draft-ietf-quic-qpack-21.txt		draft-ietf-quic-qpack-latest.txt
	QUIC Working Group C. Krasic		QUIC Working Group C. Krasic
	Internet-Draft Netflix		Internet-Draft Netflix
	Intended status: Standards Track M. Bishop		Intended status: Standards Track M. Bishop
	Expires: August 6, 2021 Akamai Technologies		Expires: June 12, 2024 Akamai Technologies
	A. Frindell, Ed.		A. Frindell, Ed.
	Facebook		Facebook
	February 2, 2021		December 10, 2023
	QPACK: Header Compression for HTTP/3		QPACK: Header Compression for HTTP/3
	draft-ietf-quic-qpack-21		draft-ietf-quic-qpack-latest
	Abstract		Abstract
	This specification defines QPACK, a compression format for		This specification defines QPACK, a compression format for
	efficiently representing HTTP fields, to be used in HTTP/3. This is		efficiently representing HTTP fields, to be used in HTTP/3. This is
	a variation of HPACK compression that seeks to reduce head-of-line		a variation of HPACK compression that seeks to reduce head-of-line
	blocking.		blocking.
	Note to Readers
	Discussion of this draft takes place on the QUIC working group
	mailing list (quic@ietf.org [1]), which is archived at
	<https://mailarchive.ietf.org/arch/search/?email_list=quic>.
	Working Group information can be found at <https://github.com/
	quicwg>; source code and issues list for this draft can be found at
	<https://github.com/quicwg/base-drafts/labels/-qpack>.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
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	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on August 6, 2021.		This Internet-Draft will expire on June 12, 2024.
	Copyright Notice		Copyright Notice
	Copyright (c) 2021 IETF Trust and the persons identified as the		Copyright (c) 2023 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://trustee.ietf.org/license-info) in effect on the date of
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	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
	1.1. Conventions and Definitions . . . . . . . . . . . . . . . 4		1.1. Conventions and Definitions . . . . . . . . . . . . . . . 4
	1.2. Notational Conventions . . . . . . . . . . . . . . . . . 5		1.2. Notational Conventions . . . . . . . . . . . . . . . . . 5
	2. Compression Process Overview . . . . . . . . . . . . . . . . 6		2. Compression Process Overview . . . . . . . . . . . . . . . . 5
	2.1. Encoder . . . . . . . . . . . . . . . . . . . . . . . . . 6		2.1. Encoder . . . . . . . . . . . . . . . . . . . . . . . . . 5
	2.1.1. Limits on Dynamic Table Insertions . . . . . . . . . 6		2.1.1. Limits on Dynamic Table Insertions . . . . . . . . . 6
	2.1.2. Blocked Streams . . . . . . . . . . . . . . . . . . . 7		2.1.2. Blocked Streams . . . . . . . . . . . . . . . . . . . 7
	2.1.3. Avoiding Flow Control Deadlocks . . . . . . . . . . . 8		2.1.3. Avoiding Flow Control Deadlocks . . . . . . . . . . . 8
	2.1.4. Known Received Count . . . . . . . . . . . . . . . . 9		2.1.4. Known Received Count . . . . . . . . . . . . . . . . 8
	2.2. Decoder . . . . . . . . . . . . . . . . . . . . . . . . . 9		2.2. Decoder . . . . . . . . . . . . . . . . . . . . . . . . . 9
	2.2.1. Blocked Decoding . . . . . . . . . . . . . . . . . . 9		2.2.1. Blocked Decoding . . . . . . . . . . . . . . . . . . 9
	2.2.2. State Synchronization . . . . . . . . . . . . . . . . 10		2.2.2. State Synchronization . . . . . . . . . . . . . . . . 9
	2.2.3. Invalid References . . . . . . . . . . . . . . . . . 11		2.2.3. Invalid References . . . . . . . . . . . . . . . . . 11
	3. Reference Tables . . . . . . . . . . . . . . . . . . . . . . 11		3. Reference Tables . . . . . . . . . . . . . . . . . . . . . . 11
	3.1. Static Table . . . . . . . . . . . . . . . . . . . . . . 11		3.1. Static Table . . . . . . . . . . . . . . . . . . . . . . 11
	3.2. Dynamic Table . . . . . . . . . . . . . . . . . . . . . . 12		3.2. Dynamic Table . . . . . . . . . . . . . . . . . . . . . . 11
	3.2.1. Dynamic Table Size . . . . . . . . . . . . . . . . . 12		3.2.1. Dynamic Table Size . . . . . . . . . . . . . . . . . 12
	3.2.2. Dynamic Table Capacity and Eviction . . . . . . . . . 12		3.2.2. Dynamic Table Capacity and Eviction . . . . . . . . . 12
