value block.
1001
1002   Stream-ID: The 31-bit identifier for this stream.
1003
1004
1005
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1011
1012   If an endpoint receives multiple SYN_REPLY frames for the same active
1013   stream ID, it MUST issue a stream error (Section 3.4.2) with the
1014   error code STREAM_IN_USE.
1015
1016   Name/Value Header Block: A set of name/value pairs carried as part of
1017   the SYN_STREAM. see Name/Value Header Block (Section 3.6.10).
1018
1019   If an endpoint receives a SYN_REPLY which is larger than the
1020   implementation supports, it MAY send a RST_STREAM with error code
1021   FRAME_TOO_LARGE.  All implementations MUST support the minimum size
1022   limits defined in the Control Frames section (Section 3.2.1).
1023
10243.6.3.  RST_STREAM
1025
1026   The RST_STREAM frame allows for abnormal termination of a stream.
1027   When sent by the creator of a stream, it indicates the creator wishes
1028   to cancel the stream.  When sent by the recipient of a stream, it
1029   indicates an error or that the recipient did not want to accept the
1030   stream, so the stream should be closed.
1031
1032   +----------------------------------+
1033   |1|   version    |         3       |
1034   +----------------------------------+
1035   | Flags (8)  |         8           |
1036   +----------------------------------+
1037   |X|          Stream-ID (31bits)    |
1038   +----------------------------------+
1039   |          Status code             |
1040   +----------------------------------+
1041
1042   Flags: Flags related to this frame.  RST_STREAM does not define any
1043   flags.  This value must be 0.
1044
1045   Length: An unsigned 24-bit value representing the number of bytes
1046   after the length field.  For RST_STREAM control frames, this value is
1047   always 8.
1048
1049   Stream-ID: The 31-bit identifier for this stream.
1050
1051   Status code: (32 bits) An indicator for why the stream is being
1052   terminated.The following status codes are defined:
1053
1054      1 - PROTOCOL_ERROR.  This is a generic error, and should only be
1055      used if a more specific error is not available.
1056
1057      2 - INVALID_STREAM.  This is returned when a frame is received for
1058      a stream which is not active.
1059
1060
1061
1062
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1066
1067
1068      3 - REFUSED_STREAM.  Indicates that the stream was refused before
1069      any processing has been done on the stream.
1070
1071      4 - UNSUPPORTED_VERSION.  Indicates that the recipient of a stream
1072      does not support the HTTP/2.0 version requested.
1073
1074      5 - CANCEL.  Used by the creator of a stream to indicate that the
1075      stream is no longer needed.
1076
1077      6 - INTERNAL_ERROR.  This is a generic error which can be used
1078      when the implementation has internally failed, not due to anything
1079      in the protocol.
1080
1081      7 - FLOW_CONTROL_ERROR.  The endpoint detected that its peer
1082      violated the flow control protocol.
1083
1084      8 - STREAM_IN_USE.  The endpoint received a SYN_REPLY for a stream
1085      already open.
1086
1087      9 - STREAM_ALREADY_CLOSED.  The endpoint received a data or
1088      SYN_REPLY frame for a stream which is half closed.
1089
1090      10 - INVALID_CREDENTIALS.  The server received a request for a
1091      resource whose origin does not have valid credentials in the
1092      client certificate vector.
1093
1094      11 - FRAME_TOO_LARGE.  The endpoint received a frame which this
1095      implementation could not support.  If FRAME_TOO_LARGE is sent for
1096      a SYN_STREAM, HEADERS, or SYN_REPLY frame without fully processing
1097      the compressed portion of those frames, then the compression state
1098      will be out-of-sync with the other endpoint.  In this case,
1099      senders of FRAME_TOO_LARGE MUST close the session.
1100
1101      Note: 0 is not a valid status code for a RST_STREAM.
1102
1103   After receiving a RST_STREAM on a stream, the recipient must not send
1104   additional frames for that stream, and the stream moves into the
1105   closed state.
1106
11073.6.4.  SETTINGS
1108
1109   A SETTINGS frame contains a set of id/value pairs for communicating
1110   configuration data about how the two endpoints may communicate.
1111   SETTINGS frames can be sent at any time by either endpoint, are
1112   optionally sent, and are fully asynchronous.  When the server is the
1113   sender, the sender can request that configuration data be persisted
1114   by the client across HTTP/2.0 sessions and returned to the server in
1115   future communications.
1116
1117
1118
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1122
1123
1124   Persistence of SETTINGS ID/Value pairs is done on a per origin/IP
1125   pair (the "origin" is the set of scheme, host, and port from the URI.
1126   See [RFC6454]).  That is, when a client connects to a server, and the
1127   server persists settings within the client, the client SHOULD return
1128   the persisted settings on future connections to the same origin AND
1129   IP address and TCP port.  Clients MUST NOT request servers to use the
1130   persistence features of the SETTINGS frames, and servers MUST ignore
1131   persistence related flags sent by a client.
1132
1133   +----------------------------------+
1134   |1|   version    |         4       |
1135   +----------------------------------+
1136   | Flags (8)  |  Length (24 bits)   |
1137   +----------------------------------+
1138   |         Number of entries        |
1139   +----------------------------------+
1140   |          ID/Value Pairs          |
1141   |             ...                  |
1142
1143   Control bit: The control bit is always 1 for this message.
1144
1145   Version: The HTTP/2.0 version number.
1146
1147   Type: The message type for a SETTINGS message is 4.
1148
1149   Flags: FLAG_SETTINGS_CLEAR_SETTINGS (0x1): When set, the client
1150   should clear any previously persisted SETTINGS ID/Value pairs.  If
1151   this frame contains ID/Value pairs with the
1152   FLAG_SETTINGS_PERSIST_VALUE set, then the client will first clear its
1153   existing, persisted settings, and then persist the values with the
1154   flag set which are contained within this frame.  Because persistence
1155   is only implemented on the client, this flag can only be used when
1156   the sender is the server.
1157
1158   Length: An unsigned 24-bit value representing the number of bytes
1159   after the length field.  The total size of a SETTINGS frame is 8
1160   bytes + length.
1161
1162   Number of entries: A 32-bit value representing the number of ID/value
1163   pairs in this message.
1164
1165   ID: A 32-bit ID number, comprised of 8 bits of flags and 24 bits of
1166   unique ID.
1167
1168      ID.flags:
1169
1170         FLAG_SETTINGS_PERSIST_VALUE (0x1): When set, the sender of this
1171         SETTINGS frame is requesting that the recipient persist the ID/
1172
1173
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1178
1179
1180         Value and return it in future SETTINGS frames sent from the
1181         sender to this recipient.  Because persistence is only
1182         implemented on the client, this flag is only sent by the
1183         server.
1184
1185         FLAG_SETTINGS_PERSISTED (0x2): When set, the sender is
1186         notifying the recipient that this ID/Value pair was previously
1187         sent to the sender by the recipient with the
1188         FLAG_SETTINGS_PERSIST_VALUE, and the sender is returning it.
1189         Because persistence is only implemented on the client, this
1190         flag is only sent by the client.
1191
1192      Defined IDs:
1193
1194         1 - SETTINGS_UPLOAD_BANDWIDTH allows the sender to send its
1195         expected upload bandwidth on this channel.  This number is an
1196         estimate.  The value should be the integral number of kilobytes
1197         per second that the sender predicts as an expected maximum
1198         upload channel capacity.
1199
1200         2 - SETTINGS_DOWNLOAD_BANDWIDTH allows the sender to send its
1201         expected download bandwidth on this channel.  This number is an
1202         estimate.  The value should be the integral number of kilobytes
1203         per second that the sender predicts as an expected maximum
1204         download channel capacity.
1205
1206         3 - SETTINGS_ROUND_TRIP_TIME allows the sender to send its
1207         expected round-trip-time on this channel.  The round trip time
1208         is defined as the minimum amount of time to send a control
1209         frame from this client to the remote and receive a response.
1210         The value is represented in milliseconds.
1211
1212         4 - SETTINGS_MAX_CONCURRENT_STREAMS allows the sender to inform
1213         the remote endpoint the maximum number of concurrent streams
1214         which it will allow.  By default there is no limit.  For
1215         implementors it is recommended that this value be no smaller
1216         than 100.
1217
1218         5 - SETTINGS_CURRENT_CWND allows the sender to inform the
1219         remote endpoint of the current TCP CWND value.
1220
1221         6 - SETTINGS_DOWNLOAD_RETRANS_RATE allows the sender to inform
1222         the remote endpoint the retransmission rate (bytes
1223         retransmitted / total bytes transmitted).
1224
1225         7 - SETTINGS_INITIAL_WINDOW_SIZE allows the sender to inform
1226         the remote endpoint the initial window size (in bytes) for new
1227         streams.
1228
1229
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1234
1235
1236         8 - SETTINGS_CLIENT_CERTIFICATE_VECTOR_SIZE allows the server
1237         to inform the client of the new size of the client certificate
1238         vector.
1239
1240   Value: A 32-bit value.
1241
1242   The message is intentionally extensible for future information which
1243   may improve client-server communications.  The sender does not need
1244   to send every type of ID/value.  It must only send those for which it
1245   has accurate values to convey.  When multiple ID/value pairs are
1246   sent, they should be sent in order of lowest id to highest id.  A
1247   single SETTINGS frame MUST not contain multiple values for the same
1248   ID.  If the recipient of a SETTINGS frame discovers multiple values
1249   for the same ID, it MUST ignore all values except the first one.
1250
1251   A server may send multiple SETTINGS frames containing different ID/
1252   Value pairs.  When the same ID/Value is sent twice, the most recent
1253   value overrides any previously sent values.  If the server sends IDs
1254   1, 2, and 3 with the FLAG_SETTINGS_PERSIST_VALUE in a first SETTINGS
1255   frame, and then sends IDs 4 and 5 with the
1256   FLAG_SETTINGS_PERSIST_VALUE, when the client returns the persisted
1257   state on its next SETTINGS frame, it SHOULD send all 5 settings (1,
1258   2, 3, 4, and 5 in this example) to the server.
1259
12603.6.5.  PING
1261
1262   The PING control frame is a mechanism for measuring a minimal round-
1263   trip time from the sender.  It can be sent from the client or the
1264   server.  Recipients of a PING frame should send an identical frame to
1265   the sender as soon as possible (if there is other pending data
1266   waiting to be sent, PING should take highest priority).  Each ping
1267   sent by a sender should use a unique ID.
1268
1269   +----------------------------------+
1270   |1|   version    |         6       |
1271   +----------------------------------+
1272   | 0 (flags) |     4 (length)       |
1273   +----------------------------------|
1274   |            32-bit ID             |
1275   +----------------------------------+
1276
1277   Control bit: The control bit is always 1 for this message.
1278
1279   Version: The HTTP/2.0 version number.
1280
1281   Type: The message type for a PING message is 6.
1282
1283   Length: This frame is always 4 bytes long.
1284
1285
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1290
1291
1292   ID: A unique ID for this ping, represented as an unsigned 32 bit
1293   value.  When the client initiates a ping, it must use an odd numbered
1294   ID.  When the server initiates a ping, it must use an even numbered
1295   ping.  Use of odd/even IDs is required in order to avoid accidental
1296   looping on PINGs (where each side initiates an identical PING at the
1297   same time).
