draft-ietf-httpbis-header-compression-05.txt   draft-ietf-httpbis-header-compression-06.txt 
HTTPbis Working Group R. Peon HTTPbis Working Group R. Peon
Internet-Draft Google, Inc Internet-Draft Google, Inc
Intended status: Informational H. Ruellan Intended status: Standards Track H. Ruellan
Expires: June 7, 2014 Canon CRF Expires: August 17, 2014 Canon CRF
December 4, 2013 February 13, 2014
HPACK - Header Compression for HTTP/2.0 HPACK - Header Compression for HTTP/2
draft-ietf-httpbis-header-compression-05 draft-ietf-httpbis-header-compression-06
Abstract Abstract
This document describes HPACK, a format adapted to efficiently This specification defines HPACK, a compression format for
represent HTTP header fields in the context of HTTP/2.0. efficiently representing HTTP header fields in the context of HTTP/2.
Editorial Note (To be removed by RFC Editor) Editorial Note (To be removed by RFC Editor)
Discussion of this draft takes place on the HTTPBIS working group Discussion of this draft takes place on the HTTPBIS working group
mailing list (ietf-http-wg@w3.org), which is archived at mailing list (ietf-http-wg@w3.org), which is archived at [1].
<http://lists.w3.org/Archives/Public/ietf-http-wg/>.
Working Group information and related documents can be found at Working Group information and related documents can be found at [2]
<http://tools.ietf.org/wg/httpbis/> (Wiki) and (Wiki) and [3] (source code and issues tracker).
<https://github.com/http2/http2-spec> (source code and issues
tracker).
The changes in this draft are summarized in Appendix A.1. The changes in this draft are summarized in Appendix A.1.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on June 7, 2014. This Internet-Draft will expire on August 17, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Outline . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Outline . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Header Field Encoding . . . . . . . . . . . . . . . . . . . . 5 3. Header Field Encoding . . . . . . . . . . . . . . . . . . . . 4
3.1. Encoding Concepts . . . . . . . . . . . . . . . . . . . . 5 3.1. Encoding Concepts . . . . . . . . . . . . . . . . . . . . 4
3.1.1. Encoding Context . . . . . . . . . . . . . . . . . . . 5 3.1.1. Encoding Context . . . . . . . . . . . . . . . . . . 5
3.1.2. Header Table . . . . . . . . . . . . . . . . . . . . . 6 3.1.2. Header Table . . . . . . . . . . . . . . . . . . . . 5
3.1.3. Reference Set . . . . . . . . . . . . . . . . . . . . 6 3.1.3. Reference Set . . . . . . . . . . . . . . . . . . . . 6
3.1.4. Header Field Representation . . . . . . . . . . . . . 7 3.1.4. Header Field Representation . . . . . . . . . . . . . 7
3.1.5. Header Field Emission . . . . . . . . . . . . . . . . 8 3.1.5. Header Field Emission . . . . . . . . . . . . . . . . 8
3.2. Header Block Decoding . . . . . . . . . . . . . . . . . . 8 3.2. Header Block Decoding . . . . . . . . . . . . . . . . . . 8
3.2.1. Header Field Representation Processing . . . . . . . . 8 3.2.1. Header Field Representation Processing . . . . . . . 8
3.2.2. Reference Set Emission . . . . . . . . . . . . . . . . 10 3.2.2. Reference Set Emission . . . . . . . . . . . . . . . 9
3.2.3. Header Set Completion . . . . . . . . . . . . . . . . 10 3.2.3. Header Set Completion . . . . . . . . . . . . . . . . 9
3.3. Header Table Management . . . . . . . . . . . . . . . . . 10 3.3. Header Table Management . . . . . . . . . . . . . . . . . 9
3.3.1. Maximum Table Size . . . . . . . . . . . . . . . . . . 10 3.3.1. Maximum Table Size . . . . . . . . . . . . . . . . . 10
3.3.2. Entry Eviction When Header Table Size Changes . . . . 10 3.3.2. Entry Eviction When Header Table Size Changes . . . . 10
3.3.3. Entry Eviction when Adding New Entries . . . . . . . . 11 3.3.3. Entry Eviction when Adding New Entries . . . . . . . 10
4. Detailed Format . . . . . . . . . . . . . . . . . . . . . . . 11 4. Detailed Format . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Low-level representations . . . . . . . . . . . . . . . . 11 4.1. Low-level representations . . . . . . . . . . . . . . . . 11
4.1.1. Integer representation . . . . . . . . . . . . . . . . 11 4.1.1. Integer representation . . . . . . . . . . . . . . . 11
4.1.2. String Literal Representation . . . . . . . . . . . . 13 4.1.2. String Literal Representation . . . . . . . . . . . . 13
4.2. Indexed Header Field Representation . . . . . . . . . . . 15 4.2. Indexed Header Field Representation . . . . . . . . . . . 15
4.3. Literal Header Field Representation . . . . . . . . . . . 15 4.3. Literal Header Field Representation . . . . . . . . . . . 15
4.3.1. Literal Header Field without Indexing . . . . . . . . 15 4.3.1. Literal Header Field without Indexing . . . . . . . . 15
4.3.2. Literal Header Field with Incremental Indexing . . . . 16 4.3.2. Literal Header Field with Incremental Indexing . . . 16
5. Security Considerations . . . . . . . . . . . . . . . . . . . 18 4.4. Encoding Context Update . . . . . . . . . . . . . . . . . 17
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 5. Security Considerations . . . . . . . . . . . . . . . . . . . 18
6.1. Normative References . . . . . . . . . . . . . . . . . . . 18 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
6.2. Informative References . . . . . . . . . . . . . . . . . . 19 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
7.1. Normative References . . . . . . . . . . . . . . . . . . 19
7.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Change Log (to be removed by RFC Editor before Appendix A. Change Log (to be removed by RFC Editor before
publication . . . . . . . . . . . . . . . . . . . . . 19 publication . . . . . . . . . . . . . . . . . . . . 20
A.1. Since draft-ietf-httpbis-header-compression-04 . . . . . . 19 A.1. Since draft-ietf-httpbis-header-compression-05 . . . . . 20
A.2. Since draft-ietf-httpbis-header-compression-03 . . . . . . 20 A.2. Since draft-ietf-httpbis-header-compression-04 . . . . . 20
A.3. Since draft-ietf-httpbis-header-compression-02 . . . . . . 20 A.3. Since draft-ietf-httpbis-header-compression-03 . . . . . 21
A.4. Since draft-ietf-httpbis-header-compression-01 . . . . . . 20 A.4. Since draft-ietf-httpbis-header-compression-02 . . . . . 21
A.5. Since draft-ietf-httpbis-header-compression-01 . . . . . . 21 A.5. Since draft-ietf-httpbis-header-compression-01 . . . . . 21
Appendix B. Static Table . . . . . . . . . . . . . . . . . . . . 21 A.6. Since draft-ietf-httpbis-header-compression-00 . . . . . 21
Appendix C. Huffman Codes For Requests . . . . . . . . . . . . . 23 Appendix B. Static Table . . . . . . . . . . . . . . . . . . . . 22
Appendix D. Huffman Codes for Responses . . . . . . . . . . . . . 29 Appendix C. Huffman Codes . . . . . . . . . . . . . . . . . . . 24
Appendix E. Examples . . . . . . . . . . . . . . . . . . . . . . 34 Appendix D. Examples . . . . . . . . . . . . . . . . . . . . . . 29
E.1. Header Field Representation Examples . . . . . . . . . . . 34 D.1. Header Field Representation Examples . . . . . . . . . . 30
E.1.1. Literal Header Field with Indexing . . . . . . . . . . 34 D.1.1. Literal Header Field with Indexing . . . . . . . . . 30
E.1.2. Literal Header Field without Indexing . . . . . . . . 35 D.1.2. Literal Header Field without Indexing . . . . . . . . 30
E.1.3. Indexed Header Field . . . . . . . . . . . . . . . . . 36 D.1.3. Indexed Header Field . . . . . . . . . . . . . . . . 31
E.1.4. Indexed Header Field from Static Table . . . . . . . . 37 D.1.4. Indexed Header Field from Static Table . . . . . . . 32
E.2. Request Examples without Huffman . . . . . . . . . . . . . 37 D.2. Request Examples without Huffman . . . . . . . . . . . . 33
E.2.1. First request . . . . . . . . . . . . . . . . . . . . 37 D.2.1. First request . . . . . . . . . . . . . . . . . . . . 33
E.2.2. Second request . . . . . . . . . . . . . . . . . . . . 38 D.2.2. Second request . . . . . . . . . . . . . . . . . . . 34
E.2.3. Third request . . . . . . . . . . . . . . . . . . . . 40 D.2.3. Third request . . . . . . . . . . . . . . . . . . . . 35
E.3. Request Examples with Huffman . . . . . . . . . . . . . . 42 D.3. Request Examples with Huffman . . . . . . . . . . . . . . 37
E.3.1. First request . . . . . . . . . . . . . . . . . . . . 42 D.3.1. First request . . . . . . . . . . . . . . . . . . . . 37
E.3.2. Second request . . . . . . . . . . . . . . . . . . . . 43 D.3.2. Second request . . . . . . . . . . . . . . . . . . . 38
E.3.3. Third request . . . . . . . . . . . . . . . . . . . . 44 D.3.3. Third request . . . . . . . . . . . . . . . . . . . . 40
E.4. Response Examples without Huffman . . . . . . . . . . . . 46 D.4. Response Examples without Huffman . . . . . . . . . . . . 42
E.4.1. First response . . . . . . . . . . . . . . . . . . . . 46 D.4.1. First response . . . . . . . . . . . . . . . . . . . 42
E.4.2. Second response . . . . . . . . . . . . . . . . . . . 48 D.4.2. Second response . . . . . . . . . . . . . . . . . . . 44
E.4.3. Third response . . . . . . . . . . . . . . . . . . . . 49 D.4.3. Third response . . . . . . . . . . . . . . . . . . . 45
E.5. Response Examples with Huffman . . . . . . . . . . . . . . 51 D.5. Response Examples with Huffman . . . . . . . . . . . . . 47
E.5.1. First response . . . . . . . . . . . . . . . . . . . . 51 D.5.1. First response . . . . . . . . . . . . . . . . . . . 47
E.5.2. Second response . . . . . . . . . . . . . . . . . . . 53 D.5.2. Second response . . . . . . . . . . . . . . . . . . . 50
E.5.3. Third response . . . . . . . . . . . . . . . . . . . . 54 D.5.3. Third response . . . . . . . . . . . . . . . . . . . 51
1. Introduction 1. Introduction
This document describes HPACK, a format adapted to efficiently This specification defines HPACK, a compression format for
represent HTTP header fields in the context of HTTP/2.0 (see efficiently representing HTTP header fields in the context of HTTP/2
[HTTP2]). (see [HTTP2]).
2. Overview 2. Overview
In HTTP (see [HTTP-p1]), header fields are sent without any form of In HTTP/1.1 (see [HTTP-p1]), header fields are encoded without any
compression. As web pages have grown to include dozens to hundreds form of compression. As web pages have grown to include dozens to
of requests, the redundant header fields in these requests now pose a hundreds of requests, the redundant header fields in these requests
problem of measurable latency and unnecessary bandwidth (see [PERF1] now measurably increase latency and unnecessarily consume bandwidth
and [PERF2]). (see [PERF1] and [PERF2]).
SPDY [SPDY] initially addressed this redundancy by compressing header SPDY [SPDY] initially addressed this redundancy by compressing header
fields with Deflate, which proved very effective at eliminating the fields using the DEFLATE format [DEFLATE], which proved very
redundant header fields. However, that approach exposed a security effective at efficiently representing the redundant header fields.
risk as demonstrated by the CRIME [CRIME]. However, that approach exposed a security risk as demonstrated by the
CRIME attack (see [CRIME]).
This document describes HPACK, a new compressor for header fields This document describes HPACK, a new compressor for header fields
which eliminates redundant header fields, is not vulnerable to known which eliminates redundant header fields, is not vulnerable to known
security attacks, and which also has a bounded memory cost for use in security attacks, and which also has a bounded memory requirement for
constrained environments. use in constrained environments.
2.1. Outline 2.1. Outline
The HTTP header field encoding described in this document is based on The HTTP header field encoding defined in this document is based on a
a header table that map name-value pairs to index values. Header header table that maps name-value pairs to index values. The header
tables are incrementally updated during the HTTP/2.0 session. table is incrementally updated during the HTTP/2 connection.
The encoder is responsible for deciding which header fields to insert A set of header fields is treated as an unordered collection of name-
as new entries in the header table. The decoder then does exactly value pairs. Names and values are considered to be opaque sequences
what the encoder prescribes, ending in a state that exactly matches of octets. The order of header fields is not guaranteed to be
the encoder's state. This enables decoders to remain simple and preserved after being compressed and decompressed.
understand a wide variety of encoders.
As two consecutive sets of header fields often have header fields in As two consecutive sets of header fields often have header fields in
common, each set of header fields is coded as a difference from the common, each set is coded as a difference from the previous set. The
previous set of header fields. The goal is to only encode the goal is to only encode the changes (header fields present in one of
changes (header fields present in one of the set and not in the the sets that are absent from the other) between the two sets of
other) between the two sets of header fields. header fields.
HTTP header field compression treats a set of header fields as an A header field is represented either literally or as a reference to a
unordered collection of name-value pairs. Names and values are name-value pair in the header table. A set of header fields is
opaque sequences of octets. The order of header fields is not stored as a set of references to entries in the header table
guaranteed to be preserved after being compression and decompression. (possibly keeping only a subset of it, as some header fields may be
missing a corresponding entry in the header table). Differences
between consecutive sets of header fields are encoded as changes to
the set of references.
The encoder is responsible for deciding which header fields to insert
as new entries in the header table. The decoder executes the
modifications to the header table and reference set prescribed by the
encoder, reconstructing the set of header fields in the process.
This enables decoders to remain simple and understand a wide variety
of encoders.
Examples illustrating the use of these different mechanisms to Examples illustrating the use of these different mechanisms to
represent header fields are available in Appendix E. represent header fields are available in Appendix D.
3. Header Field Encoding 3. Header Field Encoding
3.1. Encoding Concepts 3.1. Encoding Concepts
The encoding and decoding of header fields relies on some components The encoding and decoding of header fields relies on some components
and concepts: and concepts:
Header Field: A name-value pair. Both name and value are sequences Header Field: A name-value pair. Both the name and value are
of octets. treated as opaque sequences of octets.
Header Table: The header table (see Section 3.1.2) is a component Header Table: The header table (see Section 3.1.2) is a component
used to associate stored header fields to index values. The data used to associate stored header fields to index values.
stored in this table is in first-in, first-out order.
Static Table: The static table (see Appendix B) is a component used Static Table: The static table (see Appendix B) is a component used
to associate static header fields to index values. This data is to associate static header fields to index values. This data is
ordered, read-only, always accessible, and may be shared amongst ordered, read-only, always accessible, and may be shared amongst
all encoding contexts. all encoding contexts.
Reference Set: The reference set (see Section 3.1.3) is a component Reference Set: The reference set (see Section 3.1.3) is a component
containing an unordered set of references to entries in the header containing an unordered set of references to entries in the header
table. This is used for the differential encoding of a new header table. This is used for the differential encoding of a new header
set. set.
Header Set: A header set is a potentially ordered group of header Header Set: A header set is an unordered group of header fields that
fields that are encoded jointly. A complete set of key-value are encoded jointly. A complete set of key-value pairs contained
pairs contained in a HTTP request or response is a header set. in a HTTP request or response is a header set.
Header Field Representation: A header field can be represented in Header Field Representation: A header field can be represented in
encoded form either as a literal or as an index (see encoded form either as a literal or as an index (see
Section 3.1.4). Section 3.1.4).
Header Block: The entire set of encoded header field representations Header Block: The entire set of encoded header field representations
which, when decoded, yield a complete header set. which, when decoded, yield a complete header set.
Header Field Emission: When decoding a set of header field Header Field Emission: When decoding a set of header field
representations, some operations emit a header field (see representations, some operations emit a header field (see
Section 3.1.5). Emitted header fields can be safely passed to the Section 3.1.5). Emitted header fields are added to the current
upper processing layers as part of the current Header Set. header set and cannot be removed.
3.1.1. Encoding Context 3.1.1. Encoding Context
The set of mutable structures used within an encoding context include The set of mutable structures used within an encoding context include
a header table and a reference set. Everything else is either a header table and a reference set. Everything else is either
immutable or conceptual. immutable or conceptual.
Using HTTP, messages are exchanged between a client and a server in HTTP messages are exchanged between a client and a server in both
both direction. To keep the encoding of header fields in each directions. The encoding of header fields in each direction is
direction independent from the other direction, there is one encoding independent from the other direction. There is a single encoding
context for each direction. context for each direction used to encode all header fields sent in
that direction.
The header fields contained in a PUSH_PROMISE frame sent by a server
to a client are encoded within the same context as the header fields
contained in the HEADERS frame corresponding to a response sent from
the server to the client.
3.1.2. Header Table 3.1.2. Header Table
A header table consists of a list of header fields maintained in A header table consists of a list of header fields maintained in
first-in, first-out order. The first and newest entry in a header first-in, first-out order. The first and newest entry in a header
table is always at index 1, and the oldest entry of a header table is table is always at index 1, and the oldest entry of a header table is
at the index len(header table). at the index len(header table).
The header table is initially empty. The header table is initially empty.