	3.2.3. Maximum Dynamic Table Capacity . . . . . . . . . . . 13		3.2.3. Maximum Dynamic Table Capacity . . . . . . . . . . . 12
	3.2.4. Absolute Indexing . . . . . . . . . . . . . . . . . . 14		3.2.4. Absolute Indexing . . . . . . . . . . . . . . . . . . 13
	3.2.5. Relative Indexing . . . . . . . . . . . . . . . . . . 14		3.2.5. Relative Indexing . . . . . . . . . . . . . . . . . . 13
	3.2.6. Post-Base Indexing . . . . . . . . . . . . . . . . . 15		3.2.6. Post-Base Indexing . . . . . . . . . . . . . . . . . 14
	4. Wire Format . . . . . . . . . . . . . . . . . . . . . . . . . 15		4. Wire Format . . . . . . . . . . . . . . . . . . . . . . . . . 15
	4.1. Primitives . . . . . . . . . . . . . . . . . . . . . . . 15		4.1. Primitives . . . . . . . . . . . . . . . . . . . . . . . 15
	4.1.1. Prefixed Integers . . . . . . . . . . . . . . . . . . 16		4.1.1. Prefixed Integers . . . . . . . . . . . . . . . . . . 15
	4.1.2. String Literals . . . . . . . . . . . . . . . . . . . 16		4.1.2. String Literals . . . . . . . . . . . . . . . . . . . 15
	4.2. Encoder and Decoder Streams . . . . . . . . . . . . . . . 16		4.2. Encoder and Decoder Streams . . . . . . . . . . . . . . . 16
	4.3. Encoder Instructions . . . . . . . . . . . . . . . . . . 17		4.3. Encoder Instructions . . . . . . . . . . . . . . . . . . 16
	4.3.1. Set Dynamic Table Capacity . . . . . . . . . . . . . 17		4.3.1. Set Dynamic Table Capacity . . . . . . . . . . . . . 17
	4.3.2. Insert With Name Reference . . . . . . . . . . . . . 18		4.3.2. Insert With Name Reference . . . . . . . . . . . . . 17
	4.3.3. Insert With Literal Name . . . . . . . . . . . . . . 18		4.3.3. Insert With Literal Name . . . . . . . . . . . . . . 18
	4.3.4. Duplicate . . . . . . . . . . . . . . . . . . . . . . 19		4.3.4. Duplicate . . . . . . . . . . . . . . . . . . . . . . 18
	4.4. Decoder Instructions . . . . . . . . . . . . . . . . . . 19		4.4. Decoder Instructions . . . . . . . . . . . . . . . . . . 19
	4.4.1. Section Acknowledgment . . . . . . . . . . . . . . . 19		4.4.1. Section Acknowledgment . . . . . . . . . . . . . . . 19
	4.4.2. Stream Cancellation . . . . . . . . . . . . . . . . . 20		4.4.2. Stream Cancellation . . . . . . . . . . . . . . . . . 19
	4.4.3. Insert Count Increment . . . . . . . . . . . . . . . 20		4.4.3. Insert Count Increment . . . . . . . . . . . . . . . 20
	4.5. Field Line Representations . . . . . . . . . . . . . . . 21		4.5. Field Line Representations . . . . . . . . . . . . . . . 20
	4.5.1. Encoded Field Section Prefix . . . . . . . . . . . . 21		4.5.1. Encoded Field Section Prefix . . . . . . . . . . . . 20
	4.5.2. Indexed Field Line . . . . . . . . . . . . . . . . . 24		4.5.2. Indexed Field Line . . . . . . . . . . . . . . . . . 23
	4.5.3. Indexed Field Line With Post-Base Index . . . . . . . 25		4.5.3. Indexed Field Line With Post-Base Index . . . . . . . 24
	4.5.4. Literal Field Line With Name Reference . . . . . . . 25		4.5.4. Literal Field Line With Name Reference . . . . . . . 24
	4.5.5. Literal Field Line With Post-Base Name Reference . . 26		4.5.5. Literal Field Line With Post-Base Name Reference . . 25
	4.5.6. Literal Field Line With Literal Name . . . . . . . . 26		4.5.6. Literal Field Line With Literal Name . . . . . . . . 25
	5. Configuration . . . . . . . . . . . . . . . . . . . . . . . . 27
	6. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 27		5. Configuration . . . . . . . . . . . . . . . . . . . . . . . . 26
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 28		6. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 26
	7.1. Probing Dynamic Table State . . . . . . . . . . . . . . . 28		7. Security Considerations . . . . . . . . . . . . . . . . . . . 27
	7.1.1. Applicability to QPACK and HTTP . . . . . . . . . . . 29		7.1. Probing Dynamic Table State . . . . . . . . . . . . . . . 27
	7.1.2. Mitigation . . . . . . . . . . . . . . . . . . . . . 29		7.1.1. Applicability to QPACK and HTTP . . . . . . . . . . . 28
	7.1.3. Never-Indexed Literals . . . . . . . . . . . . . . . 30		7.1.2. Mitigation . . . . . . . . . . . . . . . . . . . . . 28
