draft-ietf-httpbis-header-compression-06.txt   draft-ietf-httpbis-header-compression-07.txt 
HTTPbis Working Group R. Peon HTTPbis Working Group R. Peon
Internet-Draft Google, Inc Internet-Draft Google, Inc
Intended status: Standards Track H. Ruellan Intended status: Standards Track H. Ruellan
Expires: August 17, 2014 Canon CRF Expires: October 05, 2014 Canon CRF
February 13, 2014 April 03, 2014
HPACK - Header Compression for HTTP/2 HPACK - Header Compression for HTTP/2
draft-ietf-httpbis-header-compression-06 draft-ietf-httpbis-header-compression-07
Abstract Abstract
This specification defines HPACK, a compression format for This specification defines HPACK, a compression format for
efficiently representing HTTP header fields in the context of HTTP/2. 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 [1]. mailing list (ietf-http-wg@w3.org), which is archived at <http://
lists.w3.org/Archives/Public/ietf-http-wg/>.
Working Group information and related documents can be found at [2] Working Group information can be found at <http://tools.ietf.org/wg/
(Wiki) and [3] (source code and issues tracker). httpbis/>; that specific to HTTP/2 are at <http://http2.github.io/>.
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-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 17, 2014. This Internet-Draft will expire on October 05, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2014 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.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Outline . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Outline . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Header Field Encoding . . . . . . . . . . . . . . . . . . . . 4 3. Header Field Encoding . . . . . . . . . . . . . . . . . . . . 5
3.1. Encoding Concepts . . . . . . . . . . . . . . . . . . . . 4 3.1. Encoding Concepts . . . . . . . . . . . . . . . . . . . . 5
3.1.1. Encoding Context . . . . . . . . . . . . . . . . . . 5 3.1.1. Encoding Context . . . . . . . . . . . . . . . . . . 6
3.1.2. Header Table . . . . . . . . . . . . . . . . . . . . 5 3.1.2. Header Table . . . . . . . . . . . . . . . . . . . . 6
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 . . . . . . . . . . . . . . . 9 3.2.2. Reference Set Emission . . . . . . . . . . . . . . . 10
3.2.3. Header Set Completion . . . . . . . . . . . . . . . . 9 3.2.3. Header Set Completion . . . . . . . . . . . . . . . . 10
3.3. Header Table Management . . . . . . . . . . . . . . . . . 9 3.3. Header Table Management . . . . . . . . . . . . . . . . . 10
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 . . . . . . . 10 3.3.3. Entry Eviction when Adding New Entries . . . . . . . 11
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 . . . . . . . . . . . . 12
4.2. Indexed Header Field Representation . . . . . . . . . . . 15 4.2. Indexed Header Field Representation . . . . . . . . . . . 13
4.3. Literal Header Field Representation . . . . . . . . . . . 15 4.3. Literal Header Field Representation . . . . . . . . . . . 14
4.3.1. Literal Header Field without Indexing . . . . . . . . 15 4.3.1. Literal Header Field with Incremental Indexing . . . 14
4.3.2. Literal Header Field with Incremental Indexing . . . 16 4.3.2. Literal Header Field without Indexing . . . . . . . . 15
4.3.3. Literal Header Field never Indexed . . . . . . . . . 16
4.4. Encoding Context Update . . . . . . . . . . . . . . . . . 17 4.4. Encoding Context Update . . . . . . . . . . . . . . . . . 17
5. Security Considerations . . . . . . . . . . . . . . . . . . . 18 5. Security Considerations . . . . . . . . . . . . . . . . . . . 18
5.1. Compression-based Attacks . . . . . . . . . . . . . . . . 18
5.2. Memory Consumption . . . . . . . . . . . . . . . . . . . 19
5.3. Implementation Limits . . . . . . . . . . . . . . . . . . 19
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.1. Normative References . . . . . . . . . . . . . . . . . . 19 7.1. Normative References . . . . . . . . . . . . . . . . . . 20
7.2. Informative References . . . . . . . . . . . . . . . . . 19 7.2. Informative References . . . . . . . . . . . . . . . . . 20
Appendix A. Change Log (to be removed by RFC Editor before Appendix A. Change Log (to be removed by RFC Editor before
publication . . . . . . . . . . . . . . . . . . . . 20 publication . . . . . . . . . . . . . . . . . . . . 21
A.1. Since draft-ietf-httpbis-header-compression-05 . . . . . 20 A.1. Since draft-ietf-httpbis-header-compression-06 . . . . . 21
A.2. Since draft-ietf-httpbis-header-compression-04 . . . . . 20 A.2. Since draft-ietf-httpbis-header-compression-05 . . . . . 21
A.3. Since draft-ietf-httpbis-header-compression-03 . . . . . 21 A.3. Since draft-ietf-httpbis-header-compression-04 . . . . . 21
A.4. Since draft-ietf-httpbis-header-compression-02 . . . . . 21 A.4. Since draft-ietf-httpbis-header-compression-03 . . . . . 21
A.5. Since draft-ietf-httpbis-header-compression-01 . . . . . 21 A.5. Since draft-ietf-httpbis-header-compression-02 . . . . . 22
A.6. Since draft-ietf-httpbis-header-compression-00 . . . . . 21 A.6. Since draft-ietf-httpbis-header-compression-01 . . . . . 22
Appendix B. Static Table . . . . . . . . . . . . . . . . . . . . 22 A.7. Since draft-ietf-httpbis-header-compression-00 . . . . . 22
Appendix C. Huffman Codes . . . . . . . . . . . . . . . . . . . 24 Appendix B. Static Table . . . . . . . . . . . . . . . . . . . . 23
Appendix D. Examples . . . . . . . . . . . . . . . . . . . . . . 29 Appendix C. Huffman Codes . . . . . . . . . . . . . . . . . . . 25
D.1. Header Field Representation Examples . . . . . . . . . . 30 Appendix D. Examples . . . . . . . . . . . . . . . . . . . . . . 31
D.1.1. Literal Header Field with Indexing . . . . . . . . . 30 D.1. Integer Representation Examples . . . . . . . . . . . . . 31
D.1.2. Literal Header Field without Indexing . . . . . . . . 30 D.1.1. Example 1: Encoding 10 using a 5-bit prefix . . . . . 31
D.1.3. Indexed Header Field . . . . . . . . . . . . . . . . 31 D.1.2. Example 2: Encoding 1337 using a 5-bit prefix . . . . 31
D.1.4. Indexed Header Field from Static Table . . . . . . . 32 D.1.3. Example 3: Encoding 42 starting at an
D.2. Request Examples without Huffman . . . . . . . . . . . . 33 octet-boundary . . . . . . . . . . . . . . . . . . . 32
D.2.1. First request . . . . . . . . . . . . . . . . . . . . 33 D.2. Header Field Representation Examples . . . . . . . . . . 32
D.2.2. Second request . . . . . . . . . . . . . . . . . . . 34 D.2.1. Literal Header Field with Indexing . . . . . . . . . 32
D.2.3. Third request . . . . . . . . . . . . . . . . . . . . 35 D.2.2. Literal Header Field without Indexing . . . . . . . . 33
D.3. Request Examples with Huffman . . . . . . . . . . . . . . 37 D.2.3. Indexed Header Field . . . . . . . . . . . . . . . . 34
D.3.1. First request . . . . . . . . . . . . . . . . . . . . 37 D.2.4. Indexed Header Field from Static Table . . . . . . . 35
D.3.2. Second request . . . . . . . . . . . . . . . . . . . 38 D.3. Request Examples without Huffman . . . . . . . . . . . . 35
D.3.3. Third request . . . . . . . . . . . . . . . . . . . . 40 D.3.1. First request . . . . . . . . . . . . . . . . . . . . 35
D.4. Response Examples without Huffman . . . . . . . . . . . . 42 D.3.2. Second request . . . . . . . . . . . . . . . . . . . 37
D.4.1. First response . . . . . . . . . . . . . . . . . . . 42 D.3.3. Third request . . . . . . . . . . . . . . . . . . . . 38
D.4.2. Second response . . . . . . . . . . . . . . . . . . . 44 D.4. Request Examples with Huffman . . . . . . . . . . . . . . 40
D.4.3. Third response . . . . . . . . . . . . . . . . . . . 45 D.4.1. First request . . . . . . . . . . . . . . . . . . . . 40
D.5. Response Examples with Huffman . . . . . . . . . . . . . 47 D.4.2. Second request . . . . . . . . . . . . . . . . . . . 41
D.5.1. First response . . . . . . . . . . . . . . . . . . . 47 D.4.3. Third request . . . . . . . . . . . . . . . . . . . . 42
D.5.2. Second response . . . . . . . . . . . . . . . . . . . 50 D.5. Response Examples without Huffman . . . . . . . . . . . . 44
D.5.3. Third response . . . . . . . . . . . . . . . . . . . 51 D.5.1. First response . . . . . . . . . . . . . . . . . . . 44
D.5.2. Second response . . . . . . . . . . . . . . . . . . . 46
D.5.3. Third response . . . . . . . . . . . . . . . . . . . 47
D.6. Response Examples with Huffman . . . . . . . . . . . . . 49
D.6.1. First response . . . . . . . . . . . . . . . . . . . 49
D.6.2. Second response . . . . . . . . . . . . . . . . . . . 52
D.6.3. Third response . . . . . . . . . . . . . . . . . . . 53
1. Introduction 1. Introduction
This specification defines HPACK, a compression format for This specification defines HPACK, a compression format for
efficiently representing HTTP header fields in the context of HTTP/2 efficiently representing HTTP header fields in the context of HTTP/2
(see [HTTP2]). (see [HTTP2]).
2. Overview 2. Overview
In HTTP/1.1 (see [HTTP-p1]), header fields are encoded without any In HTTP/1.1 (see [HTTP-p1]), header fields are encoded without any
form of compression. As web pages have grown to include dozens to form of compression. As web pages have grown to include dozens to
hundreds of requests, the redundant header fields in these requests hundreds of requests, the redundant header fields in these requests
now measurably increase latency and unnecessarily consume bandwidth now measurably increase latency and unnecessarily consume bandwidth
skipping to change at page 7, line 15 skipping to change at page 7, line 26
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.
Two different literal representations are provided: Three 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 4.3.2).
* A literal representation that does not add the header field to
the header table and require that this header field always use
a literal representation, in particular when re-encoded by an
intermediary (see Section 4.3.3).
* 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 4.3.1).
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).
Indices between 1 and len(header table), inclusive, refer to
elements in the header table, with index 1 referring to the
beginning of the table.
Indices between len(header table) + 1 and len(header table) +
len(static table), inclusive, refer to elements in the static
table, where the index len(header table) + 1 refers to the first
entry in the static table.
Any other indices MUST be treated as a decoding error.
<---------- 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
elements in the header table, with index 1 referring to the
beginning of the table.
Indices between len(header table)+1 and len(header
table)+len(static table), inclusive, refer to elements in the
static table, where the index len(header table)+1 refers to the
first entry in the static table.
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
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.
On the decoding side, an emitted header field can be safely passed to On the decoding side, an emitted header field can be safely passed to
the upper processing layer as part of the current header set. The the upper processing layer as part of the current header set. The
decoder MAY pass the emitted header fields to the upper processing decoder MAY pass the emitted header fields to the upper processing
layer in any order. layer in any order.
skipping to change at page 9, line 12 skipping to change at page 9, line 22
o If referencing an element of the static table: o If referencing an element of the static table:
* The header field corresponding to the referenced entry is * The header field corresponding to the referenced entry is
emitted. emitted.
* The referenced static entry is inserted at the beginning of the * The referenced static entry is inserted at the beginning of the
header table. header table.
* A reference to this new header table entry is added to the * A reference to this new header table entry is added to the
reference set (except if this new entry didn't fit in the reference set, except if this new entry didn't fit in the
header table). header table.
o If referencing an element of the header table: o If referencing an element of the header table:
* The header field corresponding to the referenced entry is * The header field corresponding to the referenced entry is
emitted. emitted.
* The referenced header table entry is added to the reference * The referenced header table entry is added to the reference
set. set.
