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4	HTTPbis Working Group M. Belshe
5	Internet-Draft Twist
6	Expires: 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
18	Abstract
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
29	Editorial 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
49	Status of This Memo
50
51	This Internet-Draft is submitted in full conformance with the
52
53
54
55	Belshe, et al. Expires June 1, 2013 [Page 1]
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57	Internet-Draft SPDY November 2012
58
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
74	Copyright 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
89	Table 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
172	1. 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
212	1.1. 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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227
228	has not been a goal. The framing layer is tailored to the needs of
229	the HTTP protocol and server push.
230
231	1.2. 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
253	2. SPDY Framing Layer
254
255	2.1. 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
270	2.2. 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
295	2.2.1. 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
333
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339
340	2.2.2. 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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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
407	2.3. 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
420	2.3.1. 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
430	2.3.2. 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
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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
470	2.3.2.1. 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
478	2.3.2.2. 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
484	2.3.3. 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
493	2.3.4. 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
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507
508	HEADERS frames may be interleaved with data frames.
509
510	2.3.5. 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
520	2.3.6. 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
532	2.3.7. 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
566	2.4. 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
573	2.4.1. 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
596	2.4.2. 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
614
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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
625	2.5. 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
631	2.6. Control frame types
632
633	2.6.1. 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
670
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673	Internet-Draft SPDY November 2012
674
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
707	2.6.2. 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
726
727	Belshe, et al. Expires June 1, 2013 [Page 13]
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729	Internet-Draft SPDY November 2012
730
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