	7.2. Static Huffman Encoding . . . . . . . . . . . . . . . . . 31		7.1.3. Never-Indexed Literals . . . . . . . . . . . . . . . 29
	7.3. Memory Consumption . . . . . . . . . . . . . . . . . . . 31		7.2. Static Huffman Encoding . . . . . . . . . . . . . . . . . 30
	7.4. Implementation Limits . . . . . . . . . . . . . . . . . . 33		7.3. Memory Consumption . . . . . . . . . . . . . . . . . . . 30
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33		7.4. Implementation Limits . . . . . . . . . . . . . . . . . . 32
	8.1. Settings Registration . . . . . . . . . . . . . . . . . . 33		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
	8.2. Stream Type Registration . . . . . . . . . . . . . . . . 33		8.1. Settings Registration . . . . . . . . . . . . . . . . . . 32
	8.3. Error Code Registration . . . . . . . . . . . . . . . . . 34		8.2. Stream Type Registration . . . . . . . . . . . . . . . . 32
	9. References . . . . . . . . . . . . . . . . . . . . . . . . . 34		8.3. Error Code Registration . . . . . . . . . . . . . . . . . 33
	9.1. Normative References . . . . . . . . . . . . . . . . . . 34		9. References . . . . . . . . . . . . . . . . . . . . . . . . . 33
	9.2. Informative References . . . . . . . . . . . . . . . . . 35		9.1. Normative References . . . . . . . . . . . . . . . . . . 33
	9.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 36		9.2. Informative References . . . . . . . . . . . . . . . . . 34
	Appendix A. Static Table . . . . . . . . . . . . . . . . . . . . 36		Appendix A. Static Table . . . . . . . . . . . . . . . . . . . . 35
	Appendix B. Encoding and Decoding Examples . . . . . . . . . . . 41		Appendix B. Encoding and Decoding Examples . . . . . . . . . . . 39
	B.1. Literal Field Line With Name Reference . . . . . . . . . 41		B.1. Literal Field Line With Name Reference . . . . . . . . . 40
	B.2. Dynamic Table . . . . . . . . . . . . . . . . . . . . . . 41		B.2. Dynamic Table . . . . . . . . . . . . . . . . . . . . . . 40
	B.3. Speculative Insert . . . . . . . . . . . . . . . . . . . 42		B.3. Speculative Insert . . . . . . . . . . . . . . . . . . . 41
	B.4. Duplicate Instruction, Stream Cancellation . . . . . . . 43		B.4. Duplicate Instruction, Stream Cancellation . . . . . . . 42
	B.5. Dynamic Table Insert, Eviction . . . . . . . . . . . . . 44		B.5. Dynamic Table Insert, Eviction . . . . . . . . . . . . . 43
	Appendix C. Sample One Pass Encoding Algorithm . . . . . . . . . 45		Appendix C. Sample One Pass Encoding Algorithm . . . . . . . . . 44
	Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 47		Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 46
	D.1. Since draft-ietf-quic-qpack-19 . . . . . . . . . . . . . 47		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 47
	D.2. Since draft-ietf-quic-qpack-18 . . . . . . . . . . . . . 47
	D.3. Since draft-ietf-quic-qpack-17 . . . . . . . . . . . . . 47
	D.4. Since draft-ietf-quic-qpack-16 . . . . . . . . . . . . . 47
	D.5. Since draft-ietf-quic-qpack-15 . . . . . . . . . . . . . 47
	D.6. Since draft-ietf-quic-qpack-14 . . . . . . . . . . . . . 47
	D.7. Since draft-ietf-quic-qpack-13 . . . . . . . . . . . . . 47
	D.8. Since draft-ietf-quic-qpack-12 . . . . . . . . . . . . . 47
	D.9. Since draft-ietf-quic-qpack-11 . . . . . . . . . . . . . 47
	D.10. Since draft-ietf-quic-qpack-10 . . . . . . . . . . . . . 48
	D.11. Since draft-ietf-quic-qpack-09 . . . . . . . . . . . . . 48
	D.12. Since draft-ietf-quic-qpack-08 . . . . . . . . . . . . . 48
	D.13. Since draft-ietf-quic-qpack-06 . . . . . . . . . . . . . 48
	D.14. Since draft-ietf-quic-qpack-05 . . . . . . . . . . . . . 48
	D.15. Since draft-ietf-quic-qpack-04 . . . . . . . . . . . . . 48
	D.16. Since draft-ietf-quic-qpack-03 . . . . . . . . . . . . . 48
	D.17. Since draft-ietf-quic-qpack-02 . . . . . . . . . . . . . 48
	D.18. Since draft-ietf-quic-qpack-01 . . . . . . . . . . . . . 49
	D.19. Since draft-ietf-quic-qpack-00 . . . . . . . . . . . . . 49
	D.20. Since draft-ietf-quic-qcram-00 . . . . . . . . . . . . . 49
	Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 50
