draft-ietf-quic-qpack-08.txt   draft-ietf-quic-qpack-09.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: October 25, 2019 Akamai Technologies Expires: January 9, 2020 Akamai Technologies
A. Frindell, Ed. A. Frindell, Ed.
Facebook Facebook
April 23, 2019 July 08, 2019
QPACK: Header Compression for HTTP/3 QPACK: Header Compression for HTTP/3
draft-ietf-quic-qpack-08 draft-ietf-quic-qpack-09
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
skipping to change at page 1, line 46 skipping to change at page 1, line 46
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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 October 25, 2019. This Internet-Draft will expire on January 9, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 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. 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 . . . . . . . . . . . . . . . . . 5 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 . . . . . . . . . . . . . . . . . 6 2.1.1. Reference Tracking . . . . . . . . . . . . . . . . . 5
2.1.2. Blocked Dynamic Table Insertions . . . . . . . . . . 6 2.1.2. Blocked Dynamic Table Insertions . . . . . . . . . . 6
2.1.3. Avoiding Head-of-Line Blocking . . . . . . . . . . . 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. State Synchronization . . . . . . . . . . . . . . . . 9 2.2.1. Blocked Decoding . . . . . . . . . . . . . . . . . . 8
2.2.2. Blocked Decoding . . . . . . . . . . . . . . . . . . 9 2.2.2. State Synchronization . . . . . . . . . . . . . . . . 9
3. Header Tables . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2.3. Invalid References . . . . . . . . . . . . . . . . . 10
3.1. Static Table . . . . . . . . . . . . . . . . . . . . . . 9 3. Header Tables . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2. Dynamic Table . . . . . . . . . . . . . . . . . . . . . . 10 3.1. Static Table . . . . . . . . . . . . . . . . . . . . . . 10
3.2.1. Dynamic Table Size . . . . . . . . . . . . . . . . . 10 3.2. Dynamic Table . . . . . . . . . . . . . . . . . . . . . . 11
3.2.2. Dynamic Table Capacity and Eviction . . . . . . . . . 10 3.2.1. Dynamic Table Size . . . . . . . . . . . . . . . . . 11
3.2.3. Maximum Dynamic Table Capacity . . . . . . . . . . . 11 3.2.2. Dynamic Table Capacity and Eviction . . . . . . . . . 11
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
3.2.7. Invalid References . . . . . . . . . . . . . . . . . 13
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. Instructions . . . . . . . . . . . . . . . . . . . . . . 14 4.2. Encoder and Decoder Streams . . . . . . . . . . . . . . . 15
4.2.1. Encoder and Decoder Streams . . . . . . . . . . . . . 15
4.3. Encoder Instructions . . . . . . . . . . . . . . . . . . 15 4.3. Encoder Instructions . . . . . . . . . . . . . . . . . . 15
4.3.1. Insert With Name Reference . . . . . . . . . . . . . 15 4.3.1. Set Dynamic Table Capacity . . . . . . . . . . . . . 16
4.3.2. Insert Without Name Reference . . . . . . . . . . . . 16 4.3.2. Insert With Name Reference . . . . . . . . . . . . . 16
4.3.3. Duplicate . . . . . . . . . . . . . . . . . . . . . . 16 4.3.3. Insert Without Name Reference . . . . . . . . . . . . 17
4.3.4. Set Dynamic Table Capacity . . . . . . . . . . . . . 17 4.3.4. Duplicate . . . . . . . . . . . . . . . . . . . . . . 17
4.4. Decoder Instructions . . . . . . . . . . . . . . . . . . 17 4.4. Decoder Instructions . . . . . . . . . . . . . . . . . . 18
4.4.1. Insert Count Increment . . . . . . . . . . . . . . . 17 4.4.1. Header Acknowledgement . . . . . . . . . . . . . . . 18
4.4.2. Header Acknowledgement . . . . . . . . . . . . . . . 18 4.4.2. Stream Cancellation . . . . . . . . . . . . . . . . . 18
4.4.3. Stream Cancellation . . . . . . . . . . . . . . . . . 19 4.4.3. Insert Count Increment . . . . . . . . . . . . . . . 19
4.5. Header Block Instructions . . . . . . . . . . . . . . . . 19 4.5. Header Block Representations . . . . . . . . . . . . . . 19
4.5.1. Header Block Prefix . . . . . . . . . . . . . . . . . 20 4.5.1. Header Block Prefix . . . . . . . . . . . . . . . . . 19
4.5.2. Indexed Header Field . . . . . . . . . . . . . . . . 22 4.5.2. Indexed Header Field . . . . . . . . . . . . . . . . 22
4.5.3. Indexed Header Field With Post-Base Index . . . . . . 23 4.5.3. Indexed Header Field With Post-Base Index . . . . . . 22
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 . . . . . . . . . . . . . . . . . . . 25
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 . . . . . . . . . . . . . . . . . 26 8.3. Error Code Registration . . . . . . . . . . . . . . . . . 26
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 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 . . . . . . . . . 33
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 35 Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 35
C.1. Since draft-ietf-quic-qpack-06 . . . . . . . . . . . . . 35 C.1. Since draft-ietf-quic-qpack-08 . . . . . . . . . . . . . 35
C.2. Since draft-ietf-quic-qpack-05 . . . . . . . . . . . . . 35 C.2. Since draft-ietf-quic-qpack-06 . . . . . . . . . . . . . 35
C.3. Since draft-ietf-quic-qpack-04 . . . . . . . . . . . . . 35 C.3. Since draft-ietf-quic-qpack-05 . . . . . . . . . . . . . 35
C.4. Since draft-ietf-quic-qpack-03 . . . . . . . . . . . . . 35 C.4. Since draft-ietf-quic-qpack-04 . . . . . . . . . . . . . 35
C.5. Since draft-ietf-quic-qpack-02 . . . . . . . . . . . . . 35 C.5. Since draft-ietf-quic-qpack-03 . . . . . . . . . . . . . 35
C.6. Since draft-ietf-quic-qpack-01 . . . . . . . . . . . . . 36 C.6. Since draft-ietf-quic-qpack-02 . . . . . . . . . . . . . 35
C.7. Since draft-ietf-quic-qpack-00 . . . . . . . . . . . . . 36 C.7. Since draft-ietf-quic-qpack-01 . . . . . . . . . . . . . 36
C.8. Since draft-ietf-quic-qcram-00 . . . . . . . . . . . . . 36 C.8. Since draft-ietf-quic-qpack-00 . . . . . . . . . . . . . 36
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 36 C.9. Since draft-ietf-quic-qcram-00 . . . . . . . . . . . . . 36
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37
1. Introduction 1. Introduction
The QUIC transport protocol was designed from the outset 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. HTTP/2 uses HPACK ([RFC7541]) for header compression, but HTTP/2 [RFC7540]. HTTP/2 uses HPACK ([RFC7541]) for header
QUIC's stream multiplexing comes into some conflict with HPACK. A compression. If HPACK were used for HTTP/3 [HTTP3], it would induce
key goal of the design of QUIC is to improve stream multiplexing head-of-line blocking due to built-in assumptions of a total ordering
relative to HTTP/2 by reducing head-of-line blocking. If HPACK were across frames on all streams.
used for HTTP/3, it would induce head-of-line blocking due to built-
in assumptions of a total ordering across frames on all streams.
