draft-ietf-quic-qpack-11.txt   draft-ietf-quic-qpack-12.txt 
QUIC C. Krasic QUIC C. Krasic
Internet-Draft Netflix Internet-Draft Netflix
Intended status: Standards Track M. Bishop Intended status: Standards Track M. Bishop
Expires: May 7, 2020 Akamai Technologies Expires: 25 July 2020 Akamai Technologies
A. Frindell, Ed. A. Frindell, Ed.
Facebook Facebook
November 04, 2019 22 January 2020
QPACK: Header Compression for HTTP/3 QPACK: Header Compression for HTTP/3
draft-ietf-quic-qpack-11 draft-ietf-quic-qpack-12
Abstract Abstract
This specification defines QPACK, a compression format for This specification defines QPACK, a compression format for
efficiently representing HTTP header fields, to be used in HTTP/3. efficiently representing HTTP header fields, to be used in HTTP/3.
This is a variation of HPACK header compression that seeks to reduce This is a variation of HPACK header compression that seeks to reduce
head-of-line blocking. head-of-line blocking.
Note to Readers Note to Readers
Discussion of this draft takes place on the QUIC working group Discussion of this draft takes place on the QUIC working group
mailing list (quic@ietf.org), which is archived at mailing list (quic@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/search/?email_list=quic [1]. https://mailarchive.ietf.org/arch/search/?email_list=quic
(https://mailarchive.ietf.org/arch/search/?email_list=quic).
Working Group information can be found at https://github.com/quicwg Working Group information can be found at https://github.com/quicwg
[2]; source code and issues list for this draft can be found at (https://github.com/quicwg); source code and issues list for this
https://github.com/quicwg/base-drafts/labels/-qpack [3]. draft can be found at https://github.com/quicwg/base-drafts/labels/-
qpack (https://github.com/quicwg/base-drafts/labels/-qpack).
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 https://datatracker.ietf.org/drafts/current/. Drafts is at https://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 May 7, 2020. This Internet-Draft will expire on 25 July 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions and Definitions . . . . . . . . . . . . . . . 4 1.1. Conventions and Definitions . . . . . . . . . . . . . . . 4
1.2. Notational Conventions . . . . . . . . . . . . . . . . . 4 1.2. Notational Conventions . . . . . . . . . . . . . . . . . 4
2. Compression Process Overview . . . . . . . . . . . . . . . . 5 2. Compression Process Overview . . . . . . . . . . . . . . . . 5
2.1. Encoder . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. Encoder . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1. Reference Tracking . . . . . . . . . . . . . . . . . 5 2.1.1. Reference Tracking . . . . . . . . . . . . . . . . . 6
2.1.2. Blocked Dynamic Table Insertions . . . . . . . . . . 6 2.1.2. Limits on Dynamic Table Insertions . . . . . . . . . 6
2.1.3. Blocked Streams . . . . . . . . . . . . . . . . . . . 7 2.1.3. Blocked Streams . . . . . . . . . . . . . . . . . . . 7
2.1.4. Known Received Count . . . . . . . . . . . . . . . . 8 2.1.4. Known Received Count . . . . . . . . . . . . . . . . 8
2.2. Decoder . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2. Decoder . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.1. Blocked Decoding . . . . . . . . . . . . . . . . . . 8 2.2.1. Blocked Decoding . . . . . . . . . . . . . . . . . . 8
2.2.2. State Synchronization . . . . . . . . . . . . . . . . 9 2.2.2. State Synchronization . . . . . . . . . . . . . . . . 9
2.2.3. Invalid References . . . . . . . . . . . . . . . . . 10 2.2.3. Invalid References . . . . . . . . . . . . . . . . . 10
3. Header Tables . . . . . . . . . . . . . . . . . . . . . . . . 10 3. Header Tables . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1. Static Table . . . . . . . . . . . . . . . . . . . . . . 10 3.1. Static Table . . . . . . . . . . . . . . . . . . . . . . 10
3.2. Dynamic Table . . . . . . . . . . . . . . . . . . . . . . 11 3.2. Dynamic Table . . . . . . . . . . . . . . . . . . . . . . 11
3.2.1. Dynamic Table Size . . . . . . . . . . . . . . . . . 11 3.2.1. Dynamic Table Size . . . . . . . . . . . . . . . . . 11
3.2.2. Dynamic Table Capacity and Eviction . . . . . . . . . 11 3.2.2. Dynamic Table Capacity and Eviction . . . . . . . . . 11
3.2.3. Maximum Dynamic Table Capacity . . . . . . . . . . . 12 3.2.3. Maximum Dynamic Table Capacity . . . . . . . . . . . 12
3.2.4. Absolute Indexing . . . . . . . . . . . . . . . . . . 12 3.2.4. Absolute Indexing . . . . . . . . . . . . . . . . . . 12
3.2.5. Relative Indexing . . . . . . . . . . . . . . . . . . 12 3.2.5. Relative Indexing . . . . . . . . . . . . . . . . . . 12
3.2.6. Post-Base Indexing . . . . . . . . . . . . . . . . . 13 3.2.6. Post-Base Indexing . . . . . . . . . . . . . . . . . 14
4. Wire Format . . . . . . . . . . . . . . . . . . . . . . . . . 14 4. Wire Format . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.1. Primitives . . . . . . . . . . . . . . . . . . . . . . . 14 4.1. Primitives . . . . . . . . . . . . . . . . . . . . . . . 14
4.1.1. Prefixed Integers . . . . . . . . . . . . . . . . . . 14 4.1.1. Prefixed Integers . . . . . . . . . . . . . . . . . . 14
4.1.2. String Literals . . . . . . . . . . . . . . . . . . . 14 4.1.2. String Literals . . . . . . . . . . . . . . . . . . . 14
4.2. Encoder and Decoder Streams . . . . . . . . . . . . . . . 15 4.2. Encoder and Decoder Streams . . . . . . . . . . . . . . . 15
4.3. Encoder Instructions . . . . . . . . . . . . . . . . . . 15 4.3. Encoder Instructions . . . . . . . . . . . . . . . . . . 16
4.3.1. Set Dynamic Table Capacity . . . . . . . . . . . . . 16 4.3.1. Set Dynamic Table Capacity . . . . . . . . . . . . . 16
4.3.2. Insert With Name Reference . . . . . . . . . . . . . 16 4.3.2. Insert With Name Reference . . . . . . . . . . . . . 16
4.3.3. Insert Without Name Reference . . . . . . . . . . . . 17 4.3.3. Insert Without Name Reference . . . . . . . . . . . . 17
4.3.4. Duplicate . . . . . . . . . . . . . . . . . . . . . . 17 4.3.4. Duplicate . . . . . . . . . . . . . . . . . . . . . . 17
4.4. Decoder Instructions . . . . . . . . . . . . . . . . . . 18 4.4. Decoder Instructions . . . . . . . . . . . . . . . . . . 18
4.4.1. Header Acknowledgement . . . . . . . . . . . . . . . 18 4.4.1. Header Acknowledgement . . . . . . . . . . . . . . . 18
4.4.2. Stream Cancellation . . . . . . . . . . . . . . . . . 18 4.4.2. Stream Cancellation . . . . . . . . . . . . . . . . . 19
4.4.3. Insert Count Increment . . . . . . . . . . . . . . . 19 4.4.3. Insert Count Increment . . . . . . . . . . . . . . . 19
4.5. Header Block Representations . . . . . . . . . . . . . . 19 4.5. Header Block Representations . . . . . . . . . . . . . . 19
4.5.1. Header Block Prefix . . . . . . . . . . . . . . . . . 19 4.5.1. Header Block Prefix . . . . . . . . . . . . . . . . . 20
4.5.2. Indexed Header Field . . . . . . . . . . . . . . . . 22 4.5.2. Indexed Header Field . . . . . . . . . . . . . . . . 22
4.5.3. Indexed Header Field With Post-Base Index . . . . . . 22 4.5.3. Indexed Header Field With Post-Base Index . . . . . . 23
4.5.4. Literal Header Field With Name Reference . . . . . . 23 4.5.4. Literal Header Field With Name Reference . . . . . . 23
4.5.5. Literal Header Field With Post-Base Name Reference . 24 4.5.5. Literal Header Field With Post-Base Name Reference . 24
4.5.6. Literal Header Field Without Name Reference . . . . . 24 4.5.6. Literal Header Field Without Name Reference . . . . . 24
5. Configuration . . . . . . . . . . . . . . . . . . . . . . . . 25 5. Configuration . . . . . . . . . . . . . . . . . . . . . . . . 25
6. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 25 6. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 25
7. Security Considerations . . . . . . . . . . . . . . . . . . . 26 7. Security Considerations . . . . . . . . . . . . . . . . . . . 26
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
8.1. Settings Registration . . . . . . . . . . . . . . . . . . 26 8.1. Settings Registration . . . . . . . . . . . . . . . . . . 26
8.2. Stream Type Registration . . . . . . . . . . . . . . . . 26 8.2. Stream Type Registration . . . . . . . . . . . . . . . . 26
8.3. Error Code Registration . . . . . . . . . . . . . . . . . 27 8.3. Error Code Registration . . . . . . . . . . . . . . . . . 27
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 27 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
9.1. Normative References . . . . . . . . . . . . . . . . . . 27 9.1. Normative References . . . . . . . . . . . . . . . . . . 27
9.2. Informative References . . . . . . . . . . . . . . . . . 28 9.2. Informative References . . . . . . . . . . . . . . . . . 28
9.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Appendix A. Static Table . . . . . . . . . . . . . . . . . . . . 28 Appendix A. Static Table . . . . . . . . . . . . . . . . . . . . 28
Appendix B. Sample One Pass Encoding Algorithm . . . . . . . . . 33 Appendix B. Sample One Pass Encoding Algorithm . . . . . . . . . 32
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 35 Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 33
C.1. Since draft-ietf-quic-qpack-10 . . . . . . . . . . . . . 35 C.1. Since draft-ietf-quic-qpack-11 . . . . . . . . . . . . . 34
C.2. Since draft-ietf-quic-qpack-09 . . . . . . . . . . . . . 35 C.2. Since draft-ietf-quic-qpack-10 . . . . . . . . . . . . . 34
C.3. Since draft-ietf-quic-qpack-08 . . . . . . . . . . . . . 35 C.3. Since draft-ietf-quic-qpack-09 . . . . . . . . . . . . . 34
C.4. Since draft-ietf-quic-qpack-06 . . . . . . . . . . . . . 35 C.4. Since draft-ietf-quic-qpack-08 . . . . . . . . . . . . . 34
C.5. Since draft-ietf-quic-qpack-05 . . . . . . . . . . . . . 35 C.5. Since draft-ietf-quic-qpack-06 . . . . . . . . . . . . . 34
C.6. Since draft-ietf-quic-qpack-04 . . . . . . . . . . . . . 35 C.6. Since draft-ietf-quic-qpack-05 . . . . . . . . . . . . . 34
C.7. Since draft-ietf-quic-qpack-03 . . . . . . . . . . . . . 35 C.7. Since draft-ietf-quic-qpack-04 . . . . . . . . . . . . . 34
C.8. Since draft-ietf-quic-qpack-02 . . . . . . . . . . . . . 36 C.8. Since draft-ietf-quic-qpack-03 . . . . . . . . . . . . . 34
C.9. Since draft-ietf-quic-qpack-01 . . . . . . . . . . . . . 36 C.9. Since draft-ietf-quic-qpack-02 . . . . . . . . . . . . . 35
C.10. Since draft-ietf-quic-qpack-00 . . . . . . . . . . . . . 36 C.10. Since draft-ietf-quic-qpack-01 . . . . . . . . . . . . . 35
C.11. Since draft-ietf-quic-qcram-00 . . . . . . . . . . . . . 36 C.11. Since draft-ietf-quic-qpack-00 . . . . . . . . . . . . . 35
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 37 C.12. Since draft-ietf-quic-qcram-00 . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36
1. Introduction 1. Introduction
The QUIC transport protocol [QUIC-TRANSPORT] is designed to support The QUIC transport protocol [QUIC-TRANSPORT] is designed to support
HTTP semantics, and its design subsumes many of the features of HTTP semantics, and its design subsumes many of the features of
HTTP/2 [RFC7540]. HTTP/2 uses HPACK [RFC7541] for header HTTP/2 [RFC7540]. HTTP/2 uses HPACK [RFC7541] for header
compression. If HPACK were used for HTTP/3 [HTTP3], it would induce compression. If HPACK were used for HTTP/3 [HTTP3], it would induce
head-of-line blocking due to built-in assumptions of a total ordering head-of-line blocking due to built-in assumptions of a total ordering
across frames on all streams. across frames on all streams.
skipping to change at page 5, line 16 skipping to change at page 5, line 16
x (A+) Indicates that x uses the prefixed integer encoding defined x (A+) Indicates that x uses the prefixed integer encoding defined
in Section 4.1.1, beginning with an A-bit prefix. in Section 4.1.1, beginning with an A-bit prefix.
x ... Indicates that x is variable-length and extends to the end of x ... Indicates that x is variable-length and extends to the end of
the region. the region.