1298
1299   Note: If a sender uses all possible PING ids (e.g. has sent all 2^31
1300   possible IDs), it can wrap and start re-using IDs.
1301
1302   If a server receives an even numbered PING which it did not initiate,
1303   it must ignore the PING.  If a client receives an odd numbered PING
1304   which it did not initiate, it must ignore the PING.
1305
13063.6.6.  GOAWAY
1307
1308   The GOAWAY control frame is a mechanism to tell the remote side of
1309   the connection to stop creating streams on this session.  It can be
1310   sent from the client or the server.  Once sent, the sender will not
1311   respond to any new SYN_STREAMs on this session.  Recipients of a
1312   GOAWAY frame must not send additional streams on this session,
1313   although a new session can be established for new streams.  The
1314   purpose of this message is to allow an endpoint to gracefully stop
1315   accepting new streams (perhaps for a reboot or maintenance), while
1316   still finishing processing of previously established streams.
1317
1318   There is an inherent race condition between an endpoint sending
1319   SYN_STREAMs and the remote sending a GOAWAY message.  To deal with
1320   this case, the GOAWAY contains a last-stream-id indicating the
1321   stream-id of the last stream which was created on the sending
1322   endpoint in this session.  If the receiver of the GOAWAY sent new
1323   SYN_STREAMs for sessions after this last-stream-id, they were not
1324   processed by the server and the receiver may treat the stream as
1325   though it had never been created at all (hence the receiver may want
1326   to re-create the stream later on a new session).
1327
1328   Endpoints should always send a GOAWAY message before closing a
1329   connection so that the remote can know whether a stream has been
1330   partially processed or not.  (For example, if an HTTP client sends a
1331   POST at the same time that a server closes a connection, the client
1332   cannot know if the server started to process that POST request if the
1333   server does not send a GOAWAY frame to indicate where it stopped
1334   working).
1335
1336   After sending a GOAWAY message, the sender must ignore all SYN_STREAM
1337   frames for new streams.
1338
1339
1340
1341
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1346
1347
1348   +----------------------------------+
1349   |1|   version    |         7       |
1350   +----------------------------------+
1351   | 0 (flags) |     8 (length)       |
1352   +----------------------------------|
1353   |X|  Last-good-stream-ID (31 bits) |
1354   +----------------------------------+
1355   |          Status code             |
1356   +----------------------------------+
1357
1358   Control bit: The control bit is always 1 for this message.
1359
1360   Version: The HTTP/2.0 version number.
1361
1362   Type: The message type for a GOAWAY message is 7.
1363
1364   Length: This frame is always 8 bytes long.
1365
1366   Last-good-stream-Id: The last stream id which was replied to (with
1367   either a SYN_REPLY or RST_STREAM) by the sender of the GOAWAY
1368   message.  If no streams were replied to, this value MUST be 0.
1369
1370   Status: The reason for closing the session.
1371
1372      0 - OK.  This is a normal session teardown.
1373
1374      1 - PROTOCOL_ERROR.  This is a generic error, and should only be
1375      used if a more specific error is not available.
1376
1377      2 - INTERNAL_ERROR.  This is a generic error which can be used
1378      when the implementation has internally failed, not due to anything
1379      in the protocol.
1380
13813.6.7.  HEADERS
1382
1383   The HEADERS frame augments a stream with additional headers.  It may
1384   be optionally sent on an existing stream at any time.  Specific
1385   application of the headers in this frame is application-dependent.
1386   The name/value header block within this frame is compressed.
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
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1402
1403
1404   +------------------------------------+
1405   |1|   version     |          8       |
1406   +------------------------------------+
1407   | Flags (8)  |   Length (24 bits)    |
1408   +------------------------------------+
1409   |X|          Stream-ID (31bits)      |
1410   +------------------------------------+
1411   | Number of Name/Value pairs (int32) |   <+
1412   +------------------------------------+    |
1413   |     Length of name (int32)         |    | This section is the
1414   +------------------------------------+    | "Name/Value Header
1415   |           Name (string)            |    | Block", and is
1416   +------------------------------------+    | compressed.
1417   |     Length of value  (int32)       |    |
1418   +------------------------------------+    |
1419   |          Value   (string)          |    |
1420   +------------------------------------+    |
1421   |           (repeats)                |   <+
1422
1423   Flags: Flags related to this frame.  Valid flags are:
1424
1425      0x01 = FLAG_FIN - marks this frame as the last frame to be
1426      transmitted on this stream and puts the sender in the half-closed
1427      (Section 3.3.6) state.
1428
1429   Length: An unsigned 24 bit value representing the number of bytes
1430   after the length field.  The minimum length of the length field is 4
1431   (when the number of name value pairs is 0).
1432
1433   Stream-ID: The stream this HEADERS block is associated with.
1434
1435   Name/Value Header Block: A set of name/value pairs carried as part of
1436   the SYN_STREAM. see Name/Value Header Block (Section 3.6.10).
1437
14383.6.8.  WINDOW_UPDATE
1439
1440   The WINDOW_UPDATE control frame is used to implement per stream flow
1441   control in HTTP/2.0.  Flow control in HTTP/2.0 is per hop, that is,
1442   only between the two endpoints of a HTTP/2.0 connection.  If there
1443   are one or more intermediaries between the client and the origin
1444   server, flow control signals are not explicitly forwarded by the
1445   intermediaries.  (However, throttling of data transfer by any
1446   recipient may have the effect of indirectly propagating flow control
1447   information upstream back to the original sender.)  Flow control only
1448   applies to the data portion of data frames.  Recipients must buffer
1449   all control frames.  If a recipient fails to buffer an entire control
1450   frame, it MUST issue a stream error (Section 3.4.2) with the status
1451   code FLOW_CONTROL_ERROR for the stream.
1452
1453
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1458
1459
1460   Flow control in HTTP/2.0 is implemented by a data transfer window
1461   kept by the sender of each stream.  The data transfer window is a
1462   simple uint32 that indicates how many bytes of data the sender can
1463   transmit.  After a stream is created, but before any data frames have
1464   been transmitted, the sender begins with the initial window size.
1465   This window size is a measure of the buffering capability of the
1466   recipient.  The sender must not send a data frame with data length
1467   greater than the transfer window size.  After sending each data
1468   frame, the sender decrements its transfer window size by the amount
1469   of data transmitted.  When the window size becomes less than or equal
1470   to 0, the sender must pause transmitting data frames.  At the other
1471   end of the stream, the recipient sends a WINDOW_UPDATE control back
1472   to notify the sender that it has consumed some data and freed up
1473   buffer space to receive more data.
1474
1475   +----------------------------------+
1476   |1|   version    |         9       |
1477   +----------------------------------+
1478   | 0 (flags) |     8 (length)       |
1479   +----------------------------------+
1480   |X|     Stream-ID (31-bits)        |
1481   +----------------------------------+
1482   |X|  Delta-Window-Size (31-bits)   |
1483   +----------------------------------+
1484
1485   Control bit: The control bit is always 1 for this message.
1486
1487   Version: The HTTP/2.0 version number.
1488
1489   Type: The message type for a WINDOW_UPDATE message is 9.
1490
1491   Length: The length field is always 8 for this frame (there are 8
1492   bytes after the length field).
1493
1494   Stream-ID: The stream ID that this WINDOW_UPDATE control frame is
1495   for.
1496
1497   Delta-Window-Size: The additional number of bytes that the sender can
1498   transmit in addition to existing remaining window size.  The legal
1499   range for this field is 1 to 2^31 - 1 (0x7fffffff) bytes.
1500
1501   The window size as kept by the sender must never exceed 2^31
1502   (although it can become negative in one special case).  If a sender
1503   receives a WINDOW_UPDATE that causes the its window size to exceed
1504   this limit, it must send RST_STREAM with status code
1505   FLOW_CONTROL_ERROR to terminate the stream.
1506
1507   When a HTTP/2.0 connection is first established, the default initial
1508
1509
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1514
1515
1516   window size for all streams is 64KB.  An endpoint can use the
1517   SETTINGS control frame to adjust the initial window size for the
1518   connection.  That is, its peer can start out using the 64KB default
1519   initial window size when sending data frames before receiving the
1520   SETTINGS.  Because SETTINGS is asynchronous, there may be a race
1521   condition if the recipient wants to decrease the initial window size,
1522   but its peer immediately sends 64KB on the creation of a new
1523   connection, before waiting for the SETTINGS to arrive.  This is one
1524   case where the window size kept by the sender will become negative.
1525   Once the sender detects this condition, it must stop sending data
1526   frames and wait for the recipient to catch up.  The recipient has two
1527   choices:
1528
1529      immediately send RST_STREAM with FLOW_CONTROL_ERROR status code.
1530
1531      allow the head of line blocking (as there is only one stream for
1532      the session and the amount of data in flight is bounded by the
1533      default initial window size), and send WINDOW_UPDATE as it
1534      consumes data.
1535
1536   In the case of option 2, both sides must compute the window size
1537   based on the initial window size in the SETTINGS.  For example, if
1538   the recipient sets the initial window size to be 16KB, and the sender
1539   sends 64KB immediately on connection establishment, the sender will
1540   discover its window size is -48KB on receipt of the SETTINGS.  As the
1541   recipient consumes the first 16KB, it must send a WINDOW_UPDATE of
1542   16KB back to the sender.  This interaction continues until the
1543   sender's window size becomes positive again, and it can resume
1544   transmitting data frames.
1545
1546   After the recipient reads in a data frame with FLAG_FIN that marks
1547   the end of the data stream, it should not send WINDOW_UPDATE frames
1548   as it consumes the last data frame.  A sender should ignore all the
1549   WINDOW_UPDATE frames associated with the stream after it send the
1550   last frame for the stream.
1551
1552   The data frames from the sender and the WINDOW_UPDATE frames from the
1553   recipient are completely asynchronous with respect to each other.
1554   This property allows a recipient to aggressively update the window
1555   size kept by the sender to prevent the stream from stalling.
1556
15573.6.9.  CREDENTIAL
1558
1559   The CREDENTIAL control frame is used by the client to send additional
1560   client certificates to the server.  A HTTP/2.0 client may decide to
1561   send requests for resources from different origins on the same
1562   HTTP/2.0 session if it decides that that server handles both origins.
1563   For example if the IP address associated with both hostnames matches
1564
1565
1566
1567Belshe, et al.            Expires July 26, 2013                [Page 28]
1568
1569Internet-Draft                  HTTP/2.0                    January 2013
1570
1571
1572   and the SSL server certificate presented in the initial handshake is
1573   valid for both hostnames.  However, because the SSL connection can
1574   contain at most one client certificate, the client needs a mechanism
1575   to send additional client certificates to the server.