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 51
	1. Introduction		1. Introduction
	The QUIC transport protocol ([QUIC-TRANSPORT]) is designed to support		The QUIC transport protocol ([QUIC-TRANSPORT]) is designed to support
	HTTP semantics, and its design subsumes many of the features of		HTTP semantics, and its design subsumes many of the features of
	HTTP/2 ([RFC7540]). HTTP/2 uses HPACK ([RFC7541]) for compression of		HTTP/2 ([RFC7540]). HTTP/2 uses HPACK ([RFC7541]) for compression of
	the header and trailer sections. If HPACK were used for HTTP/3		the header and trailer sections. If HPACK were used for HTTP/3
	([HTTP3]), it would induce head-of-line blocking for field sections		([HTTP3]), it would induce head-of-line blocking for field sections
	due to built-in assumptions of a total ordering across frames on all		due to built-in assumptions of a total ordering across frames on all
	streams.		streams.
	skipping to change at page 4, line 40 ¶		skipping to change at page 4, line 9 ¶
	flexibility for implementations to balance between resilience against		flexibility for implementations to balance between resilience against
	head-of-line blocking and optimal compression ratio. The design		head-of-line blocking and optimal compression ratio. The design
	goals are to closely approach the compression ratio of HPACK with		goals are to closely approach the compression ratio of HPACK with
	substantially less head-of-line blocking under the same loss		substantially less head-of-line blocking under the same loss
	conditions.		conditions.
	1.1. Conventions and Definitions		1.1. Conventions and Definitions
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in		"OPTIONAL" in this document are to be interpreted as described in BCP
	BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all		14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	Definitions of terms that are used in this document:		Definitions of terms that are used in this document:
	HTTP fields: Metadata sent as part of an HTTP message. The term		HTTP fields: Metadata sent as part of an HTTP message. The term
	encompasses both header and trailer fields. Colloquially, the		encompasses both header and trailer fields. Colloquially, the
	term "headers" has often been used to refer to HTTP header fields		term "headers" has often been used to refer to HTTP header fields
	and trailer fields; this document uses "fields" for generality.		and trailer fields; this document uses "fields" for generality.
	HTTP field line: A name-value pair sent as part of an HTTP field		HTTP field line: A name-value pair sent as part of an HTTP field
	skipping to change at page 10, line 10 ¶		skipping to change at page 9, line 32 ¶
	Required Insert Count. When the Required Insert Count is less than		Required Insert Count. When the Required Insert Count is less than
	or equal to the decoder's Insert Count, the field section can be		or equal to the decoder's Insert Count, the field section can be
	processed immediately. Otherwise, the stream on which the field		processed immediately. Otherwise, the stream on which the field
	section was received becomes blocked.		section was received becomes blocked.
	While blocked, encoded field section data SHOULD remain in the		While blocked, encoded field section data SHOULD remain in the
	blocked stream's flow control window. This data is unusable until		blocked stream's flow control window. This data is unusable until
	the stream becomes unblocked, and releasing the flow control		the stream becomes unblocked, and releasing the flow control
	prematurely makes the decoder vulnerable to memory exhaustion		prematurely makes the decoder vulnerable to memory exhaustion
	attacks. A stream becomes unblocked when the Insert Count becomes		attacks. A stream becomes unblocked when the Insert Count becomes
	unblocked when the Insert Count becomes greater than or equal to the		greater than or equal to the Required Insert Count for all encoded
	Required Insert Count for all encoded field sections the decoder has		field sections the decoder has started reading from the stream.
	started reading from the stream.