2. Compression Process Overview 2. Compression Process Overview
Like HPACK, QPACK uses two tables for associating header fields to Like HPACK, QPACK uses two tables for associating header fields to
indices. The static table (see Section 3.1) is predefined and indices. The static table (Section 3.1) is predefined and contains
contains common header fields (some of them with an empty value). common header fields (some of them with an empty value). The dynamic
The dynamic table (see Section 3.2) is built up over the course of table (Section 3.2) is built up over the course of the connection and
the connection and can be used by the encoder to index header fields can be used by the encoder to index header fields in the encoded
in the encoded header lists. header lists.
QPACK defines unidirectional streams for sending instructions from QPACK defines unidirectional streams for sending instructions from
encoder to decoder and vice versa. encoder to decoder and vice versa.
2.1. Encoder 2.1. Encoder
An encoder converts a header list into a header block by emitting An encoder converts a header list into a header block by emitting
either an indexed or a literal representation for each header field either an indexed or a literal representation for each header field
in the list (see Section 4.5). Indexed representations achieve high in the list; see Section 4.5. Indexed representations achieve high
compression by replacing the literal name and possibly the value with compression by replacing the literal name and possibly the value with
an index to either the static or dynamic table. References to the an index to either the static or dynamic table. References to the
static table and literal representations do not require any dynamic static table and literal representations do not require any dynamic
state and never risk head-of-line blocking. References to the state and never risk head-of-line blocking. References to the
dynamic table risk head-of-line blocking if the encoder has not dynamic table risk head-of-line blocking if the encoder has not
received an acknowledgement indicating the entry is available at the received an acknowledgement indicating the entry is available at the
decoder. decoder.
An encoder MAY insert any entry in the dynamic table it chooses; it An encoder MAY insert any entry in the dynamic table it chooses; it
is not limited to header fields it is compressing. is not limited to header fields it is compressing.
skipping to change at page 6, line 5 skipping to change at page 6, line 11
QPACK is designed to contain the more complex state tracking to the QPACK is designed to contain the more complex state tracking to the
encoder, while the decoder is relatively simple. encoder, while the decoder is relatively simple.
2.1.1. Reference Tracking 2.1.1. Reference Tracking
An encoder MUST ensure that a header block which references a dynamic An encoder MUST ensure that a header block which references a dynamic
table entry is not processed by the decoder after the referenced table entry is not processed by the decoder after the referenced
entry has been evicted. Hence the encoder needs to retain entry has been evicted. Hence the encoder needs to retain
information about each compressed header block that references the information about each compressed header block that references the
dynamic table until that header block is acknowledged by the decoder dynamic table until that header block is acknowledged by the decoder;
(see Section 4.4.1). see Section 4.4.1.
2.1.2. Blocked Dynamic Table Insertions 2.1.2. Limits on Dynamic Table Insertions
A dynamic table entry is considered blocking and cannot be evicted Inserting entries into the dynamic table might not be possible if the
until its insertion has been acknowledged and there are no table contains entries which cannot be evicted.
outstanding unacknowledged references to the entry. In particular, a
dynamic table entry that has never been referenced can still be
blocking.
An encoder MUST NOT insert an entry into the dynamic table (or A dynamic table entry cannot be evicted immediately after insertion,
duplicate an existing entry) if doing so would evict a blocking even if it has never been referenced. Once the insertion of a
entry. In order to avoid this, an encoder that uses the dynamic dynamic table entry has been acknowledged and there are no
table has to keep track of blocking entries. outstanding unacknowledged references to the entry, the entry becomes
evictable.
Note: A blocking entry is unrelated to a blocked stream, see If the dynamic table does not contain enough room for a new entry
Section 2.1.3. without evicting other entries, and the entries which would be
evicted are not evictable, the encoder MUST NOT insert that entry
into the dynamic table (including duplicates of existing entries).
In order to avoid this, an encoder that uses the dynamic table has to
keep track of whether each entry is currently evictable or not.
2.1.2.1. Avoiding Blocked Insertions 2.1.2.1. Avoiding Prohibited Insertions
To ensure that the encoder is not prevented from adding new entries, To ensure that the encoder is not prevented from adding new entries,
the encoder can avoid referencing entries that are close to eviction. the encoder can avoid referencing entries that are close to eviction.
Rather than reference such an entry, the encoder can emit a Duplicate Rather than reference such an entry, the encoder can emit a Duplicate
instruction (see Section 4.3.4), and reference the duplicate instead. instruction (Section 4.3.4), and reference the duplicate instead.
Determining which entries are too close to eviction to reference is Determining which entries are too close to eviction to reference is
an encoder preference. One heuristic is to target a fixed amount of an encoder preference. One heuristic is to target a fixed amount of
available space in the dynamic table: either unused space or space available space in the dynamic table: either unused space or space
that can be reclaimed by evicting non-blocking entries. To achieve that can be reclaimed by evicting non-blocking entries. To achieve
this, the encoder can maintain a draining index, which is the this, the encoder can maintain a draining index, which is the
smallest absolute index (see Section 3.2.4) in the dynamic table that smallest absolute index (Section 3.2.4) in the dynamic table that it
it will emit a reference for. As new entries are inserted, the will emit a reference for. As new entries are inserted, the encoder
encoder increases the draining index to maintain the section of the increases the draining index to maintain the section of the table
table that it will not reference. If the encoder does not create new that it will not reference. If the encoder does not create new
references to entries with an absolute index lower than the draining references to entries with an absolute index lower than the draining
index, the number of unacknowledged references to those entries will index, the number of unacknowledged references to those entries will
eventually become zero, allowing them to be evicted. eventually become zero, allowing them to be evicted.
+----------+---------------------------------+--------+ +----------+---------------------------------+--------+
| Draining | Referenceable | Unused | | Draining | Referenceable | Unused |
| Entries | Entries | Space | | Entries | Entries | Space |
+----------+---------------------------------+--------+ +----------+---------------------------------+--------+
^ ^ ^ ^ ^ ^
| | | | | |
Dropping Draining Index Insertion Point Dropping Draining Index Insertion Point
Point Point
Figure 1: Draining Dynamic Table Entries Figure 1: Draining Dynamic Table Entries
2.1.3. Blocked Streams 2.1.3. Blocked Streams
Because QUIC does not guarantee order between data on different Because QUIC does not guarantee order between data on different
streams, a decoder might encounter a header block that references a streams, a decoder might encounter a header block that references a
dynamic table entry that it has not yet received. dynamic table entry that it has not yet received.
Each header block contains a Required Insert Count (see Each header block contains a Required Insert Count (Section 4.5.1),
Section 4.5.1), the lowest possible value for the Insert Count with the lowest possible value for the Insert Count with which the header
which the header block can be decoded. For a header block with block can be decoded. For a header block with references to the
references to the dynamic table, the Required Insert Count is one dynamic table, the Required Insert Count is one larger than the
larger than the largest absolute index of all referenced dynamic largest absolute index of all referenced dynamic table entries. For
table entries. For a header block with no references to the dynamic a header block with no references to the dynamic table, the Required
table, the Required Insert Count is zero. Insert Count is zero.
When the decoder receives a header block with a Required Insert Count When the decoder receives a header block with a Required Insert Count
greater than its own Insert Count, the stream cannot be processed greater than its own Insert Count, the stream cannot be processed
immediately, and is considered "blocked" (see Section 2.2.1). immediately, and is considered "blocked"; see Section 2.2.1.
The decoder specifies an upper bound on the number of streams which The decoder specifies an upper bound on the number of streams which
can be blocked using the SETTINGS_QPACK_BLOCKED_STREAMS setting (see can be blocked using the SETTINGS_QPACK_BLOCKED_STREAMS setting; see
Section 5). An encoder MUST limit the number of streams which could Section 5. An encoder MUST limit the number of streams which could
become blocked to the value of SETTINGS_QPACK_BLOCKED_STREAMS at all become blocked to the value of SETTINGS_QPACK_BLOCKED_STREAMS at all
times. If a decoder encounters more blocked streams than it promised times. If a decoder encounters more blocked streams than it promised
to support, it MUST treat this as a connection error of type to support, it MUST treat this as a connection error of type
HTTP_QPACK_DECOMPRESSION_FAILED. HTTP_QPACK_DECOMPRESSION_FAILED.
Note that the decoder might not become blocked on every stream which Note that the decoder might not become blocked on every stream which
risks becoming blocked. risks becoming blocked.
An encoder can decide whether to risk having a stream become blocked. An encoder can decide whether to risk having a stream become blocked.
If permitted by the value of SETTINGS_QPACK_BLOCKED_STREAMS, If permitted by the value of SETTINGS_QPACK_BLOCKED_STREAMS,
skipping to change at page 8, line 14 skipping to change at page 8, line 14
result in the encoder becoming blocked on congestion or flow control result in the encoder becoming blocked on congestion or flow control
limits. limits.
2.1.4. Known Received Count 2.1.4. Known Received Count
The Known Received Count is the total number of dynamic table The Known Received Count is the total number of dynamic table
insertions and duplications acknowledged by the decoder. The encoder insertions and duplications acknowledged by the decoder. The encoder
tracks the Known Received Count in order to identify which dynamic tracks the Known Received Count in order to identify which dynamic
table entries can be referenced without potentially blocking a table entries can be referenced without potentially blocking a
stream. The decoder tracks the Known Received Count in order to be stream. The decoder tracks the Known Received Count in order to be
able to send Insert Count Increment instructions (see Section 4.4.3). able to send Insert Count Increment instructions.
If a header block was potentially blocking, the encoder infers from A Header Acknowledgement instruction (Section 4.4.1) implies that the
receiving a Header Acknowledgement instruction (Section 4.4.1) that decoder has received all dynamic table state necessary to process
the decoder has received all dynamic table state necessary to process corresponding the header block. If the Required Insert Count of the
that header block. If the Required Insert Count of the acknowledged acknowledged header block is greater than the current Known Received
header block is greater than the current Known Received Count, the Count, Known Received Count is updated to the value of the Required
encoder updates the Known Received Count to the value of the Required Insert Count.
Insert Count of the acknowledged header block.
