< draft-ietf-lemonade-compress-02.txt		draft-ietf-lemonade-compress-03.txt >
	Network Working Group Arnt Gulbrandsen		Network Working Group Arnt Gulbrandsen
	Request for Comments: DRAFT Oryx Mail Systems GmbH		Request for Comments: DRAFT Oryx Mail Systems GmbH
	July 2006		July 2006
	The IMAP COMPRESS=DEFLATE Extension		The IMAP COMPRESS Extension
	draft-ietf-lemonade-compress-02.txt		draft-ietf-lemonade-compress-03.txt
	Status of this Memo		Status of this Memo
	By submitting this Internet-Draft, each author represents that any		By submitting this Internet-Draft, each author represents that any
	applicable patent or other IPR claims of which he or she is aware		applicable patent or other IPR claims of which he or she is aware
	have been or will be disclosed, and any of which he or she becomes		have been or will be disclosed, and any of which he or she becomes
	aware will be disclosed, in accordance with Section 6 of BCP 79.		aware will be disclosed, in accordance with Section 6 of BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF), its areas, and its working groups. Note that		Task Force (IETF), its areas, and its working groups. Note that
	skipping to change at page 1, line 37 ¶		skipping to change at page 1, line 37 ¶
	http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-		http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-
	Draft Shadow Directories can be accessed at		Draft Shadow Directories can be accessed at
	http://www.ietf.org/shadow.html.		http://www.ietf.org/shadow.html.
	Copyright Notice		Copyright Notice
	Copyright (C) The Internet Society 2006.		Copyright (C) The Internet Society 2006.
	Abstract		Abstract
	The COMPRESS=DEFLATE extension allows an IMAP connection to be		The COMPRESS extension allows an IMAP connection to be effectively
	compressed using the DEFLATE algorithm, such that effective		and efficiently compressed.
	compression is available even when TLS is used.
	Table of Contents		Table of Contents
	1. Conventions Used in This Document . . . . . . . . . . . . . . 2		1. Conventions Used in This Document . . . . . . . . . . . . . . 2
	2. Introduction and Overview . . . . . . . . . . . . . . . . . . 2		2. Introduction and Overview . . . . . . . . . . . . . . . . . . 2
	3. The COMPRESS Command . . . . . . . . . . . . . . . . . . . . . 3		3. The COMPRESS Command . . . . . . . . . . . . . . . . . . . . . 3
			Internet-draft August 2006
	4. Compression Efficiency . . . . . . . . . . . . . . . . . . . . 4		4. Compression Efficiency . . . . . . . . . . . . . . . . . . . . 4
	5. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 5		5. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 5
	6. Security Considerations . . . . . . . . . . . . . . . . . . . 6		6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
	8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6		8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
	9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6		9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
	9.1. Normative References . . . . . . . . . . . . . . . . . . . 6		9.1. Normative References . . . . . . . . . . . . . . . . . . . 7
	9.2. Informative References . . . . . . . . . . . . . . . . . . 6		9.2. Informative References . . . . . . . . . . . . . . . . . . 7
	10. Author's Address . . . . . . . . . . . . . . . . . . . . . . 7		10. Author's Address . . . . . . . . . . . . . . . . . . . . . . 8
	11. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 7		11. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 8
	1. Conventions Used in This Document		1. Conventions Used in This Document
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in RFC 2119 [KEYWORDS].		document are to be interpreted as described in RFC 2119 [KEYWORDS].
	Formal syntax is defined by [ABNF] as modified by [IMAP].		Formal syntax is defined by [ABNF] as modified by [IMAP].
	In the example, "C:" and "S:" indicate lines sent by the client and		In the example, "C:" and "S:" indicate lines sent by the client and
	server respectively.		server respectively.
	2. Introduction and Overview		2. Introduction and Overview
	An IMAP server that supports this extension announces		A server which supports the COMPRESS extension indicates this with
	"COMPRESS=DEFLATE" as one of its capabilities.		one or more capability names consisting of "COMPRESS=" followed by a
			supported compression algorithm name as described in this document.
	The goal of COMPRESS=DEFLATE is to reduce the bandwidth usage of		The goal of COMPRESS is to reduce the bandwidth usage of IMAP.
