XEP-xxxx: Pubsub File Sharing

Abstract
This specification explains how to share files and optionally include directory structures similar to filesystems over XMPP Pubsub. It leverages XMPP Pubsub to enable notifications about file changes and manage permissions, providing users with real-time updates and control mechanisms. An optional mechanism is also specified for managing uploaded files.
Author
Jérôme Poisson
Copyright
© 2024 – 2024 XMPP Standards Foundation. SEE LEGAL NOTICES.
Status

ProtoXEP

WARNING: This document has not yet been accepted for consideration or approved in any official manner by the XMPP Standards Foundation, and this document is not yet an XMPP Extension Protocol (XEP). If this document is accepted as a XEP by the XMPP Council, it will be published at <https://xmpp.org/extensions/> and announced on the <standards@xmpp.org> mailing list.
Type
Standards Track
Version
0.0.1 (2024-10-19)
Document Lifecycle
  1. Experimental
  2. Proposed
  3. Stable
  4. Final

1. Introduction

File sharing is a foundational use case in XMPP, with numerous attempts to facilitate the sharing of file hierarchies. Notable efforts include Tree Transfer Stream Initiation Profile (XEP-0105) [1], File Sharing (XEP-0135) [2], File Repository and Sharing (XEP-0214) [3], and File Information Sharing (XEP-0329) [4]. However, these previous approaches often fall short in key areas, particularly in the realm of notifications, and/or use now-deprecated specifications. While File Repository and Sharing (XEP-0214) [3] is the only specification that supports file hierarchies with notifications, it has seen limited adoption and suffers from its reliance on an outdated stack and issues with PubSub Collection Nodes (XEP-0248) [5], especially concerning permission management between collection and leaf nodes.

The current specification addresses these shortcomings by leveraging a more modern stack. It adapts Stateless file sharing (XEP-0447) [6] to Pubsub for robust access management and notifications, and incorporates XEP-XXXX: Pubsub Node Relationships to handle hierarchical structures. This results in a flexible and easy-to-implement solution that supports a wide range of use cases, including server-based file hosting, ad-hoc or permanent per-device directory sharing, and gateways to other file-sharing protocols.

2. Requirements

The design goals of this XEP are:

3. Glossary

This section defines key terms used throughout this specification.

4. General Structure and Payload

Pubsub nodes represent directories, and files data are put in their items. The payload of the file items MUST be a <file-sharing> element, including metadata and sources, as specified in Stateless file sharing (XEP-0447) [6]. The <file-sharing> element MUST NOT have a 'disposition' attribute as it doesn't make sense in the context of pubsub file sharing.

5. Node Structure and Naming

To facilitate a clear and consistent approach to file sharing, this specification defines a well-known node for discovering shared files and a node/item naming convention. This ensures that files and directories can be easily identified and managed.

5.1 Well-Known Node

Entities that support file sharing through this protocol MUST have a well-known node for discovering shared files. This node is defined as "urn:xmpp:pubsub-file-sharing:0".

When a user subscribes to this node using XEP-XXXX: Pubsub Extended Subscription, they will receive notifications for any new or deleted files and directories up to the requested depth. The node's items represent the shared files.

To discover file hierarchy, use XEP-XXXX: Pubsub Extended Discovery.

Example 1. Discovering Directories From Well-known Node
<iq type='get'
    from='juliet@example.org/balcony'
    to='files.example.org'
    id='disco1'>
  <query xmlns='http://jabber.org/protocol/disco#info'
    node='urn:xmpp:pubsub-file-sharing:0'>
    <x xmlns='jabber:x:data' type='submit'>
      <field var='FORM_TYPE' type='hidden'>
        <value>urn:xmpp:pubsub-ext-disco:0</value>
      </field>
      <field var='type'>
        <value>nodes</value>
      </field>
      <field var='depth'>
        <value>1</value>
      </field>
    </x>
  </query>
</iq>

5.2 Node and Item Naming Convention

To ensure a consistent and intuitive structure while maintaining unique node names across the pubsub service, the following naming convention is used for nodes and items:

This convention allows for an easy mapping of file system structure to a pubsub node hierarchy, making it simple to navigate and manage shared files without encountering conflicts due to non-unique node names.

