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4HTTPbis Working Group                                          M. Belshe
5Internet-Draft                                                     Twist
6Expires: June 1, 2013                                            R. Peon
7                                                             Google, Inc
8                                                         M. Thomson, Ed.
9                                                               Microsoft
10                                                        A. Melnikov, Ed.
11                                                               Isode Ltd
12                                                       November 28, 2012
13
14
15                             SPDY Protocol
16                      draft-ietf-httpbis-http2-00
17
18Abstract
19
20   This document describes SPDY, a protocol designed for low-latency
21   transport of content over the World Wide Web. SPDY introduces two
22   layers of protocol.  The lower layer is a general purpose framing
23   layer which can be used atop a reliable transport (likely TCP) for
24   multiplexed, prioritized, and compressed data communication of many
25   concurrent streams.  The upper layer of the protocol provides HTTP-
26   like RFC2616 [RFC2616] semantics for compatibility with existing HTTP
27   application servers.
28
29Editorial Note (To be removed by RFC Editor)
30
31   This draft is a work-in-progress, and does not yet reflect Working
32   Group consensus.
33
34   This first draft uses the SPDY Protocol as a starting point, as per
35   the Working Group's charter.  Future drafts will add, remove and
36   change text, based upon the Working Group's decisions.
37
38   Discussion of this draft takes place on the HTTPBIS working group
39   mailing list (ietf-http-wg@w3.org), which is archived at
40   <http://lists.w3.org/Archives/Public/ietf-http-wg/>.
41
42   The current issues list is at
43   <http://tools.ietf.org/wg/httpbis/trac/report/21> and related
44   documents (including fancy diffs) can be found at
45   <http://tools.ietf.org/wg/httpbis/>.
46
47   The changes in this draft are summarized in Appendix A.1.
48
49Status of This Memo
50
51   This Internet-Draft is submitted in full conformance with the
52
53
54
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59
60   provisions of BCP 78 and BCP 79.
61
62   Internet-Drafts are working documents of the Internet Engineering
63   Task Force (IETF).  Note that other groups may also distribute
64   working documents as Internet-Drafts.  The list of current Internet-
65   Drafts is at http://datatracker.ietf.org/drafts/current/.
66
67   Internet-Drafts are draft documents valid for a maximum of six months
68   and may be updated, replaced, or obsoleted by other documents at any
69   time.  It is inappropriate to use Internet-Drafts as reference
70   material or to cite them other than as "work in progress."
71
72   This Internet-Draft will expire on June 1, 2013.
73
74Copyright Notice
75
76   Copyright (c) 2012 IETF Trust and the persons identified as the
77   document authors.  All rights reserved.
78
79   This document is subject to BCP 78 and the IETF Trust's Legal
80   Provisions Relating to IETF Documents
81   (http://trustee.ietf.org/license-info) in effect on the date of
82   publication of this document.  Please review these documents
83   carefully, as they describe your rights and restrictions with respect
84   to this document.  Code Components extracted from this document must
85   include Simplified BSD License text as described in Section 4.e of
86   the Trust Legal Provisions and are provided without warranty as
87   described in the Simplified BSD License.
88
89Table of Contents
90
91   1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
92     1.1.  Document Organization  . . . . . . . . . . . . . . . . . .  4
93     1.2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . .  5
94   2.  SPDY Framing Layer . . . . . . . . . . . . . . . . . . . . . .  5
95     2.1.  Session (Connections)  . . . . . . . . . . . . . . . . . .  5
96     2.2.  Framing  . . . . . . . . . . . . . . . . . . . . . . . . .  5
97       2.2.1.  Control frames . . . . . . . . . . . . . . . . . . . .  6
98       2.2.2.  Data frames  . . . . . . . . . . . . . . . . . . . . .  7
99     2.3.  Streams  . . . . . . . . . . . . . . . . . . . . . . . . .  8
100       2.3.1.  Stream frames  . . . . . . . . . . . . . . . . . . . .  8
101       2.3.2.  Stream creation  . . . . . . . . . . . . . . . . . . .  8
102       2.3.3.  Stream priority  . . . . . . . . . . . . . . . . . . .  9
103       2.3.4.  Stream headers . . . . . . . . . . . . . . . . . . . .  9
104       2.3.5.  Stream data exchange . . . . . . . . . . . . . . . . . 10
105       2.3.6.  Stream half-close  . . . . . . . . . . . . . . . . . . 10
106       2.3.7.  Stream close . . . . . . . . . . . . . . . . . . . . . 10
107     2.4.  Error Handling . . . . . . . . . . . . . . . . . . . . . . 11
108
109
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115
116       2.4.1.  Session Error Handling . . . . . . . . . . . . . . . . 11
117       2.4.2.  Stream Error Handling  . . . . . . . . . . . . . . . . 11
118     2.5.  Data flow  . . . . . . . . . . . . . . . . . . . . . . . . 12
119     2.6.  Control frame types  . . . . . . . . . . . . . . . . . . . 12
120       2.6.1.  SYN_STREAM . . . . . . . . . . . . . . . . . . . . . . 12
121       2.6.2.  SYN_REPLY  . . . . . . . . . . . . . . . . . . . . . . 13
122       2.6.3.  RST_STREAM . . . . . . . . . . . . . . . . . . . . . . 14
123       2.6.4.  SETTINGS . . . . . . . . . . . . . . . . . . . . . . . 16
124       2.6.5.  PING . . . . . . . . . . . . . . . . . . . . . . . . . 19
125       2.6.6.  GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . 20
126       2.6.7.  HEADERS  . . . . . . . . . . . . . . . . . . . . . . . 21
127       2.6.8.  WINDOW_UPDATE  . . . . . . . . . . . . . . . . . . . . 22
128       2.6.9.  CREDENTIAL . . . . . . . . . . . . . . . . . . . . . . 24
129       2.6.10. Name/Value Header Block  . . . . . . . . . . . . . . . 26
130   3.  HTTP Layering over SPDY  . . . . . . . . . . . . . . . . . . . 32
131     3.1.  Connection Management  . . . . . . . . . . . . . . . . . . 32
132       3.1.1.  Use of GOAWAY  . . . . . . . . . . . . . . . . . . . . 32
133     3.2.  HTTP Request/Response  . . . . . . . . . . . . . . . . . . 33
134       3.2.1.  Request  . . . . . . . . . . . . . . . . . . . . . . . 33
135       3.2.2.  Response . . . . . . . . . . . . . . . . . . . . . . . 35
136       3.2.3.  Authentication . . . . . . . . . . . . . . . . . . . . 35
137     3.3.  Server Push Transactions . . . . . . . . . . . . . . . . . 36
138       3.3.1.  Server implementation  . . . . . . . . . . . . . . . . 37
139       3.3.2.  Client implementation  . . . . . . . . . . . . . . . . 38
140   4.  Design Rationale and Notes . . . . . . . . . . . . . . . . . . 39
141     4.1.  Separation of Framing Layer and Application Layer  . . . . 39
142     4.2.  Error handling - Framing Layer . . . . . . . . . . . . . . 39
143     4.3.  One Connection Per Domain  . . . . . . . . . . . . . . . . 40
144     4.4.  Fixed vs Variable Length Fields  . . . . . . . . . . . . . 40
145     4.5.  Compression Context(s) . . . . . . . . . . . . . . . . . . 41
146     4.6.  Unidirectional streams . . . . . . . . . . . . . . . . . . 41
147     4.7.  Data Compression . . . . . . . . . . . . . . . . . . . . . 41
148     4.8.  Server Push  . . . . . . . . . . . . . . . . . . . . . . . 42
149   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 42
150     5.1.  Use of Same-origin constraints . . . . . . . . . . . . . . 42
151     5.2.  HTTP Headers and SPDY Headers  . . . . . . . . . . . . . . 42
152     5.3.  Cross-Protocol Attacks . . . . . . . . . . . . . . . . . . 42
153     5.4.  Server Push Implicit Headers . . . . . . . . . . . . . . . 42
154   6.  Privacy Considerations . . . . . . . . . . . . . . . . . . . . 43
155     6.1.  Long Lived Connections . . . . . . . . . . . . . . . . . . 43
156     6.2.  SETTINGS frame . . . . . . . . . . . . . . . . . . . . . . 43
157   7.  Incompatibilities with SPDY draft #2 . . . . . . . . . . . . . 43
158   8.  Requirements Notation  . . . . . . . . . . . . . . . . . . . . 44
159   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 44
160   10. Normative References . . . . . . . . . . . . . . . . . . . . . 44
161   Appendix A.  Change Log (to be removed by RFC Editor before
162                publication)  . . . . . . . . . . . . . . . . . . . . 45
163     A.1.  Since draft-mbelshe-httpbis-spdy-00  . . . . . . . . . . . 45
164
165
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171
1721.  Overview
173
174   One of the bottlenecks of HTTP implementations is that HTTP relies on
175   multiple connections for concurrency.  This causes several problems,
176   including additional round trips for connection setup, slow-start
177   delays, and connection rationing by the client, where it tries to
178   avoid opening too many connections to any single server.  HTTP
179   pipelining helps some, but only achieves partial multiplexing.  In
180   addition, pipelining has proven non-deployable in existing browsers
181   due to intermediary interference.
182
183   SPDY adds a framing layer for multiplexing multiple, concurrent
184   streams across a single TCP connection (or any reliable transport
185   stream).  The framing layer is optimized for HTTP-like request-
186   response streams, such that applications which run over HTTP today
187   can work over SPDY with little or no change on behalf of the web
188   application writer.
189
190   The SPDY session offers four improvements over HTTP:
191
192      Multiplexed requests: There is no limit to the number of requests
193      that can be issued concurrently over a single SPDY connection.
194
195      Prioritized requests: Clients can request certain resources to be
196      delivered first.  This avoids the problem of congesting the
197      network channel with non-critical resources when a high-priority
198      request is pending.
199
200      Compressed headers: Clients today send a significant amount of
201      redundant data in the form of HTTP headers.  Because a single web
202      page may require 50 or 100 subrequests, this data is significant.
203
204      Server pushed streams: Server Push enables content to be pushed
205      from servers to clients without a request.
206
207   SPDY attempts to preserve the existing semantics of HTTP.  All
208   features such as cookies, ETags, Vary headers, Content-Encoding
209   negotiations, etc work as they do with HTTP; SPDY only replaces the
210   way the data is written to the network.
211
2121.1.  Document Organization
213
214   The SPDY Specification is split into two parts: a framing layer
215   (Section 2), which multiplexes a TCP connection into independent,
216   length-prefixed frames, and an HTTP layer (Section 3), which
217   specifies the mechanism for overlaying HTTP request/response pairs on
218   top of the framing layer.  While some of the framing layer concepts
219   are isolated from the HTTP layer, building a generic framing layer
220
221
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228   has not been a goal.  The framing layer is tailored to the needs of
229   the HTTP protocol and server push.
230
2311.2.  Definitions
232
233      client: The endpoint initiating the SPDY session.
234
235      connection: A transport-level connection between two endpoints.
236
237      endpoint: Either the client or server of a connection.
238
239      frame: A header-prefixed sequence of bytes sent over a SPDY
240      session.
241
242      server: The endpoint which did not initiate the SPDY session.
243
244      session: A synonym for a connection.
245
246      session error: An error on the SPDY session.
247
248      stream: A bi-directional flow of bytes across a virtual channel
249      within a SPDY session.
250
251      stream error: An error on an individual SPDY stream.
252
2532.  SPDY Framing Layer
254
2552.1.  Session (Connections)
256
257   The SPDY framing layer (or "session") runs atop a reliable transport
258   layer such as TCP [RFC0793].  The client is the TCP connection
259   initiator.  SPDY connections are persistent connections.
260
261   For best performance, it is expected that clients will not close open
262   connections until the user navigates away from all web pages
263   referencing a connection, or until the server closes the connection.
264   Servers are encouraged to leave connections open for as long as
265   possible, but can terminate idle connections if necessary.  When
266   either endpoint closes the transport-level connection, it MUST first
267   send a GOAWAY (Section 2.6.6) frame so that the endpoints can
268   reliably determine if requests finished before the close.
