draft-ietf-quic-qpack-02.txt		draft-ietf-quic-qpack-03.txt
	QUIC C. Krasic		QUIC C. Krasic
	Internet-Draft Netflix		Internet-Draft Netflix
	Intended status: Standards Track M. Bishop		Intended status: Standards Track M. Bishop
	Expires: February 16, 2019 Akamai Technologies		Expires: April 6, 2019 Akamai Technologies
	A. Frindell, Ed.		A. Frindell, Ed.
	Facebook		Facebook
	August 15, 2018		October 03, 2018
	QPACK: Header Compression for HTTP over QUIC		QPACK: Header Compression for HTTP over QUIC
	draft-ietf-quic-qpack-02		draft-ietf-quic-qpack-03
	Abstract		Abstract
	This specification defines QPACK, a compression format for		This specification defines QPACK, a compression format for
	efficiently representing HTTP header fields, to be used in HTTP over		efficiently representing HTTP header fields, to be used in HTTP/QUIC.
	QUIC. This is a variation of HPACK header compression that seeks to		This is a variation of HPACK header compression that seeks to reduce
	reduce head-of-line blocking.		head-of-line blocking.
	Note to Readers		Note to Readers
	Discussion of this draft takes place on the QUIC working group		Discussion of this draft takes place on the QUIC working group
	mailing list (quic@ietf.org), which is archived at		mailing list (quic@ietf.org), which is archived at
	https://mailarchive.ietf.org/arch/search/?email_list=quic [1].		https://mailarchive.ietf.org/arch/search/?email_list=quic [1].
	Working Group information can be found at https://github.com/quicwg		Working Group information can be found at https://github.com/quicwg
	[2]; source code and issues list for this draft can be found at		[2]; source code and issues list for this draft can be found at
	https://github.com/quicwg/base-drafts/labels/-qpack [3].		https://github.com/quicwg/base-drafts/labels/-qpack [3].
	skipping to change at page 1, line 46 ¶		skipping to change at page 1, line 46 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on February 16, 2019.		This Internet-Draft will expire on April 6, 2019.
	Copyright Notice		Copyright Notice
	Copyright (c) 2018 IETF Trust and the persons identified as the		Copyright (c) 2018 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
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 26 ¶		skipping to change at page 2, line 26 ¶
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Header Tables . . . . . . . . . . . . . . . . . . . . . . . . 4		2. Header Tables . . . . . . . . . . . . . . . . . . . . . . . . 4
	2.1. Static Table . . . . . . . . . . . . . . . . . . . . . . 4		2.1. Static Table . . . . . . . . . . . . . . . . . . . . . . 4
	2.2. Dynamic Table . . . . . . . . . . . . . . . . . . . . . . 4		2.2. Dynamic Table . . . . . . . . . . . . . . . . . . . . . . 4
	2.2.1. Absolute and Relative Indexing . . . . . . . . . . . 5		2.2.1. Maximum Table Size . . . . . . . . . . . . . . . . . 5
	2.2.2. Post-Base Indexing . . . . . . . . . . . . . . . . . 6		2.2.2. Calculating Table Size . . . . . . . . . . . . . . . 6
	2.3. Avoiding Head-of-Line Blocking in HTTP/QUIC . . . . . . . 7		2.2.3. Absolute Indexing . . . . . . . . . . . . . . . . . . 6
	2.3.1. State Synchronization . . . . . . . . . . . . . . . . 8		2.2.4. Relative Indexing . . . . . . . . . . . . . . . . . . 6
	3. Conventions and Definitions . . . . . . . . . . . . . . . . . 9		2.2.5. Post-Base Indexing . . . . . . . . . . . . . . . . . 7
	3.1. Notational Conventions . . . . . . . . . . . . . . . . . 9		2.3. Avoiding Head-of-Line Blocking in HTTP/QUIC . . . . . . . 8
	4. Configuration . . . . . . . . . . . . . . . . . . . . . . . . 9		2.3.1. State Synchronization . . . . . . . . . . . . . . . . 9
	5. Wire Format . . . . . . . . . . . . . . . . . . . . . . . . . 10		3. Conventions and Definitions . . . . . . . . . . . . . . . . . 10
	5.1. Primitives . . . . . . . . . . . . . . . . . . . . . . . 10		3.1. Notational Conventions . . . . . . . . . . . . . . . . . 10
	5.1.1. Prefixed Integers . . . . . . . . . . . . . . . . . . 10		4. Configuration . . . . . . . . . . . . . . . . . . . . . . . . 10
	5.1.2. String Literals . . . . . . . . . . . . . . . . . . . 10		5. Wire Format . . . . . . . . . . . . . . . . . . . . . . . . . 11
	5.2. QPACK Encoder Stream . . . . . . . . . . . . . . . . . . 11		5.1. Primitives . . . . . . . . . . . . . . . . . . . . . . . 11
	5.2.1. Insert With Name Reference . . . . . . . . . . . . . 11		5.1.1. Prefixed Integers . . . . . . . . . . . . . . . . . . 11
	5.2.2. Insert Without Name Reference . . . . . . . . . . . . 12		5.1.2. String Literals . . . . . . . . . . . . . . . . . . . 11
	5.2.3. Duplicate . . . . . . . . . . . . . . . . . . . . . . 12		5.2. QPACK Encoder Stream . . . . . . . . . . . . . . . . . . 12
	5.2.4. Dynamic Table Size Update . . . . . . . . . . . . . . 13		5.2.1. Insert With Name Reference . . . . . . . . . . . . . 12
	5.3. QPACK Decoder Stream . . . . . . . . . . . . . . . . . . 13		5.2.2. Insert Without Name Reference . . . . . . . . . . . . 13
	5.3.1. Table State Synchronize . . . . . . . . . . . . . . . 13		5.2.3. Duplicate . . . . . . . . . . . . . . . . . . . . . . 13
	5.3.2. Header Acknowledgement . . . . . . . . . . . . . . . 14		5.2.4. Dynamic Table Size Update . . . . . . . . . . . . . . 14
	5.3.3. Stream Cancellation . . . . . . . . . . . . . . . . . 15		5.3. QPACK Decoder Stream . . . . . . . . . . . . . . . . . . 14
	5.4. Request and Push Streams . . . . . . . . . . . . . . . . 15		5.3.1. Table State Synchronize . . . . . . . . . . . . . . . 14
	5.4.1. Header Data Prefix . . . . . . . . . . . . . . . . . 15		5.3.2. Header Acknowledgement . . . . . . . . . . . . . . . 15
	5.4.2. Instructions . . . . . . . . . . . . . . . . . . . . 17		5.3.3. Stream Cancellation . . . . . . . . . . . . . . . . . 16
	6. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 19		5.4. Request and Push Streams . . . . . . . . . . . . . . . . 17
	7. Encoding Strategies . . . . . . . . . . . . . . . . . . . . . 20		5.4.1. Header Data Prefix . . . . . . . . . . . . . . . . . 17
	7.1. Single Pass Encoding . . . . . . . . . . . . . . . . . . 20		5.4.2. Instructions . . . . . . . . . . . . . . . . . . . . 18
	7.2. Preventing Eviction Races . . . . . . . . . . . . . . . . 20		6. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 21
	7.3. Reference Tracking . . . . . . . . . . . . . . . . . . . 20		7. Encoding Strategies . . . . . . . . . . . . . . . . . . . . . 22
	7.3.1. Blocked Eviction . . . . . . . . . . . . . . . . . . 20		7.1. Single Pass Encoding . . . . . . . . . . . . . . . . . . 22
	7.3.2. Blocked Decoding . . . . . . . . . . . . . . . . . . 21		7.2. Preventing Eviction Races . . . . . . . . . . . . . . . . 22
	7.4. Speculative table updates . . . . . . . . . . . . . . . . 21		7.3. Reference Tracking . . . . . . . . . . . . . . . . . . . 22
	7.5. Sample One Pass Encoding Algorithm . . . . . . . . . . . 21		7.3.1. Blocked Dynamic Table Insertions . . . . . . . . . . 22
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 23		7.3.2. Blocked Decoding . . . . . . . . . . . . . . . . . . 23
	9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23		7.4. Speculative table updates . . . . . . . . . . . . . . . . 23
	9.1. Settings Registration . . . . . . . . . . . . . . . . . . 23		7.5. Sample One Pass Encoding Algorithm . . . . . . . . . . . 24
	9.2. Stream Type Registration . . . . . . . . . . . . . . . . 23		8. Security Considerations . . . . . . . . . . . . . . . . . . . 26
	9.3. Error Code Registration . . . . . . . . . . . . . . . . . 23		9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
	10. References . . . . . . . . . . . . . . . . . . . . . . . . . 24		9.1. Settings Registration . . . . . . . . . . . . . . . . . . 26
	10.1. Normative References . . . . . . . . . . . . . . . . . . 24		9.2. Stream Type Registration . . . . . . . . . . . . . . . . 26
	10.2. Informative References . . . . . . . . . . . . . . . . . 24		9.3. Error Code Registration . . . . . . . . . . . . . . . . . 26
	10.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 24		10. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
	Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 25		10.1. Normative References . . . . . . . . . . . . . . . . . . 27
	A.1. Since draft-ietf-quic-qpack-01 . . . . . . . . . . . . . 25		10.2. Informative References . . . . . . . . . . . . . . . . . 28
	A.2. Since draft-ietf-quic-qpack-00 . . . . . . . . . . . . . 25		10.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 28
	A.3. Since draft-ietf-quic-qcram-00 . . . . . . . . . . . . . 25		Appendix A. Static Table . . . . . . . . . . . . . . . . . . . . 28
	Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 25		Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 33
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26		B.1. Since draft-ietf-quic-qpack-02 . . . . . . . . . . . . . 33
			B.2. Since draft-ietf-quic-qpack-01 . . . . . . . . . . . . . 33
			B.3. Since draft-ietf-quic-qpack-00 . . . . . . . . . . . . . 33
			B.4. Since draft-ietf-quic-qcram-00 . . . . . . . . . . . . . 34
			Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 34
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
	1. Introduction		1. Introduction
	The QUIC transport protocol was designed from the outset to support		The QUIC transport protocol was designed from the outset to support
	HTTP semantics, and its design subsumes many of the features of		HTTP semantics, and its design subsumes many of the features of
	HTTP/2. HTTP/2 uses HPACK ([RFC7541]) for header compression, but		HTTP/2. HTTP/2 uses HPACK ([RFC7541]) for header compression, but
	QUIC's stream multiplexing comes into some conflict with HPACK. A		QUIC's stream multiplexing comes into some conflict with HPACK. A
	key goal of the design of QUIC is to improve stream multiplexing		key goal of the design of QUIC is to improve stream multiplexing
	relative to HTTP/2 by reducing head-of-line blocking. If HPACK were		relative to HTTP/2 by reducing head-of-line blocking. If HPACK were
	used for HTTP/QUIC, it would induce head-of-line blocking due to		used for HTTP/QUIC, it would induce head-of-line blocking due to
	skipping to change at page 4, line 5 ¶		skipping to change at page 4, line 7 ¶
	[RFC7540]. The description of HPACK is [RFC7541].		[RFC7540]. The description of HPACK is [RFC7541].
	QPACK reuses core concepts from HPACK, but is redesigned to allow		QPACK reuses core concepts from HPACK, but is redesigned to allow
	correctness in the presence of out-of-order delivery, with		correctness in the presence of out-of-order delivery, with
	flexibility for implementations to balance between resilience against		flexibility for implementations to balance between resilience against
	head-of-line blocking and optimal compression ratio. The design		head-of-line blocking and optimal compression ratio. The design
	goals are to closely approach the compression ratio of HPACK with		goals are to closely approach the compression ratio of HPACK with
	substantially less head-of-line blocking under the same loss		substantially less head-of-line blocking under the same loss
	conditions.		conditions.
			QPACK preserves the ordering of header fields within each header
			list. An encoder MUST emit header field representations in the order
			they appear in the input header list. A decoder MUST must emit
			header fields in the order their representations appear in the input
			header block.
	2. Header Tables		2. Header Tables
	Like HPACK, QPACK uses two tables for associating header fields to		Like HPACK, QPACK uses two tables for associating header fields to
	indexes. The static table (see Section 2.1) is predefined and		indices. The static table (see Section 2.1) is predefined and
	contains common header fields (some of them with an empty value).		contains common header fields (some of them with an empty value).
	The dynamic table (see Section 2.2) built up over the course of the		The dynamic table (see Section 2.2) is built up over the course of
	connection and can be used by the encoder to index header fields		the connection and can be used by the encoder to index header fields
	repeated in the encoded header lists.		repeated in the encoded header lists.
	Unlike in HPACK, entries in the QPACK static and dynamic tables are		Unlike in HPACK, entries in the QPACK static and dynamic tables are
	addressed separately. The following sections describe how entries in		addressed separately. The following sections describe how entries in
	each table is addressed.		each table are addressed.
	2.1. Static Table		2.1. Static Table
	The static table consists of a predefined static list of header		The static table consists of a predefined static list of header
	fields, each of which has a fixed index over time. Its entries are		fields, each of which has a fixed index over time. Its entries are
	defined in Appendix A of [RFC7541]. Note that because HPACK did not		defined in Appendix A.
	use zero-based references, there is no value at index zero of the
	static table.		A decoder that encounters an invalid static table index on a request
			stream or push stream MUST treat this as a stream error of type
			"HTTP_QPACK_DECOMPRESSION_FAILED". If this index is received on the
			encoder stream, this MUST be treated as a connection error of type
			"HTTP_QPACK_ENCODER_STREAM_ERROR".
	2.2. Dynamic Table		2.2. Dynamic Table
	The dynamic table consists of a list of header fields maintained in		The dynamic table consists of a list of header fields maintained in
	first-in, first-out order. The dynamic table is initially empty.		first-in, first-out order. The dynamic table is initially empty.
	Entries are added by instructions on the encoder stream (see		Entries are added by instructions on the encoder stream (see
	Section 5.2).		Section 5.2).
			The maximum size of the dynamic table can be modified by the encoder,
			subject to a decoder-controlled limit (see Section 4 and
			Section 5.2.4). The initial maximum size is determined by the
			corresponding setting when HTTP requests or responses are first
			permitted to be sent. For clients using 0-RTT data in HTTP/QUIC, the
			table size is the remembered value of the setting, even if the server
			later specifies a larger maximum in its SETTINGS frame. For HTTP/
			QUIC servers and HTTP/QUIC clients when 0-RTT is not attempted or is
			rejected, the initial maximum table size is the value of the setting
			in the peer's SETTINGS frame.
	Before a new entry is added to the dynamic table, entries are evicted		Before a new entry is added to the dynamic table, entries are evicted
	from the end of the dynamic table until the size of the dynamic table		from the end of the dynamic table until the size of the dynamic table
	is less than or equal to (maximum size - new entry size) or until the		is less than or equal to (maximum size - new entry size) or until the
	table is empty.		table is empty. The encoder MUST NOT evict a dynamic table entry
			unless it has first been acknowledged by the decoder.
	If the size of the new entry is less than or equal to the maximum		If the size of the new entry is less than or equal to the maximum
	size, that entry is added to the table. It is an error to attempt to		size, that entry is added to the table. It is an error to attempt to
	add an entry that is larger than the maximum size; this MUST be		add an entry that is larger than the maximum size; this MUST be
	treated as a connection error of type		treated as a connection error of type
	"HTTP_QPACK_DECOMPRESSION_FAILED".		"HTTP_QPACK_ENCODER_STREAM_ERROR".
	A new entry can reference an entry in the dynamic table that will be		A new entry can reference an entry in the dynamic table that will be
	evicted when adding this new entry into the dynamic table.		evicted when adding this new entry into the dynamic table.
	Implementations are cautioned to avoid deleting the referenced name		Implementations are cautioned to avoid deleting the referenced name
	if the referenced entry is evicted from the dynamic table prior to		if the referenced entry is evicted from the dynamic table prior to
	inserting the new entry.		inserting the new entry.