A _literal representation_ that is _not added_ to the header table A _literal representation_ that is _not added_ to the header table
skipping to change at page 11, line 27 skipping to change at page 11, line 42
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 [4] the value is encoded using an unsigned variable length integer
representation. N is always between 1 and 8 bits. An integer representation (see <http://en.wikipedia.org/wiki/Variable-
length_quantity>). 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
skipping to change at page 12, line 8 skipping to change at page 12, line 23
if I < 2^N - 1, return I if I < 2^N - 1, return I
else else
M = 0 M = 0
repeat repeat
B = next octet B = next octet
I = I + (B & 127) * 2^M I = I + (B & 127) * 2^M
M = M + 7 M = M + 7
while B & 128 == 128 while B & 128 == 128
return I return I
Examples illustrating the encoding of integers are available in
Appendix D.1.
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 4.1.2. String Literal Representation
The value 10 is to be encoded with a 5-bit prefix.
o 10 is less than 31 (= 2^5 - 1) and is represented using the 5-bit
prefix.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| X | X | X | 0 | 1 | 0 | 1 | 0 | 10 stored on 5 bits
+---+---+---+---+---+---+---+---+
4.1.1.2. Example 2: Encoding 1337 using a 5-bit prefix
The value I=1337 is to be encoded with a 5-bit prefix.
1337 is greater than 31 (= 2^5 - 1).
The 5-bit prefix is filled with its max value (31).
I = 1337 - (2^5 - 1) = 1306.
I (1306) is greater than or equal to 128, the while loop body
executes:
I % 128 == 26
26 + 128 == 154
154 is encoded in 8 bits as: 10011010
I is set to 10 (1306 / 128 == 10)
I is no longer greater than or equal to 128, the while loop
terminates.
I, now 10, is encoded on 8 bits as: 00001010
The process ends.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 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
| 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 octet-boundary
The value 42 is to be encoded starting at an octet-boundary. This
implies that a 8-bit prefix is used.
o 42 is less than 255 (= 2^8 - 1) and is represented using the 8-bit Header field names and header field values can be represented as
prefix. literal string. A literal string is encoded as a sequence of octets,
either by directly encoding the literal string's octets, or by using
a canonical [CANON] Huffman encoding [HUFF].
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 | H | String Length (7+) |
+---+---+---+---+---+---+---+---+ +---+---------------------------+
| String Data (Length octets) |
4.1.2. String Literal Representation +-------------------------------+
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
three parts:
1. One bit, H, indicating whether or not the octets are Huffman
encoded.
2. The number of octets required to hold the result of the next
step, represented as an integer with a 7-bit prefix (see
Section 4.1.1), immediately following the first bit.
3. The encoded data of the string: String Literal Representation
* If H is '1', then the encoded string data is the bitwise A literal string representation contains the following fields:
concatenation of the canonical [CANON] Huffman code [HUFF]
corresponding to each octet of the data, followed by between
0-7 bits of padding.
* If H is '0', then the encoded string is the octets of the H: A one bit flag, H, indicating whether or not the octets of the
field value without modification. string are Huffman encoded.
Padding is necessary when doing Huffman encoding to ensure that the String Length: The number of octets used to encode the string
remaining bits between the actual end of the data and the next octet literal, encoded as an integer with 7-bit prefix (see
boundary are not misinterpreted as part of the input data. Section 4.1.1).
When padding for Huffman encoding, the bits from the EOS (end-of- String Data: The encoded data of the string literal. If H is '0',
string) entry in the Huffman table are used, starting with the MSB then the encoded data is the raw octets of the string literal. If
(most significant bit). This entry is guaranteed to be at least 8 H is '1', then the encoded data is the Huffman encoding of the
bits long. string literal.
String literals which use Huffman encoding are encoded with the String literals which use Huffman encoding are encoded with the
Huffman Codes Appendix C (see examples in Request Examples with Huffman codes defined in Appendix C (see examples inRequest Examples
Huffman Appendix D.3 and in Response Examples with Huffman with Huffman Appendix D.4 and in Response Examples with Huffman
Appendix D.5). Appendix D.6). The encoded data is the bitwise concatenation of the
Huffman codes corresponding to each octet of the string literal.
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
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
the EOS symbol is at least 8 bits long, it is expected that it should
never be successfully decoded.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 1 | Value Length Prefix (7) |
+---+---+---+---+---+---+---+---+
| Value Length (0-N octets) |
+---+---+---+---+---+---+---+---+
...
+---+---+---+---+---+---+---+---+
| Huffman Encoded Data |Padding|
+---+---+---+---+---+---+---+---+
String Literal with Huffman Encoding
0 1 2 3 4 5 6 7 As the Huffman encoded data doesn't always end at an octet boundary,
+---+---+---+---+---+---+---+---+ some padding is inserted after it up to the next octet boundary. To
| 0 | Value Length Prefix (7) | prevent this padding to be misinterpreted as part of the string
+---+---+---+---+---+---+---+---+ literal, the most significant bits of the EOS (end-of-string) entry
| Value Length (0-N octets) | in the Huffman table are used.
+---+---+---+---+---+---+---+---+
...
+---+---+---+---+---+---+---+---+
| Field Bytes without Encoding |
+---+---+---+---+---+---+---+---+
String Literal without Huffman Encoding Upon decoding, an incomplete Huffman code at the end of the encoded
data is to be considered as padding and discarded. A padding
strictly longer than 7 bits MUST be treated as a decoding error. A
padding not corresponding to the most significant bits of the EOS
entry MUST be treated as a decoding error. A Huffman encoded string
literal containing the EOS entry MUST be treated as a decoding error.
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 changes in the The index value of 0 is not used. It MUST be treated as a decoding
encoding context (see Section 4.4). error if found in an indexed header field representation.
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 with Incremental Indexing
A literal header field without indexing causes the emission of a A literal header field with incremental indexing adds a new entry to
header field without altering the header table. 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+) |
+---+---+---+-------------------+ +---+---+-----------------------+
| H | Value Length (7+) | | H | Value Length (7+) |
+---+---------------------------+ +---+---------------------------+
| Value String (Length octets) | | Value String (Length octets) |
+-------------------------------+ +-------------------------------+
Literal Header Field without 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 | 1 | 0 | | 0 | 1 | 0 |
+---+---+---+-------------------+ +---+---+-----------------------+
| H | Name Length (7+) | | H | Name Length (7+) |
+---+---------------------------+ +---+---------------------------+
| Name String (Length octets) | | Name String (Length octets) |
+---+---------------------------+ +---+---------------------------+
| H | Value Length (7+) | | H | Value Length (7+) |
+---+---------------------------+ +---+---------------------------+
| Value String (Length octets) | | Value String (Length octets) |
+-------------------------------+ +-------------------------------+
Literal Header Field without Indexing - New Name Literal Header Field with Incremental 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
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.
4.3.2. Literal Header Field with Incremental Indexing 4.3.2. Literal Header Field without Indexing
A literal header field with incremental indexing adds a new entry to A literal header field without indexing causes the emission of a
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 | 0 | Index (6+) | | 0 | 0 | 0 | 0 | Index (4+) |
+---+---+---+-------------------+ +---+---+-----------------------+
| H | Value Length (7+) | | H | Value Length (7+) |
+---+---------------------------+ +---+---------------------------+
| Value String (Length octets) | | Value String (Length octets) |
+-------------------------------+ +-------------------------------+
Literal Header Field with Incremental 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 | 0 | 0 | | 0 | 0 | 0 | 0 | 0 |
+---+---+---+-------------------+ +---+---+-----------------------+
| H | Name Length (7+) | | H | Name Length (7+) |
+---+---------------------------+ +---+---------------------------+
| Name String (Length octets) | | Name String (Length octets) |
+---+---------------------------+ +---+---------------------------+
| H | Value Length (7+) | | H | Value Length (7+) |
+---+---------------------------+ +---+---------------------------+
| Value String (Length octets) | | Value String (Length octets) |
+-------------------------------+ +-------------------------------+
Literal Header Field with Incremental Indexing - New Name Literal Header Field without Indexing - New Name
This representation starts with the '00' 2-bit pattern. The literal header field without indexing representation starts with
the '0000' 4-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 4 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.
4.3.3. Literal Header Field never Indexed
A literal header field never indexed causes the emission of a header
field without altering the header table.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 0 | 0 | 0 | 1 | Index (4+) |
+---+---+-----------------------+
| H | Value Length (7+) |
+---+---------------------------+
| Value String (Length octets) |
+-------------------------------+
Literal Header Field never Indexed - Indexed Name
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 0 | 0 | 0 | 1 | 0 |
+---+---+-----------------------+
| H | Name Length (7+) |
+---+---------------------------+
| Name String (Length octets) |
+---+---------------------------+
| H | Value Length (7+) |
+---+---------------------------+
| Value String (Length octets) |
+-------------------------------+
Literal Header Field never Indexed - New Name
The literal header field never indexed representation starts with the
'0001' 4-bit pattern.
When a header field is represented as a literal header field never
indexed, it MUST always be encoded with this same representation. In
particular, when a peer sends a header field that it received
represented as a literal header field never indexed, it MUST use the
same representation to forward this header field.
This representation is intended for protecting header field values
that are not to be put at risk by compressing them (see Section 5.1
for more details).
The encoding of the representation is the same as for the literal
header field without indexing representation (see Section 4.3.2).
4.4. Encoding Context Update 4.4. Encoding Context Update
An indexed value of 0 is reserved for signalling changes in the An encoding context update causes the immediate application of a
encoding context. The type of the change is encoded on the following change to the encoding context.
octet(s). Any change in the encoding context is applied immediately.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 1 | 0 | | 0 | 0 | 1 | F | ... |
+---+---------------------------+
Context Update
An encoding context update starts with the '001' 3-bit pattern.
It is followed by a flag specifying the type of the change, and by
any data necessary to describe the change itself.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 0 | 0 | 1 | 1 | 0 |
+---+---------------------------+ +---+---------------------------+
Reference Set Emptying Reference Set Emptying
An octet with its high bit set to '1' signals that the reference set The flag bit being set to '1' signals that the reference set is
is emptied. The remaining bits are set to '0'. emptied. The remaining bits are set to '0'.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | New maximum size (7+) | | 0 | 0 | 1 | 0 | Max size (4+) |
+---+---------------------------+ +---+---------------------------+
Maximum Header Table Size Change Maximum Header Table Size Change
An octet with its high bit set to '0' signals the new maximum size of The flag bit being set to '0' signals that a change to the maximum
the header table. This new maximum size MUST be lower than or equal size of the header table. This new maximum size MUST be lower than
to the value of the setting SETTINGS_HEADER_TABLE_SIZE (see [HTTP2]). 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. The new maximum size is encoded as an integer with a 4-bit prefix.
Change in the maximum size of the header table can trigger entry Change in the maximum size of the header table can trigger entry
evictions (see Section 3.3.2). evictions (see Section 3.3.2).
5. Security Considerations 5. Security Considerations
This compressor exists to solve security issues present in stream 5.1. Compression-based Attacks
compressors such as DEFLATE whereby the compression context can be
efficiently probed to reveal secrets. A conformant implementation of
this specification should be fairly safe against that kind of attack,
as the reaping of any information from the compression context
requires more work than guessing and verifying the plain text data
directly with the server. As with any secret, however, the longer
the length of the secret, the more difficult the secret is to guess.
It is inadvisable to have short cookies that are relied upon to
remain secret for any duration of time.
A proper security-conscious implementation will also need to prevent Compression can create a weak point allowing an attacker to recover
timing attacks by ensuring that the amount of time it takes to do secret data. For example, the CRIME attack (see [CRIME]) took
string comparisons is always a function of the total length of the advantage of the DEFLATE mechanism (see [DEFLATE]) of SPDY (see
strings, and not a function of the number of matched characters. [SPDY]) to efficiently probe the compression context. The full-text
compression mechanism of DEFLATE allowed the attacker to learn some
information from each failed attempt at guessing the secret.