QUIC is described in [QUIC-TRANSPORT]. The HTTP/3 mapping is
described in [HTTP3]. For a full description of HTTP/2, see
[RFC7540]. The description of HPACK is [RFC7541].
QPACK reuses core concepts from HPACK, but is redesigned to allow QPACK reuses core concepts from HPACK, but is redesigned to allow
correctness in the presence of out-of-order delivery, with correctness in the presence of out-of-order delivery, with
flexibility for implementations to balance between resilience against flexibility for implementations to balance between resilience against
head-of-line blocking and optimal compression ratio. The design head-of-line blocking and optimal compression ratio. The design
goals are to closely approach the compression ratio of HPACK with goals are to closely approach the compression ratio of HPACK with
substantially less head-of-line blocking under the same loss substantially less head-of-line blocking under the same loss
conditions. conditions.
1.1. Conventions and Definitions 1.1. Conventions and Definitions
skipping to change at page 4, line 43 skipping to change at page 4, line 39
Header block: The compressed representation of a header list. Header block: The compressed representation of a header list.
Encoder: An implementation which transforms a header list into a Encoder: An implementation which transforms a header list into a
header block. header block.
Decoder: An implementation which transforms a header block into a Decoder: An implementation which transforms a header block into a
header list. header list.
Absolute Index: A unique index for each entry in the dynamic table. Absolute Index: A unique index for each entry in the dynamic table.
Base: A reference point for relative indicies. Dynamic references Base: A reference point for relative indices. Dynamic references
are made relative to a Base in header blocks. are made relative to a Base in header blocks.
Insert Count: The total number of entries inserted in the dynamic Insert Count: The total number of entries inserted in the dynamic
table. table.
QPACK is a name, not an acronym. QPACK is a name, not an acronym.
1.2. Notational Conventions 1.2. Notational Conventions
Diagrams use the format described in Section 3.1 of [RFC2360], with Diagrams use the format described in Section 3.1 of [RFC2360], with
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table. table.
QPACK is a name, not an acronym. QPACK is a name, not an acronym.
1.2. Notational Conventions 1.2. Notational Conventions
Diagrams use the format described in Section 3.1 of [RFC2360], with Diagrams use the format described in Section 3.1 of [RFC2360], with
the following additional conventions: the following additional conventions:
x (A) Indicates that x is A bits long x (A) Indicates that x is A bits long
x (A+) Indicates that x uses the prefixed integer encoding defined x (A+) Indicates that x uses the prefixed integer encoding defined
in Section 5.1 of [RFC7541], beginning with an A-bit prefix. in Section 5.1 of [RFC7541], 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 (see Section 3.1) is predefined and
contains common header fields (some of them with an empty value). contains common header fields (some of them with an empty value).
The dynamic table (see Section 3.2) is built up over the course of The dynamic table (see Section 3.2) is built up over the course of
the connection and can be used by the encoder to index header fields the connection and can be used by the encoder to index header fields
in the encoded header lists. in the encoded header lists.
QPACK instructions appear in three different types of streams: QPACK defines unidirectional streams for sending instructions from
encoder to decoder and vice versa.
o The encoder uses a unidirectional stream to modify the state of
the dynamic table without emitting header fields associated with
any particular request.
o HEADERS and PUSH_PROMISE frames on request and push streams
reference the table state without modifying it.
o The decoder sends feedback to the encoder on a unidirectional
stream. This feedback enables the encoder to manage dynamic table
state.
2.1. Encoder 2.1. Encoder
An encoder compresses a header list by emitting either an indexed or An encoder converts a header list into a header block by emitting
a literal representation for each header field in the list. either an indexed or a literal representation for each header field
References to the static table and literal representations do not in the list (see Section 4.5). Indexed representations achieve high
require any dynamic state and never risk head-of-line blocking. compression by replacing the literal name and possibly the value with
References to the dynamic table risk head-of-line blocking if the an index to either the static or dynamic table. References to the
encoder has not received an acknowledgement indicating the entry is static table and literal representations do not require any dynamic
available at the decoder. state and never risk head-of-line blocking. References to the
dynamic table risk head-of-line blocking if the encoder has not
received an acknowledgement indicating the entry is available at the
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.
QPACK preserves the ordering of header fields within each header QPACK preserves the ordering of header fields within each header
list. An encoder MUST emit header field representations in the order list. An encoder MUST emit header field representations in the order
they appear in the input header list. they appear in the input header list.
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 received by the decoder after the referenced entry table entry is not processed by the decoder after the referenced
has been evicted. Hence the encoder needs to track information about entry has been evicted. Hence the encoder needs to track information
each compressed header block that references the dynamic table until about each compressed header block that references the dynamic table
that header block is acknowledged by the decoder. until that header block is acknowledged by the decoder (see
Section 4.4.1).
2.1.2. Blocked Dynamic Table Insertions 2.1.2. Blocked Dynamic Table Insertions
A dynamic table entry is considered blocking and cannot be evicted A dynamic table entry is considered blocking and cannot be evicted
until its insertion has been acknowledged and there are no until its insertion has been acknowledged and there are no
outstanding unacknowledged references to the entry. In particular, a outstanding unacknowledged references to the entry. In particular, a
dynamic table entry that has never been referenced can still be dynamic table entry that has never been referenced can still be
blocking. blocking.
Note: A blocking entry is unrelated to a blocked stream, which is a Note: A blocking entry is unrelated to a blocked stream, which is a
stream that a decoder cannot decode as a result of references to stream that a decoder cannot decode as a result of references to
entries that are not yet available. Any encoder that uses the entries that are not yet available. An encoder that uses the
dynamic table has to keep track of blocked entries, whereas dynamic table has to keep track of blocked entries.
blocked streams are optional.
An encoder MUST NOT insert an entry into the dynamic table (or An encoder MUST NOT insert an entry into the dynamic table (or
duplicate an existing entry) if doing so would evict a blocking duplicate an existing entry) if doing so would evict a blocking
entry. In this case, the encoder can send literal representations of entry.
header fields.
2.1.2.1. Avoiding Blocked 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 4.3.3), and reference the duplicate instead. instruction (see 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 in the dynamic table that it will emit a smallest absolute index (see Section 3.2.4) in the dynamic table that
reference for. As new entries are inserted, the encoder increases it will emit a reference for. As new entries are inserted, the
the draining index to maintain the section of the table that it will encoder increases the draining index to maintain the section of the
not reference. If the encoder does not create new references to table that it will not reference. If the encoder does not create new
entries with an absolute index lower than the draining index, the references to entries with an absolute index lower than the draining
number of unacknowledged references to those entries will eventually index, the number of unacknowledged references to those entries will
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. Avoiding Head-of-Line Blocking 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 header block might reference an entry in the dynamic table streams, a decoder might encounter a header block that references a
that has not yet been received. dynamic table entry that it has not yet received.
