Lemonade Working Group L. Nerenberg Internet-Draft Orthanc Systems Expires: January 16, 2005 S. Hole ACI Worldwide B. Leiba IBM T.J. Watson Research Center July 18, 2004 IMAP4 Channel Transport Mechanism draft-ietf-lemonade-imap-channel-02 Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 16, 2005. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract Nerenberg, et al. Expires January 16, 2005 [Page 1] Internet-Draft IMAP4 Channel Transport Mechanism July 2004 Table of Contents 1. Conventions Used in this Document . . . . . . . . . . . . . . 3 2. Protocol Framework . . . . . . . . . . . . . . . . . . . . . . 3 2.1 CAPABILITY Identification . . . . . . . . . . . . . . . . 3 2.2 CHANNEL Command . . . . . . . . . . . . . . . . . . . . . 3 2.3 UID CHANNEL Command . . . . . . . . . . . . . . . . . . . 4 2.4 CHANNEL Response . . . . . . . . . . . . . . . . . . . . . 4 2.5 CHANNELSCHEMES Command . . . . . . . . . . . . . . . . . . 4 2.6 CHANNELSCHEMES Response . . . . . . . . . . . . . . . . . 5 3. Command Sequencing . . . . . . . . . . . . . . . . . . . . . . 5 4. Formal Protocol Syntax . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. Normative References . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 7 A. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 B. Administrivia . . . . . . . . . . . . . . . . . . . . . . . . 7 C. Document Revision History . . . . . . . . . . . . . . . . . . 8 C.1 Changes in draft -02 . . . . . . . . . . . . . . . . . . . 8 D. Outstanding Issues . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . 9 Nerenberg, et al. Expires January 16, 2005 [Page 2] Internet-Draft IMAP4 Channel Transport Mechanism July 2004 1. 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]. In examples, "C:" and "S:" preface lines sent by the client and the server respectively. 2. Protocol Framework This memo defines the following extensions to [IMAP4]. 2.1 CAPABILITY Identification IMAP4 servers that support this extension MUST advertise the "CHANNEL" capability. 2.2 CHANNEL Command The CHANNEL command requests that message data be retrieved through an external scheme. Clients may issue a request specifying a partially-qualified URI, in which case the server will determine the final connection end\-point. What constitutes a partially-qualified URI is implementation defined. The syntax of the CHANNEL command is: tag CHANNEL channel-uri-list channel-set is a list of URIs and schemes specifying how the client desires to retrieve the message data. If contains more than one element the server SHOULD return the message data using the first element in the list it is capable of using. is a list of message-number/body-section pairs describing the content to be retrieved. The message number specifies the sequence number of the message to act on. The CHANNEL command is only valid in the selected state. Example: C: 0 CHANNEL (rtsp ftp://marvin@example.net/incoming/) (1 2)(3 1)(3 9.1) asks for section 2 of message 1 and sections 1 and 9.1 of message 3. The preferred retrieval scheme is RTSP. If RTSP isn't available the IMAP server should attempt to transfer the requested data to the FTP Nerenberg, et al. Expires January 16, 2005 [Page 3] Internet-Draft IMAP4 Channel Transport Mechanism July 2004 server at example.com. In either case the server will fill in the connection end-point information. 2.3 UID CHANNEL Command The UID CHANNEL command is identical to the CHANNEL command with the exception that the message numbers in the sequence sets refer to unique identifiers instead of message sequence numbers. 2.4 CHANNEL Response An untagged CHANNEL response is returned for each message-number/ body-section pair specified by the corresponding CHANNEL command: * message-number CHANNEL section-spec URI The ordering of these responses is arbitrary. The message number and in the response mirror those in the corresponding request, therefore responses to UID CHANNEL commands report the message UID rather than the message sequence number. The server MUST NOT issue an untagged CHANNEL response containing a URI until such time as that URI is avaliable for the client to dereference. The lifetime of the URI is implementation defined. For example, the responses to the example command in the previous section might look like: S: * 1 CHANNEL 2 rtsp://frobozz.example.com/144124 S: * 3 CHANNEL 1 ftp://marvin@example.com/incoming/abzzqfw11423 S: * 3 CHANNEL 9.1 NIL S: 0 OK done The NIL response to the section 9.1 request indicates that the part could not be retrieved via any of the requested schemes. For example, this could be caused by the inability to convert or represent the content via the requested schemes, or because a resource was unavailable. 