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<front> <front>
<title abbrev="QPACK">QPACK: Header Compression for HTTP/3</title> <title abbrev="QPACK">QPACK: Field Compression for HTTP/3</title>
<seriesInfo name="Internet-Draft" value="draft-ietf-quic-qpack-21"/> <seriesInfo name="RFC" value="9204"/>
<author initials="C." surname="Krasic" fullname="Charles 'Buck' Krasic"> <author initials="C." surname="Krasic" fullname="Charles 'Buck' Krasic">
<organization>Netflix</organization> <organization/>
<address> <address>
<email>ckrasic@netflix.com</email> <email>krasic@acm.org</email>
</address> </address>
</author> </author>
<author initials="M." surname="Bishop" fullname="Mike Bishop"> <author initials="M." surname="Bishop" fullname="Mike Bishop">
<organization>Akamai Technologies</organization> <organization>Akamai Technologies</organization>
<address> <address>
<email>mbishop@evequefou.be</email> <email>mbishop@evequefou.be</email>
</address> </address>
</author> </author>
<author initials="A." surname="Frindell" fullname="Alan Frindell" role="edit or"> <author initials="A." surname="Frindell" fullname="Alan Frindell" role="edit or">
<organization>Facebook</organization> <organization>Facebook</organization>
<address> <address>
<email>afrind@fb.com</email> <email>afrind@fb.com</email>
</address> </address>
</author> </author>
<date year="2021" month="February" day="02"/> <date year="2022" month="June"/>
<area>Transport</area> <area>Transport</area>
<workgroup>QUIC</workgroup> <workgroup>QUIC</workgroup>
<keyword>compression</keyword>
<keyword>HTTP/3</keyword>
<keyword>HPACK</keyword>
<keyword>header</keyword>
<keyword>field</keyword>
<keyword>trailer</keyword>
<abstract> <abstract>
<t>This specification defines QPACK, a compression format for efficiently <t>This specification defines QPACK: a compression format for efficiently
representing HTTP fields, to be used in HTTP/3. This is a variation of HPACK representing HTTP fields that is to be used in HTTP/3. This is a variation of
compression that seeks to reduce head-of-line blocking.</t> HPACK compression that seeks to reduce head-of-line blocking.</t>
</abstract> </abstract>
<note>
<name>Note to Readers</name>
<t>Discussion of this draft takes place on the QUIC working group mailing
list
(<eref target="mailto:quic@ietf.org">quic@ietf.org</eref>), which is archived at
<eref target="https://mailarchive.ietf.org/arch/search/?email_list=quic"/>.</t>
<t>Working Group information can be found at <eref target="https://github.
com/quicwg"/>; source
code and issues list for this draft can be found at
<eref target="https://github.com/quicwg/base-drafts/labels/-qpack"/>.</t>
</note>
</front> </front>
<middle> <middle>
<section anchor="introduction" numbered="true" toc="default"> <section anchor="introduction">
<name>Introduction</name> <name>Introduction</name>
<t>The QUIC transport protocol (<xref target="QUIC-TRANSPORT" format="defa <t>The QUIC transport protocol (<xref target="QUIC-TRANSPORT"/>) is design
ult"/>) is designed to support HTTP ed to support
semantics, and its design subsumes many of the features of HTTP/2 HTTP semantics, and its design subsumes many of the features of HTTP/2
(<xref target="RFC7540" format="default"/>). HTTP/2 uses HPACK (<xref target="RF (<xref target="HTTP2"/>). HTTP/2 uses HPACK (<xref target="RFC7541"/>) for compr
C7541" format="default"/>) for compression of the header ession of the header
and trailer sections. If HPACK were used for HTTP/3 (<xref target="HTTP3" forma and trailer sections. If HPACK were used for HTTP/3 (<xref target="HTTP3"/>), i
t="default"/>), it would t would
induce head-of-line blocking for field sections due to built-in assumptions of a induce head-of-line blocking for field sections due to built-in assumptions of a
total ordering across frames on all streams.</t> total ordering across frames on all streams.</t>
<t>QPACK reuses core concepts from HPACK, but is redesigned to allow corre ctness in <t>QPACK reuses core concepts from HPACK, but is redesigned to allow corre ctness in
the presence of out-of-order delivery, with flexibility for implementations to the presence of out-of-order delivery, with flexibility for implementations to
balance between resilience against head-of-line blocking and optimal compression balance between resilience against head-of-line blocking and optimal compression
ratio. The design goals are to closely approach the compression ratio of HPACK ratio. The design goals are to closely approach the compression ratio of HPACK
with substantially less head-of-line blocking under the same loss conditions.</t > with substantially less head-of-line blocking under the same loss conditions.</t >
<section anchor="conventions-and-definitions" numbered="true" toc="default "> <section anchor="conventions-and-definitions">
<name>Conventions and Definitions</name> <name>Conventions and Definitions</name>
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL <t>The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", 14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>", "<bcp1
"MAY", and "OPTIONAL" in this document are to be interpreted as 4>SHOULD</bcp14>",
described in BCP&nbsp;14 <xref target="RFC2119" format="default"/> <xref target= "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMEND
"RFC8174" format="default"/> when, and only when, they ED</bcp14>", "<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this
appear in all capitals, as shown here.</t> document are to be interpreted as described in BCP&nbsp;14 <xref target="RFC2119
<t>Definitions of terms that are used in this document:</t> "/> <xref target="RFC8174"/>
when, and only when, they appear in all capitals, as shown here.</t>
<t>The following terms are used in this document:</t>
<dl> <dl>
<dt> <dt>HTTP fields:</dt>
HTTP fields: </dt>
<dd> <dd>
<t>Metadata sent as part of an HTTP message. The term encompasses b oth header <t>Metadata sent as part of an HTTP message. The term encompasses b oth header
and trailer fields. Colloquially, the term "headers" has often been used to and trailer fields. Colloquially, the term "headers" has often been used to
refer to HTTP header fields and trailer fields; this document uses "fields" refer to HTTP header fields and trailer fields; this document uses "fields"
for generality.</t> for generality.</t>
</dd> </dd>
<dt> <dt>HTTP field line:</dt>
HTTP field line: </dt>
<dd> <dd>
<t>A name-value pair sent as part of an HTTP field section. See Sect ions <xref target="SEMANTICS" section="6.3" sectionFormat="bare" format="default "/> and <xref target="SEMANTICS" section="6.5" sectionFormat="bare" format="defa ult"/> of <xref target="SEMANTICS" format="default"/>.</t> <t>A name-value pair sent as part of an HTTP field section. See Sect ions <xref target="HTTP" section="6.3" sectionFormat="bare"/> and <xref target=" HTTP" section="6.5" sectionFormat="bare"/> of <xref target="HTTP"/>.</t>
</dd> </dd>
<dt> <dt>HTTP field value:</dt>
HTTP field value: </dt>
<dd> <dd>
<t>Data associated with a field name, composed from all field line v alues with <t>Data associated with a field name, composed from all field line v alues with
that field name in that section, concatenated together with that field name in that section, concatenated together with
comma separators.</t> comma separators.</t>
</dd> </dd>
<dt> <dt>Field section:</dt>
Field section: </dt>
<dd> <dd>
<t>An ordered collection of HTTP field lines associated with an HTTP message. A <t>An ordered collection of HTTP field lines associated with an HTTP message. A
field section can contain multiple field lines with the same name. It can field section can contain multiple field lines with the same name. It can
also contain duplicate field lines. An HTTP message can include both header also contain duplicate field lines. An HTTP message can include both header
and trailer sections.</t> and trailer sections.</t>
</dd> </dd>
<dt> <dt>Representation:</dt>
Representation: </dt>
<dd> <dd>
<t>An instruction that represents a field line, possibly by referenc e to the <t>An instruction that represents a field line, possibly by referenc e to the
dynamic and static tables.</t> dynamic and static tables.</t>
</dd> </dd>
<dt> <dt>Encoder:</dt>
Encoder: </dt>
<dd> <dd>
<t>An implementation that encodes field sections.</t> <t>An implementation that encodes field sections.</t>
</dd> </dd>
<dt> <dt>Decoder:</dt>
Decoder: </dt>
<dd> <dd>
<t>An implementation that decodes encoded field sections.</t> <t>An implementation that decodes encoded field sections.</t>
</dd> </dd>
<dt> <dt>Absolute Index:</dt>
Absolute Index: </dt>
<dd> <dd>
<t>A unique index for each entry in the dynamic table.</t> <t>A unique index for each entry in the dynamic table.</t>
</dd> </dd>
<dt> <dt>Base:</dt>
Base: </dt>
<dd> <dd>
<t>A reference point for relative and post-base indices. Representa tions that <t>A reference point for relative and post-Base indices. Representa tions that
reference dynamic table entries are relative to a Base.</t> reference dynamic table entries are relative to a Base.</t>
</dd> </dd>
<dt> <dt>Insert Count:</dt>
Insert Count: </dt>
<dd> <dd>
<t>The total number of entries inserted in the dynamic table.</t> <t>The total number of entries inserted in the dynamic table.</t>
</dd> </dd>
</dl> </dl>
<t>QPACK is a name, not an acronym.</t> <t>Note that QPACK is a name, not an abbreviation.</t>
</section> </section>
<section anchor="notational-conventions" numbered="true" toc="default"> <section anchor="notational-conventions">
<name>Notational Conventions</name> <name>Notational Conventions</name>
<t>Diagrams use the format described in <xref section="3.1" sectionForma <t>Diagrams in this document use the format described in <xref section="
t="of" target="RFC2360" format="default"/>, with the 3.1" sectionFormat="of" target="RFC2360"/>, with the following additional conven
following additional conventions:</t> tions:</t>
<dl> <dl>
<dt> <dt>x (A)</dt>
x (A) </dt>
<dd> <dd>
<t>Indicates that x is A bits long</t> <t>Indicates that x is A bits long.</t>
</dd> </dd>
<dt> <dt>x (A+)</dt>
x (A+) </dt>
<dd> <dd>
<t>Indicates that x uses the prefixed integer encoding defined in <t>Indicates that x uses the prefixed integer encoding defined in
<xref target="prefixed-integers" format="default"/>, beginning with an A-bit pre fix.</t> <xref target="prefixed-integers"/>, beginning with an A-bit prefix.</t>
</dd> </dd>
<dt> <dt>x ...</dt>
x ... </dt>
<dd> <dd>
<t>Indicates that x is variable-length and extends to the end of the region.</t> <t>Indicates that x is variable length and extends to the end of the region.</t>
</dd> </dd>
</dl> </dl>
</section> </section>
</section> </section>
<section anchor="compression-process-overview" numbered="true" toc="default" > <section anchor="compression-process-overview">
<name>Compression Process Overview</name> <name>Compression Process Overview</name>
<t>Like HPACK, QPACK uses two tables for associating field lines ("headers ") to <t>Like HPACK, QPACK uses two tables for associating field lines ("headers ") to
indices. The static table (<xref target="header-table-static" format="default"/ >) is predefined and contains indices. The static table (<xref target="header-table-static"/>) is predefined and contains
common header field lines (some of them with an empty value). The dynamic table common header field lines (some of them with an empty value). The dynamic table
(<xref target="header-table-dynamic" format="default"/>) is built up over the co urse of the connection and can (<xref target="header-table-dynamic"/>) is built up over the course of the conne ction and can
be used by the encoder to index both header and trailer field lines in the be used by the encoder to index both header and trailer field lines in the
encoded field sections.</t> encoded field sections.</t>
<t>QPACK defines unidirectional streams for sending instructions from enco der to <t>QPACK defines unidirectional streams for sending instructions from enco der to
decoder and vice versa.</t> decoder and vice versa.</t>
<section anchor="encoder" numbered="true" toc="default"> <section anchor="encoder">
<name>Encoder</name> <name>Encoder</name>
<t>An encoder converts a header or trailer section into a series of repr esentations <t>An encoder converts a header or trailer section into a series of repr esentations
by emitting either an indexed or a literal representation for each field line in by emitting either an indexed or a literal representation for each field line in
the list; see <xref target="field-line-representations" format="default"/>. Ind exed representations achieve the list; see <xref target="field-line-representations"/>. Indexed representati ons achieve
high compression by replacing the literal name and possibly the value with an high compression by replacing the literal name and possibly the value with an
index to either the static or dynamic table. References to the static table and index to either the static or dynamic table. References to the static table and
literal representations do not require any dynamic state and never risk literal representations do not require any dynamic state and never risk
head-of-line blocking. References to the dynamic table risk head-of-line head-of-line blocking. References to the dynamic table risk head-of-line
blocking if the encoder has not received an acknowledgment indicating the entry blocking if the encoder has not received an acknowledgment indicating the entry
is available at the decoder.</t> is available at the decoder.</t>
<t>An encoder MAY insert any entry in the dynamic table it chooses; it i s not <t>An encoder <bcp14>MAY</bcp14> insert any entry in the dynamic table i t chooses; it is not
limited to field lines it is compressing.</t> limited to field lines it is compressing.</t>
<t>QPACK preserves the ordering of field lines within each field section . An <t>QPACK preserves the ordering of field lines within each field section . An
encoder MUST emit field representations in the order they appear in the input encoder <bcp14>MUST</bcp14> emit field representations in the order they appear in the input
field section.</t> field section.</t>
<t>QPACK is designed to contain the more complex state tracking to the e <t>QPACK is designed to place the burden of optional state tracking on t
ncoder, he encoder,
while the decoder is relatively simple.</t> resulting in relatively simple decoders.</t>
<section anchor="blocked-insertion" numbered="true" toc="default"> <section anchor="blocked-insertion">
<name>Limits on Dynamic Table Insertions</name> <name>Limits on Dynamic Table Insertions</name>
<t>Inserting entries into the dynamic table might not be possible if t he table <t>Inserting entries into the dynamic table might not be possible if t he table
contains entries that cannot be evicted.</t> contains entries that cannot be evicted.</t>
<t>A dynamic table entry cannot be evicted immediately after insertion , even if it <t>A dynamic table entry cannot be evicted immediately after insertion , even if it
has never been referenced. Once the insertion of a dynamic table entry has been has never been referenced. Once the insertion of a dynamic table entry has been
acknowledged and there are no outstanding references to the entry in acknowledged and there are no outstanding references to the entry in
unacknowledged representations, the entry becomes evictable. Note that unacknowledged representations, the entry becomes evictable. Note that
references on the encoder stream never preclude the eviction of an entry, references on the encoder stream never preclude the eviction of an entry,
because those references are guaranteed to be processed before the instruction because those references are guaranteed to be processed before the instruction
evicting the entry.</t> evicting the entry.</t>
<t>If the dynamic table does not contain enough room for a new entry w ithout <t>If the dynamic table does not contain enough room for a new entry w ithout
evicting other entries, and the entries that would be evicted are not evicting other entries, and the entries that would be evicted are not
evictable, the encoder MUST NOT insert that entry into the dynamic table evictable, the encoder <bcp14>MUST NOT</bcp14> insert that entry into the dynami c table
(including duplicates of existing entries). In order to avoid this, an encoder (including duplicates of existing entries). In order to avoid this, an encoder
that uses the dynamic table has to keep track of each dynamic table entry that uses the dynamic table has to keep track of each dynamic table entry
referenced by each field section until those representations are acknowledged by referenced by each field section until those representations are acknowledged by
the decoder; see <xref target="header-acknowledgment" format="default"/>.</t> the decoder; see <xref target="header-acknowledgment"/>.</t>
<section anchor="avoiding-prohibited-insertions" numbered="true" toc=" <section anchor="avoiding-prohibited-insertions">
default">
<name>Avoiding Prohibited Insertions</name> <name>Avoiding Prohibited Insertions</name>
<t>To ensure that the encoder is not prevented from adding new entri es, the encoder <t>To ensure that the encoder is not prevented from adding new entri es, the encoder
can avoid referencing entries that are close to eviction. Rather than can avoid referencing entries that are close to eviction. Rather than
reference such an entry, the encoder can emit a Duplicate instruction reference such an entry, the encoder can emit a Duplicate instruction
(<xref target="duplicate" format="default"/>), and reference the duplicate inste ad.</t> (<xref target="duplicate"/>) and reference the duplicate instead.</t>
<t>Determining which entries are too close to eviction to reference is an encoder <t>Determining which entries are too close to eviction to reference is an encoder
preference. One heuristic is to target a fixed amount of available space in the preference. One heuristic is to target a fixed amount of available space in the
dynamic table: either unused space or space that can be reclaimed by evicting dynamic table: either unused space or space that can be reclaimed by evicting
non-blocking entries. To achieve this, the encoder can maintain a draining non-blocking entries. To achieve this, the encoder can maintain a draining
index, which is the smallest absolute index (<xref target="indexing" format="def ault"/>) in the dynamic table index, which is the smallest absolute index (<xref target="indexing"/>) in the d ynamic table
that it will emit a reference for. As new entries are inserted, the encoder that it will emit a reference for. As new entries are inserted, the encoder
increases the draining index to maintain the section of the table that it will increases the draining index to maintain the section of the table that it will
not reference. If the encoder does not create new references to entries with an not reference. If the encoder does not create new references to entries with an
absolute index lower than the draining index, the number of unacknowledged absolute index lower than the draining index, the number of unacknowledged
references to those entries will eventually become zero, allowing them to be references to those entries will eventually become zero, allowing them to be
evicted.</t> evicted.</t>
<figure anchor="fig-draining-index"> <figure anchor="fig-draining-index">
<name>Draining Dynamic Table Entries</name> <name>Draining Dynamic Table Entries</name>
<artwork type="drawing" name="" align="left" alt=""><![CDATA[ <artwork type="ascii-art"><![CDATA[
<-- Newer Entries Older Entries --> <-- Newer Entries Older Entries -->
(Larger Indicies) (Smaller Indicies) (Larger Indices) (Smaller Indices)
+--------+---------------------------------+----------+ +--------+---------------------------------+----------+
| Unused | Referenceable | Draining | | Unused | Referenceable | Draining |
| Space | Entries | Entries | | Space | Entries | Entries |
+--------+---------------------------------+----------+ +--------+---------------------------------+----------+
^ ^ ^ ^ ^ ^
| | | | | |
Insertion Point Draining Index Dropping Insertion Point Draining Index Dropping
Point Point
]]></artwork> ]]></artwork>
</figure> </figure>
</section> </section>
</section> </section>
<section anchor="blocked-streams" numbered="true" toc="default"> <section anchor="blocked-streams">
<name>Blocked Streams</name> <name>Blocked Streams</name>
<t>Because QUIC does not guarantee order between data on different str eams, a <t>Because QUIC does not guarantee order between data on different str eams, a
decoder might encounter a representation that references a dynamic table entry decoder might encounter a representation that references a dynamic table entry
that it has not yet received.</t> that it has not yet received.</t>
<t>Each encoded field section contains a Required Insert Count (<xref target="header-prefix" format="default"/>), <t>Each encoded field section contains a Required Insert Count (<xref target="header-prefix"/>),
the lowest possible value for the Insert Count with which the field section can the lowest possible value for the Insert Count with which the field section can
be decoded. For a field section encoded using references to the dynamic table, be decoded. For a field section encoded using references to the dynamic table,
the Required Insert Count is one larger than the largest absolute index of all the Required Insert Count is one larger than the largest absolute index of all
referenced dynamic table entries. For a field section encoded with no references referenced dynamic table entries. For a field section encoded with no references
to the dynamic table, the Required Insert Count is zero.</t> to the dynamic table, the Required Insert Count is zero.</t>
<t>When the decoder receives an encoded field section with a Required Insert Count <t>When the decoder receives an encoded field section with a Required Insert Count
greater than its own Insert Count, the stream cannot be processed immediately, greater than its own Insert Count, the stream cannot be processed immediately
and is considered "blocked"; see <xref target="blocked-decoding" format="default and is considered "blocked"; see <xref target="blocked-decoding"/>.</t>
"/>.</t>
<t>The decoder specifies an upper bound on the number of streams that can be <t>The decoder specifies an upper bound on the number of streams that can be
blocked using the SETTINGS_QPACK_BLOCKED_STREAMS setting; see <xref target="conf blocked using the SETTINGS_QPACK_BLOCKED_STREAMS setting; see <xref target="conf
iguration" format="default"/>. iguration"/>.
