XEP-0446: File metadata element

This specification defines a generic file metadata element to be used in other specifications.
Marvin Wißfeld
© 1999 – 2020 XMPP Standards Foundation. SEE LEGAL NOTICES.


WARNING: This Standards-Track document is Experimental. Publication as an XMPP Extension Protocol does not imply approval of this proposal by the XMPP Standards Foundation. Implementation of the protocol described herein is encouraged in exploratory implementations, but production systems are advised to carefully consider whether it is appropriate to deploy implementations of this protocol before it advances to a status of Draft.
Standards Track
0.1.0 (2020-11-24)
Document Lifecycle
  1. Experimental
  2. Proposed
  3. Draft
  4. Final

1. Introduction

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.

2. Element format

<file xmlns='urn:xmpp:file:metadata:0'>
    <hash xmlns='urn:xmpp:hashes:2'

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

Table 1: File Description Elements
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
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 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
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

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.

3. Security Considerations

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.

4. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [6].

5. XMPP Registrar Considerations

5.1 Protocol Namespaces

The XMPP Registrar [8] includes 'urn:xmpp:file:metadata:0' in its registry of protocol namespaces (see <https://xmpp.org/registrar/namespaces.html>).

6. Acknowledgements

Thanks to the authors of Jingle File Transfer (XEP-0234) [1] which heavily inspired this XEP.


Appendix A: Document Information

XMPP Standards Foundation
Standards Track
Last Updated
Approving Body
XMPP Council
XMPP Core, XEP-0001, XEP-0082, XEP-0264, XEP-0300
Superseded By
Short Name
Source Control

This document in other formats: XML  PDF

Appendix B: Author Information

Marvin Wißfeld


This XMPP Extension Protocol is copyright © 1999 – 2020 by the XMPP Standards Foundation (XSF).


Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the "Specification"), to make use of the Specification without restriction, including without limitation the rights to implement the Specification in a software program, deploy the Specification in a network service, and copy, modify, merge, publish, translate, distribute, sublicense, or sell copies of the Specification, and to permit persons to whom the Specification is furnished to do so, subject to the condition that the foregoing copyright notice and this permission notice shall be included in all copies or substantial portions of the Specification. Unless separate permission is granted, modified works that are redistributed shall not contain misleading information regarding the authors, title, number, or publisher of the Specification, and shall not claim endorsement of the modified works by the authors, any organization or project to which the authors belong, or the XMPP Standards Foundation.

Disclaimer of Warranty

## NOTE WELL: This Specification is provided on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. ##

Limitation of Liability

In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the XMPP Standards Foundation or any author of this Specification be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if the XMPP Standards Foundation or such author has been advised of the possibility of such damages.

IPR Conformance

This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which can be found at <https://xmpp.org/about/xsf/ipr-policy> or obtained by writing to XMPP Standards Foundation, P.O. Box 787, Parker, CO 80134 USA).

Visual Presentation

The HTML representation (you are looking at) is maintained by the XSF. It is based on the YAML CSS Framework, which is licensed under the terms of the CC-BY-SA 2.0 license.

Appendix D: Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.

Appendix E: Discussion Venue

The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.

Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.

Errata can be sent to <editor@xmpp.org>.

Appendix F: Requirements Conformance

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".

Appendix G: Notes

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/>.

Appendix H: Revision History

Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/

  1. Version 0.1.0 (2020-11-24)
    Accepted by vote of Council on 2020-11-18.
    XEP Editor (jsc)
  2. Version 0.0.1 (2020-11-03)

    First draft.