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--------------------------------------------------------------------------------
2 HTTPbis Working Group R. Peon
3 Internet-Draft Google, Inc
4 Intended status: Informational H. Ruellan
5 Expires: June 7, 2014 Canon CRF
6 December 4, 2013
8 HPACK - Header Compression for HTTP/2.0
9 draft-ietf-httpbis-header-compression-05
11 Abstract
13 This document describes HPACK, a format adapted to efficiently
14 represent HTTP header fields in the context of HTTP/2.0.
16 Editorial Note (To be removed by RFC Editor)
18 Discussion of this draft takes place on the HTTPBIS working group
19 mailing list (ietf-http-wg@w3.org), which is archived at
20 .
22 Working Group information and related documents can be found at
23 (Wiki) and
24 (source code and issues
25 tracker).
27 The changes in this draft are summarized in Appendix A.1.
29 Status of This Memo
31 This Internet-Draft is submitted in full conformance with the
32 provisions of BCP 78 and BCP 79.
34 Internet-Drafts are working documents of the Internet Engineering
35 Task Force (IETF). Note that other groups may also distribute
36 working documents as Internet-Drafts. The list of current Internet-
37 Drafts is at http://datatracker.ietf.org/drafts/current/.
39 Internet-Drafts are draft documents valid for a maximum of six months
40 and may be updated, replaced, or obsoleted by other documents at any
41 time. It is inappropriate to use Internet-Drafts as reference
42 material or to cite them other than as "work in progress."
44 This Internet-Draft will expire on June 7, 2014.
46 Copyright Notice
48 Copyright (c) 2013 IETF Trust and the persons identified as the
49 document authors. All rights reserved.
51 This document is subject to BCP 78 and the IETF Trust's Legal
52 Provisions Relating to IETF Documents
53 (http://trustee.ietf.org/license-info) in effect on the date of
54 publication of this document. Please review these documents
55 carefully, as they describe your rights and restrictions with respect
56 to this document. Code Components extracted from this document must
57 include Simplified BSD License text as described in Section 4.e of
58 the Trust Legal Provisions and are provided without warranty as
59 described in the Simplified BSD License.
61 Table of Contents
63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
64 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
65 2.1. Outline . . . . . . . . . . . . . . . . . . . . . . . . . 4
66 3. Header Field Encoding . . . . . . . . . . . . . . . . . . . . 5
67 3.1. Encoding Concepts . . . . . . . . . . . . . . . . . . . . 5
68 3.1.1. Encoding Context . . . . . . . . . . . . . . . . . . . 5
69 3.1.2. Header Table . . . . . . . . . . . . . . . . . . . . . 6
70 3.1.3. Reference Set . . . . . . . . . . . . . . . . . . . . 6
71 3.1.4. Header Field Representation . . . . . . . . . . . . . 7
72 3.1.5. Header Field Emission . . . . . . . . . . . . . . . . 8
73 3.2. Header Block Decoding . . . . . . . . . . . . . . . . . . 8
74 3.2.1. Header Field Representation Processing . . . . . . . . 8
75 3.2.2. Reference Set Emission . . . . . . . . . . . . . . . . 10
76 3.2.3. Header Set Completion . . . . . . . . . . . . . . . . 10
77 3.3. Header Table Management . . . . . . . . . . . . . . . . . 10
78 3.3.1. Maximum Table Size . . . . . . . . . . . . . . . . . . 10
79 3.3.2. Entry Eviction When Header Table Size Changes . . . . 10
80 3.3.3. Entry Eviction when Adding New Entries . . . . . . . . 11
81 4. Detailed Format . . . . . . . . . . . . . . . . . . . . . . . 11
82 4.1. Low-level representations . . . . . . . . . . . . . . . . 11
83 4.1.1. Integer representation . . . . . . . . . . . . . . . . 11
84 4.1.2. String Literal Representation . . . . . . . . . . . . 13
85 4.2. Indexed Header Field Representation . . . . . . . . . . . 15
86 4.3. Literal Header Field Representation . . . . . . . . . . . 15
87 4.3.1. Literal Header Field without Indexing . . . . . . . . 15
88 4.3.2. Literal Header Field with Incremental Indexing . . . . 16
89 5. Security Considerations . . . . . . . . . . . . . . . . . . . 18
90 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
91 6.1. Normative References . . . . . . . . . . . . . . . . . . . 18
92 6.2. Informative References . . . . . . . . . . . . . . . . . . 19
93 Appendix A. Change Log (to be removed by RFC Editor before
94 publication . . . . . . . . . . . . . . . . . . . . . 19
95 A.1. Since draft-ietf-httpbis-header-compression-04 . . . . . . 19
96 A.2. Since draft-ietf-httpbis-header-compression-03 . . . . . . 20
97 A.3. Since draft-ietf-httpbis-header-compression-02 . . . . . . 20
98 A.4. Since draft-ietf-httpbis-header-compression-01 . . . . . . 20
99 A.5. Since draft-ietf-httpbis-header-compression-01 . . . . . . 21
100 Appendix B. Static Table . . . . . . . . . . . . . . . . . . . . 21
101 Appendix C. Huffman Codes For Requests . . . . . . . . . . . . . 23
102 Appendix D. Huffman Codes for Responses . . . . . . . . . . . . . 29
103 Appendix E. Examples . . . . . . . . . . . . . . . . . . . . . . 34
104 E.1. Header Field Representation Examples . . . . . . . . . . . 34
105 E.1.1. Literal Header Field with Indexing . . . . . . . . . . 34
106 E.1.2. Literal Header Field without Indexing . . . . . . . . 35
107 E.1.3. Indexed Header Field . . . . . . . . . . . . . . . . . 36
108 E.1.4. Indexed Header Field from Static Table . . . . . . . . 37
109 E.2. Request Examples without Huffman . . . . . . . . . . . . . 37
110 E.2.1. First request . . . . . . . . . . . . . . . . . . . . 37
111 E.2.2. Second request . . . . . . . . . . . . . . . . . . . . 38
112 E.2.3. Third request . . . . . . . . . . . . . . . . . . . . 40
113 E.3. Request Examples with Huffman . . . . . . . . . . . . . . 42
114 E.3.1. First request . . . . . . . . . . . . . . . . . . . . 42
115 E.3.2. Second request . . . . . . . . . . . . . . . . . . . . 43
116 E.3.3. Third request . . . . . . . . . . . . . . . . . . . . 44
117 E.4. Response Examples without Huffman . . . . . . . . . . . . 46
118 E.4.1. First response . . . . . . . . . . . . . . . . . . . . 46
119 E.4.2. Second response . . . . . . . . . . . . . . . . . . . 48
120 E.4.3. Third response . . . . . . . . . . . . . . . . . . . . 49
121 E.5. Response Examples with Huffman . . . . . . . . . . . . . . 51
122 E.5.1. First response . . . . . . . . . . . . . . . . . . . . 51
123 E.5.2. Second response . . . . . . . . . . . . . . . . . . . 53
124 E.5.3. Third response . . . . . . . . . . . . . . . . . . . . 54
126 1. Introduction
128 This document describes HPACK, a format adapted to efficiently
129 represent HTTP header fields in the context of HTTP/2.0 (see
130 [HTTP2]).
132 2. Overview
134 In HTTP (see [HTTP-p1]), header fields are sent without any form of
135 compression. As web pages have grown to include dozens to hundreds
136 of requests, the redundant header fields in these requests now pose a
137 problem of measurable latency and unnecessary bandwidth (see [PERF1]
138 and [PERF2]).
140 SPDY [SPDY] initially addressed this redundancy by compressing header
141 fields with Deflate, which proved very effective at eliminating the
142 redundant header fields. However, that approach exposed a security
143 risk as demonstrated by the CRIME [CRIME].
145 This document describes HPACK, a new compressor for header fields
146 which eliminates redundant header fields, is not vulnerable to known
147 security attacks, and which also has a bounded memory cost for use in
148 constrained environments.
150 2.1. Outline
152 The HTTP header field encoding described in this document is based on
153 a header table that map name-value pairs to index values. Header
154 tables are incrementally updated during the HTTP/2.0 session.
156 The encoder is responsible for deciding which header fields to insert
157 as new entries in the header table. The decoder then does exactly
158 what the encoder prescribes, ending in a state that exactly matches
159 the encoder's state. This enables decoders to remain simple and
160 understand a wide variety of encoders.
162 As two consecutive sets of header fields often have header fields in
163 common, each set of header fields is coded as a difference from the
164 previous set of header fields. The goal is to only encode the
165 changes (header fields present in one of the set and not in the
166 other) between the two sets of header fields.
168 HTTP header field compression treats a set of header fields as an
169 unordered collection of name-value pairs. Names and values are
170 opaque sequences of octets. The order of header fields is not
171 guaranteed to be preserved after being compression and decompression.
173 Examples illustrating the use of these different mechanisms to
174 represent header fields are available in Appendix E.
176 3. Header Field Encoding
178 3.1. Encoding Concepts
180 The encoding and decoding of header fields relies on some components
181 and concepts:
183 Header Field: A name-value pair. Both name and value are sequences
184 of octets.
186 Header Table: The header table (see Section 3.1.2) is a component
187 used to associate stored header fields to index values. The data
188 stored in this table is in first-in, first-out order.
190 Static Table: The static table (see Appendix B) is a component used
191 to associate static header fields to index values. This data is
192 ordered, read-only, always accessible, and may be shared amongst
193 all encoding contexts.
195 Reference Set: The reference set (see Section 3.1.3) is a component
196 containing an unordered set of references to entries in the header
197 table. This is used for the differential encoding of a new header
198 set.
200 Header Set: A header set is a potentially ordered group of header
201 fields that are encoded jointly. A complete set of key-value
202 pairs contained in a HTTP request or response is a header set.
204 Header Field Representation: A header field can be represented in
205 encoded form either as a literal or as an index (see
206 Section 3.1.4).
208 Header Block: The entire set of encoded header field representations
209 which, when decoded, yield a complete header set.
211 Header Field Emission: When decoding a set of header field
212 representations, some operations emit a header field (see
213 Section 3.1.5). Emitted header fields can be safely passed to the
214 upper processing layers as part of the current Header Set.
216 3.1.1. Encoding Context
218 The set of mutable structures used within an encoding context include
219 a header table and a reference set. Everything else is either
220 immutable or conceptual.
222 Using HTTP, messages are exchanged between a client and a server in
223 both direction. To keep the encoding of header fields in each
224 direction independent from the other direction, there is one encoding
225 context for each direction.
227 The header fields contained in a PUSH_PROMISE frame sent by a server
228 to a client are encoded within the same context as the header fields
229 contained in the HEADERS frame corresponding to a response sent from
230 the server to the client.
232 3.1.2. Header Table
234 A header table consists of a list of header fields maintained in
235 first-in, first-out order. The first and newest entry in a header
236 table is always at index 1, and the oldest entry of a header table is
237 at the index len(header table).
239 The header table is initially empty.
241 There is typically no need for the header table to contain duplicate
242 entries. However, duplicate entries MUST NOT be treated as an error
243 by a decoder.
245 The encoder decides how to update the header table and as such can
246 control how much memory is used by the header table. To limit the
247 memory requirements on the decoder side, the header table size is
248 strictly bounded (see Section 3.3.1).
250 The header table is updated during the processing of a set of header
251 field representations (see header field representation processing
252 (Section 3.2.1)).
254 3.1.3. Reference Set
256 A reference set is an unordered set of references to entries of the
257 header table.
259 The reference set is initially empty.
261 The reference set is updated during the processing of a set of header
262 field representations (see header field representation processing
263 (Section 3.2.1)).
265 The reference set enables differential encoding, whereby only
266 differences between the previous header set and the current header
267 set need to be encoded. The use of differential encoding is optional
268 for any header set.
270 When an entry is evicted from the header table, if it was referenced
271 from the reference set, its reference is removed from the reference
272 set.
274 To limit the memory requirements on the decoder side for handling the
275 reference set, only entries within the header table can be contained
276 in the reference set. To still allow entries from the static table
277 to take advantage of the differential encoding, when a header field
278 is represented as a reference to an entry of the static table, this
279 entry is inserted into the header table ((see Section 3.2.1).
281 3.1.4. Header Field Representation
283 An encoded header field can be represented either as a literal or as
284 an index.
286 Literal Representation: A literal representation defines a new
287 header field. The header field name is represented either
288 literally or as a reference to an entry of the header table. The
289 header field value is represented literally.
291 Two different literal representations are provided:
293 * A literal representation that does not add the header field to
294 the header table (see Section 4.3.1).
296 * A literal representation that adds the header field as a new
297 entry at the beginning of the header table (see Section 4.3.2).
299 Indexed Representation: The indexed representation defines a header
300 field as a reference to an entry in either the header table or the
301 static table(see Section 4.2).
303 <---------- Index Address Space ---------->
304 <-- Header Table --> <-- Static Table -->
305 +---+-----------+---+ +---+-----------+---+
306 | 1 | ... | k | |k+1| ... | n |
307 +---+-----------+---+ +---+-----------+---+
308 ^ |
309 | V
310 Insertion Point Drop Point
312 Index Address Space
314 Indices between 1 and len(header table), inclusive, refer to
315 elements in the header table, with index 1 referring to the
316 beginning of the table.
318 Indices between len(header table)+1 and len(header table)+
319 len(static table), inclusive, refer to elements in the static
320 table, where the index len(header table)+1 refers to the first
321 entry in the static table.
323 Index 0 signals that the reference set MUST be emptied.
325 Any other indices MUST be treated as erroneous, and the
326 compression context considered corrupt and unusable.