1576
1577   The server is required to maintain a vector of client certificates
1578   associated with a HTTP/2.0 session.  When the client needs to send a
1579   client certificate to the server, it will send a CREDENTIAL frame
1580   that specifies the index of the slot in which to store the
1581   certificate as well as proof that the client posesses the
1582   corresponding private key.  The initial size of this vector must be
1583   8.  If the client provides a client certificate during the first TLS
1584   handshake, the contents of this certificate must be copied into the
1585   first slot (index 1) in the CREDENTIAL vector, though it may be
1586   overwritten by subsequent CREDENTIAL frames.  The server must
1587   exclusively use the CREDENTIAL vector when evaluating the client
1588   certificates associated with an origin.  The server may change the
1589   size of this vector by sending a SETTINGS frame with the setting
1590   SETTINGS_CLIENT_CERTIFICATE_VECTOR_SIZE value specified.  In the
1591   event that the new size is smaller than the current size, truncation
1592   occurs preserving lower-index slots as possible.
1593
1594   TLS renegotiation with client authentication is incompatible with
1595   HTTP/2.0 given the multiplexed nature of HTTP/2.0.  Specifically,
1596   imagine that the client has 2 requests outstanding to the server for
1597   two different pages (in different tabs).  When the renegotiation +
1598   client certificate request comes in, the browser is unable to
1599   determine which resource triggered the client certificate request, in
1600   order to prompt the user accordingly.
1601
1602   +----------------------------------+
1603   |1|000000000000001|0000000000001011|
1604   +----------------------------------+
1605   | flags (8)  |  Length (24 bits)   |
1606   +----------------------------------+
1607   |  Slot (16 bits) |                |
1608   +-----------------+                |
1609   |      Proof Length (32 bits)      |
1610   +----------------------------------+
1611   |               Proof              |
1612   +----------------------------------+ <+
1613   |   Certificate Length (32 bits)   |  |
1614   +----------------------------------+  | Repeated until end of frame
1615   |            Certificate           |  |
1616   +----------------------------------+ <+
1617
1618   Slot: The index in the server's client certificate vector where this
1619   certificate should be stored.  If there is already a certificate
1620
1621
1622
1623Belshe, et al.            Expires July 26, 2013                [Page 29]
1624
1625Internet-Draft                  HTTP/2.0                    January 2013
1626
1627
1628   stored at this index, it will be overwritten.  The index is one
1629   based, not zero based; zero is an invalid slot index.
1630
1631   Proof: Cryptographic proof that the client has possession of the
1632   private key associated with the certificate.  The format is a TLS
1633   digitally-signed element ([RFC5246], Section 4.7).  The signature
1634   algorithm must be the same as that used in the CertificateVerify
1635   message.  However, since the MD5+SHA1 signature type used in TLS 1.0
1636   connections can not be correctly encoded in a digitally-signed
1637   element, SHA1 must be used when MD5+SHA1 was used in the SSL
1638   connection.  The signature is calculated over a 32 byte TLS extractor
1639   value (http://tools.ietf.org/html/rfc5705) with a label of "EXPORTER
1640   HTTP/2.0 certificate proof" using the empty string as context.
1641   ForRSA certificates the signature would be a PKCS#1 v1.5 signature.
1642   For ECDSA, it would be an ECDSA-Sig-Value
1643   (http://tools.ietf.org/html/rfc5480#appendix-A).  For a 1024-bit RSA
1644   key, the CREDENTIAL message would be ~500 bytes.
1645
1646   Certificate: The certificate chain, starting with the leaf
1647   certificate.  Each certificate must be encoded as a 32 bit length,
1648   followed by a DER encoded certificate.  The certificate must be of
1649   the same type (RSA, ECDSA, etc) as the client certificate associated
1650   with the SSL connection.
1651
1652   If the server receives a request for a resource with unacceptable
1653   credential (either missing or invalid), it must reply with a
1654   RST_STREAM frame with the status code INVALID_CREDENTIALS.  Upon
1655   receipt of a RST_STREAM frame with INVALID_CREDENTIALS, the client
1656   should initiate a new stream directly to the requested origin and
1657   resend the request.  Note, HTTP/2.0 does not allow the server to
1658   request different client authentication for different resources in
1659   the same origin.
1660
1661   If the server receives an invalid CREDENTIAL frame, it MUST respond
1662   with a GOAWAY frame and shutdown the session.
1663
16643.6.10.  Name/Value Header Block
1665
1666   The Name/Value Header Block is found in the SYN_STREAM, SYN_REPLY and
1667   HEADERS control frames, and shares a common format:
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679Belshe, et al.            Expires July 26, 2013                [Page 30]
1680
1681Internet-Draft                  HTTP/2.0                    January 2013
1682
1683
1684   +------------------------------------+
1685   | Number of Name/Value pairs (int32) |
1686   +------------------------------------+
1687   |     Length of name (int32)         |
1688   +------------------------------------+
1689   |           Name (string)            |
1690   +------------------------------------+
1691   |     Length of value  (int32)       |
1692   +------------------------------------+
1693   |          Value   (string)          |
1694   +------------------------------------+
1695   |           (repeats)                |
1696
1697   Number of Name/Value pairs: The number of repeating name/value pairs
1698   following this field.
1699
1700   List of Name/Value pairs:
1701
1702      Length of Name: a 32-bit value containing the number of octets in
1703      the name field.  Note that in practice, this length must not
1704      exceed 2^24, as that is the maximum size of a HTTP/2.0 frame.
1705
1706      Name: 0 or more octets, 8-bit sequences of data, excluding 0.
1707
1708      Length of Value: a 32-bit value containing the number of octets in
1709      the value field.  Note that in practice, this length must not
1710      exceed 2^24, as that is the maximum size of a HTTP/2.0 frame.
1711
1712      Value: 0 or more octets, 8-bit sequences of data, excluding 0.
1713
1714   Each header name must have at least one value.  Header names are
1715   encoded using the US-ASCII character set [ASCII] and must be all
1716   lower case.  The length of each name must be greater than zero.  A
1717   recipient of a zero-length name MUST issue a stream error
1718   (Section 3.4.2) with the status code PROTOCOL_ERROR for the
1719   stream-id.
1720
1721   Duplicate header names are not allowed.  To send two identically
1722   named headers, send a header with two values, where the values are
1723   separated by a single NUL (0) byte.  A header value can either be
1724   empty (e.g. the length is zero) or it can contain multiple, NUL-
1725   separated values, each with length greater than zero.  The value
1726   never starts nor ends with a NUL character.  Recipients of illegal
1727   value fields MUST issue a stream error (Section 3.4.2) with the
1728   status code PROTOCOL_ERROR for the stream-id.
1729
1730
1731
1732
1733
1734
1735Belshe, et al.            Expires July 26, 2013                [Page 31]
1736
1737Internet-Draft                  HTTP/2.0                    January 2013
1738
1739
17403.6.10.1.  Compression
1741