A decoder needs to ensure that larger values or encodings of integers For this reason, HPACK provides only limited compression mechanisms
do not permit exploitation. Decoders MUST limit the size of in the form of an indexing table and of a static Huffman encoding.
integers, both in value and encoded length, that it accepts (see
Section 4.1.1).
Another common security problem is when the remote endpoint The indexing table can still provide information to an attacker that
successfully causes the local endpoint to exhaust its memory. This would be able to probe the compression context. However, this
compressor attempts to deal with the most obvious ways that this information is limited to the knowledge of whether the attacker's
could occur by limiting both the peak and the steady-state amount of guess is correct or not.
memory consumed in the compressor state, by providing ways for the
application to consume/flush the emitted header fields in small
chunks, and by considering overhead in the state size calculation.
Implementors must still be careful in the creation of APIs to an
implementation of this compressor by ensuring that header field keys
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.
Failure to implement these kinds of safeguards may still result in a
scenario where the local endpoint exhausts its memory.
A particular care should be used for the maximum size of the header Still, an attacker could take advantage of this limited information
table. While an endpoint can fully control the maximum size of its for breaking low-entropy secrets using a brute-force attack. A
header table for the decoding size, by using server usually has some protections against such brute-force attack.
SETTINGS_HEADER_TABLE_SIZE, the maximum size of the encoding size is Here, the attack would target the client, where it would be harder to
controlled by the remote peer. The endpoint should check the detect. The attack would be even more dangerous if the attacker is
SETTINGS_HEADER_TABLE_SIZE defined by the remote peer, and decrease able to prevent the traffic generated by its brute-force attack from
the maximum size for the encoding size if needed. reaching the server.
To offer some protection against such type of attacks, HPACK enables
an endpoint to indicate that a header field must never be compressed,
across any hop up to the other endpoint (see Section 4.3.3). An
endpoint MUST use this feature to prevent the compression of any
header field whose value contains a secret which could be put at risk
by a brute-force attack.
For optimal processing, a sensitive value (for example a cookie)
needs to have an entropy high enough to not be endangered by a brute-
force attack, in order to take advantage of HPACK indexing.
There is currently no known threat taking advantage of the use of a
fixed Huffman encoding. A study has shown that using a fixed Huffman
encoding table created an information leakage, however this same
study concluded that an attacker could not take advantage of this
information leakage to recover any meaningful amount of information
(see [PETAL]).
5.2. Memory Consumption
An attacker can try to cause an endpoint to exhaust its memory.
HPACK is designed to limit both the peak and state amounts of memory
allocated by an endpoint.
The amount of memory used by the compressor state is limited by the
value of the setting SETTINGS_HEADER_TABLE_SIZE. This limitation
takes into account both the size of the data stored in the header
table, and the overhead required by the table structure itself.
For the decoding side, an endpoint can limit the amount of state
memory used by setting an appropriate value for
SETTINGS_HEADER_TABLE_SIZE. For the encoding side, the endpoint can
limit the amount of state memory it uses by defining a header table
maximum size lower than the value of SETTINGS_HEADER_TABLE_SIZE
defined by its peer (see Section 4.4).
The amount of temporary memory consumed is linked to the set of
header fields emitted or received. However, this amount of temporary
memory can be limited by processing these header fields in a
streaming manner.
5.3. Implementation Limits
An implementation of HPACK needs to ensure that large values for
integers, long encoding for integers, or long string literal do not
create security weaknesses.
An implementation has to set a limit for the values it accepts for
integers, as well as for the encoded length (see Section 4.1.1). In
the same way, it has to set a limit to the length it accepts for
string literals (see Section 4.1.2).
6. Acknowledgements 6. Acknowledgements
This document includes substantial editorial contributions from the This document includes substantial editorial contributions from the
following individuals: Mike Bishop, Jeff Pinner, Julian Reschke, following individuals: Mike Bishop, Jeff Pinner, Julian Reschke,
Martin Thomson. Martin Thomson.
7. References 7. References
7.1. Normative References 7.1. Normative References
skipping to change at page 20, line 19 skipping to change at page 20, line 47
articleDetails.jsp?arnumber=4051119>. articleDetails.jsp?arnumber=4051119>.
[PERF1] Belshe, M., "IETF83: SPDY and What to Consider for HTTP/ [PERF1] Belshe, M., "IETF83: SPDY and What to Consider for HTTP/
2.0", March 2012, <http://www.ietf.org/proceedings/83/ 2.0", March 2012, <http://www.ietf.org/proceedings/83/
slides/slides-83-httpbis-3>. slides/slides-83-httpbis-3>.
[PERF2] McManus, P., "SPDY: What I Like About You", September [PERF2] McManus, P., "SPDY: What I Like About You", September
2011, <http://bitsup.blogspot.com/2011/09/spdy-what-i 2011, <http://bitsup.blogspot.com/2011/09/spdy-what-i
-like-about-you.html>. -like-about-you.html>.
[PETAL] Tan, J. and J. Nahata, "PETAL: Preset Encoding Table
Information Leakage", April 2013, <http://www.pdl.cmu.edu/
PDL-FTP/associated/CMU-PDL-13-106.pdf>.
[SPDY] Belshe, M. and R. Peon, "SPDY Protocol", draft-mbelshe- [SPDY] Belshe, M. and R. Peon, "SPDY Protocol", draft-mbelshe-
httpbis-spdy-00 (work in progress), February 2012. httpbis-spdy-00 (work in progress), February 2012.
Appendix A. Change Log (to be removed by RFC Editor before publication Appendix A. Change Log (to be removed by RFC Editor before publication
A.1. Since draft-ietf-httpbis-header-compression-05 A.1. Since draft-ietf-httpbis-header-compression-06
o Updated format to include literal headers that must never be
compressed.
o Updated security considerations.
o Moved integer encoding examples to the appendix.
o Updated Huffman table.
o Updated static header table (adding and removing status values).
o Updated examples.
A.2. Since draft-ietf-httpbis-header-compression-05
o Regenerated examples. o Regenerated examples.
o Only one Huffman table for requests and responses. o Only one Huffman table for requests and responses.
o Added maximum size for header table, independent of o Added maximum size for header table, independent of
SETTINGS_HEADER_TABLE_SIZE. SETTINGS_HEADER_TABLE_SIZE.
o Added pseudo-code for integer decoding. o Added pseudo-code for integer decoding.
o Improved examples (removing unnecessary removals). o Improved examples (removing unnecessary removals).
A.2. Since draft-ietf-httpbis-header-compression-04 A.3. 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.3. Since draft-ietf-httpbis-header-compression-03 A.4. 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.4. Since draft-ietf-httpbis-header-compression-02 A.5. Since draft-ietf-httpbis-header-compression-02
o Corrected error in integer encoding pseudocode. o Corrected error in integer encoding pseudocode.
A.5. Since draft-ietf-httpbis-header-compression-01 A.6. 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
skipping to change at page 21, line 46 skipping to change at page 22, line 43
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 Header Set. Changed x-my-header to mynewheader. Added text in
the HeaderEmission section indicating that the application may the HeaderEmission section indicating that the application may
also be 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.6. Since draft-ietf-httpbis-header-compression-00 A.7. 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 22, line 23 skipping to change at page 23, line 21
one octet one octet
Added descriptions of opcodes Added descriptions of opcodes
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).
[[The ordering of these tables is currently arbitrary. The tables in
this section should be updated and ordered such that the table
entries with the smallest indices are those which, based on a
statistical analysis of the frequency of use weighted by size,
achieve the largest decrease in octets transmitted subject to HTTP 2
header field rules (like removal of some header fields). This set of
header fields is currently very likely incomplete, and should be made
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 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 |
| 4 | :path | / | | 4 | :path | / |
| 5 | :path | /index.html | | 5 | :path | /index.html |
| 6 | :scheme | http | | 6 | :scheme | http |
| 7 | :scheme | https | | 7 | :scheme | https |
| 8 | :status | 200 | | 8 | :status | 200 |
| 9 | :status | 500 | | 9 | :status | 204 |
| 10 | :status | 404 | | 10 | :status | 206 |
| 11 | :status | 403 | | 11 | :status | 304 |
| 12 | :status | 400 | | 12 | :status | 400 |
| 13 | :status | 401 | | 13 | :status | 404 |
| 14 | accept-charset | | | 14 | :status | 500 |
| 15 | accept-encoding | | | 15 | accept-charset | |
| 16 | accept-language | | | 16 | accept-encoding | |
| 17 | accept-ranges | | | 17 | accept-language | |
| 18 | accept | | | 18 | accept-ranges | |
| 19 | access-control-allow-origin | | | 19 | accept | |
| 20 | age | | | 20 | access-control-allow-origin | |
| 21 | allow | | | 21 | age | |
| 22 | authorization | | | 22 | allow | |
| 23 | cache-control | | | 23 | authorization | |
| 24 | content-disposition | | | 24 | cache-control | |
| 25 | content-encoding | | | 25 | content-disposition | |
| 26 | content-language | | | 26 | content-encoding | |
| 27 | content-length | | | 27 | content-language | |
| 28 | content-location | | | 28 | content-length | |
| 29 | content-range | | | 29 | content-location | |
| 30 | content-type | | | 30 | content-range | |
| 31 | cookie | | | 31 | content-type | |
| 32 | date | | | 32 | cookie | |
| 33 | etag | | | 33 | date | |
| 34 | expect | | | 34 | etag | |
| 35 | expires | | | 35 | expect | |
| 36 | from | | | 36 | expires | |
| 37 | host | | | 37 | from | |
| 38 | if-match | | | 38 | host | |
| 39 | if-modified-since | | | 39 | if-match | |
| 40 | if-none-match | | | 40 | if-modified-since | |
| 41 | if-range | | | 41 | if-none-match | |
| 42 | if-unmodified-since | | | 42 | if-range | |
| 43 | last-modified | | | 43 | if-unmodified-since | |
| 44 | link | | | 44 | last-modified | |
| 45 | location | | | 45 | link | |
| 46 | max-forwards | | | 46 | location | |
| 47 | proxy-authenticate | | | 47 | max-forwards | |
| 48 | proxy-authorization | | | 48 | proxy-authenticate | |
| 49 | range | | | 49 | proxy-authorization | |
| 50 | referer | | | 50 | range | |
| 51 | refresh | | | 51 | referer | |
| 52 | retry-after | | | 52 | refresh | |
| 53 | server | | | 53 | retry-after | |
| 54 | set-cookie | | | 54 | server | |
| 55 | strict-transport-security | | | 55 | set-cookie | |
| 56 | transfer-encoding | | | 56 | strict-transport-security | |
| 57 | user-agent | | | 57 | transfer-encoding | |
| 58 | vary | | | 58 | user-agent | |
| 59 | via | | | 59 | vary | |
| 60 | www-authenticate | | | 60 | via | |
| 61 | 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 Appendix C. Huffman Codes
The following Huffman codes are used when encoding string literals. The following codes are used when encoding string literals with an
Huffman coding (see Section 4.1.2).
[[This table will be regenerated. ]] Each row in the table specifies one Huffman code:
aligned aligned sym: The symbol to be represented. It is the decimal value of an
to len to len octet, possibly prepended with its ASCII representation. A
MSB in LSB in specific symbol, "EOS", is used to indicate the end of a string
sym as bits bits as hex bits literal.
( 0) |11111111|11111111|11110111|010 [27] 7ffffba [27]
( 1) |11111111|11111111|11110111|011 [27] 7ffffbb [27] code as bits: The Huffman code for the symbol represented as a
( 2) |11111111|11111111|11110111|100 [27] 7ffffbc [27] base-2 integer.
( 3) |11111111|11111111|11110111|101 [27] 7ffffbd [27]
( 4) |11111111|11111111|11110111|110 [27] 7ffffbe [27] code as hex: The Huffman code for the symbol, represented as a
( 5) |11111111|11111111|11110111|111 [27] 7ffffbf [27] hexadecimal integer, aligned on the least significant bit.
( 6) |11111111|11111111|11111000|000 [27] 7ffffc0 [27]
( 7) |11111111|11111111|11111000|001 [27] 7ffffc1 [27] len: The number of bits for the Huffman code of the symbol.