269
2702.2.  Framing
271
272   Once the connection is established, clients and servers exchange
273   framed messages.  There are two types of frames: control frames
274   (Section 2.2.1) and data frames (Section 2.2.2).  Frames always have
275   a common header which is 8 bytes in length.
276
277
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283
284   The first bit is a control bit indicating whether a frame is a
285   control frame or data frame.  Control frames carry a version number,
286   a frame type, flags, and a length.  Data frames contain the stream
287   ID, flags, and the length for the payload carried after the common
288   header.  The simple header is designed to make reading and writing of
289   frames easy.
290
291   All integer values, including length, version, and type, are in
292   network byte order.  SPDY does not enforce alignment of types in
293   dynamically sized frames.
294
2952.2.1.  Control frames
296
297   +----------------------------------+
298   |C| Version(15bits) | Type(16bits) |
299   +----------------------------------+
300   | Flags (8)  |  Length (24 bits)   |
301   +----------------------------------+
302   |               Data               |
303   +----------------------------------+
304
305   Control bit: The 'C' bit is a single bit indicating if this is a
306   control message.  For control frames this value is always 1.
307
308   Version: The version number of the SPDY protocol.  This document
309   describes SPDY version 3.
310
311   Type: The type of control frame.  See Control Frames for the complete
312   list of control frames.
313
314   Flags: Flags related to this frame.  Flags for control frames and
315   data frames are different.
316
317   Length: An unsigned 24-bit value representing the number of bytes
318   after the length field.
319
320   Data: data associated with this control frame.  The format and length
321   of this data is controlled by the control frame type.
322
323   Control frame processing requirements:
324
325      Note that full length control frames (16MB) can be large for
326      implementations running on resource-limited hardware.  In such
327      cases, implementations MAY limit the maximum length frame
328      supported.  However, all implementations MUST be able to receive
329      control frames of at least 8192 octets in length.
330
331
332
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339
3402.2.2.  Data frames
341
342   +----------------------------------+
343   |C|       Stream-ID (31bits)       |
344   +----------------------------------+
345   | Flags (8)  |  Length (24 bits)   |
346   +----------------------------------+
347   |               Data               |
348   +----------------------------------+
349
350   Control bit: For data frames this value is always 0.
351
352   Stream-ID: A 31-bit value identifying the stream.
353
354   Flags: Flags related to this frame.  Valid flags are:
355
356      0x01 = FLAG_FIN - signifies that this frame represents the last
357      frame to be transmitted on this stream.  See Stream Close
358      (Section 2.3.7) below.
359
360      0x02 = FLAG_COMPRESS - indicates that the data in this frame has
361      been compressed.
362
363   Length: An unsigned 24-bit value representing the number of bytes
364   after the length field.  The total size of a data frame is 8 bytes +
365   length.  It is valid to have a zero-length data frame.
366
367   Data: The variable-length data payload; the length was defined in the
368   length field.
369
370   Data frame processing requirements:
371
372      If an endpoint receives a data frame for a stream-id which is not
373      open and the endpoint has not sent a GOAWAY (Section 2.6.6) frame,
374      it MUST send issue a stream error (Section 2.4.2) with the error
375      code INVALID_STREAM for the stream-id.
376
377      If the endpoint which created the stream receives a data frame
378      before receiving a SYN_REPLY on that stream, it is a protocol
379      error, and the recipient MUST issue a stream error (Section 2.4.2)
380      with the status code PROTOCOL_ERROR for the stream-id.
381
382      Implementors note: If an endpoint receives multiple data frames
383      for invalid stream-ids, it MAY close the session.
384
385      All SPDY endpoints MUST accept compressed data frames.
386      Compression of data frames is always done using zlib compression.
387      Each stream initializes and uses its own compression context
388
389
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395
396      dedicated to use within that stream.  Endpoints are encouraged to
397      use application level compression rather than SPDY stream level
398      compression.
399
400      Each SPDY stream sending compressed frames creates its own zlib
401      context for that stream, and these compression contexts MUST be
402      distinct from the compression contexts used with SYN_STREAM/
403      SYN_REPLY/HEADER compression.  (Thus, if both endpoints of a
404      stream are compressing data on the stream, there will be two zlib
405      contexts, one for sending and one for receiving).
406
4072.3.  Streams
408
409   Streams are independent sequences of bi-directional data divided into
410   frames with several properties:
411
412      Streams may be created by either the client or server.
413
414      Streams optionally carry a set of name/value header pairs.
415
416      Streams can concurrently send data interleaved with other streams.
417
418      Streams may be cancelled.
419
4202.3.1.  Stream frames
421
422   SPDY defines 3 control frames to manage the lifecycle of a stream:
423
424      SYN_STREAM - Open a new stream
425
426      SYN_REPLY - Remote acknowledgement of a new, open stream
427
428      RST_STREAM - Close a stream
429
4302.3.2.  Stream creation
431
432   A stream is created by sending a control frame with the type set to
433   SYN_STREAM (Section 2.6.1).  If the server is initiating the stream,
434   the Stream-ID must be even.  If the client is initiating the stream,
435   the Stream-ID must be odd. 0 is not a valid Stream-ID.  Stream-IDs
436   from each side of the connection must increase monotonically as new
437   streams are created.  E.g.  Stream 2 may be created after stream 3,
438   but stream 7 must not be created after stream 9.  Stream IDs do not
439   wrap: when a client or server cannot create a new stream id without
440   exceeding a 31 bit value, it MUST NOT create a new stream.
441
442   The stream-id MUST increase with each new stream.  If an endpoint
443   receives a SYN_STREAM with a stream id which is less than any
444
445
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451
452   previously received SYN_STREAM, it MUST issue a session error
453   (Section 2.4.1) with the status PROTOCOL_ERROR.
454
455   It is a protocol error to send two SYN_STREAMs with the same
456   stream-id.  If a recipient receives a second SYN_STREAM for the same
457   stream, it MUST issue a stream error (Section 2.4.2) with the status
458   code PROTOCOL_ERROR.
459
460   Upon receipt of a SYN_STREAM, the recipient can reject the stream by
461   sending a stream error (Section 2.4.2) with the error code
462   REFUSED_STREAM.  Note, however, that the creating endpoint may have
463   already sent additional frames for that stream which cannot be
464   immediately stopped.
465
466   Once the stream is created, the creator may immediately send HEADERS
467   or DATA frames for that stream, without needing to wait for the
468   recipient to acknowledge.
469
4702.3.2.1.  Unidirectional streams
471
472   When an endpoint creates a stream with the FLAG_UNIDIRECTIONAL flag
473   set, it creates a unidirectional stream which the creating endpoint
474   can use to send frames, but the receiving endpoint cannot.  The
475   receiving endpoint is implicitly already in the half-closed
476   (Section 2.3.6) state.
477
4782.3.2.2.  Bidirectional streams
479
480   SYN_STREAM frames which do not use the FLAG_UNIDIRECTIONAL flag are
481   bidirectional streams.  Both endpoints can send data on a bi-
482   directional stream.
483
4842.3.3.  Stream priority
485
486   The creator of a stream assigns a priority for that stream.  Priority
487   is represented as an integer from 0 to 7. 0 represents the highest
488   priority and 7 represents the lowest priority.
489
490   The sender and recipient SHOULD use best-effort to process streams in
491   the order of highest priority to lowest priority.
492
4932.3.4.  Stream headers
494
495   Streams carry optional sets of name/value pair headers which carry
496   metadata about the stream.  After the stream has been created, and as
497   long as the sender is not closed (Section 2.3.7) or half-closed
498   (Section 2.3.6), each side may send HEADERS frame(s) containing the
499   header data.  Header data can be sent in multiple HEADERS frames, and
500
501
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507
508   HEADERS frames may be interleaved with data frames.
509
5102.3.5.  Stream data exchange
511
512   Once a stream is created, it can be used to send arbitrary amounts of
513   data.  Generally this means that a series of data frames will be sent
514   on the stream until a frame containing the FLAG_FIN flag is set.  The
515   FLAG_FIN can be set on a SYN_STREAM (Section 2.6.1), SYN_REPLY
516   (Section 2.6.2), HEADERS (Section 2.6.7) or a DATA (Section 2.2.2)
517   frame.  Once the FLAG_FIN has been sent, the stream is considered to
518   be half-closed.
519
5202.3.6.  Stream half-close
521
522   When one side of the stream sends a frame with the FLAG_FIN flag set,
523   the stream is half-closed from that endpoint.  The sender of the
524   FLAG_FIN MUST NOT send further frames on that stream.  When both
525   sides have half-closed, the stream is closed.
526
527   If an endpoint receives a data frame after the stream is half-closed
528   from the sender (e.g. the endpoint has already received a prior frame
529   for the stream with the FIN flag set), it MUST send a RST_STREAM to
530   the sender with the status STREAM_ALREADY_CLOSED.
531
5322.3.7.  Stream close
533
534   There are 3 ways that streams can be terminated:
535
536      Normal termination: Normal stream termination occurs when both
537      sender and recipient have half-closed the stream by sending a
538      FLAG_FIN.
539
540      Abrupt termination: Either the client or server can send a
541      RST_STREAM control frame at any time.  A RST_STREAM contains an
542      error code to indicate the reason for failure.  When a RST_STREAM
543      is sent from the stream originator, it indicates a failure to
544      complete the stream and that no further data will be sent on the
545      stream.  When a RST_STREAM is sent from the stream recipient, the
546      sender, upon receipt, should stop sending any data on the stream.
547      The stream recipient should be aware that there is a race between
548      data already in transit from the sender and the time the
549      RST_STREAM is received.  See Stream Error Handling (Section 2.4.2)
550
551      TCP connection teardown: If the TCP connection is torn down while
552      un-closed streams exist, then the endpoint must assume that the
553      stream was abnormally interrupted and may be incomplete.
554
555   If an endpoint receives a data frame after the stream is closed, it
556
557
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563
564   must send a RST_STREAM to the sender with the status PROTOCOL_ERROR.
565
5662.4.  Error Handling
567
568   The SPDY framing layer has only two types of errors, and they are
569   always handled consistently.  Any reference in this specification to
570   "issue a session error" refers to Section 2.4.1.  Any reference to
571   "issue a stream error" refers to Section 2.4.2.
572
5732.4.1.  Session Error Handling
574
575   A session error is any error which prevents further processing of the
576   framing layer or which corrupts the session compression state.  When
577   a session error occurs, the endpoint encountering the error MUST
578   first send a GOAWAY (Section 2.6.6) frame with the stream id of most
579   recently received stream from the remote endpoint, and the error code
580   for why the session is terminating.  After sending the GOAWAY frame,
581   the endpoint MUST close the TCP connection.
582
583   Note that the session compression state is dependent upon both
584   endpoints always processing all compressed data.  If an endpoint
585   partially processes a frame containing compressed data without
586   updating compression state properly, future control frames which use
587   compression will be always be errored.  Implementations SHOULD always
588   try to process compressed data so that errors which could be handled
589   as stream errors do not become session errors.
590
591   Note that because this GOAWAY is sent during a session error case, it
592   is possible that the GOAWAY will not be reliably received by the
593   receiving endpoint.  It is a best-effort attempt to communicate with
594   the remote about why the session is going down.
595
5962.4.2.  Stream Error Handling
597
598   A stream error is an error related to a specific stream-id which does
599   not affect processing of other streams at the framing layer.  Upon a
600   stream error, the endpoint MUST send a RST_STREAM (Section 2.6.3)
601   frame which contains the stream id of the stream where the error
602   occurred and the error status which caused the error.  After sending
603   the RST_STREAM, the stream is closed to the sending endpoint.  After
604   sending the RST_STREAM, if the sender receives any frames other than
605   a RST_STREAM for that stream id, it will result in sending additional
606   RST_STREAM frames.  An endpoint MUST NOT send a RST_STREAM in
607   response to an RST_STREAM, as doing so would lead to RST_STREAM
608   loops.  Sending a RST_STREAM does not cause the SPDY session to be
609   closed.
