Network Working Group D. Cridland Internet-Draft Isode Limited Expires: August 10, 2008 February 7, 2008 Extended URLFETCH for binary and converted parts draft-cridland-urlfetch-binary-01 Status of this Memo By submitting this Internet-Draft, each author represents that any 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 aware will be disclosed, in accordance with Section 6 of BCP 79. 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 August 10, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract The URLFETCH command defined as part of URLAUTH provides a mechanism for third-parties to gain access to data held within messages in a user's private store, however, this data is sent verbatim, which is not suitable for a number of applications. This memo specifies a method for obtaining data in forms suitable for non-mail applications. Cridland Expires August 10, 2008 [Page 1] Internet-Draft URLFETCH BINARY February 2008 Table of Contents 1. Conventions used in this document . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Extended URLFETCH . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Command Parameters . . . . . . . . . . . . . . . . . . . . 3 3.2. Response Metadata . . . . . . . . . . . . . . . . . . . . . 4 4. Example Exchanges . . . . . . . . . . . . . . . . . . . . . . . 4 5. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 9.1. Normative References . . . . . . . . . . . . . . . . . . . 7 9.2. Informative References . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . . . 9 Cridland Expires August 10, 2008 [Page 2] Internet-Draft URLFETCH BINARY February 2008 1. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [KEYWORDS]. Protocol examples are line-wrapped for clarity. Protocol strings are prefixed with C: and S: for client and server respectively, and elided data is represented by [...]. Implementors should note these notations are for editorial clarity only. 2. Introduction Although [URLAUTH] provides a URLFETCH command which can be used to dereference a URL and return the body part data, it does so by returning the encoded form, without sufficient data to decode. This is suitable for use in mail applications such as [BURL], where the encoded form is suitable, but not where access to the actual content is required, such as [STREAMING]. This memo specifies a mechanism which returns additional metadata about the part, such as its media type, as well as removing any content transfer encoding used on the body part. 3. Extended URLFETCH This extension is available in any IMAP server implementation which includes URLAUTH=BINARY within its capability string. Such servers accept additional, per-URL, parameters to the URLFETCH command, and will provide, upon request, additional data for each URL dereferenced. 3.1. Command Parameters The URLFETCH command is extended by the provision of optional parameters. The extended URLFETCH command is distinct by enclosing each URL and associated parameters in a parenthesized list. The absence of any parameters, or if the URL is sent unenclosed, causes the command to behave precisely as specified in [URLAUTH]. Note that the content itself is always returned, with or without transfer encoding, as the client has requested. Available parameters are: Cridland Expires August 10, 2008 [Page 3] Internet-Draft URLFETCH BINARY February 2008 BODYPARTSTRUCTURE Provide a BODYPARTSTRUCTURE in additional to the data itself. BODYPARTSTRUCTURE is defined in [CONVERT]. BINARY Remove any Content-Transfer-Encoding. In particular, this means that the data MAY contain NUL octets, and not be formed from textual lines. Data containing NUL octets MUST be transferred using the literal8 syntax defined in [BINARY]. 3.2. Response Metadata In order to carry any requested metadata and provide additional information to the consumer, the URLFETCH response is similarly extended. Following the URL itself, servers will include a series of parenthesized metadata elements. Defined metadata elements are as follows: BODYPARTSTRUCTURE The BODYPARTSTRUCTURE provides information about the data contained in the response, as it has been returned. It will reflect any conversions or decoding that have taken place. Note that unlike [CONVERT], BODYPARTSTRUCTURE is not appended with the part specifier, as this is implicit in the URL. 4. Example Exchanges A client requests the data with no content transfer encoding. C: A001 URLFETCH ("imap://joe@example.com/INBOX/;uid=20/; section=1.2;urlauth=anonymous:internal: 91354a473744909de610943775f92038" BINARY) S: * URLFETCH "imap://joe@example.com/INBOX/;uid=20/; section=1.2;urlauth=anonymous:internal: 91354a473744909de610943775f92038" {28} S: Si vis pacem, para bellum. S: S: A001 OK URLFETCH completed Note that the data here does not contain a NUL octet, therefore a literla - not literal8 - syntax has been used. Cridland Expires August 10, 2008 [Page 4] Internet-Draft URLFETCH BINARY February 2008 A client