( 8) |11111111|11111111|11111000|010 [27] 7ffffc2 [27]
( 9) |11111111|11111111|11111000|011 [27] 7ffffc3 [27] As an example, the Huffman code for the symbol 48 (corresponding to
( 10) |11111111|11111111|11111000|100 [27] 7ffffc4 [27] the ASCII character "0") consists in the 5 bits "0", "0", "1", "0",
( 11) |11111111|11111111|11111000|101 [27] 7ffffc5 [27] "1". This corresponds to the value 5 encoded on 5 bits.
( 12) |11111111|11111111|11111000|110 [27] 7ffffc6 [27]
( 13) |11111111|11111111|11111000|111 [27] 7ffffc7 [27] code
( 14) |11111111|11111111|11111001|000 [27] 7ffffc8 [27] code as bits as hex len
( 15) |11111111|11111111|11111001|001 [27] 7ffffc9 [27] sym aligned to MSB aligned in
( 16) |11111111|11111111|11111001|010 [27] 7ffffca [27] to LSB bits
( 17) |11111111|11111111|11111001|011 [27] 7ffffcb [27] ( 0) |11111111|11111111|11101110|10 3ffffba [26]
( 18) |11111111|11111111|11111001|100 [27] 7ffffcc [27] ( 1) |11111111|11111111|11101110|11 3ffffbb [26]
( 19) |11111111|11111111|11111001|101 [27] 7ffffcd [27] ( 2) |11111111|11111111|11101111|00 3ffffbc [26]
( 20) |11111111|11111111|11111001|110 [27] 7ffffce [27] ( 3) |11111111|11111111|11101111|01 3ffffbd [26]
( 21) |11111111|11111111|11111001|111 [27] 7ffffcf [27] ( 4) |11111111|11111111|11101111|10 3ffffbe [26]
( 22) |11111111|11111111|11111010|000 [27] 7ffffd0 [27] ( 5) |11111111|11111111|11101111|11 3ffffbf [26]
( 23) |11111111|11111111|11111010|001 [27] 7ffffd1 [27] ( 6) |11111111|11111111|11110000|00 3ffffc0 [26]
( 24) |11111111|11111111|11111010|010 [27] 7ffffd2 [27] ( 7) |11111111|11111111|11110000|01 3ffffc1 [26]
( 25) |11111111|11111111|11111010|011 [27] 7ffffd3 [27] ( 8) |11111111|11111111|11110000|10 3ffffc2 [26]
( 26) |11111111|11111111|11111010|100 [27] 7ffffd4 [27] ( 9) |11111111|11111111|11110000|11 3ffffc3 [26]
( 27) |11111111|11111111|11111010|101 [27] 7ffffd5 [27] ( 10) |11111111|11111111|11110001|00 3ffffc4 [26]
( 28) |11111111|11111111|11111010|110 [27] 7ffffd6 [27] ( 11) |11111111|11111111|11110001|01 3ffffc5 [26]
( 29) |11111111|11111111|11111010|111 [27] 7ffffd7 [27] ( 12) |11111111|11111111|11110001|10 3ffffc6 [26]
( 30) |11111111|11111111|11111011|000 [27] 7ffffd8 [27] ( 13) |11111111|11111111|11110001|11 3ffffc7 [26]
( 31) |11111111|11111111|11111011|001 [27] 7ffffd9 [27] ( 14) |11111111|11111111|11110010|00 3ffffc8 [26]
' ' ( 32) |11101000| [8] e8 [8] ( 15) |11111111|11111111|11110010|01 3ffffc9 [26]
'!' ( 33) |11111111|1100 [12] ffc [12] ( 16) |11111111|11111111|11110010|10 3ffffca [26]
'"' ( 34) |11111111|111010 [14] 3ffa [14] ( 17) |11111111|11111111|11110010|11 3ffffcb [26]
'#' ( 35) |11111111|1111100 [15] 7ffc [15] ( 18) |11111111|11111111|11110011|00 3ffffcc [26]
'$' ( 36) |11111111|1111101 [15] 7ffd [15] ( 19) |11111111|11111111|11110011|01 3ffffcd [26]
'%' ( 37) |100100 [6] 24 [6] ( 20) |11111111|11111111|11110011|10 3ffffce [26]
'&' ( 38) |1101110 [7] 6e [7] ( 21) |11111111|11111111|11110011|11 3ffffcf [26]
''' ( 39) |11111111|1111110 [15] 7ffe [15] ( 22) |11111111|11111111|11110100|00 3ffffd0 [26]
'(' ( 40) |11111111|010 [11] 7fa [11] ( 23) |11111111|11111111|11110100|01 3ffffd1 [26]
')' ( 41) |11111111|011 [11] 7fb [11] ( 24) |11111111|11111111|11110100|10 3ffffd2 [26]
'*' ( 42) |11111110|10 [10] 3fa [10] ( 25) |11111111|11111111|11110100|11 3ffffd3 [26]
'+' ( 43) |11111111|100 [11] 7fc [11] ( 26) |11111111|11111111|11110101|00 3ffffd4 [26]
',' ( 44) |11101001| [8] e9 [8] ( 27) |11111111|11111111|11110101|01 3ffffd5 [26]
'-' ( 45) |100101 [6] 25 [6] ( 28) |11111111|11111111|11110101|10 3ffffd6 [26]
'.' ( 46) |00100 [5] 4 [5] ( 29) |11111111|11111111|11110101|11 3ffffd7 [26]
'/' ( 47) |0000 [4] 0 [4] ( 30) |11111111|11111111|11110110|00 3ffffd8 [26]
'0' ( 48) |00101 [5] 5 [5] ( 31) |11111111|11111111|11110110|01 3ffffd9 [26]
'1' ( 49) |00110 [5] 6 [5] ' ' ( 32) |00110 6 [ 5]
'2' ( 50) |00111 [5] 7 [5] '!' ( 33) |11111111|11100 1ffc [13]
'3' ( 51) |100110 [6] 26 [6] '"' ( 34) |11111000|0 1f0 [ 9]
'4' ( 52) |100111 [6] 27 [6] '#' ( 35) |11111111|111100 3ffc [14]
'5' ( 53) |101000 [6] 28 [6] '$' ( 36) |11111111|1111100 7ffc [15]
'6' ( 54) |101001 [6] 29 [6] '%' ( 37) |011110 1e [ 6]
'7' ( 55) |101010 [6] 2a [6] '&' ( 38) |1100100 64 [ 7]
'8' ( 56) |101011 [6] 2b [6] ''' ( 39) |11111111|11101 1ffd [13]
'9' ( 57) |101100 [6] 2c [6] '(' ( 40) |11111110|10 3fa [10]
':' ( 58) |11110110|0 [9] 1ec [9] ')' ( 41) |11111000|1 1f1 [ 9]
';' ( 59) |11101010| [8] ea [8] '*' ( 42) |11111110|11 3fb [10]
'<' ( 60) |11111111|11111111|10 [18] 3fffe [18] '+' ( 43) |11111111|00 3fc [10]
'=' ( 61) |101101 [6] 2d [6] ',' ( 44) |1100101 65 [ 7]
'>' ( 62) |11111111|11111110|0 [17] 1fffc [17] '-' ( 45) |1100110 66 [ 7]
'?' ( 63) |11110110|1 [9] 1ed [9] '.' ( 46) |011111 1f [ 6]
'@' ( 64) |11111111|111011 [14] 3ffb [14] '/' ( 47) |00111 7 [ 5]
'A' ( 65) |1101111 [7] 6f [7] '0' ( 48) |0000 0 [ 4]
'B' ( 66) |11101011| [8] eb [8] '1' ( 49) |0001 1 [ 4]
'C' ( 67) |11101100| [8] ec [8] '2' ( 50) |0010 2 [ 4]
'D' ( 68) |11101101| [8] ed [8] '3' ( 51) |01000 8 [ 5]
'E' ( 69) |11101110| [8] ee [8] '4' ( 52) |100000 20 [ 6]
'F' ( 70) |1110000 [7] 70 [7] '5' ( 53) |100001 21 [ 6]
'G' ( 71) |11110111|0 [9] 1ee [9] '6' ( 54) |100010 22 [ 6]
'H' ( 72) |11110111|1 [9] 1ef [9] '7' ( 55) |100011 23 [ 6]
'I' ( 73) |11111000|0 [9] 1f0 [9] '8' ( 56) |100100 24 [ 6]
'J' ( 74) |11111000|1 [9] 1f1 [9] '9' ( 57) |100101 25 [ 6]
'K' ( 75) |11111110|11 [10] 3fb [10] ':' ( 58) |100110 26 [ 6]
'L' ( 76) |11111001|0 [9] 1f2 [9] ';' ( 59) |11101100| ec [ 8]
'M' ( 77) |11101111| [8] ef [8] '<' ( 60) |11111111|11111110|0 1fffc [17]
'N' ( 78) |11111001|1 [9] 1f3 [9] '=' ( 61) |100111 27 [ 6]
'O' ( 79) |11111010|0 [9] 1f4 [9] '>' ( 62) |11111111|1111101 7ffd [15]
'P' ( 80) |11111010|1 [9] 1f5 [9] '?' ( 63) |11111111|01 3fd [10]
'Q' ( 81) |11111011|0 [9] 1f6 [9] '@' ( 64) |11111111|1111110 7ffe [15]
'R' ( 82) |11111011|1 [9] 1f7 [9] 'A' ( 65) |1100111 67 [ 7]
'S' ( 83) |11110000| [8] f0 [8] 'B' ( 66) |11101101| ed [ 8]
'T' ( 84) |11110001| [8] f1 [8] 'C' ( 67) |11101110| ee [ 8]
'U' ( 85) |11111100|0 [9] 1f8 [9] 'D' ( 68) |1101000 68 [ 7]
'V' ( 86) |11111100|1 [9] 1f9 [9] 'E' ( 69) |11101111| ef [ 8]
'W' ( 87) |11111101|0 [9] 1fa [9] 'F' ( 70) |1101001 69 [ 7]
'X' ( 88) |11111101|1 [9] 1fb [9] 'G' ( 71) |1101010 6a [ 7]
'Y' ( 89) |11111110|0 [9] 1fc [9] 'H' ( 72) |11111001|0 1f2 [ 9]
'Z' ( 90) |11111111|00 [10] 3fc [10] 'I' ( 73) |11110000| f0 [ 8]
'[' ( 91) |11111111|111100 [14] 3ffc [14] 'J' ( 74) |11111001|1 1f3 [ 9]
'\' ( 92) |11111111|11111111|11111011|010 [27] 7ffffda [27] 'K' ( 75) |11111010|0 1f4 [ 9]
']' ( 93) |11111111|11100 [13] 1ffc [13] 'L' ( 76) |11111010|1 1f5 [ 9]
'^' ( 94) |11111111|111101 [14] 3ffd [14] 'M' ( 77) |1101011 6b [ 7]
'_' ( 95) |101110 [6] 2e [6] 'N' ( 78) |1101100 6c [ 7]
'`' ( 96) |11111111|11111111|110 [19] 7fffe [19] 'O' ( 79) |11110001| f1 [ 8]
'a' ( 97) |01000 [5] 8 [5] 'P' ( 80) |11110010| f2 [ 8]
'b' ( 98) |101111 [6] 2f [6] 'Q' ( 81) |11111011|0 1f6 [ 9]
'c' ( 99) |01001 [5] 9 [5] 'R' ( 82) |11111011|1 1f7 [ 9]
'd' (100) |110000 [6] 30 [6] 'S' ( 83) |1101101 6d [ 7]
'e' (101) |0001 [4] 1 [4] 'T' ( 84) |101000 28 [ 6]
'f' (102) |110001 [6] 31 [6] 'U' ( 85) |11110011| f3 [ 8]
'g' (103) |110010 [6] 32 [6] 'V' ( 86) |11111100|0 1f8 [ 9]
'h' (104) |110011 [6] 33 [6] 'W' ( 87) |11111100|1 1f9 [ 9]
'i' (105) |01010 [5] a [5] 'X' ( 88) |11110100| f4 [ 8]
'j' (106) |1110001 [7] 71 [7] 'Y' ( 89) |11111101|0 1fa [ 9]
'k' (107) |1110010 [7] 72 [7] 'Z' ( 90) |11111101|1 1fb [ 9]
'l' (108) |01011 [5] b [5] '[' ( 91) |11111111|100 7fc [11]
'm' (109) |110100 [6] 34 [6] '\' ( 92) |11111111|11111111|11110110|10 3ffffda [26]
'n' (110) |01100 [5] c [5] ']' ( 93) |11111111|101 7fd [11]
'o' (111) |01101 [5] d [5] '^' ( 94) |11111111|111101 3ffd [14]
'p' (112) |01110 [5] e [5] '_' ( 95) |1101110 6e [ 7]
'q' (113) |11110010| [8] f2 [8] '`' ( 96) |11111111|11111111|10 3fffe [18]
'r' (114) |01111 [5] f [5] 'a' ( 97) |01001 9 [ 5]
's' (115) |10000 [5] 10 [5] 'b' ( 98) |1101111 6f [ 7]
't' (116) |10001 [5] 11 [5] 'c' ( 99) |01010 a [ 5]
'u' (117) |110101 [6] 35 [6] 'd' (100) |101001 29 [ 6]
'v' (118) |1110011 [7] 73 [7] 'e' (101) |01011 b [ 5]
'w' (119) |110110 [6] 36 [6] 'f' (102) |1110000 70 [ 7]
'x' (120) |11110011| [8] f3 [8] 'g' (103) |101010 2a [ 6]
'y' (121) |11110100| [8] f4 [8] 'h' (104) |101011 2b [ 6]
'z' (122) |11110101| [8] f5 [8] 'i' (105) |01100 c [ 5]