610
611   If an endpoint has multiple RST_STREAM frames to send in succession
612
613
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619
620   for the same stream-id and the same error code, it MAY coalesce them
621   into a single RST_STREAM frame.  (This can happen if a stream is
622   closed, but the remote sends multiple data frames.  There is no
623   reason to send a RST_STREAM for each frame in succession).
624
6252.5.  Data flow
626
627   Because TCP provides a single stream of data on which SPDY
628   multiplexes multiple logical streams, clients and servers must
629   intelligently interleave data messages for concurrent sessions.
630
6312.6.  Control frame types
632
6332.6.1.  SYN_STREAM
634
635   The SYN_STREAM control frame allows the sender to asynchronously
636   create a stream between the endpoints.  See Stream Creation
637   (Section 2.3.2)
638
639   +------------------------------------+
640   |1|    version    |         1        |
641   +------------------------------------+
642   |  Flags (8)  |  Length (24 bits)    |
643   +------------------------------------+
644   |X|           Stream-ID (31bits)     |
645   +------------------------------------+
646   |X| Associated-To-Stream-ID (31bits) |
647   +------------------------------------+
648   | Pri|Unused | Slot |                |
649   +-------------------+                |
650   | Number of Name/Value pairs (int32) |   <+
651   +------------------------------------+    |
652   |     Length of name (int32)         |    | This section is the
653   +------------------------------------+    | "Name/Value Header
654   |           Name (string)            |    | Block", and is
655   +------------------------------------+    | compressed.
656   |     Length of value  (int32)       |    |
657   +------------------------------------+    |
658   |          Value   (string)          |    |
659   +------------------------------------+    |
660   |           (repeats)                |   <+
661
662   Flags: Flags related to this frame.  Valid flags are:
663
664      0x01 = FLAG_FIN - marks this frame as the last frame to be
665      transmitted on this stream and puts the sender in the half-closed
666      (Section 2.3.6) state.
667
668
669
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675
676      0x02 = FLAG_UNIDIRECTIONAL - a stream created with this flag puts
677      the recipient in the half-closed (Section 2.3.6) state.
678
679   Length: The length is the number of bytes which follow the length
680   field in the frame.  For SYN_STREAM frames, this is 10 bytes plus the
681   length of the compressed Name/Value block.
682
683   Stream-ID: The 31-bit identifier for this stream.  This stream-id
684   will be used in frames which are part of this stream.
685
686   Associated-To-Stream-ID: The 31-bit identifier for a stream which
687   this stream is associated to.  If this stream is independent of all
688   other streams, it should be 0.
689
690   Priority: A 3-bit priority (Section 2.3.3) field.
691
692   Unused: 5 bits of unused space, reserved for future use.
693
694   Slot: An 8 bit unsigned integer specifying the index in the server's
695   CREDENTIAL vector of the client certificate to be used for this
696   request. see CREDENTIAL frame (Section 2.6.9).  The value 0 means no
697   client certificate should be associated with this stream.
698
699   Name/Value Header Block: A set of name/value pairs carried as part of
700   the SYN_STREAM. see Name/Value Header Block (Section 2.6.10).
701
702   If an endpoint receives a SYN_STREAM which is larger than the
703   implementation supports, it MAY send a RST_STREAM with error code
704   FRAME_TOO_LARGE.  All implementations MUST support the minimum size
705   limits defined in the Control Frames section (Section 2.2.1).
706
7072.6.2.  SYN_REPLY
708
709   SYN_REPLY indicates the acceptance of a stream creation by the
710   recipient of a SYN_STREAM frame.
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
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731
732   +------------------------------------+
733   |1|    version    |         2        |
734   +------------------------------------+
735   |  Flags (8)  |  Length (24 bits)    |
736   +------------------------------------+
737   |X|           Stream-ID (31bits)     |
738   +------------------------------------+
739   | Number of Name/Value pairs (int32) |   <+
740   +------------------------------------+    |
741   |     Length of name (int32)         |    | This section is the
742   +------------------------------------+    | "Name/Value Header
743   |           Name (string)            |    | Block", and is
744   +------------------------------------+    | compressed.
745   |     Length of value  (int32)       |    |
746   +------------------------------------+    |
747   |          Value   (string)          |    |
748   +------------------------------------+    |
749   |           (repeats)                |   <+
750
751   Flags: Flags related to this frame.  Valid flags are:
752
753      0x01 = FLAG_FIN - marks this frame as the last frame to be
754      transmitted on this stream and puts the sender in the half-closed
755      (Section 2.3.6) state.
756
757   Length: The length is the number of bytes which follow the length
758   field in the frame.  For SYN_REPLY frames, this is 4 bytes plus the
759   length of the compressed Name/Value block.
760
761   Stream-ID: The 31-bit identifier for this stream.
762
763   If an endpoint receives multiple SYN_REPLY frames for the same active
764   stream ID, it MUST issue a stream error (Section 2.4.2) with the
765   error code STREAM_IN_USE.
766
767   Name/Value Header Block: A set of name/value pairs carried as part of
768   the SYN_STREAM. see Name/Value Header Block (Section 2.6.10).
769
770   If an endpoint receives a SYN_REPLY which is larger than the
771   implementation supports, it MAY send a RST_STREAM with error code
772   FRAME_TOO_LARGE.  All implementations MUST support the minimum size
773   limits defined in the Control Frames section (Section 2.2.1).
774
7752.6.3.  RST_STREAM
776
777   The RST_STREAM frame allows for abnormal termination of a stream.
778   When sent by the creator of a stream, it indicates the creator wishes
779   to cancel the stream.  When sent by the recipient of a stream, it
780
781
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787
788   indicates an error or that the recipient did not want to accept the
789   stream, so the stream should be closed.
790
791   +----------------------------------+
792   |1|   version    |         3       |
793   +----------------------------------+
794   | Flags (8)  |         8           |
795   +----------------------------------+
796   |X|          Stream-ID (31bits)    |
797   +----------------------------------+
798   |          Status code             |
799   +----------------------------------+
800
801   Flags: Flags related to this frame.  RST_STREAM does not define any
802   flags.  This value must be 0.
803
804   Length: An unsigned 24-bit value representing the number of bytes
805   after the length field.  For RST_STREAM control frames, this value is
806   always 8.
807
808   Stream-ID: The 31-bit identifier for this stream.
809
810   Status code: (32 bits) An indicator for why the stream is being
811   terminated.The following status codes are defined:
812
813      1 - PROTOCOL_ERROR.  This is a generic error, and should only be
814      used if a more specific error is not available.
815
816      2 - INVALID_STREAM.  This is returned when a frame is received for
817      a stream which is not active.
818
819      3 - REFUSED_STREAM.  Indicates that the stream was refused before
820      any processing has been done on the stream.
821
822      4 - UNSUPPORTED_VERSION.  Indicates that the recipient of a stream
823      does not support the SPDY version requested.
824
825      5 - CANCEL.  Used by the creator of a stream to indicate that the
826      stream is no longer needed.
827
828      6 - INTERNAL_ERROR.  This is a generic error which can be used
829      when the implementation has internally failed, not due to anything
830      in the protocol.
831
832      7 - FLOW_CONTROL_ERROR.  The endpoint detected that its peer
833      violated the flow control protocol.
834
835
836
837
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843
844      8 - STREAM_IN_USE.  The endpoint received a SYN_REPLY for a stream
845      already open.
846
847      9 - STREAM_ALREADY_CLOSED.  The endpoint received a data or
848      SYN_REPLY frame for a stream which is half closed.
849
850      10 - INVALID_CREDENTIALS.  The server received a request for a
851      resource whose origin does not have valid credentials in the
852      client certificate vector.
853
854      11 - FRAME_TOO_LARGE.  The endpoint received a frame which this
855      implementation could not support.  If FRAME_TOO_LARGE is sent for
856      a SYN_STREAM, HEADERS, or SYN_REPLY frame without fully processing
857      the compressed portion of those frames, then the compression state
858      will be out-of-sync with the other endpoint.  In this case,
859      senders of FRAME_TOO_LARGE MUST close the session.
860
861      Note: 0 is not a valid status code for a RST_STREAM.
862
863   After receiving a RST_STREAM on a stream, the recipient must not send
864   additional frames for that stream, and the stream moves into the
865   closed state.
866
8672.6.4.  SETTINGS
868
869   A SETTINGS frame contains a set of id/value pairs for communicating
870   configuration data about how the two endpoints may communicate.
871   SETTINGS frames can be sent at any time by either endpoint, are
872   optionally sent, and are fully asynchronous.  When the server is the
873   sender, the sender can request that configuration data be persisted
874   by the client across SPDY sessions and returned to the server in
875   future communications.
876
877   Persistence of SETTINGS ID/Value pairs is done on a per origin/IP
878   pair (the "origin" is the set of scheme, host, and port from the URI.
879   See [RFC6454]).  That is, when a client connects to a server, and the
880   server persists settings within the client, the client SHOULD return
881   the persisted settings on future connections to the same origin AND
882   IP address and TCP port.  Clients MUST NOT request servers to use the
883   persistence features of the SETTINGS frames, and servers MUST ignore
884   persistence related flags sent by a client.
885
886
887
888
889
890
891
892
893
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899
900   +----------------------------------+
901   |1|   version    |         4       |
902   +----------------------------------+
903   | Flags (8)  |  Length (24 bits)   |
904   +----------------------------------+
905   |         Number of entries        |
906   +----------------------------------+
907   |          ID/Value Pairs          |
908   |             ...                  |
909
910   Control bit: The control bit is always 1 for this message.
911
912   Version: The SPDY version number.
913
914   Type: The message type for a SETTINGS message is 4.
915
916   Flags: FLAG_SETTINGS_CLEAR_SETTINGS (0x1): When set, the client
917   should clear any previously persisted SETTINGS ID/Value pairs.  If
918   this frame contains ID/Value pairs with the
919   FLAG_SETTINGS_PERSIST_VALUE set, then the client will first clear its
920   existing, persisted settings, and then persist the values with the
921   flag set which are contained within this frame.  Because persistence
922   is only implemented on the client, this flag can only be used when
923   the sender is the server.
924
925   Length: An unsigned 24-bit value representing the number of bytes
926   after the length field.  The total size of a SETTINGS frame is 8
927   bytes + length.
928
929   Number of entries: A 32-bit value representing the number of ID/value
930   pairs in this message.
931
932   ID: A 32-bit ID number, comprised of 8 bits of flags and 24 bits of
933   unique ID.
934
935      ID.flags:
936
937         FLAG_SETTINGS_PERSIST_VALUE (0x1): When set, the sender of this
938         SETTINGS frame is requesting that the recipient persist the ID/
939         Value and return it in future SETTINGS frames sent from the
940         sender to this recipient.  Because persistence is only
941         implemented on the client, this flag is only sent by the
942         server.
943
944         FLAG_SETTINGS_PERSISTED (0x2): When set, the sender is
945         notifying the recipient that this ID/Value pair was previously
946         sent to the sender by the recipient with the
947         FLAG_SETTINGS_PERSIST_VALUE, and the sender is returning it.
948
949
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955
956         Because persistence is only implemented on the client, this
957         flag is only sent by the client.
958
959      Defined IDs:
960
961         1 - SETTINGS_UPLOAD_BANDWIDTH allows the sender to send its
962         expected upload bandwidth on this channel.  This number is an
963         estimate.  The value should be the integral number of kilobytes
964         per second that the sender predicts as an expected maximum
965         upload channel capacity.
966
967         2 - SETTINGS_DOWNLOAD_BANDWIDTH allows the sender to send its
968         expected download bandwidth on this channel.  This number is an
969         estimate.  The value should be the integral number of kilobytes
970         per second that the sender predicts as an expected maximum
971         download channel capacity.
972
973         3 - SETTINGS_ROUND_TRIP_TIME allows the sender to send its
974         expected round-trip-time on this channel.  The round trip time
975         is defined as the minimum amount of time to send a control
976         frame from this client to the remote and receive a response.