There is typically no need for the header table to contain duplicate There is typically no need for the header table to contain duplicate
entries. However, duplicate entries MUST NOT be treated as an error entries. However, duplicate entries MUST NOT be treated as an error
by a decoder. by a decoder.
The encoder decides how to update the header table and as such can The encoder decides how to update the header table and as such can
control how much memory is used by the header table. To limit the control how much memory is used by the header table. To limit the
memory requirements on the decoder side, the header table size is memory requirements of the decoder, the header table size is strictly
strictly bounded (see Section 3.3.1). bounded (see Section 3.3.1).
The header table is updated during the processing of a set of header The header table is updated during the processing of a set of header
field representations (see header field representation processing field representations (see Section 3.2.1).
(Section 3.2.1)).
3.1.3. Reference Set 3.1.3. Reference Set
A reference set is an unordered set of references to entries of the A reference set is an unordered set of references to entries of the
header table. header table.
The reference set is initially empty. The reference set is initially empty.
The reference set is updated during the processing of a set of header The reference set is updated during the processing of a set of header
field representations (see header field representation processing field representations (see Section 3.2.1).
(Section 3.2.1)).
The reference set enables differential encoding, whereby only The reference set enables differential encoding, whereby only
differences between the previous header set and the current header differences between the previous header set and the current header
set need to be encoded. The use of differential encoding is optional set need to be encoded. The use of differential encoding is optional
for any header set. for any header set.
When an entry is evicted from the header table, if it was referenced When an entry is evicted from the header table, if it was referenced
from the reference set, its reference is removed from the reference from the reference set, its reference is removed from the reference
set. set.
To limit the memory requirements on the decoder side for handling the To limit the memory requirements on the decoder side for handling the
reference set, only entries within the header table can be contained reference set, only entries within the header table can be contained
in the reference set. To still allow entries from the static table in the reference set. To still allow entries from the static table
to take advantage of the differential encoding, when a header field to take advantage of the differential encoding, when a header field
is represented as a reference to an entry of the static table, this is represented as a reference to an entry of the static table, this
entry is inserted into the header table ((see Section 3.2.1). entry is inserted into the header table (see Section 3.2.1).
3.1.4. Header Field Representation 3.1.4. Header Field Representation
An encoded header field can be represented either as a literal or as An encoded header field can be represented either as a literal or as
an index. an index.
Literal Representation: A literal representation defines a new Literal Representation: A literal representation defines a new
header field. The header field name is represented either header field. The header field name is represented either
literally or as a reference to an entry of the header table. The literally or as a reference to an entry of the header table. The
header field value is represented literally. header field value is represented literally.
skipping to change at page 7, line 36 skipping to change at page 7, line 25
Two different literal representations are provided: Two different literal representations are provided:
* A literal representation that does not add the header field to * A literal representation that does not add the header field to
the header table (see Section 4.3.1). the header table (see Section 4.3.1).
* A literal representation that adds the header field as a new * A literal representation that adds the header field as a new
entry at the beginning of the header table (see Section 4.3.2). entry at the beginning of the header table (see Section 4.3.2).
Indexed Representation: The indexed representation defines a header Indexed Representation: The indexed representation defines a header
field as a reference to an entry in either the header table or the field as a reference to an entry in either the header table or the
static table(see Section 4.2). static table (see Section 4.2).
<---------- Index Address Space ----------> <---------- Index Address Space ---------->
<-- Header Table --> <-- Static Table --> <-- Header Table --> <-- Static Table -->
+---+-----------+---+ +---+-----------+---+ +---+-----------+---+ +---+-----------+---+
| 1 | ... | k | |k+1| ... | n | | 1 | ... | k | |k+1| ... | n |
+---+-----------+---+ +---+-----------+---+ +---+-----------+---+ +---+-----------+---+
^ | ^ |
| V | V
Insertion Point Drop Point Insertion Point Drop Point
Index Address Space Index Address Space
Indices between 1 and len(header table), inclusive, refer to Indices between 1 and len(header table), inclusive, refer to
elements in the header table, with index 1 referring to the elements in the header table, with index 1 referring to the
beginning of the table. beginning of the table.
Indices between len(header table)+1 and len(header table)+ Indices between len(header table)+1 and len(header
len(static table), inclusive, refer to elements in the static table)+len(static table), inclusive, refer to elements in the
table, where the index len(header table)+1 refers to the first static table, where the index len(header table)+1 refers to the
entry in the static table. first entry in the static table.
Index 0 signals that the reference set MUST be emptied. Index 0 signals a modification of the encoding context: either
the reference set is emptied, or the maximum size of the header
table is updated (see Section 4.4).
Any other indices MUST be treated as erroneous, and the Any other indices MUST be treated as erroneous, and the
compression context considered corrupt and unusable. compression context considered corrupt and unusable.
3.1.5. Header Field Emission 3.1.5. Header Field Emission
The emission of a header field is the process of marking a header The emission of a header field is the process of marking a header
field as belonging to the current header set. Once a header has been field as belonging to the current header set. Once a header has been
emitted, it cannot be removed from the current header set. emitted, it cannot be removed from the current header set.
skipping to change at page 8, line 50 skipping to change at page 8, line 36
The processing of a header block to obtain a header set is defined in The processing of a header block to obtain a header set is defined in
this section. To ensure that the decoding will successfully produce this section. To ensure that the decoding will successfully produce
a header set, a decoder MUST obey the following rules. a header set, a decoder MUST obey the following rules.
3.2.1. Header Field Representation Processing 3.2.1. Header Field Representation Processing
All the header field representations contained in a header block are All the header field representations contained in a header block are
processed in the order in which they are presented, as specified processed in the order in which they are presented, as specified
below. below.
An _indexed representation_ with an index value of 0 entails the An _indexed representation_ with an index value of 0 entails one of
following actions: the following actions, depending on what is encoded next:
o The reference set is emptied. o The reference set is emptied.
o The maximum size of the header table is updated.
An _indexed representation_ corresponding to an entry _present_ in An _indexed representation_ corresponding to an entry _present_ in
the reference set entails the following actions: the reference set entails the following actions:
o The entry is removed from the reference set. o The entry is removed from the reference set.
An _indexed representation_ corresponding to an entry _not present_ An _indexed representation_ corresponding to an entry _not present_
in the reference set entails the following actions: in the reference set entails the following actions:
o If referencing an element of the static table: o If referencing an element of the static table:
skipping to change at page 10, line 18 skipping to change at page 10, line 4
processed, the header fields referenced in the reference set which processed, the header fields referenced in the reference set which
have not previously been emitted during this processing are emitted. have not previously been emitted during this processing are emitted.
3.2.3. Header Set Completion 3.2.3. Header Set Completion
Once all of the header field representations have been processed, and Once all of the header field representations have been processed, and
the remaining items in the reference set have been emitted, the the remaining items in the reference set have been emitted, the
header set is complete. header set is complete.
3.3. Header Table Management 3.3. Header Table Management
3.3.1. Maximum Table Size 3.3.1. Maximum Table Size
To limit the memory requirements on the decoder side, the size of the To limit the memory requirements on the decoder side, the size of the
header table is bounded. The size of the header table MUST stay header table is bounded. The size of the header table MUST stay
lower than or equal to the value of the HTTP/2.0 setting lower than or equal to its maximum size.
SETTINGS_HEADER_TABLE_SIZE (see [HTTP2]).
By default, the maximum size of the header table is equal to the
value of the HTTP/2 setting SETTINGS_HEADER_TABLE_SIZE defined by the
decoder (see [HTTP2]). The encoder can change this maximum size (see
Section 4.4), but it must stay lower than or equal to the value of
SETTINGS_HEADER_TABLE_SIZE.
The size of the header table is the sum of the size of its entries. The size of the header table is the sum of the size of its entries.
The size of an entry is the sum of its name's length in octets (as The size of an entry is the sum of its name's length in octets (as
defined in Section 4.1.2), of its value's length in octets defined in Section 4.1.2), of its value's length in octets
(Section 4.1.2) and of 32 octets. (Section 4.1.2) and of 32 octets.
The lengths are measured on the non-encoded entry name and entry The lengths are measured on the non-encoded entry name and entry
value (for the case when a Huffman encoding is used to transmit value (for the case when a Huffman encoding is used to transmit
string values). string values).
skipping to change at page 10, line 47 skipping to change at page 10, line 37
For example, an entry structure using two 64-bits pointers to For example, an entry structure using two 64-bits pointers to
reference the name and the value and the entry, and two 64-bits reference the name and the value and the entry, and two 64-bits
integer for counting the number of references to these name and value integer for counting the number of references to these name and value
would use 32 octets. would use 32 octets.
3.3.2. Entry Eviction When Header Table Size Changes 3.3.2. Entry Eviction When Header Table Size Changes
Whenever an entry is evicted from the header table, any reference to Whenever an entry is evicted from the header table, any reference to
that entry contained by the reference set is removed. that entry contained by the reference set is removed.
Whenever SETTINGS_HEADER_TABLE_SIZE is made smaller, entries are Whenever the maximum size for the header table is made smaller,
evicted from the end of the header table until the size of the header entries are evicted from the end of the header table until the size
table is less than or equal to SETTINGS_HEADER_TABLE_SIZE. of the header table is less than or equal to the maximum size.
The eviction of an entry from the header table causes the index of The eviction of an entry from the header table causes the index of
the entries in the static table to be reduced by one. the entries in the static table to be reduced by one.
3.3.3. Entry Eviction when Adding New Entries 3.3.3. Entry Eviction when Adding New Entries
Whenever a new entry is to be added to the table, any name referenced Whenever a new entry is to be added to the table, any name referenced
by the representation of this new entry is cached, and then entries by the representation of this new entry is cached, and then entries
are evicted from the end of the header table until the size of the are evicted from the end of the header table until the size of the
header table is less than or equal to SETTINGS_HEADER_TABLE_SIZE - header table is less than or equal to (maximum size - new entry
new entry size, or until the table is empty. size), or until the table is empty.
If the size of the new entry is less than or equal to If the size of the new entry is less than or equal to the maximum
SETTINGS_HEADER_TABLE_SIZE, that entry is added to the table. It is size, that entry is added to the table. It is not an error to
not an error to attempt to add an entry that is larger than attempt to add an entry that is larger than the maximum size.
SETTINGS_HEADER_TABLE_SIZE.
4. Detailed Format 4. Detailed Format
4.1. Low-level representations 4.1. Low-level representations
4.1.1. Integer representation 4.1.1. Integer representation
Integers are used to represent name indexes, pair indexes or string Integers are used to represent name indexes, pair indexes or string
lengths. To allow for optimized processing, an integer lengths. To allow for optimized processing, an integer
representation always finishes at the end of an octet. representation always finishes at the end of an octet.
An integer is represented in two parts: a prefix that fills the An integer is represented in two parts: a prefix that fills the
current octet and an optional list of octets that are used if the current octet and an optional list of octets that are used if the
integer value does not fit within the prefix. The number of bits of integer value does not fit within the prefix. The number of bits of
the prefix (called N) is a parameter of the integer representation. the prefix (called N) is a parameter of the integer representation.
The N-bit prefix allows filling the current octet. If the value is The N-bit prefix allows filling the current octet. If the value is
small enough (strictly less than 2^N-1), it is encoded within the small enough (strictly less than 2^N-1), it is encoded within the
N-bit prefix. Otherwise all the bits of the prefix are set to 1 and N-bit prefix. Otherwise all the bits of the prefix are set to 1 and
the value is encoded using an unsigned variable length integer [1] the value is encoded using an unsigned variable length integer [4]
representation. N is always between 1 and 8 bits. An integer representation. N is always between 1 and 8 bits. An integer
starting at an octet-boundary will have an 8-bit prefix. starting at an octet-boundary will have an 8-bit prefix.
The algorithm to represent an integer I is as follows: The algorithm to represent an integer I is as follows:
If I < 2^N - 1, encode I on N bits if I < 2^N - 1, encode I on N bits
Else else
encode 2^N - 1 on N bits encode (2^N - 1) on N bits
I = I - (2^N - 1) I = I - (2^N - 1)
While I >= 128 while I >= 128
Encode (I % 128 + 128) on 8 bits encode (I % 128 + 128) on 8 bits
I = I / 128 I = I / 128
encode (I) on 8 bits encode I on 8 bits
For informational purpose, the algorithm to decode an integer I is as
follows:
decode I from the next N bits
if I < 2^N - 1, return I
else
M = 0
repeat
B = next octet
I = I + (B & 127) * 2^M
M = M + 7
while B & 128 == 128
return I
This integer representation allows for values of indefinite size. It This integer representation allows for values of indefinite size. It
is also possible for an encoder to send a large number of zero is also possible for an encoder to send a large number of zero
values, which can waste octets and could be used to overflow integer values, which can waste octets and could be used to overflow integer
values. Excessively large integer encodings - in value or octet values. Excessively large integer encodings - in value or octet
length - MUST be treated as a decoding error. Different limits can length - MUST be treated as a decoding error. Different limits can
be set for each of the different uses of integers, based on be set for each of the different uses of integers, based on
implementation constraints. implementation constraints.
4.1.1.1. Example 1: Encoding 10 using a 5-bit prefix 4.1.1.1. Example 1: Encoding 10 using a 5-bit prefix
skipping to change at page 13, line 13 skipping to change at page 13, line 19
terminates. terminates.
I, now 10, is encoded on 8 bits as: 00001010 I, now 10, is encoded on 8 bits as: 00001010
The process ends. The process ends.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| X | X | X | 1 | 1 | 1 | 1 | 1 | Prefix = 31, I = 1306 | X | X | X | 1 | 1 | 1 | 1 | 1 | Prefix = 31, I = 1306
| 1 | 0 | 0 | 1 | 1 | 0 | 1 | 0 | 1306>=128, encode(154), I=1306/128 | 1 | 0 | 0 | 1 | 1 | 0 | 1 | 0 | 1306>=128, encode(154), I=1306/128
| 0 | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 10<128, encode(10), done | 0 | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 10&lt;128, encode(10), done
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
4.1.1.3. Example 3: Encoding 42 starting at an 4.1.1.3. Example 3: Encoding 42 starting at an octet-boundary
octet-boundary
The value 42 is to be encoded starting at an octet-boundary. This The value 42 is to be encoded starting at an octet-boundary. This
implies that a 8-bit prefix is used. implies that a 8-bit prefix is used.
o 42 is less than 255 (= 2^8 - 1) and is represented using the 8-bit o 42 is less than 255 (= 2^8 - 1) and is represented using the 8-bit
prefix. prefix.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 42 stored on 8 bits | 0 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 42 stored on 8 bits
skipping to change at page 13, line 40 skipping to change at page 13, line 45
4.1.2. String Literal Representation 4.1.2. String Literal Representation
Header field names and header field values are encoded as sequences Header field names and header field values are encoded as sequences
of octets. A header field name or a header field value is encoded in of octets. A header field name or a header field value is encoded in
three parts: three parts:
1. One bit, H, indicating whether or not the octets are Huffman 1. One bit, H, indicating whether or not the octets are Huffman
encoded. encoded.
2. The number of octets required to hold the result of the next 2. The number of octets required to hold the result of the next
step, represented as a variable-length-quantity (Section 4.1.1), step, represented as an integer with a 7-bit prefix (see
starting with a 7-bit prefix immediately following the first bit. Section 4.1.1), immediately following the first bit.
3. The encoded data of the string: 3. The encoded data of the string:
1. If H is true, then the encoded string data is the bitwise * If H is '1', then the encoded string data is the bitwise
concatenation of the canonical [CANON]Huffman code [HUFF] concatenation of the canonical [CANON] Huffman code [HUFF]
corresponding to each octet of the data, followed by between corresponding to each octet of the data, followed by between
0-7 bits of padding. 0-7 bits of padding.
2. If H is false, then the encoded string is the octets of the * If H is '0', then the encoded string is the octets of the
field value without modification. field value without modification.
Padding is necessary when doing Huffman encoding to ensure that the Padding is necessary when doing Huffman encoding to ensure that the
remaining bits between the actual end of the data and the next octet remaining bits between the actual end of the data and the next octet
boundary are not misinterpreted as part of the input data. boundary are not misinterpreted as part of the input data.
When padding for Huffman encoding, use the bits from the EOS (end-of- When padding for Huffman encoding, the bits from the EOS (end-of-
string) entry in the Huffman table, starting with the MSB (most string) entry in the Huffman table are used, starting with the MSB
significant bit). This entry is guaranteed to be at least 8 bits (most significant bit). This entry is guaranteed to be at least 8
long. bits long.
String literals sent in the client to server direction which use
Huffman encoding are encoded with the codes within the request
Huffman code table (Appendix C) (see Request Examples With Huffman
(Appendix E.3)).
String literals sent in the server to client direction which use String literals which use Huffman encoding are encoded with the
Huffman encoding are encoded with the codes within the response Huffman Codes Appendix C (see examples in Request Examples with
Huffman code table (Appendix D) (see Response Examples With Huffman Huffman Appendix D.3 and in Response Examples with Huffman
(Appendix E.5)). Appendix D.5).