'{' (123) |11111111|11111110|1 [17] 1fffd [17] 'j' (106) |11110101| f5 [ 8]
'|' (124) |11111111|101 [11] 7fd [11] 'k' (107) |11110110| f6 [ 8]
'}' (125) |11111111|11111111|0 [17] 1fffe [17] 'l' (108) |101100 2c [ 6]
'~' (126) |11111111|1101 [12] ffd [12] 'm' (109) |101101 2d [ 6]
(127) |11111111|11111111|11111011|011 [27] 7ffffdb [27] 'n' (110) |101110 2e [ 6]
(128) |11111111|11111111|11111011|100 [27] 7ffffdc [27] 'o' (111) |01101 d [ 5]
(129) |11111111|11111111|11111011|101 [27] 7ffffdd [27] 'p' (112) |101111 2f [ 6]
(130) |11111111|11111111|11111011|110 [27] 7ffffde [27] 'q' (113) |11111110|0 1fc [ 9]
(131) |11111111|11111111|11111011|111 [27] 7ffffdf [27] 'r' (114) |110000 30 [ 6]
(132) |11111111|11111111|11111100|000 [27] 7ffffe0 [27] 's' (115) |110001 31 [ 6]
(133) |11111111|11111111|11111100|001 [27] 7ffffe1 [27] 't' (116) |01110 e [ 5]
(134) |11111111|11111111|11111100|010 [27] 7ffffe2 [27] 'u' (117) |1110001 71 [ 7]
(135) |11111111|11111111|11111100|011 [27] 7ffffe3 [27] 'v' (118) |1110010 72 [ 7]
(136) |11111111|11111111|11111100|100 [27] 7ffffe4 [27] 'w' (119) |1110011 73 [ 7]
(137) |11111111|11111111|11111100|101 [27] 7ffffe5 [27] 'x' (120) |1110100 74 [ 7]
(138) |11111111|11111111|11111100|110 [27] 7ffffe6 [27] 'y' (121) |1110101 75 [ 7]
(139) |11111111|11111111|11111100|111 [27] 7ffffe7 [27] 'z' (122) |11110111| f7 [ 8]
(140) |11111111|11111111|11111101|000 [27] 7ffffe8 [27] '{' (123) |11111111|11111110|1 1fffd [17]
(141) |11111111|11111111|11111101|001 [27] 7ffffe9 [27] '|' (124) |11111111|1100 ffc [12]
(142) |11111111|11111111|11111101|010 [27] 7ffffea [27] '}' (125) |11111111|11111111|0 1fffe [17]
(143) |11111111|11111111|11111101|011 [27] 7ffffeb [27] '~' (126) |11111111|1101 ffd [12]
(144) |11111111|11111111|11111101|100 [27] 7ffffec [27] (127) |11111111|11111111|11110110|11 3ffffdb [26]
(145) |11111111|11111111|11111101|101 [27] 7ffffed [27] (128) |11111111|11111111|11110111|00 3ffffdc [26]
(146) |11111111|11111111|11111101|110 [27] 7ffffee [27] (129) |11111111|11111111|11110111|01 3ffffdd [26]
(147) |11111111|11111111|11111101|111 [27] 7ffffef [27] (130) |11111111|11111111|11110111|10 3ffffde [26]
(148) |11111111|11111111|11111110|000 [27] 7fffff0 [27] (131) |11111111|11111111|11110111|11 3ffffdf [26]
(149) |11111111|11111111|11111110|001 [27] 7fffff1 [27] (132) |11111111|11111111|11111000|00 3ffffe0 [26]
(150) |11111111|11111111|11111110|010 [27] 7fffff2 [27] (133) |11111111|11111111|11111000|01 3ffffe1 [26]
(151) |11111111|11111111|11111110|011 [27] 7fffff3 [27] (134) |11111111|11111111|11111000|10 3ffffe2 [26]
(152) |11111111|11111111|11111110|100 [27] 7fffff4 [27] (135) |11111111|11111111|11111000|11 3ffffe3 [26]
(153) |11111111|11111111|11111110|101 [27] 7fffff5 [27] (136) |11111111|11111111|11111001|00 3ffffe4 [26]
(154) |11111111|11111111|11111110|110 [27] 7fffff6 [27] (137) |11111111|11111111|11111001|01 3ffffe5 [26]
(155) |11111111|11111111|11111110|111 [27] 7fffff7 [27] (138) |11111111|11111111|11111001|10 3ffffe6 [26]
(156) |11111111|11111111|11111111|000 [27] 7fffff8 [27] (139) |11111111|11111111|11111001|11 3ffffe7 [26]
(157) |11111111|11111111|11111111|001 [27] 7fffff9 [27] (140) |11111111|11111111|11111010|00 3ffffe8 [26]
(158) |11111111|11111111|11111111|010 [27] 7fffffa [27] (141) |11111111|11111111|11111010|01 3ffffe9 [26]
(159) |11111111|11111111|11111111|011 [27] 7fffffb [27] (142) |11111111|11111111|11111010|10 3ffffea [26]
(160) |11111111|11111111|11111111|100 [27] 7fffffc [27] (143) |11111111|11111111|11111010|11 3ffffeb [26]
(161) |11111111|11111111|11111111|101 [27] 7fffffd [27] (144) |11111111|11111111|11111011|00 3ffffec [26]
(162) |11111111|11111111|11111111|110 [27] 7fffffe [27] (145) |11111111|11111111|11111011|01 3ffffed [26]
(163) |11111111|11111111|11111111|111 [27] 7ffffff [27] (146) |11111111|11111111|11111011|10 3ffffee [26]
(164) |11111111|11111111|11100000|00 [26] 3ffff80 [26] (147) |11111111|11111111|11111011|11 3ffffef [26]
(165) |11111111|11111111|11100000|01 [26] 3ffff81 [26] (148) |11111111|11111111|11111100|00 3fffff0 [26]
(166) |11111111|11111111|11100000|10 [26] 3ffff82 [26] (149) |11111111|11111111|11111100|01 3fffff1 [26]
(167) |11111111|11111111|11100000|11 [26] 3ffff83 [26] (150) |11111111|11111111|11111100|10 3fffff2 [26]
(168) |11111111|11111111|11100001|00 [26] 3ffff84 [26] (151) |11111111|11111111|11111100|11 3fffff3 [26]
(169) |11111111|11111111|11100001|01 [26] 3ffff85 [26] (152) |11111111|11111111|11111101|00 3fffff4 [26]
(170) |11111111|11111111|11100001|10 [26] 3ffff86 [26] (153) |11111111|11111111|11111101|01 3fffff5 [26]
(171) |11111111|11111111|11100001|11 [26] 3ffff87 [26] (154) |11111111|11111111|11111101|10 3fffff6 [26]
(172) |11111111|11111111|11100010|00 [26] 3ffff88 [26] (155) |11111111|11111111|11111101|11 3fffff7 [26]
(173) |11111111|11111111|11100010|01 [26] 3ffff89 [26] (156) |11111111|11111111|11111110|00 3fffff8 [26]
(174) |11111111|11111111|11100010|10 [26] 3ffff8a [26] (157) |11111111|11111111|11111110|01 3fffff9 [26]
(175) |11111111|11111111|11100010|11 [26] 3ffff8b [26] (158) |11111111|11111111|11111110|10 3fffffa [26]
(176) |11111111|11111111|11100011|00 [26] 3ffff8c [26] (159) |11111111|11111111|11111110|11 3fffffb [26]
(177) |11111111|11111111|11100011|01 [26] 3ffff8d [26] (160) |11111111|11111111|11111111|00 3fffffc [26]
(178) |11111111|11111111|11100011|10 [26] 3ffff8e [26] (161) |11111111|11111111|11111111|01 3fffffd [26]
(179) |11111111|11111111|11100011|11 [26] 3ffff8f [26] (162) |11111111|11111111|11111111|10 3fffffe [26]
(180) |11111111|11111111|11100100|00 [26] 3ffff90 [26] (163) |11111111|11111111|11111111|11 3ffffff [26]
(181) |11111111|11111111|11100100|01 [26] 3ffff91 [26] (164) |11111111|11111111|11000000|0 1ffff80 [25]
(182) |11111111|11111111|11100100|10 [26] 3ffff92 [26] (165) |11111111|11111111|11000000|1 1ffff81 [25]
(183) |11111111|11111111|11100100|11 [26] 3ffff93 [26] (166) |11111111|11111111|11000001|0 1ffff82 [25]
(184) |11111111|11111111|11100101|00 [26] 3ffff94 [26] (167) |11111111|11111111|11000001|1 1ffff83 [25]
(185) |11111111|11111111|11100101|01 [26] 3ffff95 [26] (168) |11111111|11111111|11000010|0 1ffff84 [25]
(186) |11111111|11111111|11100101|10 [26] 3ffff96 [26] (169) |11111111|11111111|11000010|1 1ffff85 [25]
(187) |11111111|11111111|11100101|11 [26] 3ffff97 [26] (170) |11111111|11111111|11000011|0 1ffff86 [25]
(188) |11111111|11111111|11100110|00 [26] 3ffff98 [26] (171) |11111111|11111111|11000011|1 1ffff87 [25]
(189) |11111111|11111111|11100110|01 [26] 3ffff99 [26] (172) |11111111|11111111|11000100|0 1ffff88 [25]
(190) |11111111|11111111|11100110|10 [26] 3ffff9a [26] (173) |11111111|11111111|11000100|1 1ffff89 [25]
(191) |11111111|11111111|11100110|11 [26] 3ffff9b [26] (174) |11111111|11111111|11000101|0 1ffff8a [25]
(192) |11111111|11111111|11100111|00 [26] 3ffff9c [26] (175) |11111111|11111111|11000101|1 1ffff8b [25]
(193) |11111111|11111111|11100111|01 [26] 3ffff9d [26] (176) |11111111|11111111|11000110|0 1ffff8c [25]
(194) |11111111|11111111|11100111|10 [26] 3ffff9e [26] (177) |11111111|11111111|11000110|1 1ffff8d [25]
(195) |11111111|11111111|11100111|11 [26] 3ffff9f [26] (178) |11111111|11111111|11000111|0 1ffff8e [25]
(196) |11111111|11111111|11101000|00 [26] 3ffffa0 [26] (179) |11111111|11111111|11000111|1 1ffff8f [25]
(197) |11111111|11111111|11101000|01 [26] 3ffffa1 [26] (180) |11111111|11111111|11001000|0 1ffff90 [25]
(198) |11111111|11111111|11101000|10 [26] 3ffffa2 [26] (181) |11111111|11111111|11001000|1 1ffff91 [25]
(199) |11111111|11111111|11101000|11 [26] 3ffffa3 [26] (182) |11111111|11111111|11001001|0 1ffff92 [25]
(200) |11111111|11111111|11101001|00 [26] 3ffffa4 [26] (183) |11111111|11111111|11001001|1 1ffff93 [25]
(201) |11111111|11111111|11101001|01 [26] 3ffffa5 [26] (184) |11111111|11111111|11001010|0 1ffff94 [25]
(202) |11111111|11111111|11101001|10 [26] 3ffffa6 [26] (185) |11111111|11111111|11001010|1 1ffff95 [25]
(203) |11111111|11111111|11101001|11 [26] 3ffffa7 [26] (186) |11111111|11111111|11001011|0 1ffff96 [25]
(204) |11111111|11111111|11101010|00 [26] 3ffffa8 [26] (187) |11111111|11111111|11001011|1 1ffff97 [25]
(205) |11111111|11111111|11101010|01 [26] 3ffffa9 [26] (188) |11111111|11111111|11001100|0 1ffff98 [25]
(206) |11111111|11111111|11101010|10 [26] 3ffffaa [26] (189) |11111111|11111111|11001100|1 1ffff99 [25]