1742   The Name/Value Header Block is a section of the SYN_STREAM,
1743   SYN_REPLY, and HEADERS frames used to carry header meta-data.  This
1744   block is always compressed using zlib compression.  Within this
1745   specification, any reference to 'zlib' is referring to the ZLIB
1746   Compressed Data Format Specification Version 3.3 as part of RFC1950.
1747   [RFC1950]
1748
1749   For each HEADERS compression instance, the initial state is
1750   initialized using the following dictionary [UDELCOMPRESSION]:
1751
1752   <CODE BEGINS>
1753
1754   const unsigned char http2_dictionary_txt[] = {
1755     0x00, 0x00, 0x00, 0x07, 0x6f, 0x70, 0x74, 0x69,  \\ - - - - o p t i
1756     0x6f, 0x6e, 0x73, 0x00, 0x00, 0x00, 0x04, 0x68,  \\ o n s - - - - h
1757     0x65, 0x61, 0x64, 0x00, 0x00, 0x00, 0x04, 0x70,  \\ e a d - - - - p
1758     0x6f, 0x73, 0x74, 0x00, 0x00, 0x00, 0x03, 0x70,  \\ o s t - - - - p
1759     0x75, 0x74, 0x00, 0x00, 0x00, 0x06, 0x64, 0x65,  \\ u t - - - - d e
1760     0x6c, 0x65, 0x74, 0x65, 0x00, 0x00, 0x00, 0x05,  \\ l e t e - - - -
1761     0x74, 0x72, 0x61, 0x63, 0x65, 0x00, 0x00, 0x00,  \\ t r a c e - - -
1762     0x06, 0x61, 0x63, 0x63, 0x65, 0x70, 0x74, 0x00,  \\ - a c c e p t -
1763     0x00, 0x00, 0x0e, 0x61, 0x63, 0x63, 0x65, 0x70,  \\ - - - a c c e p
1764     0x74, 0x2d, 0x63, 0x68, 0x61, 0x72, 0x73, 0x65,  \\ t - c h a r s e
1765     0x74, 0x00, 0x00, 0x00, 0x0f, 0x61, 0x63, 0x63,  \\ t - - - - a c c
1766     0x65, 0x70, 0x74, 0x2d, 0x65, 0x6e, 0x63, 0x6f,  \\ e p t - e n c o
1767     0x64, 0x69, 0x6e, 0x67, 0x00, 0x00, 0x00, 0x0f,  \\ d i n g - - - -
1768     0x61, 0x63, 0x63, 0x65, 0x70, 0x74, 0x2d, 0x6c,  \\ a c c e p t - l
1769     0x61, 0x6e, 0x67, 0x75, 0x61, 0x67, 0x65, 0x00,  \\ a n g u a g e -
1770     0x00, 0x00, 0x0d, 0x61, 0x63, 0x63, 0x65, 0x70,  \\ - - - a c c e p
1771     0x74, 0x2d, 0x72, 0x61, 0x6e, 0x67, 0x65, 0x73,  \\ t - r a n g e s
1772     0x00, 0x00, 0x00, 0x03, 0x61, 0x67, 0x65, 0x00,  \\ - - - - a g e -
1773     0x00, 0x00, 0x05, 0x61, 0x6c, 0x6c, 0x6f, 0x77,  \\ - - - a l l o w
1774     0x00, 0x00, 0x00, 0x0d, 0x61, 0x75, 0x74, 0x68,  \\ - - - - a u t h
1775     0x6f, 0x72, 0x69, 0x7a, 0x61, 0x74, 0x69, 0x6f,  \\ o r i z a t i o
1776     0x6e, 0x00, 0x00, 0x00, 0x0d, 0x63, 0x61, 0x63,  \\ n - - - - c a c
1777     0x68, 0x65, 0x2d, 0x63, 0x6f, 0x6e, 0x74, 0x72,  \\ h e - c o n t r
1778     0x6f, 0x6c, 0x00, 0x00, 0x00, 0x0a, 0x63, 0x6f,  \\ o l - - - - c o
1779     0x6e, 0x6e, 0x65, 0x63, 0x74, 0x69, 0x6f, 0x6e,  \\ n n e c t i o n
1780     0x00, 0x00, 0x00, 0x0c, 0x63, 0x6f, 0x6e, 0x74,  \\ - - - - c o n t
1781     0x65, 0x6e, 0x74, 0x2d, 0x62, 0x61, 0x73, 0x65,  \\ e n t - b a s e
1782     0x00, 0x00, 0x00, 0x10, 0x63, 0x6f, 0x6e, 0x74,  \\ - - - - c o n t
1783     0x65, 0x6e, 0x74, 0x2d, 0x65, 0x6e, 0x63, 0x6f,  \\ e n t - e n c o
1784     0x64, 0x69, 0x6e, 0x67, 0x00, 0x00, 0x00, 0x10,  \\ d i n g - - - -
1785     0x63, 0x6f, 0x6e, 0x74, 0x65, 0x6e, 0x74, 0x2d,  \\ c o n t e n t -
1786     0x6c, 0x61, 0x6e, 0x67, 0x75, 0x61, 0x67, 0x65,  \\ l a n g u a g e
1787     0x00, 0x00, 0x00, 0x0e, 0x63, 0x6f, 0x6e, 0x74,  \\ - - - - c o n t
1788
1789
1790
1791Belshe, et al.            Expires July 26, 2013                [Page 32]
1792
1793Internet-Draft                  HTTP/2.0                    January 2013
1794
1795
1796     0x65, 0x6e, 0x74, 0x2d, 0x6c, 0x65, 0x6e, 0x67,  \\ e n t - l e n g
1797     0x74, 0x68, 0x00, 0x00, 0x00, 0x10, 0x63, 0x6f,  \\ t h - - - - c o
1798     0x6e, 0x74, 0x65, 0x6e, 0x74, 0x2d, 0x6c, 0x6f,  \\ n t e n t - l o
1799     0x63, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x00, 0x00,  \\ c a t i o n - -
1800     0x00, 0x0b, 0x63, 0x6f, 0x6e, 0x74, 0x65, 0x6e,  \\ - - c o n t e n
1801     0x74, 0x2d, 0x6d, 0x64, 0x35, 0x00, 0x00, 0x00,  \\ t - m d 5 - - -
1802     0x0d, 0x63, 0x6f, 0x6e, 0x74, 0x65, 0x6e, 0x74,  \\ - c o n t e n t
1803     0x2d, 0x72, 0x61, 0x6e, 0x67, 0x65, 0x00, 0x00,  \\ - r a n g e - -
1804     0x00, 0x0c, 0x63, 0x6f, 0x6e, 0x74, 0x65, 0x6e,  \\ - - c o n t e n
1805     0x74, 0x2d, 0x74, 0x79, 0x70, 0x65, 0x00, 0x00,  \\ t - t y p e - -
1806     0x00, 0x04, 0x64, 0x61, 0x74, 0x65, 0x00, 0x00,  \\ - - d a t e - -
1807     0x00, 0x04, 0x65, 0x74, 0x61, 0x67, 0x00, 0x00,  \\ - - e t a g - -
1808     0x00, 0x06, 0x65, 0x78, 0x70, 0x65, 0x63, 0x74,  \\ - - e x p e c t
1809     0x00, 0x00, 0x00, 0x07, 0x65, 0x78, 0x70, 0x69,  \\ - - - - e x p i
1810     0x72, 0x65, 0x73, 0x00, 0x00, 0x00, 0x04, 0x66,  \\ r e s - - - - f
1811     0x72, 0x6f, 0x6d, 0x00, 0x00, 0x00, 0x04, 0x68,  \\ r o m - - - - h
1812     0x6f, 0x73, 0x74, 0x00, 0x00, 0x00, 0x08, 0x69,  \\ o s t - - - - i
1813     0x66, 0x2d, 0x6d, 0x61, 0x74, 0x63, 0x68, 0x00,  \\ f - m a t c h -
1814     0x00, 0x00, 0x11, 0x69, 0x66, 0x2d, 0x6d, 0x6f,  \\ - - - i f - m o
1815     0x64, 0x69, 0x66, 0x69, 0x65, 0x64, 0x2d, 0x73,  \\ d i f i e d - s
1816     0x69, 0x6e, 0x63, 0x65, 0x00, 0x00, 0x00, 0x0d,  \\ i n c e - - - -
1817     0x69, 0x66, 0x2d, 0x6e, 0x6f, 0x6e, 0x65, 0x2d,  \\ i f - n o n e -
1818     0x6d, 0x61, 0x74, 0x63, 0x68, 0x00, 0x00, 0x00,  \\ m a t c h - - -
1819     0x08, 0x69, 0x66, 0x2d, 0x72, 0x61, 0x6e, 0x67,  \\ - i f - r a n g
1820     0x65, 0x00, 0x00, 0x00, 0x13, 0x69, 0x66, 0x2d,  \\ e - - - - i f -
1821     0x75, 0x6e, 0x6d, 0x6f, 0x64, 0x69, 0x66, 0x69,  \\ u n m o d i f i
1822     0x65, 0x64, 0x2d, 0x73, 0x69, 0x6e, 0x63, 0x65,  \\ e d - s i n c e
1823     0x00, 0x00, 0x00, 0x0d, 0x6c, 0x61, 0x73, 0x74,  \\ - - - - l a s t
1824     0x2d, 0x6d, 0x6f, 0x64, 0x69, 0x66, 0x69, 0x65,  \\ - m o d i f i e
1825     0x64, 0x00, 0x00, 0x00, 0x08, 0x6c, 0x6f, 0x63,  \\ d - - - - l o c
1826     0x61, 0x74, 0x69, 0x6f, 0x6e, 0x00, 0x00, 0x00,  \\ a t i o n - - -
1827     0x0c, 0x6d, 0x61, 0x78, 0x2d, 0x66, 0x6f, 0x72,  \\ - m a x - f o r
1828     0x77, 0x61, 0x72, 0x64, 0x73, 0x00, 0x00, 0x00,  \\ w a r d s - - -
1829     0x06, 0x70, 0x72, 0x61, 0x67, 0x6d, 0x61, 0x00,  \\ - p r a g m a -
1830     0x00, 0x00, 0x12, 0x70, 0x72, 0x6f, 0x78, 0x79,  \\ - - - p r o x y
1831     0x2d, 0x61, 0x75, 0x74, 0x68, 0x65, 0x6e, 0x74,  \\ - a u t h e n t
1832     0x69, 0x63, 0x61, 0x74, 0x65, 0x00, 0x00, 0x00,  \\ i c a t e - - -
1833     0x13, 0x70, 0x72, 0x6f, 0x78, 0x79, 0x2d, 0x61,  \\ - p r o x y - a
1834     0x75, 0x74, 0x68, 0x6f, 0x72, 0x69, 0x7a, 0x61,  \\ u t h o r i z a
1835     0x74, 0x69, 0x6f, 0x6e, 0x00, 0x00, 0x00, 0x05,  \\ t i o n - - - -
1836     0x72, 0x61, 0x6e, 0x67, 0x65, 0x00, 0x00, 0x00,  \\ r a n g e - - -
1837     0x07, 0x72, 0x65, 0x66, 0x65, 0x72, 0x65, 0x72,  \\ - r e f e r e r
1838     0x00, 0x00, 0x00, 0x0b, 0x72, 0x65, 0x74, 0x72,  \\ - - - - r e t r
1839     0x79, 0x2d, 0x61, 0x66, 0x74, 0x65, 0x72, 0x00,  \\ y - a f t e r -
1840     0x00, 0x00, 0x06, 0x73, 0x65, 0x72, 0x76, 0x65,  \\ - - - s e r v e
1841     0x72, 0x00, 0x00, 0x00, 0x02, 0x74, 0x65, 0x00,  \\ r - - - - t e -
1842     0x00, 0x00, 0x07, 0x74, 0x72, 0x61, 0x69, 0x6c,  \\ - - - t r a i l
1843     0x65, 0x72, 0x00, 0x00, 0x00, 0x11, 0x74, 0x72,  \\ e r - - - - t r
1844
1845
1846
1847Belshe, et al.            Expires July 26, 2013                [Page 33]
1848
1849Internet-Draft                  HTTP/2.0                    January 2013
1850
1851
1852     0x61, 0x6e, 0x73, 0x66, 0x65, 0x72, 0x2d, 0x65,  \\ a n s f e r - e
1853     0x6e, 0x63, 0x6f, 0x64, 0x69, 0x6e, 0x67, 0x00,  \\ n c o d i n g -
1854     0x00, 0x00, 0x07, 0x75, 0x70, 0x67, 0x72, 0x61,  \\ - - - u p g r a
1855     0x64, 0x65, 0x00, 0x00, 0x00, 0x0a, 0x75, 0x73,  \\ d e - - - - u s
1856     0x65, 0x72, 0x2d, 0x61, 0x67, 0x65, 0x6e, 0x74,  \\ e r - a g e n t
1857     0x00, 0x00, 0x00, 0x04, 0x76, 0x61, 0x72, 0x79,  \\ - - - - v a r y