An encoder MUST limit the number of streams that could become blocked to the An encoder <bcp14>MUST</bcp14> limit the number of streams that could become blo
cked to the
value of SETTINGS_QPACK_BLOCKED_STREAMS at all times. If a decoder encounters value of SETTINGS_QPACK_BLOCKED_STREAMS at all times. If a decoder encounters
more blocked streams than it promised to support, it MUST treat this as a more blocked streams than it promised to support, it <bcp14>MUST</bcp14> treat t his as a
connection error of type QPACK_DECOMPRESSION_FAILED.</t> connection error of type QPACK_DECOMPRESSION_FAILED.</t>
<t>Note that the decoder might not become blocked on every stream that risks <t>Note that the decoder might not become blocked on every stream that risks
becoming blocked.</t> becoming blocked.</t>
<t>An encoder can decide whether to risk having a stream become blocke d. If <t>An encoder can decide whether to risk having a stream become blocke d. If
permitted by the value of SETTINGS_QPACK_BLOCKED_STREAMS, compression efficiency permitted by the value of SETTINGS_QPACK_BLOCKED_STREAMS, compression efficiency
can often be improved by referencing dynamic table entries that are still in can often be improved by referencing dynamic table entries that are still in
transit, but if there is loss or reordering the stream can become blocked at the transit, but if there is loss or reordering, the stream can become blocked at
decoder. An encoder can avoid the risk of blocking by only referencing dynamic the decoder. An encoder can avoid the risk of blocking by only referencing
table entries that have been acknowledged, but this could mean using literals. dynamic table entries that have been acknowledged, but this could mean using
Since literals make the encoded field section larger, this can result in the literals. Since literals make the encoded field section larger, this can result
encoder becoming blocked on congestion or flow control limits.</t> in the encoder becoming blocked on congestion or flow-control limits.</t>
</section> </section>
<section anchor="avoiding-flow-control-deadlocks" numbered="true" toc="d <section anchor="avoiding-flow-control-deadlocks">
efault"> <name>Avoiding Flow-Control Deadlocks</name>
<name>Avoiding Flow Control Deadlocks</name>
<t>Writing instructions on streams that are limited by flow control ca n produce <t>Writing instructions on streams that are limited by flow control ca n produce
deadlocks.</t> deadlocks.</t>
<t>A decoder might stop issuing flow control credit on the stream that carries an <t>A decoder might stop issuing flow-control credit on the stream that carries an
encoded field section until the necessary updates are received on the encoder encoded field section until the necessary updates are received on the encoder
stream. If the granting of flow control credit on the encoder stream (or the stream. If the granting of flow-control credit on the encoder stream (or the
connection as a whole) depends on the consumption and release of data on the connection as a whole) depends on the consumption and release of data on the
stream carrying the encoded field section, a deadlock might result.</t> stream carrying the encoded field section, a deadlock might result.</t>
<t>More generally, a stream containing a large instruction can become deadlocked if <t>More generally, a stream containing a large instruction can become deadlocked if
the decoder withholds flow control credit until the instruction is completely the decoder withholds flow-control credit until the instruction is completely
received.</t> received.</t>
<t>To avoid these deadlocks, an encoder SHOULD NOT write an instructio <t>To avoid these deadlocks, an encoder <bcp14>SHOULD NOT</bcp14> writ
n unless e an instruction unless
sufficient stream and connection flow control credit is available for the entire sufficient stream and connection flow-control credit is available for the entire
instruction.</t> instruction.</t>
</section> </section>
<section anchor="known-received-count" numbered="true" toc="default"> <section anchor="known-received-count">
<name>Known Received Count</name> <name>Known Received Count</name>
<t>The Known Received Count is the total number of dynamic table inser tions and <t>The Known Received Count is the total number of dynamic table inser tions and
duplications acknowledged by the decoder. The encoder tracks the Known Received duplications acknowledged by the decoder. The encoder tracks the Known Received
Count in order to identify which dynamic table entries can be referenced without Count in order to identify which dynamic table entries can be referenced without
potentially blocking a stream. The decoder tracks the Known Received Count in potentially blocking a stream. The decoder tracks the Known Received Count in
order to be able to send Insert Count Increment instructions.</t> order to be able to send Insert Count Increment instructions.</t>
<t>A Section Acknowledgment instruction (<xref target="header-acknowle dgment" format="default"/>) implies that <t>A Section Acknowledgment instruction (<xref target="header-acknowle dgment"/>) implies that
the decoder has received all dynamic table state necessary to decode the field the decoder has received all dynamic table state necessary to decode the field
section. If the Required Insert Count of the acknowledged field section is section. If the Required Insert Count of the acknowledged field section is
greater than the current Known Received Count, Known Received Count is updated greater than the current Known Received Count, the Known Received Count is
to that Required Insert Count value.</t> updated to that Required Insert Count value.</t>
<t>An Insert Count Increment instruction (<xref target="insert-count-i <t>An Insert Count Increment instruction (<xref target="insert-count-i
ncrement" format="default"/>) increases the ncrement"/>) increases the
Known Received Count by its Increment parameter. See <xref target="new-table-en Known Received Count by its Increment parameter. See <xref target="new-table-en
tries" format="default"/> for tries"/> for
guidance.</t> guidance.</t>
</section> </section>
</section> </section>
<section anchor="decoder" numbered="true" toc="default"> <section anchor="decoder">
<name>Decoder</name> <name>Decoder</name>
<t>As in HPACK, the decoder processes a series of representations and em its the <t>As in HPACK, the decoder processes a series of representations and em its the
corresponding field sections. It also processes instructions received on the corresponding field sections. It also processes instructions received on the
encoder stream that modify the dynamic table. Note that encoded field sections encoder stream that modify the dynamic table. Note that encoded field sections
and encoder stream instructions arrive on separate streams. This is unlike and encoder stream instructions arrive on separate streams. This is unlike
HPACK, where encoded field sections (header blocks) can contain instructions HPACK, where encoded field sections (header blocks) can contain instructions
that modify the dynamic table, and there is no dedicated stream of HPACK that modify the dynamic table, and there is no dedicated stream of HPACK
instructions.</t> instructions.</t>
<t>The decoder MUST emit field lines in the order their representations appear in <t>The decoder <bcp14>MUST</bcp14> emit field lines in the order their r epresentations appear in
the encoded field section.</t> the encoded field section.</t>
<section anchor="blocked-decoding" numbered="true" toc="default"> <section anchor="blocked-decoding">
<name>Blocked Decoding</name> <name>Blocked Decoding</name>
<t>Upon receipt of an encoded field section, the decoder examines the Required <t>Upon receipt of an encoded field section, the decoder examines the Required
Insert Count. When the Required Insert Count is less than or equal to the Insert Count. When the Required Insert Count is less than or equal to the
decoder's Insert Count, the field section can be processed immediately. decoder's Insert Count, the field section can be processed immediately.
Otherwise, the stream on which the field section was received becomes blocked.</ t> Otherwise, the stream on which the field section was received becomes blocked.</ t>
<t>While blocked, encoded field section data SHOULD remain in the bloc <t>While blocked, encoded field section data <bcp14>SHOULD</bcp14> rem
ked stream's ain in the blocked stream's
flow control window. This data is unusable until the stream becomes unblocked, flow-control window. This data is unusable until the stream becomes unblocked,
and releasing the flow control prematurely makes the decoder vulnerable to and releasing the flow control prematurely makes the decoder vulnerable to
memory exhaustion attacks. A stream becomes unblocked when the Insert Count memory exhaustion attacks. A stream becomes unblocked when the Insert Count
becomes unblocked when the Insert Count becomes greater than or equal to the becomes greater than or equal to the Required Insert Count for all encoded
Required Insert Count for all encoded field sections the decoder has started field sections the decoder has started reading from the stream.</t>
reading from the stream.</t>
<t>When processing encoded field sections, the decoder expects the Req uired Insert <t>When processing encoded field sections, the decoder expects the Req uired Insert
Count to equal the lowest possible value for the Insert Count with which the Count to equal the lowest possible value for the Insert Count with which the
field section can be decoded, as prescribed in <xref target="blocked-streams" fo field section can be decoded, as prescribed in <xref target="blocked-streams"/>.
rmat="default"/>. If it If it
encounters a Required Insert Count smaller than expected, it MUST treat this as encounters a Required Insert Count smaller than expected, it <bcp14>MUST</bcp14>
treat this as
a connection error of type QPACK_DECOMPRESSION_FAILED; see a connection error of type QPACK_DECOMPRESSION_FAILED; see
<xref target="invalid-references" format="default"/>. If it encounters a Require <xref target="invalid-references"/>. If it encounters a Required Insert Count la
d Insert Count larger than rger than
expected, it MAY treat this as a connection error of type expected, it <bcp14>MAY</bcp14> treat this as a connection error of type
QPACK_DECOMPRESSION_FAILED.</t> QPACK_DECOMPRESSION_FAILED.</t>
</section> </section>
<section anchor="state-synchronization" numbered="true" toc="default"> <section anchor="state-synchronization">
<name>State Synchronization</name> <name>State Synchronization</name>
<t>The decoder signals the following events by emitting decoder instru ctions <t>The decoder signals the following events by emitting decoder instru ctions
(<xref target="decoder-instructions" format="default"/>) on the decoder stream.< (<xref target="decoder-instructions"/>) on the decoder stream.</t>
/t> <section anchor="completed-processing-of-a-field-section">
<section anchor="completed-processing-of-a-field-section" numbered="tr
ue" toc="default">
<name>Completed Processing of a Field Section</name> <name>Completed Processing of a Field Section</name>
<t>After the decoder finishes decoding a field section encoded using <t>After the decoder finishes decoding a field section encoded using
representations containing dynamic table references, it MUST emit a Section representations containing dynamic table references, it <bcp14>MUST</bcp14> emit
Acknowledgment instruction (<xref target="header-acknowledgment" format="default a Section
"/>). A stream may carry Acknowledgment instruction (<xref target="header-acknowledgment"/>). A stream m
ay carry
multiple field sections in the case of intermediate responses, trailers, and multiple field sections in the case of intermediate responses, trailers, and
pushed requests. The encoder interprets each Section Acknowledgment pushed requests. The encoder interprets each Section Acknowledgment
instruction as acknowledging the earliest unacknowledged field section instruction as acknowledging the earliest unacknowledged field section
containing dynamic table references sent on the given stream.</t> containing dynamic table references sent on the given stream.</t>
</section> </section>
<section anchor="abandonment-of-a-stream" numbered="true" toc="default "> <section anchor="abandonment-of-a-stream">
<name>Abandonment of a Stream</name> <name>Abandonment of a Stream</name>
<t>When an endpoint receives a stream reset before the end of a stre am or before <t>When an endpoint receives a stream reset before the end of a stre am or before
all encoded field sections are processed on that stream, or when it abandons all encoded field sections are processed on that stream, or when it abandons
reading of a stream, it generates a Stream Cancellation instruction; see reading of a stream, it generates a Stream Cancellation instruction; see
<xref target="stream-cancellation" format="default"/>. This signals to the enco der that all references to the <xref target="stream-cancellation"/>. This signals to the encoder that all refe rences to the
dynamic table on that stream are no longer outstanding. A decoder with a dynamic table on that stream are no longer outstanding. A decoder with a
maximum dynamic table capacity (<xref target="maximum-dynamic-table-capacity" fo maximum dynamic table capacity (<xref target="maximum-dynamic-table-capacity"/>)
rmat="default"/>) equal to equal to
zero MAY omit sending Stream Cancellations, because the encoder cannot have any zero <bcp14>MAY</bcp14> omit sending Stream Cancellations, because the encoder c
annot have any
dynamic table references. An encoder cannot infer from this instruction that dynamic table references. An encoder cannot infer from this instruction that
any updates to the dynamic table have been received.</t> any updates to the dynamic table have been received.</t>
<t>The Section Acknowledgment and Stream Cancellation instructions p ermit the <t>The Section Acknowledgment and Stream Cancellation instructions p ermit the
encoder to remove references to entries in the dynamic table. When an entry encoder to remove references to entries in the dynamic table. When an entry
with absolute index lower than the Known Received Count has zero references, with an absolute index lower than the Known Received Count has zero references,
then it is considered evictable; see <xref target="blocked-insertion" format="de then it is considered evictable; see <xref target="blocked-insertion"/>.</t>
fault"/>.</t>
</section> </section>
<section anchor="new-table-entries" numbered="true" toc="default"> <section anchor="new-table-entries">
<name>New Table Entries</name> <name>New Table Entries</name>
<t>After receiving new table entries on the encoder stream, the deco der chooses <t>After receiving new table entries on the encoder stream, the deco der chooses
when to emit Insert Count Increment instructions; see when to emit Insert Count Increment instructions; see
<xref target="insert-count-increment" format="default"/>. Emitting this instruct ion after adding each new <xref target="insert-count-increment"/>. Emitting this instruction after adding each new
dynamic table entry will provide the timeliest feedback to the encoder, but dynamic table entry will provide the timeliest feedback to the encoder, but
could be redundant with other decoder feedback. By delaying an Insert Count could be redundant with other decoder feedback. By delaying an Insert Count
Increment instruction, the decoder might be able to coalesce multiple Insert Increment instruction, the decoder might be able to coalesce multiple Insert
Count Increment instructions, or replace them entirely with Section Count Increment instructions or replace them entirely with Section
Acknowledgments; see <xref target="header-acknowledgment" format="default"/>. Ho Acknowledgments; see <xref target="header-acknowledgment"/>. However, delaying t
wever, delaying too long oo long
may lead to compression inefficiencies if the encoder waits for an entry to be may lead to compression inefficiencies if the encoder waits for an entry to be
acknowledged before using it.</t> acknowledged before using it.</t>
</section> </section>
</section> </section>
<section anchor="invalid-references" numbered="true" toc="default"> <section anchor="invalid-references">
<name>Invalid References</name> <name>Invalid References</name>
<t>If the decoder encounters a reference in a field line representatio n to a <t>If the decoder encounters a reference in a field line representatio n to a
dynamic table entry that has already been evicted or that has an absolute dynamic table entry that has already been evicted or that has an absolute
index greater than or equal to the declared Required Insert Count index greater than or equal to the declared Required Insert Count
(<xref target="header-prefix" format="default"/>), it MUST treat this as a conne ction error of type (<xref target="header-prefix"/>), it <bcp14>MUST</bcp14> treat this as a connect ion error of type
QPACK_DECOMPRESSION_FAILED.</t> QPACK_DECOMPRESSION_FAILED.</t>
<t>If the decoder encounters a reference in an encoder instruction to a dynamic <t>If the decoder encounters a reference in an encoder instruction to a dynamic
table entry that has already been evicted, it MUST treat this as a connection table entry that has already been evicted, it <bcp14>MUST</bcp14> treat this as a connection
error of type QPACK_ENCODER_STREAM_ERROR.</t> error of type QPACK_ENCODER_STREAM_ERROR.</t>
</section> </section>
</section> </section>
</section> </section>
<section anchor="reference-tables" numbered="true" toc="default"> <section anchor="reference-tables">
<name>Reference Tables</name> <name>Reference Tables</name>
<t>Unlike in HPACK, entries in the QPACK static and dynamic tables are add ressed <t>Unlike in HPACK, entries in the QPACK static and dynamic tables are add ressed
separately. The following sections describe how entries in each table are separately. The following sections describe how entries in each table are
addressed.</t> addressed.</t>
<section anchor="header-table-static" numbered="true" toc="default"> <section anchor="header-table-static">
<name>Static Table</name> <name>Static Table</name>
<t>The static table consists of a predefined list of field lines, each o f which has <t>The static table consists of a predefined list of field lines, each o f which has
a fixed index over time. Its entries are defined in <xref target="static-table" format="default"/>.</t> a fixed index over time. Its entries are defined in <xref target="static-table" />.</t>
<t>All entries in the static table have a name and a value. However, va lues can be <t>All entries in the static table have a name and a value. However, va lues can be
empty (that is, have a length of 0). Each entry is identified by a unique empty (that is, have a length of 0). Each entry is identified by a unique
index.</t> index.</t>
<t>Note that the QPACK static table is indexed from 0, whereas the HPACK static <t>Note that the QPACK static table is indexed from 0, whereas the HPACK static
table is indexed from 1.</t> table is indexed from 1.</t>
<t>When the decoder encounters an invalid static table index in a field line <t>When the decoder encounters an invalid static table index in a field line
representation it MUST treat this as a connection error of type representation, it <bcp14>MUST</bcp14> treat this as a connection error of type
QPACK_DECOMPRESSION_FAILED. If this index is received on the encoder stream, QPACK_DECOMPRESSION_FAILED. If this index is received on the encoder stream,
this MUST be treated as a connection error of type QPACK_ENCODER_STREAM_ERROR.</ t> this <bcp14>MUST</bcp14> be treated as a connection error of type QPACK_ENCODER_ STREAM_ERROR.</t>
</section> </section>
<section anchor="header-table-dynamic" numbered="true" toc="default"> <section anchor="header-table-dynamic">
<name>Dynamic Table</name> <name>Dynamic Table</name>
<t>The dynamic table consists of a list of field lines maintained in fir st-in, <t>The dynamic table consists of a list of field lines maintained in fir st-in,
first-out order. A QPACK encoder and decoder share a dynamic table that is first-out order. A QPACK encoder and decoder share a dynamic table that is
initially empty. The encoder adds entries to the dynamic table and sends them initially empty. The encoder adds entries to the dynamic table and sends them
to the decoder via instructions on the encoder stream; see to the decoder via instructions on the encoder stream; see
<xref target="encoder-instructions" format="default"/>.</t> <xref target="encoder-instructions"/>.</t>
<t>The dynamic table can contain duplicate entries (i.e., entries with t he same <t>The dynamic table can contain duplicate entries (i.e., entries with t he same
name and same value). Therefore, duplicate entries MUST NOT be treated as an name and same value). Therefore, duplicate entries <bcp14>MUST NOT</bcp14> be t reated as an
error by the decoder.</t> error by the decoder.</t>
<t>Dynamic table entries can have empty values.</t> <t>Dynamic table entries can have empty values.</t>
<section anchor="dynamic-table-size" numbered="true" toc="default"> <section anchor="dynamic-table-size">
<name>Dynamic Table Size</name> <name>Dynamic Table Size</name>
<t>The size of the dynamic table is the sum of the size of its entries .</t> <t>The size of the dynamic table is the sum of the size of its entries .</t>
<t>The size of an entry is the sum of its name's length in bytes, its value's <t>The size of an entry is the sum of its name's length in bytes, its value's
length in bytes, and 32 additional bytes. The size of an entry is calculated length in bytes, and 32 additional bytes. The size of an entry is calculated
using the length of its name and value without Huffman encoding applied.</t> using the length of its name and value without Huffman encoding applied.</t>
</section> </section>
<section anchor="eviction" numbered="true" toc="default"> <section anchor="eviction">
<name>Dynamic Table Capacity and Eviction</name> <name>Dynamic Table Capacity and Eviction</name>
<t>The encoder sets the capacity of the dynamic table, which serves as the upper <t>The encoder sets the capacity of the dynamic table, which serves as the upper
limit on its size. The initial capacity of the dynamic table is zero. The limit on its size. The initial capacity of the dynamic table is zero. The
encoder sends a Set Dynamic Table Capacity instruction encoder sends a Set Dynamic Table Capacity instruction
(<xref target="set-dynamic-capacity" format="default"/>) with a non-zero capacit y to begin using the dynamic (<xref target="set-dynamic-capacity"/>) with a non-zero capacity to begin using the dynamic
table.</t> table.</t>
<t>Before a new entry is added to the dynamic table, entries are evict ed from the <t>Before a new entry is added to the dynamic table, entries are evict ed from the
end of the dynamic table until the size of the dynamic table is less than or end of the dynamic table until the size of the dynamic table is less than or
equal to (table capacity - size of new entry). The encoder MUST NOT cause a equal to (table capacity - size of new entry). The encoder <bcp14>MUST NOT</bcp1 4> cause a
dynamic table entry to be evicted unless that entry is evictable; see dynamic table entry to be evicted unless that entry is evictable; see
<xref target="blocked-insertion" format="default"/>. The new entry is then adde d to the table. It is an <xref target="blocked-insertion"/>. The new entry is then added to the table. It is an
error if the encoder attempts to add an entry that is larger than the dynamic 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 error of type table capacity; the decoder <bcp14>MUST</bcp14> treat this as a connection error of type
QPACK_ENCODER_STREAM_ERROR.</t> QPACK_ENCODER_STREAM_ERROR.</t>
<t>A new entry can reference an entry in the dynamic table that will b e evicted <t>A new entry can reference an entry in the dynamic table that will b e evicted
when adding this new entry into the dynamic table. Implementations are when adding this new entry into the dynamic table. Implementations are
cautioned to avoid deleting the referenced name or value if the referenced entry cautioned to avoid deleting the referenced name or value if the referenced entry
is evicted from the dynamic table prior to inserting the new entry.</t> is evicted from the dynamic table prior to inserting the new entry.</t>
<t>Whenever the dynamic table capacity is reduced by the encoder <t>Whenever the dynamic table capacity is reduced by the encoder
(<xref target="set-dynamic-capacity" format="default"/>), entries are evicted fr om the end of the dynamic (<xref target="set-dynamic-capacity"/>), entries are evicted from the end of the dynamic
table until the size of the dynamic table is less than or equal to the new table table until the size of the dynamic table is less than or equal to the new table
capacity. This mechanism can be used to completely clear entries from the capacity. This mechanism can be used to completely clear entries from the
dynamic table by setting a capacity of 0, which can subsequently be restored.</t > dynamic table by setting a capacity of 0, which can subsequently be restored.</t >
</section> </section>
<section anchor="maximum-dynamic-table-capacity" numbered="true" toc="de fault"> <section anchor="maximum-dynamic-table-capacity">
<name>Maximum Dynamic Table Capacity</name> <name>Maximum Dynamic Table Capacity</name>
<t>To bound the memory requirements of the decoder, the decoder limits the maximum <t>To bound the memory requirements of the decoder, the decoder limits the maximum
value the encoder is permitted to set for the dynamic table capacity. In value the encoder is permitted to set for the dynamic table capacity. In
HTTP/3, this limit is determined by the value of HTTP/3, this limit is determined by the value of
SETTINGS_QPACK_MAX_TABLE_CAPACITY sent by the decoder; see <xref target="configu SETTINGS_QPACK_MAX_TABLE_CAPACITY sent by the decoder; see <xref target="configu
ration" format="default"/>. ration"/>.