775	2.6.3. 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
782
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786
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
838
839	Belshe, et al. Expires June 1, 2013 [Page 15]
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841	Internet-Draft SPDY November 2012
842
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
867	2.6.4. 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
894
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897	Internet-Draft SPDY November 2012
898
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
950
951	Belshe, et al. Expires June 1, 2013 [Page 17]
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953	Internet-Draft SPDY November 2012
954
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
1006
1007	Belshe, et al. Expires June 1, 2013 [Page 18]
1008
1009	Internet-Draft SPDY November 2012
1010
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
1028	2.6.5. 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
1062
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1064
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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
1075	2.6.6. 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
1118
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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
1149	2.6.7. 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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1176
1177	Internet-Draft SPDY November 2012
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
1214	2.6.8. 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
1230
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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
1286
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1289	Internet-Draft SPDY November 2012
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
1333	2.6.9. 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
1342
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1345	Internet-Draft SPDY November 2012
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
1398
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1402
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
1440	2.6.10. 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
1454
1455	Belshe, et al. Expires June 1, 2013 [Page 26]
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1457	Internet-Draft SPDY November 2012
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
1510
1511	Belshe, et al. Expires June 1, 2013 [Page 27]
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1514
1515
1516	2.6.10.1. 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
1533	0x65, 0x61, 0x64, 0x00, 0x00, 0x00, 0x04, 0x70, \\ e a d - - - - p
1534	0x6f, 0x73, 0x74, 0x00, 0x00, 0x00, 0x03, 0x70, \\ o s t - - - - p
1535	0x75, 0x74, 0x00, 0x00, 0x00, 0x06, 0x64, 0x65, \\ u t - - - - d e
1536	0x6c, 0x65, 0x74, 0x65, 0x00, 0x00, 0x00, 0x05, \\ l e t e - - - -
1537	0x74, 0x72, 0x61, 0x63, 0x65, 0x00, 0x00, 0x00, \\ t r a c e - - -
1538	0x06, 0x61, 0x63, 0x63, 0x65, 0x70, 0x74, 0x00, \\ - a c c e p t -
1539	0x00, 0x00, 0x0e, 0x61, 0x63, 0x63, 0x65, 0x70, \\ - - - a c c e p
1540	0x74, 0x2d, 0x63, 0x68, 0x61, 0x72, 0x73, 0x65, \\ t - c h a r s e