The EOS symbol is represented with value 256, and is used solely to The EOS symbol is represented with value 256, and is used solely to
signal the end of the Huffman-encoded key data or the end of the signal the end of the Huffman-encoded key data or the end of the
Huffman-encoded value data. Given that only between 0-7 bits of the Huffman-encoded value data. Given that only between 0-7 bits of the
EOS symbol is included in any Huffman-encoded string, and given that EOS symbol is included in any Huffman-encoded string, and given that
the EOS symbol is at least 8 bits long, it is expected that it should the EOS symbol is at least 8 bits long, it is expected that it should
never be successfully decoded. never be successfully decoded.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 1 | Value Length Prefix (7) | | 1 | Value Length Prefix (7) |
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| Value Length (0-N octets) | | Value Length (0-N octets) |
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
... ...
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| Huffman Encoded Data |Padding| | Huffman Encoded Data |Padding|
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
String Literal With Huffman Encoding String Literal with Huffman Encoding
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | Value Length Prefix (7) | | 0 | Value Length Prefix (7) |
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| Value Length (0-N octets) | | Value Length (0-N octets) |
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
... ...
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| Field Bytes Without Encoding | | Field Bytes without Encoding |
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
String Literal Without Huffman Encoding String Literal without Huffman Encoding
4.2. Indexed Header Field Representation 4.2. Indexed Header Field Representation
An indexed header field representation either identifies an entry in An indexed header field representation either identifies an entry in
the header table or static table. The processing of an indexed the header table or static table. The processing of an indexed
header field representation is described in Section 3.2.1. header field representation is described in Section 3.2.1.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 1 | Index (7+) | | 1 | Index (7+) |
+---+---------------------------+ +---+---------------------------+
Indexed Header Field Indexed Header Field
This representation starts with the '1' 1-bit pattern, followed by This representation starts with the '1' 1-bit pattern, followed by
the index of the matching pair, represented as an integer with a the index of the matching pair, represented as an integer with a
7-bit prefix. 7-bit prefix.
The index value of 0 is reserved for signalling that the reference The index value of 0 is reserved for signalling changes in the
set is emptied. encoding context (see Section 4.4).
4.3. Literal Header Field Representation 4.3. Literal Header Field Representation
Literal header field representations contain a literal header field Literal header field representations contain a literal header field
value. Header field names are either provided as a literal or by value. Header field names are either provided as a literal or by
reference to an existing header table or static table entry. reference to an existing header table or static table entry.
Literal representations all result in the emission of a header field Literal representations all result in the emission of a header field
when decoded. when decoded.
4.3.1. Literal Header Field without Indexing 4.3.1. Literal Header Field without Indexing
A literal header field without indexing causes the emission of a A literal header field without indexing causes the emission of a
header field without altering the header table. header field without altering the header table.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 1 | Index (6+) | | 0 | 1 | Index (6+) |
+---+---+---+-------------------+ +---+---+---+-------------------+
| Value Length (8+) | | H | Value Length (7+) |
+-------------------------------+ +---+---------------------------+
| Value String (Length octets) | | Value String (Length octets) |
+-------------------------------+ +-------------------------------+
Literal Header Field without Indexing - Indexed Name Literal Header Field without Indexing - Indexed Name
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 1 | 0 | | 0 | 1 | 0 |
+---+---+---+-------------------+ +---+---+---+-------------------+
| Name Length (8+) | | H | Name Length (7+) |
+-------------------------------+ +---+---------------------------+
| Name String (Length octets) | | Name String (Length octets) |
+-------------------------------+ +---+---------------------------+
| Value Length (8+) | | H | Value Length (7+) |
+-------------------------------+ +---+---------------------------+
| Value String (Length octets) | | Value String (Length octets) |
+-------------------------------+ +-------------------------------+
Literal Header Field without Indexing - New Name Literal Header Field without Indexing - New Name
This representation starts with the '01' 2-bit pattern. This representation starts with the '01' 2-bit pattern.
If the header field name matches the header field name of a (name, If the header field name matches the header field name of a (name,
value) pair stored in the Header Table or Static Table, the header value) pair stored in the Header Table or Static Table, the header
field name can be represented using the index of that entry. In this field name can be represented using the index of that entry. In this
skipping to change at page 17, line 9 skipping to change at page 16, line 48
4.3.2. Literal Header Field with Incremental Indexing 4.3.2. Literal Header Field with Incremental Indexing
A literal header field with incremental indexing adds a new entry to A literal header field with incremental indexing adds a new entry to
the header table. the header table.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 0 | Index (6+) | | 0 | 0 | Index (6+) |
+---+---+---+-------------------+ +---+---+---+-------------------+
| Value Length (8+) | | H | Value Length (7+) |
+-------------------------------+ +---+---------------------------+
| Value String (Length octets) | | Value String (Length octets) |
+-------------------------------+ +-------------------------------+
Literal Header Field with Incremental Indexing - Indexed Name
Literal Header Field with Incremental Indexing -
Indexed Name
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 0 | 0 | | 0 | 0 | 0 |
+---+---+---+-------------------+ +---+---+---+-------------------+
| Name Length (8+) | | H | Name Length (7+) |
+-------------------------------+ +---+---------------------------+
| Name String (Length octets) | | Name String (Length octets) |
+-------------------------------+ +---+---------------------------+
| Value Length (8+) | | H | Value Length (7+) |
+-------------------------------+ +---+---------------------------+
| Value String (Length octets) | | Value String (Length octets) |
+-------------------------------+ +-------------------------------+
Literal Header Field with Incremental Indexing - Literal Header Field with Incremental Indexing - New Name
New Name
This representation starts with the '00' 2-bit pattern. This representation starts with the '00' 2-bit pattern.
If the header field name matches the header field name of a (name, If the header field name matches the header field name of a (name,
value) pair stored in the Header Table or Static Table, the header value) pair stored in the Header Table or Static Table, the header
field name can be represented using the index of that entry. In this field name can be represented using the index of that entry. In this
case, the index of the entry, index (which is strictly greater than case, the index of the entry, index (which is strictly greater than
0), is represented as an integer with a 6-bit prefix (see 0), is represented as an integer with a 6-bit prefix (see
Section 4.1.1). Section 4.1.1).
Otherwise, the header field name is represented as a literal. The Otherwise, the header field name is represented as a literal. The
value 0 is represented on 6 bits followed by the header field name value 0 is represented on 6 bits followed by the header field name
(see Section 4.1.2). (see Section 4.1.2).
The header field name representation is followed by the header field The header field name representation is followed by the header field
value represented as a literal string as described in Section 4.1.2. value represented as a literal string as described in Section 4.1.2.
4.4. Encoding Context Update
An indexed value of 0 is reserved for signalling changes in the
encoding context. The type of the change is encoded on the following
octet(s). Any change in the encoding context is applied immediately.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 1 | 0 |
+---+---------------------------+
Reference Set Emptying
An octet with its high bit set to '1' signals that the reference set
is emptied. The remaining bits are set to '0'.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 0 | New maximum size (7+) |
+---+---------------------------+
Maximum Header Table Size Change
An octet with its high bit set to '0' signals the new maximum size of
the header table. This new maximum size MUST be lower than or equal
to the value of the setting SETTINGS_HEADER_TABLE_SIZE (see [HTTP2]).
The new maximum size is encoded as an integer with a 7-bit prefix.
Change in the maximum size of the header table can trigger entry
evictions (see Section 3.3.2).
5. Security Considerations 5. Security Considerations
This compressor exists to solve security issues present in stream This compressor exists to solve security issues present in stream
compressors such as DEFLATE whereby the compression context can be compressors such as DEFLATE whereby the compression context can be
efficiently probed to reveal secrets. A conformant implementation of efficiently probed to reveal secrets. A conformant implementation of
this specification should be fairly safe against that kind of attack, this specification should be fairly safe against that kind of attack,
as the reaping of any information from the compression context as the reaping of any information from the compression context
requires more work than guessing and verifying the plain text data requires more work than guessing and verifying the plain text data
directly with the server. As with any secret, however, the longer directly with the server. As with any secret, however, the longer
the length of the secret, the more difficult the secret is to guess. the length of the secret, the more difficult the secret is to guess.
skipping to change at page 18, line 42 skipping to change at page 19, line 9
memory consumed in the compressor state, by providing ways for the memory consumed in the compressor state, by providing ways for the
application to consume/flush the emitted header fields in small application to consume/flush the emitted header fields in small
chunks, and by considering overhead in the state size calculation. chunks, and by considering overhead in the state size calculation.
Implementors must still be careful in the creation of APIs to an Implementors must still be careful in the creation of APIs to an
implementation of this compressor by ensuring that header field keys implementation of this compressor by ensuring that header field keys
and values are either emitted as a stream, or that the compression and values are either emitted as a stream, or that the compression
implementation have a limit on the maximum size of a key or value. implementation have a limit on the maximum size of a key or value.
Failure to implement these kinds of safeguards may still result in a Failure to implement these kinds of safeguards may still result in a
scenario where the local endpoint exhausts its memory. scenario where the local endpoint exhausts its memory.
6. References A particular care should be used for the maximum size of the header
table. While an endpoint can fully control the maximum size of its
header table for the decoding size, by using
SETTINGS_HEADER_TABLE_SIZE, the maximum size of the encoding size is
controlled by the remote peer. The endpoint should check the
SETTINGS_HEADER_TABLE_SIZE defined by the remote peer, and decrease
the maximum size for the encoding size if needed.
6.1. Normative References 6. Acknowledgements
This document includes substantial editorial contributions from the
following individuals: Mike Bishop, Jeff Pinner, Julian Reschke,
Martin Thomson.
7. References
7.1. Normative References
[HTTP-p1] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [HTTP-p1] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing", Protocol (HTTP/1.1): Message Syntax and Routing", draft-
draft-ietf-httpbis-p1-messaging-25 (work in progress), ietf-httpbis-p1-messaging-26 (work in progress), February
November 2013. 2014.
[HTTP2] Belshe, M., Peon, R., Thomson, M., Ed., and A. Melnikov, [HTTP2] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Ed., "Hypertext Transfer Protocol version 2.0", Transfer Protocol version 2", draft-ietf-httpbis-http2-10
draft-ietf-httpbis-http2-08 (work in progress), (work in progress), February 2014.
November 2013.
6.2. Informative References 7.2. Informative References
[CANON] Schwartz, E. and B. Kallick, "Generating a canonical [CANON] Schwartz, E. and B. Kallick, "Generating a canonical
prefix encoding", Communications of the ACM Volume 7 Issue prefix encoding", Communications of the ACM Volume 7 Issue
3, pp. 166-169, March 1964, 3, pp. 166-169, March 1964,
<http://dl.acm.org/citation.cfm?id=363991>. <http://dl.acm.org/citation.cfm?id=363991>.
[CRIME] Rizzo, J. and T. Duong, "The Crime Attack", [CRIME] Rizzo, J. and T. Duong, "The CRIME Attack", September
September 2012, <https://docs.google.com/a/twist.com/ 2012, <https://docs.google.com/a/twist.com/presentation/d/
presentation/d/
11eBmGiHbYcHR9gL5nDyZChu_-lCa2GizeuOfaLU2HOU/ 11eBmGiHbYcHR9gL5nDyZChu_-lCa2GizeuOfaLU2HOU/
edit#slide=id.g1eb6c1b5_3_6>. edit#slide=id.g1eb6c1b5_3_6>.
[DEFLATE] Deutsch, P., "DEFLATE Compressed Data Format Specification
version 1.3", RFC 1951, May 1996.
[HUFF] Huffman, D., "A Method for the Construction of Minimum [HUFF] Huffman, D., "A Method for the Construction of Minimum
Redundancy Codes", Proceedings of the Institute of Radio Redundancy Codes", Proceedings of the Institute of Radio
Engineers Volume 40, Number 9, pp. 1098-1101, Engineers Volume 40, Number 9, pp. 1098-1101, September
September 1952, <http://ieeexplore.ieee.org/xpl/ 1952, <http://ieeexplore.ieee.org/xpl/
articleDetails.jsp?arnumber=4051119>. articleDetails.jsp?arnumber=4051119>.
[PERF1] Belshe, M., "IETF83: SPDY and What to Consider for [PERF1] Belshe, M., "IETF83: SPDY and What to Consider for HTTP/
HTTP/2.0", March 2012, <http://www.ietf.org/proceedings/ 2.0", March 2012, <http://www.ietf.org/proceedings/83/
83/slides/slides-83-httpbis-3>. slides/slides-83-httpbis-3>.
[PERF2] McManus, P., "SPDY: What I Like About You", [PERF2] McManus, P., "SPDY: What I Like About You", September
September 2011, <http://bitsup.blogspot.com/2011/09/ 2011, <http://bitsup.blogspot.com/2011/09/spdy-what-i
spdy-what-i-like-about-you.html>. -like-about-you.html>.
[SPDY] Belshe, M. and R. Peon, "SPDY Protocol", [SPDY] Belshe, M. and R. Peon, "SPDY Protocol", draft-mbelshe-
draft-mbelshe-httpbis-spdy-00 (work in progress), httpbis-spdy-00 (work in progress), February 2012.
February 2012.
URIs Appendix A. Change Log (to be removed by RFC Editor before publication
[1] <http://en.wikipedia.org/wiki/Variable-length_quantity> A.1. Since draft-ietf-httpbis-header-compression-05
Appendix A. Change Log (to be removed by RFC Editor before publication o Regenerated examples.
A.1. Since draft-ietf-httpbis-header-compression-04 o Only one Huffman table for requests and responses.
o Added maximum size for header table, independent of
SETTINGS_HEADER_TABLE_SIZE.
o Added pseudo-code for integer decoding.
o Improved examples (removing unnecessary removals).
A.2. Since draft-ietf-httpbis-header-compression-04
o Updated examples: take into account changes in the spec, and show o Updated examples: take into account changes in the spec, and show
more features. more features.
o Use 'octet' everywhere instead of having both 'byte' and 'octet'. o Use 'octet' everywhere instead of having both 'byte' and 'octet'.
o Added reference set emptying. o Added reference set emptying.
o Editorial changes and clarifications. o Editorial changes and clarifications.
o Added "host" header to the static table. o Added "host" header to the static table.
o Ordering for list of values (either NULL- or comma-separated). o Ordering for list of values (either NULL- or comma-separated).
A.2. Since draft-ietf-httpbis-header-compression-03 A.3. Since draft-ietf-httpbis-header-compression-03
o A large number of editorial changes; changed the description of o A large number of editorial changes; changed the description of
evicting/adding new entries. evicting/adding new entries.
o Removed substitution indexing o Removed substitution indexing
o Changed 'initial headers' to 'static headers', as per issue #258 o Changed 'initial headers' to 'static headers', as per issue #258
o Merged 'request' and 'response' static headers, as per issue #259 o Merged 'request' and 'response' static headers, as per issue #259
o Changed text to indicate that new headers are added at index 0 and o Changed text to indicate that new headers are added at index 0 and
expire from the largest index, as per issue #233 expire from the largest index, as per issue #233
A.3. Since draft-ietf-httpbis-header-compression-02 A.4. Since draft-ietf-httpbis-header-compression-02
o Corrected error in integer encoding pseudocode. o Corrected error in integer encoding pseudocode.
A.4. Since draft-ietf-httpbis-header-compression-01 A.5. Since draft-ietf-httpbis-header-compression-01
o Refactored of Header Encoding Section: split definitions and o Refactored of Header Encoding Section: split definitions and
processing rule. processing rule.
o Backward incompatible change: Updated reference set management as o Backward incompatible change: Updated reference set management as
per issue #214. This changes how the interaction between the per issue #214. This changes how the interaction between the
reference set and eviction works. This also changes the working reference set and eviction works. This also changes the working
of the reference set in some specific cases. of the reference set in some specific cases.
o Backward incompatible change: modified initial header list, as per o Backward incompatible change: modified initial header list, as per
issue #188. issue #188.
o Added example of 32 octets entry structure (issue #191). o Added example of 32 octets entry structure (issue #191).
o Added Header Set Completion section. Reflowed some text. o Added Header Set Completion section. Reflowed some text.
Clarified some writing which was akward. Added text about Clarified some writing which was akward. Added text about
duplicate header entry encoding. Clarified some language w.r.t duplicate header entry encoding. Clarified some language w.r.t
Header Set. Changed x-my-header to mynewheader. Added text in the Header Set. Changed x-my-header to mynewheader. Added text in
HeaderEmission section indicating that the application may also be the HeaderEmission section indicating that the application may
able to free up memory more quickly. Added information in also be able to free up memory more quickly. Added information in
Security Considerations section. Security Considerations section.
A.5. Since draft-ietf-httpbis-header-compression-01 A.6. Since draft-ietf-httpbis-header-compression-00
Fixed bug/omission in integer representation algorithm. Fixed bug/omission in integer representation algorithm.
Changed the document title. Changed the document title.
Header matching text rewritten. Header matching text rewritten.
Changed the definition of header emission. Changed the definition of header emission.
Changed the name of the setting which dictates how much memory the Changed the name of the setting which dictates how much memory the
skipping to change at page 21, line 34 skipping to change at page 22, line 26
Removed security claims from introduction. Removed security claims from introduction.
Appendix B. Static Table Appendix B. Static Table
The static table consists of an unchangeable ordered list of (name, The static table consists of an unchangeable ordered list of (name,
value) pairs. The first entry in the table is always represented by value) pairs. The first entry in the table is always represented by
the index len(header table)+1, and the last entry in the table is the index len(header table)+1, and the last entry in the table is
represented by the index len(header table)+len(static table). represented by the index len(header table)+len(static table).