	IMAP. On regular IMAP connections, the PPP or MNP compression used
	with many low-bandwidth links compresses IMAP well. However, when		Compared to PPP/MNP compression, COMPRESS offers much better
	TLS is used, PPP/MNP compression is ineffective. TLS too may provide		compression efficiency, and can be used together with TLS, SASL
	compression, but a careful IMAP implementation can do much better.		encryption, VPNs etc. Compared to TLS compression [TLSCOMP],
			COMPRESS has the following (dis)advantages:
			- COMPRESS can be implemented easily by IMAP servers and clients.
			At present, TLS compression is not widely implemented. In the
			LEMONADE WG, the general consent is that libraries implementing
			TLS compression will not be available soon enough for LEMONADE.
			- IMAP compression efficiency benefits from an API that permits
			flushing the compressor's dictionary at the right point. This is
			practical for COMPRESS, whereas typical TLS libraries don't
			currently allow that.
			Internet-draft August 2006
			- When a TLS librarly implements compression, all protocols that use
			TLS automatically are compressed (in LEMONADE's case, SMTP, IMAP,
			and some notification protocol), whereas COMPRESS is specific to
			IMAP.
	In order to increase interoperation, it is desirable to have as few		In order to increase interoperation, it is desirable to have as few
	different compression algorithms as possible, so this document		different compression algorithms as possible, so this document
	specifies only one. The DEFLATE algorithm is standard, widely		specifies only one. The [DEFLATE] algorithm is standard, widely
	available, unencumbered by patents and fairly efficient. Hopefully		available, unencumbered by patents and fairly efficient.
	it will not be necessary to define additional algorithms.
	The extension adds one new command (COMPRESS) and no new responses.		The extension adds one new command (COMPRESS) and no new responses.
	3. The COMPRESS Command		3. The COMPRESS Command
	Arguments: Name of compression mechanism: "DEFLATE".		Arguments: Name of compression mechanism: "DEFLATE".
	Responses: None		Responses: None
	Result: OK The server will compress its responses and expects the		Result: OK The server will compress its responses and expects the
	client to compress its commands.		client to compress its commands.
	NO The server doesn't support the requested mechanism.		NO The server doesn't support the requested mechanism.
	BAD Command unknown, invalid argument, or COMPRESS already		BAD Command unknown, invalid argument, or COMPRESS already
	active.		active.
	The COMPRESS command instructs the server to use the named		The COMPRESS command instructs the server to use the named
	compression mechanism ("DEFLATE" is the only one defined) for all		compression mechanism ("DEFLATE" is the only one defined) for all
	commands and/or responses after COMPRESS.		commands and/or responses after COMPRESS.
	The client MUST NOT send any commands until it has seen the result		The client MUST NOT send any commands until it has seen the result
	of COMPRESS.		of COMPRESS. If the response was OK, the client MUST compress
			starting with the first command after COMPRESS, and the server MUST
			compress starting with the first response after the OK.
	For DEFLATE (as for many other compression mechanisms), the		For DEFLATE (as for many other compression mechanisms), the
	compressor can trade speed against quality. When decompressing		compressor can trade speed against quality. When decompressing
	there isn't much of a tradeoff. Consequently, the client and server		there isn't much of a tradeoff. Consequently, the client and server
	are both free to pick the best reasonable rate of compression for		are both free to pick the best reasonable rate of compression for
	the data they send.		the data they send.
	If both [STARTTLS] and COMPRESS are in use, the data should be		If both COMPRESS and STARTTLS and/or a [SASL] security layer are in
	compressed before it is encrypted (and decrypted before it is		use, the data should be compressed before it is encrypted (and
	decompressed), independent of the order in which the client issues		decrypted before it is decompressed), independent of the order in
	COMPRESS, AUTHENTICATE and STARTTLS.		which the client issues COMPRESS, AUTHENTICATE and STARTTLS.
	The following example illustrates how commands and responses are		The following example illustrates how commands and responses are
	compressed during a simple login sequence:		compressed during a simple login sequence:
			Internet-draft August 2006
	S: * OK [CAPABILITY IMAP4REV1 STARTTLS COMPRESS=DEFLATE]		S: * OK [CAPABILITY IMAP4REV1 STARTTLS COMPRESS=DEFLATE]
	C: a starttls		C: a starttls
	S: a OK TLS active		S: a OK TLS active
	From this point on, everything is encrypted.		From this point on, everything is encrypted.
