Internet Draft: CONVERT A. Melnikov (Ed.) Document: draft-ietf-lemonade-convert-08 Isode Limited Intended status: Standard Track R. Cromwell (Ed.) S. H. Maes (Ed.) Oracle Expires: November 2007 May 2007 IMAP CONVERT extension 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/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Distribution of this memo is unlimited. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract CONVERT defines extensions to IMAP allowing clients to request adaptation and/or transcoding of attachments. Clients can specify the conversion details or allow servers to decide based on knowledge of client capabilities, on user or administrator preferences or its settings. Conventions used in this document In examples, "C:" and "S:" indicate lines sent by the client and server respectively. 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 [RFC2119]. When describing the general syntax, some definitions are omitted as they are defined in [RFC3501]. Table of Contents Status of this Memo ....................................... 1 Copyright Notice........................................... 1 Abstract................................................... 1 Conventions used in this document.......................... 1 Table of Contents.......................................... 2 1. Introduction............................................ 3 2. Relation with other E-mail specifications............... 3 3. Scope of Conversions.................................... 4 4. Discovery with the CAPABILITY and GETMETADATA Commands.. 4 4.1. CAPABILITY......................................... 4 4.2. GETMETADATA ....................................... 4 5. CONVERT extension to BODY and BINARY FETCH data items... 5 6. CONVERT transcoding parameters.......................... 7 6.1. Mandatory Transcoding support...................... 7 6.1.1. Additional features for mobile usage.......... 8 7. FETCH response extensions............................... 8 8. Status responses, Response code extensions.............. 8 9. Formal Syntax........................................... 9 10. IANA Considerations.................................... 11 11. IANA Entry and Attribute registrations ................ 11 11.1. IANA Entry "/convert"............................. 11 11.2. IANA Attribute "types"............................ 12 11.3. IANA Attribute "params"........................... 12 Security Considerations.................................... 12 Normative References....................................... 13 Informative References..................................... 14 Version History............................................ 14 Acknowledgments............................................ 15 Authors' Addresses........................................ 15 Intellectual Property Statement........................... 16 Disclaimer of Validity.................................... 16 Copyright Statement .......................................16 1. Introduction This document defines the CONVERT extension to IMAP4 [RFC3501]. CONVERT provides adaptation and transcoding of body parts as needed by the client. Conversion (adaptation, transcoding) may be requested by the client and performed by the server on a best effort basis or, when requested by the client, decided by the server based on server's knowledge of the client capabilities, user or administrator preferences or servers settings. This extension is primarily intended to be useful to mobile clients. It satisfies requirements specified in [MEMAIL] and [OMA-ME-RD]. A server that supports CONVERT can convert body parts to other formats to be viewed on a mobile device. The client can explicitly request a particular conversion or ask the server to select the best available conversion. When allowed by the client, the server determines how to convert based on its own strategy (e.g. based on knowledge of the client as discussed hereafter). If the server knows the characteristics of the device or can determine them (out of scope for CONVERT), the attachments can also be optimized for the capabilities of the devices (e.g. form factor of pictures). 