[[anchor9: The ordering of these tables is currently arbitrary. The [[The ordering of these tables is currently arbitrary. The tables in
tables in this section should be updated and ordered such that the this section should be updated and ordered such that the table
table entries with the smallest indices are those which, based on a entries with the smallest indices are those which, based on a
statistical analysis of the frequency of use weighted by size, statistical analysis of the frequency of use weighted by size,
achieve the largest decrease in octets transmitted subject to HTTP achieve the largest decrease in octets transmitted subject to HTTP 2
2.0 header field rules (like removal of some header fields). This header field rules (like removal of some header fields). This set of
set of header fields is currently very likely incomplete, and should header fields is currently very likely incomplete, and should be made
be made complete.]] complete. ]]
The following table lists the pre-defined header fields that make-up The following table lists the pre-defined header fields that make-up
the static header table. the static header table.
+-------+-----------------------------+--------------+ +-------+-----------------------------+--------------+
| Index | Header Name | Header Value | | Index | Header Name | Header Value |
+-------+-----------------------------+--------------+ +-------+-----------------------------+--------------+
| 1 | :authority | | | 1 | :authority | |
| 2 | :method | GET | | 2 | :method | GET |
| 3 | :method | POST | | 3 | :method | POST |
skipping to change at page 23, line 21 skipping to change at page 24, line 13
| 60 | www-authenticate | | | 60 | www-authenticate | |
+-------+-----------------------------+--------------+ +-------+-----------------------------+--------------+
Table 1: Static Table Entries Table 1: Static Table Entries
The table give the index of each entry in the static table. The full The table give the index of each entry in the static table. The full
index of each entry, to be used for encoding a reference to this index of each entry, to be used for encoding a reference to this
entry, is computed by adding the number of entries in the header entry, is computed by adding the number of entries in the header
table to this index. table to this index.
Appendix C. Huffman Codes For Requests Appendix C. Huffman Codes
The following Huffman codes are used when encoding string literals in
the client to server direction.
[[anchor10: This table may need to be regenerated.]]
aligned aligned
to len to len
MSB in LSB in
sym as bits bits as hex bits
( 0) |11111111|11111111|11110111|010 [27] 7ffffba [27]
( 1) |11111111|11111111|11110111|011 [27] 7ffffbb [27]
( 2) |11111111|11111111|11110111|100 [27] 7ffffbc [27]
( 3) |11111111|11111111|11110111|101 [27] 7ffffbd [27]
( 4) |11111111|11111111|11110111|110 [27] 7ffffbe [27]
( 5) |11111111|11111111|11110111|111 [27] 7ffffbf [27]
( 6) |11111111|11111111|11111000|000 [27] 7ffffc0 [27]
( 7) |11111111|11111111|11111000|001 [27] 7ffffc1 [27]
( 8) |11111111|11111111|11111000|010 [27] 7ffffc2 [27]
( 9) |11111111|11111111|11111000|011 [27] 7ffffc3 [27]
( 10) |11111111|11111111|11111000|100 [27] 7ffffc4 [27]
( 11) |11111111|11111111|11111000|101 [27] 7ffffc5 [27]
( 12) |11111111|11111111|11111000|110 [27] 7ffffc6 [27]
( 13) |11111111|11111111|11111000|111 [27] 7ffffc7 [27]
( 14) |11111111|11111111|11111001|000 [27] 7ffffc8 [27]
( 15) |11111111|11111111|11111001|001 [27] 7ffffc9 [27]
( 16) |11111111|11111111|11111001|010 [27] 7ffffca [27]
( 17) |11111111|11111111|11111001|011 [27] 7ffffcb [27]
( 18) |11111111|11111111|11111001|100 [27] 7ffffcc [27]
( 19) |11111111|11111111|11111001|101 [27] 7ffffcd [27]
( 20) |11111111|11111111|11111001|110 [27] 7ffffce [27]
( 21) |11111111|11111111|11111001|111 [27] 7ffffcf [27]
( 22) |11111111|11111111|11111010|000 [27] 7ffffd0 [27]
( 23) |11111111|11111111|11111010|001 [27] 7ffffd1 [27]
( 24) |11111111|11111111|11111010|010 [27] 7ffffd2 [27]
( 25) |11111111|11111111|11111010|011 [27] 7ffffd3 [27]
( 26) |11111111|11111111|11111010|100 [27] 7ffffd4 [27]
( 27) |11111111|11111111|11111010|101 [27] 7ffffd5 [27]
( 28) |11111111|11111111|11111010|110 [27] 7ffffd6 [27]
( 29) |11111111|11111111|11111010|111 [27] 7ffffd7 [27]
( 30) |11111111|11111111|11111011|000 [27] 7ffffd8 [27]
( 31) |11111111|11111111|11111011|001 [27] 7ffffd9 [27]
' ' ( 32) |11101000| [8] e8 [8]
'!' ( 33) |11111111|1100 [12] ffc [12]
'"' ( 34) |11111111|111010 [14] 3ffa [14]
'#' ( 35) |11111111|1111100 [15] 7ffc [15]
'$' ( 36) |11111111|1111101 [15] 7ffd [15]
'%' ( 37) |100100 [6] 24 [6]
'&' ( 38) |1101110 [7] 6e [7]
''' ( 39) |11111111|1111110 [15] 7ffe [15]
'(' ( 40) |11111111|010 [11] 7fa [11]
')' ( 41) |11111111|011 [11] 7fb [11]
'*' ( 42) |11111110|10 [10] 3fa [10]
'+' ( 43) |11111111|100 [11] 7fc [11]
',' ( 44) |11101001| [8] e9 [8]
'-' ( 45) |100101 [6] 25 [6]
'.' ( 46) |00100 [5] 4 [5]
'/' ( 47) |0000 [4] 0 [4]
'0' ( 48) |00101 [5] 5 [5]
'1' ( 49) |00110 [5] 6 [5]
'2' ( 50) |00111 [5] 7 [5]
'3' ( 51) |100110 [6] 26 [6]
'4' ( 52) |100111 [6] 27 [6]
'5' ( 53) |101000 [6] 28 [6]
'6' ( 54) |101001 [6] 29 [6]
'7' ( 55) |101010 [6] 2a [6]
'8' ( 56) |101011 [6] 2b [6]
'9' ( 57) |101100 [6] 2c [6]
':' ( 58) |11110110|0 [9] 1ec [9]
';' ( 59) |11101010| [8] ea [8]
'<' ( 60) |11111111|11111111|10 [18] 3fffe [18]
'=' ( 61) |101101 [6] 2d [6]
'>' ( 62) |11111111|11111110|0 [17] 1fffc [17]
'?' ( 63) |11110110|1 [9] 1ed [9]
'@' ( 64) |11111111|111011 [14] 3ffb [14]
'A' ( 65) |1101111 [7] 6f [7]
'B' ( 66) |11101011| [8] eb [8]
'C' ( 67) |11101100| [8] ec [8]
'D' ( 68) |11101101| [8] ed [8]
'E' ( 69) |11101110| [8] ee [8]
'F' ( 70) |1110000 [7] 70 [7]
'G' ( 71) |11110111|0 [9] 1ee [9]
'H' ( 72) |11110111|1 [9] 1ef [9]
'I' ( 73) |11111000|0 [9] 1f0 [9]
'J' ( 74) |11111000|1 [9] 1f1 [9]
'K' ( 75) |11111110|11 [10] 3fb [10]
'L' ( 76) |11111001|0 [9] 1f2 [9]
'M' ( 77) |11101111| [8] ef [8]
'N' ( 78) |11111001|1 [9] 1f3 [9]
'O' ( 79) |11111010|0 [9] 1f4 [9]
'P' ( 80) |11111010|1 [9] 1f5 [9]
'Q' ( 81) |11111011|0 [9] 1f6 [9]
'R' ( 82) |11111011|1 [9] 1f7 [9]
'S' ( 83) |11110000| [8] f0 [8]
'T' ( 84) |11110001| [8] f1 [8]
'U' ( 85) |11111100|0 [9] 1f8 [9]
'V' ( 86) |11111100|1 [9] 1f9 [9]
'W' ( 87) |11111101|0 [9] 1fa [9]
'X' ( 88) |11111101|1 [9] 1fb [9]
'Y' ( 89) |11111110|0 [9] 1fc [9]
'Z' ( 90) |11111111|00 [10] 3fc [10]
'[' ( 91) |11111111|111100 [14] 3ffc [14]
'\' ( 92) |11111111|11111111|11111011|010 [27] 7ffffda [27]
']' ( 93) |11111111|11100 [13] 1ffc [13]
'^' ( 94) |11111111|111101 [14] 3ffd [14]
'_' ( 95) |101110 [6] 2e [6]
'`' ( 96) |11111111|11111111|110 [19] 7fffe [19]
'a' ( 97) |01000 [5] 8 [5]
'b' ( 98) |101111 [6] 2f [6]
'c' ( 99) |01001 [5] 9 [5]
'd' (100) |110000 [6] 30 [6]
'e' (101) |0001 [4] 1 [4]
'f' (102) |110001 [6] 31 [6]
'g' (103) |110010 [6] 32 [6]
'h' (104) |110011 [6] 33 [6]
'i' (105) |01010 [5] a [5]
'j' (106) |1110001 [7] 71 [7]
'k' (107) |1110010 [7] 72 [7]
'l' (108) |01011 [5] b [5]
'm' (109) |110100 [6] 34 [6]
'n' (110) |01100 [5] c [5]
'o' (111) |01101 [5] d [5]
'p' (112) |01110 [5] e [5]
'q' (113) |11110010| [8] f2 [8]
'r' (114) |01111 [5] f [5]
's' (115) |10000 [5] 10 [5]
't' (116) |10001 [5] 11 [5]
'u' (117) |110101 [6] 35 [6]
'v' (118) |1110011 [7] 73 [7]
'w' (119) |110110 [6] 36 [6]
'x' (120) |11110011| [8] f3 [8]
'y' (121) |11110100| [8] f4 [8]
'z' (122) |11110101| [8] f5 [8]
'{' (123) |11111111|11111110|1 [17] 1fffd [17]
'|' (124) |11111111|101 [11] 7fd [11]
'}' (125) |11111111|11111111|0 [17] 1fffe [17]
'~' (126) |11111111|1101 [12] ffd [12]
(127) |11111111|11111111|11111011|011 [27] 7ffffdb [27]
(128) |11111111|11111111|11111011|100 [27] 7ffffdc [27]
(129) |11111111|11111111|11111011|101 [27] 7ffffdd [27]
(130) |11111111|11111111|11111011|110 [27] 7ffffde [27]
(131) |11111111|11111111|11111011|111 [27] 7ffffdf [27]
(132) |11111111|11111111|11111100|000 [27] 7ffffe0 [27]
(133) |11111111|11111111|11111100|001 [27] 7ffffe1 [27]
(134) |11111111|11111111|11111100|010 [27] 7ffffe2 [27]
(135) |11111111|11111111|11111100|011 [27] 7ffffe3 [27]
(136) |11111111|11111111|11111100|100 [27] 7ffffe4 [27]
(137) |11111111|11111111|11111100|101 [27] 7ffffe5 [27]
(138) |11111111|11111111|11111100|110 [27] 7ffffe6 [27]
(139) |11111111|11111111|11111100|111 [27] 7ffffe7 [27]
(140) |11111111|11111111|11111101|000 [27] 7ffffe8 [27]
(141) |11111111|11111111|11111101|001 [27] 7ffffe9 [27]
(142) |11111111|11111111|11111101|010 [27] 7ffffea [27]
(143) |11111111|11111111|11111101|011 [27] 7ffffeb [27]
(144) |11111111|11111111|11111101|100 [27] 7ffffec [27]
(145) |11111111|11111111|11111101|101 [27] 7ffffed [27]
(146) |11111111|11111111|11111101|110 [27] 7ffffee [27]
(147) |11111111|11111111|11111101|111 [27] 7ffffef [27]
(148) |11111111|11111111|11111110|000 [27] 7fffff0 [27]
(149) |11111111|11111111|11111110|001 [27] 7fffff1 [27]
(150) |11111111|11111111|11111110|010 [27] 7fffff2 [27]
(151) |11111111|11111111|11111110|011 [27] 7fffff3 [27]
(152) |11111111|11111111|11111110|100 [27] 7fffff4 [27]
(153) |11111111|11111111|11111110|101 [27] 7fffff5 [27]
(154) |11111111|11111111|11111110|110 [27] 7fffff6 [27]
(155) |11111111|11111111|11111110|111 [27] 7fffff7 [27]
(156) |11111111|11111111|11111111|000 [27] 7fffff8 [27]
(157) |11111111|11111111|11111111|001 [27] 7fffff9 [27]
(158) |11111111|11111111|11111111|010 [27] 7fffffa [27]
(159) |11111111|11111111|11111111|011 [27] 7fffffb [27]
(160) |11111111|11111111|11111111|100 [27] 7fffffc [27]
(161) |11111111|11111111|11111111|101 [27] 7fffffd [27]
(162) |11111111|11111111|11111111|110 [27] 7fffffe [27]
(163) |11111111|11111111|11111111|111 [27] 7ffffff [27]
(164) |11111111|11111111|11100000|00 [26] 3ffff80 [26]
(165) |11111111|11111111|11100000|01 [26] 3ffff81 [26]
(166) |11111111|11111111|11100000|10 [26] 3ffff82 [26]
(167) |11111111|11111111|11100000|11 [26] 3ffff83 [26]
(168) |11111111|11111111|11100001|00 [26] 3ffff84 [26]
(169) |11111111|11111111|11100001|01 [26] 3ffff85 [26]
(170) |11111111|11111111|11100001|10 [26] 3ffff86 [26]
(171) |11111111|11111111|11100001|11 [26] 3ffff87 [26]
(172) |11111111|11111111|11100010|00 [26] 3ffff88 [26]
(173) |11111111|11111111|11100010|01 [26] 3ffff89 [26]
(174) |11111111|11111111|11100010|10 [26] 3ffff8a [26]
(175) |11111111|11111111|11100010|11 [26] 3ffff8b [26]
(176) |11111111|11111111|11100011|00 [26] 3ffff8c [26]
(177) |11111111|11111111|11100011|01 [26] 3ffff8d [26]
(178) |11111111|11111111|11100011|10 [26] 3ffff8e [26]
(179) |11111111|11111111|11100011|11 [26] 3ffff8f [26]
(180) |11111111|11111111|11100100|00 [26] 3ffff90 [26]
(181) |11111111|11111111|11100100|01 [26] 3ffff91 [26]
(182) |11111111|11111111|11100100|10 [26] 3ffff92 [26]
(183) |11111111|11111111|11100100|11 [26] 3ffff93 [26]
(184) |11111111|11111111|11100101|00 [26] 3ffff94 [26]
(185) |11111111|11111111|11100101|01 [26] 3ffff95 [26]
(186) |11111111|11111111|11100101|10 [26] 3ffff96 [26]
(187) |11111111|11111111|11100101|11 [26] 3ffff97 [26]
(188) |11111111|11111111|11100110|00 [26] 3ffff98 [26]
(189) |11111111|11111111|11100110|01 [26] 3ffff99 [26]
(190) |11111111|11111111|11100110|10 [26] 3ffff9a [26]
(191) |11111111|11111111|11100110|11 [26] 3ffff9b [26]
(192) |11111111|11111111|11100111|00 [26] 3ffff9c [26]
(193) |11111111|11111111|11100111|01 [26] 3ffff9d [26]
(194) |11111111|11111111|11100111|10 [26] 3ffff9e [26]
(195) |11111111|11111111|11100111|11 [26] 3ffff9f [26]
(196) |11111111|11111111|11101000|00 [26] 3ffffa0 [26]
(197) |11111111|11111111|11101000|01 [26] 3ffffa1 [26]
(198) |11111111|11111111|11101000|10 [26] 3ffffa2 [26]
(199) |11111111|11111111|11101000|11 [26] 3ffffa3 [26]
(200) |11111111|11111111|11101001|00 [26] 3ffffa4 [26]
(201) |11111111|11111111|11101001|01 [26] 3ffffa5 [26]
(202) |11111111|11111111|11101001|10 [26] 3ffffa6 [26]
(203) |11111111|11111111|11101001|11 [26] 3ffffa7 [26]
(204) |11111111|11111111|11101010|00 [26] 3ffffa8 [26]
(205) |11111111|11111111|11101010|01 [26] 3ffffa9 [26]
(206) |11111111|11111111|11101010|10 [26] 3ffffaa [26]
(207) |11111111|11111111|11101010|11 [26] 3ffffab [26]
(208) |11111111|11111111|11101011|00 [26] 3ffffac [26]
(209) |11111111|11111111|11101011|01 [26] 3ffffad [26]
(210) |11111111|11111111|11101011|10 [26] 3ffffae [26]
(211) |11111111|11111111|11101011|11 [26] 3ffffaf [26]
(212) |11111111|11111111|11101100|00 [26] 3ffffb0 [26]
(213) |11111111|11111111|11101100|01 [26] 3ffffb1 [26]
(214) |11111111|11111111|11101100|10 [26] 3ffffb2 [26]
(215) |11111111|11111111|11101100|11 [26] 3ffffb3 [26]
(216) |11111111|11111111|11101101|00 [26] 3ffffb4 [26]
(217) |11111111|11111111|11101101|01 [26] 3ffffb5 [26]
(218) |11111111|11111111|11101101|10 [26] 3ffffb6 [26]
(219) |11111111|11111111|11101101|11 [26] 3ffffb7 [26]
(220) |11111111|11111111|11101110|00 [26] 3ffffb8 [26]
(221) |11111111|11111111|11101110|01 [26] 3ffffb9 [26]
(222) |11111111|11111111|11101110|10 [26] 3ffffba [26]
(223) |11111111|11111111|11101110|11 [26] 3ffffbb [26]
(224) |11111111|11111111|11101111|00 [26] 3ffffbc [26]
(225) |11111111|11111111|11101111|01 [26] 3ffffbd [26]
(226) |11111111|11111111|11101111|10 [26] 3ffffbe [26]
(227) |11111111|11111111|11101111|11 [26] 3ffffbf [26]
(228) |11111111|11111111|11110000|00 [26] 3ffffc0 [26]
(229) |11111111|11111111|11110000|01 [26] 3ffffc1 [26]
(230) |11111111|11111111|11110000|10 [26] 3ffffc2 [26]
(231) |11111111|11111111|11110000|11 [26] 3ffffc3 [26]
(232) |11111111|11111111|11110001|00 [26] 3ffffc4 [26]
(233) |11111111|11111111|11110001|01 [26] 3ffffc5 [26]
(234) |11111111|11111111|11110001|10 [26] 3ffffc6 [26]
(235) |11111111|11111111|11110001|11 [26] 3ffffc7 [26]
(236) |11111111|11111111|11110010|00 [26] 3ffffc8 [26]
(237) |11111111|11111111|11110010|01 [26] 3ffffc9 [26]
(238) |11111111|11111111|11110010|10 [26] 3ffffca [26]
(239) |11111111|11111111|11110010|11 [26] 3ffffcb [26]
(240) |11111111|11111111|11110011|00 [26] 3ffffcc [26]
(241) |11111111|11111111|11110011|01 [26] 3ffffcd [26]
(242) |11111111|11111111|11110011|10 [26] 3ffffce [26]
(243) |11111111|11111111|11110011|11 [26] 3ffffcf [26]
(244) |11111111|11111111|11110100|00 [26] 3ffffd0 [26]
(245) |11111111|11111111|11110100|01 [26] 3ffffd1 [26]
(246) |11111111|11111111|11110100|10 [26] 3ffffd2 [26]
(247) |11111111|11111111|11110100|11 [26] 3ffffd3 [26]
(248) |11111111|11111111|11110101|00 [26] 3ffffd4 [26]
(249) |11111111|11111111|11110101|01 [26] 3ffffd5 [26]
(250) |11111111|11111111|11110101|10 [26] 3ffffd6 [26]
(251) |11111111|11111111|11110101|11 [26] 3ffffd7 [26]
(252) |11111111|11111111|11110110|00 [26] 3ffffd8 [26]
(253) |11111111|11111111|11110110|01 [26] 3ffffd9 [26]
(254) |11111111|11111111|11110110|10 [26] 3ffffda [26]
(255) |11111111|11111111|11110110|11 [26] 3ffffdb [26]
EOS (256) |11111111|11111111|11110111|00 [26] 3ffffdc [26]
Appendix D. Huffman Codes for Responses
The following Huffman codes are used when encoding string literals in The following Huffman codes are used when encoding string literals.