Each header block contains a Required Insert Count, the lowest
possible value for the Insert Count with which the header block can
be decoded. For a header block with references to the dynamic table,
the Required Insert Count is one larger than the largest Absolute
Index of all referenced dynamic table entries. For a header block
with no references to the dynamic table, the Required Insert Count is
zero.
If the decoder encounters a header block with a Required Insert Count
value larger than defined above, it MAY treat this as a stream error
of type HTTP_QPACK_DECOMPRESSION_FAILED. If the decoder encounters a
header block with a Required Insert Count value smaller than defined
above, it MUST treat this as a stream error of type
HTTP_QPACK_DECOMPRESSION_FAILED as prescribed in Section 3.2.7.
When the Required Insert Count is zero, the frame contains no Each header block contains a Required Insert Count (see
references to the dynamic table and can always be processed Section 4.5.1), the lowest possible value for the Insert Count with
immediately. which the header block can be decoded. For a header block with
references to the dynamic table, the Required Insert Count is one
larger than the largest absolute index of all referenced dynamic
table entries. For a header block with no references to the dynamic
table, the Required Insert Count is zero.
If the Required Insert Count is greater than the number of dynamic When the decoder receives a header block with a Required Insert Count
table entries received, the stream is considered "blocked." While greater than its own Insert Count, the stream cannot be processed
blocked, header field data SHOULD remain in the blocked stream's flow immediately, and is considered "blocked" (see {blocked-decoding}).
control window. A stream becomes unblocked when the Insert Count
becomes greater than or equal to the Required Insert Count for all
header blocks the decoder has started reading from the stream.
The SETTINGS_QPACK_BLOCKED_STREAMS setting (see Section 5) specifies The SETTINGS_QPACK_BLOCKED_STREAMS setting (see Section 5) specifies
an upper bound on the number of streams which can be blocked. An an upper bound on the number of streams which can be blocked. An
encoder MUST limit the number of streams which could become blocked encoder MUST limit the number of streams which could become blocked
to the value of SETTINGS_QPACK_BLOCKED_STREAMS at all times. Note to the value of SETTINGS_QPACK_BLOCKED_STREAMS at all times. Note
that the decoder might not actually become blocked on every stream that the decoder might not become blocked on every stream which risks
which risks becoming blocked. If the decoder encounters more blocked becoming blocked.
streams than it promised to support, it MUST treat this as a stream
error of type HTTP_QPACK_DECOMPRESSION_FAILED.
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,
compression efficiency can often be improved by referencing dynamic compression efficiency can often be improved by referencing dynamic
table entries that are still in transit, but if there is loss or table entries that are still in transit, but if there is loss or
reordering the stream can become blocked at the decoder. An encoder reordering the stream can become blocked at the decoder. An encoder
avoids the risk of blocking by only referencing dynamic table entries avoids the risk of blocking by only referencing dynamic table entries
which have been acknowledged, but this could mean using literals. which have been acknowledged, but this could mean using literals.
Since literals make the header block larger, this can result in the Since literals make the header block larger, this can result in the
encoder becoming blocked on congestion or flow control limits. encoder becoming blocked on congestion or flow control limits.
2.1.4. Known Received Count 2.1.4. Known Received Count
In order to identify which dynamic table entries can be safely used In order to identify which dynamic table entries can be safely used
without a stream becoming blocked, the encoder tracks the number of without a stream becoming blocked, the encoder tracks the number of
entries received by the decoder. The Known Received Count tracks the entries received by the decoder. The Known Received Count tracks the
total number of acknowledged insertions. total number of acknowledged insertions.
When blocking references are permitted, the encoder uses header block When blocking references are permitted, the encoder uses Header
acknowledgement to maintain the Known Received Count, as described in Acknowledgement instructions (Section 4.4.1) to maintain the Known
Section 4.4.2. Received Count. If a header block was potentially blocking, the
acknowledgement implies that the decoder has received all dynamic
table state necessary to process the header block. If the Required
Insert Count of an acknowledged header block was greater than the
encoder's current Known Received Count, the block's Required Insert
Count becomes the new Known Received Count.
To acknowledge dynamic table entries which are not referenced by To acknowledge dynamic table entries which are not referenced by
header blocks, for example because the encoder or the decoder have header blocks, for example because the encoder or the decoder have
chosen not to risk blocked streams, the decoder sends an Insert Count chosen not to risk blocked streams, the decoder sends an Insert Count
Increment instruction (see Section 4.4.1). 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 dynamic table corresponding header lists. It also processes dynamic table
modifications from encoder instructions received on the encoder modifications from encoder instructions received on the encoder
stream. stream.
The decoder MUST emit header fields in the order their The decoder MUST emit header fields in the order their
representations appear in the input header block. representations appear in the input header block.
2.2.1. State Synchronization 2.2.1. Blocked Decoding
The decoder instructions (Section 4.4) signal key events at the Upon receipt of a header block, the decoder examines the Required
decoder that permit the encoder to track the decoder's state. These Insert Count. When the Required Insert Count is less than or equal
events are: to the decoder's Insert Count, the header block can be processed
immediately. Otherwise, the stream on which the header block was
received becomes blocked.
o Complete processing of a header block While blocked, header block data SHOULD remain in the blocked
stream's flow control window. A stream becomes unblocked when the
Insert Count becomes greater than or equal to the Required Insert
Count for all header blocks the decoder has started reading from the
stream.
o Abandonment of a stream which might have remaining header blocks When processing header blocks, the decoder expects the Required
Insert Count to exactly match the value defined in {{blocked-
streams}. If it encounters a smaller value than expected, it MUST
treat this as a connection error of type
HTTP_QPACK_DECOMPRESSION_FAILED (see Section 2.2.3). If it
encounters a larger value than expected, it MAY treat this as a
connection error of type HTTP_QPACK_DECOMPRESSION_FAILED.
o Receipt of new dynamic table entries If the decoder encounters more blocked streams than it promised to
support, it MUST treat this as a connection error of type
HTTP_QPACK_DECOMPRESSION_FAILED.
Knowledge that a header block with references to the dynamic table 2.2.2. State Synchronization
has been processed permits the encoder to evict entries to which no
unacknowledged references remain (see Section 2.1.2). When a stream
is reset or abandoned, the indication that these header blocks will
never be processed serves a similar function (see Section 4.4.3).
The decoder chooses when to emit Insert Count Increment instructions The decoder signals the following events by emitting decoder
(see Section 4.4.1). Emitting an instruction after adding each new instructions (Section 4.4) on the decoder stream.
dynamic table entry will provide the most timely feedback to the
2.2.2.1. Completed Processing of a Header Block
When the decoder finishes decoding a header block containing dynamic
table references, it emits a Header Acknowledgement instruction
(Section 4.4.1). A stream may carry multiple header blocks in the
case of intermediate responses, trailers, and pushed requests. The
encoder interprets each Header Acknowledgement instruction as
acknowledging the earliest unacknowledged header block containing
dynamic table references sent on the given stream.