2. Relation with other E-mail specifications The CONVERT extension does not address conversion during streaming of attachments. CONVERT depends on the METADATA extension [METADATA] to support discovery of supported conversion formats. In addition, to use CONVERT, the server MUST support the IMAP Binary specification [RFC3516]. 3. Scope of Conversions Conversions only affect what is sent to the client; the original data in the message store MUST NOT be altered. This document does not specify how the server performs conversions. Note: The requirement that original data be unaltered allows such data to remain accessible by other clients, permits replies or forwards of the original documents, permits signature verification (the converted body parts are not likely to contain any signatures), and preserves BODYSTRUCTURE and related information. 4. Discovery with the CAPABILITY and GETMETADATA Commands 4.1. CAPABILITY A server that supports the CONVERT extension MUST return "CONVERT", "METADATA", and "BINARY" in the CAPABILITY response. Example: A server that implements CONVERT C: a001 CAPABILITY S: * CAPABILITY IMAP4rev1 CONVERT BINARY METADATA [...] S: a001 OK CAPABILITY completed 4.2. GETMETADATA To determine which conversions are supported, server annotations are used. For each MIME format (<type>/<subtype> [MIME-IMT]) that can be converted, an annotation with the name "/convert/<type>/<subtype>/types" SHOULD exist. The "value.shared" attribute of this annotation contains a semicolon separated list of type/subtype output formats. The selection of available conversions MAY be adjustable by the server administrator, and MAY be sensitive to the current user. The selection of available conversions MAY also depend on information about the client obtained through a different mechanism outside the scope of CONVERT (e.g. dynamically through device description mechanisms or when the device was associated to the account). For each source MIME type that the client is interested in, it SHOULD determine which target conversions are supported by reading the "value.shared" attribute. In addition to the subtype-specific annotations, a special "wildcard" annotation named "/convert/<type>/@/types" MAY be used to reference any subtype of <type> media type. A client that doesn't find an "/convert/<type>/<subtype>/types" annotation SHOULD check the value of the "/convert/<type>/@/types" annotation. Note that names of server annotations are case-sensitive (see [METADATA]). In order to guaranty interoperability, clients and servers MUST use the lowercases version of <type> and <subtype> when constructing an annotation name described above. Example: Discover all image conversions C: a GETMETADATA "/convert/image/@/types" value.shared S: * METADATA "/convert/image/@/types" (value.shared "image/jpeg;image/png;image/gif;image/wbmp") S: a OK GETMETADATA complete The above example shows that the server supports one kind of input image transcoding, from image/jpeg to four different outputs: JPEG, PNG, GIF, and WBMP. For a given conversion, optional transcoding parameters MAY be present. These are mapped into the "value.shared" attribute in the "/convert/<srctype>/<srcsubtype>/<desttype>/<destsubtype>/params" annotation. A client wishing to use a conversion parameter SHOULD check if the server will accept it by reading the "value.shared" attribute. Example: Discover optional parameters for image/jpeg -> image/gif. C: a GETMETADATA /convert/image/jpeg/image/gif/params "value.shared" S: * METADATA /convert/image/jpeg/image/gif/params ("value.shared" "pix-x;pix-y") S: a OK GETMETADATA complete The above example shows that to convert from image/jpeg to image/gif, the transcoding supports the following types of option parameters: pix-x (width), pix-y (height). A client MAY use these values to check whether or not a desired conversion is possible, or it might, for example, present the parameters as a GUI preferences pane for the user to customize. This document relies on registry of transcoding parameters established by [MEDIAFEAT-REG]. The registry can be used to discover the underlying legal values that these parameters may take. Additional transcoding parameters, such as defined by [OMA-STI], are expected to be standardized in the future. 