To acknowledge dynamic table entries which are not referenced by An Insert Count Increment instruction Section 4.4.3 increases the
header blocks, for example because the encoder or the decoder have Known Received Count by its Increment parameter. See Section 2.2.2.3
chosen not to risk blocked streams, the decoder sends an Insert Count for guidance.
Increment instruction (see Section 4.4.3).
2.2. Decoder 2.2. Decoder
As in HPACK, the decoder processes header blocks and emits the As in HPACK, the decoder processes header blocks and emits the
corresponding header lists. It also processes instructions received corresponding header lists. It also processes instructions received
on the encoder stream that modify the dynamic table. Note that on the encoder stream that modify the dynamic table. Note that
header blocks and encoder stream instructions arrive on separate header blocks and encoder stream instructions arrive on separate
streams. This is unlike HPACK, where header blocks can contain streams. This is unlike HPACK, where header blocks can contain
instructions that modify the dynamic table, and there is no dedicated instructions that modify the dynamic table, and there is no dedicated
stream of HPACK instructions. stream of HPACK instructions.
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While blocked, header block data SHOULD remain in the blocked While blocked, header block data SHOULD remain in the blocked
stream's flow control window. A stream becomes unblocked when the stream's flow control window. A stream becomes unblocked when the
Insert Count becomes greater than or equal to the Required Insert Insert Count becomes greater than or equal to the Required Insert
Count for all header blocks the decoder has started reading from the Count for all header blocks the decoder has started reading from the
stream. stream.
When processing header blocks, the decoder expects the Required When processing header blocks, the decoder expects the Required
Insert Count to exactly match the value defined in Section 2.1.3. If Insert Count to exactly match the value defined in Section 2.1.3. If
it encounters a smaller value than expected, it MUST treat this as a it encounters a smaller value than expected, it MUST treat this as a
connection error of type HTTP_QPACK_DECOMPRESSION_FAILED (see connection error of type HTTP_QPACK_DECOMPRESSION_FAILED; see
Section 2.2.3). If it encounters a larger value than expected, it Section 2.2.3. If it encounters a larger value than expected, it MAY
MAY treat this as a connection error of type treat this as a connection error of type
HTTP_QPACK_DECOMPRESSION_FAILED. HTTP_QPACK_DECOMPRESSION_FAILED.
2.2.2. State Synchronization 2.2.2. State Synchronization
The decoder signals the following events by emitting decoder The decoder signals the following events by emitting decoder
instructions (Section 4.4) on the decoder stream. instructions (Section 4.4) on the decoder stream.
2.2.2.1. Completed Processing of a Header Block 2.2.2.1. Completed Processing of a Header Block
After the decoder finishes decoding a header block containing dynamic After the decoder finishes decoding a header block containing dynamic
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case of intermediate responses, trailers, and pushed requests. The case of intermediate responses, trailers, and pushed requests. The
encoder interprets each Header Acknowledgement instruction as encoder interprets each Header Acknowledgement instruction as
acknowledging the earliest unacknowledged header block containing acknowledging the earliest unacknowledged header block containing
dynamic table references sent on the given stream. dynamic table references sent on the given stream.
2.2.2.2. Abandonment of a Stream 2.2.2.2. Abandonment of a Stream
When an endpoint receives a stream reset before the end of a stream When an endpoint receives a stream reset before the end of a stream
or before all header blocks are processed on that stream, or when it or before all header blocks are processed on that stream, or when it
abandons reading of a stream, it generates a Stream Cancellation abandons reading of a stream, it generates a Stream Cancellation
instruction (see Section 4.4.2). This signals to the encoder that instruction; see Section 4.4.2. This signals to the encoder that all
all references to the dynamic table on that stream are no longer references to the dynamic table on that stream are no longer
outstanding. A decoder with a maximum dynamic table capacity equal outstanding. A decoder with a maximum dynamic table capacity
to zero (see Section 3.2.3) MAY omit sending Stream Cancellations, (Section 3.2.3) equal to zero MAY omit sending Stream Cancellations,
because the encoder cannot have any dynamic table references. An because the encoder cannot have any dynamic table references. An
encoder cannot infer from this instruction that any updates to the encoder cannot infer from this instruction that any updates to the
dynamic table have been received. dynamic table have been received.
The Header Acknowledgement and Stream Cancellation instructions The Header Acknowledgement and Stream Cancellation instructions
permit the encoder to remove references to entries in the dynamic permit the encoder to remove references to entries in the dynamic
table. When an entry with absolute index lower than the Known table. When an entry with absolute index lower than the Known
Received Count has zero references, then it is no longer considered Received Count has zero references, then it is considered evictable;
blocking (see Section 2.1.2). see Section 2.1.2.
2.2.2.3. New Table Entries 2.2.2.3. New Table Entries
After receiving new table entries on the encoder stream, the decoder After receiving new table entries on the encoder stream, the decoder
chooses when to emit Insert Count Increment instructions (see chooses when to emit Insert Count Increment instructions; see
Section 4.4.3). Emitting this instruction after adding each new Section 4.4.3. Emitting this instruction after adding each new
dynamic table entry will provide the timeliest feedback to the dynamic table entry will provide the timeliest feedback to the
encoder, but could be redundant with other decoder feedback. By encoder, but could be redundant with other decoder feedback. By
delaying an Insert Count Increment instruction, the decoder might be delaying an Insert Count Increment instruction, the decoder might be
able to coalesce multiple Insert Count Increment instructions, or able to coalesce multiple Insert Count Increment instructions, or
replace them entirely with Header Acknowledgements (see replace them entirely with Header Acknowledgements; see
Section 4.4.1). However, delaying too long may lead to compression Section 4.4.1. However, delaying too long may lead to compression
inefficiencies if the encoder waits for an entry to be acknowledged inefficiencies if the encoder waits for an entry to be acknowledged
before using it. before using it.
2.2.3. Invalid References 2.2.3. Invalid References
If the decoder encounters a reference in a header block If the decoder encounters a reference in a header block
representation to a dynamic table entry which has already been representation to a dynamic table entry which has already been
evicted or which has an absolute index greater than or equal to the evicted or which has an absolute index greater than or equal to the
declared Required Insert Count (see Section 4.5.1), it MUST treat declared Required Insert Count (Section 4.5.1), it MUST treat this as
this as a connection error of type "HTTP_QPACK_DECOMPRESSION_FAILED". a connection error of type "HTTP_QPACK_DECOMPRESSION_FAILED".
If the decoder encounters a reference in an encoder instruction to a If the decoder encounters a reference in an encoder instruction to a
dynamic table entry which has already been evicted, it MUST treat dynamic table entry which has already been evicted, it MUST treat
this as a connection error of type "HTTP_QPACK_ENCODER_STREAM_ERROR". this as a connection error of type "HTTP_QPACK_ENCODER_STREAM_ERROR".
3. Header Tables 3. Header Tables
Unlike in HPACK, entries in the QPACK static and dynamic tables are Unlike in HPACK, entries in the QPACK static and dynamic tables are
addressed separately. The following sections describe how entries in addressed separately. The following sections describe how entries in
each table are addressed. each table are addressed.
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block representation it MUST treat this as a connection error of type block representation it MUST treat this as a connection error of type
"HTTP_QPACK_DECOMPRESSION_FAILED". If this index is received on the "HTTP_QPACK_DECOMPRESSION_FAILED". If this index is received on the
encoder stream, this MUST be treated as a connection error of type encoder stream, this MUST be treated as a connection error of type
"HTTP_QPACK_ENCODER_STREAM_ERROR". "HTTP_QPACK_ENCODER_STREAM_ERROR".
3.2. Dynamic Table 3.2. Dynamic Table
The dynamic table consists of a list of header fields maintained in The dynamic table consists of a list of header fields maintained in
first-in, first-out order. Each HTTP/3 endpoint holds a dynamic first-in, first-out order. Each HTTP/3 endpoint holds a dynamic
table that is initially empty. Entries are added by encoder table that is initially empty. Entries are added by encoder
instructions received on the encoder stream (see Section 4.3). instructions received on the encoder stream; see Section 4.3.
The dynamic table can contain duplicate entries (i.e., entries with The dynamic table can contain duplicate entries (i.e., entries with
the same name and same value). Therefore, duplicate entries MUST NOT the same name and same value). Therefore, duplicate entries MUST NOT
be treated as an error by the decoder. be treated as an error by the decoder.
Dynamic table entries can have empty values. Dynamic table entries can have empty values.
3.2.1. Dynamic Table Size 3.2.1. Dynamic Table Size
The size of the dynamic table is the sum of the size of its entries. The size of the dynamic table is the sum of the size of its entries.
skipping to change at page 11, line 40 skipping to change at page 11, line 40
The encoder sets the capacity of the dynamic table, which serves as The encoder sets the capacity of the dynamic table, which serves as
the upper limit on its size. The initial capacity of the dynamic the upper limit on its size. The initial capacity of the dynamic
table is zero. The encoder sends a Set Dynamic Table Capacity table is zero. The encoder sends a Set Dynamic Table Capacity
instruction (Section 4.3.1) with a non-zero capacity to begin using instruction (Section 4.3.1) with a non-zero capacity to begin using
the dynamic table. the dynamic table.
Before a new entry is added to the dynamic table, entries are evicted Before a new entry is added to the dynamic table, entries are evicted
from the end of the dynamic table until the size of the dynamic table from the end of the dynamic table until the size of the dynamic table
is less than or equal to (table capacity - size of new entry). The is less than or equal to (table capacity - size of new entry). The
encoder MUST NOT cause a blocking dynamic table entry to be evicted encoder MUST NOT cause a dynamic table entry to be evicted unless
(see Section 2.1.2). The new entry is then added to the table. It that entry is evictable; see Section 2.1.2. The new entry is then
is an error if the encoder attempts to add an entry that is larger added to the table. It is an error if the encoder attempts to add an
than the dynamic table capacity; the decoder MUST treat this as a entry that is larger than the dynamic table capacity; the decoder
connection error of type "HTTP_QPACK_ENCODER_STREAM_ERROR". MUST treat this as a connection error of type
"HTTP_QPACK_ENCODER_STREAM_ERROR".
A new entry can reference an entry in the dynamic table that will be A new entry can reference an entry in the dynamic table that will be
evicted when adding this new entry into the dynamic table. evicted when adding this new entry into the dynamic table.
Implementations are cautioned to avoid deleting the referenced name Implementations are cautioned to avoid deleting the referenced name
or value if the referenced entry is evicted from the dynamic table or value if the referenced entry is evicted from the dynamic table
prior to inserting the new entry. prior to inserting the new entry.
Whenever the dynamic table capacity is reduced by the encoder (see Whenever the dynamic table capacity is reduced by the encoder
Section 4.3.1), entries are evicted from the end of the dynamic table (Section 4.3.1), entries are evicted from the end of the dynamic
until the size of the dynamic table is less than or equal to the new table until the size of the dynamic table is less than or equal to
table capacity. This mechanism can be used to completely clear the new table capacity. This mechanism can be used to completely
entries from the dynamic table by setting a capacity of 0, which can clear entries from the dynamic table by setting a capacity of 0,
subsequently be restored. which can subsequently be restored.
3.2.3. Maximum Dynamic Table Capacity 3.2.3. Maximum Dynamic Table Capacity
To bound the memory requirements of the decoder, the decoder limits To bound the memory requirements of the decoder, the decoder limits
the maximum value the encoder is permitted to set for the dynamic the maximum value the encoder is permitted to set for the dynamic
table capacity. In HTTP/3, this limit is determined by the value of table capacity. In HTTP/3, this limit is determined by the value of
SETTINGS_QPACK_MAX_TABLE_CAPACITY sent by the decoder (see SETTINGS_QPACK_MAX_TABLE_CAPACITY sent by the decoder; see Section 5.