the server to client direction. These codes apply for both responses
to client requests and for push-promises.
[[anchor11: This table may need to be regenerated.]] [[This table will be regenerated. ]]
aligned aligned aligned aligned
to len to len to len to len
MSB in LSB in MSB in LSB in
sym as bits bits as hex bits sym as bits bits as hex bits
( 0) |11111111|11111111|11011110|0 [25] 1ffffbc [25] ( 0) |11111111|11111111|11110111|010 [27] 7ffffba [27]
( 1) |11111111|11111111|11011110|1 [25] 1ffffbd [25] ( 1) |11111111|11111111|11110111|011 [27] 7ffffbb [27]
( 2) |11111111|11111111|11011111|0 [25] 1ffffbe [25] ( 2) |11111111|11111111|11110111|100 [27] 7ffffbc [27]
( 3) |11111111|11111111|11011111|1 [25] 1ffffbf [25] ( 3) |11111111|11111111|11110111|101 [27] 7ffffbd [27]
( 4) |11111111|11111111|11100000|0 [25] 1ffffc0 [25] ( 4) |11111111|11111111|11110111|110 [27] 7ffffbe [27]
( 5) |11111111|11111111|11100000|1 [25] 1ffffc1 [25] ( 5) |11111111|11111111|11110111|111 [27] 7ffffbf [27]
( 6) |11111111|11111111|11100001|0 [25] 1ffffc2 [25] ( 6) |11111111|11111111|11111000|000 [27] 7ffffc0 [27]
( 7) |11111111|11111111|11100001|1 [25] 1ffffc3 [25] ( 7) |11111111|11111111|11111000|001 [27] 7ffffc1 [27]
( 8) |11111111|11111111|11100010|0 [25] 1ffffc4 [25] ( 8) |11111111|11111111|11111000|010 [27] 7ffffc2 [27]
( 9) |11111111|11111111|11100010|1 [25] 1ffffc5 [25] ( 9) |11111111|11111111|11111000|011 [27] 7ffffc3 [27]
( 10) |11111111|11111111|11100011|0 [25] 1ffffc6 [25] ( 10) |11111111|11111111|11111000|100 [27] 7ffffc4 [27]
( 11) |11111111|11111111|11100011|1 [25] 1ffffc7 [25] ( 11) |11111111|11111111|11111000|101 [27] 7ffffc5 [27]
( 12) |11111111|11111111|11100100|0 [25] 1ffffc8 [25] ( 12) |11111111|11111111|11111000|110 [27] 7ffffc6 [27]
( 13) |11111111|11111111|11100100|1 [25] 1ffffc9 [25] ( 13) |11111111|11111111|11111000|111 [27] 7ffffc7 [27]
( 14) |11111111|11111111|11100101|0 [25] 1ffffca [25] ( 14) |11111111|11111111|11111001|000 [27] 7ffffc8 [27]
( 15) |11111111|11111111|11100101|1 [25] 1ffffcb [25] ( 15) |11111111|11111111|11111001|001 [27] 7ffffc9 [27]
( 16) |11111111|11111111|11100110|0 [25] 1ffffcc [25] ( 16) |11111111|11111111|11111001|010 [27] 7ffffca [27]
( 17) |11111111|11111111|11100110|1 [25] 1ffffcd [25] ( 17) |11111111|11111111|11111001|011 [27] 7ffffcb [27]
( 18) |11111111|11111111|11100111|0 [25] 1ffffce [25] ( 18) |11111111|11111111|11111001|100 [27] 7ffffcc [27]
( 19) |11111111|11111111|11100111|1 [25] 1ffffcf [25] ( 19) |11111111|11111111|11111001|101 [27] 7ffffcd [27]
( 20) |11111111|11111111|11101000|0 [25] 1ffffd0 [25] ( 20) |11111111|11111111|11111001|110 [27] 7ffffce [27]
( 21) |11111111|11111111|11101000|1 [25] 1ffffd1 [25] ( 21) |11111111|11111111|11111001|111 [27] 7ffffcf [27]
( 22) |11111111|11111111|11101001|0 [25] 1ffffd2 [25] ( 22) |11111111|11111111|11111010|000 [27] 7ffffd0 [27]
( 23) |11111111|11111111|11101001|1 [25] 1ffffd3 [25] ( 23) |11111111|11111111|11111010|001 [27] 7ffffd1 [27]
( 24) |11111111|11111111|11101010|0 [25] 1ffffd4 [25] ( 24) |11111111|11111111|11111010|010 [27] 7ffffd2 [27]
( 25) |11111111|11111111|11101010|1 [25] 1ffffd5 [25] ( 25) |11111111|11111111|11111010|011 [27] 7ffffd3 [27]
( 26) |11111111|11111111|11101011|0 [25] 1ffffd6 [25] ( 26) |11111111|11111111|11111010|100 [27] 7ffffd4 [27]
( 27) |11111111|11111111|11101011|1 [25] 1ffffd7 [25] ( 27) |11111111|11111111|11111010|101 [27] 7ffffd5 [27]
( 28) |11111111|11111111|11101100|0 [25] 1ffffd8 [25] ( 28) |11111111|11111111|11111010|110 [27] 7ffffd6 [27]
( 29) |11111111|11111111|11101100|1 [25] 1ffffd9 [25] ( 29) |11111111|11111111|11111010|111 [27] 7ffffd7 [27]
( 30) |11111111|11111111|11101101|0 [25] 1ffffda [25] ( 30) |11111111|11111111|11111011|000 [27] 7ffffd8 [27]
( 31) |11111111|11111111|11101101|1 [25] 1ffffdb [25] ( 31) |11111111|11111111|11111011|001 [27] 7ffffd9 [27]
' ' ( 32) |0000 [4] 0 [4] ' ' ( 32) |11101000| [8] e8 [8]
'!' ( 33) |11111111|1010 [12] ffa [12] '!' ( 33) |11111111|1100 [12] ffc [12]
'"' ( 34) |1101010 [7] 6a [7] '"' ( 34) |11111111|111010 [14] 3ffa [14]
'#' ( 35) |11111111|11010 [13] 1ffa [13] '#' ( 35) |11111111|1111100 [15] 7ffc [15]
'$' ( 36) |11111111|111100 [14] 3ffc [14] '$' ( 36) |11111111|1111101 [15] 7ffd [15]
'%' ( 37) |11110110|0 [9] 1ec [9] '%' ( 37) |100100 [6] 24 [6]
'&' ( 38) |11111110|00 [10] 3f8 [10] '&' ( 38) |1101110 [7] 6e [7]
''' ( 39) |11111111|11011 [13] 1ffb [13] ''' ( 39) |11111111|1111110 [15] 7ffe [15]
'(' ( 40) |11110110|1 [9] 1ed [9] '(' ( 40) |11111111|010 [11] 7fa [11]
')' ( 41) |11110111|0 [9] 1ee [9] ')' ( 41) |11111111|011 [11] 7fb [11]
'*' ( 42) |11111111|1011 [12] ffb [12] '*' ( 42) |11111110|10 [10] 3fa [10]
'+' ( 43) |11111111|010 [11] 7fa [11] '+' ( 43) |11111111|100 [11] 7fc [11]
',' ( 44) |100010 [6] 22 [6] ',' ( 44) |11101001| [8] e9 [8]
'-' ( 45) |100011 [6] 23 [6] '-' ( 45) |100101 [6] 25 [6]
'.' ( 46) |100100 [6] 24 [6] '.' ( 46) |00100 [5] 4 [5]
'/' ( 47) |1101011 [7] 6b [7] '/' ( 47) |0000 [4] 0 [4]
'0' ( 48) |0001 [4] 1 [4] '0' ( 48) |00101 [5] 5 [5]
'1' ( 49) |0010 [4] 2 [4] '1' ( 49) |00110 [5] 6 [5]
'2' ( 50) |0011 [4] 3 [4] '2' ( 50) |00111 [5] 7 [5]
'3' ( 51) |01000 [5] 8 [5] '3' ( 51) |100110 [6] 26 [6]
'4' ( 52) |01001 [5] 9 [5] '4' ( 52) |100111 [6] 27 [6]
'5' ( 53) |01010 [5] a [5] '5' ( 53) |101000 [6] 28 [6]
'6' ( 54) |100101 [6] 25 [6] '6' ( 54) |101001 [6] 29 [6]
'7' ( 55) |100110 [6] 26 [6] '7' ( 55) |101010 [6] 2a [6]
'8' ( 56) |01011 [5] b [5] '8' ( 56) |101011 [6] 2b [6]
'9' ( 57) |01100 [5] c [5] '9' ( 57) |101100 [6] 2c [6]
':' ( 58) |01101 [5] d [5] ':' ( 58) |11110110|0 [9] 1ec [9]
';' ( 59) |11110111|1 [9] 1ef [9] ';' ( 59) |11101010| [8] ea [8]
'<' ( 60) |11111111|11111010| [16] fffa [16] '<' ( 60) |11111111|11111111|10 [18] 3fffe [18]
'=' ( 61) |1101100 [7] 6c [7] '=' ( 61) |101101 [6] 2d [6]
'>' ( 62) |11111111|11100 [13] 1ffc [13] '>' ( 62) |11111111|11111110|0 [17] 1fffc [17]
'?' ( 63) |11111111|1100 [12] ffc [12] '?' ( 63) |11110110|1 [9] 1ed [9]
'@' ( 64) |11111111|11111011| [16] fffb [16] '@' ( 64) |11111111|111011 [14] 3ffb [14]
'A' ( 65) |1101101 [7] 6d [7] 'A' ( 65) |1101111 [7] 6f [7]
'B' ( 66) |11101010| [8] ea [8] 'B' ( 66) |11101011| [8] eb [8]
'C' ( 67) |11101011| [8] eb [8] 'C' ( 67) |11101100| [8] ec [8]
'D' ( 68) |11101100| [8] ec [8] 'D' ( 68) |11101101| [8] ed [8]
'E' ( 69) |11101101| [8] ed [8] 'E' ( 69) |11101110| [8] ee [8]
'F' ( 70) |11101110| [8] ee [8] 'F' ( 70) |1110000 [7] 70 [7]
'G' ( 71) |100111 [6] 27 [6] 'G' ( 71) |11110111|0 [9] 1ee [9]
'H' ( 72) |11111000|0 [9] 1f0 [9] 'H' ( 72) |11110111|1 [9] 1ef [9]
'I' ( 73) |11101111| [8] ef [8] 'I' ( 73) |11111000|0 [9] 1f0 [9]
'J' ( 74) |11110000| [8] f0 [8] 'J' ( 74) |11111000|1 [9] 1f1 [9]
'K' ( 75) |11111110|01 [10] 3f9 [10] 'K' ( 75) |11111110|11 [10] 3fb [10]
'L' ( 76) |11111000|1 [9] 1f1 [9] 'L' ( 76) |11111001|0 [9] 1f2 [9]
'M' ( 77) |101000 [6] 28 [6] 'M' ( 77) |11101111| [8] ef [8]
'N' ( 78) |11110001| [8] f1 [8] 'N' ( 78) |11111001|1 [9] 1f3 [9]
'O' ( 79) |11110010| [8] f2 [8] 'O' ( 79) |11111010|0 [9] 1f4 [9]
'P' ( 80) |11111001|0 [9] 1f2 [9] 'P' ( 80) |11111010|1 [9] 1f5 [9]
'Q' ( 81) |11111110|10 [10] 3fa [10] 'Q' ( 81) |11111011|0 [9] 1f6 [9]
'R' ( 82) |11111001|1 [9] 1f3 [9] 'R' ( 82) |11111011|1 [9] 1f7 [9]
'S' ( 83) |101001 [6] 29 [6] 'S' ( 83) |11110000| [8] f0 [8]
'T' ( 84) |01110 [5] e [5] 'T' ( 84) |11110001| [8] f1 [8]
'U' ( 85) |11111010|0 [9] 1f4 [9] 'U' ( 85) |11111100|0 [9] 1f8 [9]
'V' ( 86) |11111010|1 [9] 1f5 [9] 'V' ( 86) |11111100|1 [9] 1f9 [9]
'W' ( 87) |11110011| [8] f3 [8] 'W' ( 87) |11111101|0 [9] 1fa [9]
'X' ( 88) |11111110|11 [10] 3fb [10] 'X' ( 88) |11111101|1 [9] 1fb [9]
'Y' ( 89) |11111011|0 [9] 1f6 [9] 'Y' ( 89) |11111110|0 [9] 1fc [9]
'Z' ( 90) |11111111|00 [10] 3fc [10] 'Z' ( 90) |11111111|00 [10] 3fc [10]
'[' ( 91) |11111111|011 [11] 7fb [11] '[' ( 91) |11111111|111100 [14] 3ffc [14]
'\' ( 92) |11111111|11101 [13] 1ffd [13] '\' ( 92) |11111111|11111111|11111011|010 [27] 7ffffda [27]
']' ( 93) |11111111|100 [11] 7fc [11] ']' ( 93) |11111111|11100 [13] 1ffc [13]
'^' ( 94) |11111111|1111100 [15] 7ffc [15] '^' ( 94) |11111111|111101 [14] 3ffd [14]
'_' ( 95) |11111011|1 [9] 1f7 [9] '_' ( 95) |101110 [6] 2e [6]
'`' ( 96) |11111111|11111111|0 [17] 1fffe [17] '`' ( 96) |11111111|11111111|110 [19] 7fffe [19]
'a' ( 97) |01111 [5] f [5] 'a' ( 97) |01000 [5] 8 [5]
'b' ( 98) |1101110 [7] 6e [7] 'b' ( 98) |101111 [6] 2f [6]
'c' ( 99) |101010 [6] 2a [6] 'c' ( 99) |01001 [5] 9 [5]
'd' (100) |101011 [6] 2b [6] 'd' (100) |110000 [6] 30 [6]
'e' (101) |10000 [5] 10 [5] 'e' (101) |0001 [4] 1 [4]
'f' (102) |1101111 [7] 6f [7] 'f' (102) |110001 [6] 31 [6]
'g' (103) |1110000 [7] 70 [7] 'g' (103) |110010 [6] 32 [6]
'h' (104) |1110001 [7] 71 [7] 'h' (104) |110011 [6] 33 [6]
'i' (105) |101100 [6] 2c [6] 'i' (105) |01010 [5] a [5]
'j' (106) |11111100|0 [9] 1f8 [9] 'j' (106) |1110001 [7] 71 [7]
'k' (107) |11111100|1 [9] 1f9 [9] 'k' (107) |1110010 [7] 72 [7]
'l' (108) |1110010 [7] 72 [7] 'l' (108) |01011 [5] b [5]
'm' (109) |101101 [6] 2d [6] 'm' (109) |110100 [6] 34 [6]
'n' (110) |101110 [6] 2e [6] 'n' (110) |01100 [5] c [5]
'o' (111) |101111 [6] 2f [6] 'o' (111) |01101 [5] d [5]
'p' (112) |110000 [6] 30 [6] 'p' (112) |01110 [5] e [5]
'q' (113) |11111101|0 [9] 1fa [9] 'q' (113) |11110010| [8] f2 [8]
'r' (114) |110001 [6] 31 [6] 'r' (114) |01111 [5] f [5]
's' (115) |110010 [6] 32 [6] 's' (115) |10000 [5] 10 [5]
't' (116) |110011 [6] 33 [6] 't' (116) |10001 [5] 11 [5]
'u' (117) |110100 [6] 34 [6] 'u' (117) |110101 [6] 35 [6]
'v' (118) |1110011 [7] 73 [7] 'v' (118) |1110011 [7] 73 [7]
'w' (119) |11110100| [8] f4 [8] 'w' (119) |110110 [6] 36 [6]
'x' (120) |1110100 [7] 74 [7] 'x' (120) |11110011| [8] f3 [8]
'y' (121) |11110101| [8] f5 [8] 'y' (121) |11110100| [8] f4 [8]
'z' (122) |11111101|1 [9] 1fb [9] 'z' (122) |11110101| [8] f5 [8]
'{' (123) |11111111|11111100| [16] fffc [16] '{' (123) |11111111|11111110|1 [17] 1fffd [17]
'|' (124) |11111111|111101 [14] 3ffd [14] '|' (124) |11111111|101 [11] 7fd [11]
'}' (125) |11111111|11111101| [16] fffd [16] '}' (125) |11111111|11111111|0 [17] 1fffe [17]
'~' (126) |11111111|11111110| [16] fffe [16] '~' (126) |11111111|1101 [12] ffd [12]
(127) |11111111|11111111|11101110|0 [25] 1ffffdc [25] (127) |11111111|11111111|11111011|011 [27] 7ffffdb [27]
(128) |11111111|11111111|11101110|1 [25] 1ffffdd [25] (128) |11111111|11111111|11111011|100 [27] 7ffffdc [27]
(129) |11111111|11111111|11101111|0 [25] 1ffffde [25] (129) |11111111|11111111|11111011|101 [27] 7ffffdd [27]
(130) |11111111|11111111|11101111|1 [25] 1ffffdf [25] (130) |11111111|11111111|11111011|110 [27] 7ffffde [27]
(131) |11111111|11111111|11110000|0 [25] 1ffffe0 [25] (131) |11111111|11111111|11111011|111 [27] 7ffffdf [27]
(132) |11111111|11111111|11110000|1 [25] 1ffffe1 [25] (132) |11111111|11111111|11111100|000 [27] 7ffffe0 [27]
(133) |11111111|11111111|11110001|0 [25] 1ffffe2 [25] (133) |11111111|11111111|11111100|001 [27] 7ffffe1 [27]
(134) |11111111|11111111|11110001|1 [25] 1ffffe3 [25] (134) |11111111|11111111|11111100|010 [27] 7ffffe2 [27]
(135) |11111111|11111111|11110010|0 [25] 1ffffe4 [25] (135) |11111111|11111111|11111100|011 [27] 7ffffe3 [27]
(136) |11111111|11111111|11110010|1 [25] 1ffffe5 [25] (136) |11111111|11111111|11111100|100 [27] 7ffffe4 [27]
(137) |11111111|11111111|11110011|0 [25] 1ffffe6 [25] (137) |11111111|11111111|11111100|101 [27] 7ffffe5 [27]
(138) |11111111|11111111|11110011|1 [25] 1ffffe7 [25] (138) |11111111|11111111|11111100|110 [27] 7ffffe6 [27]
(139) |11111111|11111111|11110100|0 [25] 1ffffe8 [25] (139) |11111111|11111111|11111100|111 [27] 7ffffe7 [27]
(140) |11111111|11111111|11110100|1 [25] 1ffffe9 [25] (140) |11111111|11111111|11111101|000 [27] 7ffffe8 [27]
(141) |11111111|11111111|11110101|0 [25] 1ffffea [25] (141) |11111111|11111111|11111101|001 [27] 7ffffe9 [27]
(142) |11111111|11111111|11110101|1 [25] 1ffffeb [25] (142) |11111111|11111111|11111101|010 [27] 7ffffea [27]
(143) |11111111|11111111|11110110|0 [25] 1ffffec [25] (143) |11111111|11111111|11111101|011 [27] 7ffffeb [27]
(144) |11111111|11111111|11110110|1 [25] 1ffffed [25] (144) |11111111|11111111|11111101|100 [27] 7ffffec [27]
(145) |11111111|11111111|11110111|0 [25] 1ffffee [25] (145) |11111111|11111111|11111101|101 [27] 7ffffed [27]