	The dynamic table can contain duplicate entries (i.e., entries with		The dynamic table can contain duplicate entries (i.e., entries with
	the same name and same value). Therefore, duplicate entries MUST NOT		the same name and same value). Therefore, duplicate entries MUST NOT
	be treated as an error by a decoder.		be treated as an error by a decoder.
			2.2.1. Maximum Table Size
	The encoder decides how to update the dynamic table and as such can		The encoder decides how to update the dynamic table and as such can
	control how much memory is used by the dynamic table. To limit the		control how much memory is used by the dynamic table. To limit the
	memory requirements of the decoder, the dynamic table size is		memory requirements of the decoder, the dynamic table size is
	strictly bounded.		strictly bounded.
	The decoder determines the maximum size that the encoder is permitted		The decoder determines the maximum size that the encoder is permitted
	to use for the dynamic table. In HTTP/QUIC, this value is determined		to use for the dynamic table. In HTTP/QUIC, this value is determined
	by the SETTINGS_HEADER_TABLE_SIZE setting (see Section 4).		by the SETTINGS_HEADER_TABLE_SIZE setting (see Section 4).
	An encoder can choose to use less capacity than this maximum size		An encoder can choose to use less capacity than this maximum size
	(see Section 5.2.4), but the chosen size MUST stay lower than or		(see Section 5.2.4), but the chosen size MUST stay lower than or
	equal to the maximum set by the decoder. Whenever the maximum size		equal to the maximum set by the decoder. Whenever the maximum size
	for the dynamic table is reduced, entries are evicted from the end of		for the dynamic table is reduced, entries are evicted from the end of
	the dynamic table until the size of the dynamic table is less than or		the dynamic table until the size of the dynamic table is less than or
	equal to the maximum size.		equal to the maximum size.
	This mechanism can be used to completely clear entries from the		This mechanism can be used to completely clear entries from the
	dynamic table by setting a maximum size of 0, which can subsequently		dynamic table by setting a maximum size of 0, which can subsequently
	be restored.		be restored.
	2.2.1. Absolute and Relative Indexing		2.2.2. Calculating Table Size
			The size of the dynamic table is the sum of the size of its entries.
			The size of an entry is the sum of its name's length in octets (as
			defined in Section 5.1.2), its value's length in octets, and 32.
			The size of an entry is calculated using the length of its name and
			value without any Huffman encoding applied.
			"MaxEntries" is the maximum number of entries that the dynamic table
			can have. The smallest entry has empty name and value strings and
			has the size of 32. The MaxEntries is calculated as
			MaxEntries = floor( MaxTableSize / 32 )
			MaxTableSize is the maximum size of the dynamic table as specified by
			the decoder (see Section 2.2.1).
			2.2.3. Absolute Indexing
	Each entry possesses both an absolute index which is fixed for the		Each entry possesses both an absolute index which is fixed for the
	lifetime of that entry and a relative index which changes over time		lifetime of that entry and a relative index which changes over time
	based on the context of the reference. The first entry inserted has		based on the context of the reference. The first entry inserted has
	an absolute index of "1"; indices increase sequentially with each		an absolute index of "1"; indices increase sequentially with each
	insertion.		insertion.
			2.2.4. Relative Indexing
	The relative index begins at zero and increases in the opposite		The relative index begins at zero and increases in the opposite
	direction from the absolute index. Determining which entry has a		direction from the absolute index. Determining which entry has a
	relative index of "0" depends on the context of the reference.		relative index of "0" depends on the context of the reference.
	On the encoder stream, a relative index of "0" always refers to the		On the encoder stream, a relative index of "0" always refers to the
	most recently inserted value in the dynamic table. Note that this		most recently inserted value in the dynamic table. Note that this
	means the entry referenced by a given relative index will change		means the entry referenced by a given relative index will change
	while interpreting instructions on the encoder stream.		while interpreting instructions on the encoder stream.
	+---+---------------+-----------+		+---+---------------+-----------+
	| n | ... | d + 1 | Absolute Index		| n | ... | d + 1 | Absolute Index
	+ - +---------------+ - - - - - +		+ - +---------------+ - - - - - +
	| 0 | ... | n - d - 1 | Relative Index		| 0 | ... | n - d - 1 | Relative Index
	+---+---------------+-----------+		+---+---------------+-----------+
	^ |		^ |
	| V		| V
	Insertion Point Dropping Point		Insertion Point Dropping Point
	n = count of entries inserted		n = count of entries inserted
	d = count of entries dropped		d = count of entries dropped
	Example Dynamic Table Indexing - Control Stream		Example Dynamic Table Indexing - Control Stream
	Because frames from request streams can be delivered out of order		Because frames from request streams can be delivered out of order
	with instructions on the encoder stream, relative indices are		with instructions on the encoder stream, relative indices are
	relative to the Base Index at the beginning of the header block (see		relative to the Base Index at the beginning of the header block (see
	skipping to change at page 6, line 39 ¶		skipping to change at page 7, line 39 ¶
	V		V
	+---+-----+-----+-----+-------+		+---+-----+-----+-----+-------+
	| n | n-1 | n-2 | ... | d+1 | Absolute Index		| n | n-1 | n-2 | ... | d+1 | Absolute Index
	+---+-----+ - +-----+ - +		+---+-----+ - +-----+ - +
	| 0 | ... | n-d-3 | Relative Index		| 0 | ... | n-d-3 | Relative Index
	+-----+-----+-------+		+-----+-----+-------+
	n = count of entries inserted		n = count of entries inserted
	d = count of entries dropped		d = count of entries dropped
	Example Dynamic Table Indexing - Request Stream		Example Dynamic Table Indexing - Relative Index on Request Stream
	2.2.2. Post-Base Indexing		2.2.5. Post-Base Indexing
	A header block on the request stream can reference entries added		A header block on the request stream can reference entries added
	after the entry identified by the Base Index. This allows an encoder		after the entry identified by the Base Index. This allows an encoder
	to process a header block in a single pass and include references to		to process a header block in a single pass and include references to
	entries added while processing this (or other) header blocks. Newly		entries added while processing this (or other) header blocks. Newly
	added entries are referenced using Post-Base instructions. Indices		added entries are referenced using Post-Base instructions. Indices
	for Post-Base instructions increase in the same direction as absolute		for Post-Base instructions increase in the same direction as absolute
	indices, but the zero value is one higher than the Base Index.		indices, but the zero value is one higher than the Base Index.
	Base Index		Base Index
	skipping to change at page 7, line 17 ¶		skipping to change at page 8, line 17 ¶
	V		V
	+---+-----+-----+-----+-----+		+---+-----+-----+-----+-----+
	| n | n-1 | n-2 | ... | d+1 | Absolute Index		| n | n-1 | n-2 | ... | d+1 | 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
	Dynamic Table Indexing - Post-Base References		Example Dynamic Table Indexing - Post-Base Index on Request Stream
	If the decoder encounters a reference to an entry which has already		If the decoder encounters a reference on a request or push stream to
	been dropped from the table or which is greater than the declared		a dynamic table entry which has already been dropped or which has an
	Largest Reference (see Section 5.4.1), this MUST be treated as a		absolute index greater than the declared Largest Reference (see
	stream error of type "HTTP_QPACK_DECOMPRESSION_FAILED" error code.		Section 5.4.1), it MUST treat this as a stream error of type
	If this reference occurs on the encoder stream, this MUST be treated		"HTTP_QPACK_DECOMPRESSION_FAILED".
	as a session error.
			If the decoder encounters a reference on the encoder stream to a
			dynamic table entry which has already been dropped, it MUST treat
			this as a connection error of type "HTTP_QPACK_ENCODER_STREAM_ERROR".
	2.3. Avoiding Head-of-Line Blocking in HTTP/QUIC		2.3. Avoiding Head-of-Line Blocking in HTTP/QUIC
	Because QUIC does not guarantee order between data on different		Because QUIC does not guarantee order between data on different
	streams, a header block might reference an entry in the dynamic table		streams, a header block might reference an entry in the dynamic table
	that has not yet been received.		that has not yet been received.