Section 5). The encoder MUST not set a dynamic table capacity that The encoder MUST not set a dynamic table capacity that exceeds this
exceeds this maximum, but it can choose to use a lower dynamic table maximum, but it can choose to use a lower dynamic table capacity; see
capacity (see Section 4.3.1). Section 4.3.1.
For clients using 0-RTT data in HTTP/3, the server's maximum table For clients using 0-RTT data in HTTP/3, the server's maximum table
capacity is the remembered value of the setting, or zero if the value capacity is the remembered value of the setting, or zero if the value
was not previously sent. When the client's 0-RTT value of the was not previously sent. When the client's 0-RTT value of the
SETTING is zero, the server MAY set it to a non-zero value in its SETTING is zero, the server MAY set it to a non-zero value in its
SETTINGS frame. If the remembered value is non-zero, the server MUST SETTINGS frame. If the remembered value is non-zero, the server MUST
send the same non-zero value in its SETTINGS frame. If it specifies send the same non-zero value in its SETTINGS frame. If it specifies
any other value, or omits SETTINGS_QPACK_MAX_TABLE_CAPACITY from any other value, or omits SETTINGS_QPACK_MAX_TABLE_CAPACITY from
SETTINGS, the encoder must treat this as a connection error of type SETTINGS, the encoder must treat this as a connection error of type
"HTTP_QPACK_DECODER_STREAM_ERROR". "HTTP_QPACK_DECODER_STREAM_ERROR".
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Each entry possesses an absolute index which is fixed for the Each entry possesses an absolute index which is fixed for the
lifetime of that entry. The first entry inserted has an absolute lifetime of that entry. The first entry inserted has an absolute
index of "0"; indices increase by one with each insertion. index of "0"; indices increase by one with each insertion.
3.2.5. Relative Indexing 3.2.5. Relative Indexing
Relative indices begin at zero and increase in the opposite direction Relative indices begin at zero and increase in the opposite direction
from the absolute index. Determining which entry has a relative from the absolute index. Determining which entry has a relative
index of "0" depends on the context of the reference. index of "0" depends on the context of the reference.
In encoder instructions (see Section 4.3), a relative index of "0" In encoder instructions (Section 4.3), a relative index of "0" refers
refers to the most recently inserted value in the dynamic table. to the most recently inserted value in the dynamic table. Note that
Note that this means the entry referenced by a given relative index this means the entry referenced by a given relative index will change
will change while interpreting instructions on the encoder stream. while interpreting instructions on the encoder stream.
+-----+---------------+-------+ +-----+---------------+-------+
| n-1 | ... | d | Absolute Index | n-1 | ... | d | Absolute Index
+ - - +---------------+ - - - + + - - +---------------+ - - - +
| 0 | ... | n-d-1 | Relative Index | 0 | ... | n-d-1 | Relative Index
+-----+---------------+-------+ +-----+---------------+-------+
^ | ^ |
| V | V
Insertion Point Dropping Point Insertion Point Dropping Point
n = count of entries inserted n = count of entries inserted
d = count of entries dropped d = count of entries dropped
Example Dynamic Table Indexing - Encoder Stream Figure 2: Example Dynamic Table Indexing - Encoder Stream
Unlike in encoder instructions, relative indices in header block Unlike in encoder instructions, relative indices in header block
representations are relative to the Base at the beginning of the representations are relative to the Base at the beginning of the
header block (see Section 4.5.1). This ensures that references are header block; see Section 4.5.1. This ensures that references are
stable even if header blocks and dynamic table updates are processed stable even if header blocks and dynamic table updates are processed
out of order. out of order.
In a header block a relative index of "0" refers to the entry with In a header block a relative index of "0" refers to the entry with
absolute index equal to Base - 1. absolute index equal to Base - 1.
Base Base
| |
V V
+-----+-----+-----+-----+-------+ +-----+-----+-----+-----+-------+
| n-1 | n-2 | n-3 | ... | d | Absolute Index | n-1 | n-2 | n-3 | ... | d | Absolute Index
+-----+-----+ - +-----+ - + +-----+-----+ - +-----+ - +
| 0 | ... | n-d-3 | Relative Index | 0 | ... | n-d-3 | Relative Index
+-----+-----+-------+ +-----+-----+-------+
n = count of entries inserted n = count of entries inserted
d = count of entries dropped d = count of entries dropped
In this example, Base = n - 2 In this example, Base = n - 2
Example Dynamic Table Indexing - Relative Index in Header Block Figure 3: Example Dynamic Table Indexing - Relative Index in
Header Block
3.2.6. Post-Base Indexing 3.2.6. Post-Base Indexing
Post-Base indices are used in header block instructions for entries Post-Base indices are used in header block instructions for entries
with absolute indices greater than or equal to Base, starting at 0 with absolute indices greater than or equal to Base, starting at 0
for the entry with absolute index equal to Base, and increasing in for the entry with absolute index equal to Base, and increasing in
the same direction as the absolute index. the same direction as the absolute index.
Post-Base indices allow an encoder to process a header block in a Post-Base indices allow an encoder to process a header block in a
single pass and include references to entries added while processing single pass and include references to entries added while processing
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+-----+-----+-----+-----+-----+ +-----+-----+-----+-----+-----+
| n-1 | n-2 | n-3 | ... | d | Absolute Index | n-1 | n-2 | n-3 | ... | d | Absolute Index
+-----+-----+-----+-----+-----+ +-----+-----+-----+-----+-----+
| 1 | 0 | Post-Base Index | 1 | 0 | Post-Base Index
+-----+-----+ +-----+-----+
n = count of entries inserted n = count of entries inserted
d = count of entries dropped d = count of entries dropped
In this example, Base = n - 2 In this example, Base = n - 2
Example Dynamic Table Indexing - Post-Base Index in Header Block Figure 4: Example Dynamic Table Indexing - Post-Base Index in
Header Block
4. Wire Format 4. Wire Format
4.1. Primitives 4.1. Primitives
4.1.1. Prefixed Integers 4.1.1. Prefixed Integers
The prefixed integer from Section 5.1 of [RFC7541] is used heavily The prefixed integer from Section 5.1 of [RFC7541] is used heavily
throughout this document. The format from [RFC7541] is used throughout this document. The format from [RFC7541] is used
unmodified. Note, however, that QPACK uses some prefix sizes not unmodified. Note, however, that QPACK uses some prefix sizes not
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literal is unmodified. literal is unmodified.
A string literal without a prefix length noted is an 8-bit prefix A string literal without a prefix length noted is an 8-bit prefix
string literal and follows the definitions in [RFC7541] without string literal and follows the definitions in [RFC7541] without
modification. modification.
4.2. Encoder and Decoder Streams 4.2. Encoder and Decoder Streams
QPACK defines two unidirectional stream types: QPACK defines two unidirectional stream types:
o An encoder stream is a unidirectional stream of type "0x02". It * An encoder stream is a unidirectional stream of type "0x02". It
carries an unframed sequence of encoder instructions from encoder carries an unframed sequence of encoder instructions from encoder
to decoder. to decoder.
o A decoder stream is a unidirectional stream of type "0x03". It * A decoder stream is a unidirectional stream of type "0x03". It
carries an unframed sequence of decoder instructions from decoder carries an unframed sequence of decoder instructions from decoder
to encoder. to encoder.
HTTP/3 endpoints contain a QPACK encoder and decoder. Each endpoint HTTP/3 endpoints contain a QPACK encoder and decoder. Each endpoint
MUST initiate at most one encoder stream and at most one decoder MUST initiate at most one encoder stream and at most one decoder
stream. Receipt of a second instance of either stream type MUST be stream. Receipt of a second instance of either stream type MUST be
treated as a connection error of type HTTP_STREAM_CREATION_ERROR. treated as a connection error of type HTTP_STREAM_CREATION_ERROR.
These streams MUST NOT be closed. Closure of either unidirectional These streams MUST NOT be closed. Closure of either unidirectional
stream type MUST be treated as a connection error of type stream type MUST be treated as a connection error of type
HTTP_CLOSED_CRITICAL_STREAM. HTTP_CLOSED_CRITICAL_STREAM.
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table, the full entry can also be used by reference, creating a table, the full entry can also be used by reference, creating a
duplicate entry. duplicate entry.
This section specifies the following encoder instructions. This section specifies the following encoder instructions.
4.3.1. Set Dynamic Table Capacity 4.3.1. Set Dynamic Table Capacity
An encoder informs the decoder of a change to the dynamic table An encoder informs the decoder of a change to the dynamic table
capacity using an instruction which begins with the '001' three-bit capacity using an instruction which begins with the '001' three-bit
pattern. This is followed by the new dynamic table capacity pattern. This is followed by the new dynamic table capacity
represented as an integer with a 5-bit prefix (see Section 4.1.1). represented as an integer with a 5-bit prefix; see Section 4.1.1.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 0 | 1 | Capacity (5+) | | 0 | 0 | 1 | Capacity (5+) |
+---+---+---+-------------------+ +---+---+---+-------------------+
Figure 2: Set Dynamic Table Capacity Figure 5: Set Dynamic Table Capacity
The new capacity MUST be lower than or equal to the limit described The new capacity MUST be lower than or equal to the limit described
in Section 3.2.3. In HTTP/3, this limit is the value of the in Section 3.2.3. In HTTP/3, this limit is the value of the
SETTINGS_QPACK_MAX_TABLE_CAPACITY parameter (see Section 5) received SETTINGS_QPACK_MAX_TABLE_CAPACITY parameter (Section 5) received from
from the decoder. The decoder MUST treat a new dynamic table the decoder. The decoder MUST treat a new dynamic table capacity
capacity value that exceeds this limit as a connection error of type value that exceeds this limit as a connection error of type
"HTTP_QPACK_ENCODER_STREAM_ERROR". "HTTP_QPACK_ENCODER_STREAM_ERROR".
Reducing the dynamic table capacity can cause entries to be evicted Reducing the dynamic table capacity can cause entries to be evicted;
(see Section 3.2.2). This MUST NOT cause the eviction of blocking see Section 3.2.2. This MUST NOT cause the eviction of entries which
entries (see Section 2.1.2). Changing the capacity of the dynamic are not evictable; see Section 2.1.2. Changing the capacity of the
table is not acknowledged as this instruction does not insert an dynamic table is not acknowledged as this instruction does not insert
entry. an entry.
4.3.2. Insert With Name Reference 4.3.2. Insert With Name Reference
An encoder adds an entry to the dynamic table where the header field An encoder adds an entry to the dynamic table where the header field
name matches the header field name of an entry stored in the static name matches the header field name of an entry stored in the static
or the dynamic table using an instruction that starts with the '1' or the dynamic table using an instruction that starts with the '1'
one-bit pattern. The second ('T') bit indicates whether the one-bit pattern. The second ('T') bit indicates whether the
reference is to the static or dynamic table. The 6-bit prefix reference is to the static or dynamic table. The 6-bit prefix
integer (see Section 4.1.1) that follows is used to locate the table integer (Section 4.1.1) that follows is used to locate the table
entry for the header name. When T=1, the number represents the entry for the header name. When T=1, the number represents the
static table index; when T=0, the number is the relative index of the static table index; when T=0, the number is the relative index of the
entry in the dynamic table. entry in the dynamic table.