	C: b compress deflate		C: b compress deflate
	S: b OK DEFLATE active		S: b OK DEFLATE active
	From this point on, everything is compressed before being		From this point on, everything is compressed before being
	encrypted.		encrypted.
	C: c login arnt tnra		C: c login arnt tnra
	S: c OK Logged in as arnt		S: c OK Logged in as arnt
	4. Compression Efficiency		4. Compression Efficiency
			This section is informative, not normative.
	IMAP poses some unusual problems for a compression layer.		IMAP poses some unusual problems for a compression layer.
	Upstream is fairly simple. Most IMAP clients send the same few		Upstream is fairly simple. Most IMAP clients send the same few
	commands again and again, so any compression algorith which can		commands again and again, so any compression algorith which can
	exploit repetition works efficiently. The APPEND command is an		exploit repetition works efficiently. The APPEND command is an
	exception; clients which send many APPEND commands may want to take		exception; clients which send many APPEND commands may want to send
	special care of literals, in the same way that servers do.		flushes in the same way that servers do.
	Downstream has the unusual property that several kinds of data are		Downstream has the unusual property that several kinds of data are
	sent, confusing all dictionary-based compression algorithms.		sent, confusing all dictionary-based compression algorithms.
	One type is IMAP responses. These are highly compressible; zlib		One type is IMAP responses. These are highly compressible; zlib
	using its least CPU-intensive setting compresses typical responses		using its least CPU-intensive setting compresses typical responses
	to 25-40% of their original size.		to 25-40% of their original size.
	Another is email headers. These are equally compressible, and		Another is email headers. These are equally compressible, and
	benefit from using the same dictionary as the IMAP responses.		benefit from using the same dictionary as the IMAP responses.
	A third is email body text. Text is usually fairly short and		A third is email body text. Text is usually fairly short and
	includes much ASCII, so the same compression dictionary will do a		includes much ASCII, so the same compression dictionary will do a
	good job here, too. When multiple messages in the same thread are		good job here, too. When multiple messages in the same thread are
	read at the same time, quoted lines etc. can often be compressed		read at the same time, quoted lines etc. can often be compressed
	almost to zero.		almost to zero.
	Finally, attachments (non-text email bodies) are transmitted, either		Finally, attachments (non-text email bodies) are transmitted, either
	in [BINARY] form or encoded with base-64.		in [BINARY] form or encoded with base-64.
			Internet-draft August 2006
	When attachments are retrieved in [BINARY] form, DEFLATE may be able		When attachments are retrieved in [BINARY] form, DEFLATE may be able
	to compress them, but the format of the attachment is usually not		to compress them, but the format of the attachment is usually not
	IMAP-like, so the dictionary built while compressing IMAP does not		IMAP-like, so the dictionary built while compressing IMAP does not
	help. The compressor has to adapt its dictionary from IMAP to the		help. The compressor has to adapt its dictionary from IMAP to the
	attachment's format, and then back. A few file formats aren't		attachment's format, and then back. A few file formats aren't
	compressible at all using deflate, e.g. .gz, .zip and .jpg files.		compressible at all using deflate, e.g. .gz, .zip and .jpg files.
	When attachments are retrieved in base-64 form, the same problems		When attachments are retrieved in base-64 form, the same problems
	apply, but the base-64 encoding adds another problem. 8-bit		apply, but the base-64 encoding adds another problem. 8-bit
	compression algorithms such as deflate work well on 8-bit file		compression algorithms such as deflate work well on 8-bit file
	formats, however base-64 turns a file into something resembling		formats, however base-64 turns a file into something resembling
	6-bit bytes, hiding most of the 8-bit file format from the		6-bit bytes, hiding most of the 8-bit file format from the
	compressor.		compressor.
	When using the zlib library (see [DEFLATE]), the functions		When using the zlib library (see [DEFLATE]), the functions
	deflateInit(), deflate(), inflateInit() and inflate() suffice to		deflateInit2(), deflate(), inflateInit2() and inflate() suffice to
	implement this extension. deflateParams() can be used to improve		implement this extension. deflateParams() can be used to improve
	compression rate and resource use.		compression rate and resource use.
	A client can improve downstream compression by implementing [BINARY]		A client can improve downstream compression by implementing [BINARY]
	and using FETCH BINARY instead of FETCH BODY. In the author's		and using FETCH BINARY instead of FETCH BODY. In the author's
	experience, the improvement ranges from 5% to 40% depending on the		experience, the improvement ranges from 5% to 40% depending on the
	attachment being downloaded.		attachment being downloaded.