328 3.1.5. Header Field Emission
330 The emission of a header field is the process of marking a header
331 field as belonging to the current header set. Once a header has been
332 emitted, it cannot be removed from the current header set.
334 On the decoding side, an emitted header field can be safely passed to
335 the upper processing layer as part of the current header set. The
336 decoder MAY pass the emitted header fields to the upper processing
337 layer in any order.
339 By emitting header fields instead of emitting header sets, the
340 decoder can be implemented in a streaming way, and as such has only
341 to keep in memory the header table and the reference set. This
342 bounds the amount of memory used by the decoder, even in presence of
343 a very large set of header fields. The management of memory for
344 handling very large sets of header fields can therefore be deferred
345 to the upper processing layers.
347 3.2. Header Block Decoding
349 The processing of a header block to obtain a header set is defined in
350 this section. To ensure that the decoding will successfully produce
351 a header set, a decoder MUST obey the following rules.
353 3.2.1. Header Field Representation Processing
355 All the header field representations contained in a header block are
356 processed in the order in which they are presented, as specified
357 below.
359 An _indexed representation_ with an index value of 0 entails the
360 following actions:
362 o The reference set is emptied.
364 An _indexed representation_ corresponding to an entry _present_ in
365 the reference set entails the following actions:
367 o The entry is removed from the reference set.
369 An _indexed representation_ corresponding to an entry _not present_
370 in the reference set entails the following actions:
372 o If referencing an element of the static table:
374 * The header field corresponding to the referenced entry is
375 emitted.
377 * The referenced static entry is inserted at the beginning of the
378 header table.
380 * A reference to this new header table entry is added to the
381 reference set (except if this new entry didn't fit in the
382 header table).
384 o If referencing an element of the header table:
386 * The header field corresponding to the referenced entry is
387 emitted.
389 * The referenced header table entry is added to the reference
390 set.
392 A _literal representation_ that is _not added_ to the header table
393 entails the following action:
395 o The header field is emitted.
397 A _literal representation_ that is _added_ to the header table
398 entails the following actions:
400 o The header field is emitted.
402 o The header field is inserted at the beginning of the header table.
404 o A reference to the new entry is added to the reference set (except
405 if this new entry didn't fit in the header table).
407 3.2.2. Reference Set Emission
409 Once all the representations contained in a header block have been
410 processed, the header fields referenced in the reference set which
411 have not previously been emitted during this processing are emitted.
413 3.2.3. Header Set Completion
415 Once all of the header field representations have been processed, and
416 the remaining items in the reference set have been emitted, the
417 header set is complete.
419 3.3. Header Table Management
421 3.3.1. Maximum Table Size
423 To limit the memory requirements on the decoder side, the size of the
424 header table is bounded. The size of the header table MUST stay
425 lower than or equal to the value of the HTTP/2.0 setting
426 SETTINGS_HEADER_TABLE_SIZE (see [HTTP2]).
428 The size of the header table is the sum of the size of its entries.
430 The size of an entry is the sum of its name's length in octets (as
431 defined in Section 4.1.2), of its value's length in octets
432 (Section 4.1.2) and of 32 octets.
434 The lengths are measured on the non-encoded entry name and entry
435 value (for the case when a Huffman encoding is used to transmit
436 string values).
438 The 32 octets are an accounting for the entry structure overhead.
439 For example, an entry structure using two 64-bits pointers to
440 reference the name and the value and the entry, and two 64-bits
441 integer for counting the number of references to these name and value
442 would use 32 octets.
444 3.3.2. Entry Eviction When Header Table Size Changes
446 Whenever an entry is evicted from the header table, any reference to
447 that entry contained by the reference set is removed.
449 Whenever SETTINGS_HEADER_TABLE_SIZE is made smaller, entries are
450 evicted from the end of the header table until the size of the header
451 table is less than or equal to SETTINGS_HEADER_TABLE_SIZE.
453 The eviction of an entry from the header table causes the index of
454 the entries in the static table to be reduced by one.
456 3.3.3. Entry Eviction when Adding New Entries
458 Whenever a new entry is to be added to the table, any name referenced
459 by the representation of this new entry is cached, and then entries
460 are evicted from the end of the header table until the size of the
461 header table is less than or equal to SETTINGS_HEADER_TABLE_SIZE -
462 new entry size, or until the table is empty.
464 If the size of the new entry is less than or equal to
465 SETTINGS_HEADER_TABLE_SIZE, that entry is added to the table. It is
466 not an error to attempt to add an entry that is larger than
467 SETTINGS_HEADER_TABLE_SIZE.
469 4. Detailed Format
471 4.1. Low-level representations
473 4.1.1. Integer representation
475 Integers are used to represent name indexes, pair indexes or string
476 lengths. To allow for optimized processing, an integer
477 representation always finishes at the end of an octet.
479 An integer is represented in two parts: a prefix that fills the
480 current octet and an optional list of octets that are used if the
481 integer value does not fit within the prefix. The number of bits of
482 the prefix (called N) is a parameter of the integer representation.
484 The N-bit prefix allows filling the current octet. If the value is
485 small enough (strictly less than 2^N-1), it is encoded within the
486 N-bit prefix. Otherwise all the bits of the prefix are set to 1 and
487 the value is encoded using an unsigned variable length integer [1]
488 representation. N is always between 1 and 8 bits. An integer
489 starting at an octet-boundary will have an 8-bit prefix.
491 The algorithm to represent an integer I is as follows:
493 If I < 2^N - 1, encode I on N bits
494 Else
495 encode 2^N - 1 on N bits
496 I = I - (2^N - 1)
497 While I >= 128
498 Encode (I % 128 + 128) on 8 bits
499 I = I / 128
500 encode (I) on 8 bits
502 This integer representation allows for values of indefinite size. It
503 is also possible for an encoder to send a large number of zero
504 values, which can waste octets and could be used to overflow integer
505 values. Excessively large integer encodings - in value or octet
506 length - MUST be treated as a decoding error. Different limits can
507 be set for each of the different uses of integers, based on
508 implementation constraints.
510 4.1.1.1. Example 1: Encoding 10 using a 5-bit prefix
512 The value 10 is to be encoded with a 5-bit prefix.
514 o 10 is less than 31 (= 2^5 - 1) and is represented using the 5-bit
515 prefix.
517 0 1 2 3 4 5 6 7
518 +---+---+---+---+---+---+---+---+
519 | X | X | X | 0 | 1 | 0 | 1 | 0 | 10 stored on 5 bits
520 +---+---+---+---+---+---+---+---+
522 4.1.1.2. Example 2: Encoding 1337 using a 5-bit prefix
524 The value I=1337 is to be encoded with a 5-bit prefix.
526 1337 is greater than 31 (= 2^5 - 1).
528 The 5-bit prefix is filled with its max value (31).
530 I = 1337 - (2^5 - 1) = 1306.
532 I (1306) is greater than or equal to 128, the while loop body
533 executes:
535 I % 128 == 26
537 26 + 128 == 154
539 154 is encoded in 8 bits as: 10011010
541 I is set to 10 (1306 / 128 == 10)
543 I is no longer greater than or equal to 128, the while loop
544 terminates.
546 I, now 10, is encoded on 8 bits as: 00001010
548 The process ends.
550 0 1 2 3 4 5 6 7
551 +---+---+---+---+---+---+---+---+
552 | X | X | X | 1 | 1 | 1 | 1 | 1 | Prefix = 31, I = 1306
553 | 1 | 0 | 0 | 1 | 1 | 0 | 1 | 0 | 1306>=128, encode(154), I=1306/128
554 | 0 | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 10<128, encode(10), done
555 +---+---+---+---+---+---+---+---+
557 4.1.1.3. Example 3: Encoding 42 starting at an
558 octet-boundary
560 The value 42 is to be encoded starting at an octet-boundary. This
561 implies that a 8-bit prefix is used.
563 o 42 is less than 255 (= 2^8 - 1) and is represented using the 8-bit
564 prefix.
566 0 1 2 3 4 5 6 7
567 +---+---+---+---+---+---+---+---+
568 | 0 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 42 stored on 8 bits
569 +---+---+---+---+---+---+---+---+
571 4.1.2. String Literal Representation
573 Header field names and header field values are encoded as sequences
574 of octets. A header field name or a header field value is encoded in
575 three parts:
577 1. One bit, H, indicating whether or not the octets are Huffman
578 encoded.
580 2. The number of octets required to hold the result of the next
581 step, represented as a variable-length-quantity (Section 4.1.1),
582 starting with a 7-bit prefix immediately following the first bit.
584 3. The encoded data of the string:
586 1. If H is true, then the encoded string data is the bitwise
587 concatenation of the canonical [CANON]Huffman code [HUFF]
588 corresponding to each octet of the data, followed by between
589 0-7 bits of padding.
591 2. If H is false, then the encoded string is the octets of the
592 field value without modification.
594 Padding is necessary when doing Huffman encoding to ensure that the
595 remaining bits between the actual end of the data and the next octet
596 boundary are not misinterpreted as part of the input data.
598 When padding for Huffman encoding, use the bits from the EOS (end-of-
599 string) entry in the Huffman table, starting with the MSB (most
600 significant bit). This entry is guaranteed to be at least 8 bits
601 long.
603 String literals sent in the client to server direction which use
604 Huffman encoding are encoded with the codes within the request
605 Huffman code table (Appendix C) (see Request Examples With Huffman
606 (Appendix E.3)).
608 String literals sent in the server to client direction which use
609 Huffman encoding are encoded with the codes within the response
610 Huffman code table (Appendix D) (see Response Examples With Huffman
611 (Appendix E.5)).
613 The EOS symbol is represented with value 256, and is used solely to
614 signal the end of the Huffman-encoded key data or the end of the
615 Huffman-encoded value data. Given that only between 0-7 bits of the
616 EOS symbol is included in any Huffman-encoded string, and given that
617 the EOS symbol is at least 8 bits long, it is expected that it should
618 never be successfully decoded.
620 0 1 2 3 4 5 6 7
621 +---+---+---+---+---+---+---+---+
622 | 1 | Value Length Prefix (7) |
623 +---+---+---+---+---+---+---+---+
624 | Value Length (0-N octets) |
625 +---+---+---+---+---+---+---+---+
626 ...
627 +---+---+---+---+---+---+---+---+
628 | Huffman Encoded Data |Padding|
629 +---+---+---+---+---+---+---+---+
631 String Literal With Huffman Encoding
633 0 1 2 3 4 5 6 7
634 +---+---+---+---+---+---+---+---+
635 | 0 | Value Length Prefix (7) |
636 +---+---+---+---+---+---+---+---+
637 | Value Length (0-N octets) |
638 +---+---+---+---+---+---+---+---+
639 ...
640 +---+---+---+---+---+---+---+---+
641 | Field Bytes Without Encoding |
642 +---+---+---+---+---+---+---+---+
644 String Literal Without Huffman Encoding
646 4.2. Indexed Header Field Representation
648 An indexed header field representation either identifies an entry in
649 the header table or static table. The processing of an indexed
650 header field representation is described in Section 3.2.1.
652 0 1 2 3 4 5 6 7
653 +---+---+---+---+---+---+---+---+
654 | 1 | Index (7+) |
655 +---+---------------------------+
657 Indexed Header Field
659 This representation starts with the '1' 1-bit pattern, followed by
660 the index of the matching pair, represented as an integer with a
661 7-bit prefix.
663 The index value of 0 is reserved for signalling that the reference
664 set is emptied.
666 4.3. Literal Header Field Representation
668 Literal header field representations contain a literal header field
669 value. Header field names are either provided as a literal or by
670 reference to an existing header table or static table entry.
672 Literal representations all result in the emission of a header field
673 when decoded.
675 4.3.1. Literal Header Field without Indexing
677 A literal header field without indexing causes the emission of a
678 header field without altering the header table.
680 0 1 2 3 4 5 6 7
681 +---+---+---+---+---+---+---+---+
682 | 0 | 1 | Index (6+) |
683 +---+---+---+-------------------+
684 | Value Length (8+) |
685 +-------------------------------+
686 | Value String (Length octets) |
687 +-------------------------------+
689 Literal Header Field without Indexing - Indexed Name
691 0 1 2 3 4 5 6 7
692 +---+---+---+---+---+---+---+---+
693 | 0 | 1 | 0 |
694 +---+---+---+-------------------+
695 | Name Length (8+) |
696 +-------------------------------+
697 | Name String (Length octets) |
698 +-------------------------------+
699 | Value Length (8+) |
700 +-------------------------------+
701 | Value String (Length octets) |
702 +-------------------------------+
704 Literal Header Field without Indexing - New Name
706 This representation starts with the '01' 2-bit pattern.
708 If the header field name matches the header field name of a (name,
709 value) pair stored in the Header Table or Static Table, the header
710 field name can be represented using the index of that entry. In this
711 case, the index of the entry, index (which is strictly greater than
712 0), is represented as an integer with a 6-bit prefix (see
713 Section 4.1.1).
715 Otherwise, the header field name is represented as a literal. The
716 value 0 is represented on 6 bits followed by the header field name
717 (see Section 4.1.2).
719 The header field name representation is followed by the header field
720 value represented as a literal string as described in Section 4.1.2.
722 4.3.2. Literal Header Field with Incremental Indexing
724 A literal header field with incremental indexing adds a new entry to
725 the header table.