1541	0x74, 0x00, 0x00, 0x00, 0x0f, 0x61, 0x63, 0x63, \\ t - - - - a c c
1542	0x65, 0x70, 0x74, 0x2d, 0x65, 0x6e, 0x63, 0x6f, \\ e p t - e n c o
1543	0x64, 0x69, 0x6e, 0x67, 0x00, 0x00, 0x00, 0x0f, \\ d i n g - - - -
1544	0x61, 0x63, 0x63, 0x65, 0x70, 0x74, 0x2d, 0x6c, \\ a c c e p t - l
1545	0x61, 0x6e, 0x67, 0x75, 0x61, 0x67, 0x65, 0x00, \\ a n g u a g e -
1546	0x00, 0x00, 0x0d, 0x61, 0x63, 0x63, 0x65, 0x70, \\ - - - a c c e p
1547	0x74, 0x2d, 0x72, 0x61, 0x6e, 0x67, 0x65, 0x73, \\ t - r a n g e s
1548	0x00, 0x00, 0x00, 0x03, 0x61, 0x67, 0x65, 0x00, \\ - - - - a g e -
1549	0x00, 0x00, 0x05, 0x61, 0x6c, 0x6c, 0x6f, 0x77, \\ - - - a l l o w
1550	0x00, 0x00, 0x00, 0x0d, 0x61, 0x75, 0x74, 0x68, \\ - - - - a u t h
1551	0x6f, 0x72, 0x69, 0x7a, 0x61, 0x74, 0x69, 0x6f, \\ o r i z a t i o
1552	0x6e, 0x00, 0x00, 0x00, 0x0d, 0x63, 0x61, 0x63, \\ n - - - - c a c
1553	0x68, 0x65, 0x2d, 0x63, 0x6f, 0x6e, 0x74, 0x72, \\ h e - c o n t r
1554	0x6f, 0x6c, 0x00, 0x00, 0x00, 0x0a, 0x63, 0x6f, \\ o l - - - - c o
1555	0x6e, 0x6e, 0x65, 0x63, 0x74, 0x69, 0x6f, 0x6e, \\ n n e c t i o n
1556	0x00, 0x00, 0x00, 0x0c, 0x63, 0x6f, 0x6e, 0x74, \\ - - - - c o n t
1557	0x65, 0x6e, 0x74, 0x2d, 0x62, 0x61, 0x73, 0x65, \\ e n t - b a s e
1558	0x00, 0x00, 0x00, 0x10, 0x63, 0x6f, 0x6e, 0x74, \\ - - - - c o n t
1559	0x65, 0x6e, 0x74, 0x2d, 0x65, 0x6e, 0x63, 0x6f, \\ e n t - e n c o
1560	0x64, 0x69, 0x6e, 0x67, 0x00, 0x00, 0x00, 0x10, \\ d i n g - - - -
1561	0x63, 0x6f, 0x6e, 0x74, 0x65, 0x6e, 0x74, 0x2d, \\ c o n t e n t -
1562	0x6c, 0x61, 0x6e, 0x67, 0x75, 0x61, 0x67, 0x65, \\ l a n g u a g e
1563	0x00, 0x00, 0x00, 0x0e, 0x63, 0x6f, 0x6e, 0x74, \\ - - - - c o n t
1564
1565
1566
1567	Belshe, et al. Expires June 1, 2013 [Page 28]
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1569	Internet-Draft SPDY November 2012
1570
1571
1572	0x65, 0x6e, 0x74, 0x2d, 0x6c, 0x65, 0x6e, 0x67, \\ e n t - l e n g
1573	0x74, 0x68, 0x00, 0x00, 0x00, 0x10, 0x63, 0x6f, \\ t h - - - - c o
1574	0x6e, 0x74, 0x65, 0x6e, 0x74, 0x2d, 0x6c, 0x6f, \\ n t e n t - l o
1575	0x63, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x00, 0x00, \\ c a t i o n - -
1576	0x00, 0x0b, 0x63, 0x6f, 0x6e, 0x74, 0x65, 0x6e, \\ - - c o n t e n
1577	0x74, 0x2d, 0x6d, 0x64, 0x35, 0x00, 0x00, 0x00, \\ t - m d 5 - - -
1578	0x0d, 0x63, 0x6f, 0x6e, 0x74, 0x65, 0x6e, 0x74, \\ - c o n t e n t
1579	0x2d, 0x72, 0x61, 0x6e, 0x67, 0x65, 0x00, 0x00, \\ - r a n g e - -
1580	0x00, 0x0c, 0x63, 0x6f, 0x6e, 0x74, 0x65, 0x6e, \\ - - c o n t e n
1581	0x74, 0x2d, 0x74, 0x79, 0x70, 0x65, 0x00, 0x00, \\ t - t y p e - -
1582	0x00, 0x04, 0x64, 0x61, 0x74, 0x65, 0x00, 0x00, \\ - - d a t e - -
1583	0x00, 0x04, 0x65, 0x74, 0x61, 0x67, 0x00, 0x00, \\ - - e t a g - -
1584	0x00, 0x06, 0x65, 0x78, 0x70, 0x65, 0x63, 0x74, \\ - - e x p e c t
1585	0x00, 0x00, 0x00, 0x07, 0x65, 0x78, 0x70, 0x69, \\ - - - - e x p i
1586	0x72, 0x65, 0x73, 0x00, 0x00, 0x00, 0x04, 0x66, \\ r e s - - - - f
1587	0x72, 0x6f, 0x6d, 0x00, 0x00, 0x00, 0x04, 0x68, \\ r o m - - - - h
1588	0x6f, 0x73, 0x74, 0x00, 0x00, 0x00, 0x08, 0x69, \\ o s t - - - - i
1589	0x66, 0x2d, 0x6d, 0x61, 0x74, 0x63, 0x68, 0x00, \\ f - m a t c h -
1590	0x00, 0x00, 0x11, 0x69, 0x66, 0x2d, 0x6d, 0x6f, \\ - - - i f - m o
