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Network Working Group J. Myers Request for Comments: 2088 Carnegie Mellon Cateogry: Standards Track January 1997

                  IMAP4 non-synchronizing literals

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions 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.

1. Abstract

 The Internet Message Access Protocol [IMAP4] contains the "literal"
 syntactic construct for communicating strings.  When sending a
 literal from client to server, IMAP4 requires the client to wait for
 the server to send a command continuation request between sending the
 octet count and the string data.  This document specifies an
 alternate form of literal which does not require this network round
 trip.

2. Conventions Used in this Document

 In examples, "C:" and "S:" indicate lines sent by the client and
 server respectively.

3. Specification

 The non-synchronizing literal is added an alternate form of literal,
 and may appear in communication from client to server instead of the
 IMAP4 form of literal.  The IMAP4 form of literal, used in
 communication from client to server, is referred to as a
 synchronizing literal.

 Non-synchronizing literals may be used with any IMAP4 server
 implementation which returns "LITERAL+" as one of the supported
 capabilities to the CAPABILITY command.  If the server does not
 advertise the LITERAL+ capability, the client must use synchronizing
 literals instead.

 The non-synchronizing literal is distinguished from the original
 synchronizing literal by having a plus ('+') between the octet count
 and the closing brace ('}').  The server does not generate a command
 continuation request in response to a non-synchronizing literal, and

Myers Standards Track [Page 1]  RFC 2088 LITERAL January 1997

 clients are not required to wait before sending the octets of a non-
 synchronizing literal.

 The protocol receiver of an IMAP4 server must check the end of every
 received line for an open brace ('{') followed by an octet count, a
 plus ('+'), and a close brace ('}') immediately preceeding the CRLF.
 If it finds this sequence, it is the octet count of a non-
 synchronizing literal and the server MUST treat the specified number
 of following octets and the following line as part of the same
 command.  A server MAY still process commands and reject errors on a
 line-by-line basis, as long as it checks for non-synchronizing
 literals at the end of each line.

 Example:    C: A001 LOGIN {11+}
             C: FRED FOOBAR {7+}
             C: fat man
             S: A001 OK LOGIN completed

4. Formal Syntax

 The following syntax specification uses the augmented Backus-Naur
 Form (BNF) notation as specified in [RFC-822] as modified by [IMAP4].
 Non-terminals referenced but not defined below are as defined by
 [IMAP4].

 literal         ::= "{" number ["+"] "}" CRLF *CHAR8
                     ;; Number represents the number of CHAR8 octets

6. References

 [IMAP4] Crispin, M., "Internet Message Access Protocol - Version 4",
 draft-crispin-imap-base-XX.txt, University of Washington, April 1996.

 [RFC-822] Crocker, D., "Standard for the Format of ARPA Internet Text
 Messages", STD 11, RFC 822.

7. Security Considerations

 There are no known security issues with this extension.

8. Author's Address

 John G. Myers
 Carnegie-Mellon University
 5000 Forbes Ave.
 Pittsburgh PA, 15213-3890

 Email: jgm+@cmu.edu

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