	A server can improve downstream compression if it hints to the		A server can improve downstream compression if it hints to the
	compressor that the data type is about to change strongly, e.g. by		compressor that the data type is about to change strongly, e.g. by
	sending a Z_FULL_FLUSH at the start and end of large non-text		sending a Z_FULL_FLUSH at the start and end of large non-text
	literals (before and after '*CHAR8' in the definition of literal in		literals (before and after '*CHAR8' in the definition of literal in
	RFC 3501, page 86). Small literals are best left alone.		RFC 3501, page 86). Small literals are best left alone.
	A server can improve the CPU efficiency both of the server and the		A server can improve the CPU efficiency both of the server and the
	client if it adjusts the compression level (e.g. using the		client if it adjusts the compression level (e.g. using the
	deflateParams() function in zlib) at these points. A very simple		deflateParams() function in zlib) at these points. A very simple
	strategy is to change the level 0 to at the start of a literal		strategy is to change the level to 0 to at the start of a literal
	provided the first two bytes are either 0x1F 0x8B (as in deflate-		provided the first two bytes are either 0x1F 0x8B (as in deflate-
	compressed files) or 0xFF 0xD8 (JPEG), and to keep it at 1-5 the		compressed files) or 0xFF 0xD8 (JPEG), and to keep it at 1-5 the
	rest of the time.		rest of the time.
	Note that when using TLS, compression may actually decrease the CPU		Note that when using TLS, compression may actually decrease the CPU
	usage, depending on which algorithms are used in TLS. This is		usage, depending on which algorithms are used in TLS. This is
	because fewer bytes need to be encrypted, and encryption is		because fewer bytes need to be encrypted, and encryption is
	generally more expensive than compression.		generally more expensive than compression.
	5. Formal Syntax		5. Formal Syntax
	The following syntax specification uses the Augmented Backus-Naur		The following syntax specification uses the Augmented Backus-Naur
	Form (ABNF) notation as specified in [ABNF]. Non-terminals		Form (ABNF) notation as specified in [ABNF]. Non-terminals
			Internet-draft August 2006
	referenced but not defined below are as defined by [ABNF] (SP, CRLF)		referenced but not defined below are as defined by [ABNF] (SP, CRLF)
	or [IMAP] (all others).		or [IMAP] (all others).
	Except as noted otherwise, all alphabetic characters are case-		Except as noted otherwise, all alphabetic characters are case-
	insensitive. The use of upper or lower case characters to define		insensitive. The use of upper or lower case characters to define
	token strings is for editorial clarity only. Implementations MUST		token strings is for editorial clarity only. Implementations MUST
	accept these strings in a case-insensitive fashion.		accept these strings in a case-insensitive fashion.
	command-any =/ compress		command-any =/ compress
	compress = "COMPRESS" SP algorithm		compress = "COMPRESS" SP algorithm
			capability =/ "COMPRESS=" algorithm
			;; multiple COMPRESS capabilities allowed
	algorithm = "DEFLATE"		algorithm = "DEFLATE"
			Note that due the syntax of capability means, future algorithm names
			must be atoms.
	6. Security Considerations		6. Security Considerations
	As for [TLSCOMP] RFC 3749.		As for [TLSCOMP] RFC 3749.
	7. IANA Considerations		7. IANA Considerations
	The IANA is requested to add COMPRESS=DEFLATE to the list of IMAP		The IANA is requested to add COMPRESS=... to the list of IMAP
	extensions.		extensions.
			The IANA is requested to maintain one new registry: IMAP Compression
			Algorithms. The registry's purpose is to register compression
			algorithms that may be used with this extension. New IMAP
			algorithms MUST be defined in a standards track or IESG approved
			experimental RFC. New IMAP compression algorithms MUST include the
			following information as part of their definition:
			algorithm identifier
			standard commands affected
			specification reference
			discussion
			This registry is available at URL [RFC-EDITOR NOTE: please insert
			URL of registry]
			One IMAP compression algorithm is defined in this document, with the
			following registration definition:
			Internet-draft August 2006
			algorithm identifier: DEFLATE
			standard commands affected: none
			specification reference: RFC 1951 and XXXX
			discussion: see RFC XXXX
			[RFC-EDITOR NOTE: change XXXX to this RFC number]
	8. Acknowledgements		8. Acknowledgements
	Eric Burger, Dave Cridland, Tony Finch, Ned Freed, Philip Guenther,		Eric Burger, Dave Cridland, Tony Finch, Ned Freed, Philip Guenther,
	Randall Gellens, Tony Hansen, Alexey Melnikov, Lyndon Nerenberg and		Randall Gellens, Tony Hansen, Alexey Melnikov, Lyndon Nerenberg and
	Zoltan Ordogh have all helped with this document.		Zoltan Ordogh have all helped with this document.