The encoder MUST NOT set a dynamic table capacity that exceeds this maximum, but The encoder <bcp14>MUST NOT</bcp14> set a dynamic table capacity that exceeds th
is maximum, but
it can choose to use a lower dynamic table capacity; see it can choose to use a lower dynamic table capacity; see
<xref target="set-dynamic-capacity" format="default"/>.</t> <xref target="set-dynamic-capacity"/>.</t>
<t>For clients using 0-RTT data in HTTP/3, the server's maximum table capacity is <t>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 was not previously the remembered value of the setting or zero if the value was not previously
sent. When the client's 0-RTT value of the SETTING is zero, the server MAY set sent. When the client's 0-RTT value of the SETTING is zero, the server <bcp14>M
AY</bcp14> set
it to a non-zero value in its SETTINGS frame. If the remembered value is it to a non-zero value in its SETTINGS frame. If the remembered value is
non-zero, the server MUST send the same non-zero value in its SETTINGS frame. If non-zero, the server <bcp14>MUST</bcp14> send the same non-zero value in its SET TINGS frame. If
it specifies any other value, or omits SETTINGS_QPACK_MAX_TABLE_CAPACITY from it specifies 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
QPACK_DECODER_STREAM_ERROR.</t> QPACK_DECODER_STREAM_ERROR.</t>
<t>For HTTP/3 servers and HTTP/3 clients when 0-RTT is not attempted o <t>For clients not using 0-RTT data (whether 0-RTT is not attempted or
r is is rejected)
rejected, the maximum table capacity is 0 until the encoder processes a SETTINGS and for all HTTP/3 servers, the maximum table capacity is 0 until the encoder
frame with a non-zero value of SETTINGS_QPACK_MAX_TABLE_CAPACITY.</t> processes a SETTINGS frame with a non-zero value of
<t>When the maximum table capacity is zero, the encoder MUST NOT inser SETTINGS_QPACK_MAX_TABLE_CAPACITY.</t>
t entries <t>When the maximum table capacity is zero, the encoder <bcp14>MUST NO
into the dynamic table, and MUST NOT send any encoder instructions on the T</bcp14> insert entries
encoder stream.</t> into the dynamic table and <bcp14>MUST NOT</bcp14> send any encoder instructions
on the encoder
stream.</t>
</section> </section>
<section anchor="indexing" numbered="true" toc="default"> <section anchor="indexing">
<name>Absolute Indexing</name> <name>Absolute Indexing</name>
<t>Each entry possesses an absolute index that is fixed for the lifeti me of that <t>Each entry possesses an absolute index that is fixed for the lifeti me of that
entry. The first entry inserted has an absolute index of 0; indices increase entry. The first entry inserted has an absolute index of 0; indices increase
by one with each insertion.</t> by one with each insertion.</t>
</section> </section>
<section anchor="relative-indexing" numbered="true" toc="default"> <section anchor="relative-indexing">
<name>Relative Indexing</name> <name>Relative Indexing</name>
<t>Relative indices begin at zero and increase in the opposite directi on from the <t>Relative indices begin at zero and increase in the opposite directi on from the
absolute index. Determining which entry has a relative index of 0 depends on absolute index. Determining which entry has a relative index of 0 depends on
the context of the reference.</t> the context of the reference.</t>
<t>In encoder instructions (<xref target="encoder-instructions" format ="default"/>), a relative index of 0 <t>In encoder instructions (<xref target="encoder-instructions"/>), a relative index of 0
refers to the most recently inserted value in the dynamic table. Note that this refers to the most recently inserted value in the dynamic table. Note that this
means the entry referenced by a given relative index will change while means the entry referenced by a given relative index will change while
interpreting instructions on the encoder stream.</t> interpreting instructions on the encoder stream.</t>
<figure> <figure>
<name>Example Dynamic Table Indexing - Encoder Stream</name> <name>Example Dynamic Table Indexing - Encoder Stream</name>
<artwork type="drawing" name="" align="left" alt=""><![CDATA[ <artwork type="ascii-art"><![CDATA[
+-----+---------------+-------+ +-----+---------------+-------+
| 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
]]></artwork> ]]></artwork>
</figure> </figure>
<t>Unlike in encoder instructions, relative indices in field line repr esentations <t>Unlike in encoder instructions, relative indices in field line repr esentations
are relative to the Base at the beginning of the encoded field section; see are relative to the Base at the beginning of the encoded field section; see
<xref target="header-prefix" format="default"/>. This ensures that references ar e stable even if encoded field <xref target="header-prefix"/>. This ensures that references are stable even if encoded field
sections and dynamic table updates are processed out of order.</t> sections and dynamic table updates are processed out of order.</t>
<t>In a field line representation, a relative index of 0 refers to the entry with <t>In a field line representation, a relative index of 0 refers to the entry with
absolute index equal to Base - 1.</t> absolute index equal to Base - 1.</t>
<figure> <figure>
<name>Example Dynamic Table Indexing - Relative Index in Representat ion</name> <name>Example Dynamic Table Indexing - Relative Index in Representat ion</name>
<artwork type="drawing" name="" align="left" alt=""><![CDATA[ <artwork type="ascii-art"><![CDATA[
Base Base
| |
V V
+-----+-----+-----+-----+-------+ +-----+-----+-----+-----+-------+
| n-1 | n-2 | n-3 | ... | d | Absolute Index | n-1 | n-2 | n-3 | ... | d | Absolute Index
+-----+-----+ - +-----+ - + +-----+-----+ - +-----+ - +
| 0 | ... | n-d-3 | Relative Index | 0 | ... | n-d-3 | Relative Index
+-----+-----+-------+ +-----+-----+-------+
n = count of entries inserted n = count of entries inserted
d = count of entries dropped d = count of entries dropped
In this example, Base = n - 2 In this example, Base = n - 2
]]></artwork> ]]></artwork>
</figure> </figure>
</section> </section>
<section anchor="post-base" numbered="true" toc="default"> <section anchor="post-base">
<name>Post-Base Indexing</name> <name>Post-Base Indexing</name>
<t>Post-Base indices are used in field line representations for entrie s with <t>Post-Base indices are used in field line representations for entrie s with
absolute indices greater than or equal to Base, starting at 0 for the entry with absolute indices greater 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 equal to Base and increasing in the same direction as the
absolute index.</t> absolute index.</t>
<t>Post-Base indices allow an encoder to process a field section in a single pass <t>Post-Base indices allow an encoder to process a field section in a single pass
and include references to entries added while processing this (or other) field and include references to entries added while processing this (or other) field
sections.</t> sections.</t>
<figure> <figure>
<name>Example Dynamic Table Indexing - Post-Base Index in Representa tion</name> <name>Example Dynamic Table Indexing - Post-Base Index in Representa tion</name>
<artwork type="drawing" name="" align="left" alt=""><![CDATA[ <artwork type="ascii-art"><![CDATA[
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
In this example, Base = n - 2 In this example, Base = n - 2
]]></artwork> ]]></artwork>
</figure> </figure>
</section> </section>
</section> </section>
</section> </section>
<section anchor="wire-format" numbered="true" toc="default"> <section anchor="wire-format">
<name>Wire Format</name> <name>Wire Format</name>
<section anchor="primitives" numbered="true" toc="default"> <section anchor="primitives">
<name>Primitives</name> <name>Primitives</name>
<section anchor="prefixed-integers" numbered="true" toc="default"> <section anchor="prefixed-integers">
<name>Prefixed Integers</name> <name>Prefixed Integers</name>
<t>The prefixed integer from <xref section="5.1" sectionFormat="of" ta <t>The prefixed integer from <xref section="5.1" sectionFormat="of" ta
rget="RFC7541" format="default"/> is used heavily throughout rget="RFC7541"/> is used heavily throughout
this document. The format from <xref target="RFC7541" format="default"/> is use this document. The format from <xref target="RFC7541"/> is used unmodified. No
d unmodified. Note, however, te, however,
that QPACK uses some prefix sizes not actually used in HPACK.</t> that QPACK uses some prefix sizes not actually used in HPACK.</t>
<t>QPACK implementations MUST be able to decode integers up to and inc luding 62 <t>QPACK implementations <bcp14>MUST</bcp14> be able to decode integer s up to and including 62
bits long.</t> bits long.</t>
</section> </section>
<section anchor="string-literals" numbered="true" toc="default"> <section anchor="string-literals">
<name>String Literals</name> <name>String Literals</name>
<t>The string literal defined by <xref section="5.2" sectionFormat="of " target="RFC7541" format="default"/> is also used <t>The string literal defined by <xref section="5.2" sectionFormat="of " target="RFC7541"/> is also used
throughout. This string format includes optional Huffman encoding.</t> throughout. This string format includes optional Huffman encoding.</t>
<t>HPACK defines string literals to begin on a byte boundary. They be gin with a <t>HPACK defines string literals to begin on a byte boundary. They be gin with a
single bit flag, denoted as 'H' in this document (indicating whether the string single bit flag, denoted as 'H' in this document (indicating whether the string
is Huffman-coded), followed by the Length encoded as a 7-bit prefix integer, and is Huffman encoded), followed by the string length encoded as a 7-bit prefix
finally Length bytes of data. When Huffman encoding is enabled, the Huffman integer, and finally the indicated number of bytes of data. When Huffman
table from <xref section="B" sectionFormat="of" target="RFC7541" format="default encoding is enabled, the Huffman table from <xref section="B" sectionFormat="of"
"/> is used without modification and Length target="RFC7541"/> is used
indicates the size of the string after encoding.</t> without modification and the indicated length is the size of the string after
encoding.</t>
<t>This document expands the definition of string literals by permitti ng them to <t>This document expands the definition of string literals by permitti ng them to
begin other than on a byte boundary. An "N-bit prefix string literal" begins begin other than on a byte boundary. An "N-bit prefix string literal" begins
mid-byte, with the first (8-N) bits allocated to a previous field. The string mid-byte, with the first (8-N) bits allocated to a previous field. The string
uses one bit for the Huffman flag, followed by the Length encoded as an uses one bit for the Huffman flag, followed by the length of the encoded string
(N-1)-bit prefix integer. The prefix size, N, can have a value between 2 and 8 as a (N-1)-bit prefix integer. The prefix size, N, can have a value between 2
inclusive. The remainder of the string literal is unmodified.</t> and 8, inclusive. The remainder of the string literal is unmodified.</t>
<t>A string literal without a prefix length noted is an 8-bit prefix s tring literal <t>A string literal without a prefix length noted is an 8-bit prefix s tring literal
and follows the definitions in <xref target="RFC7541" format="default"/> without modification.</t> and follows the definitions in <xref target="RFC7541"/> without modification.</t >
</section> </section>
</section> </section>
<section anchor="enc-dec-stream-def" numbered="true" toc="default"> <section anchor="enc-dec-stream-def">
<name>Encoder and Decoder Streams</name> <name>Encoder and Decoder Streams</name>
<t>QPACK defines two unidirectional stream types:</t> <t>QPACK defines two unidirectional stream types:</t>
<ul spacing="normal"> <ul spacing="normal">
<li>An encoder stream is a unidirectional stream of type 0x02. <li>An encoder stream is a unidirectional stream of type 0x02.
It carries an unframed sequence of encoder instructions from encoder It carries an unframed sequence of encoder instructions from encoder
to decoder.</li> to decoder.</li>
<li>A decoder stream is a unidirectional stream of type 0x03. <li>A decoder stream is a unidirectional stream of type 0x03.
It carries an unframed sequence of decoder instructions from decoder It carries an unframed sequence of decoder instructions from decoder
to encoder.</li> to encoder.</li>
</ul> </ul>
<t>HTTP/3 endpoints contain a QPACK encoder and decoder. Each endpoint M <t>HTTP/3 endpoints contain a QPACK encoder and decoder. Each endpoint <
UST bcp14>MUST</bcp14>
initiate at most one encoder stream and at most one decoder stream. Receipt of a initiate, at most, one encoder stream and, at most, one decoder stream. Receipt
second instance of either stream type MUST be treated as a connection error of of a second instance of either stream type <bcp14>MUST</bcp14> be treated as a c
type H3_STREAM_CREATION_ERROR.</t> onnection error
<t>These streams MUST NOT be closed. Closure of either unidirectional st of type H3_STREAM_CREATION_ERROR.</t>
ream type <t>The sender <bcp14>MUST NOT</bcp14> close either of these streams, and
MUST be treated as a connection error of type H3_CLOSED_CRITICAL_STREAM.</t> the receiver <bcp14>MUST NOT</bcp14>
<t>An endpoint MAY avoid creating an encoder stream if it will not be us request that the sender close either of these streams. Closure of either
ed (for unidirectional stream type <bcp14>MUST</bcp14> be treated as a connection error
example if its encoder does not wish to use the dynamic table, or if the maximum of type
H3_CLOSED_CRITICAL_STREAM.</t>
<t>An endpoint <bcp14>MAY</bcp14> avoid creating an encoder stream if it
will not be used (for
example, if its encoder does not wish to use the dynamic table or if the maximum
size of the dynamic table permitted by the peer is zero).</t> size of the dynamic table permitted by the peer is zero).</t>
<t>An endpoint MAY avoid creating a decoder stream if its decoder sets t he maximum <t>An endpoint <bcp14>MAY</bcp14> avoid creating a decoder stream if its decoder sets the maximum
capacity of the dynamic table to zero.</t> capacity of the dynamic table to zero.</t>
<t>An endpoint MUST allow its peer to create an encoder stream and a dec oder stream <t>An endpoint <bcp14>MUST</bcp14> allow its peer to create an encoder s tream and a decoder stream
even if the connection's settings prevent their use.</t> even if the connection's settings prevent their use.</t>
</section> </section>
<section anchor="encoder-instructions" numbered="true" toc="default"> <section anchor="encoder-instructions">
<name>Encoder Instructions</name> <name>Encoder Instructions</name>
<t>An encoder sends encoder instructions on the encoder stream to set th e capacity <t>An encoder sends encoder instructions on the encoder stream to set th e capacity
of the dynamic table and add dynamic table entries. Instructions adding table of the dynamic table and add dynamic table entries. Instructions adding table
entries can use existing entries to avoid transmitting redundant information. entries can use existing entries to avoid transmitting redundant information.
The name can be transmitted as a reference to an existing entry in the static or The name can be transmitted as a reference to an existing entry in the static or
the dynamic table or as a string literal. For entries that already exist in the dynamic table or as a string literal. For entries that already exist in
the dynamic table, the full entry can also be used by reference, creating a the dynamic table, the full entry can also be used by reference, creating a
duplicate entry.</t> duplicate entry.</t>
<section anchor="set-dynamic-capacity" numbered="true" toc="default"> <section anchor="set-dynamic-capacity">
<name>Set Dynamic Table Capacity</name> <name>Set Dynamic Table Capacity</name>
<t>An encoder informs the decoder of a change to the dynamic table cap acity using <t>An encoder informs the decoder of a change to the dynamic table cap acity using
an instruction that starts with the '001' 3-bit pattern. This is followed an instruction that starts with the '001' 3-bit pattern. This is followed
by the new dynamic table capacity represented as an integer with a 5-bit prefix; by the new dynamic table capacity represented as an integer with a 5-bit prefix;
see <xref target="prefixed-integers" format="default"/>.</t> see <xref target="prefixed-integers"/>.</t>
<figure anchor="fig-set-capacity"> <figure anchor="fig-set-capacity">
<name>Set Dynamic Table Capacity</name> <name>Set Dynamic Table Capacity</name>
<artwork type="drawing" name="" align="left" alt=""><![CDATA[ <artwork type="ascii-art"><![CDATA[
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 0 | 1 | Capacity (5+) | | 0 | 0 | 1 | Capacity (5+) |
+---+---+---+-------------------+ +---+---+---+-------------------+
]]></artwork> ]]></artwork>
</figure> </figure>
<t>The new capacity MUST be lower than or equal to the limit described <t>The new capacity <bcp14>MUST</bcp14> be lower than or equal to the
in limit described in
<xref target="maximum-dynamic-table-capacity" format="default"/>. In HTTP/3, th <xref target="maximum-dynamic-table-capacity"/>. In HTTP/3, this limit is the v
is limit is the value of the alue of the
SETTINGS_QPACK_MAX_TABLE_CAPACITY parameter (<xref target="configuration" format SETTINGS_QPACK_MAX_TABLE_CAPACITY parameter (<xref target="configuration"/>) rec
="default"/>) received from eived from
the decoder. The decoder MUST treat a new dynamic table capacity value that the decoder. The decoder <bcp14>MUST</bcp14> treat a new dynamic table capacity
value that
exceeds this limit as a connection error of type QPACK_ENCODER_STREAM_ERROR.</t> exceeds this limit as a connection error of type QPACK_ENCODER_STREAM_ERROR.</t>
<t>Reducing the dynamic table capacity can cause entries to be evicted ; see <t>Reducing the dynamic table capacity can cause entries to be evicted ; see
<xref target="eviction" format="default"/>. This MUST NOT cause the eviction of <xref target="eviction"/>. This <bcp14>MUST NOT</bcp14> cause the eviction of e
entries that are not ntries that are not
evictable; see <xref target="blocked-insertion" format="default"/>. Changing th evictable; see <xref target="blocked-insertion"/>. Changing the capacity of the
e capacity of the dynamic dynamic
table is not acknowledged as this instruction does not insert an entry.</t> table is not acknowledged as this instruction does not insert an entry.</t>
</section> </section>
<section anchor="insert-with-name-reference" numbered="true" toc="defaul <section anchor="insert-with-name-reference">
t"> <name>Insert with Name Reference</name>
<name>Insert With Name Reference</name>
<t>An encoder adds an entry to the dynamic table where the field name matches the <t>An encoder adds an entry to the dynamic table where the field name matches the
field name of an entry stored in the static or the dynamic table using an field name of an entry stored in the static or the dynamic table using an
instruction that starts with the '1' 1-bit pattern. The second ('T') bit instruction that starts with the '1' 1-bit pattern. The second ('T') bit
indicates whether the reference is to the static or dynamic table. The 6-bit indicates whether the reference is to the static or dynamic table. The 6-bit
prefix integer (<xref target="prefixed-integers" format="default"/>) that follow s is used to locate the table prefix integer (<xref target="prefixed-integers"/>) that follows is used to loca te the table
entry for the field name. When T=1, the number represents the static table entry for the field name. When T=1, the number represents the static table
index; when T=0, the number is the relative index of the entry in the dynamic index; when T=0, the number is the relative index of the entry in the dynamic
table.</t> table.</t>
<t>The field name reference is followed by the field value represented as a string <t>The field name reference is followed by the field value represented as a string
literal; see <xref target="string-literals" format="default"/>.</t> literal; see <xref target="string-literals"/>.</t>
<figure> <figure>
<name>Insert Field Line -- Indexed Name</name> <name>Insert Field Line -- Indexed Name</name>
<artwork type="drawing" name="" align="left" alt=""><![CDATA[ <artwork type="ascii-art"><![CDATA[
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 1 | T | Name Index (6+) | | 1 | T | Name Index (6+) |
+---+---+-----------------------+ +---+---+-----------------------+
| H | Value Length (7+) | | H | Value Length (7+) |
+---+---------------------------+ +---+---------------------------+
| Value String (Length bytes) | | Value String (Length bytes) |
+-------------------------------+ +-------------------------------+
]]></artwork> ]]></artwork>
</figure> </figure>
</section> </section>
<section anchor="insert-with-literal-name" numbered="true" toc="default" <section anchor="insert-with-literal-name">
> <name>Insert with Literal Name</name>
<name>Insert With Literal Name</name>
<t>An encoder adds an entry to the dynamic table where both the field name and the <t>An encoder adds an entry to the dynamic table where both the field name and the
field value are represented as string literals using an instruction that starts field value are represented as string literals using an instruction that starts
with the '01' 2-bit pattern.</t> with the '01' 2-bit pattern.</t>
<t>This is followed by the name represented as a 6-bit prefix string l iteral, and <t>This is followed by the name represented as a 6-bit prefix string l iteral and
the value represented as an 8-bit prefix string literal; see the value represented as an 8-bit prefix string literal; see
<xref target="string-literals" format="default"/>.</t> <xref target="string-literals"/>.</t>
<figure> <figure>
<name>Insert Field Line -- New Name</name> <name>Insert Field Line -- New Name</name>
<artwork type="drawing" name="" align="left" alt=""><![CDATA[ <artwork type="ascii-art"><![CDATA[
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) |
+-------------------------------+ +-------------------------------+
]]></artwork> ]]></artwork>
</figure> </figure>
</section> </section>
<section anchor="duplicate" numbered="true" toc="default"> <section anchor="duplicate">
<name>Duplicate</name> <name>Duplicate</name>
<t>An encoder duplicates an existing entry in the dynamic table using an <t>An encoder duplicates an existing entry in the dynamic table using an
instruction that starts with the '000' 3-bit pattern. This is followed by instruction that starts with the '000' 3-bit pattern. This is followed by
the relative index of the existing entry represented as an integer with a 5-bit the relative index of the existing entry represented as an integer with a 5-bit
prefix; see <xref target="prefixed-integers" format="default"/>.</t> prefix; see <xref target="prefixed-integers"/>.</t>
<figure anchor="fig-index-with-duplication"> <figure anchor="fig-index-with-duplication">
<name>Duplicate</name> <name>Duplicate</name>
<artwork type="drawing" name="" align="left" alt=""><![CDATA[ <artwork type="ascii-art"><![CDATA[
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+) |
+---+---+---+-------------------+ +---+---+---+-------------------+
]]></artwork> ]]></artwork>
</figure> </figure>
<t>The existing entry is re-inserted into the dynamic table without re sending <t>The existing entry is reinserted into the dynamic table without res ending