727 0 1 2 3 4 5 6 7
728 +---+---+---+---+---+---+---+---+
729 | 0 | 0 | Index (6+) |
730 +---+---+---+-------------------+
731 | Value Length (8+) |
732 +-------------------------------+
733 | Value String (Length octets) |
734 +-------------------------------+
736 Literal Header Field with Incremental Indexing -
737 Indexed Name
739 0 1 2 3 4 5 6 7
740 +---+---+---+---+---+---+---+---+
741 | 0 | 0 | 0 |
742 +---+---+---+-------------------+
743 | Name Length (8+) |
744 +-------------------------------+
745 | Name String (Length octets) |
746 +-------------------------------+
747 | Value Length (8+) |
748 +-------------------------------+
749 | Value String (Length octets) |
750 +-------------------------------+
752 Literal Header Field with Incremental Indexing -
753 New Name
755 This representation starts with the '00' 2-bit pattern.
757 If the header field name matches the header field name of a (name,
758 value) pair stored in the Header Table or Static Table, the header
759 field name can be represented using the index of that entry. In this
760 case, the index of the entry, index (which is strictly greater than
761 0), is represented as an integer with a 6-bit prefix (see
762 Section 4.1.1).
764 Otherwise, the header field name is represented as a literal. The
765 value 0 is represented on 6 bits followed by the header field name
766 (see Section 4.1.2).
768 The header field name representation is followed by the header field
769 value represented as a literal string as described in Section 4.1.2.
771 5. Security Considerations
773 This compressor exists to solve security issues present in stream
774 compressors such as DEFLATE whereby the compression context can be
775 efficiently probed to reveal secrets. A conformant implementation of
776 this specification should be fairly safe against that kind of attack,
777 as the reaping of any information from the compression context
778 requires more work than guessing and verifying the plain text data
779 directly with the server. As with any secret, however, the longer
780 the length of the secret, the more difficult the secret is to guess.
781 It is inadvisable to have short cookies that are relied upon to
782 remain secret for any duration of time.
784 A proper security-conscious implementation will also need to prevent
785 timing attacks by ensuring that the amount of time it takes to do
786 string comparisons is always a function of the total length of the
787 strings, and not a function of the number of matched characters.
789 A decoder needs to ensure that larger values or encodings of integers
790 do not permit exploitation. Decoders MUST limit the size of
791 integers, both in value and encoded length, that it accepts (see
792 Section 4.1.1).
794 Another common security problem is when the remote endpoint
795 successfully causes the local endpoint to exhaust its memory. This
796 compressor attempts to deal with the most obvious ways that this
797 could occur by limiting both the peak and the steady-state amount of
798 memory consumed in the compressor state, by providing ways for the
799 application to consume/flush the emitted header fields in small
800 chunks, and by considering overhead in the state size calculation.
801 Implementors must still be careful in the creation of APIs to an
802 implementation of this compressor by ensuring that header field keys
803 and values are either emitted as a stream, or that the compression
804 implementation have a limit on the maximum size of a key or value.
805 Failure to implement these kinds of safeguards may still result in a
806 scenario where the local endpoint exhausts its memory.
808 6. References
810 6.1. Normative References
812 [HTTP-p1] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
813 Protocol (HTTP/1.1): Message Syntax and Routing",
814 draft-ietf-httpbis-p1-messaging-25 (work in progress),
815 November 2013.
817 [HTTP2] Belshe, M., Peon, R., Thomson, M., Ed., and A. Melnikov,
818 Ed., "Hypertext Transfer Protocol version 2.0",
819 draft-ietf-httpbis-http2-08 (work in progress),
820 November 2013.
822 6.2. Informative References
824 [CANON] Schwartz, E. and B. Kallick, "Generating a canonical
825 prefix encoding", Communications of the ACM Volume 7 Issue
826 3, pp. 166-169, March 1964,
827 .
829 [CRIME] Rizzo, J. and T. Duong, "The Crime Attack",
830 September 2012, .
835 [HUFF] Huffman, D., "A Method for the Construction of Minimum
836 Redundancy Codes", Proceedings of the Institute of Radio
837 Engineers Volume 40, Number 9, pp. 1098-1101,
838 September 1952, .
841 [PERF1] Belshe, M., "IETF83: SPDY and What to Consider for
842 HTTP/2.0", March 2012, .
845 [PERF2] McManus, P., "SPDY: What I Like About You",
846 September 2011, .
849 [SPDY] Belshe, M. and R. Peon, "SPDY Protocol",
850 draft-mbelshe-httpbis-spdy-00 (work in progress),
851 February 2012.
853 URIs
855 [1]
857 Appendix A. Change Log (to be removed by RFC Editor before publication
859 A.1. Since draft-ietf-httpbis-header-compression-04
861 o Updated examples: take into account changes in the spec, and show
862 more features.
864 o Use 'octet' everywhere instead of having both 'byte' and 'octet'.
866 o Added reference set emptying.
868 o Editorial changes and clarifications.
870 o Added "host" header to the static table.
872 o Ordering for list of values (either NULL- or comma-separated).
874 A.2. Since draft-ietf-httpbis-header-compression-03
876 o A large number of editorial changes; changed the description of
877 evicting/adding new entries.
879 o Removed substitution indexing
881 o Changed 'initial headers' to 'static headers', as per issue #258
883 o Merged 'request' and 'response' static headers, as per issue #259
885 o Changed text to indicate that new headers are added at index 0 and
886 expire from the largest index, as per issue #233
888 A.3. Since draft-ietf-httpbis-header-compression-02
890 o Corrected error in integer encoding pseudocode.
892 A.4. Since draft-ietf-httpbis-header-compression-01
894 o Refactored of Header Encoding Section: split definitions and
895 processing rule.
897 o Backward incompatible change: Updated reference set management as
898 per issue #214. This changes how the interaction between the
899 reference set and eviction works. This also changes the working
900 of the reference set in some specific cases.
902 o Backward incompatible change: modified initial header list, as per
903 issue #188.
905 o Added example of 32 octets entry structure (issue #191).
907 o Added Header Set Completion section. Reflowed some text.
908 Clarified some writing which was akward. Added text about
909 duplicate header entry encoding. Clarified some language w.r.t
910 Header Set. Changed x-my-header to mynewheader. Added text in the
911 HeaderEmission section indicating that the application may also be
912 able to free up memory more quickly. Added information in
913 Security Considerations section.
915 A.5. Since draft-ietf-httpbis-header-compression-01
917 Fixed bug/omission in integer representation algorithm.
919 Changed the document title.
921 Header matching text rewritten.
923 Changed the definition of header emission.
925 Changed the name of the setting which dictates how much memory the
926 compression context should use.
928 Removed "specific use cases" section
930 Corrected erroneous statement about what index can be contained in
931 one octet
933 Added descriptions of opcodes
935 Removed security claims from introduction.
937 Appendix B. Static Table
939 The static table consists of an unchangeable ordered list of (name,
940 value) pairs. The first entry in the table is always represented by
941 the index len(header table)+1, and the last entry in the table is
942 represented by the index len(header table)+len(static table).
944 [[anchor9: The ordering of these tables is currently arbitrary. The
945 tables in this section should be updated and ordered such that the
946 table entries with the smallest indices are those which, based on a
947 statistical analysis of the frequency of use weighted by size,
948 achieve the largest decrease in octets transmitted subject to HTTP
949 2.0 header field rules (like removal of some header fields). This
950 set of header fields is currently very likely incomplete, and should
951 be made complete.]]
953 The following table lists the pre-defined header fields that make-up
954 the static header table.
956 +-------+-----------------------------+--------------+
957 | Index | Header Name | Header Value |
958 +-------+-----------------------------+--------------+
959 | 1 | :authority | |
960 | 2 | :method | GET |
961 | 3 | :method | POST |
962 | 4 | :path | / |
963 | 5 | :path | /index.html |
964 | 6 | :scheme | http |
965 | 7 | :scheme | https |
966 | 8 | :status | 200 |
967 | 9 | :status | 500 |
968 | 10 | :status | 404 |
969 | 11 | :status | 403 |
970 | 12 | :status | 400 |
971 | 13 | :status | 401 |
972 | 14 | accept-charset | |
973 | 15 | accept-encoding | |
974 | 16 | accept-language | |
975 | 17 | accept-ranges | |
976 | 18 | accept | |
977 | 19 | access-control-allow-origin | |
978 | 20 | age | |
979 | 21 | allow | |
980 | 22 | authorization | |
981 | 23 | cache-control | |
982 | 24 | content-disposition | |
983 | 25 | content-encoding | |
984 | 26 | content-language | |
985 | 27 | content-length | |
986 | 28 | content-location | |
987 | 29 | content-range | |
988 | 30 | content-type | |
989 | 31 | cookie | |
990 | 32 | date | |
991 | 33 | etag | |
992 | 34 | expect | |
993 | 35 | expires | |
994 | 36 | from | |
995 | 37 | host | |
996 | 38 | if-match | |
997 | 39 | if-modified-since | |
998 | 40 | if-none-match | |
999 | 41 | if-range | |
1000 | 42 | if-unmodified-since | |
1001 | 43 | last-modified | |
1002 | 44 | link | |
1003 | 45 | location | |
1004 | 46 | max-forwards | |
1005 | 47 | proxy-authenticate | |
1006 | 48 | proxy-authorization | |
1007 | 49 | range | |
1008 | 50 | referer | |
1009 | 51 | refresh | |
1010 | 52 | retry-after | |
1011 | 53 | server | |
1012 | 54 | set-cookie | |
1013 | 55 | strict-transport-security | |
1014 | 56 | transfer-encoding | |
1015 | 57 | user-agent | |
1016 | 58 | vary | |
1017 | 59 | via | |
1018 | 60 | www-authenticate | |
1019 +-------+-----------------------------+--------------+
1021 Table 1: Static Table Entries
1023 The table give the index of each entry in the static table. The full
1024 index of each entry, to be used for encoding a reference to this
1025 entry, is computed by adding the number of entries in the header
1026 table to this index.
1028 Appendix C. Huffman Codes For Requests
1030 The following Huffman codes are used when encoding string literals in
1031 the client to server direction.
1033 [[anchor10: This table may need to be regenerated.]]
