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File Transfer Thumbnails This specification defines a way for a client supply a preview image for a file transfer. &LEGALNOTICE; 0264 Deferred Standards Track Standards Council XMPP Core XEP-0096 XEP-0231 thumbs Marcus Lundblad ml@update.uu.se mlundblad@jabber.org 0.3 2009-04-27 ml

Fixed typo in author's name :).

 0.2 2009-04-06 ml

Add paragraph in security section about protecting against malicious thumbnail dimensions in offer. Fixed a typo.

 0.1 2009-04-02 psa

Initial published version.

 0.0.3 2009-03-10 ml

Split use-case section into "Introduction", "Requirements", and "Use case".

 0.0.2 2009-02-25 ml

Removed service disovery. Added missing namespace on thumnail elements.

 0.0.1 2009-02-23 ml

First draft.

The current methods for file transfers include basic meta data about the file being offered (name, size, and date). There currently is no way to provide an image thumbnail for files such as photos.

This documents defines a way to include a thumbnail image as an additional metadata in a file transfer.

When a client wishes to supply a thumbnail in a transfer offer, it can do so by including an extra ]]> element as shown in the following exaples.

]]>

The receiver MAY now request the data using the protocol defined in &xep0231;.

This is a test. If this were a real file... ... ]]>

The following attributes are defined for the <thumbnail/> element.

Attribute Description Inclusion
cid A Content-ID that can be mapped to a cid: URL as specified in &rfc2111;. The 'cid' value SHOULD be of the form algo+hash@bob.xmpp.org, where the "algo" is the hashing algorithm used (e.g., "sha1" for the SHA-1 algorithm as specified in &rfc3174;) and the "hash" is the hex output of the algorithm applied to the binary data itself. REQUIRED
mime-type The value of the 'mime-type' attribute MUST match the syntax specified in &rfc2045;. That is, the value MUST include a top-level media type, the "/" character, and a subtype; in addition, it MAY include one or more optional parameters (e.g., the "audio/ogg" MIME type in the example shown below includes a "codecs" parameter as specified in &rfc4281;). The "type/subtype" string SHOULD be registered in the &ianamedia;, but MAY be an unregistered or yet-to-be-registered value. RECOMMENDED
width The intended display width of the thumbnail image. Used as a hint for the receiving client to prepare i.e. a dialog window. OPTIONAL
height The intended display height of the thumbnail image. Used as a hint for the receiving client to prepare i.e. a dialog window. OPTIONAL

The inclusion of an image thumbnail may leak information about a transfer otherwise taking place on an e2e encrypted file transfer stream. A client MAY wish to not include a thumbnail.

A client MUST NOT rely on the values specified for the width and height of a thumbnail to allocate a bitmap data buffer for the thumbnail, to prevent possible DoS attacks. Also a client SHOULD apply implementation-specific limits on the thumbnails, if using these values to pepare a UI element for the thumbnail image, of f.ex. 128x128 pixels, values exceeding these would then be truncated and the thumbnail image scaled down when received.

This document requires no interaction with &IANA;.

This specification defines the following XML namespace:

  • urn:xmpp:thumbs:0

The ®ISTRAR; includes this namespace in the registry located at &NAMESPACES;, as described in Section 4 of &xep0053;.

 &NSVER; The protocol documented by this schema is defined in xxx ]]>