	Each header block contains a Largest Reference which identifies the		Each header block contains a Largest Reference which identifies the
	table state necessary for decoding. If the greatest absolute index		table state necessary for decoding. If the greatest absolute index
	in the dynamic table is less than the value of the Largest Reference,		in the dynamic table is less than the value of the Largest Reference,
	the stream is considered "blocked." While blocked, header field data		the stream is considered "blocked." While blocked, header field data
	should remain in the blocked stream's flow control window. When the		should remain in the blocked stream's flow control window. When the
	Largest Reference is zero, the frame contains no references to the		Largest Reference is zero, the frame contains no references to the
	dynamic table and can always be processed immediately. A stream		dynamic table and can always be processed immediately. A stream
	becomes unblocked when the greatest absolute index in the dynamic		becomes unblocked when the greatest absolute index in the dynamic
	table becomes greater than or equal to the Largest Reference for all		table becomes greater than or equal to the Largest Reference for all
	header blocks the decoder has started reading from the stream. If a		header blocks the decoder has started reading from the stream. If a
	decoder encounters a header block where the actual largest reference		decoder encounters a header block where the actual largest reference
	is not equal to the largest reference declared in the prefix, it MAY		is not equal to the Largest Reference declared in the prefix, it MAY
	treat this as a stream error of type HTTP_QPACK_DECOMPRESSION_FAILED.		treat this as a stream error of type HTTP_QPACK_DECOMPRESSION_FAILED.
	A decoder can permit the possibility of blocked streams by setting		A decoder can permit the possibility of blocked streams by setting
	SETTINGS_QPACK_BLOCKED_STREAMS to a non-zero value (see Section 4).		SETTINGS_QPACK_BLOCKED_STREAMS to a non-zero value (see Section 4).
	This setting specifies an upper bound on the number of streams which		This setting specifies an upper bound on the number of streams which
	can be blocked.		can be blocked.
	An encoder can decide whether to risk having a stream become blocked.		An encoder can decide whether to risk having a stream become blocked.
	If permitted by the value of SETTINGS_QPACK_BLOCKED_STREAMS,		If permitted by the value of SETTINGS_QPACK_BLOCKED_STREAMS,
	compression efficiency can be improved by referencing dynamic table		compression efficiency can be improved by referencing dynamic table
	skipping to change at page 8, line 16 ¶		skipping to change at page 9, line 19 ¶
	the stream can become blocked at the decoder. An encoder avoids the		the stream can become blocked at the decoder. An encoder avoids the
	risk of blocking by only referencing dynamic table entries which have		risk of blocking by only referencing dynamic table entries which have
	been acknowledged, but this means using literals. Since literals		been acknowledged, but this means using literals. Since literals
	make the header block larger, this can result in the encoder becoming		make the header block larger, this can result in the encoder becoming
	blocked on congestion or flow control limits.		blocked on congestion or flow control limits.
	An encoder MUST limit the number of streams which could become		An encoder MUST limit the number of streams which could become
	blocked to the value of SETTINGS_QPACK_BLOCKED_STREAMS at all times.		blocked to the value of SETTINGS_QPACK_BLOCKED_STREAMS at all times.
	Note that the decoder might not actually become blocked on every		Note that the decoder might not actually become blocked on every
	stream which risks becoming blocked. If the decoder encounters more		stream which risks becoming blocked. If the decoder encounters more
	blocked streams than it promised to support, it SHOULD treat this as		blocked streams than it promised to support, it MUST treat this as a
	a stream error of type HTTP_QPACK_DECOMPRESSION_FAILED.		stream error of type HTTP_QPACK_DECOMPRESSION_FAILED.
	2.3.1. State Synchronization		2.3.1. State Synchronization
	The decoder stream signals key events at the decoder that permit the		The decoder stream (Section 5.3) signals key events at the decoder
	encoder to track the decoder's state. These events are:		that permit the encoder to track the decoder's state. These events
			are:
	o Complete processing of a header block		o Complete processing of a header block
	o Abandonment of a stream which might have remaining header blocks		o Abandonment of a stream which might have remaining header blocks
	o Receipt of new dynamic table entries		o Receipt of new dynamic table entries
	Regardless of whether a header block contained blocking references,		Regardless of whether a header block contained blocking references,
	the knowledge that it has been processed permits the encoder to evict		the knowledge that it has been processed permits the encoder to evict
	entries to which no unacknowledged references remain; see		entries to which no unacknowledged references remain; see
	skipping to change at page 9, line 15 ¶		skipping to change at page 10, line 15 ¶
	3. Conventions and Definitions		3. 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 BCP		"OPTIONAL" in this document are to be interpreted as described in 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:
	Header: A name-value pair sent as part of an HTTP message.		Header field: A name-value pair sent as part of an HTTP message.
	Header set: The full collection of headers associated with an HTTP		Header list: The ordered collection of header fields associated with
	message.		an HTTP message. A header list can contain multiple header fields
			with the same name. It can also contain duplicate header fields.
	Header block: The compressed representation of a header set.		Header block: The compressed representation of a header list.
	Encoder: An implementation which transforms a header set into a		Encoder: An implementation which transforms a header list into a
	header block.		header block.
	Decoder: An implementation which transforms a header block into a		Decoder: An implementation which transforms a header block into a
	header set.		header list.
	QPACK is a name, not an acronym.		QPACK is a name, not an acronym.
	3.1. Notational Conventions		3.1. Notational Conventions
	Diagrams use the format described in Section 3.1 of [RFC2360], with		Diagrams use the format described in Section 3.1 of [RFC2360], with
	the following additional conventions:		the following additional conventions:
	x (A) Indicates that x is A bits long		x (A) Indicates that x is A bits long
	skipping to change at page 10, line 44 ¶		skipping to change at page 11, line 44 ¶
	All table updates occur on the encoder stream. Request streams and		All table updates occur on the encoder stream. Request streams and
	push streams only carry header blocks that do not modify the state of		push streams only carry header blocks that do not modify the state of
	the table.		the table.
	5.1. Primitives		5.1. Primitives
	5.1.1. Prefixed Integers		5.1.1. Prefixed Integers
	The prefixed integer from Section 5.1 of [RFC7541] is used heavily		The prefixed integer from Section 5.1 of [RFC7541] is used heavily
	throughout this document. The format from [RFC7541] is used		throughout this document. The format from [RFC7541] is used
	unmodified.		unmodified. QPACK implementations MUST be able to decode integers up
			to 62 bits long.
	5.1.2. String Literals		5.1.2. String Literals
	The string literal defined by Section 5.2 of [RFC7541] is also used		The string literal defined by Section 5.2 of [RFC7541] is also used
	throughout. This string format includes optional Huffman encoding.		throughout. This string format includes optional Huffman encoding.
	HPACK defines string literals to begin on a byte boundary. They		HPACK defines string literals to begin on a byte boundary. They
	begin with a single flag (indicating whether the string is Huffman-		begin with a single flag (indicating whether the string is Huffman-
	coded), followed by the Length encoded as a 7-bit prefix integer, and		coded), followed by the Length encoded as a 7-bit prefix integer, and
	finally Length octets of data. When Huffman encoding is enabled, the		finally Length octets of data. When Huffman encoding is enabled, the
	skipping to change at page 13, line 24 ¶		skipping to change at page 14, line 24 ¶
	0 1 2 3 4 5 6 7		0 1 2 3 4 5 6 7
	+---+---+---+---+---+---+---+---+		+---+---+---+---+---+---+---+---+
	| 0 | 0 | 1 | Max size (5+) |		| 0 | 0 | 1 | Max size (5+) |
	+---+---+---+-------------------+		+---+---+---+-------------------+
	Figure 2: Maximum Dynamic Table Size Change		Figure 2: Maximum Dynamic Table Size Change
	The new maximum size MUST be lower than or equal to the limit		The new maximum size MUST be lower than or equal to the limit
	determined by the protocol using QPACK. A value that exceeds this		determined by the protocol using QPACK. A value that exceeds this
	limit MUST be treated as a decoding error. In HTTP/QUIC, this limit		limit MUST be treated as a connection error of type
	is the value of the SETTINGS_HEADER_TABLE_SIZE parameter (see		"HTTP_QPACK_ENCODER_STREAM_ERROR". In HTTP/QUIC, this limit is the
	Section 4) received from the decoder.		value of the SETTINGS_HEADER_TABLE_SIZE parameter (see Section 4)
			received from the decoder.