(207) |11111111|11111111|11101010|11 [26] 3ffffab [26] (190) |11111111|11111111|11001101|0 1ffff9a [25]
(208) |11111111|11111111|11101011|00 [26] 3ffffac [26] (191) |11111111|11111111|11001101|1 1ffff9b [25]
(209) |11111111|11111111|11101011|01 [26] 3ffffad [26] (192) |11111111|11111111|11001110|0 1ffff9c [25]
(210) |11111111|11111111|11101011|10 [26] 3ffffae [26] (193) |11111111|11111111|11001110|1 1ffff9d [25]
(211) |11111111|11111111|11101011|11 [26] 3ffffaf [26] (194) |11111111|11111111|11001111|0 1ffff9e [25]
(212) |11111111|11111111|11101100|00 [26] 3ffffb0 [26] (195) |11111111|11111111|11001111|1 1ffff9f [25]
(213) |11111111|11111111|11101100|01 [26] 3ffffb1 [26] (196) |11111111|11111111|11010000|0 1ffffa0 [25]
(214) |11111111|11111111|11101100|10 [26] 3ffffb2 [26] (197) |11111111|11111111|11010000|1 1ffffa1 [25]
(215) |11111111|11111111|11101100|11 [26] 3ffffb3 [26] (198) |11111111|11111111|11010001|0 1ffffa2 [25]
(216) |11111111|11111111|11101101|00 [26] 3ffffb4 [26] (199) |11111111|11111111|11010001|1 1ffffa3 [25]
(217) |11111111|11111111|11101101|01 [26] 3ffffb5 [26] (200) |11111111|11111111|11010010|0 1ffffa4 [25]
(218) |11111111|11111111|11101101|10 [26] 3ffffb6 [26] (201) |11111111|11111111|11010010|1 1ffffa5 [25]
(219) |11111111|11111111|11101101|11 [26] 3ffffb7 [26] (202) |11111111|11111111|11010011|0 1ffffa6 [25]
(220) |11111111|11111111|11101110|00 [26] 3ffffb8 [26] (203) |11111111|11111111|11010011|1 1ffffa7 [25]
(221) |11111111|11111111|11101110|01 [26] 3ffffb9 [26] (204) |11111111|11111111|11010100|0 1ffffa8 [25]
(222) |11111111|11111111|11101110|10 [26] 3ffffba [26] (205) |11111111|11111111|11010100|1 1ffffa9 [25]
(223) |11111111|11111111|11101110|11 [26] 3ffffbb [26] (206) |11111111|11111111|11010101|0 1ffffaa [25]
(224) |11111111|11111111|11101111|00 [26] 3ffffbc [26] (207) |11111111|11111111|11010101|1 1ffffab [25]
(225) |11111111|11111111|11101111|01 [26] 3ffffbd [26] (208) |11111111|11111111|11010110|0 1ffffac [25]
(226) |11111111|11111111|11101111|10 [26] 3ffffbe [26] (209) |11111111|11111111|11010110|1 1ffffad [25]
(227) |11111111|11111111|11101111|11 [26] 3ffffbf [26] (210) |11111111|11111111|11010111|0 1ffffae [25]
(228) |11111111|11111111|11110000|00 [26] 3ffffc0 [26] (211) |11111111|11111111|11010111|1 1ffffaf [25]
(229) |11111111|11111111|11110000|01 [26] 3ffffc1 [26] (212) |11111111|11111111|11011000|0 1ffffb0 [25]
(230) |11111111|11111111|11110000|10 [26] 3ffffc2 [26] (213) |11111111|11111111|11011000|1 1ffffb1 [25]
(231) |11111111|11111111|11110000|11 [26] 3ffffc3 [26] (214) |11111111|11111111|11011001|0 1ffffb2 [25]
(232) |11111111|11111111|11110001|00 [26] 3ffffc4 [26] (215) |11111111|11111111|11011001|1 1ffffb3 [25]
(233) |11111111|11111111|11110001|01 [26] 3ffffc5 [26] (216) |11111111|11111111|11011010|0 1ffffb4 [25]
(234) |11111111|11111111|11110001|10 [26] 3ffffc6 [26] (217) |11111111|11111111|11011010|1 1ffffb5 [25]
(235) |11111111|11111111|11110001|11 [26] 3ffffc7 [26] (218) |11111111|11111111|11011011|0 1ffffb6 [25]
(236) |11111111|11111111|11110010|00 [26] 3ffffc8 [26] (219) |11111111|11111111|11011011|1 1ffffb7 [25]
(237) |11111111|11111111|11110010|01 [26] 3ffffc9 [26] (220) |11111111|11111111|11011100|0 1ffffb8 [25]
(238) |11111111|11111111|11110010|10 [26] 3ffffca [26] (221) |11111111|11111111|11011100|1 1ffffb9 [25]
(239) |11111111|11111111|11110010|11 [26] 3ffffcb [26] (222) |11111111|11111111|11011101|0 1ffffba [25]
(240) |11111111|11111111|11110011|00 [26] 3ffffcc [26] (223) |11111111|11111111|11011101|1 1ffffbb [25]
(241) |11111111|11111111|11110011|01 [26] 3ffffcd [26] (224) |11111111|11111111|11011110|0 1ffffbc [25]
(242) |11111111|11111111|11110011|10 [26] 3ffffce [26] (225) |11111111|11111111|11011110|1 1ffffbd [25]
(243) |11111111|11111111|11110011|11 [26] 3ffffcf [26] (226) |11111111|11111111|11011111|0 1ffffbe [25]
(244) |11111111|11111111|11110100|00 [26] 3ffffd0 [26] (227) |11111111|11111111|11011111|1 1ffffbf [25]
(245) |11111111|11111111|11110100|01 [26] 3ffffd1 [26] (228) |11111111|11111111|11100000|0 1ffffc0 [25]
(246) |11111111|11111111|11110100|10 [26] 3ffffd2 [26] (229) |11111111|11111111|11100000|1 1ffffc1 [25]
(247) |11111111|11111111|11110100|11 [26] 3ffffd3 [26] (230) |11111111|11111111|11100001|0 1ffffc2 [25]
(248) |11111111|11111111|11110101|00 [26] 3ffffd4 [26] (231) |11111111|11111111|11100001|1 1ffffc3 [25]
(249) |11111111|11111111|11110101|01 [26] 3ffffd5 [26] (232) |11111111|11111111|11100010|0 1ffffc4 [25]
(250) |11111111|11111111|11110101|10 [26] 3ffffd6 [26] (233) |11111111|11111111|11100010|1 1ffffc5 [25]
(251) |11111111|11111111|11110101|11 [26] 3ffffd7 [26] (234) |11111111|11111111|11100011|0 1ffffc6 [25]
(252) |11111111|11111111|11110110|00 [26] 3ffffd8 [26] (235) |11111111|11111111|11100011|1 1ffffc7 [25]
(253) |11111111|11111111|11110110|01 [26] 3ffffd9 [26] (236) |11111111|11111111|11100100|0 1ffffc8 [25]
(254) |11111111|11111111|11110110|10 [26] 3ffffda [26] (237) |11111111|11111111|11100100|1 1ffffc9 [25]
(255) |11111111|11111111|11110110|11 [26] 3ffffdb [26] (238) |11111111|11111111|11100101|0 1ffffca [25]
EOS (256) |11111111|11111111|11110111|00 [26] 3ffffdc [26] (239) |11111111|11111111|11100101|1 1ffffcb [25]
(240) |11111111|11111111|11100110|0 1ffffcc [25]
(241) |11111111|11111111|11100110|1 1ffffcd [25]
(242) |11111111|11111111|11100111|0 1ffffce [25]
(243) |11111111|11111111|11100111|1 1ffffcf [25]
(244) |11111111|11111111|11101000|0 1ffffd0 [25]
(245) |11111111|11111111|11101000|1 1ffffd1 [25]
(246) |11111111|11111111|11101001|0 1ffffd2 [25]
(247) |11111111|11111111|11101001|1 1ffffd3 [25]
(248) |11111111|11111111|11101010|0 1ffffd4 [25]
(249) |11111111|11111111|11101010|1 1ffffd5 [25]
(250) |11111111|11111111|11101011|0 1ffffd6 [25]
(251) |11111111|11111111|11101011|1 1ffffd7 [25]
(252) |11111111|11111111|11101100|0 1ffffd8 [25]
(253) |11111111|11111111|11101100|1 1ffffd9 [25]
(254) |11111111|11111111|11101101|0 1ffffda [25]
(255) |11111111|11111111|11101101|1 1ffffdb [25]
EOS (256) |11111111|11111111|11101110|0 1ffffdc [25]
Appendix D. Examples Appendix D. Examples
A number of examples are worked through here, for both requests and A number of examples are worked through here, covering integer
responses, and with and without Huffman coding. encoding, header field representation, and the encoding of whole sets
of header fields, for both requests and responses, and with and
without Huffman coding.
D.1. Header Field Representation Examples D.1. Integer Representation Examples
This section show several independent representation examples. This section shows the representation of integer values in details
(see Section 4.1.1).
D.1.1. Literal Header Field with Indexing D.1.1. Example 1: Encoding 10 using a 5-bit prefix
The value 10 is to be encoded with a 5-bit prefix.
o 10 is less than 31 (2^5 - 1) and is represented using the 5-bit
prefix.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| X | X | X | 0 | 1 | 0 | 1 | 0 | 10 stored on 5 bits
+---+---+---+---+---+---+---+---+
D.1.2. Example 2: Encoding 1337 using a 5-bit prefix
The value I=1337 is to be encoded with a 5-bit prefix.
1337 is greater than 31 (2^5 - 1).
The 5-bit prefix is filled with its max value (31).
I = 1337 - (2^5 - 1) = 1306.
I (1306) is greater than or equal to 128, the while loop body
executes:
I % 128 == 26
26 + 128 == 154
154 is encoded in 8 bits as: 10011010
I is set to 10 (1306 / 128 == 10)
I is no longer greater than or equal to 128, the while loop
terminates.
I, now 10, is encoded on 8 bits as: 00001010.
The process ends.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 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
| 0 | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 10<128, encode(10), done
+---+---+---+---+---+---+---+---+
D.1.3. Example 3: Encoding 42 starting at an octet-boundary
The value 42 is to be encoded starting at an octet-boundary. This
implies that a 8-bit prefix is used.
o 42 is less than 255 (2^8 - 1) and is represented using the 8-bit
prefix.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 0 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 42 stored on 8 bits
+---+---+---+---+---+---+---+---+
D.2. Header Field Representation Examples
This section shows several independent representation examples.
D.2.1. 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.