1591	0x64, 0x69, 0x66, 0x69, 0x65, 0x64, 0x2d, 0x73, \\ d i f i e d - s
1592	0x69, 0x6e, 0x63, 0x65, 0x00, 0x00, 0x00, 0x0d, \\ i n c e - - - -
1593	0x69, 0x66, 0x2d, 0x6e, 0x6f, 0x6e, 0x65, 0x2d, \\ i f - n o n e -
1594	0x6d, 0x61, 0x74, 0x63, 0x68, 0x00, 0x00, 0x00, \\ m a t c h - - -
1595	0x08, 0x69, 0x66, 0x2d, 0x72, 0x61, 0x6e, 0x67, \\ - i f - r a n g
1596	0x65, 0x00, 0x00, 0x00, 0x13, 0x69, 0x66, 0x2d, \\ e - - - - i f -
1597	0x75, 0x6e, 0x6d, 0x6f, 0x64, 0x69, 0x66, 0x69, \\ u n m o d i f i
1598	0x65, 0x64, 0x2d, 0x73, 0x69, 0x6e, 0x63, 0x65, \\ e d - s i n c e
1599	0x00, 0x00, 0x00, 0x0d, 0x6c, 0x61, 0x73, 0x74, \\ - - - - l a s t
1600	0x2d, 0x6d, 0x6f, 0x64, 0x69, 0x66, 0x69, 0x65, \\ - m o d i f i e
1601	0x64, 0x00, 0x00, 0x00, 0x08, 0x6c, 0x6f, 0x63, \\ d - - - - l o c
1602	0x61, 0x74, 0x69, 0x6f, 0x6e, 0x00, 0x00, 0x00, \\ a t i o n - - -
1603	0x0c, 0x6d, 0x61, 0x78, 0x2d, 0x66, 0x6f, 0x72, \\ - m a x - f o r
1604	0x77, 0x61, 0x72, 0x64, 0x73, 0x00, 0x00, 0x00, \\ w a r d s - - -
1605	0x06, 0x70, 0x72, 0x61, 0x67, 0x6d, 0x61, 0x00, \\ - p r a g m a -
1606	0x00, 0x00, 0x12, 0x70, 0x72, 0x6f, 0x78, 0x79, \\ - - - p r o x y
1607	0x2d, 0x61, 0x75, 0x74, 0x68, 0x65, 0x6e, 0x74, \\ - a u t h e n t
1608	0x69, 0x63, 0x61, 0x74, 0x65, 0x00, 0x00, 0x00, \\ i c a t e - - -
1609	0x13, 0x70, 0x72, 0x6f, 0x78, 0x79, 0x2d, 0x61, \\ - p r o x y - a
1610	0x75, 0x74, 0x68, 0x6f, 0x72, 0x69, 0x7a, 0x61, \\ u t h o r i z a
1611	0x74, 0x69, 0x6f, 0x6e, 0x00, 0x00, 0x00, 0x05, \\ t i o n - - - -
1612	0x72, 0x61, 0x6e, 0x67, 0x65, 0x00, 0x00, 0x00, \\ r a n g e - - -
1613	0x07, 0x72, 0x65, 0x66, 0x65, 0x72, 0x65, 0x72, \\ - r e f e r e r
1614	0x00, 0x00, 0x00, 0x0b, 0x72, 0x65, 0x74, 0x72, \\ - - - - r e t r
1615	0x79, 0x2d, 0x61, 0x66, 0x74, 0x65, 0x72, 0x00, \\ y - a f t e r -
1616	0x00, 0x00, 0x06, 0x73, 0x65, 0x72, 0x76, 0x65, \\ - - - s e r v e
1617	0x72, 0x00, 0x00, 0x00, 0x02, 0x74, 0x65, 0x00, \\ r - - - - t e -
1618	0x00, 0x00, 0x07, 0x74, 0x72, 0x61, 0x69, 0x6c, \\ - - - t r a i l
1619	0x65, 0x72, 0x00, 0x00, 0x00, 0x11, 0x74, 0x72, \\ e r - - - - t r
1620
1621
1622
1623	Belshe, et al. Expires June 1, 2013 [Page 29]
1624
1625	Internet-Draft SPDY November 2012
1626
1627
1628	0x61, 0x6e, 0x73, 0x66, 0x65, 0x72, 0x2d, 0x65, \\ a n s f e r - e
1629	0x6e, 0x63, 0x6f, 0x64, 0x69, 0x6e, 0x67, 0x00, \\ n c o d i n g -
1630	0x00, 0x00, 0x07, 0x75, 0x70, 0x67, 0x72, 0x61, \\ - - - u p g r a
1631	0x64, 0x65, 0x00, 0x00, 0x00, 0x0a, 0x75, 0x73, \\ d e - - - - u s
1632	0x65, 0x72, 0x2d, 0x61, 0x67, 0x65, 0x6e, 0x74, \\ e r - a g e n t
1633	0x00, 0x00, 0x00, 0x04, 0x76, 0x61, 0x72, 0x79, \\ - - - - v a r y
1634	0x00, 0x00, 0x00, 0x03, 0x76, 0x69, 0x61, 0x00, \\ - - - - v i a -
1635	0x00, 0x00, 0x07, 0x77, 0x61, 0x72, 0x6e, 0x69, \\ - - - w a r n i
1636	0x6e, 0x67, 0x00, 0x00, 0x00, 0x10, 0x77, 0x77, \\ n g - - - - w w
1637	0x77, 0x2d, 0x61, 0x75, 0x74, 0x68, 0x65, 0x6e, \\ w - a u t h e n
1638	0x74, 0x69, 0x63, 0x61, 0x74, 0x65, 0x00, 0x00, \\ t i c a t e - -
1639	0x00, 0x06, 0x6d, 0x65, 0x74, 0x68, 0x6f, 0x64, \\ - - m e t h o d
1640	0x00, 0x00, 0x00, 0x03, 0x67, 0x65, 0x74, 0x00, \\ - - - - g e t -
1641	0x00, 0x00, 0x06, 0x73, 0x74, 0x61, 0x74, 0x75, \\ - - - s t a t u
1642	0x73, 0x00, 0x00, 0x00, 0x06, 0x32, 0x30, 0x30, \\ s - - - - 2 0 0