	Reducing the maximum size of the dynamic table can cause entries to		Reducing the maximum size of the dynamic table can cause entries to
	be evicted (see Section 4.3 of [RFC7541]). This MUST NOT cause the		be evicted (see Section 4.3 of [RFC7541]). This MUST NOT cause the
	eviction of entries with outstanding references (see Section 7.3).		eviction of entries with outstanding references (see Section 7.3).
	Changing the size of the dynamic table is not acknowledged as this		Changing the size of the dynamic table is not acknowledged as this
	instruction does not insert an entry.		instruction does not insert an entry.
	5.3. QPACK Decoder Stream		5.3. QPACK Decoder Stream
	The decoder stream carries information used to ensure consistency of		The decoder stream carries information used to ensure consistency of
	skipping to change at page 14, line 15 ¶		skipping to change at page 15, line 16 ¶
	encoder uses this value to determine which table entries might cause		encoder uses this value to determine which table entries might cause
	a stream to become blocked, as described in Section 2.3.1.		a stream to become blocked, as described in Section 2.3.1.
	0 1 2 3 4 5 6 7		0 1 2 3 4 5 6 7
	+---+---+---+---+---+---+---+---+		+---+---+---+---+---+---+---+---+
	| 0 | 0 | Insert Count (6+) |		| 0 | 0 | Insert Count (6+) |
	+---+---+-----------------------+		+---+---+-----------------------+
	Figure 3: Table State Synchronize		Figure 3: Table State Synchronize
			An encoder that receives an Insert Count equal to zero or one that
			increases Largest Known Received beyond what the encoder has sent
			MUST treat this as a connection error of type
			"HTTP_QPACK_DECODER_STREAM_ERROR".
	A decoder chooses when to emit Table State Synchronize instructions.		A decoder chooses when to emit Table State Synchronize instructions.
	Emitting a Table State Synchronize after adding each new dynamic		Emitting a Table State Synchronize after adding each new dynamic
	table entry will provide the most timely feedback to the encoder, but		table entry will provide the most timely feedback to the encoder, but
	could be redundant with other decoder feedback. By delaying a		could be redundant with other decoder feedback. By delaying a
	Table State Synchronize, a decoder might be able to coalesce multiple		Table State Synchronize, a decoder might be able to coalesce multiple
	Table State Synchronize instructions, or replace them entirely with		Table State Synchronize instructions, or replace them entirely with
	Header Acknowledgements. However, delaying too long may lead to		Header Acknowledgements. However, delaying too long may lead to
	compression inefficiencies if the encoder waits for an entry to be		compression inefficiencies if the encoder waits for an entry to be
	acknowledged before using it.		acknowledged before using it.
	5.3.2. Header Acknowledgement		5.3.2. Header Acknowledgement
	After processing a header block whose declared Largest Reference is		After processing a header block whose declared Largest Reference is
	not zero, the decoder emits a Header Acknowledgement instruction on		not zero, the decoder emits a Header Acknowledgement instruction on
	the decoder stream. The instruction begins with the '1' one-bit		the decoder stream. The instruction begins with the '1' one-bit
	pattern and includes the request stream's stream ID, encoded as a		pattern and includes the request stream's stream ID, encoded as a
	7-bit prefix integer. It is used by the peer's QPACK encoder to know		7-bit prefix integer. It is used by the peer's QPACK encoder to know
	when it is safe to evict an entry.		when it is safe to evict an entry.
			0 1 2 3 4 5 6 7
			+---+---+---+---+---+---+---+---+
			| 1 | Stream ID (7+) |
			+---+---------------------------+
			Figure 4: Header Acknowledgement
	The same Stream ID can be identified multiple times, as multiple		The same Stream ID can be identified multiple times, as multiple
	header blocks can be sent on a single stream in the case of		header blocks can be sent on a single stream in the case of
	intermediate responses, trailers, and pushed requests. Since header		intermediate responses, trailers, and pushed requests. Since header
	frames on each stream are received and processed in order, this gives		frames on each stream are received and processed in order, this gives
	the encoder precise feedback on which header blocks within a stream		the encoder precise feedback on which header blocks within a stream
	have been fully processed.		have been fully processed.
	0 1 2 3 4 5 6 7		If an encoder receives a Header Acknowledgement instruction referring
	+---+---+---+---+---+---+---+---+		to a stream on which every header block with a non-zero Largest
	| 1 | Stream ID (7+) |		Reference has already been acknowledged, that MUST be treated as a
	+---+---------------------------+		connection error of type "HTTP_QPACK_DECODER_STREAM_ERROR".
	Figure 4: Header Acknowledgement
	When blocking references are permitted, the encoder uses		When blocking references are permitted, the encoder uses
	acknowledgement of header blocks to update the Largest Known Received		acknowledgement of header blocks to update the Largest Known Received
	index. If a header block was potentially blocking, the		index. If a header block was potentially blocking, the
	acknowledgement implies that the decoder has received all dynamic		acknowledgement implies that the decoder has received all dynamic
	table state necessary to process the header block. If the Largest		table state necessary to process the header block. If the Largest
	Reference of an acknowledged header block was greater than the		Reference of an acknowledged header block was greater than the
	encoder's current Largest Known Received index, the block's Largest		encoder's current Largest Known Received index, the block's Largest
	Reference becomes the new Largest Known Received.		Reference becomes the new Largest Known Received.
	5.3.3. Stream Cancellation		5.3.3. Stream Cancellation
	A stream that is reset might have multiple outstanding header blocks.		A stream that is reset might have multiple outstanding header blocks
	A decoder that receives a stream reset before the end of a stream		with dynamic table references. A decoder that receives a stream
	generates a Stream Cancellation instruction on the decoder stream.		reset before the end of a stream generates a Stream Cancellation
	Similarly, a decoder that abandons reading of a stream needs to		instruction on the decoder stream. Similarly, a decoder that
	signal this using the Stream Cancellation instruction. This signals		abandons reading of a stream needs to signal this using the Stream
	to the encoder that all references to the dynamic table on that		Cancellation instruction. This signals to the encoder that all
	stream are no longer outstanding.		references to the dynamic table on that stream are no longer
			outstanding. A decoder with a maximum dynamic table size equal to
			zero MAY omit sending Stream Cancellations, because the encoder
			cannot have any dynamic table references.
	An encoder cannot infer from this instruction that any updates to the		An encoder cannot infer from this instruction that any updates to the
	dynamic table have been received.		dynamic table have been received.
	The instruction begins with the '01' two-bit pattern. The		The instruction begins with the '01' two-bit pattern. The
	instruction includes the stream ID of the affected stream - a request		instruction includes the stream ID of the affected stream - a request
	or push stream - encoded as a 6-bit prefix integer.		or push stream - encoded as a 6-bit prefix integer.
	0 1 2 3 4 5 6 7		0 1 2 3 4 5 6 7
	+---+---+---+---+---+---+---+---+		+---+---+---+---+---+---+---+---+
	skipping to change at page 16, line 18 ¶		skipping to change at page 17, line 29 ¶
	+---+---------------------------+		+---+---------------------------+
	| S | Delta Base Index (7+) |		| S | Delta Base Index (7+) |
	+---+---------------------------+		+---+---------------------------+
	| Compressed Headers ...		| Compressed Headers ...
	+-------------------------------+		+-------------------------------+
	Figure 6: Frame Payload		Figure 6: Frame Payload
	"Largest Reference" identifies the largest absolute dynamic index		"Largest Reference" identifies the largest absolute dynamic index
	referenced in the block. Blocking decoders use the Largest Reference		referenced in the block. Blocking decoders use the Largest Reference
	to determine when it is safe to process the rest of the block.		to determine when it is safe to process the rest of the block. If
			Largest Reference is greater than zero, the encoder transforms it as
			follows before encoding:
			LargestReference = LargestReference mod 2*MaxEntries + 1
			The decoder reconstructs the Largest Reference using the following
			algorithm:
			if LargestReference > 0:
			LargestReference -= 1
			CurrentWrapped = TableLargestAbsoluteIndex mod 2*MaxEntries
			if CurrentWrapped >= LargestReference + MaxEntries:
			# Largest Reference wrapped around 1 extra time
			LargestReference += 2*MaxEntries
			else if CurrentWrapped + MaxEntries < LargestReference
			# Decoder wrapped around 1 extra time
			CurrentWrapped += 2*MaxEntries
			LargestReference +=
			(TableLargestAbsoluteIndex - CurrentWrapped)
			TableLargestAbsoluteIndex is the Absolute Index of the most recently
			inserted item in the decoder's dynamic table. This encoding limits
			the length of the prefix on long-lived connections.