2.2.2.2. Abandonment 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
abandons reading of a stream, it generates a Stream Cancellation
instruction (see Section 4.4.2). This signals to the encoder that
all references to the dynamic table on that stream are no longer
outstanding. A decoder with a maximum dynamic table capacity equal
to zero (see Section 3.2.3) MAY omit sending Stream Cancellations,
because the encoder cannot have any dynamic table references. An
encoder cannot infer from this instruction that any updates to the
dynamic table have been received.
The Header Acknowledgement and Stream Cancellation instructions
permit the encoder to remove references to entries in the dynamic
table. When entries have zero references they are no longer
considered blocking (see Section 2.1.2).
2.2.2.3. New Table Entries
After receiving new table entries on the encoder stream, the decoder
chooses when to emit Insert Count Increment instructions (see
Section 4.4.3). Emitting this instruction after adding each new
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 4.4.2). 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.
2.2.2. Blocked Decoding 2.2.3. Invalid References
To track blocked streams, the Required Insert Count value for each If the decoder encounters a reference in a header block
stream can be used. Whenever the decoder processes a table update, representation to a dynamic table entry which has already been
it can begin decoding any blocked streams that now have their evicted or which has an absolute index greater than or equal to the
dependencies satisfied. declared Required Insert Count (see Section 4.5.1), it MUST treat
this as a connection error of type "HTTP_QPACK_DECOMPRESSION_FAILED".
If the decoder encounters a reference in an encoder instruction to a
dynamic table entry which has already been evicted, it MUST treat
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.
3.1. Static Table 3.1. Static Table
The static table consists of a predefined static list of header The static table consists of a predefined static list of header
fields, each of which has a fixed index over time. Its entries are fields, each of which has a fixed index over time. Its entries are
defined in Appendix A. defined in Appendix A.
All entries in the static table have a name and a value. However, All entries in the static table have a name and a value. However,
values can be empty (that is, have a length of 0). values can be empty (that is, have a length of 0). Each entry is
identified by a unique index.
Note the QPACK static table is indexed from 0, whereas the HPACK Note the QPACK static table is indexed from 0, whereas the HPACK
static table is indexed from 1. static table is indexed from 1.
When the decoder encounters an invalid static table index in a header When the decoder encounters an invalid static table index in a header
block instruction it MUST treat this as a stream 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.
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.
The size of an entry is the sum of its name's length in bytes (as The size of an entry is the sum of its name's length in bytes (as
defined in Section 4.1.2), its value's length in bytes, and 32. defined in Section 4.1.2), its value's length in bytes, and 32.
The size of an entry is calculated using the length of its name and The size of an entry is calculated using the length of its name and
value without Huffman encoding applied. value without Huffman encoding applied.
3.2.2. Dynamic Table Capacity and Eviction 3.2.2. Dynamic Table Capacity and Eviction
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 capcity of the dynamic the upper limit on its size. The initial capacity of the dynamic
table is zero. table is zero. The encoder sends a Set Dynamic Table Capacity
instruction (Section 4.3.1) with a non-zero capacity to begin using
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) or is less than or equal to (table capacity - size of new entry). The
until the table is empty. The encoder MUST NOT evict a blocking encoder MUST NOT evict a blocking dynamic table entry (see
dynamic table entry (see Section 2.1.2). Section 2.1.2). The entry is then added to the table. It is an
If the size of the new entry is less than or equal to the dynamic
table capacity, then that entry is added to the table. It is an
error if the encoder attempts to add an entry that is larger than the error if the encoder attempts to add an entry that is larger than the
dynamic table capacity; the decoder MUST treat this as a connection dynamic table capacity; the decoder MUST treat this as a connection
error of type "HTTP_QPACK_ENCODER_STREAM_ERROR". 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, Whenever the dynamic table capacity is reduced by the encoder (see
entries are evicted from the end of the dynamic table until the size Section 4.3.1), entries are evicted from the end of the dynamic table
of the dynamic table is less than or equal to the new table capacity. until the size of the dynamic table is less than or equal to the new
This mechanism can be used to completely clear entries from the table capacity. This mechanism can be used to completely clear
dynamic table by setting a capacity of 0, which can subsequently be entries from the dynamic table by setting a capacity of 0, which can
restored. 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). The encoder MUST not set a dynamic table capacity that Section 5). The encoder MUST not set a dynamic table capacity that
exceeds this maximum, but it can choose to use a lower dynamic table exceeds this maximum, but it can choose to use a lower dynamic table
capacity (see Section 4.3.4). capacity (see 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 0, the server MAY set it to a non-zero value in its SETTING is 0, 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".
skipping to change at page 12, line 14 skipping to change at page 12, line 47
3.2.4. Absolute Indexing 3.2.4. Absolute Indexing
Each entry possesses both an absolute index which is fixed for the Each entry possesses both an absolute index which is fixed for the
lifetime of that entry and a relative index which changes based on lifetime of that entry and a relative index which changes based on
the context of the reference. The first entry inserted has an the context of the reference. The first entry inserted has an
absolute index of "0"; indices increase by one with each insertion. absolute index of "0"; indices increase by one with each insertion.
3.2.5. Relative Indexing 3.2.5. Relative Indexing
The relative index begins at zero and increases in the opposite Relative indices begin at zero and increase in the opposite direction
direction from the absolute index. Determining which entry has a from the absolute index. Determining which entry has a relative
relative index of "0" depends on the context of the reference. index of "0" depends on the context of the reference.
In encoder instructions, a relative index of "0" always refers to the In encoder instructions, a relative index of "0" always refers to the
most recently inserted value in the dynamic table. Note that this most recently inserted value in the dynamic table. Note that this
means the entry referenced by a given relative index will change means the entry referenced by a given relative index 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 - Control Stream Example Dynamic Table Indexing - Encoder Stream
Unlike encoder instructions, relative indices in header block Unlike encoder instructions, relative indices in header block
instructions are relative to the Base at the beginning of the header representations are relative to the Base at the beginning of the
block (see Section 4.5.1). This ensures that references are stable header block (see Section 4.5.1). This ensures that references are
even if the dynamic table is updated while decoding a header block. stable even if header blocks and dynamic table updates are processed
out of order.
The Base is encoded as a value relative to the Required Insert Count.
The Base identifies which dynamic table entries can be referenced
using relative indexing, starting with 0 at the last entry added.
Post-Base references are used for entries inserted after base, In a header block a relative index of "0" refers to the entry with
starting at 0 for the first entry added after the Base, see absolute index equal to Base - 1.
Section 3.2.6.
Required Required
Insert Insert
Count Base Count Base
| | | |
V V 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
Example Dynamic Table Indexing - Relative Index in Header Block Example Dynamic Table Indexing - Relative Index in Header Block
3.2.6. Post-Base Indexing 3.2.6. Post-Base Indexing
A header block can reference entries added after the entry identified Post-Base indices are used for entries with absolute indexes greater
by the Base. This allows an encoder to process a header block in a than or equal to Base, starting at 0 for the entry with absolute
index equal to Base, and increasing in the same direction as the
absolute index.