1035 aligned aligned
1036 to len to len
1037 MSB in LSB in
1038 sym as bits bits as hex bits
1039 ( 0) |11111111|11111111|11110111|010 [27] 7ffffba [27]
1040 ( 1) |11111111|11111111|11110111|011 [27] 7ffffbb [27]
1041 ( 2) |11111111|11111111|11110111|100 [27] 7ffffbc [27]
1042 ( 3) |11111111|11111111|11110111|101 [27] 7ffffbd [27]
1043 ( 4) |11111111|11111111|11110111|110 [27] 7ffffbe [27]
1044 ( 5) |11111111|11111111|11110111|111 [27] 7ffffbf [27]
1045 ( 6) |11111111|11111111|11111000|000 [27] 7ffffc0 [27]
1046 ( 7) |11111111|11111111|11111000|001 [27] 7ffffc1 [27]
1047 ( 8) |11111111|11111111|11111000|010 [27] 7ffffc2 [27]
1048 ( 9) |11111111|11111111|11111000|011 [27] 7ffffc3 [27]
1049 ( 10) |11111111|11111111|11111000|100 [27] 7ffffc4 [27]
1050 ( 11) |11111111|11111111|11111000|101 [27] 7ffffc5 [27]
1051 ( 12) |11111111|11111111|11111000|110 [27] 7ffffc6 [27]
1052 ( 13) |11111111|11111111|11111000|111 [27] 7ffffc7 [27]
1053 ( 14) |11111111|11111111|11111001|000 [27] 7ffffc8 [27]
1054 ( 15) |11111111|11111111|11111001|001 [27] 7ffffc9 [27]
1055 ( 16) |11111111|11111111|11111001|010 [27] 7ffffca [27]
1056 ( 17) |11111111|11111111|11111001|011 [27] 7ffffcb [27]
1057 ( 18) |11111111|11111111|11111001|100 [27] 7ffffcc [27]
1058 ( 19) |11111111|11111111|11111001|101 [27] 7ffffcd [27]
1059 ( 20) |11111111|11111111|11111001|110 [27] 7ffffce [27]
1060 ( 21) |11111111|11111111|11111001|111 [27] 7ffffcf [27]
1061 ( 22) |11111111|11111111|11111010|000 [27] 7ffffd0 [27]
1062 ( 23) |11111111|11111111|11111010|001 [27] 7ffffd1 [27]
1063 ( 24) |11111111|11111111|11111010|010 [27] 7ffffd2 [27]
1064 ( 25) |11111111|11111111|11111010|011 [27] 7ffffd3 [27]
1065 ( 26) |11111111|11111111|11111010|100 [27] 7ffffd4 [27]
1066 ( 27) |11111111|11111111|11111010|101 [27] 7ffffd5 [27]
1067 ( 28) |11111111|11111111|11111010|110 [27] 7ffffd6 [27]
1068 ( 29) |11111111|11111111|11111010|111 [27] 7ffffd7 [27]
1069 ( 30) |11111111|11111111|11111011|000 [27] 7ffffd8 [27]
1070 ( 31) |11111111|11111111|11111011|001 [27] 7ffffd9 [27]
1071 ' ' ( 32) |11101000| [8] e8 [8]
1072 '!' ( 33) |11111111|1100 [12] ffc [12]
1073 '"' ( 34) |11111111|111010 [14] 3ffa [14]
1074 '#' ( 35) |11111111|1111100 [15] 7ffc [15]
1075 '$' ( 36) |11111111|1111101 [15] 7ffd [15]
1076 '%' ( 37) |100100 [6] 24 [6]
1077 '&' ( 38) |1101110 [7] 6e [7]
1078 ''' ( 39) |11111111|1111110 [15] 7ffe [15]
1079 '(' ( 40) |11111111|010 [11] 7fa [11]
1080 ')' ( 41) |11111111|011 [11] 7fb [11]
1081 '*' ( 42) |11111110|10 [10] 3fa [10]
1082 '+' ( 43) |11111111|100 [11] 7fc [11]
1083 ',' ( 44) |11101001| [8] e9 [8]
1084 '-' ( 45) |100101 [6] 25 [6]
1085 '.' ( 46) |00100 [5] 4 [5]
1086 '/' ( 47) |0000 [4] 0 [4]
1087 '0' ( 48) |00101 [5] 5 [5]
1088 '1' ( 49) |00110 [5] 6 [5]
1089 '2' ( 50) |00111 [5] 7 [5]
1090 '3' ( 51) |100110 [6] 26 [6]
1091 '4' ( 52) |100111 [6] 27 [6]
1092 '5' ( 53) |101000 [6] 28 [6]
1093 '6' ( 54) |101001 [6] 29 [6]
1094 '7' ( 55) |101010 [6] 2a [6]
1095 '8' ( 56) |101011 [6] 2b [6]
1096 '9' ( 57) |101100 [6] 2c [6]
1097 ':' ( 58) |11110110|0 [9] 1ec [9]
1098 ';' ( 59) |11101010| [8] ea [8]
1099 '<' ( 60) |11111111|11111111|10 [18] 3fffe [18]
1100 '=' ( 61) |101101 [6] 2d [6]
1101 '>' ( 62) |11111111|11111110|0 [17] 1fffc [17]
1102 '?' ( 63) |11110110|1 [9] 1ed [9]
1103 '@' ( 64) |11111111|111011 [14] 3ffb [14]
1104 'A' ( 65) |1101111 [7] 6f [7]
1105 'B' ( 66) |11101011| [8] eb [8]
1106 'C' ( 67) |11101100| [8] ec [8]
1107 'D' ( 68) |11101101| [8] ed [8]
1108 'E' ( 69) |11101110| [8] ee [8]
1109 'F' ( 70) |1110000 [7] 70 [7]
1110 'G' ( 71) |11110111|0 [9] 1ee [9]
1111 'H' ( 72) |11110111|1 [9] 1ef [9]
1112 'I' ( 73) |11111000|0 [9] 1f0 [9]
1113 'J' ( 74) |11111000|1 [9] 1f1 [9]
1114 'K' ( 75) |11111110|11 [10] 3fb [10]
1115 'L' ( 76) |11111001|0 [9] 1f2 [9]
1116 'M' ( 77) |11101111| [8] ef [8]
1117 'N' ( 78) |11111001|1 [9] 1f3 [9]
1118 'O' ( 79) |11111010|0 [9] 1f4 [9]
1119 'P' ( 80) |11111010|1 [9] 1f5 [9]
1120 'Q' ( 81) |11111011|0 [9] 1f6 [9]
1121 'R' ( 82) |11111011|1 [9] 1f7 [9]
1122 'S' ( 83) |11110000| [8] f0 [8]
1123 'T' ( 84) |11110001| [8] f1 [8]
1124 'U' ( 85) |11111100|0 [9] 1f8 [9]
1125 'V' ( 86) |11111100|1 [9] 1f9 [9]
1126 'W' ( 87) |11111101|0 [9] 1fa [9]
1127 'X' ( 88) |11111101|1 [9] 1fb [9]
1128 'Y' ( 89) |11111110|0 [9] 1fc [9]
1129 'Z' ( 90) |11111111|00 [10] 3fc [10]
1130 '[' ( 91) |11111111|111100 [14] 3ffc [14]
1131 '\' ( 92) |11111111|11111111|11111011|010 [27] 7ffffda [27]
1132 ']' ( 93) |11111111|11100 [13] 1ffc [13]
1133 '^' ( 94) |11111111|111101 [14] 3ffd [14]
1134 '_' ( 95) |101110 [6] 2e [6]
1135 '`' ( 96) |11111111|11111111|110 [19] 7fffe [19]
1136 'a' ( 97) |01000 [5] 8 [5]
1137 'b' ( 98) |101111 [6] 2f [6]
1138 'c' ( 99) |01001 [5] 9 [5]
1139 'd' (100) |110000 [6] 30 [6]
1140 'e' (101) |0001 [4] 1 [4]
1141 'f' (102) |110001 [6] 31 [6]
1142 'g' (103) |110010 [6] 32 [6]
1143 'h' (104) |110011 [6] 33 [6]
1144 'i' (105) |01010 [5] a [5]
1145 'j' (106) |1110001 [7] 71 [7]
1146 'k' (107) |1110010 [7] 72 [7]
1147 'l' (108) |01011 [5] b [5]
1148 'm' (109) |110100 [6] 34 [6]
1149 'n' (110) |01100 [5] c [5]
1150 'o' (111) |01101 [5] d [5]
1151 'p' (112) |01110 [5] e [5]
1152 'q' (113) |11110010| [8] f2 [8]
1153 'r' (114) |01111 [5] f [5]
1154 's' (115) |10000 [5] 10 [5]
1155 't' (116) |10001 [5] 11 [5]
1156 'u' (117) |110101 [6] 35 [6]
1157 'v' (118) |1110011 [7] 73 [7]
1158 'w' (119) |110110 [6] 36 [6]
1159 'x' (120) |11110011| [8] f3 [8]
1160 'y' (121) |11110100| [8] f4 [8]
1161 'z' (122) |11110101| [8] f5 [8]
1162 '{' (123) |11111111|11111110|1 [17] 1fffd [17]
1163 '|' (124) |11111111|101 [11] 7fd [11]
1164 '}' (125) |11111111|11111111|0 [17] 1fffe [17]
1165 '~' (126) |11111111|1101 [12] ffd [12]
1166 (127) |11111111|11111111|11111011|011 [27] 7ffffdb [27]
1167 (128) |11111111|11111111|11111011|100 [27] 7ffffdc [27]
1168 (129) |11111111|11111111|11111011|101 [27] 7ffffdd [27]
1169 (130) |11111111|11111111|11111011|110 [27] 7ffffde [27]
1170 (131) |11111111|11111111|11111011|111 [27] 7ffffdf [27]
1171 (132) |11111111|11111111|11111100|000 [27] 7ffffe0 [27]
1172 (133) |11111111|11111111|11111100|001 [27] 7ffffe1 [27]
1173 (134) |11111111|11111111|11111100|010 [27] 7ffffe2 [27]
1174 (135) |11111111|11111111|11111100|011 [27] 7ffffe3 [27]
1175 (136) |11111111|11111111|11111100|100 [27] 7ffffe4 [27]
1176 (137) |11111111|11111111|11111100|101 [27] 7ffffe5 [27]
1177 (138) |11111111|11111111|11111100|110 [27] 7ffffe6 [27]
1178 (139) |11111111|11111111|11111100|111 [27] 7ffffe7 [27]
1179 (140) |11111111|11111111|11111101|000 [27] 7ffffe8 [27]
1180 (141) |11111111|11111111|11111101|001 [27] 7ffffe9 [27]
1181 (142) |11111111|11111111|11111101|010 [27] 7ffffea [27]
1182 (143) |11111111|11111111|11111101|011 [27] 7ffffeb [27]
1183 (144) |11111111|11111111|11111101|100 [27] 7ffffec [27]
1184 (145) |11111111|11111111|11111101|101 [27] 7ffffed [27]
1185 (146) |11111111|11111111|11111101|110 [27] 7ffffee [27]
1186 (147) |11111111|11111111|11111101|111 [27] 7ffffef [27]
1187 (148) |11111111|11111111|11111110|000 [27] 7fffff0 [27]
1188 (149) |11111111|11111111|11111110|001 [27] 7fffff1 [27]
1189 (150) |11111111|11111111|11111110|010 [27] 7fffff2 [27]
1190 (151) |11111111|11111111|11111110|011 [27] 7fffff3 [27]
1191 (152) |11111111|11111111|11111110|100 [27] 7fffff4 [27]
1192 (153) |11111111|11111111|11111110|101 [27] 7fffff5 [27]
1193 (154) |11111111|11111111|11111110|110 [27] 7fffff6 [27]
1194 (155) |11111111|11111111|11111110|111 [27] 7fffff7 [27]
1195 (156) |11111111|11111111|11111111|000 [27] 7fffff8 [27]
1196 (157) |11111111|11111111|11111111|001 [27] 7fffff9 [27]
1197 (158) |11111111|11111111|11111111|010 [27] 7fffffa [27]
1198 (159) |11111111|11111111|11111111|011 [27] 7fffffb [27]
1199 (160) |11111111|11111111|11111111|100 [27] 7fffffc [27]
1200 (161) |11111111|11111111|11111111|101 [27] 7fffffd [27]
1201 (162) |11111111|11111111|11111111|110 [27] 7fffffe [27]
1202 (163) |11111111|11111111|11111111|111 [27] 7ffffff [27]
1203 (164) |11111111|11111111|11100000|00 [26] 3ffff80 [26]
1204 (165) |11111111|11111111|11100000|01 [26] 3ffff81 [26]
1205 (166) |11111111|11111111|11100000|10 [26] 3ffff82 [26]
1206 (167) |11111111|11111111|11100000|11 [26] 3ffff83 [26]
1207 (168) |11111111|11111111|11100001|00 [26] 3ffff84 [26]
1208 (169) |11111111|11111111|11100001|01 [26] 3ffff85 [26]
1209 (170) |11111111|11111111|11100001|10 [26] 3ffff86 [26]
1210 (171) |11111111|11111111|11100001|11 [26] 3ffff87 [26]
1211 (172) |11111111|11111111|11100010|00 [26] 3ffff88 [26]
1212 (173) |11111111|11111111|11100010|01 [26] 3ffff89 [26]
1213 (174) |11111111|11111111|11100010|10 [26] 3ffff8a [26]
1214 (175) |11111111|11111111|11100010|11 [26] 3ffff8b [26]
1215 (176) |11111111|11111111|11100011|00 [26] 3ffff8c [26]
1216 (177) |11111111|11111111|11100011|01 [26] 3ffff8d [26]
1217 (178) |11111111|11111111|11100011|10 [26] 3ffff8e [26]
1218 (179) |11111111|11111111|11100011|11 [26] 3ffff8f [26]
1219 (180) |11111111|11111111|11100100|00 [26] 3ffff90 [26]
1220 (181) |11111111|11111111|11100100|01 [26] 3ffff91 [26]
1221 (182) |11111111|11111111|11100100|10 [26] 3ffff92 [26]
1222 (183) |11111111|11111111|11100100|11 [26] 3ffff93 [26]
1223 (184) |11111111|11111111|11100101|00 [26] 3ffff94 [26]
1224 (185) |11111111|11111111|11100101|01 [26] 3ffff95 [26]
1225 (186) |11111111|11111111|11100101|10 [26] 3ffff96 [26]
1226 (187) |11111111|11111111|11100101|11 [26] 3ffff97 [26]
1227 (188) |11111111|11111111|11100110|00 [26] 3ffff98 [26]
1228 (189) |11111111|11111111|11100110|01 [26] 3ffff99 [26]
1229 (190) |11111111|11111111|11100110|10 [26] 3ffff9a [26]
1230 (191) |11111111|11111111|11100110|11 [26] 3ffff9b [26]
1231 (192) |11111111|11111111|11100111|00 [26] 3ffff9c [26]
1232 (193) |11111111|11111111|11100111|01 [26] 3ffff9d [26]
1233 (194) |11111111|11111111|11100111|10 [26] 3ffff9e [26]
1234 (195) |11111111|11111111|11100111|11 [26] 3ffff9f [26]
1235 (196) |11111111|11111111|11101000|00 [26] 3ffffa0 [26]
1236 (197) |11111111|11111111|11101000|01 [26] 3ffffa1 [26]
1237 (198) |11111111|11111111|11101000|10 [26] 3ffffa2 [26]
1238 (199) |11111111|11111111|11101000|11 [26] 3ffffa3 [26]
1239 (200) |11111111|11111111|11101001|00 [26] 3ffffa4 [26]
1240 (201) |11111111|11111111|11101001|01 [26] 3ffffa5 [26]
1241 (202) |11111111|11111111|11101001|10 [26] 3ffffa6 [26]
1242 (203) |11111111|11111111|11101001|11 [26] 3ffffa7 [26]
1243 (204) |11111111|11111111|11101010|00 [26] 3ffffa8 [26]
1244 (205) |11111111|11111111|11101010|01 [26] 3ffffa9 [26]
1245 (206) |11111111|11111111|11101010|10 [26] 3ffffaa [26]
1246 (207) |11111111|11111111|11101010|11 [26] 3ffffab [26]
1247 (208) |11111111|11111111|11101011|00 [26] 3ffffac [26]
1248 (209) |11111111|11111111|11101011|01 [26] 3ffffad [26]
1249 (210) |11111111|11111111|11101011|10 [26] 3ffffae [26]
1250 (211) |11111111|11111111|11101011|11 [26] 3ffffaf [26]
1251 (212) |11111111|11111111|11101100|00 [26] 3ffffb0 [26]
1252 (213) |11111111|11111111|11101100|01 [26] 3ffffb1 [26]
1253 (214) |11111111|11111111|11101100|10 [26] 3ffffb2 [26]
1254 (215) |11111111|11111111|11101100|11 [26] 3ffffb3 [26]
1255 (216) |11111111|11111111|11101101|00 [26] 3ffffb4 [26]
1256 (217) |11111111|11111111|11101101|01 [26] 3ffffb5 [26]
1257 (218) |11111111|11111111|11101101|10 [26] 3ffffb6 [26]
1258 (219) |11111111|11111111|11101101|11 [26] 3ffffb7 [26]
1259 (220) |11111111|11111111|11101110|00 [26] 3ffffb8 [26]
1260 (221) |11111111|11111111|11101110|01 [26] 3ffffb9 [26]
1261 (222) |11111111|11111111|11101110|10 [26] 3ffffba [26]
1262 (223) |11111111|11111111|11101110|11 [26] 3ffffbb [26]
1263 (224) |11111111|11111111|11101111|00 [26] 3ffffbc [26]
1264 (225) |11111111|11111111|11101111|01 [26] 3ffffbd [26]
1265 (226) |11111111|11111111|11101111|10 [26] 3ffffbe [26]
1266 (227) |11111111|11111111|11101111|11 [26] 3ffffbf [26]
1267 (228) |11111111|11111111|11110000|00 [26] 3ffffc0 [26]
1268 (229) |11111111|11111111|11110000|01 [26] 3ffffc1 [26]
1269 (230) |11111111|11111111|11110000|10 [26] 3ffffc2 [26]
1270 (231) |11111111|11111111|11110000|11 [26] 3ffffc3 [26]
1271 (232) |11111111|11111111|11110001|00 [26] 3ffffc4 [26]
1272 (233) |11111111|11111111|11110001|01 [26] 3ffffc5 [26]
1273 (234) |11111111|11111111|11110001|10 [26] 3ffffc6 [26]
1274 (235) |11111111|11111111|11110001|11 [26] 3ffffc7 [26]
1275 (236) |11111111|11111111|11110010|00 [26] 3ffffc8 [26]
1276 (237) |11111111|11111111|11110010|01 [26] 3ffffc9 [26]
1277 (238) |11111111|11111111|11110010|10 [26] 3ffffca [26]
1278 (239) |11111111|11111111|11110010|11 [26] 3ffffcb [26]
1279 (240) |11111111|11111111|11110011|00 [26] 3ffffcc [26]
1280 (241) |11111111|11111111|11110011|01 [26] 3ffffcd [26]
1281 (242) |11111111|11111111|11110011|10 [26] 3ffffce [26]
1282 (243) |11111111|11111111|11110011|11 [26] 3ffffcf [26]
1283 (244) |11111111|11111111|11110100|00 [26] 3ffffd0 [26]
1284 (245) |11111111|11111111|11110100|01 [26] 3ffffd1 [26]
1285 (246) |11111111|11111111|11110100|10 [26] 3ffffd2 [26]
1286 (247) |11111111|11111111|11110100|11 [26] 3ffffd3 [26]
1287 (248) |11111111|11111111|11110101|00 [26] 3ffffd4 [26]
1288 (249) |11111111|11111111|11110101|01 [26] 3ffffd5 [26]
1289 (250) |11111111|11111111|11110101|10 [26] 3ffffd6 [26]
1290 (251) |11111111|11111111|11110101|11 [26] 3ffffd7 [26]
1291 (252) |11111111|11111111|11110110|00 [26] 3ffffd8 [26]
1292 (253) |11111111|11111111|11110110|01 [26] 3ffffd9 [26]
1293 (254) |11111111|11111111|11110110|10 [26] 3ffffda [26]
1294 (255) |11111111|11111111|11110110|11 [26] 3ffffdb [26]
1295 EOS (256) |11111111|11111111|11110111|00 [26] 3ffffdc [26]
1297 Appendix D. Huffman Codes for Responses
1299 The following Huffman codes are used when encoding string literals in
1300 the server to client direction. These codes apply for both responses
1301 to client requests and for push-promises.
