File metadata element

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File metadata element This specification defines a generic file metadata element to be used in other specifications. &LEGALNOTICE; 0446 Experimental Standards Track Standards Council XMPP Core XEP-0001 XEP-0082 XEP-0264 XEP-0300 file-metadata &larma; 0.1.0 2020-11-24 XEP Editor (jsc) Accepted by vote of Council on 2020-11-18. 0.0.1 2020-11-03 lmw

First draft.

Several existing specification have the need to provide metadata on a file. The only specification of an element that contains file metadata so far is provided as part of &xep0234;. This resulted in the situation that XEPs like &xep0385; depend on the mostly unrelated &xep0166; just for the metadata element. The motiviation of this XEP is to get rid of such dependencies and have a dedicated place to define a file metadata element.


    text/plain
    test.txt
    2015-07-26T21:46:00+01:00
    6144
    w0mcJylzCn+AfvuGdqkty2+KP48=
]]>

The child elements of the <file/> element are as follows:

Element Name	Description	Example
date	Timestamp specifying the last modified time of the file (which MUST conform to the DateTime profile of &xep0082;).	`2015-07-26T21:46:00+01:00`
dimensions	Horizontal and vertical dimensions of image or video files, in pixels.	`1920x1080`
desc	A human readable description of the file. Multiple `<desc/>` elements MAY be included if different xml:lang values are specified.	`Picture of 24th XSF Summit`
hash	A hash of the file content, using the `<hash/>` element defined in &xep0300; and qualifed by the 'urn:xmpp:hashes:2' namespace. Multiple hashes MAY be included for hash agility.	see specification
length	Length of an audio or video file, in milliseconds.	`63000`
media-type	The media type of the file content, which SHOULD be a valid MIME-TYPE as registered with &IANA; (specifically, as listed at <http://www.iana.org/assignments/media-types>). If not specified, the content is assumed to be "application/octet-stream".	`text/plain`
name	The name of the file. The name SHOULD NOT contain characters or character sequences that would be interpreted as a directory structure by the local file system (e.g. "/", "\", "../", etc.). If any such characters or character sequences are present (possibly because the local and remote file systems use different syntax for directory structure), they SHOULD be escaped (e.g., via percent-encoding) before using the name as part of any file system operation. See Security Considerations.	`text.txt`
size	The length of the file's content, in bytes.	`6144`
thumbnail	A thumbnail element of the file, using the <thumbnail/> element defined in &xep0264; and qualified by the 'urn:xmpp:thumbs:1' namespace. Multiple thumbnails MAY be included for media type and size agility.	see specification

All child elements are OPTIONAL, however, specifications making use of the file metadata object MAY require providing some of these elements as part of their specification.

Caution needs to be exercised when using the <name/> of the metadata to control any interaction with a file system. For example, a malicious user could request a file with <name>/etc/passwd</name> or include file system specific control patterns such as <name>../../private.txt</name> to try and access a sensitive file outside of the set of files intended to be shared. Or a malicious user could offer a file named /etc/passwd to try and trick the receiver into overwriting that or other sensitive files. Therefore, implementations SHOULD escape any file system path separators in the <name/> before using that value in any file system calls.

It is RECOMMENDED for implementations to use the strongest hashing algorithm available to both parties. See &xep0300; for further discussion.

This document requires no interaction with &IANA;.

The ®ISTRAR; includes 'urn:xmpp:file:metadata:0' in its registry of protocol namespaces (see &NAMESPACES;).

urn:xmpp:file:metadata:0

Thanks to the authors of &xep0234; which heavily inspired this XEP.