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
this (or other) header blocks. Newly added entries are referenced this (or other) header blocks.
using Post-Base instructions. Indices for Post-Base instructions
increase in the same direction as absolute indices, with the zero
value being the first entry inserted after the Base.
Base Base
| |
V V
+-----+-----+-----+-----+-----+ +-----+-----+-----+-----+-----+
| 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
Example Dynamic Table Indexing - Post-Base Index in Header Block Example Dynamic Table Indexing - Post-Base Index in Header Block
3.2.7. Invalid References
If the decoder encounters a reference in a header block instruction
to a dynamic table entry which has already been 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 this as a stream
error of type "HTTP_QPACK_DECOMPRESSION_FAILED".
If the decoder encounters a reference in an encoder instruction to a
dynamic table entry which has already been dropped, it MUST treat
this as a connection error of type "HTTP_QPACK_ENCODER_STREAM_ERROR".
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. QPACK implementations MUST be able to decode integers up unmodified. QPACK implementations MUST be able to decode integers up
to 62 bits long. to 62 bits long.
skipping to change at page 14, line 42 skipping to change at page 15, line 15
This document expands the definition of string literals and permits This document expands the definition of string literals and permits
them to begin other than on a byte boundary. An "N-bit prefix string them to begin other than on a byte boundary. An "N-bit prefix string
literal" begins with the same Huffman flag, followed by the length literal" begins with the same Huffman flag, followed by the length
encoded as an (N-1)-bit prefix integer. The remainder of the string encoded as an (N-1)-bit prefix integer. The remainder of the string
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. Instructions 4.2. Encoder and Decoder Streams
There are three separate QPACK instruction spaces. Encoder
instructions (Section 4.3) carry table updates, decoder instructions
(Section 4.4) carry acknowledgments of table modifications and header
processing, and header block instructions (Section 4.5) convey an
encoded representation of a header list by referring to the QPACK
table state.
Encoder and decoder instructions appear on the unidirectional stream
types described in this section. Header block instructions are
contained in HEADERS and PUSH_PROMISE frames, which are conveyed on
request or push streams as described in [HTTP3].
4.2.1. 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 o 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 o 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 a single encoder stream and decoder stream. Receipt of MUST initiate at most one encoder stream and at most one decoder
a second instance of either stream type be MUST treated as a stream. Receipt of a second instance of either stream type MUST be
connection error of type HTTP_WRONG_STREAM_COUNT. These streams MUST treated as a connection error of type HTTP_WRONG_STREAM_COUNT. These
NOT be closed. Closure of either unidirectional stream type MUST be streams MUST NOT be closed. Closure of either unidirectional stream
treated as a connection error of type HTTP_CLOSED_CRITICAL_STREAM. type MUST be treated as a connection error of type
HTTP_CLOSED_CRITICAL_STREAM.
An endpoint MAY avoid creating its own encoder stream if it's not
going to be used (for example if the endpoint doesn't wish to use the
dynamic table, or if the maximum size of the dynamic table permitted
by the peer is zero).
An endpoint MAY avoid creating its own decoder stream if the maximum
size of its own dynamic table is zero.
An endpoint MUST allow its peer to create both encoder and decoder
streams even if the connection's settings prevent their use.
4.3. Encoder Instructions 4.3. Encoder Instructions
Table updates can add a table entry, possibly using existing entries An encoder sends encoder instructions on the encoder stream to set
to avoid transmitting redundant information. The name can be the capacity of the dynamic table and add dynamic table entries.
transmitted as a reference to an existing entry in the static or the Instructions adding table entries can use existing entries to avoid
dynamic table or as a string literal. For entries which already transmitting redundant information. The name can be transmitted as a
exist in the dynamic table, the full entry can also be used by reference to an existing entry in the static or the dynamic table or
reference, creating a duplicate entry. as a string literal. For entries which already exist in the dynamic
table, the full entry can also be used by reference, creating a
duplicate entry.
This section specifies the following encoder instructions. This section specifies the following encoder instructions.
4.3.1. Insert With Name Reference 4.3.1. Set Dynamic Table Capacity
An addition to the header table where the header field name matches An encoder informs the decoder of a change to the dynamic table
the header field name of an entry stored in the static table or the capacity using an instruction which begins with the '001' three-bit
dynamic table starts with the '1' one-bit pattern. The "S" bit pattern. The new dynamic table capacity is represented as an integer
indicates whether the reference is to the static (S=1) or dynamic with a 5-bit prefix (see Section 5.1 of [RFC7541]).
(S=0) table. The 6-bit prefix integer (see Section 5.1 of [RFC7541])
that follows is used to locate the table entry for the header name. 0 1 2 3 4 5 6 7
When S=1, the number represents the static table index; when S=0, the +---+---+---+---+---+---+---+---+
number is the relative index of the entry in the dynamic table. | 0 | 0 | 1 | Capacity (5+) |
+---+---+---+-------------------+
Figure 2: Set Dynamic Table Capacity
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
SETTINGS_QPACK_MAX_TABLE_CAPACITY parameter (see Section 5) received
from the decoder. The decoder MUST treat a new dynamic table
capacity value that exceeds this limit as a connection error of type
"HTTP_QPACK_ENCODER_STREAM_ERROR".
Reducing the dynamic table capacity can cause entries to be evicted
(see Section 3.2.2). This MUST NOT cause the eviction of blocking
entries (see Section 2.1.2). Changing the capacity of the dynamic
table is not acknowledged as this instruction does not insert an
entry.
4.3.2. Insert With Name Reference
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
or the dynamic table using an instruction that starts with the '1'
one-bit pattern. The second ("S") bit indicates whether the
reference is to the static or dynamic table. The 6-bit prefix
integer (see Section 5.1 of [RFC7541]) that follows is used to locate
the table entry for the header name. When S=1, the number represents
the static table index; when S=0, the number is the relative index of
the 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 5.2 of [RFC7541]). represented as a string literal (see Section 5.2 of [RFC7541]).
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 1 | S | Name Index (6+) | | 1 | S | Name Index (6+) |
+---+---+-----------------------+ +---+---+-----------------------+
| H | Value Length (7+) | | H | Value Length (7+) |
+---+---------------------------+ +---+---------------------------+
| Value String (Length bytes) | | Value String (Length bytes) |
+-------------------------------+ +-------------------------------+
Insert Header Field -- Indexed Name Insert Header Field -- Indexed Name
4.3.2. Insert Without Name Reference 4.3.3. Insert Without Name Reference
An addition to the header table where both the header field name and An encoder adds an entry to the dynamic table where both the header
the header field value are represented as string literals (see field name and the header field value are represented as string
Section 4.1) starts with the '01' two-bit pattern. literals (see Section 4.1) using an instruction that starts with the
'01' two-bit pattern.
The name is represented as a 6-bit prefix string literal, while the The name is represented as a 6-bit prefix string literal, while the
value is represented as an 8-bit prefix string literal. value is represented as an 8-bit prefix string literal.
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 Insert Header Field -- New Name
4.3.3. Duplicate 4.3.4. Duplicate
Duplication of an existing entry in the dynamic table starts with the An encoder duplicates an existing entry in the dynamic table using an
'000' three-bit pattern. The relative index of the existing entry is instruction that starts with the '000' three-bit pattern. The
represented as an integer with a 5-bit prefix. relative index of the existing entry is represented as an integer
with a 5-bit prefix.