6. Handling Metadata and File Changes

This section specifies how metadata and file deletions are handled in the context of shared files and directories.

6.1 Metadata and File Association

Each file item includes metadata and source information. The metadata is provided using the file element as described in File metadata element (XEP-0446) [7]. The source information is provided using the sources element, which lists the available sources for the file.

Example 2. Example of a File Item With Metadata and Sources
<iq type='result'
    from='files.example.org'
    to='juliet@example.org/balcony'
    id='items1'>
  <pubsub xmlns='http://jabber.org/protocol/pubsub'>
    <items node='urn:xmpp:pubsub-file-sharing:0:EASD1546/Images'>
      <item id='beach-sunset.jpg'>
        <file-sharing xmlns='urn:xmpp:sfs:0'>
          <file xmlns='urn:xmpp:file:metadata:0'>
            <media-type>image/jpeg</media-type>
            <name>beach-sunset.jpg</name>
            <size>8765432</size>
            <hash xmlns='urn:xmpp:hashes:2' algo='sha3-256'>GZTbL1pJmX9jzVgQwR0HfI+DyKuPcWvE2nUxYiMkS78=</hash>
            <desc>A stunning sunset on the beach.</desc>
          </file>
          <sources>
            <url-data xmlns='http://jabber.org/protocol/url-data' target='https://photos.example.org/gallery/beach-sunset.jpg' />
            <jinglepub xmlns='urn:xmpp:jinglepub:1' from='files.example.org' id='9876543B-2CFB-AE7E-B45Z-3DAA225972BB'>
              <description xmlns='urn:xmpp:jingle:apps:file-transfer:5' />
            </jinglepub>
          </sources>
        </file-sharing>
      </item>
    </items>
  </pubsub>
</iq>

6.2 Mapping of Files and Metadata

For services declaring support for this specification (as explained in the Discovering Support section), the following rules apply:

A service MAY prohibit deletion or update of items based on its internal policy. In this case, the service MUST return a <forbidden> error and SHOULD use a human-readable explanation of the error.

If support for this specification is not advertised, it means that file sharing metadata are manually set by an XMPP client on a generic pubsub service. In such cases, the mapping cannot be performed by the pubsub service and there is no guarantee of synchronization between files and metadata.

7. End to End Encryption

File sharing can optionally use end-to-end encryption. For file metadata, this can be achieved at the pubsub level using specifications such as OpenPGP for XMPP Pubsub (XEP-0473) [8] or Pubsub Targeted Encryption (XEP-0477) [9] or any relevant mechanism. For file transfers, this is dependent on the chosen source, and specifications such as Jingle Encrypted Transports (XEP-0391) [10] with Jingle Encrypted Transports - OMEMO (XEP-0396) [11] could be used.

8. Well-Known Directories

This specification introduces predefined nodes for special directories that MAY be used by pubsub services. Other specifications MAY define additional well-known nodes as needed. If these directories are implemented, they SHOULD be attached to the root node "urn:xmpp:pubsub-file-sharing:0".

The only explicitly defined directory in this specification is the 'Uploaded' directory. This directory MUST use the node named "urn:xmpp:pubsub-file-sharing:0:/uploaded", where the unique ID field is intentionally left blank. The purpose of the 'Uploaded' directory is to track files uploaded via specifications such as HTTP File Upload (XEP-0363) [12]. It enables end-users to view and manage their uploaded files (e.g., for deletion purposes), typically through the PEP service associated with each user.

9. Business Rules

The following business rules apply to the file sharing protocol:

10. Discovering Support

If an entity supports sharing files through the protocol specified in this XEP, it MUST advertise it by including the "urn:xmpp:pubsub-file-sharing:0" discovery feature in response to a Service Discovery (XEP-0030) [14] information request.