1643	0x20, 0x4f, 0x4b, 0x00, 0x00, 0x00, 0x07, 0x76, \\ - O K - - - - v
1644	0x65, 0x72, 0x73, 0x69, 0x6f, 0x6e, 0x00, 0x00, \\ e r s i o n - -
1645	0x00, 0x08, 0x48, 0x54, 0x54, 0x50, 0x2f, 0x31, \\ - - H T T P - 1
1646	0x2e, 0x31, 0x00, 0x00, 0x00, 0x03, 0x75, 0x72, \\ - 1 - - - - u r
1647	0x6c, 0x00, 0x00, 0x00, 0x06, 0x70, 0x75, 0x62, \\ l - - - - p u b
1648	0x6c, 0x69, 0x63, 0x00, 0x00, 0x00, 0x0a, 0x73, \\ l i c - - - - s
1649	0x65, 0x74, 0x2d, 0x63, 0x6f, 0x6f, 0x6b, 0x69, \\ e t - c o o k i
1650	0x65, 0x00, 0x00, 0x00, 0x0a, 0x6b, 0x65, 0x65, \\ e - - - - k e e
1651	0x70, 0x2d, 0x61, 0x6c, 0x69, 0x76, 0x65, 0x00, \\ p - a l i v e -
1652	0x00, 0x00, 0x06, 0x6f, 0x72, 0x69, 0x67, 0x69, \\ - - - o r i g i
1653	0x6e, 0x31, 0x30, 0x30, 0x31, 0x30, 0x31, 0x32, \\ n 1 0 0 1 0 1 2
1654	0x30, 0x31, 0x32, 0x30, 0x32, 0x32, 0x30, 0x35, \\ 0 1 2 0 2 2 0 5
1655	0x32, 0x30, 0x36, 0x33, 0x30, 0x30, 0x33, 0x30, \\ 2 0 6 3 0 0 3 0
1656	0x32, 0x33, 0x30, 0x33, 0x33, 0x30, 0x34, 0x33, \\ 2 3 0 3 3 0 4 3
1657	0x30, 0x35, 0x33, 0x30, 0x36, 0x33, 0x30, 0x37, \\ 0 5 3 0 6 3 0 7
1658	0x34, 0x30, 0x32, 0x34, 0x30, 0x35, 0x34, 0x30, \\ 4 0 2 4 0 5 4 0
1659	0x36, 0x34, 0x30, 0x37, 0x34, 0x30, 0x38, 0x34, \\ 6 4 0 7 4 0 8 4
1660	0x30, 0x39, 0x34, 0x31, 0x30, 0x34, 0x31, 0x31, \\ 0 9 4 1 0 4 1 1
1661	0x34, 0x31, 0x32, 0x34, 0x31, 0x33, 0x34, 0x31, \\ 4 1 2 4 1 3 4 1
1662	0x34, 0x34, 0x31, 0x35, 0x34, 0x31, 0x36, 0x34, \\ 4 4 1 5 4 1 6 4
1663	0x31, 0x37, 0x35, 0x30, 0x32, 0x35, 0x30, 0x34, \\ 1 7 5 0 2 5 0 4
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
1677
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1683
1684	0x6f, 0x72, 0x69, 0x7a, 0x65, 0x64, 0x34, 0x30, \\ o r i z e d 4 0
1685	0x33, 0x20, 0x46, 0x6f, 0x72, 0x62, 0x69, 0x64, \\ 3 - F o r b i d
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 -
1694	0x53, 0x65, 0x72, 0x76, 0x69, 0x63, 0x65, 0x20, \\ S e r v i c e -
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
1697	0x65, 0x62, 0x20, 0x4d, 0x61, 0x72, 0x20, 0x41, \\ e b - M a r - A
1698	0x70, 0x72, 0x20, 0x4d, 0x61, 0x79, 0x20, 0x4a, \\ p r - M a y - J
1699	0x75, 0x6e, 0x20, 0x4a, 0x75, 0x6c, 0x20, 0x41, \\ u n - J u l - A
1700	0x75, 0x67, 0x20, 0x53, 0x65, 0x70, 0x74, 0x20, \\ u g - S e p t -
1701	0x4f, 0x63, 0x74, 0x20, 0x4e, 0x6f, 0x76, 0x20, \\ O c t - N o v -
1702	0x44, 0x65, 0x63, 0x20, 0x30, 0x30, 0x3a, 0x30, \\ D e c - 0 0 - 0
1703	0x30, 0x3a, 0x30, 0x30, 0x20, 0x4d, 0x6f, 0x6e, \\ 0 - 0 0 - M o n
1704	0x2c, 0x20, 0x54, 0x75, 0x65, 0x2c, 0x20, 0x57, \\ - - T u e - - W
1705	0x65, 0x64, 0x2c, 0x20, 0x54, 0x68, 0x75, 0x2c, \\ e d - - T h u -
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
1758	3. 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
1769	3.1. 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
1778	3.1.1. 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
1790
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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
1817	3.2. HTTP Request/Response
1818
1819	3.2.1. 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
1846
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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
1908	3.2.2. 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
1942	3.2.3. 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
