Network Working Group D. Cridland Internet-Draft Isode Limited Intended status: Standards Track September 4, 2008 Expires: March 8, 2009 Extended URLFETCH for binary and converted parts draft-cridland-urlfetch-binary-03 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 March 8, 2009. 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 March 8, 2009 [Page 1] Internet-Draft URLFETCH BINARY September 2008 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions used in this document . . . . . . . . . . . . . . 3 3. Extended URLFETCH . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Command Parameters . . . . . . . . . . . . . . . . . . . . 3 3.2. Response Metadata . . . . . . . . . . . . . . . . . . . . 4 4. Example Exchanges . . . . . . . . . . . . . . . . . . . . . . 5 5. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 9.1. Normative References . . . . . . . . . . . . . . . . . . . 8 9.2. Informative References . . . . . . . . . . . . . . . . . . 9 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9 Intellectual Property and Copyright Statements . . . . . . . . . . 10 Cridland Expires March 8, 2009 [Page 2] Internet-Draft URLFETCH BINARY September 2008 1. 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 metadata 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 [MEDIATYPE] type, as well as removing any content transfer encoding used on the body part. 2. 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. 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, specific 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]. Similarly, if the URL is invalid, the command will behave precisely as specified in [URLAUTH], and return a simple NIL. Available parameters are: Cridland Expires March 8, 2009 [Page 3] Internet-Draft URLFETCH BINARY September 2008 BODYPARTSTRUCTURE Provide a BODYPARTSTRUCTURE. BODYPARTSTRUCTURE is defined in [CONVERT], and provides metadata useful for processing applications, such as the type of the data. BINARY Provide the data without 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]. BODY Provide the data as-is. This will provide the same data as the unextended [URLAUTH] as a metadata item. Metadata items MUST NOT appear more than once per URL requested, and clients MUST NOT request both BINARY and BODY. 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. In particular, this will show an identity encoding if BINARY is also requested. BINARY The BINARY item provides the content, without any content transfer encoding applied. If this is not possible (for example, the content transfer encoding is unknown to the server), then this MAY contain NIL. Servers MUST understand all identity content transfer encodings defined in [MIME], as well as the transformation encodings "Base64" [BASE64] and "Quoted-Printable" [MIME]. Cridland Expires March 8, 2009 [Page 4] Internet-Draft URLFETCH BINARY September 2008 BODY The BODY item provides the content as found in the message, with any content transfer encoding still applied. Requesting only the BODY will provide equivalent functionality to the unextended [URLAUTH], however using the extended syntax described herein. 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" (BINARY {28} S: Si vis pacem, para bellum. S: S: ) S: A001 OK URLFETCH completed Note that the data here does not contain a NUL octet, therefore a literal - not literal8 - syntax has been used. 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)) (BINARY ~{123} S: [123 octets of data, some of which is NUL]) S: A001 OK URLFETCH completed Cridland Expires March 8, 2009 [Page 5] Internet-Draft URLFETCH BINARY September 2008 A client requests only the body structure. C: A001 URLFETCH ("imap://joe@example.com/INBOX/;uid=20/; section=1.3;urlauth=anonymous:internal: ae354a473744909de610943775f92038" BODYPARTSTRUCTURE) S: * URLFETCH "imap://joe@example.com/INBOX/;uid=20/; section=1.3;urlauth=anonymous:internal: ae354a473744909de610943775f92038" (BODYPARTSTRUCTURE ("IMAGE" "PNG" () NIL NIL "BASE64" 164)) 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" BODYPARTSTRUCTURE BODY) S: * URLFETCH "imap://joe@example.com/INBOX/;uid=20/; section=1.3;urlauth=anonymous:internal: ae354a473744909de610943775f92038" (BODYPARTSTRUCTURE ("IMAGE" "PNG" () NIL NIL "BASE64" 164)) (BODY {164} S: [164 octets of base64 encoded data]) S: A001 OK URLFETCH completed Some parts cannot be decoded, so the server will provide the BODYPARTSTRUCTURE of the part as-is, and NIL for the binary content: C: A001 URLFETCH ("imap://joe@example.com/INBOX/;uid=20/; section=1.4;urlauth=anonymous:internal: 87ecbd02095b815e699503fc20d869c8" BODYPARTSTRUCTURE BINARY) S: * URLFETCH "imap://joe@example.com/INBOX/;uid=20/; section=1.4;urlauth=anonymous:internal: 87ecbd02095b815e699503fc20d869c8" (BODYPARTSTRUCTURE ("IMAGE" "PNG" () NIL NIL "X-BLURDYBLOOP" 123)) (BINARY NIL) S: A001 OK URLFETCH completed If a part simply doesn't exist, however, or the URI is invalid for some other reason, then NIL is returned instead of metadata: C: A001 URLFETCH ("imap://joe@example.com/INBOX/;uid=20/; section=200;urlauth=anonymous:internal: 88066d37e2e5410e1a6486350a8836ee" BODYPARTSTRUCTURE BODY) S: * URLFETCH "imap://joe@example.com/INBOX/;uid=20/; section=200;urlauth=anonymous:internal: 88066d37e2e5410e1a6486350a8836ee" NIL S: A001 OK URLFETCH completed Cridland Expires March 8, 2009 [Page 6] Internet-Draft URLFETCH BINARY September 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 = "BODY" / "BINARY" / "BODYPARTSTRUCTURE" / atom ; Response; see Section 3.2 urlfetch-data = "*" SP "URLFETCH" 1*(SP (urldata-simple / urldata-ext / urldata-error)) urldata-error = SP url-full SP nil 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 url-metadata = 1*(SP "(" url-metadata-el ")") url-metadata-el = url-meta-bodystruct / url-meta-body / url-meta-binary url-bodystruct = "BODYPARTSTRUCTURE" SP body url-binary = "BINARY" SP ( nstring / literal8 ) ; If content contains a NUL octet, literal8 MUST be used. ; Otherwise, content SHOULD use nstring. ; On decoding error NIL should be used. url-body = "BODY" SP nstring Cridland Expires March 8, 2009 [Page 7] Internet-Draft URLFETCH BINARY September 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. 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. [BASE64] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, October 2006. Cridland Expires March 8, 2009 [Page 8] Internet-Draft URLFETCH BINARY September 2008 [BINARY] Nerenberg, L., "IMAP4 Binary Content Extension", RFC 3516, April 2003. [CONVERT] Melnikov, A. and P. Coates, "Internet Message Access Protocol - CONVERT Extension", RFC 5259, July 2008. [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. [MIME] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. [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. [MEDIATYPE] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996. [STREAMING] Cook, N., "Streaming Internet Messaging Attachments", draft-ietf-lemonade-streaming-06 (work in progress), June 2008. 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 March 8, 2009 [Page 9] Internet-Draft URLFETCH BINARY September 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. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 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