	"Base Index" is used to resolve references in the dynamic table as		"Base Index" is used to resolve references in the dynamic table as
	described in Section 2.2.1.		described in Section 2.2.4.
	To save space, Base Index is encoded relative to Largest Reference		To save space, Base Index is encoded relative to Largest Reference
	using a one-bit sign and the "Delta Base Index" value. A sign bit of		using a one-bit sign and the "Delta Base Index" value. A sign bit of
	0 indicates that the Base Index has an absolute index that is greater		0 indicates that the Base Index has an absolute index that is greater
	than or equal to the Largest Reference; the value of Delta Base Index		than or equal to the Largest Reference; the value of Delta Base Index
	is added to the Largest Reference to determine the absolute value of		is added to the Largest Reference to determine the absolute value of
	the Base Index. A sign bit of 1 indicates that the Base Index is		the Base Index. A sign bit of 1 indicates that the Base Index is
	less than the Largest Reference. That is:		less than the Largest Reference. That is:
	if sign == 0:		if sign == 0:
	skipping to change at page 17, line 37 ¶		skipping to change at page 19, line 24 ¶
	starts with the '1' 1-bit pattern, followed by the "S" bit indicating		starts with the '1' 1-bit pattern, followed by the "S" bit indicating
	whether the reference is into the static (S=1) or dynamic (S=0)		whether the reference is into the static (S=1) or dynamic (S=0)
	table. Finally, the relative index of the matching header field is		table. Finally, the relative index of the matching header field is
	represented as an integer with a 6-bit prefix (see Section 5.1 of		represented as an integer with a 6-bit prefix (see Section 5.1 of
	[RFC7541]).		[RFC7541]).
	5.4.2.2. Indexed Header Field With Post-Base Index		5.4.2.2. Indexed Header Field With Post-Base Index
	If the entry is in the dynamic table with an absolute index greater		If the entry is in the dynamic table with an absolute index greater
	than Base Index, the representation starts with the '0001' 4-bit		than Base Index, the representation starts with the '0001' 4-bit
	pattern, followed by the post-base index (see Section 2.2.2) of the		pattern, followed by the post-base index (see Section 2.2.5) of the
	matching header field, represented as an integer with a 4-bit prefix		matching header field, represented as an integer with a 4-bit prefix
	(see Section 5.1 of [RFC7541]).		(see Section 5.1 of [RFC7541]).
	0 1 2 3 4 5 6 7		0 1 2 3 4 5 6 7
	+---+---+---+---+---+---+---+---+		+---+---+---+---+---+---+---+---+
	| 0 | 0 | 0 | 1 | Index (4+) |		| 0 | 0 | 0 | 1 | Index (4+) |
	+---+---+---+---+---------------+		+---+---+---+---+---------------+
	Indexed Header Field with Post-Base Index		Indexed Header Field with Post-Base Index
	skipping to change at page 18, line 43 ¶		skipping to change at page 20, line 30 ¶
	absolute index less than or equal to Base Index, the header field		absolute index less than or equal to Base Index, the header field
	name is represented using the relative index of that entry, which is		name is represented using the relative index of that entry, which is
	represented as an integer with a 4-bit prefix (see Section 5.1 of		represented as an integer with a 4-bit prefix (see Section 5.1 of
	[RFC7541]). The "S" bit indicates whether the reference is to the		[RFC7541]). The "S" bit indicates whether the reference is to the
	static (S=1) or dynamic (S=0) table.		static (S=1) or dynamic (S=0) table.
	5.4.2.4. Literal Header Field With Post-Base Name Reference		5.4.2.4. Literal Header Field With Post-Base Name Reference
	For entries in the dynamic table with an absolute index greater than		For entries in the dynamic table with an absolute index greater than
	Base Index, the header field name is represented using the post-base		Base Index, the header field name is represented using the post-base
	index of that entry (see Section 2.2.2) encoded as an integer with a		index of that entry (see Section 2.2.5) encoded as an integer with a
	3-bit prefix.		3-bit prefix.
	0 1 2 3 4 5 6 7		0 1 2 3 4 5 6 7
	+---+---+---+---+---+---+---+---+		+---+---+---+---+---+---+---+---+
	| 0 | 0 | 0 | 0 | N |NameIdx(3+)|		| 0 | 0 | 0 | 0 | N |NameIdx(3+)|
	+---+---+---+---+---+-----------+		+---+---+---+---+---+-----------+
	| H | Value Length (7+) |		| H | Value Length (7+) |
	+---+---------------------------+		+---+---------------------------+
	| Value String (Length octets) |		| Value String (Length octets) |
	+-------------------------------+		+-------------------------------+
	skipping to change at page 19, line 50 ¶		skipping to change at page 21, line 31 ¶
	+---+---------------------------+		+---+---------------------------+
	| H | Value Length (7+) |		| H | Value Length (7+) |
	+---+---------------------------+		+---+---------------------------+
	| Value String (Length octets) |		| Value String (Length octets) |
	+-------------------------------+		+-------------------------------+
	Literal Header Field Without Name Reference		Literal Header Field Without Name Reference
	6. Error Handling		6. Error Handling
	The following error code is defined for HTTP/QUIC to indicate all		The following error codes are defined for HTTP/QUIC to indicate
	failures of QPACK which prevent the stream or connection from		failures of QPACK which prevent the stream or connection from
	continuing:		continuing:
	HTTP_QPACK_DECOMPRESSION_FAILED (0x06): QPACK failed to decompress a		HTTP_QPACK_DECOMPRESSION_FAILED (TBD): The decoder failed to
	frame and cannot continue.		interpret an instruction on a request or push stream and is not
			able to continue decoding that header block.
			HTTP_QPACK_ENCODER_STREAM_ERROR (TBD):
			The decoder failed to interpret an instruction on the encoder
			stream. HTTP_QPACK_DECODER_STREAM_ERROR (TBD):
			The encoder failed to interpret an instruction on the decoder
			stream.
			Upon encountering an error, an implementation MAY elect to treat it
			as a connection error even if this document prescribes that it MUST
			be treated as a stream error.
	7. Encoding Strategies		7. Encoding Strategies
	7.1. Single Pass Encoding		7.1. Single Pass Encoding
	An encoder making a single pass over a list of headers must choose		An encoder making a single pass over a list of headers must choose
	Base Index before knowing Largest Reference. When trying to		Base Index before knowing Largest Reference. When trying to
	reference a header inserted to the table after encoding has begun,		reference a header inserted to the table after encoding has begun,
	the entry is encoded with different instructions that tell the		the entry is encoded with different instructions that tell the
	decoder to use an absolute index greater than the Base Index.		decoder to use an absolute index greater than the Base Index.
	skipping to change at page 20, line 40 ¶		skipping to change at page 22, line 37 ¶
	table entry is not received by the decoder after the referenced entry		table entry is not received by the decoder after the referenced entry
	has already been evicted. An encoder also respects the limit set by		has already been evicted. An encoder also respects the limit set by
	the decoder on the number of streams that are allowed to become		the decoder on the number of streams that are allowed to become
	blocked. Even if the decoder is willing to tolerate blocked streams,		blocked. Even if the decoder is willing to tolerate blocked streams,
	the encoder might choose to avoid them in certain cases.		the encoder might choose to avoid them in certain cases.
	In order to enable this, the encoder will need to track outstanding		In order to enable this, the encoder will need to track outstanding
	(unacknowledged) header blocks and table updates using feedback		(unacknowledged) header blocks and table updates using feedback
	received from the decoder.		received from the decoder.