either the name or the value. This is useful to avoid adding a reference to an either the name or the value. This is useful to avoid adding a reference to an
older entry, which might block inserting new entries.</t> older entry, which might block inserting new entries.</t>
</section> </section>
</section> </section>
<section anchor="decoder-instructions" numbered="true" toc="default"> <section anchor="decoder-instructions">
<name>Decoder Instructions</name> <name>Decoder Instructions</name>
<t>A decoder sends decoder instructions on the decoder stream to inform the encoder <t>A decoder sends decoder instructions on the decoder stream to inform the encoder
about the processing of field sections and table updates to ensure consistency about the processing of field sections and table updates to ensure consistency
of the dynamic table.</t> of the dynamic table.</t>
<section anchor="header-acknowledgment" numbered="true" toc="default"> <section anchor="header-acknowledgment">
<name>Section Acknowledgment</name> <name>Section Acknowledgment</name>
<t>After processing an encoded field section whose declared Required I nsert Count <t>After processing an encoded field section whose declared Required I nsert Count
is not zero, the decoder emits a Section Acknowledgment instruction. The is not zero, the decoder emits a Section Acknowledgment instruction. The
instruction starts with the '1' 1-bit pattern, followed by the field instruction starts with the '1' 1-bit pattern, followed by the field
section's associated stream ID encoded as a 7-bit prefix integer; see section's associated stream ID encoded as a 7-bit prefix integer; see
<xref target="prefixed-integers" format="default"/>.</t> <xref target="prefixed-integers"/>.</t>
<t>This instruction is used as described in <xref target="known-receiv <t>This instruction is used as described in Sections <xref format="cou
ed-count" format="default"/> and nter" target="known-received-count"/> and
in <xref target="state-synchronization" format="default"/>.</t> <xref format="counter" target="state-synchronization"/>.</t>
<figure anchor="fig-header-ack"> <figure anchor="fig-header-ack">
<name>Section Acknowledgment</name> <name>Section Acknowledgment</name>
<artwork type="drawing" name="" align="left" alt=""><![CDATA[ <artwork type="ascii-art"><![CDATA[
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 1 | Stream ID (7+) | | 1 | Stream ID (7+) |
+---+---------------------------+ +---+---------------------------+
]]></artwork> ]]></artwork>
</figure> </figure>
<t>If an encoder receives a Section Acknowledgment instruction referri ng to a <t>If an encoder receives a Section Acknowledgment instruction referri ng to a
stream on which every encoded field section with a non-zero Required Insert stream on which every encoded field section with a non-zero Required Insert
Count has already been acknowledged, this MUST be treated as a connection error Count has already been acknowledged, this <bcp14>MUST</bcp14> be treated as a co nnection error
of type QPACK_DECODER_STREAM_ERROR.</t> of type QPACK_DECODER_STREAM_ERROR.</t>
<t>The Section Acknowledgment instruction might increase the Known Rec eived Count; <t>The Section Acknowledgment instruction might increase the Known Rec eived Count;
see <xref target="known-received-count" format="default"/>.</t> see <xref target="known-received-count"/>.</t>
</section> </section>
<section anchor="stream-cancellation" numbered="true" toc="default"> <section anchor="stream-cancellation">
<name>Stream Cancellation</name> <name>Stream Cancellation</name>
<t>When a stream is reset or reading is abandoned, the decoder emits a Stream <t>When a stream is reset or reading is abandoned, the decoder emits a Stream
Cancellation instruction. The instruction starts with the '01' 2-bit Cancellation instruction. The instruction starts with the '01' 2-bit
pattern, followed by the stream ID of the affected stream encoded as a pattern, followed by the stream ID of the affected stream encoded as a
6-bit prefix integer.</t> 6-bit prefix integer.</t>
<t>This instruction is used as described in <xref target="state-synchr onization" format="default"/>.</t> <t>This instruction is used as described in <xref target="state-synchr onization"/>.</t>
<figure anchor="fig-stream-cancel"> <figure anchor="fig-stream-cancel">
<name>Stream Cancellation</name> <name>Stream Cancellation</name>
<artwork type="drawing" name="" align="left" alt=""><![CDATA[ <artwork type="ascii-art"><![CDATA[
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+) |
+---+---+-----------------------+ +---+---+-----------------------+
]]></artwork> ]]></artwork>
</figure> </figure>
</section> </section>
<section anchor="insert-count-increment" numbered="true" toc="default"> <section anchor="insert-count-increment">
<name>Insert Count Increment</name> <name>Insert Count Increment</name>
<t>The Insert Count Increment instruction starts with the '00' 2-bit p attern, <t>The Insert Count Increment instruction starts with the '00' 2-bit p attern,
followed by the Increment encoded as a 6-bit prefix integer. This instruction followed by the Increment encoded as a 6-bit prefix integer. This instruction
increases the Known Received Count (<xref target="known-received-count" format=" default"/>) by the value of increases the Known Received Count (<xref target="known-received-count"/>) by th e value of
the Increment parameter. The decoder should send an Increment value that the Increment parameter. The decoder should send an Increment value that
increases the Known Received Count to the total number of dynamic table increases the Known Received Count to the total number of dynamic table
insertions and duplications processed so far.</t> insertions and duplications processed so far.</t>
<figure anchor="fig-size-sync"> <figure anchor="fig-size-sync">
<name>Insert Count Increment</name> <name>Insert Count Increment</name>
<artwork type="drawing" name="" align="left" alt=""><![CDATA[ <artwork type="ascii-art"><![CDATA[
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 0 | Increment (6+) | | 0 | 0 | Increment (6+) |
+---+---+-----------------------+ +---+---+-----------------------+
]]></artwork> ]]></artwork>
</figure> </figure>
<t>An encoder that receives an Increment field equal to zero, or one t hat increases <t>An encoder that receives an Increment field equal to zero, or one t hat increases
the Known Received Count beyond what the encoder has sent MUST treat this as a the Known Received Count beyond what the encoder has sent, <bcp14>MUST</bcp14> t reat this as a
connection error of type QPACK_DECODER_STREAM_ERROR.</t> connection error of type QPACK_DECODER_STREAM_ERROR.</t>
</section> </section>
</section> </section>
<section anchor="field-line-representations" numbered="true" toc="default" > <section anchor="field-line-representations">
<name>Field Line Representations</name> <name>Field Line Representations</name>
<t>An encoded field section consists of a prefix and a possibly empty se quence of <t>An encoded field section consists of a prefix and a possibly empty se quence of
representations defined in this section. Each representation corresponds to a representations defined in this section. Each representation corresponds to a
single field line. These representations reference the static table or the single field line. These representations reference the static table or the
dynamic table in a particular state, but do not modify that state.</t> dynamic table in a particular state, but they do not modify that state.</t>
<t>Encoded field sections are carried in frames on streams defined by th e enclosing <t>Encoded field sections are carried in frames on streams defined by th e enclosing
protocol.</t> protocol.</t>
<section anchor="header-prefix" numbered="true" toc="default"> <section anchor="header-prefix">
<name>Encoded Field Section Prefix</name> <name>Encoded Field Section Prefix</name>
<t>Each encoded field section is prefixed with two integers. The Requ ired Insert <t>Each encoded field section is prefixed with two integers. The Requ ired Insert
Count is encoded as an integer with an 8-bit prefix using the encoding described Count is encoded as an integer with an 8-bit prefix using the encoding described
in <xref target="ric" format="default"/>. The Base is encoded as a sign bit ('S in <xref target="ric"/>. The Base is encoded as a Sign bit ('S') and a Delta Ba
') and a Delta Base value se value
with a 7-bit prefix; see <xref target="base" format="default"/>.</t> with a 7-bit prefix; see <xref target="base"/>.</t>
<figure anchor="fig-base-index"> <figure anchor="fig-base-index">
<name>Encoded Field Section</name> <name>Encoded Field Section</name>
<artwork type="drawing" name="" align="left" alt=""><![CDATA[ <artwork type="ascii-art"><![CDATA[
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+) |
+---+---------------------------+ +---+---------------------------+
| Encoded Field Lines ... | Encoded Field Lines ...
+-------------------------------+ +-------------------------------+
]]></artwork> ]]></artwork>
</figure> </figure>
<section anchor="ric" numbered="true" toc="default"> <section anchor="ric">
<name>Required Insert Count</name> <name>Required Insert Count</name>
<t>Required Insert Count identifies the state of the dynamic table n eeded to <t>Required Insert Count identifies the state of the dynamic table n eeded to
process the encoded field section. Blocking decoders use the Required Insert process the encoded field section. Blocking decoders use the Required Insert
Count to determine when it is safe to process the rest of the field section.</t> Count to determine when it is safe to process the rest of the field section.</t>
<t>The encoder transforms the Required Insert Count as follows befor e encoding:</t> <t>The encoder transforms the Required Insert Count as follows befor e encoding:</t>
<artwork name="" type="" align="left" alt=""><![CDATA[ <sourcecode type="pseudocode"><![CDATA[
if ReqInsertCount == 0: if ReqInsertCount == 0:
EncInsertCount = 0 EncInsertCount = 0
else: else:
EncInsertCount = (ReqInsertCount mod (2 * MaxEntries)) + 1 EncInsertCount = (ReqInsertCount mod (2 * MaxEntries)) + 1
]]></artwork> ]]></sourcecode>
<t>Here <tt>MaxEntries</tt> is the maximum number of entries that th e dynamic table can <t>Here <tt>MaxEntries</tt> is the maximum number of entries that th e dynamic table can
have. The smallest entry has empty name and value strings and has the size of have. The smallest entry has empty name and value strings and has the size of
32. Hence <tt>MaxEntries</tt> is calculated as</t> 32. Hence, <tt>MaxEntries</tt> is calculated as:</t>
<artwork name="" type="" align="left" alt=""><![CDATA[ <sourcecode type="pseudocode"><![CDATA[
MaxEntries = floor( MaxTableCapacity / 32 ) MaxEntries = floor( MaxTableCapacity / 32 )
]]></artwork> ]]></sourcecode>
<t><tt>MaxTableCapacity</tt> is the maximum capacity of the dynamic table as specified by <t><tt>MaxTableCapacity</tt> is the maximum capacity of the dynamic table as specified by
the decoder; see <xref target="maximum-dynamic-table-capacity" format="default"/ >.</t> the decoder; see <xref target="maximum-dynamic-table-capacity"/>.</t>
<t>This encoding limits the length of the prefix on long-lived conne ctions.</t> <t>This encoding limits the length of the prefix on long-lived conne ctions.</t>
<t>The decoder can reconstruct the Required Insert Count using an al gorithm such as <t>The decoder can reconstruct the Required Insert Count using an al gorithm such as
the following. If the decoder encounters a value of EncodedInsertCount that the following. If the decoder encounters a value of EncodedInsertCount that
could not have been produced by a conformant encoder, it MUST treat this as a could not have been produced by a conformant encoder, it <bcp14>MUST</bcp14> tre at this as a
connection error of type QPACK_DECOMPRESSION_FAILED.</t> connection error of type QPACK_DECOMPRESSION_FAILED.</t>
<t>TotalNumberOfInserts is the total number of inserts into the deco der's dynamic <t><tt>TotalNumberOfInserts</tt> is the total number of inserts into the decoder's dynamic
table.</t> table.</t>
<artwork name="" type="" align="left" alt=""><![CDATA[ <sourcecode type="pseudocode"><![CDATA[
FullRange = 2 * MaxEntries FullRange = 2 * MaxEntries
if EncodedInsertCount == 0: if EncodedInsertCount == 0:
ReqInsertCount = 0 ReqInsertCount = 0
else: else:
if EncodedInsertCount > FullRange: if EncodedInsertCount > FullRange:
Error Error
MaxValue = TotalNumberOfInserts + MaxEntries MaxValue = TotalNumberOfInserts + MaxEntries
# MaxWrapped is the largest possible value of # MaxWrapped is the largest possible value of
# ReqInsertCount that is 0 mod 2 * MaxEntries # ReqInsertCount that is 0 mod 2 * MaxEntries
skipping to change at line 872 skipping to change at line 856
# If ReqInsertCount exceeds MaxValue, the Encoder's value # If ReqInsertCount exceeds MaxValue, the Encoder's value
# must have wrapped one fewer time # must have wrapped one fewer time
if ReqInsertCount > MaxValue: if ReqInsertCount > MaxValue:
if ReqInsertCount <= FullRange: if ReqInsertCount <= FullRange:
Error Error
ReqInsertCount -= FullRange ReqInsertCount -= FullRange
# Value of 0 must be encoded as 0. # Value of 0 must be encoded as 0.
if ReqInsertCount == 0: if ReqInsertCount == 0:
Error Error
]]></artwork> ]]></sourcecode>
<t>For example, if the dynamic table is 100 bytes, then the Required Insert Count <t>For example, if the dynamic table is 100 bytes, then the Required Insert Count
will be encoded modulo 6. If a decoder has received 10 inserts, then an encoded will be encoded modulo 6. If a decoder has received 10 inserts, then an encoded
value of 4 indicates that the Required Insert Count is 9 for the field section.< /t> value of 4 indicates that the Required Insert Count is 9 for the field section.< /t>
</section> </section>
<section anchor="base" numbered="true" toc="default"> <section anchor="base">
<name>Base</name> <name>Base</name>
<t>The Base is used to resolve references in the dynamic table as de scribed in <t>The Base is used to resolve references in the dynamic table as de scribed in
<xref target="relative-indexing" format="default"/>.</t> <xref target="relative-indexing"/>.</t>
<t>To save space, the Base is encoded relative to the Required Inser t Count using a <t>To save space, the Base is encoded relative to the Required Inser t Count using a
one-bit sign ('S') and the Delta Base value. A sign bit of 0 indicates that the one-bit Sign ('S' in <xref target="fig-base-index"/>) and the Delta Base value.
Base is greater than or equal to the value of the Required Insert Count; the A Sign bit
decoder adds the value of Delta Base to the Required Insert Count to determine of 0 indicates that the Base is greater than or equal to the value of the
the value of the Base. A sign bit of 1 indicates that the Base is less than the Required Insert Count; the decoder adds the value of Delta Base to the Required
Required Insert Count; the decoder subtracts the value of Delta Base from the Insert Count to determine the value of the Base. A Sign bit of 1 indicates that
Required Insert Count and also subtracts one to determine the value of the Base. the Base is less than the Required Insert Count; the decoder subtracts the value
That is:</t> of Delta Base from the Required Insert Count and also subtracts one to determine
<artwork name="" type="" align="left" alt=""><![CDATA[ the value of the Base. That is:</t>
if S == 0: <sourcecode type="pseudocode"><![CDATA[
if Sign == 0:
Base = ReqInsertCount + DeltaBase Base = ReqInsertCount + DeltaBase
else: else:
Base = ReqInsertCount - DeltaBase - 1 Base = ReqInsertCount - DeltaBase - 1
]]></artwork> ]]></sourcecode>
<t>A single-pass encoder determines the Base before encoding a field section. If <t>A single-pass encoder determines the Base before encoding a field section. If
the encoder inserted entries in the dynamic table while encoding the field the encoder inserted entries in the dynamic table while encoding the field
section and is referencing them, Required Insert Count will be greater than the section and is referencing them, Required Insert Count will be greater than the
Base, so the encoded difference is negative and the sign bit is set to 1. If Base, so the encoded difference is negative and the Sign bit is set to 1. If
the field section was not encoded using representations that reference the most the field section was not encoded using representations that reference the most
recent entry in the table and did not insert any new entries, the Base will be recent entry in the table and did not insert any new entries, the Base will be
greater than the Required Insert Count, so the delta will be positive and the greater than the Required Insert Count, so the encoded difference will be
sign bit is set to 0.</t> positive and the Sign bit is set to 0.</t>
<t>The value of Base <bcp14>MUST NOT</bcp14> be negative. Though the
protocol might operate
correctly with a negative Base using post-Base indexing, it is unnecessary and
inefficient. An endpoint <bcp14>MUST</bcp14> treat a field block with a Sign bit
of 1 as
invalid if the value of Required Insert Count is less than or equal to the value
of Delta Base.</t>
<t>An encoder that produces table updates before encoding a field se ction might set <t>An encoder that produces table updates before encoding a field se ction might set
Base to the value of Required Insert Count. In such case, both the sign bit and Base to the value of Required Insert Count. In such a case, both the Sign bit
the Delta Base will be set to zero.</t> and the Delta Base will be set to zero.</t>
<t>A field section that was encoded without references to the dynami c table can use <t>A field section that was encoded without references to the dynami c table can use
any value for the Base; setting Delta Base to zero is one of the most efficient any value for the Base; setting Delta Base to zero is one of the most efficient
encodings.</t> encodings.</t>
<t>For example, with a Required Insert Count of 9, a decoder receive <t>For example, with a Required Insert Count of 9, a decoder receive
s an S bit of 1 s a Sign bit
and a Delta Base of 2. This sets the Base to 6 and enables post-base indexing of 1 and a Delta Base of 2. This sets the Base to 6 and enables post-Base
for three entries. In this example, a relative index of 1 refers to the 5th indexing for three entries. In this example, a relative index of 1 refers to
entry that was added to the table; a post-base index of 1 refers to the 8th the fifth entry that was added to the table; a post-Base index of 1 refers to
entry.</t> the eighth entry.</t>
</section> </section>
</section> </section>
<section anchor="indexed-field-line" numbered="true" toc="default"> <section anchor="indexed-field-line">
<name>Indexed Field Line</name> <name>Indexed Field Line</name>
<t>An indexed field line representation identifies an entry in the sta tic table, <t>An indexed field line representation identifies an entry in the sta tic table
or an entry in the dynamic table with an absolute index less than the value of or an entry in the dynamic table with an absolute index less than the value of
the Base.</t> the Base.</t>
<figure> <figure>
<name>Indexed Field Line</name> <name>Indexed Field Line</name>
<artwork type="drawing" name="" align="left" alt=""><![CDATA[ <artwork type="ascii-art"><![CDATA[
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 1 | T | Index (6+) | | 1 | T | Index (6+) |
+---+---+-----------------------+ +---+---+-----------------------+
]]></artwork> ]]></artwork>
</figure> </figure>
<t>This representation starts with the '1' 1-bit pattern, followed by the 'T' bit <t>This representation starts with the '1' 1-bit pattern, followed by the 'T' bit,
indicating whether the reference is into the static or dynamic table. The 6-bit indicating whether the reference is into the static or dynamic table. The 6-bit
prefix integer (<xref target="prefixed-integers" format="default"/>) that follow s is used to locate the prefix integer (<xref target="prefixed-integers"/>) that follows is used to loca te the
table entry for the field line. When T=1, the number represents the static table entry for the field line. When T=1, the number represents the static
table index; when T=0, the number is the relative index of the entry in the table index; when T=0, the number is the relative index of the entry in the
dynamic table.</t> dynamic table.</t>
</section> </section>
<section anchor="indexed-field-line-with-post-base-index" numbered="true <section anchor="indexed-field-line-with-post-base-index">
" toc="default"> <name>Indexed Field Line with Post-Base Index</name>
<name>Indexed Field Line With Post-Base Index</name> <t>An indexed field line with post-Base index representation identifie
<t>An indexed field line with post-base index representation identifie s an entry
s an entry
in the dynamic table with an absolute index greater than or equal to the value in the dynamic table with an absolute index greater than or equal to the value
of the Base.</t> of the Base.</t>
<figure> <figure>
<name>Indexed Field Line with Post-Base Index</name> <name>Indexed Field Line with Post-Base Index</name>
<artwork type="drawing" name="" align="left" alt=""><![CDATA[ <artwork type="ascii-art"><![CDATA[
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 0 | 0 | 1 | Index (4+) | | 0 | 0 | 0 | 1 | Index (4+) |
+---+---+---+---+---------------+ +---+---+---+---+---------------+
]]></artwork> ]]></artwork>
</figure> </figure>
<t>This representation starts with the '0001' 4-bit pattern. This is followed <t>This representation starts with the '0001' 4-bit pattern. This is followed
by the post-base index (<xref target="post-base" format="default"/>) of the matc by the post-Base index (<xref target="post-base"/>) of the matching field line,
hing field line, represented represented
as an integer with a 4-bit prefix; see <xref target="prefixed-integers" format=" as an integer with a 4-bit prefix; see <xref target="prefixed-integers"/>.</t>
default"/>.</t>
</section> </section>
<section anchor="literal-name-reference" numbered="true" toc="default"> <section anchor="literal-name-reference">
<name>Literal Field Line With Name Reference</name> <name>Literal Field Line with Name Reference</name>
<t>A literal field line with name reference representation encodes a f ield line <t>A literal field line with name reference representation encodes a f ield line
where the field name matches the field name of an entry in the static table, or where the field name matches the field name of an entry in the static table or
the field name of an entry in the dynamic table with an absolute index less than the field name of an entry in the dynamic table with an absolute index less than
the value of the Base.</t> the value of the Base.</t>
<figure> <figure>
<name>Literal Field Line With Name Reference</name> <name>Literal Field Line with Name Reference</name>
<artwork type="drawing" name="" align="left" alt=""><![CDATA[ <artwork type="ascii-art"><![CDATA[
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 1 | N | T |Name Index (4+)| | 0 | 1 | N | T |Name Index (4+)|
+---+---+---+---+---------------+ +---+---+---+---+---------------+
| H | Value Length (7+) | | H | Value Length (7+) |
+---+---------------------------+ +---+---------------------------+
| Value String (Length bytes) | | Value String (Length bytes) |
+-------------------------------+ +-------------------------------+
]]></artwork> ]]></artwork>
</figure> </figure>
<t>This representation starts with the '01' 2-bit pattern. The follow ing bit, <t>This representation starts with the '01' 2-bit pattern. The follow ing bit,
