< draft-nerenberg-imap-binary-06.txt		draft-nerenberg-imap-binary-07.txt >
			A new Request for Comments is now available in online RFC libraries.
	Network Working Group L. Nerenberg		RFC 3516
	Internet Draft: IMAP4 Binary Content Extension ACI Worldwide
	Document: draft-nerenberg-imap-binary-06.txt January 2002
	IMAP4 Binary Content Extension
	Status of this memo
	This document is an Internet Draft and is in full conformance with
	all provisions of Section 10 of RFC 2026.
	Internet Drafts are working documents of the Internet Engineering
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	A revised version of this draft document will be submitted to the
	RFC editor as a Proposed Standard for the Internet Community.
	Discussion and suggestions for improvement are requested.
	Distribution of this draft is unlimited.
	1. Abstract
	This memo defines the BINARY extension to the Internet Message
	Access Protocol [IMAP4rev1]. It provides a mechanism for IMAP4
	clients and servers to exchange message body data without using a
	MIME content-transfer-encoding.
	2. Conventions Used in this Document
	The key words "MUST," "MUST NOT," "SHOULD," "SHOULD NOT," and "MAY"
	in this document are to be interpreted as described in [KEYWORD].
	The abbreviation "CTE" means content-transfer-encoding.
	3. Overview
	The MIME extensions to Internet messaging allow for the transmis-
	sion of non-textual (binary) message content [MIME-IMB]. Since the
	traditional transports for messaging are not always capable of
	passing binary data transparently, MIME provides encoding schemes
	that allow binary content to be transmitted over transports that
	are not otherwise able to do so.
	The overhead of MIME encoding this content can be considerable in
	some contexts (e.g. slow radio links, streaming multimedia). Reduc-
	ing the overhead associated with CTE schemes such as base64 can
	give a noticeable reduction in resource consumption. The BINARY
	extension lets the server perform CTE decoding prior to transmit-
	ting message data to the client.
	4. Content-Transfer-Encoding Considerations
	Every IMAP4 body section has a MIME content-transfer-encoding.
	(Those without an explicit Content-Transfer-Encoding header are
	implicitly labeled as "7bit" content.) In the terminology of [MIME-
	IMB], the CTE specifies both a decoding algorithm and the domain of
	the decoded data. In the context of this memo, "decoding" refers to
	the CTE decoding step described in [MIME-IMB].
	Certain CTEs use an identity encoding transformation. For these
	CTEs there is no decoding required, however the domain of the
	underlying data may not be expressable in the IMAP4 protocol (e.g.
	MIME "binary" content containing NUL octets). To accommodate these
	cases the BINARY extension introduces a new type of literal proto-
	col element that is fully 8bit transparent.
	Thus, server processing of the FETCH BINARY command involves two
	logical steps:
	1) perform any CTE-related decoding
	2) determine the domain of the decoded data
	Step 2 is necessary to determine which protocol element should be
	used to transmit the decoded data. (See FETCH Response Extensions
	for further details.)
	5. Framework for the IMAP4 Binary Extension
	This memo defines the following extensions to [IMAP4rev1].
	5.1. CAPABILITY Identification
	IMAP4 servers that support this extension MUST include "BINARY" in
	the response list to the CAPABILITY command.
	5.2. FETCH Command Extensions
	This extension defines three new FETCH command data items.
	BINARY[<section>]<<partial>>
	Requests that the specified section be transmitted after per-
	forming CTE-related decoding.
	When performing a partial FETCH, the offset argument refers to
	the offset into the DECODED section.
	BINARY.PEEK[<section>]<<partial>>
	An alternate form of BINARY[<section>] that does not implic-
	itly set the \Seen flag.
	BINARY.SIZE[<section>]
	Requests the decoded size of the section (i.e. the size to
	expect in response to the corresponding FETCH BINARY request).
	Note: client authors are cautioned that this may be an expen-
	sive operation for some server implementations. Needlessly
	issuing this request could result in degraded performance due
	to servers having to calculate the value every time the
	request is issued.
	5.3. FETCH Response Extensions
	This extension defines two new FETCH response data items.
	BINARY[<section>]<<origin_octet>>
	A <string> or <literal8> expressing the content of the speci-
	fied section after removing any CTE-related encoding.
	If the domain of the decoded data is "8bit" and the data does
	not contain the NUL character, the server SHOULD return the
	data in a <string> instead of a <literal8>; this allows the
	client to determine if the "8bit" data contains the NUL char-
	acter without having to explicitly scan the data stream for
	NULs.
	If the server does not know how to decode the section's CTE,
	it MUST fail the request and issue a "NO" response that con-
	tains the "UNKNOWN-CTE" extended response code.
	BINARY.SIZE[<section>]
	The size of the section after removing any CTE-related encod-
	ing. The value returned MUST match the <literal> or <lit-
	eral8> size that will be returned by the corresponding FETCH
	BINARY request.
	If the server does not know how to decode the section's CTE,
	it MUST fail the request and issue a "NO" response that con-
	tains the "UNKNOWN-CTE" extended response code.
	5.4. APPEND Command Extensions
	The APPEND command is extended to allow the client to append data
	containing NULs by using the <literal8> syntax. The server MAY mod-
	ify the CTE of the appended data, however any such transformation
	MUST NOT result in a loss of data.
	If the specified mailbox does not support the storage of binary
	content, the server MUST fail the request and issue a "NO" response
	that contains the "UNKNOWN-CTE" extended response code.