2.5 CHANNELSCHEMES Command The CHANNELSCHEMES command queries the server for the list of schemes it supports. Nerenberg, et al. Expires January 16, 2005 [Page 4] Internet-Draft IMAP4 Channel Transport Mechanism July 2004 The syntax of the CHANNELSCHEMES command is: tag CHANNELSCHEMES 2.6 CHANNELSCHEMES Response A tagged CHANNELSCHEMES response is returned in response to a CHANNELSCHEMES command. The syntax of the CHANNELSCHEMES response is: tag CHANNELSCHEMES channelschemes-data 3. Command Sequencing There is no way to distinguish between a response to a CHANNEL command and a UID CHANNEL command, therefore clients MUST NOT issue a UID CHANNEL command while a CHANNEL command is in progress. Conversely, clients MUST NOT issue a CHANNEL command while a UID CHANNEL command is in progress. These restrictions are in addition to the normal sequencing rules that apply to UID-style commands. Servers MUST NOT send an EXPUNGE response while responding to a CHANNEL command, however a server MAY send an EXPUNGE response during a UID CHANNEL command. 4. Formal Protocol Syntax The following syntax specification uses the augmented Backus-Naur Form (ABNF) notation as defined in [ABNF], and incorporates by reference the Core Rules from that document. This syntax extends the grammar specified in [IMAP4]. The following tokens are incorporated from [URI]: absoluteURI, scheme. Nerenberg, et al. Expires January 16, 2005 [Page 5] Internet-Draft IMAP4 Channel Transport Mechanism July 2004 channel = "CHANNEL" SP channel-uri-list SP channel-set channelschemes = "CHANNELSCHEMES" channelschemes-data = astring / "(" astring 1*(SP astring) ")" ; encodes a channel-data = nz-number SP "CHANNEL" SP section-spec SP astring ; encodes an channel-set = 1*("(" nz-number SP section-spec ")") ; refers to the message sequence ; number or unique identifier. channel-uri-list = "(" channel-uri *(SP channel-uri) ")" channel-uri = astring ; / ; represented as an IMAP command-auth =/ channelschemes command-select =/ channel response-data = "*" SP (resp-cond-state / resp-cond-bye / mailbox-data / message-data / capability-data / channel-data) CRLF ; adds to uid =/ channel 5. Security Considerations It is assumed that the IMAP server and its cooperating client share an authorization (and authentication) namespace. 6 Normative References [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [IMAP4] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1", RFC 3501, March 2003. Nerenberg, et al. Expires January 16, 2005 [Page 6] Internet-Draft IMAP4 Channel Transport Mechanism July 2004 [KEYWORD] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [URI] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998. Authors' Addresses Lyndon Nerenberg Orthanc Systems 304 - 1755 Robson Street Vancouver, BC V6G 3B7 CA EMail: lyndon+rfc-imap-channel@orthanc.ca Steve Hole ACI Worldwide Suite 1807 10088 - 102 Avenue Edmonton, Alberta T5J 2Z1 CA Phone: +1 780 424 4922 Fax: +1 780 424 4925 EMail: steve.hole@messagingdirect.com Barry Leiba IBM T.J. Watson Research Center 30 Saw Mill River Road Hawthorne, NY 10532 US Phone: +1 914 784 7941 EMail: leiba@watson.ibm.com Appendix A. IANA Considerations IANA is requested to update the IMAP capabilities registry to add the CHANNEL capability defined by this memo. Appendix B. Administrivia [This appendix will not appear in the final document.] Nerenberg, et al. Expires January 16, 2005 [Page 7] Internet-Draft IMAP4 Channel Transport Mechanism July 2004 Discussion concerning this draft should be directed to the mailing list. Appendix C. Document Revision History [This appendix will not appear in the final document.] Appendix C.1 Changes in draft -02 1. Revert text to that from draft-nerenberg-imap-channel-01, which again forms the baseline document for the specification. The usage and implementation guide will be split out into another memo seperate from the specification itself. 2. Revert to the simple string "channel" for the capability. The old scheme (channel=foo,bar) required parsable capabilities. A new command (CHANNELSCHEMES) is proposed for discovering the supported scheme list. 3. The grammar has been cleaned up and synced with RFC3501. 4. References to schemes in the protocol no longer include the trailing ":" in the scheme name (e.g. we now use "ftp" rather than "ftp:"). The grammar is now unambiguous with reference to the use of and (a scheme name cannot contain a ":", and an requires one). Both types are now encoded as . 5. Document reformatted to meet the latest RFC Editor's requirements. 6. Added a CHANNELSCHEMES command, used to discover the schemes supported by the server. Appendix D. Outstanding Issues [This appendix will not appear in the final document.] 1. The Security Considerations section needs to be expanded. 2. Examples need a seperate section. Nerenberg, et al. Expires January 16, 2005 [Page 8] Internet-Draft IMAP4 Channel Transport Mechanism July 2004 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. 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Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Nerenberg, et al. Expires January 16, 2005 [Page 9]