5. CONVERT extension to BODY and BINARY FETCH data items CONVERT defines a FETCH extension used to transcode the media type of a MIME part into another media type, and/or the same media type with different encoding parameters. It adds new options to the section-spec part of the BODY data item, a new FETCH data item CONVERT.SIZE, a new FETCH response data item BODYPARTSTRUCTURE, and new response codes. It is also expected to work with the IMAP BINARY data item extension, whose grammar is modified as well. The response to a CONVERT request always includes a BODYPARTSTRUCTURE. Each request for a BODY or BINARY FETCH data item that contains CONVERT MUST result in a FETCH response containing BODY/BINARY and BODYPARTSTRUCTURE data items containing the same section specifier (including the CONVERT keyword and its parameters). This is needed so that the client can match the requested data items with the received ones. This also allows the client to request multiple conversions of the same body part in a single request. Typically clients will request conversion of leaf body parts. In addition to support of leaf body part conversion, servers MAY offer conversion of non-leaf body parts (e.g. conversion from multipart/related). Instead of specifying the exact target MIME media type the client wants to convert to, the client MAY use a special marker NIL (also known as "default conversion") to request the server to pick a suitable target media type. This document doesn't describe how the server makes such choice. For example, the server can know characteristics of the device through a device description mechanism, or it can have a prioritized lists of MIME types based on how widespread they are, how difficult their rendering is, etc. Note that servers are REQUIRED to support "default conversion" requests. CONVERT's syntax is modeled after the HEADER.FIELDS syntax in [RFC3501], and is generally structured as: BODY[section-part.CONVERT ("media type/subtype" (parameters))] BODY.PEEK[section-part.CONVERT ("media type/subtype" (parameters))]<partial> BINARY[section-part.CONVERT ("media type/subtype" (parameters))]<partial> BINARY.PEEK[section-part.CONVERT ("media type/subtype" (parameters))]<partial> BINARY.SIZE[section-part.CONVERT ("media type/subtype" (parameters))]<partial> CONVERT.SIZE[section-part ("media type/subtype" (parameters))] Example: The client fetches body part section 3 in the message with the message sequence number of 2 and asks to have that attachment converted to pdf format. C: a001 FETCH 2 BODY[3.CONVERT ("APPLICATION/PDF")] S: * 2 FETCH (BODYPARTSTRUCTURE[3.CONVERT ("APPLICATION/PDF")] ("APPLICATION" "PDF" () NIL NIL "Base64" 2135 NIL NIL NIL) BODY[3.CONVERT ("APPLICATION/PDF")] {2135} <the document in .pdf format> ) S: a001 OK FETCH COMPLETED Example: The client requests for conversion of a text/html section as text/plain and asks for a charset of us-ascii. The server cannot respect the charset conversion request because there are non-us-ascii characters in the html code, so it fails the request with tagged NO response, containing the BADPARAMETERS response code (see section 8). C: b001 FETCH 2 BODY[3.CONVERT ("text/plain" ("charset" "us-ascii"))] S: b001 NO [BADPARAMETERS text/html text/plain (charset)] Source text has non us-ascii If the client also specified the "replace-unknown-character" conversion parameter (see Section 10.2), the same example can look like this: C: b001 FETCH 2 BODY[3.CONVERT ("text/plain" ("charset" "us-ascii" "replace-unknown-character" "TRUE"))] S: * 2 FETCH (BODYPARTSTRUCTURE[3.CONVERT ("text/plain" ("charset" "us-ascii" "replace-unknown-character" "TRUE"))] ("TEXT" "PLAIN" ("charset" "us-ascii") NIL NIL "Base64" 2135 181 NIL NIL NIL) BODY [3.CONVERT ("text/plain" ("charset" "us-ascii" "replace-unknown-character" "TRUE"))] {2135} <the document in text/plain format with us-ascii character set> ) S: b001 OK FETCH COMPLETED The server replaced non-us-ascii characters with a us-ascii character such as "?". Example: The client first requests the converted size of a text/html body part converted to text/plain: C: c000 FETCH 2 CONVERT.SIZE[4 ("TEXT/PLAIN" ("CHARSET" "us-ascii"))] S: * 2 FETCH (CONVERT.SIZE[4 ("TEXT/PLAIN" ("CHARSET" "us-ascii"))] 3135) S: c000 OK