'N', indicates whether an intermediary is permitted to add this field line to 'N', indicates whether an intermediary is permitted to add this field line to
the dynamic table on subsequent hops. When the 'N' bit is set, the encoded field the dynamic table on subsequent hops. When the 'N' bit is set, the encoded field
line MUST always be encoded with a literal representation. In particular, when a line <bcp14>MUST</bcp14> always be encoded with a literal representation. In par ticular, when a
peer sends a field line that it received represented as a literal field line peer sends a field line that it received represented as a literal field line
with the 'N' bit set, it MUST use a literal representation to forward this field with the 'N' bit set, it <bcp14>MUST</bcp14> use a literal representation to for ward this field
line. This bit is intended for protecting field values that are not to be put line. This bit is intended for protecting field values that are not to be put
at risk by compressing them; see <xref target="probing-dynamic-table-state" form at="default"/> for more at risk by compressing them; see <xref target="probing-dynamic-table-state"/> fo r more
details.</t> details.</t>
<t>The fourth ('T') bit indicates whether the reference is to the stat ic or dynamic <t>The fourth ('T') bit indicates whether the reference is to the stat ic or dynamic
table. The 4-bit prefix integer (<xref target="prefixed-integers" format="defau lt"/>) that follows is used to table. The 4-bit prefix integer (<xref target="prefixed-integers"/>) that follo ws is used to
locate the table entry for the field name. When T=1, the number represents the locate the table entry for the field name. When T=1, the number represents the
static table index; when T=0, the number is the relative index of the entry in static table index; when T=0, the number is the relative index of the entry in
the dynamic table.</t> the dynamic table.</t>
<t>Only the field name is taken from the dynamic table entry; the fiel d value is <t>Only the field name is taken from the dynamic table entry; the fiel d value is
encoded as an 8-bit prefix string literal; see <xref target="string-literals" fo rmat="default"/>.</t> encoded as an 8-bit prefix string literal; see <xref target="string-literals"/>. </t>
</section> </section>
<section anchor="literal-field-line-with-post-base-name-reference" numbe <section anchor="literal-field-line-with-post-base-name-reference">
red="true" toc="default"> <name>Literal Field Line with Post-Base Name Reference</name>
<name>Literal Field Line With Post-Base Name Reference</name> <t>A literal field line with post-Base name reference representation e
<t>A literal field line with post-base name reference representation e ncodes a
ncodes a
field line where the field name matches the field name of a dynamic table entry field line where the field name matches the field name of a dynamic table entry
with an absolute index greater than or equal to the value of the Base.</t> with an absolute index greater than or equal to the value of the Base.</t>
<figure> <figure>
<name>Literal Field Line With Post-Base Name Reference</name> <name>Literal Field Line with Post-Base Name Reference</name>
<artwork type="drawing" name="" align="left" alt=""><![CDATA[ <artwork type="ascii-art"><![CDATA[
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) |
+-------------------------------+ +-------------------------------+
]]></artwork> ]]></artwork>
</figure> </figure>
<t>This representation starts with the '0000' 4-bit pattern. The fift h bit is <t>This representation starts with the '0000' 4-bit pattern. The fift h bit is
the 'N' bit as described in <xref target="literal-name-reference" format="defaul the 'N' bit as described in <xref target="literal-name-reference"/>. This is fo
t"/>. This is followed by a llowed by a
post-base index of the dynamic table entry (<xref target="post-base" format="def post-Base index of the dynamic table entry (<xref target="post-base"/>) encoded
ault"/>) encoded as an as an
integer with a 3-bit prefix; see <xref target="prefixed-integers" format="defaul integer with a 3-bit prefix; see <xref target="prefixed-integers"/>.</t>
t"/>.</t>
<t>Only the field name is taken from the dynamic table entry; the fiel d value is <t>Only the field name is taken from the dynamic table entry; the fiel d value is
encoded as an 8-bit prefix string literal; see <xref target="string-literals" fo rmat="default"/>.</t> encoded as an 8-bit prefix string literal; see <xref target="string-literals"/>. </t>
</section> </section>
<section anchor="literal-field-line-with-literal-name" numbered="true" t <section anchor="literal-field-line-with-literal-name">
oc="default"> <name>Literal Field Line with Literal Name</name>
<name>Literal Field Line With Literal Name</name>
<t>The literal field line with literal name representation encodes a <t>The literal field line with literal name representation encodes a
field name and a field value as string literals.</t> field name and a field value as string literals.</t>
<figure> <figure>
<name>Literal Field Line With Literal Name</name> <name>Literal Field Line with Literal Name</name>
<artwork type="drawing" name="" align="left" alt=""><![CDATA[ <artwork type="ascii-art"><![CDATA[
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| 0 | 0 | 1 | N | H |NameLen(3+)| | 0 | 0 | 1 | N | H |NameLen(3+)|
+---+---+---+---+---+-----------+ +---+---+---+---+---+-----------+
| Name String (Length bytes) | | Name String (Length bytes) |
+---+---------------------------+ +---+---------------------------+
| H | Value Length (7+) | | H | Value Length (7+) |
+---+---------------------------+ +---+---------------------------+
| Value String (Length bytes) | | Value String (Length bytes) |
+-------------------------------+ +-------------------------------+
]]></artwork> ]]></artwork>
</figure> </figure>
<t>This representation starts with the '001' 3-bit pattern. The fourt h bit is <t>This representation starts with the '001' 3-bit pattern. The fourt h bit is
the 'N' bit as described in <xref target="literal-name-reference" format="defaul t"/>. The name follows, the 'N' bit as described in <xref target="literal-name-reference"/>. The name f ollows,
represented as a 4-bit prefix string literal, then the value, represented as an represented as a 4-bit prefix string literal, then the value, represented as an
8-bit prefix string literal; see <xref target="string-literals" format="default" />.</t> 8-bit prefix string literal; see <xref target="string-literals"/>.</t>
</section> </section>
</section> </section>
</section> </section>
<section anchor="configuration" numbered="true" toc="default"> <section anchor="configuration">
<name>Configuration</name> <name>Configuration</name>
<t>QPACK defines two settings for the HTTP/3 SETTINGS frame:</t> <t>QPACK defines two settings for the HTTP/3 SETTINGS frame:</t>
<dl> <dl>
<dt> <dt>SETTINGS_QPACK_MAX_TABLE_CAPACITY (0x01):</dt>
SETTINGS_QPACK_MAX_TABLE_CAPACITY (0x1): </dt>
<dd> <dd>
<t>The default value is zero. See <xref target="header-table-dynamic" format="default"/> for usage. This is <t>The default value is zero. See <xref target="header-table-dynamic" /> for usage. This is
the equivalent of the SETTINGS_HEADER_TABLE_SIZE from HTTP/2.</t> the equivalent of the SETTINGS_HEADER_TABLE_SIZE from HTTP/2.</t>
</dd> </dd>
<dt> <dt>SETTINGS_QPACK_BLOCKED_STREAMS (0x07):</dt>
SETTINGS_QPACK_BLOCKED_STREAMS (0x7): </dt>
<dd> <dd>
<t>The default value is zero. See <xref target="blocked-streams" form at="default"/>.</t> <t>The default value is zero. See <xref target="blocked-streams"/>.</ t>
</dd> </dd>
</dl> </dl>
</section> </section>
<section anchor="error-handling" numbered="true" toc="default"> <section anchor="error-handling">
<name>Error Handling</name> <name>Error Handling</name>
<t>The following error codes are defined for HTTP/3 to indicate failures o f <t>The following error codes are defined for HTTP/3 to indicate failures o f
QPACK that prevent the stream or connection from continuing:</t> QPACK that prevent the stream or connection from continuing:</t>
<dl> <dl>
<dt> <dt>QPACK_DECOMPRESSION_FAILED (0x0200):</dt>
QPACK_DECOMPRESSION_FAILED (0x200): </dt>
<dd> <dd>
<t>The decoder failed to interpret an encoded field section and is not able to <t>The decoder failed to interpret an encoded field section and is not able to
continue decoding that field section.</t> continue decoding that field section.</t>
</dd> </dd>
<dt> <dt>QPACK_ENCODER_STREAM_ERROR (0x0201):</dt>
QPACK_ENCODER_STREAM_ERROR (0x201): </dt>
<dd> <dd>
<t>The decoder failed to interpret an encoder instruction received on the <t>The decoder failed to interpret an encoder instruction received on the
encoder stream.</t> encoder stream.</t>
</dd> </dd>
<dt> <dt>QPACK_DECODER_STREAM_ERROR (0x0202):</dt>
QPACK_DECODER_STREAM_ERROR (0x202): </dt>
<dd> <dd>
<t>The encoder failed to interpret a decoder instruction received on t he <t>The encoder failed to interpret a decoder instruction received on t he
decoder stream.</t> decoder stream.</t>
</dd> </dd>
</dl> </dl>
</section> </section>
<section anchor="security-considerations" numbered="true" toc="default"> <section anchor="security-considerations">
<name>Security Considerations</name> <name>Security Considerations</name>
<t>This section describes potential areas of security concern with QPACK:< /t> <t>This section describes potential areas of security concern with QPACK:< /t>
<ul spacing="normal"> <ul spacing="normal">
<li>Use of compression as a length-based oracle for verifying guesses ab out <li>Use of compression as a length-based oracle for verifying guesses ab out
secrets that are compressed into a shared compression context.</li> secrets that are compressed into a shared compression context.</li>
<li>Denial of service resulting from exhausting processing or memory cap acity at <li>Denial of service resulting from exhausting processing or memory cap acity at
a decoder.</li> a decoder.</li>
</ul> </ul>
<section anchor="probing-dynamic-table-state" numbered="true" toc="default "> <section anchor="probing-dynamic-table-state">
<name>Probing Dynamic Table State</name> <name>Probing Dynamic Table State</name>
<t>QPACK reduces the encoded size of field sections by exploiting the re dundancy <t>QPACK reduces the encoded size of field sections by exploiting the re dundancy
inherent in protocols like HTTP. The ultimate goal of this is to reduce the inherent in protocols like HTTP. The ultimate goal of this is to reduce the
amount of data that is required to send HTTP requests or responses.</t> amount of data that is required to send HTTP requests or responses.</t>
<t>The compression context used to encode header and trailer fields can be probed <t>The compression context used to encode header and trailer fields can be probed
by an attacker who can both define fields to be encoded and transmitted and by an attacker who can both define fields to be encoded and transmitted and
observe the length of those fields once they are encoded. When an attacker can observe the length of those fields once they are encoded. When an attacker can
do both, they can adaptively modify requests in order to confirm guesses about do both, they can adaptively modify requests in order to confirm guesses about
the dynamic table state. If a guess is compressed into a shorter length, the the dynamic table state. If a guess is compressed into a shorter length, the
attacker can observe the encoded length and infer that the guess was correct.</t > attacker can observe the encoded length and infer that the guess was correct.</t >
<t>This is possible even over the Transport Layer Security Protocol (TLS <t>This is possible even over the Transport Layer Security Protocol
, see (<xref target="TLS"/>) and the QUIC Transport Protocol (<xref target="QUIC-TRANS
<xref target="TLS" format="default"/>) and the QUIC Transport Protocol (see <xre PORT"/>), because
f target="QUIC-TRANSPORT" format="default"/>), while TLS and QUIC provide confidentiality protection for content, they only
because while TLS and QUIC provide confidentiality protection for content, they provide a limited amount of protection for the length of that content.</t>
only provide a limited amount of protection for the length of that content.</t> <aside>
<dl> <t>Note: Padding schemes only provide limited protection against an at
<dt> tacker with
Note: </dt> these capabilities, potentially only forcing an increased number of guesses to
<dd> learn the length associated with a given guess. Padding schemes also work
<t>Padding schemes only provide limited protection against an attack directly against compression by increasing the number of bits that are
er with these transmitted.</t>
capabilities, potentially only forcing an increased number of guesses to learn </aside>
the length associated with a given guess. Padding schemes also work directly <t>Attacks like CRIME (<xref target="CRIME"/>) demonstrated the existenc
against compression by increasing the number of bits that are transmitted.</t> e of these general
</dd>
</dl>
<t>Attacks like CRIME (<xref target="CRIME" format="default"/>) demonstr
ated the existence of these general
attacker capabilities. The specific attack exploited the fact that DEFLATE attacker capabilities. The specific attack exploited the fact that DEFLATE
(<xref target="RFC1951" format="default"/>) removes redundancy based on prefix m atching. This permitted the (<xref target="RFC1951"/>) removes redundancy based on prefix matching. This per mitted the
attacker to confirm guesses a character at a time, reducing an exponential-time attacker to confirm guesses a character at a time, reducing an exponential-time
attack into a linear-time attack.</t> attack into a linear-time attack.</t>
<section anchor="applicability-to-qpack-and-http" numbered="true" toc="d efault"> <section anchor="applicability-to-qpack-and-http">
<name>Applicability to QPACK and HTTP</name> <name>Applicability to QPACK and HTTP</name>
<t>QPACK mitigates but does not completely prevent attacks modeled on <t>QPACK mitigates, but does not completely prevent, attacks modeled o
CRIME n CRIME
(<xref target="CRIME" format="default"/>) by forcing a guess to match an entire (<xref target="CRIME"/>) by forcing a guess to match an entire field line rather
field line, rather than than
individual characters. An attacker can only learn whether a guess is correct or individual characters. An attacker can only learn whether a guess is correct or
not, so is reduced to a brute force guess for the field values associated with a not, so the attacker is reduced to a brute-force guess for the field values
given field name.</t> associated with a given field name.</t>
<t>The viability of recovering specific field values therefore depends <t>Therefore, the viability of recovering specific field values depend
on the s on the
entropy of values. As a result, values with high entropy are unlikely to be entropy of values. As a result, values with high entropy are unlikely to be
recovered successfully. However, values with low entropy remain vulnerable.</t> recovered successfully. However, values with low entropy remain vulnerable.</t>
<t>Attacks of this nature are possible any time that two mutually dist rustful <t>Attacks of this nature are possible any time that two mutually dist rustful
entities control requests or responses that are placed onto a single HTTP/3 entities control requests or responses that are placed onto a single HTTP/3
connection. If the shared QPACK compressor permits one entity to add entries to connection. If the shared QPACK compressor permits one entity to add entries to
the dynamic table, and the other to refer to those entries while encoding the dynamic table, and the other to refer to those entries while encoding
chosen field lines, then the attacker (the second entity) can learn the state chosen field lines, then the attacker (the second entity) can learn the state
of the table by observing the length of the encoded output.</t> of the table by observing the length of the encoded output.</t>
<t>For example, requests or responses from mutually distrustful entiti es can occur <t>For example, requests or responses from mutually distrustful entiti es can occur
when an intermediary either:</t> when an intermediary either:</t>
<ul spacing="normal"> <ul spacing="normal">
<li>sends requests from multiple clients on a single connection towa rd an origin <li>sends requests from multiple clients on a single connection towa rd an origin
server, or</li> server, or</li>
<li>takes responses from multiple origin servers and places them on a shared <li>takes responses from multiple origin servers and places them on a shared
connection toward a client.</li> connection toward a client.</li>
</ul> </ul>
<t>Web browsers also need to assume that requests made on the same con nection by <t>Web browsers also need to assume that requests made on the same con nection by
different web origins (<xref target="RFC6454" format="default"/>) are made by mu tually distrustful entities. different web origins (<xref target="RFC6454"/>) are made by mutually distrustfu l entities.
Other scenarios involving mutually distrustful entities are also possible.</t> Other scenarios involving mutually distrustful entities are also possible.</t>
</section> </section>
<section anchor="mitigation" numbered="true" toc="default"> <section anchor="mitigation">
<name>Mitigation</name> <name>Mitigation</name>
<t>Users of HTTP that require confidentiality for header or trailer fi elds can use <t>Users of HTTP that require confidentiality for header or trailer fi elds can use
values with entropy sufficient to make guessing infeasible. However, this is values with entropy sufficient to make guessing infeasible. However, this is
impractical as a general solution because it forces all users of HTTP to take impractical as a general solution because it forces all users of HTTP to take
steps to mitigate attacks. It would impose new constraints on how HTTP is used.< /t> steps to mitigate attacks. It would impose new constraints on how HTTP is used.< /t>
<t>Rather than impose constraints on users of HTTP, an implementation of QPACK can <t>Rather than impose constraints on users of HTTP, an implementation of QPACK can
instead constrain how compression is applied in order to limit the potential for instead constrain how compression is applied in order to limit the potential for
dynamic table probing.</t> dynamic table probing.</t>
<t>An ideal solution segregates access to the dynamic table based on t he entity <t>An ideal solution segregates access to the dynamic table based on t he entity
that is constructing the message. Field values that are added to the table are that is constructing the message. Field values that are added to the table are
skipping to change at line 1180 skipping to change at line 1161
a field value to result in the field not being compared to the dynamic table a field value to result in the field not being compared to the dynamic table
entries in future messages, effectively preventing further guesses.</t> entries in future messages, effectively preventing further guesses.</t>
<t>This response might be made inversely proportional to the length of the <t>This response might be made inversely proportional to the length of the
field value. Disabling access to the dynamic table for a given field name might field value. Disabling access to the dynamic table for a given field name might
occur for shorter values more quickly or with higher probability than for longer occur for shorter values more quickly or with higher probability than for longer
values.</t> values.</t>
<t>This mitigation is most effective between two endpoints. If message s are <t>This mitigation is most effective between two endpoints. If message s are
re-encoded by an intermediary without knowledge of which entity constructed a re-encoded by an intermediary without knowledge of which entity constructed a
given message, the intermediary could inadvertently merge compression contexts given message, the intermediary could inadvertently merge compression contexts
that the original encoder had specifically kept separate.</t> that the original encoder had specifically kept separate.</t>
<dl> <aside>
<dt> <t>Note: Simply removing entries corresponding to the field from the
Note: </dt> dynamic table
<dd> can be ineffectual if the attacker has a reliable way of causing values to be
<t>Simply removing entries corresponding to the field from the dyn reinstalled. For example, a request to load an image in a web browser typically
amic table can includes the Cookie header field (a potentially highly valued target for this
be ineffectual if the attacker has a reliable way of causing values to be sort of attack), and websites can easily force an image to be loaded, thereby
reinstalled. For example, a request to load an image in a web browser refreshing the entry in the dynamic table.</t>
typically includes the Cookie header field (a potentially highly valued target </aside>
for this sort of attack), and web sites can easily force an image to be
loaded, thereby refreshing the entry in the dynamic table.</t>
</dd>
</dl>
</section> </section>
<section anchor="never-indexed-literals" numbered="true" toc="default"> <section anchor="never-indexed-literals">
<name>Never-Indexed Literals</name> <name>Never-Indexed Literals</name>
<t>Implementations can also choose to protect sensitive fields by not compressing <t>Implementations can also choose to protect sensitive fields by not compressing
them and instead encoding their value as literals.</t> them and instead encoding their value as literals.</t>
<t>Refusing to insert a field line into the dynamic table is only effe ctive if <t>Refusing to insert a field line into the dynamic table is only effe ctive if
doing so is avoided on all hops. The never-indexed literal bit (see doing so is avoided on all hops. The never-indexed literal bit (see
<xref target="literal-name-reference" format="default"/>) can be used to signal to intermediaries that a <xref target="literal-name-reference"/>) can be used to signal to intermediaries that a
particular value was intentionally sent as a literal.</t> particular value was intentionally sent as a literal.</t>
<t>An intermediary MUST NOT re-encode a value that uses a literal repr esentation <t>An intermediary <bcp14>MUST NOT</bcp14> re-encode a value that uses a literal representation
with the 'N' bit set with another representation that would index it. If QPACK with the 'N' bit set with another representation that would index it. If QPACK
is used for re-encoding, a literal representation with the 'N' bit set MUST be is used for re-encoding, a literal representation with the 'N' bit set <bcp14>MU ST</bcp14> be
used. If HPACK is used for re-encoding, the never-indexed literal used. If HPACK is used for re-encoding, the never-indexed literal
representation (see <xref section="6.2.3" sectionFormat="of" target="RFC7541" fo rmat="default"/>) MUST be used.</t> representation (see <xref section="6.2.3" sectionFormat="of" target="RFC7541"/>) <bcp14>MUST</bcp14> be used.</t>
<t>The choice to mark that a field value should never be indexed depen ds on several <t>The choice to mark that a field value should never be indexed depen ds on several
factors. Since QPACK does not protect against guessing an entire field value, factors. Since QPACK does not protect against guessing an entire field value,
short or low-entropy values are more readily recovered by an adversary. short or low-entropy values are more readily recovered by an adversary.