977         The value is represented in milliseconds.
978
979         4 - SETTINGS_MAX_CONCURRENT_STREAMS allows the sender to inform
980         the remote endpoint the maximum number of concurrent streams
981         which it will allow.  By default there is no limit.  For
982         implementors it is recommended that this value be no smaller
983         than 100.
984
985         5 - SETTINGS_CURRENT_CWND allows the sender to inform the
986         remote endpoint of the current TCP CWND value.
987
988         6 - SETTINGS_DOWNLOAD_RETRANS_RATE allows the sender to inform
989         the remote endpoint the retransmission rate (bytes
990         retransmitted / total bytes transmitted).
991
992         7 - SETTINGS_INITIAL_WINDOW_SIZE allows the sender to inform
993         the remote endpoint the initial window size (in bytes) for new
994         streams.
995
996         8 - SETTINGS_CLIENT_CERTIFICATE_VECTOR_SIZE allows the server
997         to inform the client if the new size of the client certificate
998         vector.
999
1000   Value: A 32-bit value.
1001
1002   The message is intentionally extensible for future information which
1003   may improve client-server communications.  The sender does not need
1004
1005
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1011
1012   to send every type of ID/value.  It must only send those for which it
1013   has accurate values to convey.  When multiple ID/value pairs are
1014   sent, they should be sent in order of lowest id to highest id.  A
1015   single SETTINGS frame MUST not contain multiple values for the same
1016   ID.  If the recipient of a SETTINGS frame discovers multiple values
1017   for the same ID, it MUST ignore all values except the first one.
1018
1019   A server may send multiple SETTINGS frames containing different ID/
1020   Value pairs.  When the same ID/Value is sent twice, the most recent
1021   value overrides any previously sent values.  If the server sends IDs
1022   1, 2, and 3 with the FLAG_SETTINGS_PERSIST_VALUE in a first SETTINGS
1023   frame, and then sends IDs 4 and 5 with the
1024   FLAG_SETTINGS_PERSIST_VALUE, when the client returns the persisted
1025   state on its next SETTINGS frame, it SHOULD send all 5 settings (1,
1026   2, 3, 4, and 5 in this example) to the server.
1027
10282.6.5.  PING
1029
1030   The PING control frame is a mechanism for measuring a minimal round-
1031   trip time from the sender.  It can be sent from the client or the
1032   server.  Recipients of a PING frame should send an identical frame to
1033   the sender as soon as possible (if there is other pending data
1034   waiting to be sent, PING should take highest priority).  Each ping
1035   sent by a sender should use a unique ID.
1036
1037   +----------------------------------+
1038   |1|   version    |         6       |
1039   +----------------------------------+
1040   | 0 (flags) |     4 (length)       |
1041   +----------------------------------|
1042   |            32-bit ID             |
1043   +----------------------------------+
1044
1045   Control bit: The control bit is always 1 for this message.
1046
1047   Version: The SPDY version number.
1048
1049   Type: The message type for a PING message is 6.
1050
1051   Length: This frame is always 4 bytes long.
1052
1053   ID: A unique ID for this ping, represented as an unsigned 32 bit
1054   value.  When the client initiates a ping, it must use an odd numbered
1055   ID.  When the server initiates a ping, it must use an even numbered
1056   ping.  Use of odd/even IDs is required in order to avoid accidental
1057   looping on PINGs (where each side initiates an identical PING at the
1058   same time).
1059
1060
1061
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1066
1067
1068   Note: If a sender uses all possible PING ids (e.g. has sent all 2^31
1069   possible IDs), it can wrap and start re-using IDs.
1070
1071   If a server receives an even numbered PING which it did not initiate,
1072   it must ignore the PING.  If a client receives an odd numbered PING
1073   which it did not initiate, it must ignore the PING.
1074
10752.6.6.  GOAWAY
1076
1077   The GOAWAY control frame is a mechanism to tell the remote side of
1078   the connection to stop creating streams on this session.  It can be
1079   sent from the client or the server.  Once sent, the sender will not
1080   respond to any new SYN_STREAMs on this session.  Recipients of a
1081   GOAWAY frame must not send additional streams on this session,
1082   although a new session can be established for new streams.  The
1083   purpose of this message is to allow an endpoint to gracefully stop
1084   accepting new streams (perhaps for a reboot or maintenance), while
1085   still finishing processing of previously established streams.
1086
1087   There is an inherent race condition between an endpoint sending
1088   SYN_STREAMs and the remote sending a GOAWAY message.  To deal with
1089   this case, the GOAWAY contains a last-stream-id indicating the
1090   stream-id of the last stream which was created on the sending
1091   endpoint in this session.  If the receiver of the GOAWAY sent new
1092   SYN_STREAMs for sessions after this last-stream-id, they were not
1093   processed by the server and the receiver may treat the stream as
1094   though it had never been created at all (hence the receiver may want
1095   to re-create the stream later on a new session).
1096
1097   Endpoints should always send a GOAWAY message before closing a
1098   connection so that the remote can know whether a stream has been
1099   partially processed or not.  (For example, if an HTTP client sends a
1100   POST at the same time that a server closes a connection, the client
1101   cannot know if the server started to process that POST request if the
1102   server does not send a GOAWAY frame to indicate where it stopped
1103   working).
1104
1105   After sending a GOAWAY message, the sender must ignore all SYN_STREAM
1106   frames for new streams.
1107
1108   +----------------------------------+
1109   |1|   version    |         7       |
1110   +----------------------------------+
1111   | 0 (flags) |     8 (length)       |
1112   +----------------------------------|
1113   |X|  Last-good-stream-ID (31 bits) |
1114   +----------------------------------+
1115   |          Status code             |
1116
1117
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1122
1123
1124   +----------------------------------+
1125
1126   Control bit: The control bit is always 1 for this message.
1127
1128   Version: The SPDY version number.
1129
1130   Type: The message type for a GOAWAY message is 7.
1131
1132   Length: This frame is always 8 bytes long.
1133
1134   Last-good-stream-Id: The last stream id which was replied to (with
1135   either a SYN_REPLY or RST_STREAM) by the sender of the GOAWAY
1136   message.  If no streams were replied to, this value MUST be 0.
1137
1138   Status: The reason for closing the session.
1139
1140      0 - OK.  This is a normal session teardown.
1141
1142      1 - PROTOCOL_ERROR.  This is a generic error, and should only be
1143      used if a more specific error is not available.
1144
1145      11 - INTERNAL_ERROR.  This is a generic error which can be used
1146      when the implementation has internally failed, not due to anything
1147      in the protocol.
1148
11492.6.7.  HEADERS
1150
1151   The HEADERS frame augments a stream with additional headers.  It may
1152   be optionally sent on an existing stream at any time.  Specific
1153   application of the headers in this frame is application-dependent.
1154   The name/value header block within this frame is compressed.
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
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1178
1179
1180   +------------------------------------+
1181   |1|   version     |          8       |
1182   +------------------------------------+
1183   | Flags (8)  |   Length (24 bits)    |
1184   +------------------------------------+
1185   |X|          Stream-ID (31bits)      |
1186   +------------------------------------+
1187   | Number of Name/Value pairs (int32) |   <+
1188   +------------------------------------+    |
1189   |     Length of name (int32)         |    | This section is the
1190   +------------------------------------+    | "Name/Value Header
1191   |           Name (string)            |    | Block", and is
1192   +------------------------------------+    | compressed.
1193   |     Length of value  (int32)       |    |
1194   +------------------------------------+    |
1195   |          Value   (string)          |    |
1196   +------------------------------------+    |
1197   |           (repeats)                |   <+
1198
1199   Flags: Flags related to this frame.  Valid flags are:
1200
1201      0x01 = FLAG_FIN - marks this frame as the last frame to be
1202      transmitted on this stream and puts the sender in the half-closed
1203      (Section 2.3.6) state.
1204
1205   Length: An unsigned 24 bit value representing the number of bytes
1206   after the length field.  The minimum length of the length field is 4
1207   (when the number of name value pairs is 0).
1208
1209   Stream-ID: The stream this HEADERS block is associated with.
1210
1211   Name/Value Header Block: A set of name/value pairs carried as part of
1212   the SYN_STREAM. see Name/Value Header Block (Section 2.6.10).
1213
12142.6.8.  WINDOW_UPDATE
1215
1216   The WINDOW_UPDATE control frame is used to implement per stream flow
1217   control in SPDY.  Flow control in SPDY is per hop, that is, only
1218   between the two endpoints of a SPDY connection.  If there are one or
1219   more intermediaries between the client and the origin server, flow
1220   control signals are not explicitly forwarded by the intermediaries.
1221   (However, throttling of data transfer by any recipient may have the
1222   effect of indirectly propagating flow control information upstream
1223   back to the original sender.)  Flow control only applies to the data
1224   portion of data frames.  Recipients must buffer all control frames.
1225   If a recipient fails to buffer an entire control frame, it MUST issue
1226   a stream error (Section 2.4.2) with the status code
1227   FLOW_CONTROL_ERROR for the stream.
1228
1229
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1234
1235
1236   Flow control in SPDY is implemented by a data transfer window kept by
1237   the sender of each stream.  The data transfer window is a simple
1238   uint32 that indicates how many bytes of data the sender can transmit.
1239   After a stream is created, but before any data frames have been
1240   transmitted, the sender begins with the initial window size.  This
1241   window size is a measure of the buffering capability of the
1242   recipient.  The sender must not send a data frame with data length
1243   greater than the transfer window size.  After sending each data
1244   frame, the sender decrements its transfer window size by the amount
1245   of data transmitted.  When the window size becomes less than or equal
1246   to 0, the sender must pause transmitting data frames.  At the other
1247   end of the stream, the recipient sends a WINDOW_UPDATE control back
1248   to notify the sender that it has consumed some data and freed up
1249   buffer space to receive more data.
1250
1251   +----------------------------------+
1252   |1|   version    |         9       |
1253   +----------------------------------+
1254   | 0 (flags) |     8 (length)       |
1255   +----------------------------------+
1256   |X|     Stream-ID (31-bits)        |
1257   +----------------------------------+
1258   |X|  Delta-Window-Size (31-bits)   |
1259   +----------------------------------+
1260
1261   Control bit: The control bit is always 1 for this message.
1262
1263   Version: The SPDY version number.
1264
1265   Type: The message type for a WINDOW_UPDATE message is 9.
1266
1267   Length: The length field is always 8 for this frame (there are 8
1268   bytes after the length field).
1269
1270   Stream-ID: The stream ID that this WINDOW_UPDATE control frame is
1271   for.
1272
1273   Delta-Window-Size: The additional number of bytes that the sender can
1274   transmit in addition to existing remaining window size.  The legal
1275   range for this field is 1 to 2^31 - 1 (0x7fffffff) bytes.
1276
1277   The window size as kept by the sender must never exceed 2^31
1278   (although it can become negative in one special case).  If a sender
1279   receives a WINDOW_UPDATE that causes the its window size to exceed
1280   this limit, it must send RST_STREAM with status code
1281   FLOW_CONTROL_ERROR to terminate the stream.
1282
1283   When a SPDY connection is first established, the default initial
1284
1285
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1290
1291
1292   window size for all streams is 64KB.  An endpoint can use the
1293   SETTINGS control frame to adjust the initial window size for the
1294   connection.  That is, its peer can start out using the 64KB default
1295   initial window size when sending data frames before receiving the
1296   SETTINGS.  Because SETTINGS is asynchronous, there may be a race
1297   condition if the recipient wants to decrease the initial window size,
1298   but its peer immediately sends 64KB on the creation of a new
1299   connection, before waiting for the SETTINGS to arrive.  This is one
1300   case where the window size kept by the sender will become negative.
1301   Once the sender detects this condition, it must stop sending data
1302   frames and wait for the recipient to catch up.  The recipient has two
1303   choices:
1304
1305      immediately send RST_STREAM with FLOW_CONTROL_ERROR status code.
1306
1307      allow the head of line blocking (as there is only one stream for
1308      the session and the amount of data in flight is bounded by the
1309      default initial window size), and send WINDOW_UPDATE as it
1310      consumes data.