The header name reference is followed by the header field value The header name reference is followed by the header field value
represented as a string literal (see Section 4.1.2). represented as a string literal; see Section 4.1.2.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 1 | T | Name Index (6+) | | 1 | T | Name Index (6+) |
+---+---+-----------------------+ +---+---+-----------------------+
| H | Value Length (7+) | | H | Value Length (7+) |
+---+---------------------------+ +---+---------------------------+
| Value String (Length bytes) | | Value String (Length bytes) |
+-------------------------------+ +-------------------------------+
Insert Header Field -- Indexed Name Figure 6: Insert Header Field -- Indexed Name
4.3.3. Insert Without Name Reference 4.3.3. Insert Without Name Reference
An encoder adds an entry to the dynamic table where both the header An encoder adds an entry to the dynamic table where both the header
field name and the header field value are represented as string field name and the header field value are represented as string
literals using an instruction that starts with the '01' two-bit literals using an instruction that starts with the '01' two-bit
pattern. pattern.
This is followed by the name represented as a 6-bit prefix string This is followed by the name represented as a 6-bit prefix string
literal, and the value represented as an 8-bit prefix string literal literal, and the value represented as an 8-bit prefix string literal;
(see Section 4.1.2). see Section 4.1.2.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 1 | H | Name Length (5+) | | 0 | 1 | H | Name Length (5+) |
+---+---+---+-------------------+ +---+---+---+-------------------+
| Name String (Length bytes) | | Name String (Length bytes) |
+---+---------------------------+ +---+---------------------------+
| H | Value Length (7+) | | H | Value Length (7+) |
+---+---------------------------+ +---+---------------------------+
| Value String (Length bytes) | | Value String (Length bytes) |
+-------------------------------+ +-------------------------------+
Insert Header Field -- New Name Figure 7: Insert Header Field -- New Name
4.3.4. Duplicate 4.3.4. Duplicate
An encoder duplicates an existing entry in the dynamic table using an An encoder duplicates an existing entry in the dynamic table using an
instruction that begins with the '000' three-bit pattern. This is instruction that begins with the '000' three-bit pattern. This is
followed by the relative index of the existing entry represented as followed by the relative index of the existing entry represented as
an integer with a 5-bit prefix (see Section 4.1.1. an integer with a 5-bit prefix; see Section 4.1.1.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 0 | 0 | Index (5+) | | 0 | 0 | 0 | Index (5+) |
+---+---+---+-------------------+ +---+---+---+-------------------+
Figure 3: Duplicate Figure 8: Duplicate
The existing entry is re-inserted into the dynamic table without The existing entry is re-inserted into the dynamic table without
resending either the name or the value. This is useful to avoid resending either the name or the value. This is useful to avoid
adding a reference to an older entry, which might block inserting new adding a reference to an older entry, which might block inserting new
entries. entries.
4.4. Decoder Instructions 4.4. Decoder Instructions
A decoder sends decoder instructions on the decoder stream to inform A decoder sends decoder instructions on the decoder stream to inform
the encoder about the processing of header blocks and table updates the encoder about the processing of header blocks and table updates
to ensure consistency of the dynamic table. to ensure consistency of the dynamic table.
This section specifies the following decoder instructions. This section specifies the following decoder instructions.
4.4.1. Header Acknowledgement 4.4.1. Header Acknowledgement
After processing a header block whose declared Required Insert Count After processing a header block whose declared Required Insert Count
is not zero, the decoder emits a Header Acknowledgement instruction. is not zero, the decoder emits a Header Acknowledgement instruction.
The instruction begins with the '1' one-bit pattern which is followed The instruction begins with the '1' one-bit pattern which is followed
by the header block's associated stream ID encoded as a 7-bit prefix by the header block's associated stream ID encoded as a 7-bit prefix
integer (see Section 4.1.1). integer; see Section 4.1.1.
This instruction is used as described in Section 2.1.4 and in This instruction is used as described in Section 2.1.4 and in
Section 2.2.2. Section 2.2.2.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 1 | Stream ID (7+) | | 1 | Stream ID (7+) |
+---+---------------------------+ +---+---------------------------+
Figure 4: Header Acknowledgement Figure 9: Header Acknowledgement
If an encoder receives a Header Acknowledgement instruction referring If an encoder receives a Header Acknowledgement instruction referring
to a stream on which every header block with a non-zero Required to a stream on which every header block with a non-zero Required
Insert Count has already been acknowledged, that MUST be treated as a Insert Count has already been acknowledged, that MUST be treated as a
connection error of type "HTTP_QPACK_DECODER_STREAM_ERROR". connection error of type "HTTP_QPACK_DECODER_STREAM_ERROR".
The Header Acknowledgement instruction might increase the Known
Received Count; see Section 2.1.4.
4.4.2. Stream Cancellation 4.4.2. Stream Cancellation
When a stream is reset or reading is abandoned, the decoder emits a When a stream is reset or reading is abandoned, the decoder emits a
Stream Cancellation instruction. The instruction begins with the Stream Cancellation instruction. The instruction begins with the
'01' two-bit pattern, which is followed by the stream ID of the '01' two-bit pattern, which is followed by the stream ID of the
affected stream encoded as a 6-bit prefix integer. affected stream encoded as a 6-bit prefix integer.
This instruction is used as described in Section 2.2.2. This instruction is used as described in Section 2.2.2.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 1 | Stream ID (6+) | | 0 | 1 | Stream ID (6+) |
+---+---+-----------------------+ +---+---+-----------------------+
Figure 5: Stream Cancellation Figure 10: Stream Cancellation
4.4.3. Insert Count Increment 4.4.3. Insert Count Increment
The Insert Count Increment instruction begins with the '00' two-bit The Insert Count Increment instruction begins with the '00' two-bit
pattern, followed by the Increment encoded as a 6-bit prefix integer. pattern, followed by the Increment encoded as a 6-bit prefix integer.
The value of the Increment is the total number of dynamic table This instruction increases the Known Received Count (Section 2.1.4)
insertions and duplications processed by the decoder since the last by the value of the Increment parameter. The decoder should send an
time it sent a Header Acknowledgement instruction that increased the Increment value that increases the Known Received Count to the total
Known Received Count (see Section 2.1.4) or an Insert Count Increment number of dynamic table insertions and duplications processed so far.
instruction. The encoder uses this value to update the Known
Received Count, as described in Section 2.2.2.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 0 | Increment (6+) | | 0 | 0 | Increment (6+) |
+---+---+-----------------------+ +---+---+-----------------------+
Figure 6: Insert Count Increment Figure 11: Insert Count Increment
An encoder that receives an Increment field equal to zero, or one An encoder that receives an Increment field equal to zero, or one
that increases the Known Received Count beyond what the encoder has that increases the Known Received Count beyond what the encoder has
sent MUST treat this as a connection error of type sent MUST treat this as a connection error of type
"HTTP_QPACK_DECODER_STREAM_ERROR". "HTTP_QPACK_DECODER_STREAM_ERROR".
4.5. Header Block Representations 4.5. Header Block Representations
A header block consists of a prefix and a possibly empty sequence of A header block consists of a prefix and a possibly empty sequence of
representations defined in this section. Each representation representations defined in this section. Each representation
skipping to change at page 19, line 51 skipping to change at page 20, line 10
state, but do not modify that state. state, but do not modify that state.
Header blocks are carried in frames on streams defined by the Header blocks are carried in frames on streams defined by the
enclosing protocol. enclosing protocol.
4.5.1. Header Block Prefix 4.5.1. Header Block Prefix
Each header block is prefixed with two integers. The Required Insert Each header block is prefixed with two integers. The Required Insert
Count is encoded as an integer with an 8-bit prefix after the Count is encoded as an integer with an 8-bit prefix after the
encoding described in Section 4.5.1.1). The Base is encoded as a encoding described in Section 4.5.1.1). The Base is encoded as a
sign bit ('S') and a Delta Base value with a 7-bit prefix (see sign bit ('S') and a Delta Base value with a 7-bit prefix; see
Section 4.5.1.2). Section 4.5.1.2.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| Required Insert Count (8+) | | Required Insert Count (8+) |
+---+---------------------------+ +---+---------------------------+
| S | Delta Base (7+) | | S | Delta Base (7+) |
+---+---------------------------+ +---+---------------------------+
| Compressed Headers ... | Compressed Headers ...
+-------------------------------+ +-------------------------------+
Figure 7: Header Block Figure 12: Header Block
4.5.1.1. Required Insert Count 4.5.1.1. Required Insert Count
Required Insert Count identifies the state of the dynamic table Required Insert Count identifies the state of the dynamic table
needed to process the header block. Blocking decoders use the needed to process the header block. Blocking decoders use the
Required Insert Count to determine when it is safe to process the Required Insert Count to determine when it is safe to process the
rest of the block. rest of the block.
The encoder transforms the Required Insert Count as follows before The encoder transforms the Required Insert Count as follows before
encoding: encoding:
skipping to change at page 20, line 38 skipping to change at page 20, line 46
else: else:
EncInsertCount = (ReqInsertCount mod (2 * MaxEntries)) + 1 EncInsertCount = (ReqInsertCount mod (2 * MaxEntries)) + 1
Here "MaxEntries" is the maximum number of entries that the dynamic Here "MaxEntries" is the maximum number of entries that the dynamic
table can have. The smallest entry has empty name and value strings table can have. The smallest entry has empty name and value strings
and has the size of 32. Hence "MaxEntries" is calculated as and has the size of 32. Hence "MaxEntries" is calculated as
MaxEntries = floor( MaxTableCapacity / 32 ) MaxEntries = floor( MaxTableCapacity / 32 )
"MaxTableCapacity" is the maximum capacity of the dynamic table as "MaxTableCapacity" is the maximum capacity of the dynamic table as
specified by the decoder (see Section 3.2.3). specified by the decoder; see Section 3.2.3.
This encoding limits the length of the prefix on long-lived This encoding limits the length of the prefix on long-lived
connections. connections.
The decoder can reconstruct the Required Insert Count using an The decoder can reconstruct the Required Insert Count using an
algorithm such as the following. If the decoder encounters a value algorithm such as the following. If the decoder encounters a value
of EncodedInsertCount that could not have been produced by a of EncodedInsertCount that could not have been produced by a
conformant encoder, it MUST treat this as a connection error of type conformant encoder, it MUST treat this as a connection error of type
"HTTP_QPACK_DECOMPRESSION_FAILED". "HTTP_QPACK_DECOMPRESSION_FAILED".
skipping to change at page 22, line 32 skipping to change at page 22, line 39
For example, with a Required Insert Count of 9, a decoder receives an For example, with a Required Insert Count of 9, a decoder receives an
S bit of 1 and a Delta Base of 2. This sets the Base to 6 and S bit of 1 and a Delta Base of 2. This sets the Base to 6 and
enables post-base indexing for three entries. In this example, a enables post-base indexing for three entries. In this example, a
relative index of 1 refers to the 5th entry that was added to the relative index of 1 refers to the 5th entry that was added to the
table; a post-base index of 1 refers to the 8th entry. table; a post-base index of 1 refers to the 8th entry.
4.5.2. Indexed Header Field 4.5.2. Indexed Header Field
An indexed header field representation identifies an entry in the An indexed header field representation identifies an entry in the
static table, or an entry in the dynamic table with an absolute index static table, or an entry in the dynamic table with an absolute index
less than the Base. less than the value of the Base.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 1 | T | Index (6+) | | 1 | T | Index (6+) |
+---+---+-----------------------+ +---+---+-----------------------+
Indexed Header Field Figure 13: 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 'T' bit indicating whether the reference is into the static or the 'T' bit indicating whether the reference is into the static or
dynamic table. The 6-bit prefix integer (see Section 4.1.1) that dynamic table. The 6-bit prefix integer (Section 4.1.1) that follows
follows is used to locate the table entry for the header field. When is used to locate the table entry for the header field. When T=1,
T=1, the number represents the static table index; when T=0, the the number represents the static table index; when T=0, the number is
number is the relative index of the entry in the dynamic table. the relative index of the entry in the dynamic table.