Therefore, an encoder might choose not to index values with low entropy.</t> Therefore, an encoder might choose not to index values with low entropy.</t>
<t>An encoder might also choose not to index values for fields that ar e considered <t>An encoder might also choose not to index values for fields that ar e considered
to be highly valuable or sensitive to recovery, such as the Cookie or to be highly valuable or sensitive to recovery, such as the Cookie or
Authorization header fields.</t> Authorization header fields.</t>
<t>On the contrary, an encoder might prefer indexing values for fields that have <t>On the contrary, an encoder might prefer indexing values for fields that have
little or no value if they were exposed. For instance, a User-Agent header field little or no value if they were exposed. For instance, a User-Agent header field
does not commonly vary between requests and is sent to any server. In that case, does not commonly vary between requests and is sent to any server. In that case,
confirmation that a particular User-Agent value has been used provides little confirmation that a particular User-Agent value has been used provides little
value.</t> value.</t>
<t>Note that these criteria for deciding to use a never-indexed litera l <t>Note that these criteria for deciding to use a never-indexed litera l
representation will evolve over time as new attacks are discovered.</t> representation will evolve over time as new attacks are discovered.</t>
</section> </section>
</section> </section>
<section anchor="static-huffman-encoding" numbered="true" toc="default"> <section anchor="static-huffman-encoding">
<name>Static Huffman Encoding</name> <name>Static Huffman Encoding</name>
<t>There is no currently known attack against a static Huffman encoding. A study <t>There is no currently known attack against a static Huffman encoding. A study
has shown that using a static Huffman encoding table created an information has shown that using a static Huffman encoding table created an information
leakage, however this same study concluded that an attacker could not take leakage; however, this same study concluded that an attacker could not take
advantage of this information leakage to recover any meaningful amount of advantage of this information leakage to recover any meaningful amount of
information (see <xref target="PETAL" format="default"/>).</t> information (see <xref target="PETAL"/>).</t>
</section> </section>
<section anchor="memory-consumption" numbered="true" toc="default"> <section anchor="memory-consumption">
<name>Memory Consumption</name> <name>Memory Consumption</name>
<t>An attacker can try to cause an endpoint to exhaust its memory. QPACK is <t>An attacker can try to cause an endpoint to exhaust its memory. QPACK is
designed to limit both the peak and stable amounts of memory allocated by an designed to limit both the peak and stable amounts of memory allocated by an
endpoint.</t> endpoint.</t>
<t>QPACK uses the definition of the maximum size of the dynamic table an d the <t>QPACK uses the definition of the maximum size of the dynamic table an d the
maximum number of blocking streams to limit the amount of memory the encoder can maximum number of blocking streams to limit the amount of memory the encoder can
cause the decoder to consume. In HTTP/3, these values are controlled by the cause the decoder to consume. In HTTP/3, these values are controlled by the
decoder through the settings parameters SETTINGS_QPACK_MAX_TABLE_CAPACITY and decoder through the settings parameters SETTINGS_QPACK_MAX_TABLE_CAPACITY and
SETTINGS_QPACK_BLOCKED_STREAMS, respectively (see SETTINGS_QPACK_BLOCKED_STREAMS, respectively (see
<xref target="maximum-dynamic-table-capacity" format="default"/> and <xref targe t="blocked-streams" format="default"/>). The limit on the <xref target="maximum-dynamic-table-capacity"/> and <xref target="blocked-stream s"/>). The limit on the
size of the dynamic table takes into account the size of the data stored in the size of the dynamic table takes into account the size of the data stored in the
dynamic table, plus a small allowance for overhead. The limit on the number of dynamic table, plus a small allowance for overhead. The limit on the number of
blocked streams is only a proxy for the maximum amount of memory required by the blocked streams is only a proxy for the maximum amount of memory required by the
decoder. The actual maximum amount of memory will depend on how much memory the decoder. The actual maximum amount of memory will depend on how much memory the
decoder uses to track each blocked stream.</t> decoder uses to track each blocked stream.</t>
<t>A decoder can limit the amount of state memory used for the dynamic t able by <t>A decoder can limit the amount of state memory used for the dynamic t able by
setting an appropriate value for the maximum size of the dynamic table. In setting an appropriate value for the maximum size of the dynamic table. In
HTTP/3, this is realized by setting an appropriate value for the HTTP/3, this is realized by setting an appropriate value for the
SETTINGS_QPACK_MAX_TABLE_CAPACITY parameter. An encoder can limit the amount of SETTINGS_QPACK_MAX_TABLE_CAPACITY parameter. An encoder can limit the amount of
state memory it uses by choosing a smaller dynamic table size than the decoder state memory it uses by choosing a smaller dynamic table size than the decoder
allows and signaling this to the decoder (see <xref target="set-dynamic-capacity " format="default"/>).</t> allows and signaling this to the decoder (see <xref target="set-dynamic-capacity "/>).</t>
<t>A decoder can limit the amount of state memory used for blocked strea ms by <t>A decoder can limit the amount of state memory used for blocked strea ms by
setting an appropriate value for the maximum number of blocked streams. In setting an appropriate value for the maximum number of blocked streams. In
HTTP/3, this is realized by setting an appropriate value for the HTTP/3, this is realized by setting an appropriate value for the
SETTINGS_QPACK_BLOCKED_STREAMS parameter. Streams which risk becoming blocked SETTINGS_QPACK_BLOCKED_STREAMS parameter. Streams that risk becoming blocked
consume no additional state memory on the encoder.</t> consume no additional state memory on the encoder.</t>
<t>An encoder allocates memory to track all dynamic table references in <t>An encoder allocates memory to track all dynamic table references in
unacknowledged field sections. An implementation can directly limit the amount unacknowledged field sections. An implementation can directly limit the amount
of state memory by only using as many references to the dynamic table as it of state memory by only using as many references to the dynamic table as it
wishes to track; no signaling to the decoder is required. However, limiting wishes to track; no signaling to the decoder is required. However, limiting
references to the dynamic table will reduce compression effectiveness.</t> references to the dynamic table will reduce compression effectiveness.</t>
<t>The amount of temporary memory consumed by an encoder or decoder can be limited <t>The amount of temporary memory consumed by an encoder or decoder can be limited
by processing field lines sequentially. A decoder implementation does not need by processing field lines sequentially. A decoder implementation does not need
to retain a complete list of field lines while decoding a field section. An to retain a complete list of field lines while decoding a field section. An
encoder implementation does not need to retain a complete list of field lines encoder implementation does not need to retain a complete list of field lines
skipping to change at line 1279 skipping to change at line 1256
constraints might make this necessary.</t> constraints might make this necessary.</t>
<t>While the negotiated limit on the dynamic table size accounts for muc h of the <t>While the negotiated limit on the dynamic table size accounts for muc h of the
memory that can be consumed by a QPACK implementation, data that cannot be memory that can be consumed by a QPACK implementation, data that cannot be
immediately sent due to flow control is not affected by this limit. immediately sent due to flow control is not affected by this limit.
Implementations should limit the size of unsent data, especially on the decoder Implementations should limit the size of unsent data, especially on the decoder
stream where flexibility to choose what to send is limited. Possible responses stream where flexibility to choose what to send is limited. Possible responses
to an excess of unsent data might include limiting the ability of the peer to to an excess of unsent data might include limiting the ability of the peer to
open new streams, reading only from the encoder stream, or closing the open new streams, reading only from the encoder stream, or closing the
connection.</t> connection.</t>
</section> </section>
<section anchor="implementation-limits" numbered="true" toc="default"> <section anchor="implementation-limits">
<name>Implementation Limits</name> <name>Implementation Limits</name>
<t>An implementation of QPACK needs to ensure that large values for inte gers, long <t>An implementation of QPACK needs to ensure that large values for inte gers, long
encoding for integers, or long string literals do not create security encoding for integers, or long string literals do not create security
weaknesses.</t> weaknesses.</t>
<t>An implementation has to set a limit for the values it accepts for in tegers, as <t>An implementation has to set a limit for the values it accepts for in tegers, as
well as for the encoded length; see <xref target="prefixed-integers" format="def ault"/>. In the same way, it well as for the encoded length; see <xref target="prefixed-integers"/>. In the s ame way, it
has to set a limit to the length it accepts for string literals; see has to set a limit to the length it accepts for string literals; see
<xref target="string-literals" format="default"/>. These limits SHOULD be large enough to process the <xref target="string-literals"/>. These limits <bcp14>SHOULD</bcp14> be large e nough to process the
largest individual field the HTTP implementation can be configured to accept.</t > largest individual field the HTTP implementation can be configured to accept.</t >
<t>If an implementation encounters a value larger than it is able to dec ode, this <t>If an implementation encounters a value larger than it is able to dec ode, this
MUST be treated as a stream error of type QPACK_DECOMPRESSION_FAILED if on a <bcp14>MUST</bcp14> be treated as a stream error of type QPACK_DECOMPRESSION_FAI
request stream, or a connection error of the appropriate type if on the encoder LED if on a
request stream or a connection error of the appropriate type if on the encoder
or decoder stream.</t> or decoder stream.</t>
</section> </section>
</section> </section>
<section anchor="iana-considerations" numbered="true" toc="default"> <section anchor="iana-considerations">
<name>IANA Considerations</name> <name>IANA Considerations</name>
<section anchor="settings-registration" numbered="true" toc="default"> <t>This document makes multiple registrations in the registries defined by
<xref target="HTTP3"/>. The allocations created by this document are all assigne
d permanent
status and list a change controller of the IETF and a contact of the HTTP
working group (ietf-http-wg@w3.org).</t>
<section anchor="settings-registration">
<name>Settings Registration</name> <name>Settings Registration</name>
<t>This document specifies two settings. The entries in the following ta ble are <t>This document specifies two settings. The entries in the following ta ble are
registered in the "HTTP/3 Settings" registry established in <xref target="HTTP3" registered in the "HTTP/3 Settings" registry established in <xref target="HTTP3"
format="default"/>.</t> />.</t>
<table align="center"> <table>
<name>Additions to the HTTP/3 Settings Registry</name>
<thead> <thead>
<tr> <tr>
<th align="left">Setting Name</th> <th align="left">Setting Name</th>
<th align="center">Code</th> <th align="center">Code</th>
<th align="left">Specification</th> <th align="left">Specification</th>
<th align="left">Default</th> <th align="left">Default</th>
</tr> </tr>
</thead> </thead>
<tbody> <tbody>
<tr> <tr>
<td align="left">QPACK_MAX_TABLE_CAPACITY</td> <td align="left">QPACK_MAX_TABLE_CAPACITY</td>
<td align="center">0x1</td> <td align="center">0x01</td>
<td align="left"> <td align="left"><xref target="configuration"/></td>
<xref target="configuration" format="default"/></td>
<td align="left">0</td> <td align="left">0</td>
</tr> </tr>
<tr> <tr>
<td align="left">QPACK_BLOCKED_STREAMS</td> <td align="left">QPACK_BLOCKED_STREAMS</td>
<td align="center">0x7</td> <td align="center">0x07</td>
<td align="left"> <td align="left"><xref target="configuration"/></td>
<xref target="configuration" format="default"/></td>
<td align="left">0</td> <td align="left">0</td>
</tr> </tr>
</tbody> </tbody>
</table> </table>
<t>For fomatting reasons, the setting names here are abbreviated by remo <t>For formatting reasons, the setting names here are abbreviated by rem
ving the oving the
'SETTING_' prefix.</t> 'SETTINGS_' prefix.</t>
</section> </section>
<section anchor="stream-type-registration" numbered="true" toc="default"> <section anchor="stream-type-registration">
<name>Stream Type Registration</name> <name>Stream Type Registration</name>
<t>This document specifies two stream types. The entries in the followin g table are <t>This document specifies two stream types. The entries in the followin g table are
registered in the "HTTP/3 Stream Type" registry established in <xref target="HTT registered in the "HTTP/3 Stream Types" registry established in <xref target="HT
P3" format="default"/>.</t> TP3"/>.</t>
<table align="center"> <table>
<name>Additions to the HTTP/3 Stream Types Registry</name>
<thead> <thead>
<tr> <tr>
<th align="left">Stream Type</th> <th align="left">Stream Type</th>
<th align="center">Code</th> <th align="center">Code</th>
<th align="left">Specification</th> <th align="left">Specification</th>
<th align="left">Sender</th> <th align="left">Sender</th>
</tr> </tr>
</thead> </thead>
<tbody> <tbody>
<tr> <tr>
<td align="left">QPACK Encoder Stream</td> <td align="left">QPACK Encoder Stream</td>
<td align="center">0x02</td> <td align="center">0x02</td>
<td align="left"> <td align="left"><xref target="enc-dec-stream-def"/></td>
<xref target="enc-dec-stream-def" format="default"/></td>
<td align="left">Both</td> <td align="left">Both</td>
</tr> </tr>
<tr> <tr>
<td align="left">QPACK Decoder Stream</td> <td align="left">QPACK Decoder Stream</td>
<td align="center">0x03</td> <td align="center">0x03</td>
<td align="left"> <td align="left"><xref target="enc-dec-stream-def"/></td>
<xref target="enc-dec-stream-def" format="default"/></td>
<td align="left">Both</td> <td align="left">Both</td>
</tr> </tr>
</tbody> </tbody>
</table> </table>
</section> </section>
<section anchor="error-code-registration" numbered="true" toc="default"> <section anchor="error-code-registration">
<name>Error Code Registration</name> <name>Error Code Registration</name>
<t>This document specifies three error codes. The entries in the followi ng table <t>This document specifies three error codes. The entries in the followi ng table
are registered in the "HTTP/3 Error Code" registry established in <xref target=" are registered in the "HTTP/3 Error Codes" registry established in <xref target=
HTTP3" format="default"/>.</t> "HTTP3"/>.</t>
<table align="center"> <table>
<name>Additions to the HTTP/3 Error Codes Registry</name>
<thead> <thead>
<tr> <tr>
<th align="left">Name</th> <th align="left">Name</th>
<th align="left">Code</th> <th align="left">Code</th>
<th align="left">Description</th> <th align="left">Description</th>
<th align="left">Specification</th> <th align="left">Specification</th>
</tr> </tr>
</thead> </thead>
<tbody> <tbody>
<tr> <tr>
<td align="left">QPACK_DECOMPRESSION_FAILED</td> <td align="left">QPACK_DECOMPRESSION_FAILED</td>
<td align="left">0x200</td> <td align="left">0x0200</td>
<td align="left">Decoding of a field section failed</td> <td align="left">Decoding of a field section failed</td>
<td align="left"> <td align="left"><xref target="error-handling"/></td>
<xref target="error-handling" format="default"/></td>
</tr> </tr>
<tr> <tr>
<td align="left">QPACK_ENCODER_STREAM_ERROR</td> <td align="left">QPACK_ENCODER_STREAM_ERROR</td>
<td align="left">0x201</td> <td align="left">0x0201</td>
<td align="left">Error on the encoder stream</td> <td align="left">Error on the encoder stream</td>
<td align="left"> <td align="left"><xref target="error-handling"/></td>
<xref target="error-handling" format="default"/></td>
</tr> </tr>
<tr> <tr>
<td align="left">QPACK_DECODER_STREAM_ERROR</td> <td align="left">QPACK_DECODER_STREAM_ERROR</td>
<td align="left">0x202</td> <td align="left">0x0202</td>
<td align="left">Error on the decoder stream</td> <td align="left">Error on the decoder stream</td>
<td align="left"> <td align="left"><xref target="error-handling"/></td>
<xref target="error-handling" format="default"/></td>
</tr> </tr>
</tbody> </tbody>
</table> </table>
</section> </section>
</section> </section>
</middle> </middle>
<back> <back>
<displayreference target="HTTP2" to="HTTP/2"/>
<displayreference target="HTTP3" to="HTTP/3"/>
<references> <references>
<name>References</name> <name>References</name>
<references> <references>
<name>Normative References</name> <name>Normative References</name>
<reference anchor="HTTP3"> <reference anchor="HTTP3" target="https://www.rfc-editor.org/info/rfc911 4">
<front> <front>
<title>Hypertext Transfer Protocol Version 3 (HTTP/3)</title> <title>HTTP/3</title>
<author initials="M." surname="Bishop" fullname="Mike Bishop" role=" editor"> <author initials="M." surname="Bishop" fullname="Mike Bishop" role=" editor">
<organization>Akamai Technologies</organization> <organization>Akamai Technologies</organization>
</author> </author>
<date year="2021" month="February" day="02"/> <date year="2022" month="June"/>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-quic-http-34"/>
</reference>
<reference anchor="QUIC-TRANSPORT">
<front>
<title>QUIC: A UDP-Based Multiplexed and Secure Transport</title>
<author initials="J." surname="Iyengar" fullname="Jana Iyengar" role
="editor">
<organization>Fastly</organization>
</author>
<author initials="M." surname="Thomson" fullname="Martin Thomson" ro
le="editor">
<organization>Mozilla</organization>
</author>
<date year="2021" month="February" day="02"/>
</front> </front>
<seriesInfo name="Internet-Draft" value="draft-ietf-quic-transport-34" <seriesInfo name="RFC" value="9114"/>
/> <seriesInfo name="DOI" value="10.17487/RFC9114"/>
</reference> </reference>
<reference anchor="SEMANTICS" target="http://www.ietf.org/internet-draft s/draft-ietf-httpbis-semantics-14.txt"> <reference anchor="HTTP" target="https://www.rfc-editor.org/info/rfc9110 ">
<front> <front>
<title>HTTP Semantics</title> <title>HTTP Semantics</title>
<author initials="R" surname="Fielding" fullname="Roy Fielding"> <author fullname="Roy T. Fielding" initials="R" surname="Fielding" r
<organization/> ole="editor">
<organization>Adobe</organization>
</author> </author>
<author initials="M" surname="Nottingham" fullname="Mark Nottingham" <author fullname="Mark Nottingham" initials="M" surname="Nottingham"
> role="editor">
<organization/> <organization>Fastly</organization>
</author> </author>
<author initials="J" surname="Reschke" fullname="Julian Reschke"> <author fullname="Julian Reschke" initials="J" surname="Reschke" rol
<organization/> e="editor">
<organization>greenbytes GmbH</organization>
</author> </author>
<date month="January" day="12" year="2021"/> <date month="June" year="2022"/>
<abstract> <abstract>
<t>The Hypertext Transfer Protocol (HTTP) is a stateless applicati <t>The Hypertext Transfer Protocol (HTTP) is a stateless applicati
on- level protocol for distributed, collaborative, hypertext information systems on-
. This document describes the overall architecture of HTTP, establishes common level protocol for distributed, collaborative, hypertext information
terminology, and defines aspects of the protocol that are shared by all versions systems. This document describes the overall architecture of HTTP,
. In this definition are core protocol elements, extensibility mechanisms, and establishes common terminology, and defines aspects of the protocol
the "http" and "https" Uniform Resource Identifier (URI) schemes. This document that are shared by all versions. In this definition are core
obsoletes RFC 2818, RFC 7231, RFC 7232, RFC 7233, RFC 7235, RFC 7538, RFC 7615, protocol elements, extensibility mechanisms, and the "http" and
RFC 7694, and portions of RFC 7230.</t> "https" Uniform Resource Identifier (URI) schemes.
This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232,
7233, 7235, 7538, 7615, 7694, and portions of 7230.</t>
</abstract> </abstract>
</front> </front>
<seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-semantics- <seriesInfo name="STD" value="97"/>
14"/> <seriesInfo name="RFC" value="9110"/>
<seriesInfo name="DOI" value="10.17487/RFC9110"/>
</reference> </reference>
<reference anchor="RFC2360" target="https://www.rfc-editor.org/info/rfc2 360"> <reference anchor="RFC2360" target="https://www.rfc-editor.org/info/rfc2 360">
<front> <front>
<title>Guide for Internet Standards Writers</title> <title>Guide for Internet Standards Writers</title>
<author initials="G." surname="Scott" fullname="G. Scott"> <author fullname="G. Scott" initials="G." surname="Scott">
<organization/> <organization/>
</author> </author>
<date year="1998" month="June"/> <date month="June" year="1998"/>
<abstract> <abstract>
<t>This document is a guide for Internet standard writers. It def ines those characteristics that make standards coherent, unambiguous, and easy t o interpret. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</ t> <t>This document is a guide for Internet standard writers. It def ines those characteristics that make standards coherent, unambiguous, and easy t o interpret. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</ t>
</abstract> </abstract>
</front> </front>
<seriesInfo name="BCP" value="22"/> <seriesInfo name="BCP" value="22"/>
<seriesInfo name="RFC" value="2360"/> <seriesInfo name="RFC" value="2360"/>
<seriesInfo name="DOI" value="10.17487/RFC2360"/> <seriesInfo name="DOI" value="10.17487/RFC2360"/>
</reference> </reference>
<reference anchor="RFC7541" target="https://www.rfc-editor.org/info/rfc7 <reference anchor="QUIC-TRANSPORT" target="https://www.rfc-editor.org/i
541"> nfo/rfc9000">
<front>
<title>QUIC: A UDP-Based Multiplexed and Secure Transport</title>
<author fullname="J. Iyengar" initials="J." role="editor" surname="I
yengar">
<organization/>
</author>
<author fullname="M. Thomson" initials="M." role="editor" surname="T
homson">
<organization/>
</author>
<date month="May" year="2021"/>
<abstract>
<t>This document defines the core of the QUIC transport protocol.