1311
1312   In the case of option 2, both sides must compute the window size
1313   based on the initial window size in the SETTINGS.  For example, if
1314   the recipient sets the initial window size to be 16KB, and the sender
1315   sends 64KB immediately on connection establishment, the sender will
1316   discover its window size is -48KB on receipt of the SETTINGS.  As the
1317   recipient consumes the first 16KB, it must send a WINDOW_UPDATE of
1318   16KB back to the sender.  This interaction continues until the
1319   sender's window size becomes positive again, and it can resume
1320   transmitting data frames.
1321
1322   After the recipient reads in a data frame with FLAG_FIN that marks
1323   the end of the data stream, it should not send WINDOW_UPDATE frames
1324   as it consumes the last data frame.  A sender should ignore all the
1325   WINDOW_UPDATE frames associated with the stream after it send the
1326   last frame for the stream.
1327
1328   The data frames from the sender and the WINDOW_UPDATE frames from the
1329   recipient are completely asynchronous with respect to each other.
1330   This property allows a recipient to aggressively update the window
1331   size kept by the sender to prevent the stream from stalling.
1332
13332.6.9.  CREDENTIAL
1334
1335   The CREDENTIAL control frame is used by the client to send additional
1336   client certificates to the server.  A SPDY client may decide to send
1337   requests for resources from different origins on the same SPDY
1338   session if it decides that that server handles both origins.  For
1339   example if the IP address associated with both hostnames matches and
1340
1341
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1346
1347
1348   the SSL server certificate presented in the initial handshake is
1349   valid for both hostnames.  However, because the SSL connection can
1350   contain at most one client certificate, the client needs a mechanism
1351   to send additional client certificates to the server.
1352
1353   The server is required to maintain a vector of client certificates
1354   associated with a SPDY session.  When the client needs to send a
1355   client certificate to the server, it will send a CREDENTIAL frame
1356   that specifies the index of the slot in which to store the
1357   certificate as well as proof that the client posesses the
1358   corresponding private key.  The initial size of this vector must be
1359   8.  If the client provides a client certificate during the first TLS
1360   handshake, the contents of this certificate must be copied into the
1361   first slot (index 1) in the CREDENTIAL vector, though it may be
1362   overwritten by subsequent CREDENTIAL frames.  The server must
1363   exclusively use the CREDNETIAL vector when evaluating the client
1364   certificates associated with an origin.  The server may change the
1365   size of this vector by sending a SETTINGS frame with the setting
1366   SETTINGS_CLIENT_CERTIFICATE_VECTOR_SIZE value specified.  In the
1367   event that the new size is smaller than the current size, truncation
1368   occurs preserving lower-index slots as possible.
1369
1370   TLS renegotiation with client authentication is incompatible with
1371   SPDY given the multiplexed nature of SPDY.  Specifically, imagine
1372   that the client has 2 requests outstanding to the server for two
1373   different pages (in different tabs).  When the renegotiation + client
1374   certificate request comes in, the browser is unable to determine
1375   which resource triggered the client certificate request, in order to
1376   prompt the user accordingly.
1377
1378   +----------------------------------+
1379   |1|000000000000001|0000000000001011|
1380   +----------------------------------+
1381   | flags (8)  |  Length (24 bits)   |
1382   +----------------------------------+
1383   |  Slot (16 bits) |                |
1384   +-----------------+                |
1385   |      Proof Length (32 bits)      |
1386   +----------------------------------+
1387   |               Proof              |
1388   +----------------------------------+ <+
1389   |   Certificate Length (32 bits)   |  |
1390   +----------------------------------+  | Repeated until end of frame
1391   |            Certificate           |  |
1392   +----------------------------------+ <+
1393
1394   Slot: The index in the server's client certificate vector where this
1395   certificate should be stored.  If there is already a certificate
1396
1397
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1403
1404   stored at this index, it will be overwritten.  The index is one
1405   based, not zero based; zero is an invalid slot index.
1406
1407   Proof: Cryptographic proof that the client has possession of the
1408   private key associated with the certificate.  The format is a TLS
1409   digitally-signed element ([RFC5246], Section 4.7).  The signature
1410   algorithm must be the same as that used in the CertificateVerify
1411   message.  However, since the MD5+SHA1 signature type used in TLS 1.0
1412   connections can not be correctly encoded in a digitally-signed
1413   element, SHA1 must be used when MD5+SHA1 was used in the SSL
1414   connection.  The signature is calculated over a 32 byte TLS extractor
1415   value (http://tools.ietf.org/html/rfc5705) with a label of "EXPORTER
1416   SPDY certificate proof" using the empty string as context.  ForRSA
1417   certificates the signature would be a PKCS#1 v1.5 signature.  For
1418   ECDSA, it would be an ECDSA-Sig-Value
1419   (http://tools.ietf.org/html/rfc5480#appendix-A).  For a 1024-bit RSA
1420   key, the CREDENTIAL message would be ~500 bytes.
1421
1422   Certificate: The certificate chain, starting with the leaf
1423   certificate.  Each certificate must be encoded as a 32 bit length,
1424   followed by a DER encoded certificate.  The certificate must be of
1425   the same type (RSA, ECDSA, etc) as the client certificate associated
1426   with the SSL connection.
1427
1428   If the server receives a request for a resource with unacceptable
1429   credential (either missing or invalid), it must reply with a
1430   RST_STREAM frame with the status code INVALID_CREDENTIALS.  Upon
1431   receipt of a RST_STREAM frame with INVALID_CREDENTIALS, the client
1432   should initiate a new stream directly to the requested origin and
1433   resend the request.  Note, SPDY does not allow the server to request
1434   different client authentication for different resources in the same
1435   origin.
1436
1437   If the server receives an invalid CREDENTIAL frame, it MUST respond
1438   with a GOAWAY frame and shutdown the session.
1439
14402.6.10.  Name/Value Header Block
1441
1442   The Name/Value Header Block is found in the SYN_STREAM, SYN_REPLY and
1443   HEADERS control frames, and shares a common format:
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
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1458
1459
1460   +------------------------------------+
1461   | Number of Name/Value pairs (int32) |
1462   +------------------------------------+
1463   |     Length of name (int32)         |
1464   +------------------------------------+
1465   |           Name (string)            |
1466   +------------------------------------+
1467   |     Length of value  (int32)       |
1468   +------------------------------------+
1469   |          Value   (string)          |
1470   +------------------------------------+
1471   |           (repeats)                |
1472
1473   Number of Name/Value pairs: The number of repeating name/value pairs
1474   following this field.
1475
1476   List of Name/Value pairs:
1477
1478      Length of Name: a 32-bit value containing the number of octets in
1479      the name field.  Note that in practice, this length must not
1480      exceed 2^24, as that is the maximum size of a SPDY frame.
1481
1482      Name: 0 or more octets, 8-bit sequences of data, excluding 0.
1483
1484      Length of Value: a 32-bit value containing the number of octets in
1485      the value field.  Note that in practice, this length must not
1486      exceed 2^24, as that is the maximum size of a SPDY frame.
1487
1488      Value: 0 or more octets, 8-bit sequences of data, excluding 0.
1489
1490   Each header name must have at least one value.  Header names are
1491   encoded using the US-ASCII character set [ASCII] and must be all
1492   lower case.  The length of each name must be greater than zero.  A
1493   recipient of a zero-length name MUST issue a stream error
1494   (Section 2.4.2) with the status code PROTOCOL_ERROR for the
1495   stream-id.
1496
1497   Duplicate header names are not allowed.  To send two identically
1498   named headers, send a header with two values, where the values are
1499   separated by a single NUL (0) byte.  A header value can either be
1500   empty (e.g. the length is zero) or it can contain multiple, NUL-
1501   separated values, each with length greater than zero.  The value
1502   never starts nor ends with a NUL character.  Recipients of illegal
1503   value fields MUST issue a stream error (Section 2.4.2) with the
1504   status code PROTOCOL_ERROR for the stream-id.
1505
1506
1507
1508
1509
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1514
1515
15162.6.10.1.  Compression
1517
1518   The Name/Value Header Block is a section of the SYN_STREAM,
1519   SYN_REPLY, and HEADERS frames used to carry header meta-data.  This
1520   block is always compressed using zlib compression.  Within this
1521   specification, any reference to 'zlib' is referring to the ZLIB
1522   Compressed Data Format Specification Version 3.3 as part of RFC1950.
1523   [RFC1950]
1524
1525   For each HEADERS compression instance, the initial state is
1526   initialized using the following dictionary [UDELCOMPRESSION]:
1527
1528   <CODE BEGINS>
1529
1530   const unsigned char SPDY_dictionary_txt[] = {
1531     0x00, 0x00, 0x00, 0x07, 0x6f, 0x70, 0x74, 0x69,  \\ - - - - o p t i
1532     0x6f, 0x6e, 0x73, 0x00, 0x00, 0x00, 0x04, 0x68,  \\ o n s - - - - h
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1564
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1571
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1620
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1627
1628     0x61, 0x6e, 0x73, 0x66, 0x65, 0x72, 0x2d, 0x65,  \\ a n s f e r - e
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1650     0x65, 0x00, 0x00, 0x00, 0x0a, 0x6b, 0x65, 0x65,  \\ e - - - - k e e
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1653     0x6e, 0x31, 0x30, 0x30, 0x31, 0x30, 0x31, 0x32,  \\ n 1 0 0 1 0 1 2
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1664     0x35, 0x30, 0x35, 0x32, 0x30, 0x33, 0x20, 0x4e,  \\ 5 0 5 2 0 3 - N
1665     0x6f, 0x6e, 0x2d, 0x41, 0x75, 0x74, 0x68, 0x6f,  \\ o n - A u t h o
1666     0x72, 0x69, 0x74, 0x61, 0x74, 0x69, 0x76, 0x65,  \\ r i t a t i v e
1667     0x20, 0x49, 0x6e, 0x66, 0x6f, 0x72, 0x6d, 0x61,  \\ - I n f o r m a
1668     0x74, 0x69, 0x6f, 0x6e, 0x32, 0x30, 0x34, 0x20,  \\ t i o n 2 0 4 -
1669     0x4e, 0x6f, 0x20, 0x43, 0x6f, 0x6e, 0x74, 0x65,  \\ N o - C o n t e
1670     0x6e, 0x74, 0x33, 0x30, 0x31, 0x20, 0x4d, 0x6f,  \\ n t 3 0 1 - M o
1671     0x76, 0x65, 0x64, 0x20, 0x50, 0x65, 0x72, 0x6d,  \\ v e d - P e r m
1672     0x61, 0x6e, 0x65, 0x6e, 0x74, 0x6c, 0x79, 0x34,  \\ a n e n t l y 4
1673     0x30, 0x30, 0x20, 0x42, 0x61, 0x64, 0x20, 0x52,  \\ 0 0 - B a d - R
1674     0x65, 0x71, 0x75, 0x65, 0x73, 0x74, 0x34, 0x30,  \\ e q u e s t 4 0
1675     0x31, 0x20, 0x55, 0x6e, 0x61, 0x75, 0x74, 0x68,  \\ 1 - U n a u t h
1676
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1683
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1686     0x64, 0x65, 0x6e, 0x34, 0x30, 0x34, 0x20, 0x4e,  \\ d e n 4 0 4 - N
1687     0x6f, 0x74, 0x20, 0x46, 0x6f, 0x75, 0x6e, 0x64,  \\ o t - F o u n d