1858     0x00, 0x00, 0x00, 0x03, 0x76, 0x69, 0x61, 0x00,  \\ - - - - v i a -
1859     0x00, 0x00, 0x07, 0x77, 0x61, 0x72, 0x6e, 0x69,  \\ - - - w a r n i
1860     0x6e, 0x67, 0x00, 0x00, 0x00, 0x10, 0x77, 0x77,  \\ n g - - - - w w
1861     0x77, 0x2d, 0x61, 0x75, 0x74, 0x68, 0x65, 0x6e,  \\ w - a u t h e n
1862     0x74, 0x69, 0x63, 0x61, 0x74, 0x65, 0x00, 0x00,  \\ t i c a t e - -
1863     0x00, 0x06, 0x6d, 0x65, 0x74, 0x68, 0x6f, 0x64,  \\ - - m e t h o d
1864     0x00, 0x00, 0x00, 0x03, 0x67, 0x65, 0x74, 0x00,  \\ - - - - g e t -
1865     0x00, 0x00, 0x06, 0x73, 0x74, 0x61, 0x74, 0x75,  \\ - - - s t a t u
1866     0x73, 0x00, 0x00, 0x00, 0x06, 0x32, 0x30, 0x30,  \\ s - - - - 2 0 0
1867     0x20, 0x4f, 0x4b, 0x00, 0x00, 0x00, 0x07, 0x76,  \\ - O K - - - - v
1868     0x65, 0x72, 0x73, 0x69, 0x6f, 0x6e, 0x00, 0x00,  \\ e r s i o n - -
1869     0x00, 0x08, 0x48, 0x54, 0x54, 0x50, 0x2f, 0x31,  \\ - - H T T P - 1
1870     0x2e, 0x31, 0x00, 0x00, 0x00, 0x03, 0x75, 0x72,  \\ - 1 - - - - u r
1871     0x6c, 0x00, 0x00, 0x00, 0x06, 0x70, 0x75, 0x62,  \\ l - - - - p u b
1872     0x6c, 0x69, 0x63, 0x00, 0x00, 0x00, 0x0a, 0x73,  \\ l i c - - - - s
1873     0x65, 0x74, 0x2d, 0x63, 0x6f, 0x6f, 0x6b, 0x69,  \\ e t - c o o k i
1874     0x65, 0x00, 0x00, 0x00, 0x0a, 0x6b, 0x65, 0x65,  \\ e - - - - k e e
1875     0x70, 0x2d, 0x61, 0x6c, 0x69, 0x76, 0x65, 0x00,  \\ p - a l i v e -
1876     0x00, 0x00, 0x06, 0x6f, 0x72, 0x69, 0x67, 0x69,  \\ - - - o r i g i
1877     0x6e, 0x31, 0x30, 0x30, 0x31, 0x30, 0x31, 0x32,  \\ n 1 0 0 1 0 1 2
1878     0x30, 0x31, 0x32, 0x30, 0x32, 0x32, 0x30, 0x35,  \\ 0 1 2 0 2 2 0 5
1879     0x32, 0x30, 0x36, 0x33, 0x30, 0x30, 0x33, 0x30,  \\ 2 0 6 3 0 0 3 0
1880     0x32, 0x33, 0x30, 0x33, 0x33, 0x30, 0x34, 0x33,  \\ 2 3 0 3 3 0 4 3
1881     0x30, 0x35, 0x33, 0x30, 0x36, 0x33, 0x30, 0x37,  \\ 0 5 3 0 6 3 0 7
1882     0x34, 0x30, 0x32, 0x34, 0x30, 0x35, 0x34, 0x30,  \\ 4 0 2 4 0 5 4 0
1883     0x36, 0x34, 0x30, 0x37, 0x34, 0x30, 0x38, 0x34,  \\ 6 4 0 7 4 0 8 4
1884     0x30, 0x39, 0x34, 0x31, 0x30, 0x34, 0x31, 0x31,  \\ 0 9 4 1 0 4 1 1
1885     0x34, 0x31, 0x32, 0x34, 0x31, 0x33, 0x34, 0x31,  \\ 4 1 2 4 1 3 4 1
1886     0x34, 0x34, 0x31, 0x35, 0x34, 0x31, 0x36, 0x34,  \\ 4 4 1 5 4 1 6 4
1887     0x31, 0x37, 0x35, 0x30, 0x32, 0x35, 0x30, 0x34,  \\ 1 7 5 0 2 5 0 4
1888     0x35, 0x30, 0x35, 0x32, 0x30, 0x33, 0x20, 0x4e,  \\ 5 0 5 2 0 3 - N
1889     0x6f, 0x6e, 0x2d, 0x41, 0x75, 0x74, 0x68, 0x6f,  \\ o n - A u t h o
1890     0x72, 0x69, 0x74, 0x61, 0x74, 0x69, 0x76, 0x65,  \\ r i t a t i v e
1891     0x20, 0x49, 0x6e, 0x66, 0x6f, 0x72, 0x6d, 0x61,  \\ - I n f o r m a
1892     0x74, 0x69, 0x6f, 0x6e, 0x32, 0x30, 0x34, 0x20,  \\ t i o n 2 0 4 -
1893     0x4e, 0x6f, 0x20, 0x43, 0x6f, 0x6e, 0x74, 0x65,  \\ N o - C o n t e
1894     0x6e, 0x74, 0x33, 0x30, 0x31, 0x20, 0x4d, 0x6f,  \\ n t 3 0 1 - M o
1895     0x76, 0x65, 0x64, 0x20, 0x50, 0x65, 0x72, 0x6d,  \\ v e d - P e r m
1896     0x61, 0x6e, 0x65, 0x6e, 0x74, 0x6c, 0x79, 0x34,  \\ a n e n t l y 4
1897     0x30, 0x30, 0x20, 0x42, 0x61, 0x64, 0x20, 0x52,  \\ 0 0 - B a d - R
1898     0x65, 0x71, 0x75, 0x65, 0x73, 0x74, 0x34, 0x30,  \\ e q u e s t 4 0
1899     0x31, 0x20, 0x55, 0x6e, 0x61, 0x75, 0x74, 0x68,  \\ 1 - U n a u t h
1900
1901
1902
1903Belshe, et al.            Expires July 26, 2013                [Page 34]
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1906
1907
1908     0x6f, 0x72, 0x69, 0x7a, 0x65, 0x64, 0x34, 0x30,  \\ o r i z e d 4 0
1909     0x33, 0x20, 0x46, 0x6f, 0x72, 0x62, 0x69, 0x64,  \\ 3 - F o r b i d
1910     0x64, 0x65, 0x6e, 0x34, 0x30, 0x34, 0x20, 0x4e,  \\ d e n 4 0 4 - N
1911     0x6f, 0x74, 0x20, 0x46, 0x6f, 0x75, 0x6e, 0x64,  \\ o t - F o u n d
1912     0x35, 0x30, 0x30, 0x20, 0x49, 0x6e, 0x74, 0x65,  \\ 5 0 0 - I n t e
1913     0x72, 0x6e, 0x61, 0x6c, 0x20, 0x53, 0x65, 0x72,  \\ r n a l - S e r
1914     0x76, 0x65, 0x72, 0x20, 0x45, 0x72, 0x72, 0x6f,  \\ v e r - E r r o
1915     0x72, 0x35, 0x30, 0x31, 0x20, 0x4e, 0x6f, 0x74,  \\ r 5 0 1 - N o t
1916     0x20, 0x49, 0x6d, 0x70, 0x6c, 0x65, 0x6d, 0x65,  \\ - I m p l e m e
1917     0x6e, 0x74, 0x65, 0x64, 0x35, 0x30, 0x33, 0x20,  \\ n t e d 5 0 3 -
1918     0x53, 0x65, 0x72, 0x76, 0x69, 0x63, 0x65, 0x20,  \\ S e r v i c e -
1919     0x55, 0x6e, 0x61, 0x76, 0x61, 0x69, 0x6c, 0x61,  \\ U n a v a i l a
1920     0x62, 0x6c, 0x65, 0x4a, 0x61, 0x6e, 0x20, 0x46,  \\ b l e J a n - F
1921     0x65, 0x62, 0x20, 0x4d, 0x61, 0x72, 0x20, 0x41,  \\ e b - M a r - A
1922     0x70, 0x72, 0x20, 0x4d, 0x61, 0x79, 0x20, 0x4a,  \\ p r - M a y - J
1923     0x75, 0x6e, 0x20, 0x4a, 0x75, 0x6c, 0x20, 0x41,  \\ u n - J u l - A
1924     0x75, 0x67, 0x20, 0x53, 0x65, 0x70, 0x74, 0x20,  \\ u g - S e p t -
1925     0x4f, 0x63, 0x74, 0x20, 0x4e, 0x6f, 0x76, 0x20,  \\ O c t - N o v -
1926     0x44, 0x65, 0x63, 0x20, 0x30, 0x30, 0x3a, 0x30,  \\ D e c - 0 0 - 0
1927     0x30, 0x3a, 0x30, 0x30, 0x20, 0x4d, 0x6f, 0x6e,  \\ 0 - 0 0 - M o n
1928     0x2c, 0x20, 0x54, 0x75, 0x65, 0x2c, 0x20, 0x57,  \\ - - T u e - - W
1929     0x65, 0x64, 0x2c, 0x20, 0x54, 0x68, 0x75, 0x2c,  \\ e d - - T h u -
1930     0x20, 0x46, 0x72, 0x69, 0x2c, 0x20, 0x53, 0x61,  \\ - F r i - - S a
1931     0x74, 0x2c, 0x20, 0x53, 0x75, 0x6e, 0x2c, 0x20,  \\ t - - S u n - -
1932     0x47, 0x4d, 0x54, 0x63, 0x68, 0x75, 0x6e, 0x6b,  \\ G M T c h u n k
1933     0x65, 0x64, 0x2c, 0x74, 0x65, 0x78, 0x74, 0x2f,  \\ e d - t e x t -
1934     0x68, 0x74, 0x6d, 0x6c, 0x2c, 0x69, 0x6d, 0x61,  \\ h t m l - i m a
1935     0x67, 0x65, 0x2f, 0x70, 0x6e, 0x67, 0x2c, 0x69,  \\ g e - p n g - i
1936     0x6d, 0x61, 0x67, 0x65, 0x2f, 0x6a, 0x70, 0x67,  \\ m a g e - j p g
1937     0x2c, 0x69, 0x6d, 0x61, 0x67, 0x65, 0x2f, 0x67,  \\ - i m a g e - g
1938     0x69, 0x66, 0x2c, 0x61, 0x70, 0x70, 0x6c, 0x69,  \\ i f - a p p l i
1939     0x63, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x2f, 0x78,  \\ c a t i o n - x
1940     0x6d, 0x6c, 0x2c, 0x61, 0x70, 0x70, 0x6c, 0x69,  \\ m l - a p p l i
1941     0x63, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x2f, 0x78,  \\ c a t i o n - x
1942     0x68, 0x74, 0x6d, 0x6c, 0x2b, 0x78, 0x6d, 0x6c,  \\ h t m l - x m l
1943     0x2c, 0x74, 0x65, 0x78, 0x74, 0x2f, 0x70, 0x6c,  \\ - t e x t - p l
1944     0x61, 0x69, 0x6e, 0x2c, 0x74, 0x65, 0x78, 0x74,  \\ a i n - t e x t
1945     0x2f, 0x6a, 0x61, 0x76, 0x61, 0x73, 0x63, 0x72,  \\ - j a v a s c r
1946     0x69, 0x70, 0x74, 0x2c, 0x70, 0x75, 0x62, 0x6c,  \\ i p t - p u b l
1947     0x69, 0x63, 0x70, 0x72, 0x69, 0x76, 0x61, 0x74,  \\ i c p r i v a t
1948     0x65, 0x6d, 0x61, 0x78, 0x2d, 0x61, 0x67, 0x65,  \\ e m a x - a g e
1949     0x3d, 0x67, 0x7a, 0x69, 0x70, 0x2c, 0x64, 0x65,  \\ - g z i p - d e
1950     0x66, 0x6c, 0x61, 0x74, 0x65, 0x2c, 0x73, 0x64,  \\ f l a t e - s d
1951     0x63, 0x68, 0x63, 0x68, 0x61, 0x72, 0x73, 0x65,  \\ c h c h a r s e
1952     0x74, 0x3d, 0x75, 0x74, 0x66, 0x2d, 0x38, 0x63,  \\ t - u t f - 8 c
1953     0x68, 0x61, 0x72, 0x73, 0x65, 0x74, 0x3d, 0x69,  \\ h a r s e t - i
1954     0x73, 0x6f, 0x2d, 0x38, 0x38, 0x35, 0x39, 0x2d,  \\ s o - 8 8 5 9 -
1955     0x31, 0x2c, 0x75, 0x74, 0x66, 0x2d, 0x2c, 0x2a,  \\ 1 - u t f - - -
1956
1957
1958
1959Belshe, et al.            Expires July 26, 2013                [Page 35]
1960
1961Internet-Draft                  HTTP/2.0                    January 2013
1962
1963
1964     0x2c, 0x65, 0x6e, 0x71, 0x3d, 0x30, 0x2e         \\ - e n q - 0 -
1965   };
1966
1967   <CODE ENDS>
1968
1969   The entire contents of the name/value header block is compressed
1970   using zlib.  There is a single zlib stream for all name value pairs
1971   in one direction on a connection.  HTTP/2.0 uses a SYNC_FLUSH between
1972   each compressed frame.