QUIC provides applications with flow-controlled streams for structured communic
ation, low-latency connection establishment, and network path migration. QUIC in
cludes security measures that ensure confidentiality, integrity, and availabilit
y in a range of deployment circumstances. Accompanying documents describe the i
ntegration of TLS for key negotiation, loss detection, and an exemplary congesti
on control algorithm.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="9000"/>
<seriesInfo name="DOI" value="10.17487/RFC9000"/>
</reference>
<reference anchor="RFC7541" target="https://www.rfc-editor.org/info/rfc
7541">
<front> <front>
<title>HPACK: Header Compression for HTTP/2</title> <title>HPACK: Header Compression for HTTP/2</title>
<author initials="R." surname="Peon" fullname="R. Peon"> <author fullname="R. Peon" initials="R." surname="Peon">
<organization/> <organization/>
</author> </author>
<author initials="H." surname="Ruellan" fullname="H. Ruellan"> <author fullname="H. Ruellan" initials="H." surname="Ruellan">
<organization/> <organization/>
</author> </author>
<date year="2015" month="May"/> <date month="May" year="2015"/>
<abstract> <abstract>
<t>This specification defines HPACK, a compression format for effi ciently representing HTTP header fields, to be used in HTTP/2.</t> <t>This specification defines HPACK, a compression format for effi ciently representing HTTP header fields, to be used in HTTP/2.</t>
</abstract> </abstract>
</front> </front>
<seriesInfo name="RFC" value="7541"/> <seriesInfo name="RFC" value="7541"/>
<seriesInfo name="DOI" value="10.17487/RFC7541"/> <seriesInfo name="DOI" value="10.17487/RFC7541"/>
</reference> </reference>
<reference anchor="RFC2119" target="https://www.rfc-editor.org/info/rfc2 119"> <reference anchor="RFC2119" target="https://www.rfc-editor.org/info/rfc 2119">
<front> <front>
<title>Key words for use in RFCs to Indicate Requirement Levels</tit le> <title>Key words for use in RFCs to Indicate Requirement Levels</tit le>
<author initials="S." surname="Bradner" fullname="S. Bradner"> <author fullname="S. Bradner" initials="S." surname="Bradner">
<organization/> <organization/>
</author> </author>
<date year="1997" month="March"/> <date month="March" year="1997"/>
<abstract> <abstract>
<t>In many standards track documents several words are used to sig nify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF document s. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t> <t>In many standards track documents several words are used to sig nify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF document s. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t>
</abstract> </abstract>
</front> </front>
<seriesInfo name="BCP" value="14"/> <seriesInfo name="BCP" value="14"/>
<seriesInfo name="RFC" value="2119"/> <seriesInfo name="RFC" value="2119"/>
<seriesInfo name="DOI" value="10.17487/RFC2119"/> <seriesInfo name="DOI" value="10.17487/RFC2119"/>
</reference> </reference>
<reference anchor="RFC8174" target="https://www.rfc-editor.org/info/rfc8 174"> <reference anchor="RFC8174" target="https://www.rfc-editor.org/info/rfc 8174">
<front> <front>
<title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</ti tle> <title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</ti tle>
<author initials="B." surname="Leiba" fullname="B. Leiba"> <author fullname="B. Leiba" initials="B." surname="Leiba">
<organization/> <organization/>
</author> </author>
<date year="2017" month="May"/> <date month="May" year="2017"/>
<abstract> <abstract>
<t>RFC 2119 specifies common key words that may be used in protoco l specifications. This document aims to reduce the ambiguity by clarifying tha t only UPPERCASE usage of the key words have the defined special meanings.</t> <t>RFC 2119 specifies common key words that may be used in protoco l specifications. This document aims to reduce the ambiguity by clarifying tha t only UPPERCASE usage of the key words have the defined special meanings.</t>
</abstract> </abstract>
</front> </front>
<seriesInfo name="BCP" value="14"/> <seriesInfo name="BCP" value="14"/>
<seriesInfo name="RFC" value="8174"/> <seriesInfo name="RFC" value="8174"/>
<seriesInfo name="DOI" value="10.17487/RFC8174"/> <seriesInfo name="DOI" value="10.17487/RFC8174"/>
</reference> </reference>
</references> </references>
<references> <references>
skipping to change at line 1534 skipping to change at line 1529
<title>PETAL: Preset Encoding Table Information Leakage</title> <title>PETAL: Preset Encoding Table Information Leakage</title>
<author initials="J." surname="Tan" fullname="Jiaqi Tan"> <author initials="J." surname="Tan" fullname="Jiaqi Tan">
<organization/> <organization/>
</author> </author>
<author initials="J." surname="Nahata" fullname="Jayvardhan Nahata"> <author initials="J." surname="Nahata" fullname="Jayvardhan Nahata">
<organization/> <organization/>
</author> </author>
<date year="2013" month="April"/> <date year="2013" month="April"/>
</front> </front>
</reference> </reference>
<reference anchor="RFC7540" target="https://www.rfc-editor.org/info/rfc7 <reference anchor="HTTP2" target="https://www.rfc-editor.org/info/rfc911
540"> 3">
<front> <front>
<title>Hypertext Transfer Protocol Version 2 (HTTP/2)</title> <title>HTTP/2</title>
<author initials="M." surname="Belshe" fullname="M. Belshe"> <author initials="M." surname="Thomson" fullname="Martin Thomson" r
<organization/> ole="editor"/>
</author> <author initials="C." surname="Benfield" fullname="Cory Benfield" r
<author initials="R." surname="Peon" fullname="R. Peon"> ole="editor"/>
<organization/> <date year="2022" month="June"/>
</author> </front>
<author initials="M." surname="Thomson" fullname="M. Thomson" role=" <seriesInfo name="RFC" value="9113"/>
editor"> <seriesInfo name="DOI" value="10.17487/RFC9113"/>
<organization/>
</author>
<date year="2015" month="May"/>
<abstract>
<t>This specification describes an optimized expression of the sem
antics of the Hypertext Transfer Protocol (HTTP), referred to as HTTP version 2
(HTTP/2). HTTP/2 enables a more efficient use of network resources and a reduce
d perception of latency by introducing header field compression and allowing mul
tiple concurrent exchanges on the same connection. It also introduces unsolicit
ed push of representations from servers to clients.</t>
<t>This specification is an alternative to, but does not obsolete,
the HTTP/1.1 message syntax. HTTP's existing semantics remain unchanged.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="7540"/>
<seriesInfo name="DOI" value="10.17487/RFC7540"/>
</reference> </reference>
<reference anchor="TLS" target="https://www.rfc-editor.org/info/rfc8446" > <reference anchor="TLS" target="https://www.rfc-editor.org/info/rfc8446 ">
<front> <front>
<title>The Transport Layer Security (TLS) Protocol Version 1.3</titl e> <title>The Transport Layer Security (TLS) Protocol Version 1.3</titl e>
<author initials="E." surname="Rescorla" fullname="E. Rescorla"> <author fullname="E. Rescorla" initials="E." surname="Rescorla">
<organization/> <organization/>
</author> </author>
<date year="2018" month="August"/> <date month="August" year="2018"/>
<abstract> <abstract>
<t>This document specifies version 1.3 of the Transport Layer Secu rity (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery.</t> <t>This document specifies version 1.3 of the Transport Layer Secu rity (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery.</t>
<t>This document updates RFCs 5705 and 6066, and obsoletes RFCs 50 77, 5246, and 6961. This document also specifies new requirements for TLS 1.2 i mplementations.</t> <t>This document updates RFCs 5705 and 6066, and obsoletes RFCs 50 77, 5246, and 6961. This document also specifies new requirements for TLS 1.2 i mplementations.</t>
</abstract> </abstract>
</front> </front>
<seriesInfo name="RFC" value="8446"/> <seriesInfo name="RFC" value="8446"/>
<seriesInfo name="DOI" value="10.17487/RFC8446"/> <seriesInfo name="DOI" value="10.17487/RFC8446"/>
</reference> </reference>
<reference anchor="RFC1951" target="https://www.rfc-editor.org/info/rfc1 951"> <reference anchor="RFC1951" target="https://www.rfc-editor.org/info/rfc 1951">
<front> <front>
<title>DEFLATE Compressed Data Format Specification version 1.3</tit le> <title>DEFLATE Compressed Data Format Specification version 1.3</tit le>
<author initials="P." surname="Deutsch" fullname="P. Deutsch"> <author fullname="P. Deutsch" initials="P." surname="Deutsch">
<organization/> <organization/>
</author> </author>
<date year="1996" month="May"/> <date month="May" year="1996"/>
<abstract> <abstract>
<t>This specification defines a lossless compressed data format th at compresses data using a combination of the LZ77 algorithm and Huffman coding, with efficiency comparable to the best currently available general-purpose comp ression methods. This memo provides information for the Internet community. Th is memo does not specify an Internet standard of any kind.</t> <t>This specification defines a lossless compressed data format th at compresses data using a combination of the LZ77 algorithm and Huffman coding, with efficiency comparable to the best currently available general-purpose comp ression methods. This memo provides information for the Internet community. Th is memo does not specify an Internet standard of any kind.</t>
</abstract> </abstract>
</front> </front>
<seriesInfo name="RFC" value="1951"/> <seriesInfo name="RFC" value="1951"/>
<seriesInfo name="DOI" value="10.17487/RFC1951"/> <seriesInfo name="DOI" value="10.17487/RFC1951"/>
</reference> </reference>
<reference anchor="RFC6454" target="https://www.rfc-editor.org/info/rfc6 454"> <reference anchor="RFC6454" target="https://www.rfc-editor.org/info/rfc 6454">
<front> <front>
<title>The Web Origin Concept</title> <title>The Web Origin Concept</title>
<author initials="A." surname="Barth" fullname="A. Barth"> <author fullname="A. Barth" initials="A." surname="Barth">
<organization/> <organization/>
</author> </author>
<date year="2011" month="December"/> <date month="December" year="2011"/>
<abstract> <abstract>
<t>This document defines the concept of an "origin", which is ofte n used as the scope of authority or privilege by user agents. Typically, user a gents isolate content retrieved from different origins to prevent malicious web site operators from interfering with the operation of benign web sites. In addi tion to outlining the principles that underlie the concept of origin, this docum ent details how to determine the origin of a URI and how to serialize an origin into a string. It also defines an HTTP header field, named "Origin", that indic ates which origins are associated with an HTTP request. [STANDARDS-TRACK]</t> <t>This document defines the concept of an "origin", which is ofte n used as the scope of authority or privilege by user agents. Typically, user a gents isolate content retrieved from different origins to prevent malicious web site operators from interfering with the operation of benign web sites. In addi tion to outlining the principles that underlie the concept of origin, this docum ent details how to determine the origin of a URI and how to serialize an origin into a string. It also defines an HTTP header field, named "Origin", that indic ates which origins are associated with an HTTP request. [STANDARDS-TRACK]</t>
</abstract> </abstract>
</front> </front>
<seriesInfo name="RFC" value="6454"/> <seriesInfo name="RFC" value="6454"/>
<seriesInfo name="DOI" value="10.17487/RFC6454"/> <seriesInfo name="DOI" value="10.17487/RFC6454"/>
</reference> </reference>
</references> </references>
</references> </references>
<section anchor="static-table" numbered="true" toc="default"> <section anchor="static-table">
<name>Static Table</name> <name>Static Table</name>
<t>This table was generated by analyzing actual Internet traffic in 2018 a nd <t>This table was generated by analyzing actual Internet traffic in 2018 a nd
including the most common header fields, after filtering out some unsupported including the most common header fields, after filtering out some unsupported
and non-standard values. Due to this methodology, some of the entries may be and non-standard values. Due to this methodology, some of the entries may be
inconsistent or appear multiple times with similar but not identical values. The inconsistent or appear multiple times with similar but not identical values. The
order of the entries is optimized to encode the most common header fields with order of the entries is optimized to encode the most common header fields with
the smallest number of bytes.</t> the smallest number of bytes.</t>
<table align="center"> <table>
<name>Static Table</name>
<thead> <thead>
<tr> <tr>
<th align="left">Index</th> <th align="left">Index</th>
<th align="left">Name</th> <th align="left">Name</th>
<th align="left">Value</th> <th align="left">Value</th>
</tr> </tr>
</thead> </thead>
<tbody> <tbody>
<tr> <tr>
<td align="left">0</td> <td align="left">0</td>
<td align="left">:authority</td> <td align="left">:authority</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">1</td> <td align="left">1</td>
<td align="left">:path</td> <td align="left">:path</td>
<td align="left">/</td> <td align="left">/</td>
</tr> </tr>
<tr> <tr>
<td align="left">2</td> <td align="left">2</td>
<td align="left">age</td> <td align="left">age</td>
<td align="left">0</td> <td align="left">0</td>
</tr> </tr>
<tr> <tr>
<td align="left">3</td> <td align="left">3</td>
<td align="left">content-disposition</td> <td align="left">content-disposition</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">4</td> <td align="left">4</td>
<td align="left">content-length</td> <td align="left">content-length</td>
<td align="left">0</td> <td align="left">0</td>
</tr> </tr>
<tr> <tr>
<td align="left">5</td> <td align="left">5</td>
<td align="left">cookie</td> <td align="left">cookie</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">6</td> <td align="left">6</td>
<td align="left">date</td> <td align="left">date</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">7</td> <td align="left">7</td>
<td align="left">etag</td> <td align="left">etag</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">8</td> <td align="left">8</td>
<td align="left">if-modified-since</td> <td align="left">if-modified-since</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">9</td> <td align="left">9</td>
<td align="left">if-none-match</td> <td align="left">if-none-match</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">10</td> <td align="left">10</td>
<td align="left">last-modified</td> <td align="left">last-modified</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">11</td> <td align="left">11</td>
<td align="left">link</td> <td align="left">link</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">12</td> <td align="left">12</td>
<td align="left">location</td> <td align="left">location</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">13</td> <td align="left">13</td>
<td align="left">referer</td> <td align="left">referer</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">14</td> <td align="left">14</td>
<td align="left">set-cookie</td> <td align="left">set-cookie</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">15</td> <td align="left">15</td>
<td align="left">:method</td> <td align="left">:method</td>
<td align="left">CONNECT</td> <td align="left">CONNECT</td>
</tr> </tr>
<tr> <tr>
<td align="left">16</td> <td align="left">16</td>
<td align="left">:method</td> <td align="left">:method</td>
<td align="left">DELETE</td> <td align="left">DELETE</td>
skipping to change at line 1980 skipping to change at line 1965
<td align="left">425</td> <td align="left">425</td>
</tr> </tr>
<tr> <tr>
<td align="left">71</td> <td align="left">71</td>
<td align="left">:status</td> <td align="left">:status</td>
<td align="left">500</td> <td align="left">500</td>
</tr> </tr>
<tr> <tr>
<td align="left">72</td> <td align="left">72</td>
<td align="left">accept-language</td> <td align="left">accept-language</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">73</td> <td align="left">73</td>
<td align="left">access-control-allow-credentials</td> <td align="left">access-control-allow-credentials</td>
<td align="left">FALSE</td> <td align="left">FALSE</td>
</tr> </tr>
<tr> <tr>
<td align="left">74</td> <td align="left">74</td>
<td align="left">access-control-allow-credentials</td> <td align="left">access-control-allow-credentials</td>
<td align="left">TRUE</td> <td align="left">TRUE</td>
skipping to change at line 2040 skipping to change at line 2025
<td align="left">post</td> <td align="left">post</td>
</tr> </tr>
<tr> <tr>
<td align="left">83</td> <td align="left">83</td>
<td align="left">alt-svc</td> <td align="left">alt-svc</td>
<td align="left">clear</td> <td align="left">clear</td>
</tr> </tr>
<tr> <tr>
<td align="left">84</td> <td align="left">84</td>
<td align="left">authorization</td> <td align="left">authorization</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">85</td> <td align="left">85</td>
<td align="left">content-security-policy</td> <td align="left">content-security-policy</td>
<td align="left">script-src 'none'; object-src 'none'; base-uri 'non e'</td> <td align="left">script-src 'none'; object-src 'none'; base-uri 'non e'</td>
</tr> </tr>
<tr> <tr>
<td align="left">86</td> <td align="left">86</td>
<td align="left">early-data</td> <td align="left">early-data</td>
<td align="left">1</td> <td align="left">1</td>
</tr> </tr>
<tr> <tr>
<td align="left">87</td> <td align="left">87</td>
<td align="left">expect-ct</td> <td align="left">expect-ct</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">88</td> <td align="left">88</td>
<td align="left">forwarded</td> <td align="left">forwarded</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">89</td> <td align="left">89</td>
<td align="left">if-range</td> <td align="left">if-range</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">90</td> <td align="left">90</td>
<td align="left">origin</td> <td align="left">origin</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">91</td> <td align="left">91</td>
<td align="left">purpose</td> <td align="left">purpose</td>
<td align="left">prefetch</td> <td align="left">prefetch</td>
</tr> </tr>
<tr> <tr>
<td align="left">92</td> <td align="left">92</td>
<td align="left">server</td> <td align="left">server</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">93</td> <td align="left">93</td>
<td align="left">timing-allow-origin</td> <td align="left">timing-allow-origin</td>
<td align="left">*</td> <td align="left">*</td>
</tr> </tr>
<tr> <tr>
<td align="left">94</td> <td align="left">94</td>
<td align="left">upgrade-insecure-requests</td> <td align="left">upgrade-insecure-requests</td>
<td align="left">1</td> <td align="left">1</td>
</tr> </tr>
<tr> <tr>
<td align="left">95</td> <td align="left">95</td>
<td align="left">user-agent</td> <td align="left">user-agent</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">96</td> <td align="left">96</td>
<td align="left">x-forwarded-for</td> <td align="left">x-forwarded-for</td>
<td align="left">&nbsp;</td> <td align="left"/>
</tr> </tr>
<tr> <tr>
<td align="left">97</td> <td align="left">97</td>
<td align="left">x-frame-options</td> <td align="left">x-frame-options</td>
<td align="left">deny</td> <td align="left">deny</td>
</tr> </tr>
<tr> <tr>
<td align="left">98</td> <td align="left">98</td>
<td align="left">x-frame-options</td> <td align="left">x-frame-options</td>
<td align="left">sameorigin</td> <td align="left">sameorigin</td>
</tr> </tr>
</tbody> </tbody>
</table> </table>
<t>Any line breaks that appear within field names or values are due to for matting.</t> <t>Any line breaks that appear within field names or values are due to for matting.</t>
</section> </section>
<section anchor="encoding-and-decoding-examples" numbered="true" toc="defaul t"> <section anchor="encoding-and-decoding-examples">
<name>Encoding and Decoding Examples</name> <name>Encoding and Decoding Examples</name>
<t>The following examples represent a series of exchanges between an encod er and a <t>The following examples represent a series of exchanges between an encod er and a
decoder. The exchanges are designed to exercise most QPACK instructions, and decoder. The exchanges are designed to exercise most QPACK instructions and
highlight potentially common patterns and their impact on dynamic table state. highlight potentially common patterns and their impact on dynamic table state.