1303 [[anchor11: This table may need to be regenerated.]]
1305 aligned aligned
1306 to len to len
1307 MSB in LSB in
1308 sym as bits bits as hex bits
1309 ( 0) |11111111|11111111|11011110|0 [25] 1ffffbc [25]
1310 ( 1) |11111111|11111111|11011110|1 [25] 1ffffbd [25]
1311 ( 2) |11111111|11111111|11011111|0 [25] 1ffffbe [25]
1312 ( 3) |11111111|11111111|11011111|1 [25] 1ffffbf [25]
1313 ( 4) |11111111|11111111|11100000|0 [25] 1ffffc0 [25]
1314 ( 5) |11111111|11111111|11100000|1 [25] 1ffffc1 [25]
1315 ( 6) |11111111|11111111|11100001|0 [25] 1ffffc2 [25]
1316 ( 7) |11111111|11111111|11100001|1 [25] 1ffffc3 [25]
1317 ( 8) |11111111|11111111|11100010|0 [25] 1ffffc4 [25]
1318 ( 9) |11111111|11111111|11100010|1 [25] 1ffffc5 [25]
1319 ( 10) |11111111|11111111|11100011|0 [25] 1ffffc6 [25]
1320 ( 11) |11111111|11111111|11100011|1 [25] 1ffffc7 [25]
1321 ( 12) |11111111|11111111|11100100|0 [25] 1ffffc8 [25]
1322 ( 13) |11111111|11111111|11100100|1 [25] 1ffffc9 [25]
1323 ( 14) |11111111|11111111|11100101|0 [25] 1ffffca [25]
1324 ( 15) |11111111|11111111|11100101|1 [25] 1ffffcb [25]
1325 ( 16) |11111111|11111111|11100110|0 [25] 1ffffcc [25]
1326 ( 17) |11111111|11111111|11100110|1 [25] 1ffffcd [25]
1327 ( 18) |11111111|11111111|11100111|0 [25] 1ffffce [25]
1328 ( 19) |11111111|11111111|11100111|1 [25] 1ffffcf [25]
1329 ( 20) |11111111|11111111|11101000|0 [25] 1ffffd0 [25]
1330 ( 21) |11111111|11111111|11101000|1 [25] 1ffffd1 [25]
1331 ( 22) |11111111|11111111|11101001|0 [25] 1ffffd2 [25]
1332 ( 23) |11111111|11111111|11101001|1 [25] 1ffffd3 [25]
1333 ( 24) |11111111|11111111|11101010|0 [25] 1ffffd4 [25]
1334 ( 25) |11111111|11111111|11101010|1 [25] 1ffffd5 [25]
1335 ( 26) |11111111|11111111|11101011|0 [25] 1ffffd6 [25]
1336 ( 27) |11111111|11111111|11101011|1 [25] 1ffffd7 [25]
1337 ( 28) |11111111|11111111|11101100|0 [25] 1ffffd8 [25]
1338 ( 29) |11111111|11111111|11101100|1 [25] 1ffffd9 [25]
1339 ( 30) |11111111|11111111|11101101|0 [25] 1ffffda [25]
1340 ( 31) |11111111|11111111|11101101|1 [25] 1ffffdb [25]
1341 ' ' ( 32) |0000 [4] 0 [4]
1342 '!' ( 33) |11111111|1010 [12] ffa [12]
1343 '"' ( 34) |1101010 [7] 6a [7]
1344 '#' ( 35) |11111111|11010 [13] 1ffa [13]
1345 '$' ( 36) |11111111|111100 [14] 3ffc [14]
1346 '%' ( 37) |11110110|0 [9] 1ec [9]
1347 '&' ( 38) |11111110|00 [10] 3f8 [10]
1348 ''' ( 39) |11111111|11011 [13] 1ffb [13]
1349 '(' ( 40) |11110110|1 [9] 1ed [9]
1350 ')' ( 41) |11110111|0 [9] 1ee [9]
1351 '*' ( 42) |11111111|1011 [12] ffb [12]
1352 '+' ( 43) |11111111|010 [11] 7fa [11]
1353 ',' ( 44) |100010 [6] 22 [6]
1354 '-' ( 45) |100011 [6] 23 [6]
1355 '.' ( 46) |100100 [6] 24 [6]
1356 '/' ( 47) |1101011 [7] 6b [7]
1357 '0' ( 48) |0001 [4] 1 [4]
1358 '1' ( 49) |0010 [4] 2 [4]
1359 '2' ( 50) |0011 [4] 3 [4]
1360 '3' ( 51) |01000 [5] 8 [5]
1361 '4' ( 52) |01001 [5] 9 [5]
1362 '5' ( 53) |01010 [5] a [5]
1363 '6' ( 54) |100101 [6] 25 [6]
1364 '7' ( 55) |100110 [6] 26 [6]
1365 '8' ( 56) |01011 [5] b [5]
1366 '9' ( 57) |01100 [5] c [5]
1367 ':' ( 58) |01101 [5] d [5]
1368 ';' ( 59) |11110111|1 [9] 1ef [9]
1369 '<' ( 60) |11111111|11111010| [16] fffa [16]
1370 '=' ( 61) |1101100 [7] 6c [7]
1371 '>' ( 62) |11111111|11100 [13] 1ffc [13]
1372 '?' ( 63) |11111111|1100 [12] ffc [12]
1373 '@' ( 64) |11111111|11111011| [16] fffb [16]
1374 'A' ( 65) |1101101 [7] 6d [7]
1375 'B' ( 66) |11101010| [8] ea [8]
1376 'C' ( 67) |11101011| [8] eb [8]
1377 'D' ( 68) |11101100| [8] ec [8]
1378 'E' ( 69) |11101101| [8] ed [8]
1379 'F' ( 70) |11101110| [8] ee [8]
1380 'G' ( 71) |100111 [6] 27 [6]
1381 'H' ( 72) |11111000|0 [9] 1f0 [9]
1382 'I' ( 73) |11101111| [8] ef [8]
1383 'J' ( 74) |11110000| [8] f0 [8]
1384 'K' ( 75) |11111110|01 [10] 3f9 [10]
1385 'L' ( 76) |11111000|1 [9] 1f1 [9]
1386 'M' ( 77) |101000 [6] 28 [6]
1387 'N' ( 78) |11110001| [8] f1 [8]
1388 'O' ( 79) |11110010| [8] f2 [8]
1389 'P' ( 80) |11111001|0 [9] 1f2 [9]
1390 'Q' ( 81) |11111110|10 [10] 3fa [10]
1391 'R' ( 82) |11111001|1 [9] 1f3 [9]
1392 'S' ( 83) |101001 [6] 29 [6]
1393 'T' ( 84) |01110 [5] e [5]
1394 'U' ( 85) |11111010|0 [9] 1f4 [9]
1395 'V' ( 86) |11111010|1 [9] 1f5 [9]
1396 'W' ( 87) |11110011| [8] f3 [8]
1397 'X' ( 88) |11111110|11 [10] 3fb [10]
1398 'Y' ( 89) |11111011|0 [9] 1f6 [9]
1399 'Z' ( 90) |11111111|00 [10] 3fc [10]
1400 '[' ( 91) |11111111|011 [11] 7fb [11]
1401 '\' ( 92) |11111111|11101 [13] 1ffd [13]
1402 ']' ( 93) |11111111|100 [11] 7fc [11]
1403 '^' ( 94) |11111111|1111100 [15] 7ffc [15]
1404 '_' ( 95) |11111011|1 [9] 1f7 [9]
1405 '`' ( 96) |11111111|11111111|0 [17] 1fffe [17]
1406 'a' ( 97) |01111 [5] f [5]
1407 'b' ( 98) |1101110 [7] 6e [7]
1408 'c' ( 99) |101010 [6] 2a [6]
1409 'd' (100) |101011 [6] 2b [6]
1410 'e' (101) |10000 [5] 10 [5]
1411 'f' (102) |1101111 [7] 6f [7]
1412 'g' (103) |1110000 [7] 70 [7]
1413 'h' (104) |1110001 [7] 71 [7]
1414 'i' (105) |101100 [6] 2c [6]
1415 'j' (106) |11111100|0 [9] 1f8 [9]
1416 'k' (107) |11111100|1 [9] 1f9 [9]
1417 'l' (108) |1110010 [7] 72 [7]
1418 'm' (109) |101101 [6] 2d [6]
1419 'n' (110) |101110 [6] 2e [6]
1420 'o' (111) |101111 [6] 2f [6]
1421 'p' (112) |110000 [6] 30 [6]
1422 'q' (113) |11111101|0 [9] 1fa [9]
1423 'r' (114) |110001 [6] 31 [6]
1424 's' (115) |110010 [6] 32 [6]
1425 't' (116) |110011 [6] 33 [6]
1426 'u' (117) |110100 [6] 34 [6]
1427 'v' (118) |1110011 [7] 73 [7]
1428 'w' (119) |11110100| [8] f4 [8]
1429 'x' (120) |1110100 [7] 74 [7]
1430 'y' (121) |11110101| [8] f5 [8]
1431 'z' (122) |11111101|1 [9] 1fb [9]
1432 '{' (123) |11111111|11111100| [16] fffc [16]
1433 '|' (124) |11111111|111101 [14] 3ffd [14]
1434 '}' (125) |11111111|11111101| [16] fffd [16]
1435 '~' (126) |11111111|11111110| [16] fffe [16]
1436 (127) |11111111|11111111|11101110|0 [25] 1ffffdc [25]
1437 (128) |11111111|11111111|11101110|1 [25] 1ffffdd [25]
1438 (129) |11111111|11111111|11101111|0 [25] 1ffffde [25]
1439 (130) |11111111|11111111|11101111|1 [25] 1ffffdf [25]
1440 (131) |11111111|11111111|11110000|0 [25] 1ffffe0 [25]
1441 (132) |11111111|11111111|11110000|1 [25] 1ffffe1 [25]
1442 (133) |11111111|11111111|11110001|0 [25] 1ffffe2 [25]
1443 (134) |11111111|11111111|11110001|1 [25] 1ffffe3 [25]
1444 (135) |11111111|11111111|11110010|0 [25] 1ffffe4 [25]
1445 (136) |11111111|11111111|11110010|1 [25] 1ffffe5 [25]
1446 (137) |11111111|11111111|11110011|0 [25] 1ffffe6 [25]
1447 (138) |11111111|11111111|11110011|1 [25] 1ffffe7 [25]
1448 (139) |11111111|11111111|11110100|0 [25] 1ffffe8 [25]
1449 (140) |11111111|11111111|11110100|1 [25] 1ffffe9 [25]
1450 (141) |11111111|11111111|11110101|0 [25] 1ffffea [25]
1451 (142) |11111111|11111111|11110101|1 [25] 1ffffeb [25]
1452 (143) |11111111|11111111|11110110|0 [25] 1ffffec [25]
1453 (144) |11111111|11111111|11110110|1 [25] 1ffffed [25]
1454 (145) |11111111|11111111|11110111|0 [25] 1ffffee [25]
1455 (146) |11111111|11111111|11110111|1 [25] 1ffffef [25]
1456 (147) |11111111|11111111|11111000|0 [25] 1fffff0 [25]
1457 (148) |11111111|11111111|11111000|1 [25] 1fffff1 [25]
1458 (149) |11111111|11111111|11111001|0 [25] 1fffff2 [25]
1459 (150) |11111111|11111111|11111001|1 [25] 1fffff3 [25]
1460 (151) |11111111|11111111|11111010|0 [25] 1fffff4 [25]
1461 (152) |11111111|11111111|11111010|1 [25] 1fffff5 [25]
1462 (153) |11111111|11111111|11111011|0 [25] 1fffff6 [25]
1463 (154) |11111111|11111111|11111011|1 [25] 1fffff7 [25]
1464 (155) |11111111|11111111|11111100|0 [25] 1fffff8 [25]
1465 (156) |11111111|11111111|11111100|1 [25] 1fffff9 [25]
1466 (157) |11111111|11111111|11111101|0 [25] 1fffffa [25]
1467 (158) |11111111|11111111|11111101|1 [25] 1fffffb [25]
1468 (159) |11111111|11111111|11111110|0 [25] 1fffffc [25]
1469 (160) |11111111|11111111|11111110|1 [25] 1fffffd [25]
1470 (161) |11111111|11111111|11111111|0 [25] 1fffffe [25]
1471 (162) |11111111|11111111|11111111|1 [25] 1ffffff [25]
1472 (163) |11111111|11111111|10000000| [24] ffff80 [24]
1473 (164) |11111111|11111111|10000001| [24] ffff81 [24]
1474 (165) |11111111|11111111|10000010| [24] ffff82 [24]
1475 (166) |11111111|11111111|10000011| [24] ffff83 [24]
1476 (167) |11111111|11111111|10000100| [24] ffff84 [24]
1477 (168) |11111111|11111111|10000101| [24] ffff85 [24]
1478 (169) |11111111|11111111|10000110| [24] ffff86 [24]
1479 (170) |11111111|11111111|10000111| [24] ffff87 [24]
1480 (171) |11111111|11111111|10001000| [24] ffff88 [24]
1481 (172) |11111111|11111111|10001001| [24] ffff89 [24]
1482 (173) |11111111|11111111|10001010| [24] ffff8a [24]
1483 (174) |11111111|11111111|10001011| [24] ffff8b [24]
1484 (175) |11111111|11111111|10001100| [24] ffff8c [24]
1485 (176) |11111111|11111111|10001101| [24] ffff8d [24]
1486 (177) |11111111|11111111|10001110| [24] ffff8e [24]