1973
1974   Implementation notes: the compression engine can be tuned to favor
1975   speed or size.  Optimizing for size increases memory use and CPU
1976   consumption.  Because header blocks are generally small, implementors
1977   may want to reduce the window-size of the compression engine from the
1978   default 15bits (a 32KB window) to more like 11bits (a 2KB window).
1979   The exact setting is chosen by the compressor, the decompressor will
1980   work with any setting.
1981
19824.  HTTP Layering over HTTP/2.0
1983
1984   HTTP/2.0 is intended to be as compatible as possible with current
1985   web-based applications.  This means that, from the perspective of the
1986   server business logic or application API, the features of HTTP are
1987   unchanged.  To achieve this, all of the application request and
1988   response header semantics are preserved, although the syntax of
1989   conveying those semantics has changed.  Thus, the rules from the
1990   HTTP/1.1 specification in RFC2616 [RFC2616] apply with the changes in
1991   the sections below.
1992
19934.1.  Connection Management
1994
1995   Clients SHOULD NOT open more than one HTTP/2.0 session to a given
1996   origin [RFC6454] concurrently.
1997
1998   Note that it is possible for one HTTP/2.0 session to be finishing
1999   (e.g. a GOAWAY message has been sent, but not all streams have
2000   finished), while another HTTP/2.0 session is starting.
2001
20024.1.1.  Use of GOAWAY
2003
2004   HTTP/2.0 provides a GOAWAY message which can be used when closing a
2005   connection from either the client or server.  Without a server GOAWAY
2006   message, HTTP has a race condition where the client sends a request
2007   (a new SYN_STREAM) just as the server is closing the connection, and
2008   the client cannot know if the server received the stream or not.  By
2009   using the last-stream-id in the GOAWAY, servers can indicate to the
2010   client if a request was processed or not.
2011
2012
2013
2014
2015Belshe, et al.            Expires July 26, 2013                [Page 36]
2016
2017Internet-Draft                  HTTP/2.0                    January 2013
2018
2019
2020   Note that some servers will choose to send the GOAWAY and immediately
2021   terminate the connection without waiting for active streams to
2022   finish.  The client will be able to determine this because HTTP/2.0
2023   streams are determinstically closed.  This abrupt termination will
2024   force the client to heuristically decide whether to retry the pending
2025   requests.  Clients always need to be capable of dealing with this
2026   case because they must deal with accidental connection termination
2027   cases, which are the same as the server never having sent a GOAWAY.
2028
2029   More sophisticated servers will use GOAWAY to implement a graceful
2030   teardown.  They will send the GOAWAY and provide some time for the
2031   active streams to finish before terminating the connection.
2032
2033   If a HTTP/2.0 client closes the connection, it should also send a
2034   GOAWAY message.  This allows the server to know if any server-push
2035   streams were received by the client.
2036
2037   If the endpoint closing the connection has not received any
2038   SYN_STREAMs from the remote, the GOAWAY will contain a last-stream-id
2039   of 0.
2040
20414.2.  HTTP Request/Response
2042
20434.2.1.  Request
2044
2045   The client initiates a request by sending a SYN_STREAM frame.  For
2046   requests which do not contain a body, the SYN_STREAM frame MUST set
2047   the FLAG_FIN, indicating that the client intends to send no further
2048   data on this stream.  For requests which do contain a body, the
2049   SYN_STREAM will not contain the FLAG_FIN, and the body will follow
2050   the SYN_STREAM in a series of DATA frames.  The last DATA frame will
2051   set the FLAG_FIN to indicate the end of the body.
2052
2053   The SYN_STREAM Name/Value section will contain all of the HTTP
2054   headers which are associated with an HTTP request.  The header block
2055   in HTTP/2.0 is mostly unchanged from today's HTTP header block, with
2056   the following differences:
2057
2058      The first line of the request is unfolded into name/value pairs
2059      like other HTTP headers and MUST be present:
2060
2061         ":method" - the HTTP method for this request (e.g.  "GET",
2062         "POST", "HEAD", etc)
2063
2064         ":path" - the url-path for this url with "/" prefixed.  (See
2065         RFC1738 [RFC1738]).  For example, for
2066         "http://www.google.com/search?q=dogs" the path would be
2067         "/search?q=dogs".
2068
2069
2070
2071Belshe, et al.            Expires July 26, 2013                [Page 37]
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2074
2075
2076         ":version" - the HTTP version of this request (e.g.
2077         "HTTP/1.1")
2078
2079      In addition, the following two name/value pairs must also be
2080      present in every request:
2081
2082         ":host" - the hostport (See RFC1738 [RFC1738]) portion of the
2083         URL for this request (e.g. "www.google.com:1234").  This header
2084         is the same as the HTTP 'Host' header.
2085
2086         ":scheme" - the scheme portion of the URL for this request
2087         (e.g. "https"))
2088
2089      Header names are all lowercase.
2090
2091      The Connection, Host, Keep-Alive, Proxy-Connection, and Transfer-
2092      Encoding headers are not valid and MUST not be sent.
2093
2094      User-agents MUST support gzip compression.  Regardless of the
2095      Accept-Encoding sent by the user-agent, the server may always send
2096      content encoded with gzip or deflate encoding.
2097
2098      If a server receives a request where the sum of the data frame
2099      payload lengths does not equal the size of the Content-Length
2100      header, the server MUST return a 400 (Bad Request) error.
2101
2102      POST-specific changes:
2103
2104         Although POSTs are inherently chunked, POST requests SHOULD
2105         also be accompanied by a Content-Length header.  There are two
2106         reasons for this: First, it assists with upload progress meters
2107         for an improved user experience.  But second, we know from
2108         early versions of HTTP/2.0 that failure to send a content
2109         length header is incompatible with many existing HTTP server
2110         implementations.  Existing user-agents do not omit the Content-
2111         Length header, and server implementations have come to depend
2112         upon this.
2113
2114   The user-agent is free to prioritize requests as it sees fit.  If the
2115   user-agent cannot make progress without receiving a resource, it
2116   should attempt to raise the priority of that resource.  Resources
2117   such as images, SHOULD generally use the lowest priority.
2118
2119   If a client sends a SYN_STREAM without all of the method, host, path,
2120   scheme, and version headers, the server MUST reply with a HTTP 400
2121   Bad Request reply.
2122
2123
2124
2125
2126
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2130
2131
21324.2.2.  Response
2133
2134   The server responds to a client request with a SYN_REPLY frame.
2135   Symmetric to the client's upload stream, server will send data after
2136   the SYN_REPLY frame via a series of DATA frames, and the last data
2137   frame will contain the FLAG_FIN to indicate successful end-of-stream.
2138   If a response (like a 202 or 204 response) contains no body, the
2139   SYN_REPLY frame may contain the FLAG_FIN flag to indicate no further
2140   data will be sent on the stream.
2141
2142      The response status line is unfolded into name/value pairs like
2143      other HTTP headers and must be present:
2144
2145         ":status" - The HTTP response status code (e.g. "200" or "200
2146         OK")
2147
2148         ":version" - The HTTP response version (e.g.  "HTTP/1.1")
2149
2150      All header names must be lowercase.
2151
2152      The Connection, Keep-Alive, Proxy-Connection, and Transfer-
2153      Encoding headers are not valid and MUST not be sent.
2154
2155      Responses MAY be accompanied by a Content-Length header for
2156      advisory purposes. (e.g. for UI progress meters)
2157
2158      If a client receives a response where the sum of the data frame
2159      payload lengths does not equal the size of the Content-Length
2160      header, the client MUST ignore the content length header.
2161
2162   If a client receives a SYN_REPLY without a status or without a
2163   version header, the client must reply with a RST_STREAM frame
2164   indicating a PROTOCOL ERROR.
2165
21664.2.3.  Authentication
2167
2168   When a client sends a request to an origin server that requires
2169   authentication, the server can reply with a "401 Unauthorized"
2170   response, and include a WWW-Authenticate challenge header that
2171   defines the authentication scheme to be used.  The client then
2172   retries the request with an Authorization header appropriate to the
2173   specified authentication scheme.
2174
2175   There are four options for proxy authentication, Basic, Digest, NTLM
2176   and Negotiate (SPNEGO).  The first two options were defined in
2177   RFC2617 [RFC2617], and are stateless.  The second two options were
2178   developed by Microsoft and specified in RFC4559 [RFC4559], and are
2179   stateful; otherwise known as multi-round authentication, or
2180
2181
2182
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2186
2187
2188   connection authentication.
2189
21904.2.3.1.  Stateless Authentication
2191
2192   Stateless Authentication over HTTP/2.0 is identical to how it is
2193   performed over HTTP.  If multiple HTTP/2.0 streams are concurrently
2194   sent to a single server, each will authenticate independently,
2195   similar to how two HTTP connections would independently authenticate
2196   to a proxy server.
2197
21984.2.3.2.  Stateful Authentication
2199
2200   Unfortunately, the stateful authentication mechanisms were
2201   implemented and defined in a such a way that directly violates
2202   RFC2617 - they do not include a "realm" as part of the request.  This
2203   is problematic in HTTP/2.0 because it makes it impossible for a
2204   client to disambiguate two concurrent server authentication
2205   challenges.
2206
2207   To deal with this case, HTTP/2.0 servers using Stateful
2208   Authentication MUST implement one of two changes:
2209
2210      Servers can add a "realm=<desired realm>" header so that the two
2211      authentication requests can be disambiguated and run concurrently.
2212      Unfortunately, given how these mechanisms work, this is probably
2213      not practical.
2214
2215      Upon sending the first stateful challenge response, the server
2216      MUST buffer and defer all further frames which are not part of
2217      completing the challenge until the challenge has completed.
2218      Completing the authentication challenge may take multiple round
2219      trips.  Once the client receives a "401 Authenticate" response for
2220      a stateful authentication type, it MUST stop sending new requests
2221      to the server until the authentication has completed by receiving
2222      a non-401 response on at least one stream.