1958
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1962
1963
1964	connection authentication.
1965
1966	3.2.3.1. 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
1974	3.2.3.2. 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
1999	3.3. 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
2014
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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
2045	3.3.1. 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
2070
2071	Belshe, et al. Expires June 1, 2013 [Page 37]
2072
2073	Internet-Draft SPDY November 2012
2074
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
2098	3.3.2. 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
2126
2127	Belshe, et al. Expires June 1, 2013 [Page 38]
2128
2129	Internet-Draft SPDY November 2012
2130
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
2150	4. 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
2159	4.1. 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
2173	4.2. 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
2183	Belshe, et al. Expires June 1, 2013 [Page 39]
2184
2185	Internet-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
2195	4.3. 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
2216	4.4. 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
2239	Belshe, et al. Expires June 1, 2013 [Page 40]
2240
2241	Internet-Draft SPDY November 2012
2242
2243
2244	4.5. 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
2267	4.6. 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
2280	4.7. 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
2295	Belshe, et al. Expires June 1, 2013 [Page 41]
2296
2297	Internet-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
2304	4.8. 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
2314	5. Security Considerations
2315
2316	5.1. 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
2321	5.2. 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
2331	5.3. 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
2338	5.4. 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
2351	Belshe, et al. Expires June 1, 2013 [Page 42]
2352
2353	Internet-Draft SPDY November 2012
2354
2355
2356	6. Privacy Considerations
2357
2358	6.1. 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
2369	6.2. 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
2387	7. 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
2407	Belshe, et al. Expires June 1, 2013 [Page 43]
2408
2409	Internet-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
2427	8. 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
2433	9. 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
2441	10. 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
2463	Belshe, et al. Expires June 1, 2013 [Page 44]
2464
2465	Internet-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
2507	Appendix A. Change Log (to be removed by RFC Editor before publication)
2508
2509	A.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
2519	Belshe, et al. Expires June 1, 2013 [Page 45]
2520
2521	Internet-Draft SPDY November 2012
2522
2523
2524	Authors' 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
2575	Belshe, et al. Expires June 1, 2013 [Page 46]
2576

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