1487 (178) |11111111|11111111|10001111| [24] ffff8f [24]
1488 (179) |11111111|11111111|10010000| [24] ffff90 [24]
1489 (180) |11111111|11111111|10010001| [24] ffff91 [24]
1490 (181) |11111111|11111111|10010010| [24] ffff92 [24]
1491 (182) |11111111|11111111|10010011| [24] ffff93 [24]
1492 (183) |11111111|11111111|10010100| [24] ffff94 [24]
1493 (184) |11111111|11111111|10010101| [24] ffff95 [24]
1494 (185) |11111111|11111111|10010110| [24] ffff96 [24]
1495 (186) |11111111|11111111|10010111| [24] ffff97 [24]
1496 (187) |11111111|11111111|10011000| [24] ffff98 [24]
1497 (188) |11111111|11111111|10011001| [24] ffff99 [24]
1498 (189) |11111111|11111111|10011010| [24] ffff9a [24]
1499 (190) |11111111|11111111|10011011| [24] ffff9b [24]
1500 (191) |11111111|11111111|10011100| [24] ffff9c [24]
1501 (192) |11111111|11111111|10011101| [24] ffff9d [24]
1502 (193) |11111111|11111111|10011110| [24] ffff9e [24]
1503 (194) |11111111|11111111|10011111| [24] ffff9f [24]
1504 (195) |11111111|11111111|10100000| [24] ffffa0 [24]
1505 (196) |11111111|11111111|10100001| [24] ffffa1 [24]
1506 (197) |11111111|11111111|10100010| [24] ffffa2 [24]
1507 (198) |11111111|11111111|10100011| [24] ffffa3 [24]
1508 (199) |11111111|11111111|10100100| [24] ffffa4 [24]
1509 (200) |11111111|11111111|10100101| [24] ffffa5 [24]
1510 (201) |11111111|11111111|10100110| [24] ffffa6 [24]
1511 (202) |11111111|11111111|10100111| [24] ffffa7 [24]
1512 (203) |11111111|11111111|10101000| [24] ffffa8 [24]
1513 (204) |11111111|11111111|10101001| [24] ffffa9 [24]
1514 (205) |11111111|11111111|10101010| [24] ffffaa [24]
1515 (206) |11111111|11111111|10101011| [24] ffffab [24]
1516 (207) |11111111|11111111|10101100| [24] ffffac [24]
1517 (208) |11111111|11111111|10101101| [24] ffffad [24]
1518 (209) |11111111|11111111|10101110| [24] ffffae [24]
1519 (210) |11111111|11111111|10101111| [24] ffffaf [24]
1520 (211) |11111111|11111111|10110000| [24] ffffb0 [24]
1521 (212) |11111111|11111111|10110001| [24] ffffb1 [24]
1522 (213) |11111111|11111111|10110010| [24] ffffb2 [24]
1523 (214) |11111111|11111111|10110011| [24] ffffb3 [24]
1524 (215) |11111111|11111111|10110100| [24] ffffb4 [24]
1525 (216) |11111111|11111111|10110101| [24] ffffb5 [24]
1526 (217) |11111111|11111111|10110110| [24] ffffb6 [24]
1527 (218) |11111111|11111111|10110111| [24] ffffb7 [24]
1528 (219) |11111111|11111111|10111000| [24] ffffb8 [24]
1529 (220) |11111111|11111111|10111001| [24] ffffb9 [24]
1530 (221) |11111111|11111111|10111010| [24] ffffba [24]
1531 (222) |11111111|11111111|10111011| [24] ffffbb [24]
1532 (223) |11111111|11111111|10111100| [24] ffffbc [24]
1533 (224) |11111111|11111111|10111101| [24] ffffbd [24]
1534 (225) |11111111|11111111|10111110| [24] ffffbe [24]
1535 (226) |11111111|11111111|10111111| [24] ffffbf [24]
1536 (227) |11111111|11111111|11000000| [24] ffffc0 [24]
1537 (228) |11111111|11111111|11000001| [24] ffffc1 [24]
1538 (229) |11111111|11111111|11000010| [24] ffffc2 [24]
1539 (230) |11111111|11111111|11000011| [24] ffffc3 [24]
1540 (231) |11111111|11111111|11000100| [24] ffffc4 [24]
1541 (232) |11111111|11111111|11000101| [24] ffffc5 [24]
1542 (233) |11111111|11111111|11000110| [24] ffffc6 [24]
1543 (234) |11111111|11111111|11000111| [24] ffffc7 [24]
1544 (235) |11111111|11111111|11001000| [24] ffffc8 [24]
1545 (236) |11111111|11111111|11001001| [24] ffffc9 [24]
1546 (237) |11111111|11111111|11001010| [24] ffffca [24]
1547 (238) |11111111|11111111|11001011| [24] ffffcb [24]
1548 (239) |11111111|11111111|11001100| [24] ffffcc [24]
1549 (240) |11111111|11111111|11001101| [24] ffffcd [24]
1550 (241) |11111111|11111111|11001110| [24] ffffce [24]
1551 (242) |11111111|11111111|11001111| [24] ffffcf [24]
1552 (243) |11111111|11111111|11010000| [24] ffffd0 [24]
1553 (244) |11111111|11111111|11010001| [24] ffffd1 [24]
1554 (245) |11111111|11111111|11010010| [24] ffffd2 [24]
1555 (246) |11111111|11111111|11010011| [24] ffffd3 [24]
1556 (247) |11111111|11111111|11010100| [24] ffffd4 [24]
1557 (248) |11111111|11111111|11010101| [24] ffffd5 [24]
1558 (249) |11111111|11111111|11010110| [24] ffffd6 [24]
1559 (250) |11111111|11111111|11010111| [24] ffffd7 [24]
1560 (251) |11111111|11111111|11011000| [24] ffffd8 [24]
1561 (252) |11111111|11111111|11011001| [24] ffffd9 [24]
1562 (253) |11111111|11111111|11011010| [24] ffffda [24]
1563 (254) |11111111|11111111|11011011| [24] ffffdb [24]
1564 (255) |11111111|11111111|11011100| [24] ffffdc [24]
1565 EOS (256) |11111111|11111111|11011101| [24] ffffdd [24]
1567 Appendix E. Examples
1569 A number of examples are worked through here, for both requests and
1570 responses, and with and without Huffman coding.
1572 E.1. Header Field Representation Examples
1574 This section show several independent representation examples.
1576 E.1.1. Literal Header Field with Indexing
1578 The header field representation uses a literal name and a literal
1579 value.
1581 Header set to encode:
1583 custom-key: custom-header
1585 Reference set: empty.
1587 Hex dump of encoded data:
1589 000a 6375 7374 6f6d 2d6b 6579 0d63 7573 | ..custom-key.cus
1590 746f 6d2d 6865 6164 6572 | tom-header
1592 Decoding process:
1594 00 | == Literal indexed ==
1595 0a | Literal name (len = 10)
1596 6375 7374 6f6d 2d6b 6579 | custom-key
1597 0d | Literal value (len = 13)
1598 6375 7374 6f6d 2d68 6561 6465 72 | custom-header
1599 | -> custom-key: custom-head\
1600 | er
1602 Header Table (after decoding):
1604 [ 1] (s = 55) custom-key: custom-header
1605 Table size: 55
1607 Decoded header set:
1609 custom-key: custom-header
1611 E.1.2. Literal Header Field without Indexing
1613 The header field representation uses an indexed name and a literal
1614 value.
1616 Header set to encode:
1618 :path: /sample/path
1620 Reference set: empty.
1622 Hex dump of encoded data:
1624 440c 2f73 616d 706c 652f 7061 7468 | D./sample/path
1625 Decoding process:
1627 44 | == Literal not indexed ==
1628 | Indexed name (idx = 4)
1629 | :path
1630 0c | Literal value (len = 12)
1631 2f73 616d 706c 652f 7061 7468 | /sample/path
1632 | -> :path: /sample/path
1634 Header table (after decoding): empty.
1636 Decoded header set:
1638 :path: /sample/path
1640 E.1.3. Indexed Header Field
1642 The header field representation uses an indexed header field, from
1643 the static table. Upon using it, the static table entry is copied
1644 into the header table.
1646 Header set to encode:
1648 :method: GET
1650 Reference set: empty.
1652 Hex dump of encoded data:
1654 82 | .
1656 Decoding process:
1658 82 | == Indexed - Add ==
1659 | idx = 2
1660 | -> :method: GET
1662 Header Table (after decoding):
1664 [ 1] (s = 42) :method: GET
1665 Table size: 42
1667 Decoded header set:
1669 :method: GET
1671 E.1.4. Indexed Header Field from Static Table
1673 The header field representation uses an indexed header field, from
1674 the static table. In this example, the SETTINGS_HEADER_TABLE_SIZE is
1675 set to 0, therefore, the entry is not copied into the header table.
1677 Header set to encode:
1679 :method: GET
1681 Reference set: empty.
1683 Hex dump of encoded data:
1685 82 | .
1687 Decoding process:
1689 82 | == Indexed - Add ==
1690 | idx = 2
1691 | -> :method: GET
1693 Header table (after decoding): empty.
1695 Decoded header set:
1697 :method: GET
1699 E.2. Request Examples without Huffman
1701 This section shows several consecutive header sets, corresponding to
1702 HTTP requests, on the same connection.
1704 E.2.1. First request
1706 Header set to encode:
1708 :method: GET
1709 :scheme: http
1710 :path: /
1711 :authority: www.example.com
1713 Reference set: empty.
1715 Hex dump of encoded data:
1717 8287 8604 0f77 7777 2e65 7861 6d70 6c65 | .....www.example
1718 2e63 6f6d | .com
1720 Decoding process:
1722 82 | == Indexed - Add ==
1723 | idx = 2
1724 | -> :method: GET
1725 87 | == Indexed - Add ==
1726 | idx = 7
1727 | -> :scheme: http
1728 86 | == Indexed - Add ==
1729 | idx = 6
1730 | -> :path: /
1731 04 | == Literal indexed ==
1732 | Indexed name (idx = 4)
1733 | :authority
1734 0f | Literal value (len = 15)
1735 7777 772e 6578 616d 706c 652e 636f 6d | www.example.com
1736 | -> :authority: www.example\
1737 | .com
1739 Header Table (after decoding):
1741 [ 1] (s = 57) :authority: www.example.com
1742 [ 2] (s = 38) :path: /
1743 [ 3] (s = 43) :scheme: http
1744 [ 4] (s = 42) :method: GET
1745 Table size: 180
1747 Decoded header set:
1749 :method: GET
1750 :scheme: http
1751 :path: /
1752 :authority: www.example.com
1754 E.2.2. Second request
1756 This request takes advantage of the differential encoding of header
1757 sets.