4.5.3. Indexed Header Field With Post-Base Index 4.5.3. Indexed Header Field With Post-Base Index
An indexed header field with post-base index representation An indexed header field with post-base index representation
identifies an entry in the dynamic table with an absolute index identifies an entry in the dynamic table with an absolute index
greater than or equal to the Base. greater than or equal to the value of the Base.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 0 | 0 | 1 | Index (4+) | | 0 | 0 | 0 | 1 | Index (4+) |
+---+---+---+---+---------------+ +---+---+---+---+---------------+
Indexed Header Field with Post-Base Index Figure 14: Indexed Header Field with Post-Base Index
This representation starts with the '0001' 4-bit pattern. This is This representation starts with the '0001' 4-bit pattern. This is
followed by the post-base index (see Section 3.2.6) of the matching followed by the post-base index (Section 3.2.6) of the matching
header field, represented as an integer with a 4-bit prefix (see header field, represented as an integer with a 4-bit prefix; see
Section 4.1.1). Section 4.1.1.
4.5.4. Literal Header Field With Name Reference 4.5.4. Literal Header Field With Name Reference
A literal header field with name reference representation encodes a A literal header field with name reference representation encodes a
header field where the header field name matches the header field header field where the header field name matches the header field
name of an entry in the static table, or the header field name of an name of an entry in the static table, or the header field name of an
entry in the dynamic table with an absolute index less than the Base. entry in the dynamic table with an absolute index less than the value
of the Base.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 1 | N | T |Name Index (4+)| | 0 | 1 | N | T |Name Index (4+)|
+---+---+---+---+---------------+ +---+---+---+---+---------------+
| H | Value Length (7+) | | H | Value Length (7+) |
+---+---------------------------+ +---+---------------------------+
| Value String (Length bytes) | | Value String (Length bytes) |
+-------------------------------+ +-------------------------------+
Literal Header Field With Name Reference Figure 15: Literal Header Field With Name Reference
This representation starts with the '01' two-bit pattern. The This representation starts with the '01' two-bit pattern. The
following bit, 'N', indicates whether an intermediary is permitted to following bit, 'N', indicates whether an intermediary is permitted to
add this header to the dynamic header table on subsequent hops. When add this header to the dynamic header table on subsequent hops. When
the 'N' bit is set, the encoded header MUST always be encoded with a the 'N' bit is set, the encoded header MUST always be encoded with a
literal representation. In particular, when a peer sends a header literal representation. In particular, when a peer sends a header
field that it received represented as a literal header field with the field that it received represented as a literal header field with the
'N' bit set, it MUST use a literal representation to forward this 'N' bit set, it MUST use a literal representation to forward this
header field. This bit is intended for protecting header field header field. This bit is intended for protecting header field
values that are not to be put at risk by compressing them (see values that are not to be put at risk by compressing them; see
Section 7 for more details). Section 7 for more details.
The fourth ('T') bit indicates whether the reference is to the static The fourth ('T') bit indicates whether the reference is to the static
or dynamic table. The 4-bit prefix integer (see Section 4.1.1) that or dynamic table. The 4-bit prefix integer (Section 4.1.1) that
follows is used to locate the table entry for the header name. When follows is used to locate the table entry for the header name. When
T=1, the number represents the static table index; when T=0, the T=1, the number represents the static table index; when T=0, the
number is the relative index of the entry in the dynamic table. number is the relative index of the entry in the dynamic table.
Only the header field name is taken from the dynamic table entry; the Only the header field name is taken from the dynamic table entry; the
header field value is encoded as an 8-bit prefix string literal (see header field value is encoded as an 8-bit prefix string literal; see
Section 4.1.2). Section 4.1.2.
4.5.5. Literal Header Field With Post-Base Name Reference 4.5.5. Literal Header Field With Post-Base Name Reference
A literal header field with post-base name reference representation A literal header field with post-base name reference representation
encodes a header field where the header field name matches the header encodes a header field where the header field name matches the header
field name of a dynamic table entry with an absolute index greater field name of a dynamic table entry with an absolute index greater
than or equal to the Base. than or equal to the value of the Base.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 0 | 0 | 0 | N |NameIdx(3+)| | 0 | 0 | 0 | 0 | N |NameIdx(3+)|
+---+---+---+---+---+-----------+ +---+---+---+---+---+-----------+
| H | Value Length (7+) | | H | Value Length (7+) |
+---+---------------------------+ +---+---------------------------+
| Value String (Length bytes) | | Value String (Length bytes) |
+-------------------------------+ +-------------------------------+
Literal Header Field With Post-Base Name Reference Figure 16: Literal Header Field With Post-Base Name Reference
This representation starts with the '0000' four-bit pattern. The This representation starts with the '0000' four-bit pattern. The
fifth bit is the 'N' bit as described in Section 4.5.4. This is fifth bit is the 'N' bit as described in Section 4.5.4. This is
followed by a post-base index of the dynamic table entry (see followed by a post-base index of the dynamic table entry
Section 3.2.6) encoded as an integer with a 3-bit prefix (see (Section 3.2.6) encoded as an integer with a 3-bit prefix; see
Section 4.1.1). Section 4.1.1.
Only the header field name is taken from the dynamic table entry; the Only the header field name is taken from the dynamic table entry; the
header field value is encoded as an 8-bit prefix string literal (see header field value is encoded as an 8-bit prefix string literal; see
Section 4.1.2). Section 4.1.2.
4.5.6. Literal Header Field Without Name Reference 4.5.6. Literal Header Field Without Name Reference
The literal header field without name reference representation The literal header field without name reference representation
encodes a header field name and a header field value as string encodes a header field name and a header field value as string
literals. literals.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 0 | 1 | N | H |NameLen(3+)| | 0 | 0 | 1 | N | H |NameLen(3+)|
+---+---+---+---+---+-----------+ +---+---+---+---+---+-----------+
| Name String (Length bytes) | | Name String (Length bytes) |
+---+---------------------------+ +---+---------------------------+
| H | Value Length (7+) | | H | Value Length (7+) |
+---+---------------------------+ +---+---------------------------+
| Value String (Length bytes) | | Value String (Length bytes) |
+-------------------------------+ +-------------------------------+
Literal Header Field Without Name Reference Figure 17: Literal Header Field Without Name Reference
This representation begins with the '001' three-bit pattern. The This representation begins with the '001' three-bit pattern. The
fourth bit is the 'N' bit as described in Section 4.5.4. The name fourth bit is the 'N' bit as described in Section 4.5.4. The name
follows, represented as a 4-bit prefix string literal, then the follows, represented as a 4-bit prefix string literal, then the
value, represented as an 8-bit prefix string literal (see value, represented as an 8-bit prefix string literal; see
Section 4.1.2). Section 4.1.2.
5. Configuration 5. Configuration
QPACK defines two settings which are included in the HTTP/3 SETTINGS QPACK defines two settings which are included in the HTTP/3 SETTINGS
frame. frame.
SETTINGS_QPACK_MAX_TABLE_CAPACITY (0x1): The default value is zero. SETTINGS_QPACK_MAX_TABLE_CAPACITY (0x1): The default value is zero.
See Section 3.2 for usage. This is the equivalent of the See Section 3.2 for usage. This is the equivalent of the
SETTINGS_HEADER_TABLE_SIZE from HTTP/2. SETTINGS_HEADER_TABLE_SIZE from HTTP/2.
skipping to change at page 26, line 29 skipping to change at page 26, line 29
8. IANA Considerations 8. IANA Considerations
8.1. Settings Registration 8.1. Settings Registration
This document specifies two settings. The entries in the following This document specifies two settings. The entries in the following
table are registered in the "HTTP/3 Settings" registry established in table are registered in the "HTTP/3 Settings" registry established in
[HTTP3]. [HTTP3].
+--------------------------+------+---------------+---------+ +--------------------------+------+---------------+---------+
| Setting Name | Code | Specification | Default | | Setting Name | Code | Specification | Default |
+--------------------------+------+---------------+---------+ +==========================+======+===============+=========+
| QPACK_MAX_TABLE_CAPACITY | 0x1 | Section 5 | 0 | | QPACK_MAX_TABLE_CAPACITY | 0x1 | Section 5 | 0 |
| | | | | +--------------------------+------+---------------+---------+
| QPACK_BLOCKED_STREAMS | 0x7 | Section 5 | 0 | | QPACK_BLOCKED_STREAMS | 0x7 | Section 5 | 0 |
+--------------------------+------+---------------+---------+ +--------------------------+------+---------------+---------+
Table 1
8.2. Stream Type Registration 8.2. Stream Type Registration
This document specifies two stream types. The entries in the This document specifies two stream types. The entries in the
following table are registered in the "HTTP/3 Stream Type" registry following table are registered in the "HTTP/3 Stream Type" registry
established in [HTTP3]. established in [HTTP3].
+----------------------+------+---------------+--------+ +----------------------+------+---------------+--------+
| Stream Type | Code | Specification | Sender | | Stream Type | Code | Specification | Sender |
+----------------------+------+---------------+--------+ +======================+======+===============+========+
| QPACK Encoder Stream | 0x02 | Section 4.2 | Both | | QPACK Encoder Stream | 0x02 | Section 4.2 | Both |
| | | | | +----------------------+------+---------------+--------+
| QPACK Decoder Stream | 0x03 | Section 4.2 | Both | | QPACK Decoder Stream | 0x03 | Section 4.2 | Both |
+----------------------+------+---------------+--------+ +----------------------+------+---------------+--------+
Table 2
8.3. Error Code Registration 8.3. Error Code Registration
This document specifies three error codes. The entries in the This document specifies three error codes. The entries in the
following table are registered in the "HTTP/3 Error Code" registry following table are registered in the "HTTP/3 Error Code" registry
established in [HTTP3]. established in [HTTP3].
+-----------------------------+-------+--------------+--------------+ +---------------------------------+-----+-------------+-------------+
| Name | Code | Description | Specificatio | | Name |Code | Description |Specification|
| | | | n | +=================================+=====+=============+=============+
+-----------------------------+-------+--------------+--------------+ | HTTP_QPACK_DECOMPRESSION_FAILED |0x200|Decompression| Section 6 |
| HTTP_QPACK_DECOMPRESSION_FA | 0x200 | Decompressio | Section 6 | | | | of a header | |
| ILED | | n of a | | | | |block failed | |
| | | header block | | +---------------------------------+-----+-------------+-------------+
| | | failed | | | HTTP_QPACK_ENCODER_STREAM_ERROR |0x201|Error on the | Section 6 |
| | | | | | | | encoder | |
| HTTP_QPACK_ENCODER_STREAM_E | 0x201 | Error on the | Section 6 | | | | stream | |
| RROR | | encoder | | +---------------------------------+-----+-------------+-------------+
| | | stream | | | HTTP_QPACK_DECODER_STREAM_ERROR |0x202|Error on the | Section 6 |
| | | | | | | | decoder | |
| HTTP_QPACK_DECODER_STREAM_E | 0x202 | Error on the | Section 6 | | | | stream | |
| RROR | | decoder | | +---------------------------------+-----+-------------+-------------+
| | | stream | |
+-----------------------------+-------+--------------+--------------+ Table 3
9. References 9. References
9.1. Normative References 9.1. Normative References
[HTTP3] Bishop, M., Ed., "Hypertext Transfer Protocol Version 3 [HTTP3] Bishop, M., Ed., "Hypertext Transfer Protocol Version 3
(HTTP/3)", draft-ietf-quic-http-24 (work in progress), (HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
November 2019. quic-http-25, 22 January 2020,
<https://tools.ietf.org/html/draft-ietf-quic-http-25>.