Hex dump of encoded data: Hex dump of encoded data:
000a 6375 7374 6f6d 2d6b 6579 0d63 7573 | ..custom-key.cus 400a 6375 7374 6f6d 2d6b 6579 0d63 7573 | @.custom-key.cus
746f 6d2d 6865 6164 6572 | tom-header 746f 6d2d 6865 6164 6572 | tom-header
Decoding process: Decoding process:
00 | == Literal indexed == 40 | == Literal indexed ==
0a | Literal name (len = 10) 0a | Literal name (len = 10)
6375 7374 6f6d 2d6b 6579 | custom-key 6375 7374 6f6d 2d6b 6579 | custom-key
0d | Literal value (len = 13) 0d | Literal value (len = 13)
6375 7374 6f6d 2d68 6561 6465 72 | custom-header 6375 7374 6f6d 2d68 6561 6465 72 | custom-header
| -> custom-key: custom-head\ | -> custom-key: custom-head\
| er | er
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
D.1.2. Literal Header Field without Indexing D.2.2. 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.
Hex dump of encoded data: Hex dump of encoded data:
440c 2f73 616d 706c 652f 7061 7468 | D./sample/path 040c 2f73 616d 706c 652f 7061 7468 | ../sample/path
Decoding process: Decoding process:
44 | == Literal not indexed == 04 | == Literal not indexed ==
| Indexed name (idx = 4) | Indexed name (idx = 4)
| :path | :path
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
D.1.3. Indexed Header Field D.2.3. 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 32, line 20 skipping to change at page 35, line 7
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
D.1.4. Indexed Header Field from Static Table D.2.4. 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 33, line 9 skipping to change at page 35, line 35
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
D.2. Request Examples without Huffman D.3. 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.
D.2.1. 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.
Hex dump of encoded data: Hex dump of encoded data:
8287 8604 0f77 7777 2e65 7861 6d70 6c65 | .....www.example 8287 8644 0f77 7777 2e65 7861 6d70 6c65 | ...D.www.example
2e63 6f6d | .com 2e63 6f6d | .com
Decoding process: Decoding process:
82 | == Indexed - Add == 82 | == Indexed - Add ==
| idx = 2 | idx = 2
| -> :method: GET | -> :method: GET
87 | == Indexed - Add == 87 | == Indexed - Add ==
| idx = 7 | idx = 7
| -> :scheme: http | -> :scheme: http
86 | == Indexed - Add == 86 | == Indexed - Add ==
| idx = 6 | idx = 6
| -> :path: / | -> :path: /
04 | == Literal indexed == 44 | == Literal indexed ==
| Indexed name (idx = 4) | Indexed name (idx = 4)
| :authority | :authority
0f | Literal value (len = 15) 0f | Literal value (len = 15)
7777 772e 6578 616d 706c 652e 636f 6d | www.example.com 7777 772e 6578 616d 706c 652e 636f 6d | www.example.com
| -> :authority: www.example\ | -> :authority: www.example\
| .com | .com
Header Table (after decoding): Header Table (after decoding):
[ 1] (s = 57) :authority: www.example.com [ 1] (s = 57) :authority: www.example.com
skipping to change at page 34, line 20 skipping to change at page 37, line 10
[ 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
D.2.2. 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 34, line 42 skipping to change at page 37, line 32
Reference set: Reference set:
[ 1] :authority: www.example.com [ 1] :authority: www.example.com
[ 2] :path: / [ 2] :path: /
[ 3] :scheme: http [ 3] :scheme: http
[ 4] :method: GET [ 4] :method: GET
Hex dump of encoded data: Hex dump of encoded data:
1b08 6e6f 2d63 6163 6865 | ..no-cache 5c08 6e6f 2d63 6163 6865 | \.no-cache
Decoding process: Decoding process:
1b | == Literal indexed == 5c | == Literal indexed ==
| Indexed name (idx = 27) | Indexed name (idx = 28)
| cache-control | cache-control
08 | Literal value (len = 8) 08 | Literal value (len = 8)
6e6f 2d63 6163 6865 | no-cache 6e6f 2d63 6163 6865 | no-cache
| -> cache-control: no-cache | -> cache-control: no-cache
Header Table (after decoding): Header Table (after decoding):
[ 1] (s = 53) cache-control: no-cache [ 1] (s = 53) cache-control: no-cache
[ 2] (s = 57) :authority: www.example.com [ 2] (s = 57) :authority: www.example.com
[ 3] (s = 38) :path: / [ 3] (s = 38) :path: /
skipping to change at page 35, line 29 skipping to change at page 38, line 20
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
D.2.3. 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 36, line 13 skipping to change at page 38, line 44
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:
8080 858c 8b84 000a 6375 7374 6f6d 2d6b | ........custom-k 3085 8c8b 8440 0a63 7573 746f 6d2d 6b65 | 0....@.custom-ke
6579 0c63 7573 746f 6d2d 7661 6c75 65 | ey.custom-value 790c 6375 7374 6f6d 2d76 616c 7565 | y.custom-value
Decoding process: Decoding process:
80 80 | == Empty reference set == 30 | == Empty reference set ==
| idx = 0 | idx = 0
| flag = 1 | 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 ==
| idx = 4 | idx = 4
| -> :authority: www.example\ | -> :authority: www.example\
| .com | .com
00 | == Literal indexed == 40 | == Literal indexed ==
0a | Literal name (len = 10) 0a | Literal name (len = 10)
6375 7374 6f6d 2d6b 6579 | custom-key 6375 7374 6f6d 2d6b 6579 | custom-key
0c | Literal value (len = 12) 0c | Literal value (len = 12)
6375 7374 6f6d 2d76 616c 7565 | custom-value 6375 7374 6f6d 2d76 616c 7565 | custom-value
| -> custom-key: custom-valu\ | -> custom-key: custom-valu\
| e | e
Header Table (after decoding): Header Table (after decoding):
[ 1] (s = 54) custom-key: custom-value [ 1] (s = 54) custom-key: custom-value
skipping to change at page 37, line 23 skipping to change at page 40, line 5
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
D.3. Request Examples with Huffman D.4. 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.
D.3.1. First request D.4.1. 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.
Hex dump of encoded data: Hex dump of encoded data:
8287 8604 8bdb 6d88 3e68 d1cb 1225 ba7f | ......m..h...%.. 8287 8644 8ce7 cf9b ebe8 9b6f b16f a9b6 | ...D.......o.o..
ff | .
Decoding process: Decoding process:
82 | == Indexed - Add == 82 | == Indexed - Add ==
| idx = 2 | idx = 2
| -> :method: GET | -> :method: GET
87 | == Indexed - Add == 87 | == Indexed - Add ==
| idx = 7 | idx = 7
| -> :scheme: http | -> :scheme: http
86 | == Indexed - Add == 86 | == Indexed - Add ==
| idx = 6 | idx = 6
| -> :path: / | -> :path: /
04 | == Literal indexed == 44 | == Literal indexed ==
| Indexed name (idx = 4) | Indexed name (idx = 4)
| :authority | :authority
8b | Literal value (len = 15) 8c | Literal value (len = 15)
| Huffman encoded: | Huffman encoded:
db6d 883e 68d1 cb12 25ba 7f | .m..h...%.. e7cf 9beb e89b 6fb1 6fa9 b6ff | ......o.o...
| Decoded: | Decoded:
| www.example.com | www.example.com
| -> :authority: www.example\ | -> :authority: www.example\
| .com | .com
Header Table (after decoding): Header Table (after decoding):
[ 1] (s = 57) :authority: www.example.com [ 1] (s = 57) :authority: www.example.com
[ 2] (s = 38) :path: / [ 2] (s = 38) :path: /
[ 3] (s = 43) :scheme: http [ 3] (s = 43) :scheme: http
[ 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
D.3.2. Second request D.4.2. 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 39, line 20 skipping to change at page 41, line 40
Reference set: Reference set:
[ 1] :authority: www.example.com [ 1] :authority: www.example.com
[ 2] :path: / [ 2] :path: /
[ 3] :scheme: http [ 3] :scheme: http
[ 4] :method: GET [ 4] :method: GET
Hex dump of encoded data: Hex dump of encoded data:
1b86 6365 4a13 98ff | ..ceJ... 5c86 b9b9 9495 56bf | \.....V.
Decoding process: Decoding process:
1b | == Literal indexed == 5c | == Literal indexed ==
| Indexed name (idx = 27) | Indexed name (idx = 28)
| cache-control | cache-control
86 | Literal value (len = 8) 86 | Literal value (len = 8)
| Huffman encoded: | Huffman encoded:
6365 4a13 98ff | ceJ... b9b9 9495 56bf | ....V.
| Decoded: | Decoded:
| no-cache | no-cache
| -> cache-control: no-cache | -> cache-control: no-cache
Header Table (after decoding): Header Table (after decoding):
[ 1] (s = 53) cache-control: no-cache [ 1] (s = 53) cache-control: no-cache
[ 2] (s = 57) :authority: www.example.com [ 2] (s = 57) :authority: www.example.com
[ 3] (s = 38) :path: / [ 3] (s = 38) :path: /
[ 4] (s = 43) :scheme: http [ 4] (s = 43) :scheme: http
skipping to change at page 40, line 11 skipping to change at page 42, line 32
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
D.3.3. Third request D.4.3. 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 35 skipping to change at page 43, 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:
8080 858c 8b84 0088 4eb0 8b74 9790 fa7f | ........N..t.... 3085 8c8b 8440 8857 1c5c db73 7b2f af89 | 0....@.W.\.s{/..
894e b08b 7497 9a17 a8ff | .N..t..... 571c 5cdb 7372 4d9c 57 | W.\.srM.W
Decoding process: Decoding process:
80 80 | == Empty reference set == 30 | == Empty reference set ==
| idx = 0 | idx = 0
| flag = 1 | 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 ==
| idx = 4 | idx = 4
| -> :authority: www.example\ | -> :authority: www.example\
| .com | .com
00 | == Literal indexed == 40 | == Literal indexed ==
88 | Literal name (len = 10) 88 | Literal name (len = 10)
| Huffman encoded: | Huffman encoded:
4eb0 8b74 9790 fa7f | N..t.... 571c 5cdb 737b 2faf | W.\.s{/.
| Decoded: | Decoded:
| custom-key | custom-key
89 | Literal value (len = 12) 89 | Literal value (len = 12)
| Huffman encoded: | Huffman encoded:
4eb0 8b74 979a 17a8 ff | N..t..... 571c 5cdb 7372 4d9c 57 | W.\.srM.W
| Decoded: | Decoded:
| custom-value | custom-value
| -> custom-key: custom-valu\ | -> custom-key: custom-valu\
| e | e
Header Table (after decoding): Header Table (after decoding):
[ 1] (s = 54) custom-key: custom-value [ 1] (s = 54) custom-key: custom-value
[ 2] (s = 48) :path: /index.html [ 2] (s = 48) :path: /index.html
[ 3] (s = 44) :scheme: https [ 3] (s = 44) :scheme: https
skipping to change at page 42, line 11 skipping to change at page 44, 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
D.4. Response Examples without Huffman D.5. 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.
D.4.1. 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:
0803 3330 3218 0770 7269 7661 7465 221d | ..302..private". 4803 3330 3259 0770 7269 7661 7465 631d | H.302Y.privatec.
