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 Jingle File Transfer (XEP-0234) [1]. This resulted in the situation that XEPs like Stateless Inline Media Sharing (XEP-0385) [2] depend on the mostly unrelated Jingle (XEP-0166) [3] 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.
<file xmlns='urn:xmpp:file:metadata:0'>
<media-type>text/plain</media-type>
<name>test.txt</name>
<date>2015-07-26T21:46:00+01:00</date>
<size>6144</size>
<hash xmlns='urn:xmpp:hashes:2'
algo='sha-1'>w0mcJylzCn+AfvuGdqkty2+KP48=</hash>
</file>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 XMPP Date and Time Profiles (XEP-0082) [4]). | 2015-07-26T21:46:00+01:00 |
| 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 Use of Cryptographic Hash Functions in XMPP (XEP-0300) [5] and qualifed by the 'urn:xmpp:hashes:2' namespace. Multiple hashes MAY be included for hash agility. |
see specification |
| height | Vertical dimensions of image or video files, in pixels. | 1920 |
| 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 the Internet Assigned Numbers Authority (IANA) [6] (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 File Transfer Thumbnails (XEP-0264) [7] and qualified by the 'urn:xmpp:thumbs:1' namespace. Multiple thumbnails MAY be included for media type and size agility. | see specification |
| width | Horizontal dimensions of image or video files, in pixels. | 1080 |
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 Use of Cryptographic Hash Functions in XMPP (XEP-0300) [5] for further discussion.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [6].
The XMPP Registrar [8] includes 'urn:xmpp:file:metadata:0' in its registry of protocol namespaces (see <https://xmpp.org/registrar/namespaces.html>).
Thanks to the authors of Jingle File Transfer (XEP-0234) [1] which heavily inspired this XEP.
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The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
1. XEP-0234: Jingle File Transfer <https://xmpp.org/extensions/xep-0234.html>.
2. XEP-0385: Stateless Inline Media Sharing (SIMS) <https://xmpp.org/extensions/xep-0385.html>.
3. XEP-0166: Jingle <https://xmpp.org/extensions/xep-0166.html>.
4. XEP-0082: XMPP Date and Time Profiles <https://xmpp.org/extensions/xep-0082.html>.
5. XEP-0300: Use of Cryptographic Hash Functions in XMPP <https://xmpp.org/extensions/xep-0300.html>.
6. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.
7. XEP-0264: File Transfer Thumbnails <https://xmpp.org/extensions/xep-0264.html>.
8. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <https://xmpp.org/registrar/>.
Note: Older versions of this specification might be available at https://xmpp.org/extensions/attic/
First draft.
@report{wißfeld2020file-metadata,
title = {File metadata element},
author = {Wißfeld, Marvin},
type = {XEP},
number = {0446},
version = {0.2.0},
institution = {XMPP Standards Foundation},
url = {https://xmpp.org/extensions/xep-0446.html},
date = {2020-11-03/2022-07-17},
}END