	When processing encoded field sections, the decoder expects the		When processing encoded field sections, the decoder expects the
	Required Insert Count to equal the lowest possible value for the		Required Insert Count to equal the lowest possible value for the
	Insert Count with which the field section can be decoded, as		Insert Count with which the field section can be decoded, as
	prescribed in Section 2.1.2. If it encounters a Required Insert		prescribed in Section 2.1.2. If it encounters a Required Insert
	Count smaller than expected, it MUST treat this as a connection error		Count smaller than expected, it MUST treat this as a connection error
	of type QPACK_DECOMPRESSION_FAILED; see Section 2.2.3. If it		of type QPACK_DECOMPRESSION_FAILED; see Section 2.2.3. If it
	encounters a Required Insert Count larger than expected, it MAY treat		encounters a Required Insert Count larger than expected, it MAY treat
	this as a connection error of type QPACK_DECOMPRESSION_FAILED.		this as a connection error of type QPACK_DECOMPRESSION_FAILED.
	skipping to change at page 27, line 27 ¶		skipping to change at page 26, line 27 ¶
	This representation starts with the '001' 3-bit pattern. The fourth		This representation starts with the '001' 3-bit pattern. The fourth
	bit is the 'N' bit as described in Section 4.5.4. The name follows,		bit is the 'N' bit as described in Section 4.5.4. The name follows,
	represented as a 4-bit prefix string literal, then the value,		represented as a 4-bit prefix string literal, then the value,
	represented as an 8-bit prefix string literal; see Section 4.1.2.		represented as an 8-bit prefix string literal; see Section 4.1.2.
	5. Configuration		5. Configuration
	QPACK defines two settings for the HTTP/3 SETTINGS frame:		QPACK defines two settings for the HTTP/3 SETTINGS frame:
	SETTINGS_QPACK_MAX_TABLE_CAPACITY (0x1): The default value is zero.		SETTINGS_QPACK_MAX_TABLE_CAPACITY (0x01): The default value is zero.
	See Section 3.2 for usage. This is the equivalent of the		See Section 3.2 for usage. This is the equivalent of the
	SETTINGS_HEADER_TABLE_SIZE from HTTP/2.		SETTINGS_HEADER_TABLE_SIZE from HTTP/2.
	SETTINGS_QPACK_BLOCKED_STREAMS (0x7): The default value is zero.		SETTINGS_QPACK_BLOCKED_STREAMS (0x07): The default value is zero.
	See Section 2.1.2.		See Section 2.1.2.
	6. Error Handling		6. Error Handling
	The following error codes are defined for HTTP/3 to indicate failures		The following error codes are defined for HTTP/3 to indicate failures
	of QPACK that prevent the stream or connection from continuing:		of QPACK that prevent the stream or connection from continuing:
	QPACK_DECOMPRESSION_FAILED (0x200): The decoder failed to interpret		QPACK_DECOMPRESSION_FAILED (0x0200): The decoder failed to interpret
	an encoded field section and is not able to continue decoding that		an encoded field section and is not able to continue decoding that
	field section.		field section.
	QPACK_ENCODER_STREAM_ERROR (0x201): The decoder failed to interpret		QPACK_ENCODER_STREAM_ERROR (0x0201): The decoder failed to interpret
	an encoder instruction received on the encoder stream.		an encoder instruction received on the encoder stream.
	QPACK_DECODER_STREAM_ERROR (0x202): The encoder failed to interpret		QPACK_DECODER_STREAM_ERROR (0x0202): The encoder failed to interpret
	a decoder instruction received on the decoder stream.		a decoder instruction received on the decoder stream.
	7. Security Considerations		7. Security Considerations
	This section describes potential areas of security concern with		This section describes potential areas of security concern with
	QPACK:		QPACK:
	o Use of compression as a length-based oracle for verifying guesses		o Use of compression as a length-based oracle for verifying guesses
	about secrets that are compressed into a shared compression		about secrets that are compressed into a shared compression
	context.		context.
	skipping to change at page 33, line 25 ¶		skipping to change at page 32, line 25 ¶
	enough to process the largest individual field the HTTP		enough to process the largest individual field the HTTP
	implementation can be configured to accept.		implementation can be configured to accept.
	If an implementation encounters a value larger than it is able to		If an implementation encounters a value larger than it is able to
	decode, this MUST be treated as a stream error of type		decode, this MUST be treated as a stream error of type
	QPACK_DECOMPRESSION_FAILED if on a request stream, or a connection		QPACK_DECOMPRESSION_FAILED if on a request stream, or a connection
	error of the appropriate type if on the encoder or decoder stream.		error of the appropriate type if on the encoder or decoder stream.
	8. IANA Considerations		8. IANA Considerations
			This document makes multiple registrations in the registries defined
			by [HTTP3]. The allocations created by this document are all
			assigned permanent status and list a change controller of the IETF
			and a contact of the HTTP working group (ietf-http-wg@w3.org).