4d6f 6e2c 2032 3120 4f63 7420 3230 3133 | Mon, 21 Oct 2013 4d6f 6e2c 2032 3120 4f63 7420 3230 3133 | Mon, 21 Oct 2013
2032 303a 3133 3a32 3120 474d 5430 1768 | 20:13:21 GMT0.h 2032 303a 3133 3a32 3120 474d 5471 1768 | 20:13:21 GMTq.h
7474 7073 3a2f 2f77 7777 2e65 7861 6d70 | ttps://www.examp 7474 7073 3a2f 2f77 7777 2e65 7861 6d70 | ttps://www.examp
6c65 2e63 6f6d | le.com 6c65 2e63 6f6d | le.com
Decoding process: Decoding process:
08 | == Literal indexed == 48 | == Literal indexed ==
| Indexed name (idx = 8) | Indexed name (idx = 8)
| :status | :status
03 | Literal value (len = 3) 03 | Literal value (len = 3)
3330 32 | 302 3330 32 | 302
| -> :status: 302 | -> :status: 302
18 | == Literal indexed == 59 | == Literal indexed ==
| Indexed name (idx = 24) | Indexed name (idx = 25)
| cache-control | cache-control
07 | Literal value (len = 7) 07 | Literal value (len = 7)
7072 6976 6174 65 | private 7072 6976 6174 65 | private
| -> cache-control: private | -> cache-control: private
22 | == Literal indexed == 63 | == Literal indexed ==
| Indexed name (idx = 34) | Indexed name (idx = 35)
| date | date
1d | Literal value (len = 29) 1d | Literal value (len = 29)
4d6f 6e2c 2032 3120 4f63 7420 3230 3133 | Mon, 21 Oct 2013 4d6f 6e2c 2032 3120 4f63 7420 3230 3133 | Mon, 21 Oct 2013
2032 303a 3133 3a32 3120 474d 54 | 20:13:21 GMT 2032 303a 3133 3a32 3120 474d 54 | 20:13:21 GMT
| -> date: Mon, 21 Oct 2013 \ | -> date: Mon, 21 Oct 2013 \
| 20:13:21 GMT | 20:13:21 GMT
30 | == Literal indexed == 71 | == Literal indexed ==
| Indexed name (idx = 48) | Indexed name (idx = 49)
| location | location
17 | Literal value (len = 23) 17 | Literal value (len = 23)
6874 7470 733a 2f2f 7777 772e 6578 616d | https://www.exam 6874 7470 733a 2f2f 7777 772e 6578 616d | https://www.exam
706c 652e 636f 6d | ple.com 706c 652e 636f 6d | ple.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
skipping to change at page 44, line 5 skipping to change at page 46, 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
D.4.2. 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 free space to allow adding the (":status", "200") header field,
copied from the static table into the header table. The (":status", copied from the static table into the header table. The (":status",
"302") header field doesn't need to be removed from the reference set "302") header field doesn't need to be removed from the reference set
as it is evicted from the header table. as it is evicted from the header table.
Header set to encode: Header set to encode:
:status: 200 :status: 200
skipping to change at page 45, line 10 skipping to change at page 47, line 10
[ 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
D.4.3. 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 45, line 37 skipping to change at page 47, 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:
8484 031d 4d6f 6e2c 2032 3120 4f63 7420 | ....Mon, 21 Oct 8484 431d 4d6f 6e2c 2032 3120 4f63 7420 | ..C.Mon, 21 Oct
3230 3133 2032 303a 3133 3a32 3220 474d | 2013 20:13:22 GM 3230 3133 2032 303a 3133 3a32 3220 474d | 2013 20:13:22 GM
541d 0467 7a69 7084 8483 833a 3866 6f6f | T..gzip....:8foo 545e 0467 7a69 7084 8483 837b 3866 6f6f | T^.gzip....{8foo
3d41 5344 4a4b 4851 4b42 5a58 4f51 5745 | =ASDJKHQKBZXOQWE 3d41 5344 4a4b 4851 4b42 5a58 4f51 5745 | =ASDJKHQKBZXOQWE
4f50 4955 4158 5157 454f 4955 3b20 6d61 | OPIUAXQWEOIU; ma 4f50 4955 4158 5157 454f 4955 3b20 6d61 | OPIUAXQWEOIU; ma
782d 6167 653d 3336 3030 3b20 7665 7273 | x-age=3600; vers 782d 6167 653d 3336 3030 3b20 7665 7273 | x-age=3600; vers
696f 6e3d 31 | ion=1 696f 6e3d 31 | ion=1
Decoding process: Decoding process:
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 == 43 | == Literal indexed ==
| Indexed name (idx = 3) | Indexed name (idx = 3)
| date | date
1d | Literal value (len = 29) 1d | Literal value (len = 29)
4d6f 6e2c 2032 3120 4f63 7420 3230 3133 | Mon, 21 Oct 2013 4d6f 6e2c 2032 3120 4f63 7420 3230 3133 | Mon, 21 Oct 2013
2032 303a 3133 3a32 3220 474d 54 | 20:13:22 GMT 2032 303a 3133 3a32 3220 474d 54 | 20:13:22 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 == 5e | == Literal indexed ==
| Indexed name (idx = 29) | Indexed name (idx = 30)
| content-encoding | content-encoding
04 | Literal value (len = 4) 04 | Literal value (len = 4)
677a 6970 | gzip 677a 6970 | 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 ==
| idx = 4 | idx = 4
| -> location: https://www.e\ | -> location: https://www.e\
| xample.com | xample.com
83 | == Indexed - Remove == 83 | == Indexed - Remove ==
| 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 == 7b | == Literal indexed ==
| Indexed name (idx = 58) | Indexed name (idx = 59)
| set-cookie | set-cookie
38 | Literal value (len = 56) 38 | Literal value (len = 56)
666f 6f3d 4153 444a 4b48 514b 425a 584f | foo=ASDJKHQKBZXO 666f 6f3d 4153 444a 4b48 514b 425a 584f | foo=ASDJKHQKBZXO
5157 454f 5049 5541 5851 5745 4f49 553b | QWEOPIUAXQWEOIU; 5157 454f 5049 5541 5851 5745 4f49 553b | QWEOPIUAXQWEOIU;
206d 6178 2d61 6765 3d33 3630 303b 2076 | max-age=3600; v 206d 6178 2d61 6765 3d33 3630 303b 2076 | max-age=3600; v
6572 7369 6f6e 3d31 | ersion=1 6572 7369 6f6e 3d31 | ersion=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\
skipping to change at page 47, line 24 skipping to change at page 49, 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
D.5. Response Examples with Huffman D.6. 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.
D.5.1. First response D.6.1. 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 98a7 1885 73d5 cd11 1f22 98ef 6b3a | ......s...."..k: 4882 4017 5985 bf06 724b 9763 93d6 dbb2 | H.@.Y...rK.c....
7a0e 6e8f a263 d072 9a6e 8397 d869 bd87 | z.n..c.r.n...i.. 9884 de2a 7188 0506 2098 5131 09b5 6ba3 | ...*q... .Q1..k.
3747 bbbf c730 90ce 3174 3d80 1b6d b107 | 7G...0..1t=..m.. 7191 adce bf19 8e7e 7cf9 bebe 89b6 fb16 | q.......|.......
cd1a 3962 44b7 4f | ..9bD.O fa9b 6f | ..o
Decoding process: Decoding process:
08 | == Literal indexed == 48 | == 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:
98a7 | .. 4017 | @.
| Decoded: | Decoded:
| 302 | 302
| -> :status: 302 | -> :status: 302
18 | == Literal indexed == 59 | == Literal indexed ==
| Indexed name (idx = 24) | Indexed name (idx = 25)
| cache-control | cache-control
85 | Literal value (len = 7) 85 | Literal value (len = 7)
| Huffman encoded: | Huffman encoded:
73d5 cd11 1f | s.... bf06 724b 97 | ..rK.
| Decoded: | Decoded:
| private | private
| -> cache-control: private | -> cache-control: private
22 | == Literal indexed == 63 | == Literal indexed ==
| Indexed name (idx = 34) | Indexed name (idx = 35)
| date | date
98 | Literal value (len = 29) 93 | Literal value (len = 29)
| Huffman encoded: | Huffman encoded:
ef6b 3a7a 0e6e 8fa2 63d0 729a 6e83 97d8 | .k:z.n..c.r.n... d6db b298 84de 2a71 8805 0620 9851 3109 | ......*q... .Q1.
69bd 8737 47bb bfc7 | i..7G... b56b a3 | .k.
| 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 == 71 | == Literal indexed ==
| Indexed name (idx = 48) | Indexed name (idx = 49)
| location | location
90 | Literal value (len = 23) 91 | Literal value (len = 23)
| Huffman encoded: | Huffman encoded:
ce31 743d 801b 6db1 07cd 1a39 6244 b74f | .1t=..m....9bD.O adce bf19 8e7e 7cf9 bebe 89b6 fb16 fa9b | ......|.........
6f | o
| 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
D.5.2. Second response D.6.2. 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 free space to allow adding the (":status", "200") header field,
copied from the static table into the header table. The (":status", copied from the static table into the header table. The (":status",
"302") header field doesn't need to be removed from the reference set "302") header field doesn't need to be removed from the reference set
as it is evicted from the header table. as it is evicted from the header table.
Header set to encode: Header set to encode:
:status: 200 :status: 200
skipping to change at page 51, line 25 skipping to change at page 53, line 25
[ 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
D.5.3. Third response D.6.3. 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 52, line 13 skipping to change at page 54, 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:
8484 0398 ef6b 3a7a 0e6e 8fa2 63d0 729a | .....k:z.n..c.r. 8484 4393 d6db b298 84de 2a71 8805 0620 | ..C.......*q...
6e83 97d8 69bd 873f 47bb bfc7 1d83 cbd5 | n...i..?G....... 9851 3111 b56b a35e 84ab dd97 ff84 8483 | .Q1..k.^........
4e84 8483 833a b3c5 adb7 7f87 6fc7 fbf7 | N....:......o... 837b b1e0 d6cf 9f6e 8f9f d3e5 f6fa 76fe | .{.....n......v.
fdbf bebf f3f7 f4fb 7ebb be9f 5f87 e37f | ............_... fd3c 7edf 9eff 1f2f 0f3c fe9f 6fcf 7f8f | ......./....o...
efed faee fa7c 3f1d 5d1a 23ce 5464 36cd | .....|?.].#.Td6. 879f 61ad 4f4c c9a9 73a2 200e c372 5e18 | ..a.OL..s. ..r^.
494b d5d1 cc5f 0535 969b | IK..._.5.. b1b7 4e3f | ..N?
Decoding process: Decoding process:
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 == 43 | == Literal indexed ==
| Indexed name (idx = 3) | Indexed name (idx = 3)
| date | date
98 | Literal value (len = 29) 93 | Literal value (len = 29)
| Huffman encoded: | Huffman encoded:
ef6b 3a7a 0e6e 8fa2 63d0 729a 6e83 97d8 | .k:z.n..c.r.n... d6db b298 84de 2a71 8805 0620 9851 3111 | ......*q... .Q1.
69bd 873f 47bb bfc7 | i..?G... b56b a3 | .k.
| 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 == 5e | == Literal indexed ==
| Indexed name (idx = 29) | Indexed name (idx = 30)
| content-encoding | content-encoding
83 | Literal value (len = 4) 84 | Literal value (len = 4)
| Huffman encoded: | Huffman encoded:
cbd5 4e | ..N abdd 97ff | ....
| 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 ==
| idx = 4 | idx = 4
| -> location: https://www.e\ | -> location: https://www.e\
| xample.com | xample.com
83 | == Indexed - Remove == 83 | == Indexed - Remove ==
| 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 == 7b | == Literal indexed ==
| Indexed name (idx = 58) | Indexed name (idx = 59)
| set-cookie | set-cookie
b3 | Literal value (len = 56) b1 | Literal value (len = 56)
| Huffman encoded: | Huffman encoded:
c5ad b77f 876f c7fb f7fd bfbe bff3 f7f4 | .....o.......... e0d6 cf9f 6e8f 9fd3 e5f6 fa76 fefd 3c7e | ....n......v....
fb7e bbbe 9f5f 87e3 7fef edfa eefa 7c3f | ....._........|? df9e ff1f 2f0f 3cfe 9f6f cf7f 8f87 9f61 | ..../....o.....a
1d5d 1a23 ce54 6436 cd49 4bd5 d1cc 5f05 | .].#.Td6.IK..._. ad4f 4cc9 a973 a220 0ec3 725e 18b1 b74e | .OL..s. ..r^...N
3596 9b | 5.. 3f | ?
| 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. 153 change blocks. 
705 lines changed or deleted 827 lines changed or added

This html diff was produced by rfcdiff 1.41. The latest version is available from http://tools.ietf.org/tools/rfcdiff/