FETCH COMPLETED Later on the client requests 1000 bytes from the converted bodypart, starting from byte 2001: C: c001 FETCH 2 BODY[4.CONVERT ("TEXT/PLAIN" ("CHARSET" "us-ascii"))]<2001.1000> S: * 2 FETCH (BODYPARTSTRUCTURE[4.CONVERT ("TEXT/PLAIN" ("CHARSET" "us-ascii"))] ("TEXT" "PLAIN" ("charset" "us-ascii") NIL NIL "7bit" 2135 181 NIL NIL NIL) BODY[4.CONVERT ("TEXT/PLAIN" ("CHARSET" "us-ascii"))] <2001>{135} <bytes 2001 - 2135 of the document in text/plain format> ) S: c001 OK FETCH COMPLETED The server MUST respect the target MIME type and transcoding parameters specified by the client in the transcoding request. Note that some transcoding parameters can restrict what kind of conversion is possible, while others can remove some restrictions. 6. CONVERT transcoding parameters IMAP servers which support CONVERT MAY support additional transcoding parameters for each media type, as defined by the registry established by [MEDIAFEAT-REG]. All such servers MUST minally support recognition of the "charset" [CHARSET-REG] parameter for text/plain, text/html, text/css, text/csv, text/enriched and text/xml MIME types. (Note, a server implementation is not required to implement any conversion from the text MIME subtypes specified above, except for the mandatory to implement conversion described in section 6.1. I.e., a server implementation MUST support the "charset" parameter for text/csv, only if it supports any conversion from text/csv.) The following example illustrates how target picture dimensions can be specified in a CONVERT request using the PIX-X and PIX-Y parameters defined in [DISPLAY-FEATURES]. C: d001 UID FETCH 100 BINARY[2.CONVERT ("IMAGE/JPG" ( "PIX-X" "128" "PIX-Y" "96"))] S: * 2 FETCH (UID 100 BODYPARTSTRUCTURE[2.CONVERT ( "IMAGE/JPG" ("PIX-X" "128" "PIX-Y" "96"))] ("IMAGE/JPG" () NIL NIL "8bit" 4182 NIL NIL NIL) BINARY[2.CONVERT ("IMAGE/JPG" ("PIX-X" "128" "PIX-Y" "96"))] ~{4182} <this part of a document is a rescaled image in JPG format with width=128, height=96.> ) S: d001 OK UID FETCH COMPLETED 6.1. Mandatory Transcoding support A server implementing CONVERT MUST support character set conversions for the text/plain MIME type, and MUST support character set conversions from iso-8859-1, iso-8859-2, iso-8859-3, iso-8859-4, iso-8859-5, iso-8859-6, iso-8859-7, iso-8859-8 and iso-8859-15 to utf-8. The server MUST list "text/plain" as an allowed destination conversion in the "/convert/text/plain/types" annotation. A request for annotation "/convert/text/plain/text/plain/params" MUST return "charset" and "replace-unknown-character" (see Section 10.2) as a supported transcoding parameter. Servers SHOULD offer additional character encoding conversions where they make sense as character conversion libraries are generally available on many platforms. If the server cannot carry out the charset conversion while preserving all the characters (i.e. a source character can't be represented in the target character set), and the "replace-unknown-character" conversion parameter is not specified or specified with the value "FALSE", then the server MUST fail the conversion and MUST return the BADPARAMETERS response code (see Section 8). 6.1.1. Additional features for mobile usage This section is non normative. Based on the expected usage of convert in mobile environments, server implementors should consider support for the following conversions: - Conversion of HTML and XHTML documents to text/plain in ways that preserve at the minimum the document structure and tables. - Image conversions among the types image/gif, image/jpeg and image/png for at least the following parameters: o Size limit (i.e. reduce quality), o width, o height, o resize directive (crop, stretch, aspect ratio) The support for "depth" may also be of interest. Audio conversion is also of interest but the relevant formats depend significantly on the usage context. 7. FETCH request/response extensions 7.1. BODYPARTSTRUCTURE FETCH response item The BODYPARTSTRUCTURE data item is introduced when using the CONVERT extension. Its data follows the exact syntax specified in the [RFC3501] BODYSTRUCTURE data item, but contains information for only the converted part. All information contained in BODYPARTSTRUCTURE pertains to the state of the part after it is converted, such as the converted MIME type, sub-type, size, or charset. Note that the client can expect the returned MIME type to match the one it requested (as the server is required to obey the requested MIME type) and can treat mismatch as an error. 