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 2: Duplicate Figure 3: 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 mitigate resending either the name or the value. This is useful to mitigate
the eviction of older entries which are frequently referenced, both the eviction of older entries which are frequently referenced, both
to avoid the need to resend the header and to avoid the entry in the to avoid the need to resend the header and to avoid the entry in the
table blocking the ability to insert new headers. table blocking the ability to insert new headers.
4.3.4. Set Dynamic Table Capacity
An encoder informs the decoder of a change to the dynamic table
capacity using an instruction which begins with the '001' three-bit
pattern. The new dynamic table capacity is represented as an integer
with a 5-bit prefix (see Section 5.1 of [RFC7541]).
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 0 | 0 | 1 | Capacity (5+) |
+---+---+---+-------------------+
Figure 3: Set Dynamic Table Capacity
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
SETTINGS_QPACK_MAX_TABLE_CAPACITY parameter (see Section 5) received
from the decoder. The decoder MUST treat a new dynamic table
capacity value that exceeds this limit as a connection error of type
"HTTP_QPACK_ENCODER_STREAM_ERROR".
Reducing the dynamic table capacity can cause entries to be evicted
(see Section 3.2.2). This MUST NOT cause the eviction of blocking
entries (see Section 2.1.2). Changing the capacity of the dynamic
table is not acknowledged as this instruction does not insert an
entry.
4.4. Decoder Instructions 4.4. Decoder Instructions
Decoder instructions provide information used to ensure consistency Decoder instructions provide information used to ensure consistency
of the dynamic table. They are sent from the decoder to the encoder of the dynamic table. They are sent from the decoder to the encoder
on a decoder stream; that is, the server informs the client about the on a decoder stream; that is, the server informs the client about the
processing of the client's header blocks and table updates, and the processing of the client's header blocks and table updates, and the
client informs the server about the processing of the server's header client informs the server about the processing of the server's header
blocks and table updates. blocks and table updates.
This section specifies the following decoder instructions. This section specifies the following decoder instructions.
4.4.1. Insert Count Increment 4.4.1. Header Acknowledgement
The Insert Count Increment instruction begins with the '00' two-bit
pattern. The instruction specifies the total number of dynamic table
inserts and duplications since the last Insert Count Increment or
Header Acknowledgement that increased the Known Received Count for
the dynamic table (see Section 2.1.4). The Increment field is
encoded as a 6-bit prefix integer. The encoder uses this value to
determine which table entries might cause a stream to become blocked,
as described in Section 2.2.1.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 0 | 0 | Increment (6+) |
+---+---+-----------------------+
Figure 4: Insert Count Increment
An encoder that receives an Increment field equal to zero or one that
increases the Known Received Count beyond what the encoder has sent
MUST treat this as a connection error of type
"HTTP_QPACK_DECODER_STREAM_ERROR".
4.4.2. 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.
on the decoder stream. The instruction begins with the '1' one-bit The instruction begins with the '1' one-bit pattern and includes the
pattern and includes the header block's associated stream ID, encoded header block's associated stream ID, encoded as a 7-bit prefix
as a 7-bit prefix integer. It is used by the peer's encoder to know integer. It is used by the peer's encoder to know when it is safe to
when it is safe to evict an entry, and possibly update the Known evict an entry (Section 2.1.2), and possibly update the Known
Received Count. Received Count (Section 2.1.4).
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 5: Header Acknowledgement Figure 4: Header Acknowledgement
The same Stream ID can be identified multiple times, as multiple
header blocks can be sent on a single stream in the case of
intermediate responses, trailers, and pushed requests. Since HEADERS
and PUSH_PROMISE frames on each stream are received and processed in
order, this gives the encoder precise feedback on which header blocks
within a stream have been fully processed.
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".
When blocking references are permitted, the encoder uses 4.4.2. Stream Cancellation
acknowledgement of header blocks to update the Known Received Count.
If a header block was potentially blocking, the acknowledgement
implies that the decoder has received all dynamic table state
necessary to process the header block. If the Required Insert Count
of an acknowledged header block was greater than the encoder's
current Known Received Count, the block's Required Insert Count
becomes the new Known Received Count.
4.4.3. Stream Cancellation
The instruction begins with the '01' two-bit pattern. The When a stream is reset or reading is abandoned, the decoder emits a
instruction includes the stream ID of the affected stream - a request Stream Cancellation instruction. The instruction begins with the
or push stream - encoded as a 6-bit prefix integer. '01' two-bit pattern. The instruction includes the stream ID of the
affected stream encoded as a 6-bit prefix integer. See
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 6: Stream Cancellation Figure 5: Stream Cancellation
A stream that is reset might have multiple outstanding header blocks 4.4.3. Insert Count Increment
with dynamic table references. When an endpoint receives a stream
reset before the end of a stream, it generates a Stream Cancellation
instruction on the decoder stream. Similarly, when an endpoint
abandons reading of a stream it needs to signal this using the Stream
Cancellation instruction. This signals to the encoder that all
references to the dynamic table on that stream are no longer
outstanding. A decoder with a maximum dynamic table capacity equal
to zero (see Section 3.2.3) MAY omit sending Stream Cancellations,
because the encoder cannot have any dynamic table references.
An encoder cannot infer from this instruction that any updates to the The Insert Count Increment instruction begins with the '00' two-bit
dynamic table have been received. pattern. The instruction specifies the total number of dynamic table
inserts and duplications since the last Insert Count Increment or
Header Acknowledgement that increased the Known Received Count for
the dynamic table (see Section 2.1.4). The Increment field is
encoded as a 6-bit prefix integer. The encoder uses this value to
determine which table entries might cause a stream to become blocked,
as described in Section 2.2.2.
4.5. Header Block Instructions 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 0 | 0 | Increment (6+) |
+---+---+-----------------------+
HTTP/3 endpoints convert header lists to headers blocks and exchange Figure 6: Insert Count Increment
them inside HEADERS and PUSH_PROMISE frames. A decoder interprets
header block instructions in order to construct a header list. These
instructions reference the static table, or dynamic table in a
particular state without modifying it.
This section specifies the following header block instructions. An encoder that receives an Increment field equal to zero or one that
increases the Known Received Count beyond what the encoder has sent
MUST treat this as a connection error of type
"HTTP_QPACK_DECODER_STREAM_ERROR".
4.5. Header Block Representations
Header blocks contain compressed representations of header lists and
are carried in frames on streams defined by the enclosing protocol.
These representations reference the static table, or dynamic table in
a particular state without modifying it.
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 sign- encoding described in Section 4.5.1.1). The Base is encoded as sign-
and-modulus integer, using a single sign bit and a value with a 7-bit and-modulus integer, using a single sign bit and a value with a 7-bit
prefix (see Section 4.5.1.2). prefix (see Section 4.5.1.2).
These two values are followed by instructions for compressed headers. These two values are followed by representations for compressed
The entire block is expected to be framed by the using protocol. headers.