again requests data with no content transfer encoding, but this time requests the body structure. C: A001 URLFETCH ("imap://joe@example.com/INBOX/;uid=20/; section=1.3;urlauth=anonymous:internal: ae354a473744909de610943775f92038" BINARY BODYPARTSTRUCTURE) S: * URLFETCH "imap://joe@example.com/INBOX/;uid=20/; section=1.3;urlauth=anonymous:internal: ae354a473744909de610943775f92038" ((BODYPARTSTRUCTURE ("IMAGE" "PNG" () NIL NIL "BINARY" 123))) ~{123} S: [123 octets of data, some of which is NUL] S: A001 OK URLFETCH completed A client requests the body structure, and the original content. C: A001 URLFETCH ("imap://joe@example.com/INBOX/;uid=20/; section=1.3;urlauth=anonymous:internal: ae354a473744909de610943775f92038" BINARY BODYPARTSTRUCTURE) S: * URLFETCH "imap://joe@example.com/INBOX/;uid=20/; section=1.3;urlauth=anonymous:internal: ae354a473744909de610943775f92038" ((BODYPARTSTRUCTURE ("IMAGE" "PNG" () NIL NIL "BASE64" 164))) {164} S: [164 octets of base64 encoded data] S: A001 OK URLFETCH completed Cridland Expires August 10, 2008 [Page 5] Internet-Draft URLFETCH BINARY February 2008 5. Formal Syntax This formal syntax uses ABNF as specified in [ABNF], and includes productions defined in [URLAUTH], [BINARY] and [IMAP]. capability =/ "URLAUTH=BINARY" ; Command parameters; see Section 3.1 urlfetch = "URLFETCH" 1*(SP url-fetch-arg) url-fetch-arg = url-fetch-simple / url-fetch-ext url-fetch-simple = url-full ; Unextended URLFETCH. url-fetch-ext = "(" url-full *(SP url-fetch-param) ")" ; If no url-fetch-param present, as unextended. url-fetch-param = "BINARY" / "BODYPARTSTRUCTURE" / atom ; TODO: Should this be iana-token? ; Response; see Section 3.2 urlfetch-data = "*" SP "URLFETCH" 1*(SP (urldata-simple / urldata-ext)) urldata-simple = SP url-full SP nstring ; If client issues url-fetch-simple, server MUST respond with ; urldata-simple urldata-ext = SP url-full [url-metadata] SP (nstring / literal8) ; Note that content is always returned. ; If the content contains a NUL octet, the server MUST use literal8. ; Otherwise, the server SHOULD use nstring syntax. url-metadata = 1*(SP "(" url-metadata-el ")") url-metadata-el = "BODYPARTSTRUCTURE" SP body / "BINARY" Cridland Expires August 10, 2008 [Page 6] Internet-Draft URLFETCH BINARY February 2008 6. IANA Considerations IMAP4 capabilities are registered by publishing a standards track or IESG approved experimental RFC. The registry is currently located at: http://www.iana.org/assignments/imap4-capabilities This document defines the URLFETCH=BINARY IMAP capability. IANA is requested to add it to the registry accordingly. This document has no actions for IANA. 7. Security Considerations Implementors are directed to the security considerations within [IMAP], [URLAUTH], and [BINARY]. The ability of the holder of a URL to be able to fetch metadata about the content pointed to by the URL as well as the content itself allows a potential attacker to discover more about the content than was previously possible, including its original filename, and user- supplied description. The additional value of this information to an attacker in marginal, and applies only to those URLs for which the attacker does not have direct access, such as those produced by [URLAUTH]. Implementors are therefore directed to the security considerations present in [URLAUTH]. 8. Acknowledgements Comments were received on the idea, and/or this draft, from Neil Cook, Philip Guenther, Alexey Melnikov, Ken Murchison and others. Whether in agreement or dissent, the comments have refined and otherwise influenced the document. 9. References 9.1. Normative References [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. [BINARY] Nerenberg, L., "IMAP4 Binary Content Extension", RFC 3516, Cridland Expires August 10, 2008 [Page 7] Internet-Draft URLFETCH BINARY February 2008 April 2003. [CONVERT] Melnikov, A. and P. Coates, "IMAP CONVERT extension", draft-ietf-lemonade-convert-13 (work in progress), December 2007. [IMAP] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1", RFC 3501, March 2003. [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [URLAUTH] Crispin, M., "Internet Message Access Protocol (IMAP) - URLAUTH Extension", RFC 4467, May 2006. 9.2. Informative References [BURL] Newman, C., "Message Submission BURL Extension", RFC 4468, May 2006. [STREAMING] Cook, N., "Streaming Internet Messaging Attachments", draft-ietf-lemonade-streaming-03 (work in progress), September 2007. Author's Address Dave Cridland Isode Limited 5 Castle Business Village 36, Station Road Hampton, Middlesex TW12 2BX GB Email: dave.cridland@isode.com Cridland Expires August 10, 2008 [Page 8] Internet-Draft URLFETCH BINARY February 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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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. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Cridland Expires August 10, 2008 [Page 9]