(146) |11111111|11111111|11110111|1 [25] 1ffffef [25] (146) |11111111|11111111|11111101|110 [27] 7ffffee [27]
(147) |11111111|11111111|11111000|0 [25] 1fffff0 [25] (147) |11111111|11111111|11111101|111 [27] 7ffffef [27]
(148) |11111111|11111111|11111000|1 [25] 1fffff1 [25] (148) |11111111|11111111|11111110|000 [27] 7fffff0 [27]
(149) |11111111|11111111|11111001|0 [25] 1fffff2 [25] (149) |11111111|11111111|11111110|001 [27] 7fffff1 [27]
(150) |11111111|11111111|11111001|1 [25] 1fffff3 [25] (150) |11111111|11111111|11111110|010 [27] 7fffff2 [27]
(151) |11111111|11111111|11111010|0 [25] 1fffff4 [25] (151) |11111111|11111111|11111110|011 [27] 7fffff3 [27]
(152) |11111111|11111111|11111010|1 [25] 1fffff5 [25] (152) |11111111|11111111|11111110|100 [27] 7fffff4 [27]
(153) |11111111|11111111|11111011|0 [25] 1fffff6 [25] (153) |11111111|11111111|11111110|101 [27] 7fffff5 [27]
(154) |11111111|11111111|11111011|1 [25] 1fffff7 [25] (154) |11111111|11111111|11111110|110 [27] 7fffff6 [27]
(155) |11111111|11111111|11111100|0 [25] 1fffff8 [25] (155) |11111111|11111111|11111110|111 [27] 7fffff7 [27]
(156) |11111111|11111111|11111100|1 [25] 1fffff9 [25] (156) |11111111|11111111|11111111|000 [27] 7fffff8 [27]
(157) |11111111|11111111|11111101|0 [25] 1fffffa [25] (157) |11111111|11111111|11111111|001 [27] 7fffff9 [27]
(158) |11111111|11111111|11111101|1 [25] 1fffffb [25] (158) |11111111|11111111|11111111|010 [27] 7fffffa [27]
(159) |11111111|11111111|11111110|0 [25] 1fffffc [25] (159) |11111111|11111111|11111111|011 [27] 7fffffb [27]
(160) |11111111|11111111|11111110|1 [25] 1fffffd [25] (160) |11111111|11111111|11111111|100 [27] 7fffffc [27]
(161) |11111111|11111111|11111111|0 [25] 1fffffe [25] (161) |11111111|11111111|11111111|101 [27] 7fffffd [27]
(162) |11111111|11111111|11111111|1 [25] 1ffffff [25] (162) |11111111|11111111|11111111|110 [27] 7fffffe [27]
(163) |11111111|11111111|10000000| [24] ffff80 [24] (163) |11111111|11111111|11111111|111 [27] 7ffffff [27]
(164) |11111111|11111111|10000001| [24] ffff81 [24] (164) |11111111|11111111|11100000|00 [26] 3ffff80 [26]
(165) |11111111|11111111|10000010| [24] ffff82 [24] (165) |11111111|11111111|11100000|01 [26] 3ffff81 [26]
(166) |11111111|11111111|10000011| [24] ffff83 [24] (166) |11111111|11111111|11100000|10 [26] 3ffff82 [26]
(167) |11111111|11111111|10000100| [24] ffff84 [24] (167) |11111111|11111111|11100000|11 [26] 3ffff83 [26]
(168) |11111111|11111111|10000101| [24] ffff85 [24] (168) |11111111|11111111|11100001|00 [26] 3ffff84 [26]
(169) |11111111|11111111|10000110| [24] ffff86 [24] (169) |11111111|11111111|11100001|01 [26] 3ffff85 [26]
(170) |11111111|11111111|10000111| [24] ffff87 [24] (170) |11111111|11111111|11100001|10 [26] 3ffff86 [26]
(171) |11111111|11111111|10001000| [24] ffff88 [24] (171) |11111111|11111111|11100001|11 [26] 3ffff87 [26]
(172) |11111111|11111111|10001001| [24] ffff89 [24] (172) |11111111|11111111|11100010|00 [26] 3ffff88 [26]
(173) |11111111|11111111|10001010| [24] ffff8a [24] (173) |11111111|11111111|11100010|01 [26] 3ffff89 [26]
(174) |11111111|11111111|10001011| [24] ffff8b [24] (174) |11111111|11111111|11100010|10 [26] 3ffff8a [26]
(175) |11111111|11111111|10001100| [24] ffff8c [24] (175) |11111111|11111111|11100010|11 [26] 3ffff8b [26]
(176) |11111111|11111111|10001101| [24] ffff8d [24] (176) |11111111|11111111|11100011|00 [26] 3ffff8c [26]
(177) |11111111|11111111|10001110| [24] ffff8e [24] (177) |11111111|11111111|11100011|01 [26] 3ffff8d [26]
(178) |11111111|11111111|10001111| [24] ffff8f [24] (178) |11111111|11111111|11100011|10 [26] 3ffff8e [26]
(179) |11111111|11111111|10010000| [24] ffff90 [24] (179) |11111111|11111111|11100011|11 [26] 3ffff8f [26]
(180) |11111111|11111111|10010001| [24] ffff91 [24] (180) |11111111|11111111|11100100|00 [26] 3ffff90 [26]
(181) |11111111|11111111|10010010| [24] ffff92 [24] (181) |11111111|11111111|11100100|01 [26] 3ffff91 [26]
(182) |11111111|11111111|10010011| [24] ffff93 [24] (182) |11111111|11111111|11100100|10 [26] 3ffff92 [26]
(183) |11111111|11111111|10010100| [24] ffff94 [24] (183) |11111111|11111111|11100100|11 [26] 3ffff93 [26]
(184) |11111111|11111111|10010101| [24] ffff95 [24] (184) |11111111|11111111|11100101|00 [26] 3ffff94 [26]
(185) |11111111|11111111|10010110| [24] ffff96 [24] (185) |11111111|11111111|11100101|01 [26] 3ffff95 [26]
(186) |11111111|11111111|10010111| [24] ffff97 [24] (186) |11111111|11111111|11100101|10 [26] 3ffff96 [26]
(187) |11111111|11111111|10011000| [24] ffff98 [24] (187) |11111111|11111111|11100101|11 [26] 3ffff97 [26]
(188) |11111111|11111111|10011001| [24] ffff99 [24] (188) |11111111|11111111|11100110|00 [26] 3ffff98 [26]
(189) |11111111|11111111|10011010| [24] ffff9a [24] (189) |11111111|11111111|11100110|01 [26] 3ffff99 [26]
(190) |11111111|11111111|10011011| [24] ffff9b [24] (190) |11111111|11111111|11100110|10 [26] 3ffff9a [26]
(191) |11111111|11111111|10011100| [24] ffff9c [24] (191) |11111111|11111111|11100110|11 [26] 3ffff9b [26]
(192) |11111111|11111111|10011101| [24] ffff9d [24] (192) |11111111|11111111|11100111|00 [26] 3ffff9c [26]
(193) |11111111|11111111|10011110| [24] ffff9e [24] (193) |11111111|11111111|11100111|01 [26] 3ffff9d [26]
(194) |11111111|11111111|10011111| [24] ffff9f [24] (194) |11111111|11111111|11100111|10 [26] 3ffff9e [26]
(195) |11111111|11111111|10100000| [24] ffffa0 [24] (195) |11111111|11111111|11100111|11 [26] 3ffff9f [26]
(196) |11111111|11111111|10100001| [24] ffffa1 [24] (196) |11111111|11111111|11101000|00 [26] 3ffffa0 [26]
(197) |11111111|11111111|10100010| [24] ffffa2 [24] (197) |11111111|11111111|11101000|01 [26] 3ffffa1 [26]
(198) |11111111|11111111|10100011| [24] ffffa3 [24] (198) |11111111|11111111|11101000|10 [26] 3ffffa2 [26]
(199) |11111111|11111111|10100100| [24] ffffa4 [24] (199) |11111111|11111111|11101000|11 [26] 3ffffa3 [26]
(200) |11111111|11111111|10100101| [24] ffffa5 [24] (200) |11111111|11111111|11101001|00 [26] 3ffffa4 [26]
(201) |11111111|11111111|10100110| [24] ffffa6 [24] (201) |11111111|11111111|11101001|01 [26] 3ffffa5 [26]
(202) |11111111|11111111|10100111| [24] ffffa7 [24] (202) |11111111|11111111|11101001|10 [26] 3ffffa6 [26]
(203) |11111111|11111111|10101000| [24] ffffa8 [24] (203) |11111111|11111111|11101001|11 [26] 3ffffa7 [26]
(204) |11111111|11111111|10101001| [24] ffffa9 [24] (204) |11111111|11111111|11101010|00 [26] 3ffffa8 [26]
(205) |11111111|11111111|10101010| [24] ffffaa [24] (205) |11111111|11111111|11101010|01 [26] 3ffffa9 [26]
(206) |11111111|11111111|10101011| [24] ffffab [24] (206) |11111111|11111111|11101010|10 [26] 3ffffaa [26]
(207) |11111111|11111111|10101100| [24] ffffac [24] (207) |11111111|11111111|11101010|11 [26] 3ffffab [26]
(208) |11111111|11111111|10101101| [24] ffffad [24] (208) |11111111|11111111|11101011|00 [26] 3ffffac [26]
(209) |11111111|11111111|10101110| [24] ffffae [24] (209) |11111111|11111111|11101011|01 [26] 3ffffad [26]
(210) |11111111|11111111|10101111| [24] ffffaf [24] (210) |11111111|11111111|11101011|10 [26] 3ffffae [26]
(211) |11111111|11111111|10110000| [24] ffffb0 [24] (211) |11111111|11111111|11101011|11 [26] 3ffffaf [26]
(212) |11111111|11111111|10110001| [24] ffffb1 [24] (212) |11111111|11111111|11101100|00 [26] 3ffffb0 [26]
(213) |11111111|11111111|10110010| [24] ffffb2 [24] (213) |11111111|11111111|11101100|01 [26] 3ffffb1 [26]
(214) |11111111|11111111|10110011| [24] ffffb3 [24] (214) |11111111|11111111|11101100|10 [26] 3ffffb2 [26]
(215) |11111111|11111111|10110100| [24] ffffb4 [24] (215) |11111111|11111111|11101100|11 [26] 3ffffb3 [26]
(216) |11111111|11111111|10110101| [24] ffffb5 [24] (216) |11111111|11111111|11101101|00 [26] 3ffffb4 [26]
(217) |11111111|11111111|10110110| [24] ffffb6 [24] (217) |11111111|11111111|11101101|01 [26] 3ffffb5 [26]
(218) |11111111|11111111|10110111| [24] ffffb7 [24] (218) |11111111|11111111|11101101|10 [26] 3ffffb6 [26]
(219) |11111111|11111111|10111000| [24] ffffb8 [24] (219) |11111111|11111111|11101101|11 [26] 3ffffb7 [26]
(220) |11111111|11111111|10111001| [24] ffffb9 [24] (220) |11111111|11111111|11101110|00 [26] 3ffffb8 [26]
(221) |11111111|11111111|10111010| [24] ffffba [24] (221) |11111111|11111111|11101110|01 [26] 3ffffb9 [26]
(222) |11111111|11111111|10111011| [24] ffffbb [24] (222) |11111111|11111111|11101110|10 [26] 3ffffba [26]
(223) |11111111|11111111|10111100| [24] ffffbc [24] (223) |11111111|11111111|11101110|11 [26] 3ffffbb [26]
(224) |11111111|11111111|10111101| [24] ffffbd [24] (224) |11111111|11111111|11101111|00 [26] 3ffffbc [26]
(225) |11111111|11111111|10111110| [24] ffffbe [24] (225) |11111111|11111111|11101111|01 [26] 3ffffbd [26]
(226) |11111111|11111111|10111111| [24] ffffbf [24] (226) |11111111|11111111|11101111|10 [26] 3ffffbe [26]
(227) |11111111|11111111|11000000| [24] ffffc0 [24] (227) |11111111|11111111|11101111|11 [26] 3ffffbf [26]
(228) |11111111|11111111|11000001| [24] ffffc1 [24] (228) |11111111|11111111|11110000|00 [26] 3ffffc0 [26]
(229) |11111111|11111111|11000010| [24] ffffc2 [24] (229) |11111111|11111111|11110000|01 [26] 3ffffc1 [26]
(230) |11111111|11111111|11000011| [24] ffffc3 [24] (230) |11111111|11111111|11110000|10 [26] 3ffffc2 [26]
(231) |11111111|11111111|11000100| [24] ffffc4 [24] (231) |11111111|11111111|11110000|11 [26] 3ffffc3 [26]
(232) |11111111|11111111|11000101| [24] ffffc5 [24] (232) |11111111|11111111|11110001|00 [26] 3ffffc4 [26]
(233) |11111111|11111111|11000110| [24] ffffc6 [24] (233) |11111111|11111111|11110001|01 [26] 3ffffc5 [26]
(234) |11111111|11111111|11000111| [24] ffffc7 [24] (234) |11111111|11111111|11110001|10 [26] 3ffffc6 [26]
(235) |11111111|11111111|11001000| [24] ffffc8 [24] (235) |11111111|11111111|11110001|11 [26] 3ffffc7 [26]
(236) |11111111|11111111|11001001| [24] ffffc9 [24] (236) |11111111|11111111|11110010|00 [26] 3ffffc8 [26]
(237) |11111111|11111111|11001010| [24] ffffca [24] (237) |11111111|11111111|11110010|01 [26] 3ffffc9 [26]
(238) |11111111|11111111|11001011| [24] ffffcb [24] (238) |11111111|11111111|11110010|10 [26] 3ffffca [26]
(239) |11111111|11111111|11001100| [24] ffffcc [24] (239) |11111111|11111111|11110010|11 [26] 3ffffcb [26]
(240) |11111111|11111111|11001101| [24] ffffcd [24] (240) |11111111|11111111|11110011|00 [26] 3ffffcc [26]
(241) |11111111|11111111|11001110| [24] ffffce [24] (241) |11111111|11111111|11110011|01 [26] 3ffffcd [26]
(242) |11111111|11111111|11001111| [24] ffffcf [24] (242) |11111111|11111111|11110011|10 [26] 3ffffce [26]
(243) |11111111|11111111|11010000| [24] ffffd0 [24] (243) |11111111|11111111|11110011|11 [26] 3ffffcf [26]
(244) |11111111|11111111|11010001| [24] ffffd1 [24] (244) |11111111|11111111|11110100|00 [26] 3ffffd0 [26]
(245) |11111111|11111111|11010010| [24] ffffd2 [24] (245) |11111111|11111111|11110100|01 [26] 3ffffd1 [26]
(246) |11111111|11111111|11010011| [24] ffffd3 [24] (246) |11111111|11111111|11110100|10 [26] 3ffffd2 [26]
(247) |11111111|11111111|11010100| [24] ffffd4 [24] (247) |11111111|11111111|11110100|11 [26] 3ffffd3 [26]
(248) |11111111|11111111|11010101| [24] ffffd5 [24] (248) |11111111|11111111|11110101|00 [26] 3ffffd4 [26]
(249) |11111111|11111111|11010110| [24] ffffd6 [24] (249) |11111111|11111111|11110101|01 [26] 3ffffd5 [26]
(250) |11111111|11111111|11010111| [24] ffffd7 [24] (250) |11111111|11111111|11110101|10 [26] 3ffffd6 [26]
(251) |11111111|11111111|11011000| [24] ffffd8 [24] (251) |11111111|11111111|11110101|11 [26] 3ffffd7 [26]
(252) |11111111|11111111|11011001| [24] ffffd9 [24] (252) |11111111|11111111|11110110|00 [26] 3ffffd8 [26]
(253) |11111111|11111111|11011010| [24] ffffda [24] (253) |11111111|11111111|11110110|01 [26] 3ffffd9 [26]
(254) |11111111|11111111|11011011| [24] ffffdb [24] (254) |11111111|11111111|11110110|10 [26] 3ffffda [26]
(255) |11111111|11111111|11011100| [24] ffffdc [24] (255) |11111111|11111111|11110110|11 [26] 3ffffdb [26]
EOS (256) |11111111|11111111|11011101| [24] ffffdd [24] EOS (256) |11111111|11111111|11110111|00 [26] 3ffffdc [26]
Appendix E. Examples Appendix D. Examples
A number of examples are worked through here, for both requests and A number of examples are worked through here, for both requests and
responses, and with and without Huffman coding. responses, and with and without Huffman coding.