[QUIC-TRANSPORT] [QUIC-TRANSPORT]
Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", draft-ietf-quic- Multiplexed and Secure Transport", Work in Progress,
transport-24 (work in progress), November 2019. Internet-Draft, draft-ietf-quic-transport-25, 22 January
2020, <https://tools.ietf.org/html/draft-ietf-quic-
transport-25>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC7541] Peon, R. and H. Ruellan, "HPACK: Header Compression for [RFC7541] Peon, R. and H. Ruellan, "HPACK: Header Compression for
HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015, HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015,
<https://www.rfc-editor.org/info/rfc7541>. <https://www.rfc-editor.org/info/rfc7541>.
skipping to change at page 28, line 20 skipping to change at page 28, line 20
[RFC2360] Scott, G., "Guide for Internet Standards Writers", BCP 22, [RFC2360] Scott, G., "Guide for Internet Standards Writers", BCP 22,
RFC 2360, DOI 10.17487/RFC2360, June 1998, RFC 2360, DOI 10.17487/RFC2360, June 1998,
<https://www.rfc-editor.org/info/rfc2360>. <https://www.rfc-editor.org/info/rfc2360>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540, Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015, DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>. <https://www.rfc-editor.org/info/rfc7540>.
9.3. URIs
[1] https://mailarchive.ietf.org/arch/search/?email_list=quic
[2] https://github.com/quicwg
[3] https://github.com/quicwg/base-drafts/labels/-qpack
Appendix A. Static Table Appendix A. Static Table
+------+-----------------------------+------------------------------+ +-------+----------------------------------+-----------------------+
| Inde | Name | Value | | Index | Name | Value |
| x | | | +=======+==================================+=======================+
+------+-----------------------------+------------------------------+ | 0 | :authority | |
| 0 | :authority | | +-------+----------------------------------+-----------------------+
| | | | | 1 | :path | / |
| 1 | :path | / | +-------+----------------------------------+-----------------------+
| | | | | 2 | age | 0 |
| 2 | age | 0 | +-------+----------------------------------+-----------------------+
| | | | | 3 | content-disposition | |
| 3 | content-disposition | | +-------+----------------------------------+-----------------------+
| | | | | 4 | content-length | 0 |
| 4 | content-length | 0 | +-------+----------------------------------+-----------------------+
| | | | | 5 | cookie | |
| 5 | cookie | | +-------+----------------------------------+-----------------------+
| | | | | 6 | date | |
| 6 | date | | +-------+----------------------------------+-----------------------+
| | | | | 7 | etag | |
| 7 | etag | | +-------+----------------------------------+-----------------------+
| | | | | 8 | if-modified-since | |
| 8 | if-modified-since | | +-------+----------------------------------+-----------------------+
| | | | | 9 | if-none-match | |
| 9 | if-none-match | | +-------+----------------------------------+-----------------------+
| | | | | 10 | last-modified | |
| 10 | last-modified | | +-------+----------------------------------+-----------------------+
| | | | | 11 | link | |
| 11 | link | | +-------+----------------------------------+-----------------------+
| | | | | 12 | location | |
| 12 | location | | +-------+----------------------------------+-----------------------+
| | | | | 13 | referer | |
| 13 | referer | | +-------+----------------------------------+-----------------------+
| | | | | 14 | set-cookie | |
| 14 | set-cookie | | +-------+----------------------------------+-----------------------+
| | | | | 15 | :method | CONNECT |
| 15 | :method | CONNECT | +-------+----------------------------------+-----------------------+
| | | | | 16 | :method | DELETE |
| 16 | :method | DELETE | +-------+----------------------------------+-----------------------+
| | | | | 17 | :method | GET |
| 17 | :method | GET | +-------+----------------------------------+-----------------------+
| | | | | 18 | :method | HEAD |
| 18 | :method | HEAD | +-------+----------------------------------+-----------------------+
| | | | | 19 | :method | OPTIONS |
| 19 | :method | OPTIONS | +-------+----------------------------------+-----------------------+
| | | | | 20 | :method | POST |
| 20 | :method | POST | +-------+----------------------------------+-----------------------+
| | | | | 21 | :method | PUT |
| 21 | :method | PUT | +-------+----------------------------------+-----------------------+
| | | | | 22 | :scheme | http |
| 22 | :scheme | http | +-------+----------------------------------+-----------------------+
| | | | | 23 | :scheme | https |
| 23 | :scheme | https | +-------+----------------------------------+-----------------------+
| | | | | 24 | :status | 103 |
| 24 | :status | 103 | +-------+----------------------------------+-----------------------+
| | | | | 25 | :status | 200 |
| 25 | :status | 200 | +-------+----------------------------------+-----------------------+
| | | | | 26 | :status | 304 |
| 26 | :status | 304 | +-------+----------------------------------+-----------------------+
| | | | | 27 | :status | 404 |
| 27 | :status | 404 | +-------+----------------------------------+-----------------------+
| | | | | 28 | :status | 503 |
| 28 | :status | 503 | +-------+----------------------------------+-----------------------+
| | | | | 29 | accept | */* |
| 29 | accept | */* | +-------+----------------------------------+-----------------------+
| | | | | 30 | accept | application/dns- |
| 30 | accept | application/dns-message | | | | message |
| | | | +-------+----------------------------------+-----------------------+
| 31 | accept-encoding | gzip, deflate, br | | 31 | accept-encoding | gzip, deflate, br |
| | | | +-------+----------------------------------+-----------------------+
| 32 | accept-ranges | bytes | | 32 | accept-ranges | bytes |
| | | | +-------+----------------------------------+-----------------------+
| 33 | access-control-allow- | cache-control | | 33 | access-control-allow-headers | cache-control |
| | headers | | +-------+----------------------------------+-----------------------+
| | | | | 34 | access-control-allow-headers | content-type |
| 34 | access-control-allow- | content-type | +-------+----------------------------------+-----------------------+
| | headers | | | 35 | access-control-allow-origin | * |
| | | | +-------+----------------------------------+-----------------------+
| 35 | access-control-allow-origin | * | | 36 | cache-control | max-age=0 |
| | | | +-------+----------------------------------+-----------------------+
| 36 | cache-control | max-age=0 | | 37 | cache-control | max-age=2592000 |
| | | | +-------+----------------------------------+-----------------------+
| 37 | cache-control | max-age=2592000 | | 38 | cache-control | max-age=604800 |
| | | | +-------+----------------------------------+-----------------------+
| 38 | cache-control | max-age=604800 | | 39 | cache-control | no-cache |
| | | | +-------+----------------------------------+-----------------------+
| 39 | cache-control | no-cache | | 40 | cache-control | no-store |
| | | | +-------+----------------------------------+-----------------------+
| 40 | cache-control | no-store | | 41 | cache-control | public, max- |
| | | | | | | age=31536000 |
| 41 | cache-control | public, max-age=31536000 | +-------+----------------------------------+-----------------------+
| | | | | 42 | content-encoding | br |
| 42 | content-encoding | br | +-------+----------------------------------+-----------------------+
| | | | | 43 | content-encoding | gzip |
| 43 | content-encoding | gzip | +-------+----------------------------------+-----------------------+
| | | | | 44 | content-type | application/dns- |
| 44 | content-type | application/dns-message | | | | message |
| | | | +-------+----------------------------------+-----------------------+
| 45 | content-type | application/javascript | | 45 | content-type | application/ |
| | | | | | | javascript |
| 46 | content-type | application/json | +-------+----------------------------------+-----------------------+
| | | | | 46 | content-type | application/json |
| 47 | content-type | application/x-www-form- | +-------+----------------------------------+-----------------------+
| | | urlencoded | | 47 | content-type | application/x-www- |
| | | | | | | form-urlencoded |
| 48 | content-type | image/gif | +-------+----------------------------------+-----------------------+
| | | | | 48 | content-type | image/gif |
| 49 | content-type | image/jpeg | +-------+----------------------------------+-----------------------+
| | | | | 49 | content-type | image/jpeg |
| 50 | content-type | image/png | +-------+----------------------------------+-----------------------+
| | | | | 50 | content-type | image/png |
| 51 | content-type | text/css | +-------+----------------------------------+-----------------------+
| | | | | 51 | content-type | text/css |
| 52 | content-type | text/html; charset=utf-8 | +-------+----------------------------------+-----------------------+
| | | | | 52 | content-type | text/html; |
| 53 | content-type | text/plain | | | | charset=utf-8 |
| | | | +-------+----------------------------------+-----------------------+
| 54 | content-type | text/plain;charset=utf-8 | | 53 | content-type | text/plain |
| | | | +-------+----------------------------------+-----------------------+
| 55 | range | bytes=0- | | 54 | content-type | text/ |
| | | | | | | plain;charset=utf-8 |
| 56 | strict-transport-security | max-age=31536000 | +-------+----------------------------------+-----------------------+
| | | | | 55 | range | bytes=0- |
| 57 | strict-transport-security | max-age=31536000; | +-------+----------------------------------+-----------------------+
| | | includesubdomains | | 56 | strict-transport-security | max-age=31536000 |
| | | | +-------+----------------------------------+-----------------------+
| 58 | strict-transport-security | max-age=31536000; | | 57 | strict-transport-security | max-age=31536000; |
| | | includesubdomains; preload | | | | includesubdomains |
| | | | +-------+----------------------------------+-----------------------+
| 59 | vary | accept-encoding | | 58 | strict-transport-security | max-age=31536000; |
| | | | | | | includesubdomains; |
| 60 | vary | origin | | | | preload |
| | | | +-------+----------------------------------+-----------------------+
| 61 | x-content-type-options | nosniff | | 59 | vary | accept-encoding |
| | | | +-------+----------------------------------+-----------------------+
| 62 | x-xss-protection | 1; mode=block | | 60 | vary | origin |
| | | | +-------+----------------------------------+-----------------------+
| 63 | :status | 100 | | 61 | x-content-type-options | nosniff |
| | | | +-------+----------------------------------+-----------------------+
| 64 | :status | 204 | | 62 | x-xss-protection | 1; mode=block |
| | | | +-------+----------------------------------+-----------------------+
| 65 | :status | 206 | | 63 | :status | 100 |
| | | | +-------+----------------------------------+-----------------------+
| 66 | :status | 302 | | 64 | :status | 204 |
| | | | +-------+----------------------------------+-----------------------+
| 67 | :status | 400 | | 65 | :status | 206 |
| | | | +-------+----------------------------------+-----------------------+
| 68 | :status | 403 | | 66 | :status | 302 |
| | | | +-------+----------------------------------+-----------------------+
| 69 | :status | 421 | | 67 | :status | 400 |
| | | | +-------+----------------------------------+-----------------------+
| 70 | :status | 425 | | 68 | :status | 403 |
| | | | +-------+----------------------------------+-----------------------+
| 71 | :status | 500 | | 69 | :status | 421 |
| | | | +-------+----------------------------------+-----------------------+
| 72 | accept-language | | | 70 | :status | 425 |