1759 Header set to encode:
1761 :method: GET
1762 :scheme: http
1763 :path: /
1764 :authority: www.example.com
1765 cache-control: no-cache
1767 Reference set:
1769 [ 1] :authority: www.example.com
1770 [ 2] :path: /
1771 [ 3] :scheme: http
1772 [ 4] :method: GET
1774 Hex dump of encoded data:
1776 1b08 6e6f 2d63 6163 6865 | ..no-cache
1778 Decoding process:
1780 1b | == Literal indexed ==
1781 | Indexed name (idx = 27)
1782 | cache-control
1783 08 | Literal value (len = 8)
1784 6e6f 2d63 6163 6865 | no-cache
1785 | -> cache-control: no-cache
1787 Header Table (after decoding):
1789 [ 1] (s = 53) cache-control: no-cache
1790 [ 2] (s = 57) :authority: www.example.com
1791 [ 3] (s = 38) :path: /
1792 [ 4] (s = 43) :scheme: http
1793 [ 5] (s = 42) :method: GET
1794 Table size: 233
1796 Decoded header set:
1798 cache-control: no-cache
1799 :authority: www.example.com
1800 :path: /
1801 :scheme: http
1802 :method: GET
1804 E.2.3. Third request
1806 This request has not enough headers in common with the previous
1807 request to take advantage of the differential encoding. Therefore,
1808 the reference set is emptied before encoding the header fields.
1810 Header set to encode:
1812 :method: GET
1813 :scheme: https
1814 :path: /index.html
1815 :authority: www.example.com
1816 custom-key: custom-value
1818 Reference set:
1820 [ 1] cache-control: no-cache
1821 [ 2] :authority: www.example.com
1822 [ 3] :path: /
1823 [ 4] :scheme: http
1824 [ 5] :method: GET
1826 Hex dump of encoded data:
1828 8085 8c8b 8400 0a63 7573 746f 6d2d 6b65 | .......custom-ke
1829 790c 6375 7374 6f6d 2d76 616c 7565 | y.custom-value
1830 Decoding process:
1832 80 | == Empty reference set ==
1833 | idx = 0
1834 85 | == Indexed - Add ==
1835 | idx = 5
1836 | -> :method: GET
1837 8c | == Indexed - Add ==
1838 | idx = 12
1839 | -> :scheme: https
1840 8b | == Indexed - Add ==
1841 | idx = 11
1842 | -> :path: /index.html
1843 84 | == Indexed - Add ==
1844 | idx = 4
1845 | -> :authority: www.example\
1846 | .com
1847 00 | == Literal indexed ==
1848 0a | Literal name (len = 10)
1849 6375 7374 6f6d 2d6b 6579 | custom-key
1850 0c | Literal value (len = 12)
1851 6375 7374 6f6d 2d76 616c 7565 | custom-value
1852 | -> custom-key: custom-valu\
1853 | e
1855 Header Table (after decoding):
1857 [ 1] (s = 54) custom-key: custom-value
1858 [ 2] (s = 48) :path: /index.html
1859 [ 3] (s = 44) :scheme: https
1860 [ 4] (s = 53) cache-control: no-cache
1861 [ 5] (s = 57) :authority: www.example.com
1862 [ 6] (s = 38) :path: /
1863 [ 7] (s = 43) :scheme: http
1864 [ 8] (s = 42) :method: GET
1865 Table size: 379
1867 Decoded header set:
1869 :method: GET
1870 :scheme: https
1871 :path: /index.html
1872 :authority: www.example.com
1873 custom-key: custom-value
1875 E.3. Request Examples with Huffman
1877 This section shows the same examples as the previous section, but
1878 using Huffman encoding for the literal values.
1880 E.3.1. First request
1882 Header set to encode:
1884 :method: GET
1885 :scheme: http
1886 :path: /
1887 :authority: www.example.com
1889 Reference set: empty.
1891 Hex dump of encoded data:
1893 8287 8604 8bdb 6d88 3e68 d1cb 1225 ba7f | ......m..h...%..
1895 Decoding process:
1897 82 | == Indexed - Add ==
1898 | idx = 2
1899 | -> :method: GET
1900 87 | == Indexed - Add ==
1901 | idx = 7
1902 | -> :scheme: http
1903 86 | == Indexed - Add ==
1904 | idx = 6
1905 | -> :path: /
1906 04 | == Literal indexed ==
1907 | Indexed name (idx = 4)
1908 | :authority
1909 8b | Literal value (len = 15)
1910 | Huffman encoded:
1911 db6d 883e 68d1 cb12 25ba 7f | .m..h...%..
1912 | Decoded:
1913 | www.example.com
1914 | -> :authority: www.example\
1915 | .com
1917 Header Table (after decoding):
1919 [ 1] (s = 57) :authority: www.example.com
1920 [ 2] (s = 38) :path: /
1921 [ 3] (s = 43) :scheme: http
1922 [ 4] (s = 42) :method: GET
1923 Table size: 180
1925 Decoded header set:
1927 :method: GET
1928 :scheme: http
1929 :path: /
1930 :authority: www.example.com
1932 E.3.2. Second request
1934 This request takes advantage of the differential encoding of header
1935 sets.
1937 Header set to encode:
1939 :method: GET
1940 :scheme: http
1941 :path: /
1942 :authority: www.example.com
1943 cache-control: no-cache
1945 Reference set:
1947 [ 1] :authority: www.example.com
1948 [ 2] :path: /
1949 [ 3] :scheme: http
1950 [ 4] :method: GET
1952 Hex dump of encoded data:
1954 1b86 6365 4a13 98ff | ..ceJ...
1956 Decoding process:
1958 1b | == Literal indexed ==
1959 | Indexed name (idx = 27)
1960 | cache-control
1961 86 | Literal value (len = 8)
1962 | Huffman encoded:
1963 6365 4a13 98ff | ceJ...
1964 | Decoded:
1965 | no-cache
1966 | -> cache-control: no-cache
1968 Header Table (after decoding):
1970 [ 1] (s = 53) cache-control: no-cache
1971 [ 2] (s = 57) :authority: www.example.com
1972 [ 3] (s = 38) :path: /
1973 [ 4] (s = 43) :scheme: http
1974 [ 5] (s = 42) :method: GET
1975 Table size: 233
1977 Decoded header set:
1979 cache-control: no-cache
1980 :authority: www.example.com
1981 :path: /
1982 :scheme: http
1983 :method: GET
1985 E.3.3. Third request
1987 This request has not enough headers in common with the previous
1988 request to take advantage of the differential encoding. Therefore,
1989 the reference set is emptied before encoding the header fields.
1991 Header set to encode:
1993 :method: GET
1994 :scheme: https
1995 :path: /index.html
1996 :authority: www.example.com
1997 custom-key: custom-value
1998 Reference set:
2000 [ 1] cache-control: no-cache
2001 [ 2] :authority: www.example.com
2002 [ 3] :path: /
2003 [ 4] :scheme: http
2004 [ 5] :method: GET
2006 Hex dump of encoded data:
2008 8085 8c8b 8400 884e b08b 7497 90fa 7f89 | .......N..t.....
2009 4eb0 8b74 979a 17a8 ff | N..t.....
2011 Decoding process:
2013 80 | == Empty reference set ==
2014 | idx = 0
2015 85 | == Indexed - Add ==
2016 | idx = 5
2017 | -> :method: GET
2018 8c | == Indexed - Add ==
2019 | idx = 12
2020 | -> :scheme: https
2021 8b | == Indexed - Add ==
2022 | idx = 11
2023 | -> :path: /index.html
2024 84 | == Indexed - Add ==
2025 | idx = 4
2026 | -> :authority: www.example\
2027 | .com
2028 00 | == Literal indexed ==
2029 88 | Literal name (len = 10)
2030 | Huffman encoded:
2031 4eb0 8b74 9790 fa7f | N..t....
2032 | Decoded:
2033 | custom-key
2034 89 | Literal value (len = 12)
2035 | Huffman encoded:
2036 4eb0 8b74 979a 17a8 ff | N..t.....
2037 | Decoded:
2038 | custom-value
2039 | -> custom-key: custom-valu\
2040 | e
2042 Header Table (after decoding):
2044 [ 1] (s = 54) custom-key: custom-value
2045 [ 2] (s = 48) :path: /index.html
2046 [ 3] (s = 44) :scheme: https
2047 [ 4] (s = 53) cache-control: no-cache
2048 [ 5] (s = 57) :authority: www.example.com
2049 [ 6] (s = 38) :path: /
2050 [ 7] (s = 43) :scheme: http
2051 [ 8] (s = 42) :method: GET
2052 Table size: 379
2054 Decoded header set:
2056 :method: GET
2057 :scheme: https
2058 :path: /index.html
2059 :authority: www.example.com
2060 custom-key: custom-value
2062 E.4. Response Examples without Huffman
2064 This section shows several consecutive header sets, corresponding to
2065 HTTP responses, on the same connection. SETTINGS_HEADER_TABLE_SIZE
2066 is set to the value of 256 octets, causing some evictions to occur.
2068 E.4.1. First response
2070 Header set to encode:
2072 :status: 302
2073 cache-control: private
2074 date: Mon, 21 Oct 2013 20:13:21 GMT
2075 location: https://www.example.com
2077 Reference set: empty.
2079 Hex dump of encoded data:
2081 0803 3330 3218 0770 7269 7661 7465 221d | ..302..private".
2082 4d6f 6e2c 2032 3120 4f63 7420 3230 3133 | Mon, 21 Oct 2013
2083 2032 303a 3133 3a32 3120 474d 5430 1768 | 20:13:21 GMT0.h
2084 7474 7073 3a2f 2f77 7777 2e65 7861 6d70 | ttps://www.examp
2085 6c65 2e63 6f6d | le.com
2086 Decoding process:
2088 08 | == Literal indexed ==
2089 | Indexed name (idx = 8)
2090 | :status
2091 03 | Literal value (len = 3)
2092 3330 32 | 302
2093 | -> :status: 302
2094 18 | == Literal indexed ==
2095 | Indexed name (idx = 24)
2096 | cache-control
2097 07 | Literal value (len = 7)
2098 7072 6976 6174 65 | private
2099 | -> cache-control: private
2100 22 | == Literal indexed ==
2101 | Indexed name (idx = 34)
2102 | date
2103 1d | Literal value (len = 29)
2104 4d6f 6e2c 2032 3120 4f63 7420 3230 3133 | Mon, 21 Oct 2013
2105 2032 303a 3133 3a32 3120 474d 54 | 20:13:21 GMT
2106 | -> date: Mon, 21 Oct 2013 \
2107 | 20:13:21 GMT
2108 30 | == Literal indexed ==
2109 | Indexed name (idx = 48)
2110 | location
2111 17 | Literal value (len = 23)
2112 6874 7470 733a 2f2f 7777 772e 6578 616d | https://www.exam
2113 706c 652e 636f 6d | ple.com
2114 | -> location: https://www.e\
2115 | xample.com
2117 Header Table (after decoding):
2119 [ 1] (s = 63) location: https://www.example.com
2120 [ 2] (s = 65) date: Mon, 21 Oct 2013 20:13:21 GMT
2121 [ 3] (s = 52) cache-control: private
2122 [ 4] (s = 42) :status: 302
2123 Table size: 222
2125 Decoded header set:
2127 :status: 302
2128 cache-control: private
2129 date: Mon, 21 Oct 2013 20:13:21 GMT
2130 location: https://www.example.com
2132 E.4.2. Second response
2134 The (":status", "302") header field is evicted from the header table
2135 to free space to allow adding the (":status", "200") header field to
2136 be copied from the static table into the header table.
2138 Header set to encode:
2140 :status: 200
2141 cache-control: private
2142 date: Mon, 21 Oct 2013 20:13:21 GMT
2143 location: https://www.example.com
2145 Reference set:
2147 [ 1] location: https://www.example.com
2148 [ 2] date: Mon, 21 Oct 2013 20:13:21 GMT
2149 [ 3] cache-control: private
2150 [ 4] :status: 302
2152 Hex dump of encoded data:
2154 848c | ..
2156 Decoding process:
2158 84 | == Indexed - Remove ==
2159 | idx = 4
2160 | -> :status: 302
2161 8c | == Indexed - Add ==
2162 | idx = 12
2163 | - evict: :status: 302
2164 | -> :status: 200
2166 Header Table (after decoding):
2168 [ 1] (s = 42) :status: 200
2169 [ 2] (s = 63) location: https://www.example.com
2170 [ 3] (s = 65) date: Mon, 21 Oct 2013 20:13:21 GMT
2171 [ 4] (s = 52) cache-control: private
2172 Table size: 222
2174 Decoded header set:
2176 :status: 200
2177 location: https://www.example.com
2178 date: Mon, 21 Oct 2013 20:13:21 GMT
2179 cache-control: private
2181 E.4.3. Third response
2183 Several header fields are evicted from the header table during the
2184 processing of this header set. Before evicting a header belonging to
2185 the reference set, it is emitted, by coding it twice as an Indexed
2186 Representation. The first representation removes the header field
2187 from the reference set, the second one adds it again to the reference
2188 set, also emitting it.