E.1. Header Field Representation Examples D.1. Header Field Representation Examples
This section show several independent representation examples. This section show several independent representation examples.
E.1.1. Literal Header Field with Indexing D.1.1. Literal Header Field with Indexing
The header field representation uses a literal name and a literal The header field representation uses a literal name and a literal
value. value.
Header set to encode: Header set to encode:
custom-key: custom-header custom-key: custom-header
Reference set: empty. Reference set: empty.
skipping to change at page 35, line 35 skipping to change at page 30, line 44
Header Table (after decoding): Header Table (after decoding):
[ 1] (s = 55) custom-key: custom-header [ 1] (s = 55) custom-key: custom-header
Table size: 55 Table size: 55
Decoded header set: Decoded header set:
custom-key: custom-header custom-key: custom-header
E.1.2. Literal Header Field without Indexing D.1.2. Literal Header Field without Indexing
The header field representation uses an indexed name and a literal The header field representation uses an indexed name and a literal
value. value.
Header set to encode: Header set to encode:
:path: /sample/path :path: /sample/path
Reference set: empty. Reference set: empty.
skipping to change at page 36, line 19 skipping to change at page 31, line 30
0c | Literal value (len = 12) 0c | Literal value (len = 12)
2f73 616d 706c 652f 7061 7468 | /sample/path 2f73 616d 706c 652f 7061 7468 | /sample/path
| -> :path: /sample/path | -> :path: /sample/path
Header table (after decoding): empty. Header table (after decoding): empty.
Decoded header set: Decoded header set:
:path: /sample/path :path: /sample/path
E.1.3. Indexed Header Field D.1.3. Indexed Header Field
The header field representation uses an indexed header field, from The header field representation uses an indexed header field, from
the static table. Upon using it, the static table entry is copied the static table. Upon using it, the static table entry is copied
into the header table. into the header table.
Header set to encode: Header set to encode:
:method: GET :method: GET
Reference set: empty. Reference set: empty.
skipping to change at page 37, line 5 skipping to change at page 32, line 20
Header Table (after decoding): Header Table (after decoding):
[ 1] (s = 42) :method: GET [ 1] (s = 42) :method: GET
Table size: 42 Table size: 42
Decoded header set: Decoded header set:
:method: GET :method: GET
E.1.4. Indexed Header Field from Static Table D.1.4. Indexed Header Field from Static Table
The header field representation uses an indexed header field, from The header field representation uses an indexed header field, from
the static table. In this example, the SETTINGS_HEADER_TABLE_SIZE is the static table. In this example, the SETTINGS_HEADER_TABLE_SIZE is
set to 0, therefore, the entry is not copied into the header table. set to 0, therefore, the entry is not copied into the header table.
Header set to encode: Header set to encode:
:method: GET :method: GET
Reference set: empty. Reference set: empty.
skipping to change at page 37, line 33 skipping to change at page 33, line 9
82 | == Indexed - Add == 82 | == Indexed - Add ==
| idx = 2 | idx = 2
| -> :method: GET | -> :method: GET
Header table (after decoding): empty. Header table (after decoding): empty.
Decoded header set: Decoded header set:
:method: GET :method: GET
E.2. Request Examples without Huffman D.2. Request Examples without Huffman
This section shows several consecutive header sets, corresponding to This section shows several consecutive header sets, corresponding to
HTTP requests, on the same connection. HTTP requests, on the same connection.
E.2.1. First request D.2.1. First request
Header set to encode: Header set to encode:
:method: GET :method: GET
:scheme: http :scheme: http
:path: / :path: /
:authority: www.example.com :authority: www.example.com
Reference set: empty. Reference set: empty.
skipping to change at page 38, line 44 skipping to change at page 34, line 20
[ 4] (s = 42) :method: GET [ 4] (s = 42) :method: GET
Table size: 180 Table size: 180
Decoded header set: Decoded header set:
:method: GET :method: GET
:scheme: http :scheme: http
:path: / :path: /
:authority: www.example.com :authority: www.example.com
E.2.2. Second request D.2.2. Second request
This request takes advantage of the differential encoding of header This request takes advantage of the differential encoding of header
sets. sets.
Header set to encode: Header set to encode:
:method: GET :method: GET
:scheme: http :scheme: http
:path: / :path: /
:authority: www.example.com :authority: www.example.com
skipping to change at page 40, line 5 skipping to change at page 35, line 29
Table size: 233 Table size: 233
Decoded header set: Decoded header set:
cache-control: no-cache cache-control: no-cache
:authority: www.example.com :authority: www.example.com
:path: / :path: /
:scheme: http :scheme: http
:method: GET :method: GET
E.2.3. Third request D.2.3. Third request
This request has not enough headers in common with the previous This request has not enough headers in common with the previous
request to take advantage of the differential encoding. Therefore, request to take advantage of the differential encoding. Therefore,
the reference set is emptied before encoding the header fields. the reference set is emptied before encoding the header fields.
Header set to encode: Header set to encode:
:method: GET :method: GET
:scheme: https :scheme: https
:path: /index.html :path: /index.html
skipping to change at page 40, line 29 skipping to change at page 36, line 13
Reference set: Reference set:
[ 1] cache-control: no-cache [ 1] cache-control: no-cache
[ 2] :authority: www.example.com [ 2] :authority: www.example.com
[ 3] :path: / [ 3] :path: /
[ 4] :scheme: http [ 4] :scheme: http
[ 5] :method: GET [ 5] :method: GET
Hex dump of encoded data: Hex dump of encoded data:
8085 8c8b 8400 0a63 7573 746f 6d2d 6b65 | .......custom-ke 8080 858c 8b84 000a 6375 7374 6f6d 2d6b | ........custom-k
790c 6375 7374 6f6d 2d76 616c 7565 | y.custom-value 6579 0c63 7573 746f 6d2d 7661 6c75 65 | ey.custom-value
Decoding process: Decoding process:
80 | == Empty reference set == 80 80 | == Empty reference set ==
| idx = 0 | idx = 0
| flag = 1
85 | == Indexed - Add == 85 | == Indexed - Add ==
| idx = 5 | idx = 5
| -> :method: GET | -> :method: GET
8c | == Indexed - Add == 8c | == Indexed - Add ==
| idx = 12 | idx = 12
| -> :scheme: https | -> :scheme: https
8b | == Indexed - Add == 8b | == Indexed - Add ==
| idx = 11 | idx = 11
| -> :path: /index.html | -> :path: /index.html
84 | == Indexed - Add == 84 | == Indexed - Add ==
skipping to change at page 42, line 5 skipping to change at page 37, line 23
Table size: 379 Table size: 379
Decoded header set: Decoded header set:
:method: GET :method: GET
:scheme: https :scheme: https
:path: /index.html :path: /index.html
:authority: www.example.com :authority: www.example.com
custom-key: custom-value custom-key: custom-value
E.3. Request Examples with Huffman D.3. Request Examples with Huffman
This section shows the same examples as the previous section, but This section shows the same examples as the previous section, but
using Huffman encoding for the literal values. using Huffman encoding for the literal values.
E.3.1. First request D.3.1. First request
Header set to encode: Header set to encode:
:method: GET :method: GET
:scheme: http :scheme: http
:path: / :path: /
:authority: www.example.com :authority: www.example.com
Reference set: empty. Reference set: empty.
skipping to change at page 43, line 20 skipping to change at page 38, line 40
[ 4] (s = 42) :method: GET [ 4] (s = 42) :method: GET
Table size: 180 Table size: 180
Decoded header set: Decoded header set:
:method: GET :method: GET
:scheme: http :scheme: http
:path: / :path: /
:authority: www.example.com :authority: www.example.com
E.3.2. Second request D.3.2. Second request
This request takes advantage of the differential encoding of header This request takes advantage of the differential encoding of header
sets. sets.
Header set to encode: Header set to encode:
:method: GET :method: GET
:scheme: http :scheme: http
:path: / :path: /
:authority: www.example.com :authority: www.example.com
skipping to change at page 44, line 34 skipping to change at page 40, line 11
Table size: 233 Table size: 233
Decoded header set: Decoded header set:
cache-control: no-cache cache-control: no-cache
:authority: www.example.com :authority: www.example.com
:path: / :path: /
:scheme: http :scheme: http
:method: GET :method: GET
E.3.3. Third request D.3.3. Third request
This request has not enough headers in common with the previous This request has not enough headers in common with the previous
request to take advantage of the differential encoding. Therefore, request to take advantage of the differential encoding. Therefore,
the reference set is emptied before encoding the header fields. the reference set is emptied before encoding the header fields.
Header set to encode: Header set to encode:
:method: GET :method: GET
:scheme: https :scheme: https
:path: /index.html :path: /index.html
skipping to change at page 45, line 14 skipping to change at page 40, line 35
Reference set: Reference set:
[ 1] cache-control: no-cache [ 1] cache-control: no-cache
[ 2] :authority: www.example.com [ 2] :authority: www.example.com
[ 3] :path: / [ 3] :path: /
[ 4] :scheme: http [ 4] :scheme: http
[ 5] :method: GET [ 5] :method: GET
Hex dump of encoded data: Hex dump of encoded data:
8085 8c8b 8400 884e b08b 7497 90fa 7f89 | .......N..t..... 8080 858c 8b84 0088 4eb0 8b74 9790 fa7f | ........N..t....
4eb0 8b74 979a 17a8 ff | N..t..... 894e b08b 7497 9a17 a8ff | .N..t.....
Decoding process: Decoding process:
80 | == Empty reference set == 80 80 | == Empty reference set ==
| idx = 0 | idx = 0
| flag = 1
85 | == Indexed - Add == 85 | == Indexed - Add ==
| idx = 5 | idx = 5
| -> :method: GET | -> :method: GET
8c | == Indexed - Add == 8c | == Indexed - Add ==
| idx = 12 | idx = 12
| -> :scheme: https | -> :scheme: https
8b | == Indexed - Add == 8b | == Indexed - Add ==
| idx = 11 | idx = 11
| -> :path: /index.html | -> :path: /index.html
84 | == Indexed - Add == 84 | == Indexed - Add ==
skipping to change at page 46, line 25 skipping to change at page 42, line 11
Table size: 379 Table size: 379
Decoded header set: Decoded header set:
:method: GET :method: GET
:scheme: https :scheme: https
:path: /index.html :path: /index.html
:authority: www.example.com :authority: www.example.com
custom-key: custom-value custom-key: custom-value
E.4. Response Examples without Huffman D.4. Response Examples without Huffman
This section shows several consecutive header sets, corresponding to This section shows several consecutive header sets, corresponding to
HTTP responses, on the same connection. SETTINGS_HEADER_TABLE_SIZE HTTP responses, on the same connection. SETTINGS_HEADER_TABLE_SIZE
is set to the value of 256 octets, causing some evictions to occur. is set to the value of 256 octets, causing some evictions to occur.
E.4.1. First response D.4.1. First response
Header set to encode: Header set to encode:
:status: 302 :status: 302
cache-control: private cache-control: private
date: Mon, 21 Oct 2013 20:13:21 GMT date: Mon, 21 Oct 2013 20:13:21 GMT
location: https://www.example.com location: https://www.example.com
Reference set: empty. Reference set: empty.
skipping to change at page 48, line 5 skipping to change at page 44, line 5
[ 4] (s = 42) :status: 302 [ 4] (s = 42) :status: 302
Table size: 222 Table size: 222
Decoded header set: Decoded header set:
:status: 302 :status: 302
cache-control: private cache-control: private
date: Mon, 21 Oct 2013 20:13:21 GMT date: Mon, 21 Oct 2013 20:13:21 GMT
location: https://www.example.com location: https://www.example.com
E.4.2. Second response D.4.2. Second response
The (":status", "302") header field is evicted from the header table The (":status", "302") header field is evicted from the header table
to free space to allow adding the (":status", "200") header field to to free space to allow adding the (":status", "200") header field,
be copied from the static table into the header table. copied from the static table into the header table. The (":status",
"302") header field doesn't need to be removed from the reference set
as it is evicted from the header table.
Header set to encode: Header set to encode:
:status: 200 :status: 200
cache-control: private cache-control: private
date: Mon, 21 Oct 2013 20:13:21 GMT date: Mon, 21 Oct 2013 20:13:21 GMT
location: https://www.example.com location: https://www.example.com
Reference set: Reference set:
[ 1] location: https://www.example.com [ 1] location: https://www.example.com
[ 2] date: Mon, 21 Oct 2013 20:13:21 GMT [ 2] date: Mon, 21 Oct 2013 20:13:21 GMT
[ 3] cache-control: private [ 3] cache-control: private
[ 4] :status: 302 [ 4] :status: 302
Hex dump of encoded data: Hex dump of encoded data:
848c | .. 8c | .
Decoding process: Decoding process:
84 | == Indexed - Remove ==
| idx = 4
| -> :status: 302
8c | == Indexed - Add == 8c | == Indexed - Add ==
| idx = 12 | idx = 12
| - evict: :status: 302 | - evict: :status: 302
| -> :status: 200 | -> :status: 200
Header Table (after decoding): Header Table (after decoding):
[ 1] (s = 42) :status: 200 [ 1] (s = 42) :status: 200
[ 2] (s = 63) location: https://www.example.com [ 2] (s = 63) location: https://www.example.com
[ 3] (s = 65) date: Mon, 21 Oct 2013 20:13:21 GMT [ 3] (s = 65) date: Mon, 21 Oct 2013 20:13:21 GMT
[ 4] (s = 52) cache-control: private [ 4] (s = 52) cache-control: private
Table size: 222 Table size: 222
Decoded header set: Decoded header set:
:status: 200 :status: 200
location: https://www.example.com location: https://www.example.com
date: Mon, 21 Oct 2013 20:13:21 GMT date: Mon, 21 Oct 2013 20:13:21 GMT
cache-control: private cache-control: private
E.4.3. Third response D.4.3. Third response
Several header fields are evicted from the header table during the Several header fields are evicted from the header table during the
processing of this header set. Before evicting a header belonging to processing of this header set. Before evicting a header belonging to
the reference set, it is emitted, by coding it twice as an Indexed the reference set, it is emitted, by coding it twice as an Indexed
Representation. The first representation removes the header field Representation. The first representation removes the header field
from the reference set, the second one adds it again to the reference from the reference set, the second one adds it again to the reference
set, also emitting it. set, also emitting it.