7.2. CONVERT.SIZE FETCH request and response item CONVERT.SIZE[section-part ("media type/subtype" (parameters))] Requests the converted size of the section (i.e., the size to expect in response to the corresponding FETCH BODY request). Note: client authors are cautioned that this might be an expensive operation for some server implementations. Needlessly issuing this request could result in degraded performance due to servers having to calculate the value every time the request is issued. 8. Status responses, Response code extensions A syntactically invalid MIME media type SHOULD generate a BAD tagged response from the server. An unrecognized MIME media type generates a NO tagged response. Some transcodings may require parameters. If a transcoding request with no parameters is sent for a format which requires parameters, the server MUST reply with a tagged NO response that contains the MISSINGPARAMETERS response code. If the server is unable to perform the requested conversion because a resource is temporary unavailable (e.g., lack of disk space, temporary internal error, transcoding service down) then the server MUST return a tagged NO response. The response SHOULD contain the TEMPFAIL response code (see below). If the requested conversion cannot be performed because of a permanent error, for example if a proprietary document format has no existing transcoding implementation, the server MUST return a tagged NO response. Otherwise, the server returns an OK response. The client in general can tell from the BODYPARTSTRUCTURE response whether or not its request was honored exactly, but may not know the reasons why. The following extension response codes are provided for OK and NO responses to disambiguate those situations: TEMPFAIL - the transcoding request failed temporarily. It might succeed later, so the client may retry. BADPARAMETERS from-concrete-mime-type to-mime-type "(" convert-params ")" - the listed parameters were not understood, not valid for the source/destination MIME type pair, had invalid values or could not be honored for another reason noted in the human readable text that follows the response code. MISSINGPARAMETERS from-concrete-mime-type to-mime-type "(" convert-params ")" - the listed parameters are required for conversion of the specified source MIME type to the destination MIME type, but were not seen in the request. 9. Formal Syntax The following syntax specification uses the augmented Backus-Naur Form (ABNF) notation as used in [ABNF], and incorporates by reference the Core Rules defined in that document. This syntax augments the grammar specified in [RFC3501] and [RFC3516]. Non-terminals not defined in this document can be found in [RFC3501], [RFC3516], [MIME-MTSRP] and [MEDIAFEAT-REG]. In the ABNF section-msgtext grammar in section 9 of [RFC3501], Section-msgtext is hereby amended to read: section-convert = "CONVERT" SP convert-params section-msgtext =/ section-convert convert-params = "(" (quoted-to-mime-type / default-conversion) [SP "(" transcoding-params ")"] ")" quoted-to-mime-type = DQUOTE to-mime-type DQUOTE transcoding-params = transcoding-param *(SP transcoding-param) transcoding-param = transcoding-param-name SP transcoding-param-value transcoding-param-name = astring ; <transcod-param-name-nq> represented as a quoted, ; literal or atom. Note that ; <transcod-param-name-nq> allows for "%" which is ; not allowed in atoms. Such values must be ; represented as quoted or literal. transcod-param-name-nq = Feature-tag ; Feature-tag is defined in [MEDIAFEAT-REG]. transcoding-param-value = astring default-conversion = "NIL" fetch-att =/ "CONVERT.SIZE" convert-size-section msg-att-static =/ "CONVERT.SIZE" convert-size-section SP number convert-size-section = "[" section-part SP convert-params "]" In the ABNF syntax "section-binary" of [RFC3516], is amended to: section-binary = "[" [section-binary-spec] "]" section-binary-spec = section-part ["." section-convert] / section-convert ; Note that conversion of a top level ; multipart/* is allowed. In the ABNF syntax "msg-att-static" of [RFC3501], is amended to: msg-att-static =/ "BODYPARTSTRUCTURE" section SP body In the ABNF syntax "resp-text-code" of [RFC3501], is amended to: resp-text-code =/ "TEMPFAIL" / bad-params-resp-code / missing-params-resp-code / mimetype-and-params = from-concrete-mime-type SP to-mime-type SP "(" transcoding-params ")" ; The values can't include the ']' character, as this ; non-terminal is returned in an IMAP response code. <<Does this include param values? If not, then the value in () must be changed to "transcod-param-name-nq *(SP transcod-param-name-nq)" >> bad-params-resp-code = "BADPARAMETERS" 1*(SP mimetype-and-params) missing-params-resp-code = "MISSINGPARAMETERS" SP 1*(SP mimetype-and-params) In addition, the following ABNF describes the syntax of the GETMETADATA entries in Section 4.2 convert-entry-req = available-conversions / available-transcoding-parameters available-conversions = "/convert/" from-mime-type "/types" any-mime-type = "@" from-mime-type = (type-name "/" any-mime-type) / concrete-mime-type ; "type/@" or "type/subtype" ; type-name is defined in [MIME-MTSRP]. concrete-mime-type = type-name "/" subtype-name ; i.e. "type/subtype". ; type-name and subtype-name ; are defined in [MIME-MTSRP]. <<Are '.' allowed in annotation names? Yes, as long as the name doesn't contain "priv" or "shared" component, e.g. foo.priv.bar is disallowed.>> from-concrete-mime-type = concrete-mime-type to-mime-type = concrete-mime-type available-transcoding-parameters = "/convert/" from-concrete-mime-type "/" to-mime-type "/params" ; Name of an annotation containing transcoding parameters. ; i.e. /convert/frmtype/frmsubtype/totype/tosubtype/params. The "value.shared" syntax of any "/convert/<type>/<subtype>/types" annotation has the following syntax: types-shared-value = from-concrete-mime-type *(";" from-concrete-mime-type) The "value.shared" syntax of any "/convert/<fromtype>/<fromsubtype>/ <totype>/<tosubtype>/params" annotation has the following syntax: params-shared-value = transcoding-param-name *(";" transcoding-param-name) 10. 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 CONVERT IMAP capability. IANA is requested to add this extension to the IANA IMAP Capability registry. IANA is also requested to perform registrations as defined in sections 10.1 and 10.2 of this document. 10.1. IANA Entry and Attribute registrations The following sections specify IANA registrations for entries and attributes used in this document. 10.1.1. IANA Entry "/convert" To: iana@iana.org Subject: IMAP METADATA Registration Please register the following IMAP METADATA item: [x] Entry [ ] Attribute [ ] Mailbox [x] Server Name: /convert Description: All annotations below this one are reserved for use by [this RFC] and its extensions. Content-type: text/plain; charset=utf-8 Contact person: Alexey Melnikov email: alexey.melnikov@isode.com 10.1.2. IANA Entry "/convert/<type>/<subtype>/types" To: iana@iana.org Subject: IMAP METADATA Registration Please register the following IMAP METADATA item: [x] Entry [ ] Attribute [ ] Mailbox [x] Server Name: /convert/<type>/<subtype>/types Description: Defined in [this RFC], Section 4.2. Content-type: text/plain; charset=us-ascii Contact person: Alexey Melnikov email: alexey.melnikov@isode.com 10.1.3. IANA Entry "/convert/.../params" To: iana@iana.org Subject: IMAP METADATA Registration Please register the following IMAP METADATA item: [x] Entry [ ] Attribute [ ] Mailbox [x] Server Name: /convert/<fromtype>/<fromsubtype>/<totype>/ <tosubtype>/params Description: Defined in [this RFC], Section 4.2. Content-type: text/plain; charset=utf-8 Contact person: Alexey Melnikov email: alexey.melnikov@isode.com 10.2. Registration of replace-unknown-character media type parameter IANA is requested to add the following registration to the registry established by RFC 2506. To: "Media feature tags mailing list" <media-feature-tags@apps.ietf.org> Subject: Registration of media feature tag replace-unknown-character Media feature tag name: replace-unknown-character ASN.1 identifier associated with feature tag: New assignment by IANA Summary of the media feature indicated by this feature tag: Allows servers that can perform charset conversion for text/plain text/html, text/css, text/csv, text/enriched and text/xml MIME types to replace characters not supported by the target charset with a fixed character, such as '?'