| | | | +-------+----------------------------------+-----------------------+
| 73 | access-control-allow- | FALSE | | 71 | :status | 500 |
| | credentials | | +-------+----------------------------------+-----------------------+
| | | | | 72 | accept-language | |
| 74 | access-control-allow- | TRUE | +-------+----------------------------------+-----------------------+
| | credentials | | | 73 | access-control-allow-credentials | FALSE |
| | | | +-------+----------------------------------+-----------------------+
| 75 | access-control-allow- | * | | 74 | access-control-allow-credentials | TRUE |
| | headers | | +-------+----------------------------------+-----------------------+
| | | | | 75 | access-control-allow-headers | * |
| 76 | access-control-allow- | get | +-------+----------------------------------+-----------------------+
| | methods | | | 76 | access-control-allow-methods | get |
| | | | +-------+----------------------------------+-----------------------+
| 77 | access-control-allow- | get, post, options | | 77 | access-control-allow-methods | get, post, options |
| | methods | | +-------+----------------------------------+-----------------------+
| | | | | 78 | access-control-allow-methods | options |
| 78 | access-control-allow- | options | +-------+----------------------------------+-----------------------+
| | methods | | | 79 | access-control-expose-headers | content-length |
| | | | +-------+----------------------------------+-----------------------+
| 79 | access-control-expose- | content-length | | 80 | access-control-request-headers | content-type |
| | headers | | +-------+----------------------------------+-----------------------+
| | | | | 81 | access-control-request-method | get |
| 80 | access-control-request- | content-type | +-------+----------------------------------+-----------------------+
| | headers | | | 82 | access-control-request-method | post |
| | | | +-------+----------------------------------+-----------------------+
| 81 | access-control-request- | get | | 83 | alt-svc | clear |
| | method | | +-------+----------------------------------+-----------------------+
| | | | | 84 | authorization | |
| 82 | access-control-request- | post | +-------+----------------------------------+-----------------------+
| | method | | | 85 | content-security-policy | script-src 'none'; |
| | | | | | | object-src 'none'; |
| 83 | alt-svc | clear | | | | base-uri 'none' |
| | | | +-------+----------------------------------+-----------------------+
| 84 | authorization | | | 86 | early-data | 1 |
| | | | +-------+----------------------------------+-----------------------+
| 85 | content-security-policy | script-src 'none'; object- | | 87 | expect-ct | |
| | | src 'none'; base-uri 'none' | +-------+----------------------------------+-----------------------+
| | | | | 88 | forwarded | |
| 86 | early-data | 1 | +-------+----------------------------------+-----------------------+
| | | | | 89 | if-range | |
| 87 | expect-ct | | +-------+----------------------------------+-----------------------+
| | | | | 90 | origin | |
| 88 | forwarded | | +-------+----------------------------------+-----------------------+
| | | | | 91 | purpose | prefetch |
| 89 | if-range | | +-------+----------------------------------+-----------------------+
| | | | | 92 | server | |
| 90 | origin | | +-------+----------------------------------+-----------------------+
| | | | | 93 | timing-allow-origin | * |
| 91 | purpose | prefetch | +-------+----------------------------------+-----------------------+
| | | | | 94 | upgrade-insecure-requests | 1 |
| 92 | server | | +-------+----------------------------------+-----------------------+
| | | | | 95 | user-agent | |
| 93 | timing-allow-origin | * | +-------+----------------------------------+-----------------------+
| | | | | 96 | x-forwarded-for | |
| 94 | upgrade-insecure-requests | 1 | +-------+----------------------------------+-----------------------+
| | | | | 97 | x-frame-options | deny |
| 95 | user-agent | | +-------+----------------------------------+-----------------------+
| | | | | 98 | x-frame-options | sameorigin |
| 96 | x-forwarded-for | | +-------+----------------------------------+-----------------------+
| | | |
| 97 | x-frame-options | deny | Table 4
| | | |
| 98 | x-frame-options | sameorigin |
+------+-----------------------------+------------------------------+
Appendix B. Sample One Pass Encoding Algorithm Appendix B. Sample One Pass Encoding Algorithm
Pseudo-code for single pass encoding, excluding handling of Pseudo-code for single pass encoding, excluding handling of
duplicates, non-blocking mode, and reference tracking. duplicates, non-blocking mode, and reference tracking.
baseIndex = dynamicTable.baseIndex baseIndex = dynamicTable.baseIndex
largestReference = 0 largestReference = 0
for header in headers: for header in headers:
staticIdx = staticTable.getIndex(header) staticIdx = staticTable.getIndex(header)
skipping to change at page 35, line 6 skipping to change at page 34, line 4
encodeInteger(prefixBuffer, 0x00, largestReference, 8) encodeInteger(prefixBuffer, 0x00, largestReference, 8)
if baseIndex >= largestReference: if baseIndex >= largestReference:
encodeInteger(prefixBuffer, 0, baseIndex - largestReference, 7) encodeInteger(prefixBuffer, 0, baseIndex - largestReference, 7)
else: else:
encodeInteger(prefixBuffer, 0x80, encodeInteger(prefixBuffer, 0x80,
largestReference - baseIndex, 7) largestReference - baseIndex, 7)
return controlBuffer, prefixBuffer + streamBuffer return controlBuffer, prefixBuffer + streamBuffer
Appendix C. Change Log Appendix C. Change Log
*RFC Editor's Note:* Please remove this section prior to *RFC Editor's Note:* Please remove this section prior to
publication of a final version of this document. publication of a final version of this document.
C.1. Since draft-ietf-quic-qpack-10 C.1. Since draft-ietf-quic-qpack-11
Editorial changes Editorial changes only
C.2. Since draft-ietf-quic-qpack-09 C.2. Since draft-ietf-quic-qpack-10
o Decoders MUST emit Header Acknowledgements (#2939) Editorial changes only
o Updated error code for multiple encoder or decoder streams (#2970) C.3. Since draft-ietf-quic-qpack-09
o Added explicit defaults for new SETTINGS (#2974) * Decoders MUST emit Header Acknowledgements (#2939)
C.3. Since draft-ietf-quic-qpack-08 * Updated error code for multiple encoder or decoder streams (#2970)
o Endpoints are permitted to create encoder and decoder streams even * Added explicit defaults for new SETTINGS (#2974)
C.4. Since draft-ietf-quic-qpack-08
* Endpoints are permitted to create encoder and decoder streams even
if they can't use them (#2100, #2529) if they can't use them (#2100, #2529)
o Maximum values for settings removed (#2766, #2767) * Maximum values for settings removed (#2766, #2767)
C.4. Since draft-ietf-quic-qpack-06 C.5. Since draft-ietf-quic-qpack-06
o Clarify initial dynamic table capacity maximums (#2276, #2330, * Clarify initial dynamic table capacity maximums (#2276, #2330,
#2330) #2330)
C.5. Since draft-ietf-quic-qpack-05 C.6. Since draft-ietf-quic-qpack-05
o Introduced the terms dynamic table capacity and maximum dynamic * Introduced the terms dynamic table capacity and maximum dynamic
table capacity. table capacity.
o Renamed SETTINGS_HEADER_TABLE_SIZE to * Renamed SETTINGS_HEADER_TABLE_SIZE to
SETTINGS_QPACK_MAX_TABLE_CAPACITY. SETTINGS_QPACK_MAX_TABLE_CAPACITY.
C.6. Since draft-ietf-quic-qpack-04 C.7. Since draft-ietf-quic-qpack-04
o Changed calculation of Delta Base Index to avoid an illegal value * Changed calculation of Delta Base Index to avoid an illegal value
(#2002, #2005) (#2002, #2005)
C.7. Since draft-ietf-quic-qpack-03 C.8. Since draft-ietf-quic-qpack-03
o Change HTTP settings defaults (#2038)
o Substantial editorial reorganization * Change HTTP settings defaults (#2038)
* Substantial editorial reorganization
C.8. Since draft-ietf-quic-qpack-02 C.9. Since draft-ietf-quic-qpack-02
o Largest Reference encoded modulo MaxEntries (#1763) * Largest Reference encoded modulo MaxEntries (#1763)
o New Static Table (#1355) * New Static Table (#1355)
o Table Size Update with Insert Count=0 is a connection error * Table Size Update with Insert Count=0 is a connection error
(#1762) (#1762)
o Stream Cancellations are optional when * Stream Cancellations are optional when
SETTINGS_HEADER_TABLE_SIZE=0 (#1761) SETTINGS_HEADER_TABLE_SIZE=0 (#1761)
o Implementations must handle 62 bit integers (#1760) * Implementations must handle 62 bit integers (#1760)
o Different error types for each QPACK stream, other changes to * Different error types for each QPACK stream, other changes to
error handling (#1726) error handling (#1726)
o Preserve header field order (#1725) * Preserve header field order (#1725)
o Initial table size is the maximum permitted when table is first * Initial table size is the maximum permitted when table is first
usable (#1642) usable (#1642)
C.9. Since draft-ietf-quic-qpack-01 C.10. Since draft-ietf-quic-qpack-01
o Only header blocks that reference the dynamic table are * Only header blocks that reference the dynamic table are
acknowledged (#1603, #1605) acknowledged (#1603, #1605)
C.10. Since draft-ietf-quic-qpack-00 C.11. Since draft-ietf-quic-qpack-00
o Renumbered instructions for consistency (#1471, #1472) * Renumbered instructions for consistency (#1471, #1472)
o Decoder is allowed to validate largest reference (#1404, #1469) * Decoder is allowed to validate largest reference (#1404, #1469)
o Header block acknowledgments also acknowledge the associated * Header block acknowledgments also acknowledge the associated
largest reference (#1370, #1400) largest reference (#1370, #1400)
o Added an acknowledgment for unread streams (#1371, #1400) * Added an acknowledgment for unread streams (#1371, #1400)
o Removed framing from encoder stream (#1361,#1467) * Removed framing from encoder stream (#1361,#1467)
o Control streams use typed unidirectional streams rather than fixed * Control streams use typed unidirectional streams rather than fixed
stream IDs (#910,#1359) stream IDs (#910,#1359)
C.11. Since draft-ietf-quic-qcram-00 C.12. Since draft-ietf-quic-qcram-00
* Separate instruction sets for table updates and header blocks
o Separate instruction sets for table updates and header blocks
(#1235, #1142, #1141) (#1235, #1142, #1141)
o Reworked indexing scheme (#1176, #1145, #1136, #1130, #1125, * Reworked indexing scheme (#1176, #1145, #1136, #1130, #1125,
#1314) #1314)
o Added mechanisms that support one-pass encoding (#1138, #1320) * Added mechanisms that support one-pass encoding (#1138, #1320)
o Added a setting to control the number of blocked decoders (#238, * Added a setting to control the number of blocked decoders (#238,
#1140, #1143) #1140, #1143)
o Moved table updates and acknowledgments to dedicated streams * Moved table updates and acknowledgments to dedicated streams
(#1121, #1122, #1238) (#1121, #1122, #1238)
Acknowledgments Acknowledgments
This draft draws heavily on the text of [RFC7541]. The indirect This draft draws heavily on the text of [RFC7541]. The indirect
input of those authors is gratefully acknowledged, as well as ideas input of those authors is gratefully acknowledged, as well as ideas
from: from:
o Ryan Hamilton * Ryan Hamilton
o Patrick McManus * Patrick McManus
o Kazuho Oku * Kazuho Oku
o Biren Roy * Biren Roy
o Ian Swett * Ian Swett
o Dmitri Tikhonov * Dmitri Tikhonov
Buck's contribution was supported by Google during his employment Buck's contribution was supported by Google during his employment
there. there.
A substantial portion of Mike's contribution was supported by A substantial portion of Mike's contribution was supported by
Microsoft during his employment there. Microsoft during his employment there.
Authors' Addresses Authors' Addresses
Charles 'Buck' Krasic Charles 'Buck' Krasic
 End of changes. 147 change blocks. 
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