2223
22244.3.  Server Push Transactions
2225
2226   HTTP/2.0 enables a server to send multiple replies to a client for a
2227   single request.  The rationale for this feature is that sometimes a
2228   server knows that it will need to send multiple resources in response
2229   to a single request.  Without server push features, the client must
2230   first download the primary resource, then discover the secondary
2231   resource(s), and request them.  Pushing of resources avoids the
2232   round-trip delay, but also creates a potential race where a server
2233   can be pushing content which a user-agent is in the process of
2234   requesting.  The following mechanics attempt to prevent the race
2235   condition while enabling the performance benefit.
2236
2237
2238
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2242
2243
2244   Browsers receiving a pushed response MUST validate that the server is
2245   authorized to push the URL using the browser same-origin [RFC6454]
2246   policy.  For example, a HTTP/2.0 connection to www.foo.com is
2247   generally not permitted to push a response for www.evil.com.
2248
2249   If the browser accepts a pushed response (e.g. it does not send a
2250   RST_STREAM), the browser MUST attempt to cache the pushed response in
2251   same way that it would cache any other response.  This means
2252   validating the response headers and inserting into the disk cache.
2253
2254   Because pushed responses have no request, they have no request
2255   headers associated with them.  At the framing layer, HTTP/2.0 pushed
2256   streams contain an "associated-stream-id" which indicates the
2257   requested stream for which the pushed stream is related.  The pushed
2258   stream inherits all of the headers from the associated-stream-id with
2259   the exception of ":host", ":scheme", and ":path", which are provided
2260   as part of the pushed response stream headers.  The browser MUST
2261   store these inherited and implied request headers with the cached
2262   resource.
2263
2264   Implementation note: With server push, it is theoretically possible
2265   for servers to push unreasonable amounts of content or resources to
2266   the user-agent.  Browsers MUST implement throttles to protect against
2267   unreasonable push attacks.
2268
22694.3.1.  Server implementation
2270
2271   When the server intends to push a resource to the user-agent, it
2272   opens a new stream by sending a unidirectional SYN_STREAM.  The
2273   SYN_STREAM MUST include an Associated-To-Stream-ID, and MUST set the
2274   FLAG_UNIDIRECTIONAL flag.  The SYN_STREAM MUST include headers for
2275   ":scheme", ":host", ":path", which represent the URL for the resource
2276   being pushed.  Subsequent headers may follow in HEADERS frames.  The
2277   purpose of the association is so that the user-agent can
2278   differentiate which request induced the pushed stream; without it, if
2279   the user-agent had two tabs open to the same page, each pushing
2280   unique content under a fixed URL, the user-agent would not be able to
2281   differentiate the requests.
2282
2283   The Associated-To-Stream-ID must be the ID of an existing, open
2284   stream.  The reason for this restriction is to have a clear endpoint
2285   for pushed content.  If the user-agent requested a resource on stream
2286   11, the server replies on stream 11.  It can push any number of
2287   additional streams to the client before sending a FLAG_FIN on stream
2288   11.  However, once the originating stream is closed no further push
2289   streams may be associated with it.  The pushed streams do not need to
2290   be closed (FIN set) before the originating stream is closed, they
2291   only need to be created before the originating stream closes.
2292
2293
2294
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2298
2299
2300   It is illegal for a server to push a resource with the Associated-To-
2301   Stream-ID of 0.
2302
2303   To minimize race conditions with the client, the SYN_STREAM for the
2304   pushed resources MUST be sent prior to sending any content which
2305   could allow the client to discover the pushed resource and request
2306   it.
2307
2308   The server MUST only push resources which would have been returned
2309   from a GET request.
2310
2311   Note: If the server does not have all of the Name/Value Response
2312   headers available at the time it issues the HEADERS frame for the
2313   pushed resource, it may later use an additional HEADERS frame to
2314   augment the name/value pairs to be associated with the pushed stream.
2315   The subsequent HEADERS frame(s) must not contain a header for
2316   ':host', ':scheme', or ':path' (e.g. the server can't change the
2317   identity of the resource to be pushed).  The HEADERS frame must not
2318   contain duplicate headers with a previously sent HEADERS frame.  The
2319   server must send a HEADERS frame including the scheme/host/port
2320   headers before sending any data frames on the stream.
2321
23224.3.2.  Client implementation
2323
2324   When fetching a resource the client has 3 possibilities:
2325
2326      the resource is not being pushed
2327
2328      the resource is being pushed, but the data has not yet arrived
2329
2330      the resource is being pushed, and the data has started to arrive
2331
2332   When a SYN_STREAM and HEADERS frame which contains an Associated-To-
2333   Stream-ID is received, the client must not issue GET requests for the
2334   resource in the pushed stream, and instead wait for the pushed stream
2335   to arrive.
2336
2337   If a client receives a server push stream with stream-id 0, it MUST
2338   issue a session error (Section 3.4.1) with the status code
2339   PROTOCOL_ERROR.
2340
2341   When a client receives a SYN_STREAM from the server without a the
2342   ':host', ':scheme', and ':path' headers in the Name/Value section, it
2343   MUST reply with a RST_STREAM with error code HTTP_PROTOCOL_ERROR.
2344
2345   To cancel individual server push streams, the client can issue a
2346   stream error (Section 3.4.2) with error code CANCEL.  Upon receipt,
2347   the server MUST stop sending on this stream immediately (this is an
2348
2349
2350
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2354
2355
2356   Abrupt termination).
2357
2358   To cancel all server push streams related to a request, the client
2359   may issue a stream error (Section 3.4.2) with error code CANCEL on
2360   the associated-stream-id.  By cancelling that stream, the server MUST
2361   immediately stop sending frames for any streams with
2362   in-association-to for the original stream.
2363
2364   If the server sends a HEADER frame containing duplicate headers with
2365   a previous HEADERS frame for the same stream, the client must issue a
2366   stream error (Section 3.4.2) with error code PROTOCOL ERROR.
2367
2368   If the server sends a HEADERS frame after sending a data frame for
2369   the same stream, the client MAY ignore the HEADERS frame.  Ignoring
2370   the HEADERS frame after a data frame prevents handling of HTTP's
2371   trailing headers
2372   (http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.40).
2373
23745.  Design Rationale and Notes
2375
2376   Authors' notes: The notes in this section have no bearing on the
2377   HTTP/2.0 protocol as specified within this document, and none of
2378   these notes should be considered authoritative about how the protocol
2379   works.  However, these notes may prove useful in future debates about
2380   how to resolve protocol ambiguities or how to evolve the protocol
2381   going forward.  They may be removed before the final draft.
2382
23835.1.  Separation of Framing Layer and Application Layer
2384
2385   Readers may note that this specification sometimes blends the framing
2386   layer (Section 3) with requirements of a specific application - HTTP
2387   (Section 4).  This is reflected in the request/response nature of the
2388   streams, the definition of the HEADERS and compression contexts which
2389   are very similar to HTTP, and other areas as well.
2390
2391   This blending is intentional - the primary goal of this protocol is
2392   to create a low-latency protocol for use with HTTP.  Isolating the
2393   two layers is convenient for description of the protocol and how it
2394   relates to existing HTTP implementations.  However, the ability to
2395   reuse the HTTP/2.0 framing layer is a non goal.
2396
23975.2.  Error handling - Framing Layer
2398
2399   Error handling at the HTTP/2.0 layer splits errors into two groups:
2400   Those that affect an individual HTTP/2.0 stream, and those that do
2401   not.
2402
2403   When an error is confined to a single stream, but general framing is
2404
2405
2406
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2410
2411
2412   in tact, HTTP/2.0 attempts to use the RST_STREAM as a mechanism to
2413   invalidate the stream but move forward without aborting the
2414   connection altogether.
2415
2416   For errors occuring outside of a single stream context, HTTP/2.0
2417   assumes the entire session is hosed.  In this case, the endpoint
2418   detecting the error should initiate a connection close.
2419
24205.3.  One Connection Per Domain
2421
2422   HTTP/2.0 attempts to use fewer connections than other protocols have
2423   traditionally used.  The rationale for this behavior is because it is
2424   very difficult to provide a consistent level of service (e.g.  TCP
2425   slow-start), prioritization, or optimal compression when the client
2426   is connecting to the server through multiple channels.
2427
2428   Through lab measurements, we have seen consistent latency benefits by
2429   using fewer connections from the client.  The overall number of
2430   packets sent by HTTP/2.0 can be as much as 40% less than HTTP.
2431   Handling large numbers of concurrent connections on the server also
2432   does become a scalability problem, and HTTP/2.0 reduces this load.
2433
2434   The use of multiple connections is not without benefit, however.
2435   Because HTTP/2.0 multiplexes multiple, independent streams onto a
2436   single stream, it creates a potential for head-of-line blocking
2437   problems at the transport level.  In tests so far, the negative
2438   effects of head-of-line blocking (especially in the presence of
2439   packet loss) is outweighed by the benefits of compression and
2440   prioritization.
2441
24425.4.  Fixed vs Variable Length Fields
2443
2444   HTTP/2.0 favors use of fixed length 32bit fields in cases where
2445   smaller, variable length encodings could have been used.  To some,
2446   this seems like a tragic waste of bandwidth.  HTTP/2.0 choses the
2447   simple encoding for speed and simplicity.
2448
2449   The goal of HTTP/2.0 is to reduce latency on the network.  The
2450   overhead of HTTP/2.0 frames is generally quite low.  Each data frame
2451   is only an 8 byte overhead for a 1452 byte payload (~0.6%).  At the
2452   time of this writing, bandwidth is already plentiful, and there is a
2453   strong trend indicating that bandwidth will continue to increase.
2454   With an average worldwide bandwidth of 1Mbps, and assuming that a
2455   variable length encoding could reduce the overhead by 50%, the
2456   latency saved by using a variable length encoding would be less than
2457   100 nanoseconds.  More interesting are the effects when the larger
2458   encodings force a packet boundary, in which case a round-trip could
2459   be induced.  However, by addressing other aspects of HTTP/2.0 and TCP
2460
2461
2462
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2466
2467
2468   interactions, we believe this is completely mitigated.
2469
24705.5.  Compression Context(s)
2471
2472   When isolating the compression contexts used for communicating with
2473   multiple origins, we had a few choices to make.  We could have
2474   maintained a map (or list) of compression contexts usable for each
2475   origin.  The basic case is easy - each HEADERS frame would need to
2476   identify the context to use for that frame.  However, compression
2477   contexts are not cheap, so the lifecycle of each context would need
2478   to be bounded.  For proxy servers, where we could churn through many
2479   contexts, this would be a concern.  We considered using a static set
2480   of contexts, say 16 of them, which would bound the memory use.  We
2481   also considered dynamic contexts, which could be created on the fly,
2482   and would need to be subsequently destroyed.  All of these are
2483   complicated, and ultimately we decided that such a mechanism creates
2484   too many problems to solve.