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: Frame Payload Figure 7: 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 21, line 8 skipping to change at page 20, line 46
"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 stream error of type conformant encoder, it MUST treat this as a connection error of type
"HTTP_QPACK_DECOMPRESSION_FAILED". "HTTP_QPACK_DECOMPRESSION_FAILED".
TotalNumberOfInserts is the total number of inserts into the TotalNumberOfInserts is the total number of inserts into the
decoder's dynamic table. decoder's dynamic table.
FullRange = 2 * MaxEntries FullRange = 2 * MaxEntries
if EncodedInsertCount == 0: if EncodedInsertCount == 0:
ReqInsertCount = 0 ReqInsertCount = 0
else: else:
if EncodedInsertCount > FullRange: if EncodedInsertCount > FullRange:
skipping to change at page 22, line 27 skipping to change at page 22, line 15
positive and the sign bit is set to 0. positive and the sign bit is set to 0.
An encoder that produces table updates before encoding a header block An encoder that produces table updates before encoding a header block
might set Required Insert Count and the Base to the same value. In might set Required Insert Count and the Base to the same value. In
such case, both the sign bit and the Delta Base will be set to zero. such case, both the sign bit and the Delta Base will be set to zero.
A header block that does not reference the dynamic table can use any A header block that does not reference the dynamic table can use any
value for the Base; setting Delta Base to zero is the most efficient value for the Base; setting Delta Base to zero is the most efficient
encoding. encoding.
For example, with an Required Insert Count of 9, a decoder receives a For example, with a Required Insert Count of 9, a decoder receives a
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
regular index of 1 refers to the 5th entry that was added to the regular 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 either An indexed header field representation identifies an entry in either
the static table or the dynamic table and causes that header field to the static table or the dynamic table and causes that header field to
be added to the decoded header list, as described in Section 3.2 of be added to the decoded header list, as described in Section 3.2 of
skipping to change at page 22, line 50 skipping to change at page 22, line 38
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 1 | S | Index (6+) | | 1 | S | Index (6+) |
+---+---+-----------------------+ +---+---+-----------------------+
Indexed Header Field Indexed Header Field
If the entry is in the static table, or in the dynamic table with an If the entry is in the static table, or in the dynamic table with an
absolute index less than the Base, this representation starts with absolute index less than the Base, this representation starts with
the '1' 1-bit pattern, followed by the "S" bit indicating whether the the '1' 1-bit pattern, followed by the "S" bit indicating whether the
reference is into the static (S=1) or dynamic (S=0) table. Finally, reference is into the static or dynamic table. The 6-bit prefix
the relative index of the matching header field is represented as an integer (see Section 5.1 of [RFC7541]) that follows is used to locate
integer with a 6-bit prefix (see Section 5.1 of [RFC7541]). the table entry for the header name. When S=1, the number represents
the static table index; when S=0, the number is 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
If the entry is in the dynamic table with an absolute index greater If the entry is in the dynamic table with an absolute index greater
than or equal to the Base, the representation starts with the '0001' than or equal to the Base, the representation starts with the '0001'
4-bit pattern, followed by the post-base index (see Section 3.2.6) of 4-bit pattern, followed by the post-base index (see Section 3.2.6) of
the matching header field, represented as an integer with a 4-bit the matching header field, represented as an integer with a 4-bit
prefix (see Section 5.1 of [RFC7541]). prefix (see Section 5.1 of [RFC7541]).
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
skipping to change at page 23, line 28 skipping to change at page 23, line 20
Indexed Header Field with Post-Base Index Indexed Header Field with Post-Base Index
4.5.4. Literal Header Field With Name Reference 4.5.4. Literal Header Field With Name Reference
A literal header field with a name reference represents a header A literal header field with a name reference represents a header
where the header field name matches the header field name of an entry where the header field name matches the header field name of an entry
stored in the static table or the dynamic table. stored in the static table or the dynamic table.
If the entry is in the static table, or in the dynamic table with an If the entry is in the static table, or in the dynamic table with an
absolute index less than the Base, this representation starts with absolute index less than the Base, this representation starts with
the '01' two-bit pattern. If the entry is in the dynamic table with the '01' two-bit pattern.
an absolute index greater than or equal to the Base, the
representation starts with the '0000' four-bit pattern.
Only the header field name stored in the static or dynamic table is Only the header field name stored in the static or dynamic table is
used. Any header field value MUST be ignored. used. Any header field value MUST be ignored.
The following bit, 'N', indicates whether an intermediary is The following bit, 'N', indicates whether an intermediary is
permitted to add this header to the dynamic header table on permitted to add this header to the dynamic header table on
subsequent hops. When the 'N' bit is set, the encoded header MUST subsequent hops. When the 'N' bit is set, the encoded header MUST
always be encoded with a literal representation. In particular, when always be encoded with a literal representation. In particular, when
a peer sends a header field that it received represented as a literal a peer sends a header field that it received represented as a literal
header field with the 'N' bit set, it MUST use a literal header field with the 'N' bit set, it MUST use a literal
skipping to change at page 24, line 16 skipping to change at page 23, line 46
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 1 | N | S |Name Index (4+)| | 0 | 1 | N | S |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 Literal Header Field With Name Reference
For entries in the static table or in the dynamic table with an The fourth ("S") bit indicates whether the reference is to the static
absolute index less than the Base, the header field name is or dynamic table. The 4-bit prefix integer (see Section 5.1 of
represented using the relative index of that entry, which is [RFC7541]) that follows is used to locate the table entry for the
represented as an integer with a 4-bit prefix (see Section 5.1 of header name. When S=1, the number represents the static table index;
[RFC7541]). The "S" bit indicates whether the reference is to the when S=0, the number is the relative index of the entry in the
static (S=1) or dynamic (S=0) table. dynamic table.
4.5.5. Literal Header Field With Post-Base Name Reference 4.5.5. Literal Header Field With Post-Base Name Reference
For entries in the dynamic table with an absolute index greater than If the name entry is in the dynamic table with an absolute index
or equal to the Base, the header field name is represented using the greater than or equal to the Base, the representation starts with the
post-base index of that entry (see Section 3.2.6) encoded as an '0000' four-bit pattern. The fifth bit is the 'N' bit as described
integer with a 3-bit prefix. in Section 4.5.4. Finally, the header field name is represented
using the post-base index of that entry (see Section 3.2.6) encoded
as an integer with a 3-bit prefix.
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) |
+-------------------------------+ +-------------------------------+
skipping to change at page 25, line 29 skipping to change at page 25, line 23
| Value String (Length bytes) | | Value String (Length bytes) |
+-------------------------------+ +-------------------------------+
Literal Header Field Without Name Reference Literal Header Field Without Name Reference
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): An integer with a maximum SETTINGS_QPACK_MAX_TABLE_CAPACITY (0x1): The default value is zero.
value of 2^30 - 1. The default value is zero bytes. See See Section 3.2 for usage. This is the equivalent of the
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.