	7.3.1. Blocked Eviction		7.3.1. Blocked Dynamic Table Insertions
	The encoder MUST NOT permit an entry to be evicted while a reference		An encoder MUST NOT insert an entry into the dynamic table (or
	to that entry remains unacknowledged. If a new header to be inserted		duplicate an existing entry) if doing so would evict an entry with
	into the dynamic table would cause the eviction of such an entry, the		unacknowledged references. For header blocks that might rely on the
	encoder MUST NOT emit the insert instruction until the reference has		newly added entry, the encoder can use a literal representation and
	been processed by the decoder and acknowledged.		maybe insert the entry later.
	The encoder can emit a literal representation for the new header in		To ensure that the encoder is not prevented from adding new entries,
	order to avoid encoding delays, and MAY insert the header into the		the encoder can avoid referencing entries that will be evicted
	table later if desired.		soonest. Rather than reference such an entry, the encoder SHOULD
			emit a Duplicate instruction (see Section 5.2.3), and reference the
			duplicate instead.
	To ensure that the blocked eviction case is rare, references to the		Determining which entries are too close to eviction to reference is
	oldest entries in the dynamic table SHOULD be avoided. When one of		an encoder preference. One heuristic is to target a fixed amount of
	the oldest entries in the table is still actively used for		available space in the dynamic table: either unused space or space
	references, the encoder SHOULD emit an Duplicate representation		that can be reclaimed by evicting unreferenced entries. To achieve
	instead (see Section 5.2.3).		this, the encoder can maintain a draining index, which is the
			smallest absolute index in the dynamic table 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
			not reference. Draining entries - entries with an absolute index
			lower than the draining index - will not accumulate new references.
			The number of unacknowledged references to draining entries will
			eventually become zero, making the entry available for eviction.
			+----------+---------------------------------+--------+
			| Draining | Referenceable | Unused |
			| Entries | Entries | Space |
			+----------+---------------------------------+--------+
			^ ^ ^
			| | |
			Dropping Draining Index Base Index /
			Point Insertion Point
			Figure 7: Draining Dynamic Table Entries
	7.3.2. Blocked Decoding		7.3.2. Blocked Decoding
	For header blocks encoded in non-blocking mode, the encoder needs to		For header blocks encoded in non-blocking mode, the encoder needs to
	forego indexed representations that refer to table updates which have		forego indexed representations that refer to table updates which have
	not yet been acknowledged with Section 5.3. Since all table updates		not yet been acknowledged (see Section 5.3). Since all table updates
	are processed in sequence on the encoder stream, an index into the		are processed in sequence on the control stream, an index into the
	dynamic table is sufficient to track which entries have been		dynamic table is sufficient to track which entries have been
	acknowledged.		acknowledged.
	To track blocked streams, the necessary Base Index value for each		To track blocked streams, the necessary Base Index value for each
	stream can be used. Whenever the decoder processes a table update,		stream can be used. Whenever the decoder processes a table update,
	it can begin decoding any blocked streams that now have their		it can begin decoding any blocked streams that now have their
	dependencies satisfied.		dependencies satisfied.
	7.4. Speculative table updates		7.4. Speculative table updates
	Implementations can _speculatively_ send header frames on the HTTP		Implementations can _speculatively_ send instructions on the encoder
	Control Streams which are not needed for any current HTTP request or		stream which are not needed for any current HTTP request or response.
	response. Such headers could be used strategically to improve		Such headers could be used strategically to improve performance. For
	performance. For instance, the encoder might decide to _refresh_ by		instance, the encoder might decide to _refresh_ by sending Duplicate
	sending Duplicate representations for popular header fields		representations for popular header fields (Section 5.2.3), ensuring
	(Section 5.2.3), ensuring they have small indices and hence minimal		they have small indices and hence minimal size on the wire.
	size on the wire.
	7.5. Sample One Pass Encoding Algorithm		7.5. Sample One Pass Encoding Algorithm
	Pseudo-code for single pass encoding, excluding handling of		Pseudo-code for single pass encoding, excluding handling of
	duplicates, non-blocking mode, and reference tracking.		duplicates, non-blocking mode, and reference tracking.
	baseIndex = dynamicTable.baseIndex		baseIndex = dynamicTable.baseIndex
	largestReference = 0		largestReference = 0
	for header in headers:		for header in headers:
	staticIdx = staticTable.getIndex(header)		staticIdx = staticTable.getIndex(header)
	skipping to change at page 23, line 43 ¶		skipping to change at page 26, line 43 ¶
	+----------------------+------+---------------+--------+		+----------------------+------+---------------+--------+
	| Stream Type | Code | Specification | Sender |		| Stream Type | Code | Specification | Sender |
	+----------------------+------+---------------+--------+		+----------------------+------+---------------+--------+
	| QPACK Encoder Stream | 0x48 | Section 5 | Both |		| QPACK Encoder Stream | 0x48 | Section 5 | Both |
	| | | | |		| | | | |
	| QPACK Decoder Stream | 0x68 | Section 5 | Both |		| QPACK Decoder Stream | 0x68 | Section 5 | Both |
	+----------------------+------+---------------+--------+		+----------------------+------+---------------+--------+
	9.3. Error Code Registration		9.3. Error Code Registration
	This document establishes one new error code in the "HTTP/QUIC Error		This document establishes the following new error codes in the "HTTP/
	Code" registry established in [QUIC-HTTP].		QUIC Error Code" registry established in [QUIC-HTTP].
	Name: HTTP_QPACK_DECOMPRESSION_FAILED
	Code: 0x06
	Description: QPACK failed to interpret an instruction and cannot		+------------------------------+------+--------------+--------------+
	continue.		| Name | Code | Description | Specificatio |
			| | | | n |
			+------------------------------+------+--------------+--------------+
			| HTTP_QPACK_DECOMPRESSION_FAI | TBD | Decompressio | Section 6 |
			| LED | | n of a | |
			| | | header block | |
			| | | failed | |
			| | | | |
			| HTTP_QPACK_ENCODER_STREAM_ER | TBD | Error on the | Section 6 |
			| ROR | | encoder | |
			| | | stream | |
			| | | | |
			| HTTP_QPACK_DECODER_STREAM_ER | TBD | Error on the | Section 6 |
			| ROR | | decoder | |
			| | | stream | |
			+------------------------------+------+--------------+--------------+
	10. References		10. References
	10.1. Normative References		10.1. Normative References
	[QUIC-HTTP]		[QUIC-HTTP]
	Bishop, M., Ed., "Hypertext Transfer Protocol (HTTP) over		Bishop, M., Ed., "Hypertext Transfer Protocol (HTTP) over
	QUIC", draft-ietf-quic-http-14 (work in progress), August		QUIC", draft-ietf-quic-http-15 (work in progress), October
	2018.		2018.
	[QUIC-TRANSPORT]		[QUIC-TRANSPORT]
	Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based		Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
	Multiplexed and Secure Transport", draft-ietf-quic-		Multiplexed and Secure Transport", draft-ietf-quic-
	transport-13 (work in progress), August 2018.		transport-14 (work in progress), October 2018.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119,		Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<https://www.rfc-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc2119>.
	[RFC7541] Peon, R. and H. Ruellan, "HPACK: Header Compression for		[RFC7541] Peon, R. and H. Ruellan, "HPACK: Header Compression for
	HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015,		HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015,
	<https://www.rfc-editor.org/info/rfc7541>.		<https://www.rfc-editor.org/info/rfc7541>.
	skipping to change at page 25, line 5 ¶		skipping to change at page 28, line 24 ¶
	<https://www.rfc-editor.org/info/rfc7540>.		<https://www.rfc-editor.org/info/rfc7540>.