1688     0x35, 0x30, 0x30, 0x20, 0x49, 0x6e, 0x74, 0x65,  \\ 5 0 0 - I n t e
1689     0x72, 0x6e, 0x61, 0x6c, 0x20, 0x53, 0x65, 0x72,  \\ r n a l - S e r
1690     0x76, 0x65, 0x72, 0x20, 0x45, 0x72, 0x72, 0x6f,  \\ v e r - E r r o
1691     0x72, 0x35, 0x30, 0x31, 0x20, 0x4e, 0x6f, 0x74,  \\ r 5 0 1 - N o t
1692     0x20, 0x49, 0x6d, 0x70, 0x6c, 0x65, 0x6d, 0x65,  \\ - I m p l e m e
1693     0x6e, 0x74, 0x65, 0x64, 0x35, 0x30, 0x33, 0x20,  \\ n t e d 5 0 3 -
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1695     0x55, 0x6e, 0x61, 0x76, 0x61, 0x69, 0x6c, 0x61,  \\ U n a v a i l a
1696     0x62, 0x6c, 0x65, 0x4a, 0x61, 0x6e, 0x20, 0x46,  \\ b l e J a n - F
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1698     0x70, 0x72, 0x20, 0x4d, 0x61, 0x79, 0x20, 0x4a,  \\ p r - M a y - J
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1701     0x4f, 0x63, 0x74, 0x20, 0x4e, 0x6f, 0x76, 0x20,  \\ O c t - N o v -
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1703     0x30, 0x3a, 0x30, 0x30, 0x20, 0x4d, 0x6f, 0x6e,  \\ 0 - 0 0 - M o n
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1706     0x20, 0x46, 0x72, 0x69, 0x2c, 0x20, 0x53, 0x61,  \\ - F r i - - S a
1707     0x74, 0x2c, 0x20, 0x53, 0x75, 0x6e, 0x2c, 0x20,  \\ t - - S u n - -
1708     0x47, 0x4d, 0x54, 0x63, 0x68, 0x75, 0x6e, 0x6b,  \\ G M T c h u n k
1709     0x65, 0x64, 0x2c, 0x74, 0x65, 0x78, 0x74, 0x2f,  \\ e d - t e x t -
1710     0x68, 0x74, 0x6d, 0x6c, 0x2c, 0x69, 0x6d, 0x61,  \\ h t m l - i m a
1711     0x67, 0x65, 0x2f, 0x70, 0x6e, 0x67, 0x2c, 0x69,  \\ g e - p n g - i
1712     0x6d, 0x61, 0x67, 0x65, 0x2f, 0x6a, 0x70, 0x67,  \\ m a g e - j p g
1713     0x2c, 0x69, 0x6d, 0x61, 0x67, 0x65, 0x2f, 0x67,  \\ - i m a g e - g
1714     0x69, 0x66, 0x2c, 0x61, 0x70, 0x70, 0x6c, 0x69,  \\ i f - a p p l i
1715     0x63, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x2f, 0x78,  \\ c a t i o n - x
1716     0x6d, 0x6c, 0x2c, 0x61, 0x70, 0x70, 0x6c, 0x69,  \\ m l - a p p l i
1717     0x63, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x2f, 0x78,  \\ c a t i o n - x
1718     0x68, 0x74, 0x6d, 0x6c, 0x2b, 0x78, 0x6d, 0x6c,  \\ h t m l - x m l
1719     0x2c, 0x74, 0x65, 0x78, 0x74, 0x2f, 0x70, 0x6c,  \\ - t e x t - p l
1720     0x61, 0x69, 0x6e, 0x2c, 0x74, 0x65, 0x78, 0x74,  \\ a i n - t e x t
1721     0x2f, 0x6a, 0x61, 0x76, 0x61, 0x73, 0x63, 0x72,  \\ - j a v a s c r
1722     0x69, 0x70, 0x74, 0x2c, 0x70, 0x75, 0x62, 0x6c,  \\ i p t - p u b l
1723     0x69, 0x63, 0x70, 0x72, 0x69, 0x76, 0x61, 0x74,  \\ i c p r i v a t
1724     0x65, 0x6d, 0x61, 0x78, 0x2d, 0x61, 0x67, 0x65,  \\ e m a x - a g e
1725     0x3d, 0x67, 0x7a, 0x69, 0x70, 0x2c, 0x64, 0x65,  \\ - g z i p - d e
1726     0x66, 0x6c, 0x61, 0x74, 0x65, 0x2c, 0x73, 0x64,  \\ f l a t e - s d
1727     0x63, 0x68, 0x63, 0x68, 0x61, 0x72, 0x73, 0x65,  \\ c h c h a r s e
1728     0x74, 0x3d, 0x75, 0x74, 0x66, 0x2d, 0x38, 0x63,  \\ t - u t f - 8 c
1729     0x68, 0x61, 0x72, 0x73, 0x65, 0x74, 0x3d, 0x69,  \\ h a r s e t - i
1730     0x73, 0x6f, 0x2d, 0x38, 0x38, 0x35, 0x39, 0x2d,  \\ s o - 8 8 5 9 -
1731     0x31, 0x2c, 0x75, 0x74, 0x66, 0x2d, 0x2c, 0x2a,  \\ 1 - u t f - - -
1732
1733
1734
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1738
1739
1740     0x2c, 0x65, 0x6e, 0x71, 0x3d, 0x30, 0x2e         \\ - e n q - 0 -
1741   };
1742
1743   <CODE ENDS>
1744
1745   The entire contents of the name/value header block is compressed
1746   using zlib.  There is a single zlib stream for all name value pairs
1747   in one direction on a connection.  SPDY uses a SYNC_FLUSH between
1748   each compressed frame.
1749
1750   Implementation notes: the compression engine can be tuned to favor
1751   speed or size.  Optimizing for size increases memory use and CPU
1752   consumption.  Because header blocks are generally small, implementors
1753   may want to reduce the window-size of the compression engine from the
1754   default 15bits (a 32KB window) to more like 11bits (a 2KB window).
1755   The exact setting is chosen by the compressor, the decompressor will
1756   work with any setting.
1757
17583.  HTTP Layering over SPDY
1759
1760   SPDY is intended to be as compatible as possible with current web-
1761   based applications.  This means that, from the perspective of the
1762   server business logic or application API, the features of HTTP are
1763   unchanged.  To achieve this, all of the application request and
1764   response header semantics are preserved, although the syntax of
1765   conveying those semantics has changed.  Thus, the rules from the
1766   HTTP/1.1 specification in RFC2616 [RFC2616] apply with the changes in
1767   the sections below.
1768
17693.1.  Connection Management
1770
1771   Clients SHOULD NOT open more than one SPDY session to a given origin
1772   [RFC6454] concurrently.
1773
1774   Note that it is possible for one SPDY session to be finishing (e.g. a
1775   GOAWAY message has been sent, but not all streams have finished),
1776   while another SPDY session is starting.
1777
17783.1.1.  Use of GOAWAY
1779
1780   SPDY provides a GOAWAY message which can be used when closing a
1781   connection from either the client or server.  Without a server GOAWAY
1782   message, HTTP has a race condition where the client sends a request
1783   (a new SYN_STREAM) just as the server is closing the connection, and
1784   the client cannot know if the server received the stream or not.  By
1785   using the last-stream-id in the GOAWAY, servers can indicate to the
1786   client if a request was processed or not.
1787
1788
1789
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1794
1795
1796   Note that some servers will choose to send the GOAWAY and immediately
1797   terminate the connection without waiting for active streams to
1798   finish.  The client will be able to determine this because SPDY
1799   streams are determinstically closed.  This abrupt termination will
1800   force the client to heuristically decide whether to retry the pending
1801   requests.  Clients always need to be capable of dealing with this
1802   case because they must deal with accidental connection termination
1803   cases, which are the same as the server never having sent a GOAWAY.
1804
1805   More sophisticated servers will use GOAWAY to implement a graceful
1806   teardown.  They will send the GOAWAY and provide some time for the
1807   active streams to finish before terminating the connection.
1808
1809   If a SPDY client closes the connection, it should also send a GOAWAY
1810   message.  This allows the server to know if any server-push streams
1811   were received by the client.
1812
1813   If the endpoint closing the connection has not received any
1814   SYN_STREAMs from the remote, the GOAWAY will contain a last-stream-id
1815   of 0.
1816
18173.2.  HTTP Request/Response
1818
18193.2.1.  Request
1820
1821   The client initiates a request by sending a SYN_STREAM frame.  For
1822   requests which do not contain a body, the SYN_STREAM frame MUST set
1823   the FLAG_FIN, indicating that the client intends to send no further
1824   data on this stream.  For requests which do contain a body, the
1825   SYN_STREAM will not contain the FLAG_FIN, and the body will follow
1826   the SYN_STREAM in a series of DATA frames.  The last DATA frame will
1827   set the FLAG_FIN to indicate the end of the body.
1828
1829   The SYN_STREAM Name/Value section will contain all of the HTTP
1830   headers which are associated with an HTTP request.  The header block
1831   in SPDY is mostly unchanged from today's HTTP header block, with the
1832   following differences:
1833
1834      The first line of the request is unfolded into name/value pairs
1835      like other HTTP headers and MUST be present:
1836
1837         ":method" - the HTTP method for this request (e.g.  "GET",
1838         "POST", "HEAD", etc)
1839
1840         ":path" - the url-path for this url with "/" prefixed.  (See
1841         RFC1738 [RFC1738]).  For example, for
1842         "http://www.google.com/search?q=dogs" the path would be
1843         "/search?q=dogs".
1844
1845
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1850
1851
1852         ":version" - the HTTP version of this request (e.g.
1853         "HTTP/1.1")
1854
1855      In addition, the following two name/value pairs must also be
1856      present in every request:
1857
1858         ":host" - the hostport (See RFC1738 [RFC1738]) portion of the
1859         URL for this request (e.g. "www.google.com:1234").  This header
1860         is the same as the HTTP 'Host' header.
1861
1862         ":scheme" - the scheme portion of the URL for this request
1863         (e.g. "https"))
1864
1865      Header names are all lowercase.
1866
1867      The Connection, Host, Keep-Alive, Proxy-Connection, and Transfer-
1868      Encoding headers are not valid and MUST not be sent.
1869
1870      User-agents MUST support gzip compression.  Regardless of the
1871      Accept-Encoding sent by the user-agent, the server may always send
1872      content encoded with gzip or deflate encoding.
1873
1874      If a server receives a request where the sum of the data frame
1875      payload lengths does not equal the size of the Content-Length
1876      header, the server MUST return a 400 (Bad Request) error.
1877
1878      POST-specific changes:
1879
1880         Although POSTs are inherently chunked, POST requests SHOULD
1881         also be accompanied by a Content-Length header.  There are two
1882         reasons for this: First, it assists with upload progress meters
1883         for an improved user experience.  But second, we know from
1884         early versions of SPDY that failure to send a content length
1885         header is incompatible with many existing HTTP server
1886         implementations.  Existing user-agents do not omit the Content-
1887         Length header, and server implementations have come to depend
1888         upon this.
1889
1890   The user-agent is free to prioritize requests as it sees fit.  If the
1891   user-agent cannot make progress without receiving a resource, it
1892   should attempt to raise the priority of that resource.  Resources
1893   such as images, SHOULD generally use the lowest priority.
1894
1895   If a client sends a SYN_STREAM without all of the method, host, path,
1896   scheme, and version headers, the server MUST reply with a HTTP 400
1897   Bad Request reply.
1898
1899
1900
1901
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1906
1907
19083.2.2.  Response
1909
1910   The server responds to a client request with a SYN_REPLY frame.
1911   Symmetric to the client's upload stream, server will send data after
1912   the SYN_REPLY frame via a series of DATA frames, and the last data
1913   frame will contain the FLAG_FIN to indicate successful end-of-stream.
1914   If a response (like a 202 or 204 response) contains no body, the
1915   SYN_REPLY frame may contain the FLAG_FIN flag to indicate no further
1916   data will be sent on the stream.
1917
1918      The response status line is unfolded into name/value pairs like
1919      other HTTP headers and must be present:
1920
1921         ":status" - The HTTP response status code (e.g. "200" or "200
1922         OK")
1923
1924         ":version" - The HTTP response version (e.g.  "HTTP/1.1")
1925
1926      All header names must be lowercase.
1927
1928      The Connection, Keep-Alive, Proxy-Connection, and Transfer-
1929      Encoding headers are not valid and MUST not be sent.
1930
1931      Responses MAY be accompanied by a Content-Length header for
1932      advisory purposes. (e.g. for UI progress meters)
1933
1934      If a client receives a response where the sum of the data frame
1935      payload lengths does not equal the size of the Content-Length
1936      header, the client MUST ignore the content length header.