. Values appropriate for use with this feature tag: The feature tag is Boolean and may have values of TRUE or FALSE. When this media feature is not specified in an IMAP CONVERT request, the default of FALSE is assumed. The feature tag is intended primarily for use in the following applications, protocols, services, or negotiation mechanisms: IMAP CONVERT extension [RFC XXXX] Examples of typical use: C: b001 FETCH 2 BODY[3.CONVERT ("text/plain" ("charset" "us-ascii" "replace-unknown-character" "TRUE"))] Related standards or documents: [RFC XXXX] [CHARSET-REG] Considerations particular to use in individual applications, protocols, services, or negotiation mechanisms: None Interoperability considerations: None Security considerations: None Additional information: This media feature only make sense for MIME types that also support the "charset" media type parameter [CHARSET-REG]. Name(s) & email address(es) of person(s) to contact for further information: Alexey Melnikov <alexey.melnikov@isode.com> Intended usage: COMMON Author/Change controller: IETF Requested IANA publication delay: None Other information: None 11. Security Considerations It is to be noted that some conversions may present security threats (e.g. converting a document to a damaging executable, exploiting a buffer overflow in a media codec/parser, or a denial of service attack against a client or server such as requesting an image be scaled to extremely large dimensions). Clients should be careful when requesting conversions or processing transformed attachments. Servers should avoid dangerous conversions if possible. Whenever possible, servers should perform verification of the converted attachments before returning them to the client. A client can create a carefully crafted bad message with the APPEND command followed by the FETCH command to attack the server. If the server's conversion function or library has a security problem, this could result in provilege escalation or Denial of Service. On bandwidth limited mobile networks where users pay per data volumes, spam may become an important issue. It can be mitigated with appropriate filters and server-side spam prevention tools. These are of course outside the scope of CONVERT. Deployments in which the actual transcoding is done outside the IMAP server in a separate server are recommended to keep the servers in the same trusted domain (e.g. subnet) 12. References 12.1. Normative References [METADATA] Daboo, C., "IMAP METADATA Extension", work in progress, draft-daboo-imap-annotatemore-11, 2007. [ABNF] D. Crocker, et al. "Augmented BNF for Syntax Specifications: ABNF", RFC 4234, October 2005. http://www.ietf.org/rfc/rfc4234 [RFC2119] Brader, S. "Keywords for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. http://www.ietf.org/rfc/rfc2119 [RFC3501] Crispin, M. "IMAP4, Internet Message Access Protocol Version 4 rev1", RFC 3501, March 2003. http://www.ietf.org/rfc/rfc3501 [RFC3516] Nerenberg, L. "IMAP4 Binary Content Extension", RFC 3516, April 2003. http://www.ietf.org/rfc/rfc3516.txt [MIME-IMT] Freed, N. and N. Borenstein, "MIME (Multipurpose Internet Mail Extensions) Part Two: Media Types", RFC 2046, November 1996. [MIME-MTSRP] Freed, N. and J. Klensin, "Media Type Specifications and Registration Procedures", RFC 4288, December 2005. [MEDIAFEAT-REG] Holtman, K., Mutz, A. and T. Hardie, "Media Feature Tag Registration Procedure", RFC 2506, BCP 31, March 1999. [CHARSET-REG] Hoffman, P., "Registration of Charset and Languages Media Features Tags", RFC 2987, November 2000. 12.2. Informative References [MEMAIL] Maes, S.H., "Lemonade and Mobile e-mail", draft-maes- lemonade-mobile-email-xx.txt, (work in progress). [OMA-ME-RD] Open Mobile Alliance Mobile Email Requirement Document, work in progress, http://www.openmobilealliance.org/ [OMA-STI] Open Mobile Alliance, Standard Transcoding Interface Specification, version 1.0, work in progress, <http://member.openmobilealliance.org/ftp/Public_documents/BAC/STI /Permanent_documents/OMA-STI-V1_0-20050209-D.zip>. [DISPLAY-FEATURES] Masinter, L., Holtman, K., Mutz, A. and D. Wing, "Media Features for Display, Print, and Fax", RFC 2534, March 1999. 