	The author would also like to thank various people in the rooms at		The author would also like to thank various people in the rooms at
	meetings, whose help is real, but not reflected in the author's		meetings, whose help is real, but not reflected in the author's
	mailbox.		mailbox.
	skipping to change at page 6, line 38 ¶		skipping to change at page 7, line 42 ¶
	[IMAP] Crispin, "Internet Message Access Protocol - Version		[IMAP] Crispin, "Internet Message Access Protocol - Version
	4rev1", RFC 3501, University of Washington, June 2003.		4rev1", RFC 3501, University of Washington, June 2003.
	[KEYWORDS] Bradner, "Key words for use in RFCs to Indicate		[KEYWORDS] Bradner, "Key words for use in RFCs to Indicate
	Requirement Levels", RFC 2119, Harvard University, March		Requirement Levels", RFC 2119, Harvard University, March
	1997.		1997.
	[DEFLATE] Deutsch, "DEFLATE Compressed Data Format Specification		[DEFLATE] Deutsch, "DEFLATE Compressed Data Format Specification
	version 1.3", RFC 1951, Aladdin Enterprises, May 1996.		version 1.3", RFC 1951, Aladdin Enterprises, May 1996.
	[STARTTLS] Newman, C. "Using TLS with IMAP, POP3 and ACAP", RFC
	2595, June 1999.
	9.2. Informative References		9.2. Informative References
	[TLSCOMP] Hollenbeck, "Transport Layer Security Protocol		[TLSCOMP] Hollenbeck, "Transport Layer Security Protocol
	Compression Methods", RFC 3749, VeriSign, May 2004.		Compression Methods", RFC 3749, VeriSign, May 2004.
			[SASL] A. Melnikov, K. Zeilenga, "Simple Authentication and
			Security Layer (SASL)", RFC 4422, Isode Limited, June
			2006
			Internet-draft August 2006
	[BINARY] Nerenberg, "IMAP4 Binary Content Extension", Orthanc		[BINARY] Nerenberg, "IMAP4 Binary Content Extension", Orthanc
	Systems, April 2003.		Systems, April 2003.
	10. Author's Address		10. Author's Address
	Arnt Gulbrandsen		Arnt Gulbrandsen
	Oryx Mail Systems GmbH		Oryx Mail Systems GmbH
	Schweppermannstr. 8		Schweppermannstr. 8
	D-81671 Muenchen		D-81671 Muenchen
	Germany		Germany
	skipping to change at page 7, line 46 ¶		skipping to change at page 9, line 5 ¶
	of such proprietary rights by implementers or users of this		of such proprietary rights by implementers or users of this
	specification can be obtained from the IETF on-line IPR repository		specification can be obtained from the IETF on-line IPR repository
	at http://www.ietf.org/ipr.		at http://www.ietf.org/ipr.
	The IETF invites any interested party to bring to its attention any		The IETF invites any interested party to bring to its attention any
	copyrights, patents or patent applications, or other proprietary		copyrights, patents or patent applications, or other proprietary
	rights that may cover technology that may be required to implement		rights that may cover technology that may be required to implement
	this standard. Please address the information to the IETF at ietf-		this standard. Please address the information to the IETF at ietf-
	ipr@ietf.org.		ipr@ietf.org.
			Internet-draft August 2006
	Copyright Statement		Copyright Statement
	Copyright (C) The Internet Society (2006).		Copyright (C) The Internet Society (2006).
	This document is subject to the rights, licenses and restrictions		This document is subject to the rights, licenses and restrictions
	contained in BCP 78, and except as set forth therein, the authors		contained in BCP 78, and except as set forth therein, the authors
	retain all their rights.		retain all their rights.
	Disclaimer of Validity		Disclaimer of Validity
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