Network Working Group L. Nerenberg
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.
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1. Abstract libraries.
RFC 3516
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
I-D Tag: draft-nerenberg-imap-binary-07.txt
URL: ftp://ftp.rfc-editor.org/in-notes/rfc3516.txt
This memo defines the BINARY Binary extension to the Internet Message Access
Protocol [IMAP4rev1]. (IMAP4). 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
This is now a Proposed Standard Protocol.
This document are to be interpreted as described in [KEYWORD].
The abbreviation "CTE" means content-transfer-encoding.
3. Overview
The MIME extensions to specifies an Internet messaging allow standards track protocol for
the transmis-
sion of non-textual (binary) message content [MIME-IMB]. Since the
traditional transports Internet community, and requests discussion and suggestions
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 improvements. Please refer 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 current edition of [MIME-
IMB], the CTE specifies both a decoding algorithm and
"Internet Official Protocol Standards" (STD 1) for the domain
standardization state and status of
the decoded data. In the context this protocol. Distribution
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 memo 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 unlimited.
This announcement is fully 8bit transparent.
Thus, server processing of the FETCH BINARY command involves two
logical steps:
1) perform any CTE-related decoding
2) determine sent to the domain of IETF list and the decoded data
Step 2 is necessary RFC-DIST list.
Requests to determine which protocol element should be
used added 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 or deleted from the response IETF distribution 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
should be transmitted after per-
forming CTE-related decoding.
When performing a partial FETCH, the offset argument refers sent 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>] IETF-REQUEST@IETF.ORG. 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
added 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 deleted from the server does not know how RFC-DIST distribution list should
be sent 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> RFC-DIST-REQUEST@RFC-EDITOR.ORG.
Details on obtaining RFCs via FTP or <lit-
eral8> size that will EMAIL may be returned obtained 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 sending
an encoding that allows for non-US-ASCII text in EMAIL 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 rfc-info@RFC-EDITOR.ORG with 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
help: ways_to_get_rfcs. For example:
To: rfc-info@RFC-EDITOR.ORG
Subject: getting rfcs
help: ways_to_get_rfcs
Requests for special distribution should be addressed to either the IMAP4 base specification (see [IMAP4rev1]
section 4.3.1). Furthermore, the results
author of a FETCH BODY MUST
return the message body content RFC in the format described by the cor-
responding FETCH BODYSTRUCTURE response.
While the server is allowed question, or 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 RFC-Manager@RFC-EDITOR.ORG. Unless
specifically noted otherwise 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 RFC itself, 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 RFCs are for
unlimited distribution.echo
Submissions for Requests for Comments should be an absolute list;
;; it was done this way due sent to ABNF syntax
;; restrictions.
resp_code_text =/ "UNKNOWN-CTE"
section_number = (nz_number *["." nz_number])
9. References
[IMAP4rev1] Crispin, M., "Internet Message Access Protocol Version
4rev1," Work in progress (son-of-RFC 2060)
[KEYWORD] Bradner, S., "Key words for use in RFCs
RFC-EDITOR@RFC-EDITOR.ORG. Please consult RFC 2223, Instructions to Indicate
Requirement Levels," BCP 9, RFC2119, March 1997
[MIME-IMB] Freed, N., N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies,"
RFC2045, November 1996.
[MIME-MHE] Moore, K., "MIME (Multipurpose Internet Mail Extensions)
Part Three: Message Header Extensions RFC
Authors, for Non-ASCII Text," RFC2047,
November 1996.
10. Security Considerations
There are no known security issues with this extension.
11. Authors' Address
Lyndon Nerenberg
ACI Worldwide
Suite 900
10117 - Jasper Avenue
Edmonton, Alberta
Canada T5J 1W8
Email: lyndon@atg.aciworldwide.com further information.