The encoder sends three encoded field sections containing one field line each, The encoder sends three encoded field sections containing one field line each,
as well as two speculative inserts that are not referenced.</t> as well as two speculative inserts that are not referenced.</t>
<t>The state of the encoder's dynamic table is shown, along with its <t>The state of the encoder's dynamic table is shown, along with its
current size. Each entry is shown with the Absolute Index of the entry (Abs), current size. Each entry is shown with the Absolute Index of the entry (Abs),
the current number of outstanding encoded field sections with references to that the current number of outstanding encoded field sections with references to that
entry (Ref), along with the name and value. Entries above the 'acknowledged' entry (Ref), along with the name and value. Entries above the 'acknowledged'
line have been acknowledged by the decoder.</t> line have been acknowledged by the decoder.</t>
<section anchor="literal-field-line-with-name-reference" numbered="true" t <section anchor="literal-field-line-with-name-reference">
oc="default"> <name>Literal Field Line with Name Reference</name>
<name>Literal Field Line With Name Reference</name>
<t>The encoder sends an encoded field section containing a literal repre sentation <t>The encoder sends an encoded field section containing a literal repre sentation
of a field with a static name reference.</t> of a field with a static name reference.</t>
<artwork name="" type="" align="left" alt=""><![CDATA[ <artwork><![CDATA[
Data | Interpretation Data | Interpretation
| Encoder's Dynamic Table | Encoder's Dynamic Table
Stream: 0 Stream: 0
0000 | Required Insert Count = 0, Base = 0 0000 | Required Insert Count = 0, Base = 0
510b 2f69 6e64 6578 | Literal Field Line with Name Reference 510b 2f69 6e64 6578 | Literal Field Line with Name Reference
2e68 746d 6c | Static Table, Index=1 2e68 746d 6c | Static Table, Index=1
| (:path=/index.html) | (:path=/index.html)
Abs Ref Name Value Abs Ref Name Value
^-- acknowledged --^ ^-- acknowledged --^
Size=0 Size=0
]]></artwork> ]]></artwork>
</section> </section>
<section anchor="dynamic-table" numbered="true" toc="default"> <section anchor="dynamic-table">
<name>Dynamic Table</name> <name>Dynamic Table</name>
<t>The encoder sets the dynamic table capacity, inserts a header with a dynamic <t>The encoder sets the dynamic table capacity, inserts a header with a dynamic
name reference, then sends a potentially blocking, encoded field section name reference, then sends a potentially blocking, encoded field section
referencing this new entry. The decoder acknowledges processing the encoded referencing this new entry. The decoder acknowledges processing the encoded
field section, which implicitly acknowledges all dynamic table insertions up to field section, which implicitly acknowledges all dynamic table insertions up to
the Required Insert Count.</t> the Required Insert Count.</t>
<artwork name="" type="" align="left" alt=""><![CDATA[ <artwork><![CDATA[
Stream: Encoder Stream: Encoder
3fbd01 | Set Dynamic Table Capacity=220 3fbd01 | Set Dynamic Table Capacity=220
c00f 7777 772e 6578 | Insert With Name Reference c00f 7777 772e 6578 | Insert With Name Reference
616d 706c 652e 636f | Static Table, Index=0 616d 706c 652e 636f | Static Table, Index=0
6d | (:authority=www.example.com) 6d | (:authority=www.example.com)
c10c 2f73 616d 706c | Insert With Name Reference c10c 2f73 616d 706c | Insert With Name Reference
652f 7061 7468 | Static Table, Index=1 652f 7061 7468 | Static Table, Index=1
| (:path=/sample/path) | (:path=/sample/path)
Abs Ref Name Value Abs Ref Name Value
skipping to change at line 2195 skipping to change at line 2180
Stream: Decoder Stream: Decoder
84 | Section Acknowledgment (stream=4) 84 | Section Acknowledgment (stream=4)
Abs Ref Name Value Abs Ref Name Value
0 0 :authority www.example.com 0 0 :authority www.example.com
1 0 :path /sample/path 1 0 :path /sample/path
^-- acknowledged --^ ^-- acknowledged --^
Size=106 Size=106
]]></artwork> ]]></artwork>
</section> </section>
<section anchor="speculative-insert" numbered="true" toc="default"> <section anchor="speculative-insert">
<name>Speculative Insert</name> <name>Speculative Insert</name>
<t>The encoder inserts a header into the dynamic table with a literal na me. <t>The encoder inserts a header into the dynamic table with a literal na me.
The decoder acknowledges receipt of the entry. The encoder does not send The decoder acknowledges receipt of the entry. The encoder does not send
any encoded field sections.</t> any encoded field sections.</t>
<artwork name="" type="" align="left" alt=""><![CDATA[ <artwork><![CDATA[
Stream: Encoder Stream: Encoder
4a63 7573 746f 6d2d | Insert With Literal Name 4a63 7573 746f 6d2d | Insert With Literal Name
6b65 790c 6375 7374 | (custom-key=custom-value) 6b65 790c 6375 7374 | (custom-key=custom-value)
6f6d 2d76 616c 7565 | 6f6d 2d76 616c 7565 |
Abs Ref Name Value Abs Ref Name Value
0 0 :authority www.example.com 0 0 :authority www.example.com
1 0 :path /sample/path 1 0 :path /sample/path
^-- acknowledged --^ ^-- acknowledged --^
2 0 custom-key custom-value 2 0 custom-key custom-value
skipping to change at line 2225 skipping to change at line 2210
Abs Ref Name Value Abs Ref Name Value
0 0 :authority www.example.com 0 0 :authority www.example.com
1 0 :path /sample/path 1 0 :path /sample/path
2 0 custom-key custom-value 2 0 custom-key custom-value
^-- acknowledged --^ ^-- acknowledged --^
Size=160 Size=160
]]></artwork> ]]></artwork>
</section> </section>
<section anchor="duplicate-instruction-stream-cancellation" numbered="true " toc="default"> <section anchor="duplicate-instruction-stream-cancellation">
<name>Duplicate Instruction, Stream Cancellation</name> <name>Duplicate Instruction, Stream Cancellation</name>
<t>The encoder duplicates an existing entry in the dynamic table, then s ends an <t>The encoder duplicates an existing entry in the dynamic table, then s ends an
encoded field section referencing the dynamic table entries including the encoded field section referencing the dynamic table entries including the
duplicated entry. The packet containing the encoder stream data is delayed. duplicated entry. The packet containing the encoder stream data is delayed.
Before the packet arrives, the decoder cancels the stream and notifies the Before the packet arrives, the decoder cancels the stream and notifies the
encoder that the encoded field section was not processed.</t> encoder that the encoded field section was not processed.</t>
<artwork name="" type="" align="left" alt=""><![CDATA[ <artwork><![CDATA[
Stream: Encoder Stream: Encoder
02 | Duplicate (Relative Index = 2) 02 | Duplicate (Relative Index = 2)
| Absolute Index = | Absolute Index =
| Insert Count(4) - Index(2) - 1 = 1 | Insert Count(3) - Index(2) - 1 = 0
Abs Ref Name Value Abs Ref Name Value
0 0 :authority www.example.com 0 0 :authority www.example.com
1 0 :path /sample/path 1 0 :path /sample/path
2 0 custom-key custom-value 2 0 custom-key custom-value
^-- acknowledged --^ ^-- acknowledged --^
3 0 :authority www.example.com 3 0 :authority www.example.com
Size=217 Size=217
Stream: 8 Stream: 8
skipping to change at line 2273 skipping to change at line 2258
Size=217 Size=217
Stream: Decoder Stream: Decoder
48 | Stream Cancellation (Stream=8) 48 | Stream Cancellation (Stream=8)
Abs Ref Name Value Abs Ref Name Value
0 0 :authority www.example.com 0 0 :authority www.example.com
1 0 :path /sample/path 1 0 :path /sample/path
2 0 custom-key custom-value 2 0 custom-key custom-value
^-- acknowledged --^ ^-- acknowledged --^
4 0 :authority www.example.com 3 0 :authority www.example.com
Size=217 Size=217
]]></artwork> ]]></artwork>
</section> </section>
<section anchor="dynamic-table-insert-eviction" numbered="true" toc="defau lt"> <section anchor="dynamic-table-insert-eviction">
<name>Dynamic Table Insert, Eviction</name> <name>Dynamic Table Insert, Eviction</name>
<t>The encoder inserts another header into the dynamic table, which evic ts the <t>The encoder inserts another header into the dynamic table, which evic ts the
oldest entry. The encoder does not send any encoded field sections.</t> oldest entry. The encoder does not send any encoded field sections.</t>
<artwork name="" type="" align="left" alt=""><![CDATA[ <artwork><![CDATA[
Stream: Encoder Stream: Encoder
810d 6375 7374 6f6d | Insert With Name Reference 810d 6375 7374 6f6d | Insert With Name Reference
2d76 616c 7565 32 | Dynamic Table, Relative Index = 1 2d76 616c 7565 32 | Dynamic Table, Relative Index = 1
| Absolute Index = | Absolute Index =
| Insert Count(4) - Index(1) - 1 = 2 | Insert Count(4) - Index(1) - 1 = 2
| (custom-key=custom-value2) | (custom-key=custom-value2)
Abs Ref Name Value Abs Ref Name Value
1 0 :path /sample/path 1 0 :path /sample/path
2 0 custom-key custom-value 2 0 custom-key custom-value
^-- acknowledged --^ ^-- acknowledged --^
3 0 :authority www.example.com 3 0 :authority www.example.com
4 0 custom-key custom-value2 4 0 custom-key custom-value2
Size=215 Size=215
]]></artwork> ]]></artwork>
</section> </section>
</section> </section>
<section anchor="sample-one-pass-encoding-algorithm" numbered="true" toc="de <section anchor="sample-single-pass-encoding-algorithm">
fault"> <name>Sample Single-Pass Encoding Algorithm</name>
<name>Sample One Pass Encoding Algorithm</name> <t>Pseudocode for single-pass encoding, excluding handling of duplicates,
<t>Pseudo-code for single pass encoding, excluding handling of duplicates,
non-blocking mode, available encoder stream flow control and reference tracking. </t> non-blocking mode, available encoder stream flow control and reference tracking. </t>
<artwork name="" type="" align="left" alt=""><![CDATA[ <sourcecode type="pseudocode"><![CDATA[
# Helper functions: # Helper functions:
# ==== # ====
# Encode an interger with the specified prefix and length # Encode an integer with the specified prefix and length
encodeInteger(buffer, prefix, value, prefixLength) encodeInteger(buffer, prefix, value, prefixLength)
# Encode a dynamic table insert instruction with optional static # Encode a dynamic table insert instruction with optional static
# or dynamic name index (but not both) # or dynamic name index (but not both)
encodeInsert(buffer, staticNameIndex, dynamicNameIndex, fieldLine) encodeInsert(buffer, staticNameIndex, dynamicNameIndex, fieldLine)
# Encode a static index reference # Encode a static index reference
encodeStaticIndexReference(buffer, staticIndex) encodeStaticIndexReference(buffer, staticIndex)
# Encode a dynamic index reference relative to base # Encode a dynamic index reference relative to Base
encodeDynamicIndexReference(buffer, dynamicIndex, base) encodeDynamicIndexReference(buffer, dynamicIndex, base)
# Encode a literal with an optional static name index # Encode a literal with an optional static name index
encodeLiteral(buffer, staticNameIndex, fieldLine) encodeLiteral(buffer, staticNameIndex, fieldLine)
# Encode a literal with a dynamic name index relative to base # Encode a literal with a dynamic name index relative to Base
encodeDynamicLiteral(buffer, dynamicNameIndex, base, fieldLine) encodeDynamicLiteral(buffer, dynamicNameIndex, base, fieldLine)
# Encoding Algorithm # Encoding Algorithm
# ==== # ====
base = dynamicTable.getInsertCount() base = dynamicTable.getInsertCount()
requiredInsertCount = 0 requiredInsertCount = 0
for line in fieldLines: for line in fieldLines:
staticIndex = staticTable.findIndex(line) staticIndex = staticTable.findIndex(line)
if staticIndex is not None: if staticIndex is not None:
encodeStaticIndexReference(streamBuffer, staticIndex) encodeStaticIndexReference(streamBuffer, staticIndex)
skipping to change at line 2350 skipping to change at line 2335
dynamicNameIndex = dynamicTable.findName(line.name) dynamicNameIndex = dynamicTable.findName(line.name)
if shouldIndex(line) and dynamicTable.canIndex(line): if shouldIndex(line) and dynamicTable.canIndex(line):
encodeInsert(encoderBuffer, staticNameIndex, encodeInsert(encoderBuffer, staticNameIndex,
dynamicNameIndex, line) dynamicNameIndex, line)
dynamicIndex = dynamicTable.add(line) dynamicIndex = dynamicTable.add(line)
if dynamicIndex is None: if dynamicIndex is None:
# Could not index it, literal # Could not index it, literal
if dynamicNameIndex is not None: if dynamicNameIndex is not None:
# Encode literal with dynamic name, possibly above base # Encode literal with dynamic name, possibly above Base
encodeDynamicLiteral(streamBuffer, dynamicNameIndex, encodeDynamicLiteral(streamBuffer, dynamicNameIndex,
base, line) base, line)
requiredInsertCount = max(requiredInsertCount, requiredInsertCount = max(requiredInsertCount,
dynamicNameIndex) dynamicNameIndex)
else: else:
# Encodes a literal with a static name or literal name # Encodes a literal with a static name or literal name
encodeLiteral(streamBuffer, staticNameIndex, line) encodeLiteral(streamBuffer, staticNameIndex, line)
else: else:
# Dynamic index reference # Dynamic index reference
assert(dynamicIndex is not None) assert(dynamicIndex is not None)
requiredInsertCount = max(requiredInsertCount, dynamicIndex) requiredInsertCount = max(requiredInsertCount, dynamicIndex)
# Encode dynamicIndex, possibly above base # Encode dynamicIndex, possibly above Base
encodeDynamicIndexReference(streamBuffer, dynamicIndex, base) encodeDynamicIndexReference(streamBuffer, dynamicIndex, base)
# encode the prefix # encode the prefix
if requiredInsertCount == 0: if requiredInsertCount == 0:
encodeInteger(prefixBuffer, 0x00, 0, 8) encodeInteger(prefixBuffer, 0x00, 0, 8)
encodeInteger(prefixBuffer, 0x00, 0, 7) encodeInteger(prefixBuffer, 0x00, 0, 7)
else: else:
wireRIC = ( wireRIC = (
requiredInsertCount requiredInsertCount
% (2 * getMaxEntries(maxTableCapacity)) % (2 * getMaxEntries(maxTableCapacity))
) + 1; ) + 1;
encodeInteger(prefixBuffer, 0x00, wireRIC, 8) encodeInteger(prefixBuffer, 0x00, wireRIC, 8)
if base >= requiredInsertCount: if base >= requiredInsertCount:
encodeInteger(prefixBuffer, 0x00, encodeInteger(prefixBuffer, 0x00,
base - requiredInsertCount, 7) base - requiredInsertCount, 7)
else: else:
encodeInteger(prefixBuffer, 0x80, encodeInteger(prefixBuffer, 0x80,
requiredInsertCount - base - 1, 7) requiredInsertCount - base - 1, 7)
return encoderBuffer, prefixBuffer + streamBuffer return encoderBuffer, prefixBuffer + streamBuffer
]]></artwork> ]]></sourcecode>
</section>
<section anchor="change-log" numbered="true" toc="default">
<name>Change Log</name>
<ul empty="true" spacing="normal">
<li>
<strong>RFC Editor's Note:</strong> Please remove this section prior t
o publication of a
final version of this document.</li>
</ul>
<section anchor="since-draft-ietf-quic-qpack-19" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-19</name>
<t>Editorial changes only</t>
</section>
<section anchor="since-draft-ietf-quic-qpack-18" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-18</name>
<t>Editorial changes only</t>
</section>
<section anchor="since-draft-ietf-quic-qpack-17" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-17</name>
<t>Editorial changes only</t>
</section>
<section anchor="since-draft-ietf-quic-qpack-16" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-16</name>
<t>Editorial changes only</t>
</section>
<section anchor="since-draft-ietf-quic-qpack-15" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-15</name>
<t>No changes</t>
</section>
<section anchor="since-draft-ietf-quic-qpack-14" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-14</name>
<t>Added security considerations</t>
</section>
<section anchor="since-draft-ietf-quic-qpack-13" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-13</name>
<t>No changes</t>
</section>
<section anchor="since-draft-ietf-quic-qpack-12" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-12</name>
<t>Editorial changes only</t>
</section>
<section anchor="since-draft-ietf-quic-qpack-11" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-11</name>
<t>Editorial changes only</t>
</section>
<section anchor="since-draft-ietf-quic-qpack-10" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-10</name>
<t>Editorial changes only</t>
</section>
<section anchor="since-draft-ietf-quic-qpack-09" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-09</name>
<ul spacing="normal">
<li>Decoders MUST emit Header Acknowledgments (#2939)</li>
<li>Updated error code for multiple encoder or decoder streams (#2970)
</li>
<li>Added explicit defaults for new SETTINGS (#2974)</li>
</ul>
</section>
<section anchor="since-draft-ietf-quic-qpack-08" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-08</name>
<ul spacing="normal">
<li>Endpoints are permitted to create encoder and decoder streams even
if they
can't use them (#2100, #2529)</li>
<li>Maximum values for settings removed (#2766, #2767)</li>
</ul>
</section>
<section anchor="since-draft-ietf-quic-qpack-06" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-06</name>
<ul spacing="normal">
<li>Clarify initial dynamic table capacity maximums (#2276, #2330, #23
30)</li>
</ul>
</section>
<section anchor="since-draft-ietf-quic-qpack-05" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-05</name>
<ul spacing="normal">
<li>Introduced the terms dynamic table capacity and maximum dynamic ta
ble
capacity.</li>
<li>Renamed SETTINGS_HEADER_TABLE_SIZE to SETTINGS_QPACK_MAX_TABLE_CAP
ACITY.</li>
</ul>
</section>
<section anchor="since-draft-ietf-quic-qpack-04" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-04</name>
<ul spacing="normal">
<li>Changed calculation of Delta Base Index to avoid an illegal value
(#2002,
#2005)</li>
</ul>
</section>
<section anchor="since-draft-ietf-quic-qpack-03" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-03</name>
<ul spacing="normal">
<li>Change HTTP settings defaults (#2038)</li>
<li>Substantial editorial reorganization</li>
</ul>
</section>
<section anchor="since-draft-ietf-quic-qpack-02" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-02</name>
<ul spacing="normal">
<li>Largest Reference encoded modulo MaxEntries (#1763)</li>
<li>New Static Table (#1355)</li>
<li>Table Size Update with Insert Count=0 is a connection error (#1762
)</li>
<li>Stream Cancellations are optional when SETTINGS_HEADER_TABLE_SIZE=
0 (#1761)</li>
<li>Implementations must handle 62 bit integers (#1760)</li>
<li>Different error types for each QPACK stream, other changes to erro
r
handling (#1726)</li>
<li>Preserve header field order (#1725)</li>
<li>Initial table size is the maximum permitted when table is first us
able (#1642)</li>
</ul>
</section>
<section anchor="since-draft-ietf-quic-qpack-01" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-01</name>
<ul spacing="normal">
<li>Only header blocks that reference the dynamic table are acknowledg
ed (#1603,
#1605)</li>
</ul>
</section>
<section anchor="since-draft-ietf-quic-qpack-00" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qpack-00</name>
<ul spacing="normal">
<li>Renumbered instructions for consistency (#1471, #1472)</li>
<li>Decoder is allowed to validate largest reference (#1404, #1469)</l
i>
<li>Header block acknowledgments also acknowledge the associated large
st reference
(#1370, #1400)</li>
<li>Added an acknowledgment for unread streams (#1371, #1400)</li>
<li>Removed framing from encoder stream (#1361,#1467)</li>
<li>Control streams use typed unidirectional streams rather than fixed
stream IDs
(#910,#1359)</li>
</ul>
</section>
<section anchor="since-draft-ietf-quic-qcram-00" numbered="true" toc="defa
ult">
<name>Since draft-ietf-quic-qcram-00</name>
<ul spacing="normal">
<li>Separate instruction sets for table updates and header blocks (#12
35, #1142,
#1141)</li>
<li>Reworked indexing scheme (#1176, #1145, #1136, #1130, #1125, #1314
)</li>
<li>Added mechanisms that support one-pass encoding (#1138, #1320)</li
>
<li>Added a setting to control the number of blocked decoders (#238, #
1140, #1143)</li>
<li>Moved table updates and acknowledgments to dedicated streams (#112
1, #1122,
#1238)</li>
</ul>
</section>
</section> </section>
<section numbered="false" anchor="acknowledgments" toc="default"> <section numbered="false" anchor="acknowledgments">
<name>Acknowledgments</name> <name>Acknowledgments</name>
<t>The IETF QUIC Working Group received an enormous amount of support from many <t>The IETF QUIC Working Group received an enormous amount of support from many
people.</t> people.</t>
<t>The compression design team did substantial work exploring the problem space and <t>The compression design team did substantial work exploring the problem space and
influencing the initial draft. The contributions of design team members Roberto influencing the initial draft version of this document. The contributions of
Peon, Martin Thomson, and Dmitri Tikhonov are gratefully acknowledged.</t> design team members <contact fullname="Roberto Peon"/>, <contact fullname="Marti
n Thomson"/>, and
<contact fullname="Dmitri Tikhonov"/> are gratefully acknowledged.</t>
<t>The following people also provided substantial contributions to this do cument:</t> <t>The following people also provided substantial contributions to this do cument:</t>
<ul spacing="normal"> <ul spacing="compact">
<li>Bence Beky</li>
<li>Alessandro Ghedini</li>
<li>Ryan Hamilton</li>
<li>Robin Marx</li>
<li>Patrick McManus</li>
<li> <li>
<t> <contact asciiFullname="Kazuho Oku" fullname="奥 一穂"/> <t><contact fullname="Bence Beky"/></t>
</t> </li>
<li>
<t><contact fullname="Alessandro Ghedini"/></t>
</li>
<li>
<t><contact fullname="Ryan Hamilton"/></t>
</li>
<li>
<t><contact fullname="Robin Marx"/></t>
</li>
<li>
<t><contact fullname="Patrick McManus"/></t>
</li>
<li>
<t><contact asciiFullname="Kazuho Oku" fullname="奥 一穂"/></t>
</li>
<li>
<t><contact fullname="Lucas Pardue"/></t>
</li>
<li>
<t><contact fullname="Biren Roy"/></t>
</li>
<li>
<t><contact fullname="Ian Swett"/></t>
</li> </li>
<li>Lucas Pardue</li>
<li>Biren Roy</li>
<li>Ian Swett</li>
</ul> </ul>
<t>This draft draws heavily on the text of <xref target="RFC7541" format=" default"/>. The indirect input of <t>This document draws heavily on the text of <xref target="RFC7541"/>. T he indirect input of
those authors is also gratefully acknowledged.</t> those authors is also gratefully acknowledged.</t>
<t>Buck's contribution was supported by Google during his employment there <t><contact fullname="Buck Krasic"/>'s contribution was supported by Googl
.</t> e during his employment
<t>A portion of Mike's contribution was supported by Microsoft during his there.</t>
employment there.</t> <t>A portion of <contact fullname="Mike Bishop"/>'s contribution was suppo
rted by Microsoft during
his employment there.</t>
</section> </section>
</back> </back>
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