	8.1. Settings Registration		8.1. Settings Registration
	This document specifies two settings. The entries in the following		This document specifies two settings. The entries in the following
	table are registered in the "HTTP/3 Settings" registry established in		table are registered in the "HTTP/3 Settings" registry established in
	[HTTP3].		[HTTP3].
	+--------------------------+------+---------------+---------+		+--------------------------+------+---------------+---------+
	| Setting Name | Code | Specification | Default |		| Setting Name | Code | Specification | Default |
	+--------------------------+------+---------------+---------+		+--------------------------+------+---------------+---------+
	| QPACK_MAX_TABLE_CAPACITY | 0x1 | Section 5 | 0 |		| QPACK_MAX_TABLE_CAPACITY | 0x01 | Section 5 | 0 |
	| | | | |		| | | | |
	| QPACK_BLOCKED_STREAMS | 0x7 | Section 5 | 0 |		| QPACK_BLOCKED_STREAMS | 0x07 | Section 5 | 0 |
	+--------------------------+------+---------------+---------+		+--------------------------+------+---------------+---------+
	For fomatting reasons, the setting names here are abbreviated by		For fomatting reasons, the setting names here are abbreviated by
	removing the 'SETTING_' prefix.		removing the 'SETTING_' prefix.
	8.2. Stream Type Registration		8.2. Stream Type Registration
	This document specifies two stream types. The entries in the		This document specifies two stream types. The entries in the
	following table are registered in the "HTTP/3 Stream Type" registry		following table are registered in the "HTTP/3 Stream Type" registry
	established in [HTTP3].		established in [HTTP3].
	skipping to change at page 34, line 19 ¶		skipping to change at page 33, line 19 ¶
	| | | | |		| | | | |
	| QPACK Decoder Stream | 0x03 | Section 4.2 | Both |		| QPACK Decoder Stream | 0x03 | Section 4.2 | Both |
	+----------------------+------+---------------+--------+		+----------------------+------+---------------+--------+
	8.3. Error Code Registration		8.3. Error Code Registration
	This document specifies three error codes. The entries in the		This document specifies three error codes. The entries in the
	following table are registered in the "HTTP/3 Error Code" registry		following table are registered in the "HTTP/3 Error Code" registry
	established in [HTTP3].		established in [HTTP3].
	+----------------------------+-------+--------------+---------------+		+----------------------------+--------+-------------+---------------+
	| Name | Code | Description | Specification |		| Name | Code | Description | Specification |
	+----------------------------+-------+--------------+---------------+		+----------------------------+--------+-------------+---------------+
	| QPACK_DECOMPRESSION_FAILED | 0x200 | Decoding of | Section 6 |		| QPACK_DECOMPRESSION_FAILED | 0x0200 | Decoding of | Section 6 |
	| | | a field | |		| | | a field | |
	| | | section | |		| | | section | |
	| | | failed | |		| | | failed | |
	| | | | |		| | | | |
	| QPACK_ENCODER_STREAM_ERROR | 0x201 | Error on the | Section 6 |		| QPACK_ENCODER_STREAM_ERROR | 0x0201 | Error on | Section 6 |
	| | | encoder | |		| | | the encoder | |
	| | | stream | |		| | | stream | |
	| | | | |		| | | | |
	| QPACK_DECODER_STREAM_ERROR | 0x202 | Error on the | Section 6 |		| QPACK_DECODER_STREAM_ERROR | 0x0202 | Error on | Section 6 |
	| | | decoder | |		| | | the decoder | |
	| | | stream | |		| | | stream | |
	+----------------------------+-------+--------------+---------------+		+----------------------------+--------+-------------+---------------+
	9. References		9. References
	9.1. Normative References		9.1. Normative References
	[HTTP3] Bishop, M., Ed., "Hypertext Transfer Protocol Version 3		[HTTP3] Bishop, M., Ed., "Hypertext Transfer Protocol Version 3
	(HTTP/3)", draft-ietf-quic-http-34 (work in progress).		(HTTP/3)", draft-ietf-quic-http-latest (work in progress).
	[QUIC-TRANSPORT]		[QUIC-TRANSPORT]
	Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based		Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
	Multiplexed and Secure Transport", draft-ietf-quic-		Multiplexed and Secure Transport", RFC 9000,
	transport-34 (work in progress).		DOI 10.17487/RFC9000,
			<https://www.rfc-editor.org/info/rfc9000>.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119,		Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<https://www.rfc-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc2119>.