	6. MIME Encoded Headers
	[MIME-MHE] defines an encoding that allows for non-US-ASCII text in
	message headers. This encoding is not the same as the content-
	transfer-encoding applied to message bodies, and the decoding
	transformations described in this memo do not apply to [MIME-MHE]
	encoded header text. A server MUST NOT perform any conversion of
	[MIME-MHE] encoded header text in response to any binary FETCH or
	APPEND request.
	7. Implementation Considerations
	Messaging clients and servers have been notoriously lax in their
	adherence to the Internet CRLF convention for terminating lines of
	textual data in Internet protocols. When sending data using the
	BINARY extension, servers MUST ensure that textual line-oriented
	sections are always transmitted using the IMAP4 CRLF line termina-
	tion syntax, regardless of the underlying storage representation of
	the data on the server.
	A server may choose to store message body binary content in a non-
	encoded format. Regardless of the internal storage representation
	used, the server MUST issue BODYSTRUCTURE responses that describe
	the message as though the binary-encoded sections are encoded in a
	CTE acceptable to the IMAP4 base specification (see [IMAP4rev1]
	section 4.3.1). Furthermore, the results of a FETCH BODY MUST
	return the message body content in the format described by the cor-
	responding FETCH BODYSTRUCTURE response.
	While the server is allowed to modify the CTE of APPENDed <lit-
	eral8> data, this should only be done when it is absolutely neces-
	sary. Gratuitous encoding changes will render useless most crypto-
	graphic operations that have been performed on the message.
	This extension provides an optimization that is useful in certain
	specific situations. It does not absolve clients from providing
	basic functionality (content transfer decoding) that should be
	available in all messaging clients. Clients supporting this exten-
	sion SHOULD be prepared to perform their own CTE decoding opera-
	tions.
	8. Formal Protocol Syntax
	The following syntax specification uses the augmented Backus-Naur
	Form (ABNF) notation as used in [ABNF], and incorporates by refer-
	ence the Core Rules defined in that document.
	This syntax augments the grammar specified in [IMAP4rev1].
	append =/ "APPEND" SP mailbox [SP flag_list]
	[SP date_time] SP literal8
	fetch_att =/ "BINARY" [".PEEK"] section_number
	["<" number "." nz_number ">"] /
	"BINARY.SIZE" section_number
	literal8 = "~{" number "}" CRLF *OCTET
	; <number> represents the number of OCTETs
	; in the response string.
	msg_att = "(" 1#("ENVELOPE" SP envelope /
	"FLAGS" SP "(" #(flag / "\Recent") ")" /
	"INTERNALDATE" SP date_time /
	"RFC822" [".HEADER" / ".TEXT"] SP nstring /
	"RFC822.SIZE" SP number /
	"BODY" ["STRUCTURE"] SP body /
	"BODY" section ["<" number ">"] SP nstring /
	"UID" SP uniqueid /
	"BINARY" section_number ["<" number ">"] SP
	(nstring / literal8) /
	"BINARY.SIZE" section_number SP number) ")"
	;; Append BINARY and BINARY.SIZE to <msg_att>.
	;; This is not meant to be an absolute list;
	;; it was done this way due to ABNF syntax
	;; restrictions.
	resp_code_text =/ "UNKNOWN-CTE"
	section_number = (nz_number *["." nz_number])		Title: IMAP4 Binary Content Extension
			Author(s): L. Nerenberg
			Status: Standards Track
			Date: April 2003
			Mailbox: lyndon@orthanc.ab.ca
			Pages: 8
			Characters: 14598
			Updates/Obsoletes/SeeAlso: None
	9. References		I-D Tag: draft-nerenberg-imap-binary-07.txt
	[IMAP4rev1] Crispin, M., "Internet Message Access Protocol Version		URL: ftp://ftp.rfc-editor.org/in-notes/rfc3516.txt
	4rev1," Work in progress (son-of-RFC 2060)
	[KEYWORD] Bradner, S., "Key words for use in RFCs to Indicate		This memo defines the Binary extension to the Internet Message Access
	Requirement Levels," BCP 9, RFC2119, March 1997		Protocol (IMAP4). It provides a mechanism for IMAP4
			clients and servers to exchange message body data without using a MIME
			content-transfer-encoding.
	[MIME-IMB] Freed, N., N. Borenstein, "Multipurpose Internet Mail		This is now a Proposed Standard Protocol.
	Extensions (MIME) Part One: Format of Internet Message Bodies,"
	RFC2045, November 1996.
	[MIME-MHE] Moore, K., "MIME (Multipurpose Internet Mail Extensions)		This document specifies an Internet standards track protocol for
	Part Three: Message Header Extensions for Non-ASCII Text," RFC2047,		the Internet community, and requests discussion and suggestions
	November 1996.		for improvements. Please refer to the current edition of the
			"Internet Official Protocol Standards" (STD 1) for the
			standardization state and status of this protocol. Distribution
			of this memo is unlimited.
	10. Security Considerations		This announcement is sent to the IETF list and the RFC-DIST list.
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	There are no known security issues with this extension.		Details on obtaining RFCs via FTP or EMAIL may be obtained by sending
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	11. Authors' Address		To: rfc-info@RFC-EDITOR.ORG
			Subject: getting rfcs
	Lyndon Nerenberg		help: ways_to_get_rfcs
	ACI Worldwide
	Suite 900
	10117 - Jasper Avenue
	Edmonton, Alberta
	Canada T5J 1W8
	Email: lyndon@atg.aciworldwide.com		Requests for special distribution should be addressed to either the
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