1937
1938   If a client receives a SYN_REPLY without a status or without a
1939   version header, the client must reply with a RST_STREAM frame
1940   indicating a PROTOCOL ERROR.
1941
19423.2.3.  Authentication
1943
1944   When a client sends a request to an origin server that requires
1945   authentication, the server can reply with a "401 Unauthorized"
1946   response, and include a WWW-Authenticate challenge header that
1947   defines the authentication scheme to be used.  The client then
1948   retries the request with an Authorization header appropriate to the
1949   specified authentication scheme.
1950
1951   There are four options for proxy authentication, Basic, Digest, NTLM
1952   and Negotiate (SPNEGO).  The first two options were defined in
1953   RFC2617 [RFC2617], and are stateless.  The second two options were
1954   developed by Microsoft and specified in RFC4559 [RFC4559], and are
1955   stateful; otherwise known as multi-round authentication, or
1956
1957
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1962
1963
1964   connection authentication.
1965
19663.2.3.1.  Stateless Authentication
1967
1968   Stateless Authentication over SPDY is identical to how it is
1969   performed over HTTP.  If multiple SPDY streams are concurrently sent
1970   to a single server, each will authenticate independently, similar to
1971   how two HTTP connections would independently authenticate to a proxy
1972   server.
1973
19743.2.3.2.  Stateful Authentication
1975
1976   Unfortunately, the stateful authentication mechanisms were
1977   implemented and defined in a such a way that directly violates
1978   RFC2617 - they do not include a "realm" as part of the request.  This
1979   is problematic in SPDY because it makes it impossible for a client to
1980   disambiguate two concurrent server authentication challenges.
1981
1982   To deal with this case, SPDY servers using Stateful Authentication
1983   MUST implement one of two changes:
1984
1985      Servers can add a "realm=<desired realm>" header so that the two
1986      authentication requests can be disambiguated and run concurrently.
1987      Unfortunately, given how these mechanisms work, this is probably
1988      not practical.
1989
1990      Upon sending the first stateful challenge response, the server
1991      MUST buffer and defer all further frames which are not part of
1992      completing the challenge until the challenge has completed.
1993      Completing the authentication challenge may take multiple round
1994      trips.  Once the client receives a "401 Authenticate" response for
1995      a stateful authentication type, it MUST stop sending new requests
1996      to the server until the authentication has completed by receiving
1997      a non-401 response on at least one stream.
1998
19993.3.  Server Push Transactions
2000
2001   SPDY enables a server to send multiple replies to a client for a
2002   single request.  The rationale for this feature is that sometimes a
2003   server knows that it will need to send multiple resources in response
2004   to a single request.  Without server push features, the client must
2005   first download the primary resource, then discover the secondary
2006   resource(s), and request them.  Pushing of resources avoids the
2007   round-trip delay, but also creates a potential race where a server
2008   can be pushing content which a user-agent is in the process of
2009   requesting.  The following mechanics attempt to prevent the race
2010   condition while enabling the performance benefit.
2011
2012
2013
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2018
2019
2020   Browsers receiving a pushed response MUST validate that the server is
2021   authorized to push the URL using the browser same-origin [RFC6454]
2022   policy.  For example, a SPDY connection to www.foo.com is generally
2023   not permitted to push a response for www.evil.com.
2024
2025   If the browser accepts a pushed response (e.g. it does not send a
2026   RST_STREAM), the browser MUST attempt to cache the pushed response in
2027   same way that it would cache any other response.  This means
2028   validating the response headers and inserting into the disk cache.
2029
2030   Because pushed responses have no request, they have no request
2031   headers associated with them.  At the framing layer, SPDY pushed
2032   streams contain an "associated-stream-id" which indicates the
2033   requested stream for which the pushed stream is related.  The pushed
2034   stream inherits all of the headers from the associated-stream-id with
2035   the exception of ":host", ":scheme", and ":path", which are provided
2036   as part of the pushed response stream headers.  The browser MUST
2037   store these inherited and implied request headers with the cached
2038   resource.
2039
2040   Implementation note: With server push, it is theoretically possible
2041   for servers to push unreasonable amounts of content or resources to
2042   the user-agent.  Browsers MUST implement throttles to protect against
2043   unreasonable push attacks.
2044
20453.3.1.  Server implementation
2046
2047   When the server intends to push a resource to the user-agent, it
2048   opens a new stream by sending a unidirectional SYN_STREAM.  The
2049   SYN_STREAM MUST include an Associated-To-Stream-ID, and MUST set the
2050   FLAG_UNIDIRECTIONAL flag.  The SYN_STREAM MUST include headers for
2051   ":scheme", ":host", ":path", which represent the URL for the resource
2052   being pushed.  Subsequent headers may follow in HEADERS frames.  The
2053   purpose of the association is so that the user-agent can
2054   differentiate which request induced the pushed stream; without it, if
2055   the user-agent had two tabs open to the same page, each pushing
2056   unique content under a fixed URL, the user-agent would not be able to
2057   differentiate the requests.
2058
2059   The Associated-To-Stream-ID must be the ID of an existing, open
2060   stream.  The reason for this restriction is to have a clear endpoint
2061   for pushed content.  If the user-agent requested a resource on stream
2062   11, the server replies on stream 11.  It can push any number of
2063   additional streams to the client before sending a FLAG_FIN on stream
2064   11.  However, once the originating stream is closed no further push
2065   streams may be associated with it.  The pushed streams do not need to
2066   be closed (FIN set) before the originating stream is closed, they
2067   only need to be created before the originating stream closes.
2068
2069
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2075
2076   It is illegal for a server to push a resource with the Associated-To-
2077   Stream-ID of 0.
2078
2079   To minimize race conditions with the client, the SYN_STREAM for the
2080   pushed resources MUST be sent prior to sending any content which
2081   could allow the client to discover the pushed resource and request
2082   it.
2083
2084   The server MUST only push resources which would have been returned
2085   from a GET request.
2086
2087   Note: If the server does not have all of the Name/Value Response
2088   headers available at the time it issues the HEADERS frame for the
2089   pushed resource, it may later use an additional HEADERS frame to
2090   augment the name/value pairs to be associated with the pushed stream.
2091   The subsequent HEADERS frame(s) must not contain a header for
2092   ':host', ':scheme', or ':path' (e.g. the server can't change the
2093   identity of the resource to be pushed).  The HEADERS frame must not
2094   contain duplicate headers with a previously sent HEADERS frame.  The
2095   server must send a HEADERS frame including the scheme/host/port
2096   headers before sending any data frames on the stream.
2097
20983.3.2.  Client implementation
2099
2100   When fetching a resource the client has 3 possibilities:
2101
2102      the resource is not being pushed
2103
2104      the resource is being pushed, but the data has not yet arrived
2105
2106      the resource is being pushed, and the data has started to arrive
2107
2108   When a SYN_STREAM and HEADERS frame which contains an Associated-To-
2109   Stream-ID is received, the client must not issue GET requests for the
2110   resource in the pushed stream, and instead wait for the pushed stream
2111   to arrive.
2112
2113   If a client receives a server push stream with stream-id 0, it MUST
2114   issue a session error (Section 2.4.1) with the status code
2115   PROTOCOL_ERROR.
2116
2117   When a client receives a SYN_STREAM from the server without a the
2118   ':host', ':scheme', and ':path' headers in the Name/Value section, it
2119   MUST reply with a RST_STREAM with error code HTTP_PROTOCOL_ERROR.
2120
2121   To cancel individual server push streams, the client can issue a
2122   stream error (Section 2.4.2) with error code CANCEL.  Upon receipt,
2123   the server MUST stop sending on this stream immediately (this is an
2124
2125
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2131
2132   Abrupt termination).
2133
2134   To cancel all server push streams related to a request, the client
2135   may issue a stream error (Section 2.4.2) with error code CANCEL on
2136   the associated-stream-id.  By cancelling that stream, the server MUST
2137   immediately stop sending frames for any streams with
2138   in-association-to for the original stream.
2139
2140   If the server sends a HEADER frame containing duplicate headers with
2141   a previous HEADERS frame for the same stream, the client must issue a
2142   stream error (Section 2.4.2) with error code PROTOCOL ERROR.
2143
2144   If the server sends a HEADERS frame after sending a data frame for
2145   the same stream, the client MAY ignore the HEADERS frame.  Ignoring
2146   the HEADERS frame after a data frame prevents handling of HTTP's
2147   trailing headers
2148   (http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.40).
2149
21504.  Design Rationale and Notes
2151
2152   Authors' notes: The notes in this section have no bearing on the SPDY
2153   protocol as specified within this document, and none of these notes
2154   should be considered authoritative about how the protocol works.
2155   However, these notes may prove useful in future debates about how to
2156   resolve protocol ambiguities or how to evolve the protocol going
2157   forward.  They may be removed before the final draft.
2158
21594.1.  Separation of Framing Layer and Application Layer
2160
2161   Readers may note that this specification sometimes blends the framing
2162   layer (Section 2) with requirements of a specific application - HTTP
2163   (Section 3).  This is reflected in the request/response nature of the
2164   streams, the definition of the HEADERS and compression contexts which
2165   are very similar to HTTP, and other areas as well.
2166
2167   This blending is intentional - the primary goal of this protocol is
2168   to create a low-latency protocol for use with HTTP.  Isolating the
2169   two layers is convenient for description of the protocol and how it
2170   relates to existing HTTP implementations.  However, the ability to
2171   reuse the SPDY framing layer is a non goal.
2172
21734.2.  Error handling - Framing Layer
2174
2175   Error handling at the SPDY layer splits errors into two groups: Those
2176   that affect an individual SPDY stream, and those that do not.
2177
2178   When an error is confined to a single stream, but general framing is
2179   in tact, SPDY attempts to use the RST_STREAM as a mechanism to
2180
2181
2182
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2185Internet-Draft                    SPDY                     November 2012
2186
2187
2188   invalidate the stream but move forward without aborting the
2189   connection altogether.
2190
2191   For errors occuring outside of a single stream context, SPDY assumes
2192   the entire session is hosed.  In this case, the endpoint detecting
2193   the error should initiate a connection close.
2194
21954.3.  One Connection Per Domain
2196
2197   SPDY attempts to use fewer connections than other protocols have
2198   traditionally used.  The rationale for this behavior is because it is
2199   very difficult to provide a consistent level of service (e.g.  TCP
2200   slow-start), prioritization, or optimal compression when the client
2201   is connecting to the server through multiple channels.
2202
2203   Through lab measurements, we have seen consistent latency benefits by
2204   using fewer connections from the client.  The overall number of
2205   packets sent by SPDY can be as much as 40% less than HTTP.  Handling
2206   large numbers of concurrent connections on the server also does
2207   become a scalability problem, and SPDY reduces this load.
2208
2209   The use of multiple connections is not without benefit, however.
2210   Because SPDY multiplexes multiple, independent streams onto a single
2211   stream, it creates a potential for head-of-line blocking problems at
2212   the transport level.  In tests so far, the negative effects of head-
2213   of-line blocking (especially in the presence of packet loss) is
2214   outweighed by the benefits of compression and prioritization.
2215
22164.4.  Fixed vs Variable Length Fields
2217
2218   SPDY favors use of fixed length 32bit fields in cases where smaller,
2219   variable length encodings could have been used.  To some, this seems
2220   like a tragic waste of bandwidth.  SPDY choses the simple encoding
2221   for speed and simplicity.
2222
2223   The goal of SPDY is to reduce latency on the network.  The overhead
2224   of SPDY frames is generally quite low.  Each data frame is only an 8
2225   byte overhead for a 1452 byte payload (~0.6%).  At the time of this
2226   writing, bandwidth is already plentiful, and there is a strong trend
2227   indicating that bandwidth will continue to increase.  With an average
2228   worldwide bandwidth of 1Mbps, and assuming that a variable length
2229   encoding could reduce the overhead by 50%, the latency saved by using
2230   a variable length encoding would be less than 100 nanoseconds.  More
2231   interesting are the effects when the larger encodings force a packet
2232   boundary, in which case a round-trip could be induced.  However, by
2233   addressing other aspects of SPDY and TCP interactions, we believe
2234   this is completely mitigated.