	10.3. URIs		10.3. URIs
	[1] https://mailarchive.ietf.org/arch/search/?email_list=quic		[1] https://mailarchive.ietf.org/arch/search/?email_list=quic
	[2] https://github.com/quicwg		[2] https://github.com/quicwg
	[3] https://github.com/quicwg/base-drafts/labels/-qpack		[3] https://github.com/quicwg/base-drafts/labels/-qpack
	Appendix A. Change Log		Appendix A. Static Table
			+------+-----------------------------+------------------------------+
			| Inde | Name | Value |
			| x | | |
			+------+-----------------------------+------------------------------+
			| 0 | :authority | |
			| | | |
			| 1 | :path | / |
			| | | |
			| 2 | age | 0 |
			| | | |
			| 3 | content-disposition | |
			| | | |
			| 4 | content-length | 0 |
			| | | |
			| 5 | cookie | |
			| | | |
			| 6 | date | |
			| | | |
			| 7 | etag | |
			| | | |
			| 8 | if-modified-since | |
			| | | |
			| 9 | if-none-match | |
			| | | |
			| 10 | last-modified | |
			| | | |
			| 11 | link | |
			| | | |
			| 12 | location | |
			| | | |
			| 13 | referer | |
			| | | |
			| 14 | set-cookie | |
			| | | |
			| 15 | :method | CONNECT |
			| | | |
			| 16 | :method | DELETE |
			| | | |
			| 17 | :method | GET |
			| | | |
			| 18 | :method | HEAD |
			| | | |
			| 19 | :method | OPTIONS |
			| | | |
			| 20 | :method | POST |
			| | | |
			| 21 | :method | PUT |
			| | | |
			| 22 | :scheme | http |
			| | | |
			| 23 | :scheme | https |
			| | | |
			| 24 | :status | 103 |
			| | | |
			| 25 | :status | 200 |
			| | | |
			| 26 | :status | 304 |
			| | | |
			| 27 | :status | 404 |
			| | | |
			| 28 | :status | 503 |
			| | | |
			| 29 | accept | */* |
			| | | |
			| 30 | accept | application/dns-message |
			| | | |
			| 31 | accept-encoding | gzip, deflate, br |
			| | | |
			| 32 | accept-ranges | bytes |
			| | | |
			| 33 | access-control-allow- | cache-control |
			| | headers | |
			| | | |
			| 34 | access-control-allow- | content-type |
			| | headers | |
			| | | |
			| 35 | access-control-allow-origin | * |
			| | | |
			| 36 | cache-control | max-age=0 |
			| | | |
			| 37 | cache-control | max-age=2592000 |
			| | | |
			| 38 | cache-control | max-age=604800 |
			| | | |
			| 39 | cache-control | no-cache |
			| | | |
			| 40 | cache-control | no-store |
			| | | |
			| 41 | cache-control | public, max-age=31536000 |
			| | | |
			| 42 | content-encoding | br |
			| | | |
			| 43 | content-encoding | gzip |
			| | | |
			| 44 | content-type | application/dns-message |
			| | | |
			| 45 | content-type | application/javascript |
			| | | |
			| 46 | content-type | application/json |
			| | | |
			| 47 | content-type | application/x-www-form- |
			| | | urlencoded |
			| | | |
			| 48 | content-type | image/gif |
			| | | |
			| 49 | content-type | image/jpeg |
			| | | |
			| 50 | content-type | image/png |
			| | | |
			| 51 | content-type | text/css |
			| | | |
			| 52 | content-type | text/html; charset=utf-8 |
			| | | |
			| 53 | content-type | text/plain |
			| | | |
			| 54 | content-type | text/plain;charset=utf-8 |
			| | | |
			| 55 | range | bytes=0- |
			| | | |
			| 56 | strict-transport-security | max-age=31536000 |
			| | | |
			| 57 | strict-transport-security | max-age=31536000; |
			| | | includesubdomains |
			| | | |
			| 58 | strict-transport-security | max-age=31536000; |
			| | | includesubdomains; preload |
			| | | |
			| 59 | vary | accept-encoding |
			| | | |
			| 60 | vary | origin |
			| | | |
			| 61 | x-content-type-options | nosniff |
			| | | |
			| 62 | x-xss-protection | 1; mode=block |
			| | | |
			| 63 | :status | 100 |
			| | | |
			| 64 | :status | 204 |
			| | | |
			| 65 | :status | 206 |
			| | | |
			| 66 | :status | 302 |
			| | | |
			| 67 | :status | 400 |
			| | | |
			| 68 | :status | 403 |
			| | | |
			| 69 | :status | 421 |
			| | | |
			| 70 | :status | 425 |
			| | | |
			| 71 | :status | 500 |
			| | | |
			| 72 | accept-language | |
			| | | |
			| 73 | access-control-allow- | FALSE |
			| | credentials | |
			| | | |
			| 74 | access-control-allow- | TRUE |
			| | credentials | |
			| | | |
			| 75 | access-control-allow- | * |
			| | headers | |
			| | | |
			| 76 | access-control-allow- | get |
			| | methods | |
			| | | |
			| 77 | access-control-allow- | get, post, options |
			| | methods | |
			| | | |
			| 78 | access-control-allow- | options |
			| | methods | |
			| | | |
			| 79 | access-control-expose- | content-length |
			| | headers | |
			| | | |
			| 80 | access-control-request- | content-type |
			| | headers | |
			| | | |
			| 81 | access-control-request- | get |
			| | method | |
			| | | |
			| 82 | access-control-request- | post |
			| | method | |
			| | | |
			| 83 | alt-svc | clear |
			| | | |
			| 84 | authorization | |
			| | | |
			| 85 | content-security-policy | script-src 'none'; object- |
			| | | src 'none'; base-uri 'none' |
			| | | |
			| 86 | early-data | 1 |
			| | | |
			| 87 | expect-ct | |
			| | | |
			| 88 | forwarded | |
			| | | |
			| 89 | if-range | |
			| | | |
			| 90 | origin | |
			| | | |
			| 91 | purpose | prefetch |
			| | | |
			| 92 | server | |
			| | | |
			| 93 | timing-allow-origin | * |
			| | | |
			| 94 | upgrade-insecure-requests | 1 |
			| | | |
			| 95 | user-agent | |
			| | | |
			| 96 | x-forwarded-for | |
			| | | |
			| 97 | x-frame-options | deny |
			| | | |
			| 98 | x-frame-options | sameorigin |
			+------+-----------------------------+------------------------------+
			Appendix B. Change Log
	*RFC Editor's Note:* Please remove this section prior to		*RFC Editor's Note:* Please remove this section prior to
	publication of a final version of this document.		publication of a final version of this document.
	A.1. Since draft-ietf-quic-qpack-01		B.1. 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)
			B.2. Since draft-ietf-quic-qpack-01
	o Only header blocks that reference the dynamic table are		o Only header blocks that reference the dynamic table are
	acknowledged (#1603, #1605)		acknowledged (#1603, #1605)
	A.2. Since draft-ietf-quic-qpack-00		B.3. Since draft-ietf-quic-qpack-00
	o Renumbered instructions for consistency (#1471, #1472)		o Renumbered instructions for consistency (#1471, #1472)
	o Decoder is allowed to validate largest reference (#1404, #1469)		o Decoder is allowed to validate largest reference (#1404, #1469)
	o Header block acknowledgments also acknowledge the associated		o Header block acknowledgments also acknowledge the associated
	largest reference (#1370, #1400)		largest reference (#1370, #1400)
	o Added an acknowledgment for unread streams (#1371, #1400)		o Added an acknowledgment for unread streams (#1371, #1400)
	o Removed framing from encoder stream (#1361,#1467)		o Removed framing from encoder stream (#1361,#1467)
	o Control streams use typed unidirectional streams rather than fixed		o Control streams use typed unidirectional streams rather than fixed
	stream IDs (#910,#1359)		stream IDs (#910,#1359)
	A.3. Since draft-ietf-quic-qcram-00		B.4. Since draft-ietf-quic-qcram-00
	o Separate instruction sets for table updates and header blocks		o Separate instruction sets for table updates and header blocks
	(#1235, #1142, #1141)		(#1235, #1142, #1141)
	o Reworked indexing scheme (#1176, #1145, #1136, #1130, #1125,		o Reworked indexing scheme (#1176, #1145, #1136, #1130, #1125,
	#1314)		#1314)
	o Added mechanisms that support one-pass encoding (#1138, #1320)		o Added mechanisms that support one-pass encoding (#1138, #1320)
	o Added a setting to control the number of blocked decoders (#238,		o Added a setting to control the number of blocked decoders (#238,
End of changes. 56 change blocks.
	147 lines changed or deleted		527 lines changed or added
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