	[RFC2360] Scott, G., "Guide for Internet Standards Writers", BCP 22,		[RFC2360] Scott, G., "Guide for Internet Standards Writers", BCP 22,
	RFC 2360, DOI 10.17487/RFC2360, June 1998,		RFC 2360, DOI 10.17487/RFC2360, June 1998,
	<https://www.rfc-editor.org/info/rfc2360>.		<https://www.rfc-editor.org/info/rfc2360>.
	[RFC7541] Peon, R. and H. Ruellan, "HPACK: Header Compression for		[RFC7541] Peon, R. and H. Ruellan, "HPACK: Header Compression for
	HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015,		HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015,
	<https://www.rfc-editor.org/info/rfc7541>.		<https://www.rfc-editor.org/info/rfc7541>.
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	[SEMANTICS]		[SEMANTICS]
	Fielding, R., Nottingham, M., and J. Reschke, "HTTP		Fielding, R., Nottingham, M., and J. Reschke, "HTTP
	Semantics", draft-ietf-httpbis-semantics-14 (work in		Semantics", draft-ietf-httpbis-semantics-19 (work in
	progress), January 2021.		progress), September 2021.
	9.2. Informative References		9.2. Informative References
	[CRIME] Wikipedia, "CRIME", May 2015, <http://en.wikipedia.org/w/		[CRIME] Wikipedia, "CRIME", May 2015, <http://en.wikipedia.org/w/
	index.php?title=CRIME&oldid=660948120>.		index.php?title=CRIME&oldid=660948120>.
	[PETAL] Tan, J. and J. Nahata, "PETAL: Preset Encoding		[PETAL] Tan, J. and J. Nahata, "PETAL: Preset Encoding
	Table Information Leakage", April 2013,		Table Information Leakage", April 2013,
	<http://www.pdl.cmu.edu/PDL-FTP/associated/CMU-PDL-		<http://www.pdl.cmu.edu/PDL-FTP/associated/CMU-PDL-
	13-106.pdf>.		13-106.pdf>.
	skipping to change at page 36, line 5 ¶		skipping to change at page 35, line 5 ¶
	[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext		[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
	Transfer Protocol Version 2 (HTTP/2)", RFC 7540,		Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
	DOI 10.17487/RFC7540, May 2015,		DOI 10.17487/RFC7540, May 2015,
	<https://www.rfc-editor.org/info/rfc7540>.		<https://www.rfc-editor.org/info/rfc7540>.
	[TLS] Rescorla, E., "The Transport Layer Security (TLS) Protocol		[TLS] Rescorla, E., "The Transport Layer Security (TLS) Protocol
	Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,		Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
	<https://www.rfc-editor.org/info/rfc8446>.		<https://www.rfc-editor.org/info/rfc8446>.
	9.3. URIs
	[1] mailto:quic@ietf.org
	Appendix A. Static Table		Appendix A. Static Table
	This table was generated by analyzing actual Internet traffic in 2018		This table was generated by analyzing actual Internet traffic in 2018
	and including the most common header fields, after filtering out some		and including the most common header fields, after filtering out some
	unsupported and non-standard values. Due to this methodology, some		unsupported and non-standard values. Due to this methodology, some
	of the entries may be inconsistent or appear multiple times with		of the entries may be inconsistent or appear multiple times with
	similar but not identical values. The order of the entries is		similar but not identical values. The order of the entries is
	optimized to encode the most common header fields with the smallest		optimized to encode the most common header fields with the smallest
	number of bytes.		number of bytes.
	skipping to change at page 44, line 8 ¶		skipping to change at page 43, line 8 ¶
	The encoder duplicates an existing entry in the dynamic table, then		The encoder duplicates an existing entry in the dynamic table, then
	sends an encoded field section referencing the dynamic table entries		sends an encoded field section referencing the dynamic table entries
	including the duplicated entry. The packet containing the encoder		including the duplicated entry. The packet containing the encoder
	stream data is delayed. Before the packet arrives, the decoder		stream data is delayed. Before the packet arrives, the decoder
	cancels the stream and notifies the encoder that the encoded field		cancels the stream and notifies the encoder that the encoded field
	section was not processed.		section was not processed.
	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 page 44, line 45 ¶		skipping to change at page 43, line 45 ¶
	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
	B.5. Dynamic Table Insert, Eviction		B.5. Dynamic Table Insert, Eviction
	The encoder inserts another header into the dynamic table, which		The encoder inserts another header into the dynamic table, which
	evicts the oldest entry. The encoder does not send any encoded field		evicts the oldest entry. The encoder does not send any encoded field
	sections.		sections.