2235
2236
2237
2238
2239Belshe, et al.            Expires June 1, 2013                 [Page 40]
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2242
2243
22444.5.  Compression Context(s)
2245
2246   When isolating the compression contexts used for communicating with
2247   multiple origins, we had a few choices to make.  We could have
2248   maintained a map (or list) of compression contexts usable for each
2249   origin.  The basic case is easy - each HEADERS frame would need to
2250   identify the context to use for that frame.  However, compression
2251   contexts are not cheap, so the lifecycle of each context would need
2252   to be bounded.  For proxy servers, where we could churn through many
2253   contexts, this would be a concern.  We considered using a static set
2254   of contexts, say 16 of them, which would bound the memory use.  We
2255   also considered dynamic contexts, which could be created on the fly,
2256   and would need to be subsequently destroyed.  All of these are
2257   complicated, and ultimately we decided that such a mechanism creates
2258   too many problems to solve.
2259
2260   Alternatively, we've chosen the simple approach, which is to simply
2261   provide a flag for resetting the compression context.  For the common
2262   case (no proxy), this fine because most requests are to the same
2263   origin and we never need to reset the context.  For cases where we
2264   are using two different origins over a single SPDY session, we simply
2265   reset the compression state between each transition.
2266
22674.6.  Unidirectional streams
2268
2269   Many readers notice that unidirectional streams are both a bit
2270   confusing in concept and also somewhat redundant.  If the recipient
2271   of a stream doesn't wish to send data on a stream, it could simply
2272   send a SYN_REPLY with the FLAG_FIN bit set.  The FLAG_UNIDIRECTIONAL
2273   is, therefore, not necessary.
2274
2275   It is true that we don't need the UNIDIRECTIONAL markings.  It is
2276   added because it avoids the recipient of pushed streams from needing
2277   to send a set of empty frames (e.g. the SYN_STREAM w/ FLAG_FIN) which
2278   otherwise serve no purpose.
2279
22804.7.  Data Compression
2281
2282   Generic compression of data portion of the streams (as opposed to
2283   compression of the headers) without knowing the content of the stream
2284   is redundant.  There is no value in compressing a stream which is
2285   already compressed.  Because of this, SPDY does allow data
2286   compression to be optional.  We included it because study of existing
2287   websites shows that many sites are not using compression as they
2288   should, and users suffer because of it.  We wanted a mechanism where,
2289   at the SPDY layer, site administrators could simply force compression
2290   - it is better to compress twice than to not compress.
2291
2292
2293
2294
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2297Internet-Draft                    SPDY                     November 2012
2298
2299
2300   Overall, however, with this feature being optional and sometimes
2301   redundant, it is unclear if it is useful at all.  We will likely
2302   remove it from the specification.
2303
23044.8.  Server Push
2305
2306   A subtle but important point is that server push streams must be
2307   declared before the associated stream is closed.  The reason for this
2308   is so that proxies have a lifetime for which they can discard
2309   information about previous streams.  If a pushed stream could
2310   associate itself with an already-closed stream, then endpoints would
2311   not have a specific lifecycle for when they could disavow knowledge
2312   of the streams which went before.
2313
23145.  Security Considerations
2315
23165.1.  Use of Same-origin constraints
2317
2318   This specification uses the same-origin policy [RFC6454] in all cases
2319   where verification of content is required.
2320
23215.2.  HTTP Headers and SPDY Headers
2322
2323   At the application level, HTTP uses name/value pairs in its headers.
2324   Because SPDY merges the existing HTTP headers with SPDY headers,
2325   there is a possibility that some HTTP applications already use a
2326   particular header name.  To avoid any conflicts, all headers
2327   introduced for layering HTTP over SPDY are prefixed with ":". ":" is
2328   not a valid sequence in HTTP header naming, preventing any possible
2329   conflict.
2330
23315.3.  Cross-Protocol Attacks
2332
2333   By utilizing TLS, we believe that SPDY introduces no new cross-
2334   protocol attacks.  TLS encrypts the contents of all transmission
2335   (except the handshake itself), making it difficult for attackers to
2336   control the data which could be used in a cross-protocol attack.
2337
23385.4.  Server Push Implicit Headers
2339
2340   Pushed resources do not have an associated request.  In order for
2341   existing HTTP cache control validations (such as the Vary header) to
2342   work, however, all cached resources must have a set of request
2343   headers.  For this reason, browsers MUST be careful to inherit
2344   request headers from the associated stream for the push.  This
2345   includes the 'Cookie' header.
2346
2347
2348
2349
2350
2351Belshe, et al.            Expires June 1, 2013                 [Page 42]
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2353Internet-Draft                    SPDY                     November 2012
2354
2355
23566.  Privacy Considerations
2357
23586.1.  Long Lived Connections
2359
2360   SPDY aims to keep connections open longer between clients and servers
2361   in order to reduce the latency when a user makes a request.  The
2362   maintenance of these connections over time could be used to expose
2363   private information.  For example, a user using a browser hours after
2364   the previous user stopped using that browser may be able to learn
2365   about what the previous user was doing.  This is a problem with HTTP
2366   in its current form as well, however the short lived connections make
2367   it less of a risk.
2368
23696.2.  SETTINGS frame
2370
2371   The SPDY SETTINGS frame allows servers to store out-of-band
2372   transmitted information about the communication between client and
2373   server on the client.  Although this is intended only to be used to
2374   reduce latency, renegade servers could use it as a mechanism to store
2375   identifying information about the client in future requests.
2376
2377   Clients implementing privacy modes, such as Google Chrome's
2378   "incognito mode", may wish to disable client-persisted SETTINGS
2379   storage.
2380
2381   Clients MUST clear persisted SETTINGS information when clearing the
2382   cookies.
2383
2384   TODO: Put range maximums on each type of setting to limit
2385   inappropriate uses.
2386
23877.  Incompatibilities with SPDY draft #2
2388
2389   Here is a list of the major changes between this draft and draft #2.
2390
2391      Addition of flow control
2392
2393      Increased 16 bit length fields in SYN_STREAM and SYN_REPLY to 32
2394      bits.
2395
2396      Changed definition of compression for DATA frames
2397
2398      Updated compression dictionary
2399
2400      Fixed off-by-one on the compression dictionary for headers
2401
2402      Increased priority field from 2bits to 3bits.
2403
2404
2405
2406
2407Belshe, et al.            Expires June 1, 2013                 [Page 43]
2408
2409Internet-Draft                    SPDY                     November 2012
2410
2411
2412      Removed NOOP frame
2413
2414      Split the request "url" into "scheme", "host", and "path"
2415
2416      Added the requirement that POSTs contain content-length.
2417
2418      Removed wasted 16bits of unused space from the end of the
2419      SYN_REPLY and HEADERS frames.
2420
2421      Fixed bug: Priorities were described backward (0 was lowest
2422      instead of highest).
2423
2424      Fixed bug: Name/Value header counts were duplicated in both the
2425      Name Value header block and also the containing frame.
2426
24278.  Requirements Notation
2428
2429   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
2430   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
2431   document are to be interpreted as described in RFC 2119 [RFC2119].
2432
24339.  Acknowledgements
2434
2435   Many individuals have contributed to the design and evolution of
2436   SPDY: Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham,
2437   Alyssa Wilk, Costin Manolache, William Chan, Vitaliy Lvin, Joe Chan,
2438   Adam Barth, Ryan Hamilton, Gavin Peters, Kent Alstad, Kevin Lindsay,
2439   Paul Amer, Fan Yang, Jonathan Leighton.
2440
244110.  Normative References
2442
2443   [ASCII]            "US-ASCII. Coded Character Set - 7-Bit American
2444                      Standard Code for Information Interchange.
2445                      Standard ANSI X3.4-1986, ANSI, 1986.".
2446
2447   [RFC0793]          Postel, J., "Transmission Control Protocol",
2448                      STD 7, RFC 793, September 1981.
2449
2450   [RFC1738]          Berners-Lee, T., Masinter, L., and M. McCahill,
2451                      "Uniform Resource Locators (URL)", RFC 1738,
2452                      December 1994.
2453
2454   [RFC1950]          Deutsch, L. and J. Gailly, "ZLIB Compressed Data
2455                      Format Specification version 3.3", RFC 1950,
2456                      May 1996.
2457
2458   [RFC2119]          Bradner, S., "Key words for use in RFCs to
2459                      Indicate Requirement Levels", BCP 14, RFC 2119,
2460
2461
2462
2463Belshe, et al.            Expires June 1, 2013                 [Page 44]
2464
2465Internet-Draft                    SPDY                     November 2012
2466
2467
2468                      March 1997.
2469
2470   [RFC2285]          Mandeville, R., "Benchmarking Terminology for LAN
2471                      Switching Devices", RFC 2285, February 1998.
2472
2473   [RFC2616]          Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
2474                      Masinter, L., Leach, P., and T. Berners-Lee,
2475                      "Hypertext Transfer Protocol -- HTTP/1.1",
2476                      RFC 2616, June 1999.
2477
2478   [RFC2617]          Franks, J., Hallam-Baker, P., Hostetler, J.,
2479                      Lawrence, S., Leach, P., Luotonen, A., and L.
2480                      Stewart, "HTTP Authentication: Basic and Digest
2481                      Access Authentication", RFC 2617, June 1999.
2482
2483   [RFC4366]          Blake-Wilson, S., Nystrom, M., Hopwood, D.,
2484                      Mikkelsen, J., and T. Wright, "Transport Layer
2485                      Security (TLS) Extensions", RFC 4366, April 2006.
2486
2487   [RFC4559]          Jaganathan, K., Zhu, L., and J. Brezak, "SPNEGO-
2488                      based Kerberos and NTLM HTTP Authentication in
2489                      Microsoft Windows", RFC 4559, June 2006.
2490
2491   [RFC5246]          Dierks, T. and E. Rescorla, "The Transport Layer
2492                      Security (TLS) Protocol Version 1.2", RFC 5246,
2493                      August 2008.
2494
2495   [RFC6454]          Barth, A., "The Web Origin Concept", RFC 6454,
2496                      December 2011.
2497
2498   [TLSNPN]           Langley, A., "TLS Next Protocol Negotiation",
2499                      draft-agl-tls-nextprotoneg-01 (work in progress),
2500                      August 2010.
2501
2502   [UDELCOMPRESSION]  Yang, F., Amer, P., and J. Leighton, "A
2503                      Methodology to Derive SPDY's Initial Dictionary
2504                      for Zlib Compression", <http://www.eecis.udel.edu/
2505                      ~amer/PEL/poc/pdf/SPDY-Fan.pdf>.
2506
2507Appendix A.  Change Log (to be removed by RFC Editor before publication)
2508
2509A.1.  Since draft-mbelshe-httpbis-spdy-00
2510
2511   Adopted as base for draft-ietf-httpbis-http2.
2512
2513   Updated authors/editors list.
2514
2515   Added status note.
2516
2517
2518
2519Belshe, et al.            Expires June 1, 2013                 [Page 45]
2520
2521Internet-Draft                    SPDY                     November 2012
2522
2523
2524Authors' Addresses
2525
2526   Mike Belshe
2527   Twist
2528
2529   EMail: mbelshe@chromium.org
2530
2531
2532   Roberto Peon
2533   Google, Inc
2534
2535   EMail: fenix@google.com
2536
2537
2538   Martin Thomson (editor)
2539   Microsoft
2540   3210 Porter Drive
2541   Palo Alto  94043
2542   US
2543
2544   EMail: martin.thomson@skype.net
2545
2546
2547   Alexey Melnikov (editor)
2548   Isode Ltd
2549   5 Castle Business Village
2550   36 Station Road
2551   Hampton, Middlesex  TW12 2BX
2552   UK
2553
2554   EMail: Alexey.Melnikov@isode.com
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575Belshe, et al.            Expires June 1, 2013                 [Page 46]
2576
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