SETTINGS_QPACK_BLOCKED_STREAMS (0x7): An integer with a maximum SETTINGS_QPACK_BLOCKED_STREAMS (0x7): The default value is zero.
value of 2^16 - 1. The default value is zero. See Section 2.1.3. See Section 2.1.3.
6. Error Handling 6. Error Handling
The following error codes are defined for HTTP/3 to indicate failures The following error codes are defined for HTTP/3 to indicate failures
of QPACK which prevent the stream or connection from continuing: of QPACK which prevent the connection from continuing:
HTTP_QPACK_DECOMPRESSION_FAILED (0x200): The decoder failed to HTTP_QPACK_DECOMPRESSION_FAILED (0x200): The decoder failed to
interpret a header block instruction and is not able to continue interpret a header block and is not able to continue decoding that
decoding that header block. header block.
HTTP_QPACK_ENCODER_STREAM_ERROR (0x201): The decoder failed to HTTP_QPACK_ENCODER_STREAM_ERROR (0x201): The decoder failed to
interpret an encoder instruction received on the encoder stream. interpret an encoder instruction received on the encoder stream.
HTTP_QPACK_DECODER_STREAM_ERROR (0x202): The encoder failed to HTTP_QPACK_DECODER_STREAM_ERROR (0x202): The encoder failed to
interpret a decoder instruction received on the decoder stream. interpret a decoder instruction received on the decoder stream.
Upon encountering an error, an implementation MAY elect to treat it
as a connection error even if this document prescribes that it MUST
be treated as a stream error.
7. Security Considerations 7. Security Considerations
TBD. TBD.
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
skipping to change at page 26, line 38 skipping to change at page 26, line 30
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 4.2.1 | Both | | QPACK Encoder Stream | 0x02 | Section 4.2 | Both |
| | | | | | | | | |
| QPACK Decoder Stream | 0x03 | Section 4.2.1 | Both | | QPACK Decoder Stream | 0x03 | Section 4.2 | Both |
+----------------------+------+---------------+--------+ +----------------------+------+---------------+--------+
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 | Specificatio |
skipping to change at page 27, line 28 skipping to change at page 27, line 28
| HTTP_QPACK_DECODER_STREAM_E | 0x202 | Error on the | Section 6 | | HTTP_QPACK_DECODER_STREAM_E | 0x202 | Error on the | Section 6 |
| RROR | | decoder | | | RROR | | decoder | |
| | | stream | | | | | stream | |
+-----------------------------+-------+--------------+--------------+ +-----------------------------+-------+--------------+--------------+
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-20 (work in progress), (HTTP/3)", draft-ietf-quic-http-21 (work in progress),
April 2019. July 2019.
[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", draft-ietf-quic-
transport-18 (work in progress), April 2019. transport-20 (work in progress), July 2019.
[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 35, line 10 skipping to change at page 35, line 10
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-06 C.1. Since draft-ietf-quic-qpack-08
o Endpoints are permitted to create encoder and decoder streams even
if they can't use them (#2100, #2529)
o Maximum values for settings removed (#2766, #2767)
C.2. Since draft-ietf-quic-qpack-06
o Clarify initial dynamic table capacity maximums (#2276, #2330, o Clarify initial dynamic table capacity maximums (#2276, #2330,
#2330) #2330)
C.2. Since draft-ietf-quic-qpack-05 C.3. Since draft-ietf-quic-qpack-05
o Introduced the terms dynamic table capacity and maximum dynamic o Introduced the terms dynamic table capacity and maximum dynamic
table capacity. table capacity.
o Renamed SETTINGS_HEADER_TABLE_SIZE to o Renamed SETTINGS_HEADER_TABLE_SIZE to
SETTINGS_QPACK_MAX_TABLE_CAPACITY. SETTINGS_QPACK_MAX_TABLE_CAPACITY.
C.3. Since draft-ietf-quic-qpack-04 C.4. Since draft-ietf-quic-qpack-04
o Changed calculation of Delta Base Index to avoid an illegal value o Changed calculation of Delta Base Index to avoid an illegal value
(#2002, #2005) (#2002, #2005)
C.4. Since draft-ietf-quic-qpack-03 C.5. Since draft-ietf-quic-qpack-03
o Change HTTP settings defaults (#2038) o Change HTTP settings defaults (#2038)
o Substantial editorial reorganization o Substantial editorial reorganization
C.5. Since draft-ietf-quic-qpack-02 C.6. Since draft-ietf-quic-qpack-02
o Largest Reference encoded modulo MaxEntries (#1763) o Largest Reference encoded modulo MaxEntries (#1763)
o New Static Table (#1355) o New Static Table (#1355)
o Table Size Update with Insert Count=0 is a connection error o Table Size Update with Insert Count=0 is a connection error
(#1762) (#1762)
o Stream Cancellations are optional when o Stream Cancellations are optional when
SETTINGS_HEADER_TABLE_SIZE=0 (#1761) SETTINGS_HEADER_TABLE_SIZE=0 (#1761)
skipping to change at page 36, line 4 skipping to change at page 36, line 11
o Stream Cancellations are optional when o 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) o Implementations must handle 62 bit integers (#1760)
o Different error types for each QPACK stream, other changes to o Different error types for each QPACK stream, other changes to
error handling (#1726) error handling (#1726)
o Preserve header field order (#1725) o Preserve header field order (#1725)
o Initial table size is the maximum permitted when table is first o Initial table size is the maximum permitted when table is first
usable (#1642) usable (#1642)
C.6. Since draft-ietf-quic-qpack-01 C.7. Since draft-ietf-quic-qpack-01
o Only header blocks that reference the dynamic table are o Only header blocks that reference the dynamic table are
acknowledged (#1603, #1605) acknowledged (#1603, #1605)
C.7. Since draft-ietf-quic-qpack-00 C.8. Since draft-ietf-quic-qpack-00
o Renumbered instructions for consistency (#1471, #1472) o Renumbered instructions for consistency (#1471, #1472)
o Decoder is allowed to validate largest reference (#1404, #1469) o Decoder is allowed to validate largest reference (#1404, #1469)
o Header block acknowledgments also acknowledge the associated o Header block acknowledgments also acknowledge the associated
largest reference (#1370, #1400) largest reference (#1370, #1400)
o Added an acknowledgment for unread streams (#1371, #1400) o Added an acknowledgment for unread streams (#1371, #1400)
o Removed framing from encoder stream (#1361,#1467) o Removed framing from encoder stream (#1361,#1467)
o Control streams use typed unidirectional streams rather than fixed o Control streams use typed unidirectional streams rather than fixed
stream IDs (#910,#1359) stream IDs (#910,#1359)
C.8. Since draft-ietf-quic-qcram-00 C.9. Since draft-ietf-quic-qcram-00
o 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, o Reworked indexing scheme (#1176, #1145, #1136, #1130, #1125,
#1314) #1314)
o Added mechanisms that support one-pass encoding (#1138, #1320) o Added mechanisms that support one-pass encoding (#1138, #1320)
o Added a setting to control the number of blocked decoders (#238, o Added a setting to control the number of blocked decoders (#238,
 End of changes. 104 change blocks. 
383 lines changed or deleted 371 lines changed or added

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