Header set to encode: Header set to encode:
skipping to change at page 49, line 39 skipping to change at page 45, line 37
Reference set: Reference set:
[ 1] :status: 200 [ 1] :status: 200
[ 2] location: https://www.example.com [ 2] location: https://www.example.com
[ 3] date: Mon, 21 Oct 2013 20:13:21 GMT [ 3] date: Mon, 21 Oct 2013 20:13:21 GMT
[ 4] cache-control: private [ 4] cache-control: private
Hex dump of encoded data: Hex dump of encoded data:
8384 8403 1d4d 6f6e 2c20 3231 204f 6374 | .....Mon, 21 Oct 8484 031d 4d6f 6e2c 2032 3120 4f63 7420 | ....Mon, 21 Oct
2032 3031 3320 3230 3a31 333a 3232 2047 | 2013 20:13:22 G 3230 3133 2032 303a 3133 3a32 3220 474d | 2013 20:13:22 GM
4d54 1d04 677a 6970 8484 8383 3a38 666f | MT..gzip....:8fo 541d 0467 7a69 7084 8483 833a 3866 6f6f | T..gzip....:8foo
6f3d 4153 444a 4b48 514b 425a 584f 5157 | o=ASDJKHQKBZXOQW 3d41 5344 4a4b 4851 4b42 5a58 4f51 5745 | =ASDJKHQKBZXOQWE
454f 5049 5541 5851 5745 4f49 553b 206d | EOPIUAXQWEOIU; m 4f50 4955 4158 5157 454f 4955 3b20 6d61 | OPIUAXQWEOIU; ma
6178 2d61 6765 3d33 3630 303b 2076 6572 | ax-age=3600; ver 782d 6167 653d 3336 3030 3b20 7665 7273 | x-age=3600; vers
7369 6f6e 3d31 | sion=1 696f 6e3d 31 | ion=1
Decoding process: Decoding process:
83 | == Indexed - Remove ==
| idx = 3
| -> date: Mon, 21 Oct 2013 \
| 20:13:21 GMT
84 | == Indexed - Remove == 84 | == Indexed - Remove ==
| idx = 4 | idx = 4
| -> cache-control: private | -> cache-control: private
84 | == Indexed - Add == 84 | == Indexed - Add ==
| idx = 4 | idx = 4
| -> cache-control: private | -> cache-control: private
03 | == Literal indexed == 03 | == Literal indexed ==
| Indexed name (idx = 3) | Indexed name (idx = 3)
| date | date
1d | Literal value (len = 29) 1d | Literal value (len = 29)
skipping to change at page 51, line 26 skipping to change at page 47, line 24
Decoded header set: Decoded header set:
cache-control: private cache-control: private
date: Mon, 21 Oct 2013 20:13:22 GMT date: Mon, 21 Oct 2013 20:13:22 GMT
content-encoding: gzip content-encoding: gzip
location: https://www.example.com location: https://www.example.com
:status: 200 :status: 200
set-cookie: foo=ASDJKHQKBZXOQWEOPIUAXQWEOIU; max-age=3600; version=1 set-cookie: foo=ASDJKHQKBZXOQWEOPIUAXQWEOIU; max-age=3600; version=1
E.5. Response Examples with Huffman D.5. Response Examples with Huffman
This section shows the same examples as the previous section, but This section shows the same examples as the previous section, but
using Huffman encoding for the literal values. The eviction using Huffman encoding for the literal values. The eviction
mechanism uses the length of the decoded literal values, so the same mechanism uses the length of the decoded literal values, so the same
evictions occurs as in the previous section. evictions occurs as in the previous section.
E.5.1. First response D.5.1. First response
Header set to encode: Header set to encode:
:status: 302 :status: 302
cache-control: private cache-control: private
date: Mon, 21 Oct 2013 20:13:21 GMT date: Mon, 21 Oct 2013 20:13:21 GMT
location: https://www.example.com location: https://www.example.com
Reference set: empty. Reference set: empty.
Hex dump of encoded data: Hex dump of encoded data:
0882 409f 1886 c31b 39bf 387f 2292 a2fb | ..@.....9.8."... 0882 98a7 1885 73d5 cd11 1f22 98ef 6b3a | ......s...."..k:
a203 20f2 ab30 3124 018b 490d 3209 e877 | .. ..01$..I.2..w 7a0e 6e8f a263 d072 9a6e 8397 d869 bd87 | z.n..c.r.n...i..
3093 e39e 7864 dd7a fd3d 3d24 8747 db87 | 0...xd.z.==$.G.. 3747 bbbf c730 90ce 3174 3d80 1b6d b107 | 7G...0..1t=..m..
2849 55f6 ff | (IU.. cd1a 3962 44b7 4f | ..9bD.O
Decoding process: Decoding process:
08 | == Literal indexed == 08 | == Literal indexed ==
| Indexed name (idx = 8) | Indexed name (idx = 8)
| :status | :status
82 | Literal value (len = 3) 82 | Literal value (len = 3)
| Huffman encoded: | Huffman encoded:
409f | @. 98a7 | ..
| Decoded: | Decoded:
| 302 | 302
| -> :status: 302 | -> :status: 302
18 | == Literal indexed == 18 | == Literal indexed ==
| Indexed name (idx = 24) | Indexed name (idx = 24)
| cache-control | cache-control
86 | Literal value (len = 7) 85 | Literal value (len = 7)
| Huffman encoded: | Huffman encoded:
c31b 39bf 387f | ..9.8. 73d5 cd11 1f | s....
| Decoded: | Decoded:
| private | private
| -> cache-control: private | -> cache-control: private
22 | == Literal indexed == 22 | == Literal indexed ==
| Indexed name (idx = 34) | Indexed name (idx = 34)
| date | date
92 | Literal value (len = 29) 98 | Literal value (len = 29)
| Huffman encoded: | Huffman encoded:
a2fb a203 20f2 ab30 3124 018b 490d 3209 | .... ..01$..I.2. ef6b 3a7a 0e6e 8fa2 63d0 729a 6e83 97d8 | .k:z.n..c.r.n...
e877 | .w 69bd 8737 47bb bfc7 | i..7G...
| Decoded: | Decoded:
| Mon, 21 Oct 2013 20:13:21 \ | Mon, 21 Oct 2013 20:13:21 \
| GMT | GMT
| -> date: Mon, 21 Oct 2013 \ | -> date: Mon, 21 Oct 2013 \
| 20:13:21 GMT | 20:13:21 GMT
30 | == Literal indexed == 30 | == Literal indexed ==
| Indexed name (idx = 48) | Indexed name (idx = 48)
| location | location
93 | Literal value (len = 23) 90 | Literal value (len = 23)
| Huffman encoded: | Huffman encoded:
e39e 7864 dd7a fd3d 3d24 8747 db87 2849 | ..xd.z.==$.G..(I ce31 743d 801b 6db1 07cd 1a39 6244 b74f | .1t=..m....9bD.O
55f6 ff | U..
| Decoded: | Decoded:
| https://www.example.com | https://www.example.com
| -> location: https://www.e\ | -> location: https://www.e\
| xample.com | xample.com
Header Table (after decoding): Header Table (after decoding):
[ 1] (s = 63) location: https://www.example.com [ 1] (s = 63) location: https://www.example.com
[ 2] (s = 65) date: Mon, 21 Oct 2013 20:13:21 GMT [ 2] (s = 65) date: Mon, 21 Oct 2013 20:13:21 GMT
[ 3] (s = 52) cache-control: private [ 3] (s = 52) cache-control: private
[ 4] (s = 42) :status: 302 [ 4] (s = 42) :status: 302
Table size: 222 Table size: 222
Decoded header set: Decoded header set:
:status: 302 :status: 302
cache-control: private cache-control: private
date: Mon, 21 Oct 2013 20:13:21 GMT date: Mon, 21 Oct 2013 20:13:21 GMT
location: https://www.example.com location: https://www.example.com
E.5.2. Second response D.5.2. Second response
The (":status", "302") header field is evicted from the header table The (":status", "302") header field is evicted from the header table
to free space to allow adding the (":status", "200") header field to to free space to allow adding the (":status", "200") header field,
be copied from the static table into the header table. copied from the static table into the header table. The (":status",
"302") header field doesn't need to be removed from the reference set
as it is evicted from the header table.
Header set to encode: Header set to encode:
:status: 200 :status: 200
cache-control: private cache-control: private
date: Mon, 21 Oct 2013 20:13:21 GMT date: Mon, 21 Oct 2013 20:13:21 GMT
location: https://www.example.com location: https://www.example.com
Reference set: Reference set:
[ 1] location: https://www.example.com [ 1] location: https://www.example.com
[ 2] date: Mon, 21 Oct 2013 20:13:21 GMT [ 2] date: Mon, 21 Oct 2013 20:13:21 GMT
[ 3] cache-control: private [ 3] cache-control: private
[ 4] :status: 302 [ 4] :status: 302
Hex dump of encoded data: Hex dump of encoded data:
848c | .. 8c | .
Decoding process: Decoding process:
84 | == Indexed - Remove ==
| idx = 4
| -> :status: 302
8c | == Indexed - Add == 8c | == Indexed - Add ==
| idx = 12 | idx = 12
| - evict: :status: 302 | - evict: :status: 302
| -> :status: 200 | -> :status: 200
Header Table (after decoding): Header Table (after decoding):
[ 1] (s = 42) :status: 200 [ 1] (s = 42) :status: 200
[ 2] (s = 63) location: https://www.example.com [ 2] (s = 63) location: https://www.example.com
[ 3] (s = 65) date: Mon, 21 Oct 2013 20:13:21 GMT [ 3] (s = 65) date: Mon, 21 Oct 2013 20:13:21 GMT
[ 4] (s = 52) cache-control: private [ 4] (s = 52) cache-control: private
Table size: 222 Table size: 222
Decoded header set: Decoded header set:
:status: 200 :status: 200
location: https://www.example.com location: https://www.example.com
date: Mon, 21 Oct 2013 20:13:21 GMT date: Mon, 21 Oct 2013 20:13:21 GMT
cache-control: private cache-control: private
E.5.3. Third response D.5.3. Third response
Several header fields are evicted from the header table during the Several header fields are evicted from the header table during the
processing of this header set. Before evicting a header belonging to processing of this header set. Before evicting a header belonging to
the reference set, it is emitted, by coding it twice as an Indexed the reference set, it is emitted, by coding it twice as an Indexed
Representation. The first representation removes the header field Representation. The first representation removes the header field
from the reference set, the second one adds it again to the reference from the reference set, the second one adds it again to the reference
set, also emitting it. set, also emitting it.
Header set to encode: Header set to encode:
skipping to change at page 55, line 13 skipping to change at page 52, line 13
set-cookie: foo=ASDJKHQKBZXOQWEOPIUAXQWEOIU; max-age=3600; version=1 set-cookie: foo=ASDJKHQKBZXOQWEOPIUAXQWEOIU; max-age=3600; version=1
Reference set: Reference set:
[ 1] :status: 200 [ 1] :status: 200
[ 2] location: https://www.example.com [ 2] location: https://www.example.com
[ 3] date: Mon, 21 Oct 2013 20:13:21 GMT [ 3] date: Mon, 21 Oct 2013 20:13:21 GMT
[ 4] cache-control: private [ 4] cache-control: private
Hex dump of encoded data: Hex dump of encoded data:
8384 8403 92a2 fba2 0320 f2ab 3031 2401 | ......... ..01$. 8484 0398 ef6b 3a7a 0e6e 8fa2 63d0 729a | .....k:z.n..c.r.
8b49 0d33 09e8 771d 84e1 fbb3 0f84 8483 | .I.3..w......... 6e83 97d8 69bd 873f 47bb bfc7 1d83 cbd5 | n...i..?G.......
833a b3df 7dfb 36d3 d9e1 fcfc 3faf e7ab | .:..}.6.....?... 4e84 8483 833a b3c5 adb7 7f87 6fc7 fbf7 | N....:......o...
fcfe fcbf af3e df2f 977f d36f f7fd 79f6 | ......./...o..y. fdbf bebf f3f7 f4fb 7ebb be9f 5f87 e37f | ............_...
f977 fd3d e16b fa46 fe10 d889 447d e1ce | .w.=.k.F....D}.. efed faee fa7c 3f1d 5d1a 23ce 5464 36cd | .....|?.].#.Td6.
18e5 65f7 6c2f | ..e.l/ 494b d5d1 cc5f 0535 969b | IK..._.5..
Decoding process: Decoding process:
83 | == Indexed - Remove ==
| idx = 3
| -> date: Mon, 21 Oct 2013 \
| 20:13:21 GMT
84 | == Indexed - Remove == 84 | == Indexed - Remove ==
| idx = 4 | idx = 4
| -> cache-control: private | -> cache-control: private
84 | == Indexed - Add == 84 | == Indexed - Add ==
| idx = 4 | idx = 4
| -> cache-control: private | -> cache-control: private
03 | == Literal indexed == 03 | == Literal indexed ==
| Indexed name (idx = 3) | Indexed name (idx = 3)
| date | date
92 | Literal value (len = 29) 98 | Literal value (len = 29)
| Huffman encoded: | Huffman encoded:
a2fb a203 20f2 ab30 3124 018b 490d 3309 | .... ..01$..I.3. ef6b 3a7a 0e6e 8fa2 63d0 729a 6e83 97d8 | .k:z.n..c.r.n...
e877 | .w 69bd 873f 47bb bfc7 | i..?G...
| Decoded: | Decoded:
| Mon, 21 Oct 2013 20:13:22 \ | Mon, 21 Oct 2013 20:13:22 \
| GMT | GMT
| - evict: cache-control: pr\ | - evict: cache-control: pr\
| ivate | ivate
| -> date: Mon, 21 Oct 2013 \ | -> date: Mon, 21 Oct 2013 \
| 20:13:22 GMT | 20:13:22 GMT
1d | == Literal indexed == 1d | == Literal indexed ==
| Indexed name (idx = 29) | Indexed name (idx = 29)
| content-encoding | content-encoding
84 | Literal value (len = 4) 83 | Literal value (len = 4)
| Huffman encoded: | Huffman encoded:
e1fb b30f | .... cbd5 4e | ..N
| Decoded: | Decoded:
| gzip | gzip
| - evict: date: Mon, 21 Oct\ | - evict: date: Mon, 21 Oct\
| 2013 20:13:21 GMT | 2013 20:13:21 GMT
| -> content-encoding: gzip | -> content-encoding: gzip
84 | == Indexed - Remove == 84 | == Indexed - Remove ==
| idx = 4 | idx = 4
| -> location: https://www.e\ | -> location: https://www.e\
| xample.com | xample.com
84 | == Indexed - Add == 84 | == Indexed - Add ==
skipping to change at page 56, line 29 skipping to change at page 53, line 26
| idx = 3 | idx = 3
| -> :status: 200 | -> :status: 200
83 | == Indexed - Add == 83 | == Indexed - Add ==
| idx = 3 | idx = 3
| -> :status: 200 | -> :status: 200
3a | == Literal indexed == 3a | == Literal indexed ==
| Indexed name (idx = 58) | Indexed name (idx = 58)
| set-cookie | set-cookie
b3 | Literal value (len = 56) b3 | Literal value (len = 56)
| Huffman encoded: | Huffman encoded:
df7d fb36 d3d9 e1fc fc3f afe7 abfc fefc | .}.6.....?...... c5ad b77f 876f c7fb f7fd bfbe bff3 f7f4 | .....o..........
bfaf 3edf 2f97 7fd3 6ff7 fd79 f6f9 77fd | ..../...o..y..w. fb7e bbbe 9f5f 87e3 7fef edfa eefa 7c3f | ....._........|?
3de1 6bfa 46fe 10d8 8944 7de1 ce18 e565 | =.k.F....D}....e 1d5d 1a23 ce54 6436 cd49 4bd5 d1cc 5f05 | .].#.Td6.IK..._.
f76c 2f | .l/ 3596 9b | 5..
| Decoded: | Decoded:
| foo=ASDJKHQKBZXOQWEOPIUAXQ\ | foo=ASDJKHQKBZXOQWEOPIUAXQ\
| WEOIU; max-age=3600; versi\ | WEOIU; max-age=3600; versi\
| on=1 | on=1
| - evict: location: https:/\ | - evict: location: https:/\
| /www.example.com | /www.example.com
| - evict: :status: 200 | - evict: :status: 200
| -> set-cookie: foo=ASDJKHQ\ | -> set-cookie: foo=ASDJKHQ\
| KBZXOQWEOPIUAXQWEOIU; ma\ | KBZXOQWEOPIUAXQWEOIU; ma\
| x-age=3600; version=1 | x-age=3600; version=1
 End of changes. 139 change blocks. 
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