2190 Header set to encode:
2192 :status: 200
2193 cache-control: private
2194 date: Mon, 21 Oct 2013 20:13:22 GMT
2195 location: https://www.example.com
2196 content-encoding: gzip
2197 set-cookie: foo=ASDJKHQKBZXOQWEOPIUAXQWEOIU; max-age=3600; version=1
2199 Reference set:
2201 [ 1] :status: 200
2202 [ 2] location: https://www.example.com
2203 [ 3] date: Mon, 21 Oct 2013 20:13:21 GMT
2204 [ 4] cache-control: private
2206 Hex dump of encoded data:
2208 8384 8403 1d4d 6f6e 2c20 3231 204f 6374 | .....Mon, 21 Oct
2209 2032 3031 3320 3230 3a31 333a 3232 2047 | 2013 20:13:22 G
2210 4d54 1d04 677a 6970 8484 8383 3a38 666f | MT..gzip....:8fo
2211 6f3d 4153 444a 4b48 514b 425a 584f 5157 | o=ASDJKHQKBZXOQW
2212 454f 5049 5541 5851 5745 4f49 553b 206d | EOPIUAXQWEOIU; m
2213 6178 2d61 6765 3d33 3630 303b 2076 6572 | ax-age=3600; ver
2214 7369 6f6e 3d31 | sion=1
2216 Decoding process:
2218 83 | == Indexed - Remove ==
2219 | idx = 3
2220 | -> date: Mon, 21 Oct 2013 \
2221 | 20:13:21 GMT
2223 84 | == Indexed - Remove ==
2224 | idx = 4
2225 | -> cache-control: private
2226 84 | == Indexed - Add ==
2227 | idx = 4
2228 | -> cache-control: private
2229 03 | == Literal indexed ==
2230 | Indexed name (idx = 3)
2231 | date
2232 1d | Literal value (len = 29)
2233 4d6f 6e2c 2032 3120 4f63 7420 3230 3133 | Mon, 21 Oct 2013
2234 2032 303a 3133 3a32 3220 474d 54 | 20:13:22 GMT
2235 | - evict: cache-control: pr\
2236 | ivate
2237 | -> date: Mon, 21 Oct 2013 \
2238 | 20:13:22 GMT
2239 1d | == Literal indexed ==
2240 | Indexed name (idx = 29)
2241 | content-encoding
2242 04 | Literal value (len = 4)
2243 677a 6970 | gzip
2244 | - evict: date: Mon, 21 Oct\
2245 | 2013 20:13:21 GMT
2246 | -> content-encoding: gzip
2247 84 | == Indexed - Remove ==
2248 | idx = 4
2249 | -> location: https://www.e\
2250 | xample.com
2251 84 | == Indexed - Add ==
2252 | idx = 4
2253 | -> location: https://www.e\
2254 | xample.com
2255 83 | == Indexed - Remove ==
2256 | idx = 3
2257 | -> :status: 200
2258 83 | == Indexed - Add ==
2259 | idx = 3
2260 | -> :status: 200
2261 3a | == Literal indexed ==
2262 | Indexed name (idx = 58)
2263 | set-cookie
2264 38 | Literal value (len = 56)
2265 666f 6f3d 4153 444a 4b48 514b 425a 584f | foo=ASDJKHQKBZXO
2266 5157 454f 5049 5541 5851 5745 4f49 553b | QWEOPIUAXQWEOIU;
2267 206d 6178 2d61 6765 3d33 3630 303b 2076 | max-age=3600; v
2268 6572 7369 6f6e 3d31 | ersion=1
2269 | - evict: location: https:/\
2270 | /www.example.com
2271 | - evict: :status: 200
2272 | -> set-cookie: foo=ASDJKHQ\
2273 | KBZXOQWEOPIUAXQWEOIU; ma\
2274 | x-age=3600; version=1
2276 Header Table (after decoding):
2278 [ 1] (s = 98) set-cookie: foo=ASDJKHQKBZXOQWEOPIUAXQWEOIU; max-age\
2279 =3600; version=1
2280 [ 2] (s = 52) content-encoding: gzip
2281 [ 3] (s = 65) date: Mon, 21 Oct 2013 20:13:22 GMT
2282 Table size: 215
2284 Decoded header set:
2286 cache-control: private
2287 date: Mon, 21 Oct 2013 20:13:22 GMT
2288 content-encoding: gzip
2289 location: https://www.example.com
2290 :status: 200
2291 set-cookie: foo=ASDJKHQKBZXOQWEOPIUAXQWEOIU; max-age=3600; version=1
2293 E.5. Response Examples with Huffman
2295 This section shows the same examples as the previous section, but
2296 using Huffman encoding for the literal values. The eviction
2297 mechanism uses the length of the decoded literal values, so the same
2298 evictions occurs as in the previous section.
2300 E.5.1. First response
2302 Header set to encode:
2304 :status: 302
2305 cache-control: private
2306 date: Mon, 21 Oct 2013 20:13:21 GMT
2307 location: https://www.example.com
2309 Reference set: empty.
2311 Hex dump of encoded data:
2313 0882 409f 1886 c31b 39bf 387f 2292 a2fb | ..@.....9.8."...
2314 a203 20f2 ab30 3124 018b 490d 3209 e877 | .. ..01$..I.2..w
2315 3093 e39e 7864 dd7a fd3d 3d24 8747 db87 | 0...xd.z.==$.G..
2316 2849 55f6 ff | (IU..
2318 Decoding process:
2320 08 | == Literal indexed ==
2321 | Indexed name (idx = 8)
2322 | :status
2323 82 | Literal value (len = 3)
2324 | Huffman encoded:
2325 409f | @.
2326 | Decoded:
2327 | 302
2328 | -> :status: 302
2329 18 | == Literal indexed ==
2330 | Indexed name (idx = 24)
2331 | cache-control
2332 86 | Literal value (len = 7)
2333 | Huffman encoded:
2334 c31b 39bf 387f | ..9.8.
2335 | Decoded:
2336 | private
2337 | -> cache-control: private
2338 22 | == Literal indexed ==
2339 | Indexed name (idx = 34)
2340 | date
2341 92 | Literal value (len = 29)
2342 | Huffman encoded:
2343 a2fb a203 20f2 ab30 3124 018b 490d 3209 | .... ..01$..I.2.
2344 e877 | .w
2345 | Decoded:
2346 | Mon, 21 Oct 2013 20:13:21 \
2347 | GMT
2348 | -> date: Mon, 21 Oct 2013 \
2349 | 20:13:21 GMT
2350 30 | == Literal indexed ==
2351 | Indexed name (idx = 48)
2352 | location
2353 93 | Literal value (len = 23)
2354 | Huffman encoded:
2355 e39e 7864 dd7a fd3d 3d24 8747 db87 2849 | ..xd.z.==$.G..(I
2356 55f6 ff | U..
2357 | Decoded:
2358 | https://www.example.com
2359 | -> location: https://www.e\
2360 | xample.com
2362 Header Table (after decoding):
2364 [ 1] (s = 63) location: https://www.example.com
2365 [ 2] (s = 65) date: Mon, 21 Oct 2013 20:13:21 GMT
2366 [ 3] (s = 52) cache-control: private
2367 [ 4] (s = 42) :status: 302
2368 Table size: 222
2370 Decoded header set:
2372 :status: 302
2373 cache-control: private
2374 date: Mon, 21 Oct 2013 20:13:21 GMT
2375 location: https://www.example.com
2377 E.5.2. Second response
2379 The (":status", "302") header field is evicted from the header table
2380 to free space to allow adding the (":status", "200") header field to
2381 be copied from the static table into the header table.
2383 Header set to encode:
2385 :status: 200
2386 cache-control: private
2387 date: Mon, 21 Oct 2013 20:13:21 GMT
2388 location: https://www.example.com
2390 Reference set:
2392 [ 1] location: https://www.example.com
2393 [ 2] date: Mon, 21 Oct 2013 20:13:21 GMT
2394 [ 3] cache-control: private
2395 [ 4] :status: 302
2397 Hex dump of encoded data:
2399 848c | ..
2401 Decoding process:
2403 84 | == Indexed - Remove ==
2404 | idx = 4
2405 | -> :status: 302
2406 8c | == Indexed - Add ==
2407 | idx = 12
2408 | - evict: :status: 302
2409 | -> :status: 200
2411 Header Table (after decoding):
2413 [ 1] (s = 42) :status: 200
2414 [ 2] (s = 63) location: https://www.example.com
2415 [ 3] (s = 65) date: Mon, 21 Oct 2013 20:13:21 GMT
2416 [ 4] (s = 52) cache-control: private
2417 Table size: 222
2419 Decoded header set:
2421 :status: 200
2422 location: https://www.example.com
2423 date: Mon, 21 Oct 2013 20:13:21 GMT
2424 cache-control: private
2426 E.5.3. Third response
2428 Several header fields are evicted from the header table during the
2429 processing of this header set. Before evicting a header belonging to
2430 the reference set, it is emitted, by coding it twice as an Indexed
2431 Representation. The first representation removes the header field
2432 from the reference set, the second one adds it again to the reference
2433 set, also emitting it.
2435 Header set to encode:
2437 :status: 200
2438 cache-control: private
2439 date: Mon, 21 Oct 2013 20:13:22 GMT
2440 location: https://www.example.com
2441 content-encoding: gzip
2442 set-cookie: foo=ASDJKHQKBZXOQWEOPIUAXQWEOIU; max-age=3600; version=1
2443 Reference set:
2445 [ 1] :status: 200
2446 [ 2] location: https://www.example.com
2447 [ 3] date: Mon, 21 Oct 2013 20:13:21 GMT
2448 [ 4] cache-control: private
2450 Hex dump of encoded data:
2452 8384 8403 92a2 fba2 0320 f2ab 3031 2401 | ......... ..01$.
2453 8b49 0d33 09e8 771d 84e1 fbb3 0f84 8483 | .I.3..w.........
2454 833a b3df 7dfb 36d3 d9e1 fcfc 3faf e7ab | .:..}.6.....?...
2455 fcfe fcbf af3e df2f 977f d36f f7fd 79f6 | ......./...o..y.
2456 f977 fd3d e16b fa46 fe10 d889 447d e1ce | .w.=.k.F....D}..
2457 18e5 65f7 6c2f | ..e.l/
2459 Decoding process:
2461 83 | == Indexed - Remove ==
2462 | idx = 3
2463 | -> date: Mon, 21 Oct 2013 \
2464 | 20:13:21 GMT
2465 84 | == Indexed - Remove ==
2466 | idx = 4
2467 | -> cache-control: private
2468 84 | == Indexed - Add ==
2469 | idx = 4
2470 | -> cache-control: private
2471 03 | == Literal indexed ==
2472 | Indexed name (idx = 3)
2473 | date
2474 92 | Literal value (len = 29)
2475 | Huffman encoded:
2476 a2fb a203 20f2 ab30 3124 018b 490d 3309 | .... ..01$..I.3.
2477 e877 | .w
2478 | Decoded:
2479 | Mon, 21 Oct 2013 20:13:22 \
2480 | GMT
2481 | - evict: cache-control: pr\
2482 | ivate
2483 | -> date: Mon, 21 Oct 2013 \
2484 | 20:13:22 GMT
2485 1d | == Literal indexed ==
2486 | Indexed name (idx = 29)
2487 | content-encoding
2488 84 | Literal value (len = 4)
2489 | Huffman encoded:
2490 e1fb b30f | ....
2492 | Decoded:
2493 | gzip
2494 | - evict: date: Mon, 21 Oct\
2495 | 2013 20:13:21 GMT
2496 | -> content-encoding: gzip
2497 84 | == Indexed - Remove ==
2498 | idx = 4
2499 | -> location: https://www.e\
2500 | xample.com
2501 84 | == Indexed - Add ==
2502 | idx = 4
2503 | -> location: https://www.e\
2504 | xample.com
2505 83 | == Indexed - Remove ==
2506 | idx = 3
2507 | -> :status: 200
2508 83 | == Indexed - Add ==
2509 | idx = 3
2510 | -> :status: 200
2511 3a | == Literal indexed ==
2512 | Indexed name (idx = 58)
2513 | set-cookie
2514 b3 | Literal value (len = 56)
2515 | Huffman encoded:
2516 df7d fb36 d3d9 e1fc fc3f afe7 abfc fefc | .}.6.....?......
2517 bfaf 3edf 2f97 7fd3 6ff7 fd79 f6f9 77fd | ..../...o..y..w.
2518 3de1 6bfa 46fe 10d8 8944 7de1 ce18 e565 | =.k.F....D}....e
2519 f76c 2f | .l/
2520 | Decoded:
2521 | foo=ASDJKHQKBZXOQWEOPIUAXQ\
2522 | WEOIU; max-age=3600; versi\
2523 | on=1
2524 | - evict: location: https:/\
2525 | /www.example.com
2526 | - evict: :status: 200
2527 | -> set-cookie: foo=ASDJKHQ\
2528 | KBZXOQWEOPIUAXQWEOIU; ma\
2529 | x-age=3600; version=1
2531 Header Table (after decoding):
2533 [ 1] (s = 98) set-cookie: foo=ASDJKHQKBZXOQWEOPIUAXQWEOIU; max-age\
2534 =3600; version=1
2535 [ 2] (s = 52) content-encoding: gzip
2536 [ 3] (s = 65) date: Mon, 21 Oct 2013 20:13:22 GMT
2537 Table size: 215
2539 Decoded header set:
2541 cache-control: private
2542 date: Mon, 21 Oct 2013 20:13:22 GMT
2543 content-encoding: gzip
2544 location: https://www.example.com
2545 :status: 200
2546 set-cookie: foo=ASDJKHQKBZXOQWEOPIUAXQWEOIU; max-age=3600; version=1
2548 Authors' Addresses
2550 Roberto Peon
2551 Google, Inc
2553 EMail: fenix@google.com
2555 Herve Ruellan
2556 Canon CRF
2558 EMail: herve.ruellan@crf.canon.fr