	Stream: Encoder		Stream: Encoder
	810d 6375 7374 6f6d | Insert With Name Reference		810d 6375 7374 6f6d | Insert With Name Reference
	skipping to change at page 47, line 10 ¶		skipping to change at page 46, line 10 ¶
	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
	Appendix D. Change Log
	*RFC Editor's Note:* Please remove this section prior to
	publication of a final version of this document.
	D.1. Since draft-ietf-quic-qpack-19
	Editorial changes only
	D.2. Since draft-ietf-quic-qpack-18
	Editorial changes only
	D.3. Since draft-ietf-quic-qpack-17
	Editorial changes only
	D.4. Since draft-ietf-quic-qpack-16
	Editorial changes only
	D.5. Since draft-ietf-quic-qpack-15
	No changes
	D.6. Since draft-ietf-quic-qpack-14
	Added security considerations
	D.7. Since draft-ietf-quic-qpack-13
	No changes
	D.8. Since draft-ietf-quic-qpack-12
	Editorial changes only
	D.9. Since draft-ietf-quic-qpack-11
	Editorial changes only
	D.10. Since draft-ietf-quic-qpack-10
	Editorial changes only
	D.11. Since draft-ietf-quic-qpack-09
	o Decoders MUST emit Header Acknowledgments (#2939)
	o Updated error code for multiple encoder or decoder streams (#2970)
	o Added explicit defaults for new SETTINGS (#2974)
	D.12. Since draft-ietf-quic-qpack-08
	o Endpoints are permitted to create encoder and decoder streams even
	if they can't use them (#2100, #2529)
	o Maximum values for settings removed (#2766, #2767)
	D.13. Since draft-ietf-quic-qpack-06
	o Clarify initial dynamic table capacity maximums (#2276, #2330,
	#2330)
	D.14. Since draft-ietf-quic-qpack-05
	o Introduced the terms dynamic table capacity and maximum dynamic
	table capacity.
	o Renamed SETTINGS_HEADER_TABLE_SIZE to
	SETTINGS_QPACK_MAX_TABLE_CAPACITY.
	D.15. Since draft-ietf-quic-qpack-04
	o Changed calculation of Delta Base Index to avoid an illegal value
	(#2002, #2005)
	D.16. Since draft-ietf-quic-qpack-03
	o Change HTTP settings defaults (#2038)
	o Substantial editorial reorganization
	D.17. Since draft-ietf-quic-qpack-02
	o Largest Reference encoded modulo MaxEntries (#1763)
	o New Static Table (#1355)
	o Table Size Update with Insert Count=0 is a connection error
	(#1762)
	o Stream Cancellations are optional when
	SETTINGS_HEADER_TABLE_SIZE=0 (#1761)
	o Implementations must handle 62 bit integers (#1760)
	o Different error types for each QPACK stream, other changes to
	error handling (#1726)
	o Preserve header field order (#1725)
	o Initial table size is the maximum permitted when table is first
	usable (#1642)
	D.18. Since draft-ietf-quic-qpack-01
	o Only header blocks that reference the dynamic table are
	acknowledged (#1603, #1605)
	D.19. Since draft-ietf-quic-qpack-00
	o Renumbered instructions for consistency (#1471, #1472)
	o Decoder is allowed to validate largest reference (#1404, #1469)
	o Header block acknowledgments also acknowledge the associated
	largest reference (#1370, #1400)
	o Added an acknowledgment for unread streams (#1371, #1400)
	o Removed framing from encoder stream (#1361,#1467)
	o Control streams use typed unidirectional streams rather than fixed
	stream IDs (#910,#1359)
	D.20. Since draft-ietf-quic-qcram-00
	o Separate instruction sets for table updates and header blocks
	(#1235, #1142, #1141)
	o Reworked indexing scheme (#1176, #1145, #1136, #1130, #1125,
	#1314)
	o Added mechanisms that support one-pass encoding (#1138, #1320)
	o Added a setting to control the number of blocked decoders (#238,
	#1140, #1143)
	o Moved table updates and acknowledgments to dedicated streams
	(#1121, #1122, #1238)
	Acknowledgments		Acknowledgments
	The IETF QUIC Working Group received an enormous amount of support		The IETF QUIC Working Group received an enormous amount of support
	from many people.		from many people.
	The compression design team did substantial work exploring the		The compression design team did substantial work exploring the
	problem space and influencing the initial draft. The contributions		problem space and influencing the initial draft. The contributions
	of design team members Roberto Peon, Martin Thomson, and Dmitri		of design team members Roberto Peon, Martin Thomson, and Dmitri
	Tikhonov are gratefully acknowledged.		Tikhonov are gratefully acknowledged.
End of changes. 36 change blocks.
	267 lines changed or deleted		96 lines changed or added
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