2485
2486   Alternatively, we've chosen the simple approach, which is to simply
2487   provide a flag for resetting the compression context.  For the common
2488   case (no proxy), this fine because most requests are to the same
2489   origin and we never need to reset the context.  For cases where we
2490   are using two different origins over a single HTTP/2.0 session, we
2491   simply reset the compression state between each transition.
2492
24935.6.  Unidirectional streams
2494
2495   Many readers notice that unidirectional streams are both a bit
2496   confusing in concept and also somewhat redundant.  If the recipient
2497   of a stream doesn't wish to send data on a stream, it could simply
2498   send a SYN_REPLY with the FLAG_FIN bit set.  The FLAG_UNIDIRECTIONAL
2499   is, therefore, not necessary.
2500
2501   It is true that we don't need the UNIDIRECTIONAL markings.  It is
2502   added because it avoids the recipient of pushed streams from needing
2503   to send a set of empty frames (e.g. the SYN_STREAM w/ FLAG_FIN) which
2504   otherwise serve no purpose.
2505
25065.7.  Data Compression
2507
2508   Generic compression of data portion of the streams (as opposed to
2509   compression of the headers) without knowing the content of the stream
2510   is redundant.  There is no value in compressing a stream which is
2511   already compressed.  Because of this, HTTP/2.0 does allow data
2512   compression to be optional.  We included it because study of existing
2513   websites shows that many sites are not using compression as they
2514   should, and users suffer because of it.  We wanted a mechanism where,
2515   at the HTTP/2.0 layer, site administrators could simply force
2516
2517
2518
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2522
2523
2524   compression - it is better to compress twice than to not compress.
2525
2526   Overall, however, with this feature being optional and sometimes
2527   redundant, it is unclear if it is useful at all.  We will likely
2528   remove it from the specification.
2529
25305.8.  Server Push
2531
2532   A subtle but important point is that server push streams must be
2533   declared before the associated stream is closed.  The reason for this
2534   is so that proxies have a lifetime for which they can discard
2535   information about previous streams.  If a pushed stream could
2536   associate itself with an already-closed stream, then endpoints would
2537   not have a specific lifecycle for when they could disavow knowledge
2538   of the streams which went before.
2539
25406.  Security Considerations
2541
25426.1.  Use of Same-origin constraints
2543
2544   This specification uses the same-origin policy [RFC6454] in all cases
2545   where verification of content is required.
2546
25476.2.  HTTP Headers and HTTP/2.0 Headers
2548
2549   At the application level, HTTP uses name/value pairs in its headers.
2550   Because HTTP/2.0 merges the existing HTTP headers with HTTP/2.0
2551   headers, there is a possibility that some HTTP applications already
2552   use a particular header name.  To avoid any conflicts, all headers
2553   introduced for layering HTTP over HTTP/2.0 are prefixed with ":". ":"
2554   is not a valid sequence in HTTP header naming, preventing any
2555   possible conflict.
2556
25576.3.  Cross-Protocol Attacks
2558
2559   By utilizing TLS, we believe that HTTP/2.0 introduces no new cross-
2560   protocol attacks.  TLS encrypts the contents of all transmission
2561   (except the handshake itself), making it difficult for attackers to
2562   control the data which could be used in a cross-protocol attack.
2563
25646.4.  Server Push Implicit Headers
2565
2566   Pushed resources do not have an associated request.  In order for
2567   existing HTTP cache control validations (such as the Vary header) to
2568   work, however, all cached resources must have a set of request
2569   headers.  For this reason, browsers MUST be careful to inherit
2570   request headers from the associated stream for the push.  This
2571   includes the 'Cookie' header.
2572
2573
2574
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2578
2579
25807.  Privacy Considerations
2581
25827.1.  Long Lived Connections
2583
2584   HTTP/2.0 aims to keep connections open longer between clients and
2585   servers in order to reduce the latency when a user makes a request.
2586   The maintenance of these connections over time could be used to
2587   expose private information.  For example, a user using a browser
2588   hours after the previous user stopped using that browser may be able
2589   to learn about what the previous user was doing.  This is a problem
2590   with HTTP in its current form as well, however the short lived
2591   connections make it less of a risk.
2592
25937.2.  SETTINGS frame
2594
2595   The HTTP/2.0 SETTINGS frame allows servers to store out-of-band
2596   transmitted information about the communication between client and
2597   server on the client.  Although this is intended only to be used to
2598   reduce latency, renegade servers could use it as a mechanism to store
2599   identifying information about the client in future requests.
2600
2601   Clients implementing privacy modes, such as Google Chrome's
2602   "incognito mode", may wish to disable client-persisted SETTINGS
2603   storage.
2604
2605   Clients MUST clear persisted SETTINGS information when clearing the
2606   cookies.
2607
2608   TODO: Put range maximums on each type of setting to limit
2609   inappropriate uses.
2610
26118.  Requirements Notation
2612
2613   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
2614   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
2615   document are to be interpreted as described in RFC 2119 [RFC2119].
2616
26179.  Acknowledgements
2618
2619   This document includes substantial input from the following
2620   individuals:
2621
2622   o  Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham, Alyssa
2623      Wilk, Costin Manolache, William Chan, Vitaliy Lvin, Joe Chan, Adam
2624      Barth, Ryan Hamilton, Gavin Peters, Kent Alstad, Kevin Lindsay,
2625      Paul Amer, Fan Yang, Jonathan Leighton (SPDY contributors).
2626
2627
2628
2629
2630
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2634
2635
2636   o  Gabriel Montenegro and Willy Tarreau (Upgrade mechanism)
2637
2638   o  William Chan, Salvatore Loreto, Osama Mazahir, Gabriel Montenegro,
2639      Jitu Padhye, Roberto Peon, Rob Trace (Flow control principles)
2640
2641   o  Mark Nottingham and Julian Reschke
2642
264310.  Normative References
2644
2645   [ASCII]            "US-ASCII. Coded Character Set - 7-Bit American
2646                      Standard Code for Information Interchange.
2647                      Standard ANSI X3.4-1986, ANSI, 1986.".
2648
2649   [HTTP-p1]          Fielding, R. and J. Reschke, "Hypertext Transfer
2650                      Protocol (HTTP/1.1): Message Syntax and Routing",
2651                      draft-ietf-httpbis-p1-messaging-21 (work in
2652                      progress), October 2012.
2653
2654   [HTTP-p2]          Fielding, R. and J. Reschke, "Hypertext Transfer
2655                      Protocol (HTTP/1.1): Semantics and Content",
2656                      draft-ietf-httpbis-p2-semantics-21 (work in
2657                      progress), October 2012.
2658
2659   [RFC0793]          Postel, J., "Transmission Control Protocol",
2660                      STD 7, RFC 793, September 1981.
2661
2662   [RFC1738]          Berners-Lee, T., Masinter, L., and M. McCahill,
2663                      "Uniform Resource Locators (URL)", RFC 1738,
2664                      December 1994.
2665
2666   [RFC1950]          Deutsch, L. and J. Gailly, "ZLIB Compressed Data
2667                      Format Specification version 3.3", RFC 1950,
2668                      May 1996.
2669
2670   [RFC2119]          Bradner, S., "Key words for use in RFCs to
2671                      Indicate Requirement Levels", BCP 14, RFC 2119,
2672                      March 1997.
2673
2674   [RFC2616]          Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
2675                      Masinter, L., Leach, P., and T. Berners-Lee,
2676                      "Hypertext Transfer Protocol -- HTTP/1.1",
2677                      RFC 2616, June 1999.
2678
2679   [RFC2617]          Franks, J., Hallam-Baker, P., Hostetler, J.,
2680                      Lawrence, S., Leach, P., Luotonen, A., and L.
2681                      Stewart, "HTTP Authentication: Basic and Digest
2682                      Access Authentication", RFC 2617, June 1999.
2683
2684
2685
2686
2687Belshe, et al.            Expires July 26, 2013                [Page 48]
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2689Internet-Draft                  HTTP/2.0                    January 2013
2690
2691
2692   [RFC4559]          Jaganathan, K., Zhu, L., and J. Brezak, "SPNEGO-
2693                      based Kerberos and NTLM HTTP Authentication in
2694                      Microsoft Windows", RFC 4559, June 2006.
2695
2696   [RFC5246]          Dierks, T. and E. Rescorla, "The Transport Layer
2697                      Security (TLS) Protocol Version 1.2", RFC 5246,
2698                      August 2008.
2699
2700   [RFC6454]          Barth, A., "The Web Origin Concept", RFC 6454,
2701                      December 2011.
2702
2703   [TLSNPN]           Langley, A., "TLS Next Protocol Negotiation",
2704                      draft-agl-tls-nextprotoneg-01 (work in progress),
2705                      August 2010.
2706
2707   [UDELCOMPRESSION]  Yang, F., Amer, P., and J. Leighton, "A
2708                      Methodology to Derive SPDY's Initial Dictionary
2709                      for Zlib Compression", <http://www.eecis.udel.edu/
2710                      ~amer/PEL/poc/pdf/SPDY-Fan.pdf>.
2711
2712Appendix A.  Change Log (to be removed by RFC Editor before publication)
2713
2714A.1.  Since draft-ietf-httpbis-http2-00
2715
2716   Changed title throughout.
2717
2718   Removed section on Incompatibilities with SPDY draft#2.
2719
2720   Changed INTERNAL_ERROR on GOAWAY to have a value of 2 <https://
2721   groups.google.com/forum/?fromgroups#!topic/spdy-dev/cfUef2gL3iU>.
2722
2723   Replaced abstract and introduction.
2724
2725   Added section on starting HTTP/2.0, including upgrade mechanism.
2726
2727   Removed unused references.
2728
2729   Added flow control principles (Section 3.5.1) based on <http://
2730   tools.ietf.org/html/draft-montenegro-httpbis-http2-fc-principles-01>.
2731
2732A.2.  Since draft-mbelshe-httpbis-spdy-00
2733
2734   Adopted as base for draft-ietf-httpbis-http2.
2735
2736   Updated authors/editors list.
2737
2738   Added status note.
2739
2740
2741
2742
2743Belshe, et al.            Expires July 26, 2013                [Page 49]
2744
2745Internet-Draft                  HTTP/2.0                    January 2013
2746
2747
2748Authors' Addresses
2749
2750   Mike Belshe
2751   Twist
2752
2753   EMail: mbelshe@chromium.org
2754
2755
2756   Roberto Peon
2757   Google, Inc
2758
2759   EMail: fenix@google.com
2760
2761
2762   Martin Thomson (editor)
2763   Microsoft
2764   3210 Porter Drive
2765   Palo Alto  94043
2766   US
2767
2768   EMail: martin.thomson@skype.net
2769
2770
2771   Alexey Melnikov (editor)
2772   Isode Ltd
2773   5 Castle Business Village
2774   36 Station Road
2775   Hampton, Middlesex  TW12 2BX
2776   UK
2777
2778   EMail: Alexey.Melnikov@isode.com
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799Belshe, et al.            Expires July 26, 2013                [Page 50]
2800
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