13. Acknowledgments The authors want to specifically acknowledge the excellent criticism and comments received from Randall Gellens (Qualcomm), Arnt Gulbrandsen (Oryx), Zoltan Ordogh (Nokia), Ben Last (Emccsoft), Dan Karp (Zimbra), Pete Resnick (Qualcomm), Chris Newman (Sun) which improved the quality of the CONVERT specification considerably. The authors also want to thank all who have contributed key insight and extensively reviewed and discussed the concepts of CONVERT and its predecessor P-IMAP. In particular, this includes the authors of the LCONVERT draft: Rafiul Ahad (Oracle Corporation), Eugene Chiu (Oracle Corporation), Ray Cromwell (Oracle Corporation), Jia-der Day (Oracle Corporation), Vi Ha (Oracle Corporation), Wook- Hyun Jeong (Samsung Electronics Co. LTF), Chang Kuang (Oracle Corporation), Rodrigo Lima (Oracle Corporation), Stephane H. Maes (Oracle Corporation), Gustaf Rosell (Sony Ericsson), Jean Sini (Symbol Technologies), Sung-Mu Son (LG Electronics), Fan Xiaohui (CHINA MOBILE COMMUNICATIONS CORPORATION (CMCC)), Zhao Lijun (CHINA MOBILE COMMUNICATIONS CORPORATION (CMCC)). 14. Authors' Addresses Stephane H. Maes (Editor) Oracle Corporation 500 Oracle Parkway M/S 4op634 Redwood Shores, CA 94065 USA Phone: +1-650-607-6296 Email: stephane.maes@oracle.com Ray Cromwell (Editor) Oracle Corporation 500 Oracle Parkway Redwood Shores, CA 94065 USA Alexey Melnikov (Editor) Isode Limited 5 Castle Business Village, 36 Station Road, Hampton, Middlesex, TW12 2BX, UK Email: Alexey.Melnikov@isode.com Version History Note to RFC-editor: Please delete this section before publication Release 08 - Updated the document to use the media feature IANA registry established by RFC 2506 - Allow for conversion to non-leaf body parts - Removed .STRICT (all conversion is strict now) - Added replace-unknown-character media feature tag Release 07 - Made default conversion mandatory for servers to support - Added CONVERT.SIZE FETCH data item - Removed INFORMATIONLOSS and SERVEROVERRIDE response codes - Added TEMPFAIL and MISSINGPARAMETERS response codes - Addressed editorial comments from Randy Gellens - Updated examples and ABNF Release 06 - Allow conversion of non-leaf body parts. - Clarified that the target MIME type must be obeyed. - Changed from using new annotation attributes to standard ones - Major corrections to the ABNF section. - Disallow /convert/* annotation entry. - The * character is not allowed in annotation names, so the @ character is used instead. - Clarified handling of default conversion. - Updated examples to match ABNF. - Updated or added missing references. Release 05 - Client not mandated to support BINARY - Misc syntax and spelling fixes - New abstract contributed by Randall Gellens Release 04 - Remove compression and encryption - Update to use latest METADATA draft - Add IANA registrations Release 03 - Add mandatory character set conversions. - Add object level compression - Add object level encryption Release 02 Fixed a normative example to be informative. Added formal syntax for BODYPARTSTUCTURE, response text codes, and formal structure of composite GETANNOTATE values. Release 01 Corrected some grammatical mistakes. Clarified meaning of GETTANNOTATION response properties. Changed CONVERT grammar to merge media type and subtype into a single parameter instead of two parameters. Clarified that BODYSTRUCTURERESPONSE is always returned for CONVERT requests. Moved transcoding parameter discussion to main body from appendix. Release 00 Initial release published in October 2005 based on draft-maes- lemonade-lconvert-00 and the comments received at the London face to face meeting end of September 2005. Intellectual Property 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. 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. Full Copyright Statement Copyright (C) The IETF Trust (2007). 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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