Example 3. Service Discovery Information Request
<iq type='get'
    from='juliet@example.org/balcony'
    to='files.example.org'
    id='disco1'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
Example 4. Service Discovery Information Response
<iq type='result'
    from='files.example.org'
    to='juliet@example.org/balcony'
    id='disco1'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    ...
    <feature var='urn:xmpp:pubsub-file-sharing:0'/>
    ...
  </query>
</iq>

When declaring support for this protocol, a pubsub service MUST manage a mapping between files and pubsub nodes.

Alternatively, XMPP clients can use this specification by filling in metadata related to files on any generic pubsub service. In such cases, there is no need to advertise support at the discovery level. File sharing nodes are identified either by searching for the well-known node 'urn:xmpp:pubsub-file-sharing:0' or any other node that starts with a similar prefix.

11. Security Considerations

The following security considerations apply to the file sharing protocol:

12. IANA Considerations

This document does not require interaction with the Internet Assigned Numbers Authority (IANA) [15].

13. XMPP Registrar Considerations

TODO

14. Acknowledgements

Thanks to NLNet foundation/NGI Zero Core for funding the work on this specification.


Appendices

Appendix A: Document Information

Series
XEP
Number
xxxx
Publisher
XMPP Standards Foundation
Status
ProtoXEP
Type
Standards Track
Version
0.0.1
Last Updated
2024-10-19
Approving Body
XMPP Council
Dependencies
XMPP Core, XEP-0001, XEP-0060, XEP-0447
Supersedes
None
Superseded By
None
Short Name
pubsub-relationships

This document in other formats: XML  PDF

Appendix B: Author Information

Jérôme Poisson
Email
goffi@goffi.org
JabberID
goffi@jabber.fr

Copyright

This XMPP Extension Protocol is copyright © 1999 – 2024 by the XMPP Standards Foundation (XSF).

Permissions

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 <https://xmpp.org/community/> 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-0105: Tree Transfer Stream Initiation Profile <https://xmpp.org/extensions/xep-0105.html>.

2. XEP-0135: File Sharing <https://xmpp.org/extensions/xep-0135.html>.

3. XEP-0214: File Repository and Sharing <https://xmpp.org/extensions/xep-0214.html>.

4. XEP-0329: File Information Sharing <https://xmpp.org/extensions/xep-0329.html>.

5. XEP-0248: PubSub Collection Nodes <https://xmpp.org/extensions/xep-0248.html>.

6. XEP-0447: Stateless file sharing <https://xmpp.org/extensions/xep-0447.html>.

7. XEP-0446: File metadata element <https://xmpp.org/extensions/xep-0446.html>.

8. XEP-0473: OpenPGP for XMPP Pubsub <https://xmpp.org/extensions/xep-0473.html>.

9. XEP-0477: Pubsub Targeted Encryption <https://xmpp.org/extensions/xep-0477.html>.

10. XEP-0391: Jingle Encrypted Transports <https://xmpp.org/extensions/xep-0391.html>.

11. XEP-0396: Jingle Encrypted Transports - OMEMO <https://xmpp.org/extensions/xep-0396.html>.

12. XEP-0363: HTTP File Upload <https://xmpp.org/extensions/xep-0363.html>.

13. XEP-0059: Result Set Management <https://xmpp.org/extensions/xep-0059.html>.

14. XEP-0030: Service Discovery <https://xmpp.org/extensions/xep-0030.html>.

15. 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/>.

Appendix H: Revision History

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

  1. Version 0.0.1 (2024-10-19)

    First draft.

    jp

Appendix I: Bib(La)TeX Entry

@report{poisson2024pubsub-relationships,
  title = {Pubsub File Sharing},
  author = {Poisson, Jérôme},
  type = {XEP},
  number = {xxxx},
  version = {0.0.1},
  institution = {XMPP Standards Foundation},
  url = {https://xmpp.org/extensions/xep-xxxx.html},
  date = {2024-10-19/2024-10-19},
}

END