XEP-0363: HTTP File Upload

1. Introduction¶

XMPP protocol extensions already define methods for peer-to-peer file transfer such as SI File Transfer (XEP-0096) [3] or Jingle File Transfer (XEP-0234) [4] however due to their very nature of being peer-to-peer they don't work very well in scenarios where it is requeried to send a file to multiple recipients or multiple resources of the same recipient at once. They also don’t work alongside offline storage, MUC history and Message Archive Management (XEP-0313) [5].

Uploading files manually to an HTTP server and sharing the link has been a workaround for this for a long time now. While users have a variety of services to choose from the downside of this manual approach is that an XMPP client can not automate this process on behalf of the user since these services don’t share a common API. Furthermore using a third party service would probably require the user to enter additional credentials into their XMPP client specifically for the file upload.

This XEP defines an approach to request permissions from another entity to upload a file to a specific path on an HTTP server and at the same time receive an URL from which that file can later be downloaded again. These tuples consisting of a PUT and a GET-URL are called slots.

2. Requirements¶

• Be as easy to implement as possible. This is grounded on the idea that most programming languages already have HTTP libraries available.
• Be agnostic toward the distribution of the actual URL. Users can choose to send the URL in the body of a message stanza, utilize Out-of-Band Data (XEP-0066) [6], Jingle HTTP Transport Method (XEP-0370) [7], or even use it as their avatar in User Avatar (XEP-0084) [8].
• Anyone who knows the URL SHOULD be able to access it.

3. Discovering Support¶

An entity advertises support for this protocol by including the "urn:xmpp:http:upload:0" in its service discovery information features as specified in Service Discovery (XEP-0030) [9] or section 6.3 of Entity Capabilities (XEP-0115) [10]. To avoid unnecessary round trips an entity SHOULD also include the maximum file size as specified in Service Discovery Extensions (XEP-0128) [2] if such a limitation exists. The field name MUST be "max-file-size" and the value MUST be in bytes.

A user’s server SHOULD include any known entities that provide such services into its service discovery items.

<iq from='romeo@montague.tld/garden'
    id='step_01'
    to='montague.tld'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#items'/>
</iq>

<iq from='montague.tld'
    id='step_01'
    to='romeo@montague.tld/garden'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#items'>
    <item jid='upload.montague.tld' name='HTTP File Upload' />
    <item jid='conference.montague.tld' name='Chatroom Service' />
  </query>
</iq>

<iq from='romeo@montague.tld/garden'
    id='step_02'
    to='upload.montague.tld'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>

<iq from='upload.montague.tld'
    id='step_02'
    to='romeo@montague.tld/garden'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    <identity category='store'
              type='file'
              name='HTTP File Upload' />
    <feature var='urn:xmpp:http:upload:0' />
    <x type='result' xmlns='jabber:x:data'>
      <field var='FORM_TYPE' type='hidden'>
        <value>urn:xmpp:http:upload:0</value>
      </field>
      <field var='max-file-size'>
        <value>5242880</value>
      </field>
    </x>
  </query>
</iq>

4. Requesting a slot¶

A client requests a new upload slot by sending an IQ-get to the upload service containing a <request> child element qualified by the urn:xmpp:http:upload:0 namespace. This element MUST include the attributes filename and size containing the file name and size (in bytes) respectively.

An additional attribute content-type containing the Content-Type is OPTIONAL.

<iq from='romeo@montague.tld/garden'
    id='step_03'
    to='upload.montague.tld'
    type='get'>
  <request xmlns='urn:xmpp:http:upload:0'
    filename='très cool.jpg'
    size='23456'
    content-type='image/jpeg' />
</iq>

The upload service responds with both a PUT and a GET URL wrapped by a <slot> element. The service SHOULD keep the file name and especially the file ending intact. Using the same hostname for PUT and GET is OPTIONAL. The host MUST provide Transport Layer Security (RFC 5246 [11]). Both HTTPS URLs MUST adhere to RFC 3986 [12]. Non ASCII characters MUST be percent-encoded.

The <put> element MAY also contain a number of <header> elements which correspond to HTTP header fields. Each <header> element MUST have a name-attribute and a content with the value of the header. Only the following header names are allowed: Authorization, Cookie, Expires. The allowed headers provided in the response MUST be included in the HTTP PUT request. Other header names MUST be ignored by the requesting entity and MUST NOT be included in the HTTP request. The requesting entity MUST strip any newline characters from the header name and value before performing the HTTP request, but MUST preserve the relative order of multiple values for the same header in the request. Each header name MAY be present zero or more times, and are case insensitive (eXpires is the same as Expires).

<iq from='upload.montague.tld'
    id='step_03'
    to='romeo@montague.tld/garden'
    type='result'>
  <slot xmlns='urn:xmpp:http:upload:0'>
    <put url='https://upload.montague.tld/4a771ac1-f0b2-4a4a-9700-f2a26fa2bb67/tr%C3%A8s%20cool.jpg'>
      <header name='Authorization'>Basic Base64String==</header>
      <header name='Cookie'>foo=bar; user=romeo</header>
    </put>
    <get url='https://download.montague.tld/4a771ac1-f0b2-4a4a-9700-f2a26fa2bb67/tr%C3%A8s%20cool.jpg' />
  </slot>
</iq>

5. Error conditions¶

Instead of providing the client with a slot the service MAY respond with an error if the requested file size is too large. In addition the entity MAY inform the requester about the maximum file size.

<iq from='upload.montague.tld'
    id='step_03'
    to='romeo@montague.tld/garden'
    type='error'>
  <request xmlns='urn:xmpp:http:upload:0'
    filename='très cool.jpg'
    size='23456'
    content-type='image/jpeg' />
  <error type='modify'>
    <not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas' />
    <text xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>File too large. The maximum file size is 20000 bytes</text>
    <file-too-large xmlns='urn:xmpp:http:upload:0'>
      <max-file-size>20000</max-file-size>
    </file-too-large>
  </error>
</iq>

For any other type of error the service SHOULD respond with appropriate error types to indicate temporary or permanent errors.

For temporary errors such as exceeding a personal quota the service MAY include a <retry/> element qualified by the urn:xmpp:http:upload:0 namespace as a child of the <error/> element. The retry element MUST include an attribute 'stamp' which indicates the time at which the requesting entity may try again. The format of the timestamp MUST adhere to the date-time format specified in XMPP Date and Time Profiles (XEP-0082) [13] and MUST be expressed in UTC.

<iq from='upload.montague.tld'
    id='step_03'
    to='romeo@montague.tld/garden'
    type='error'>
  <request xmlns='urn:xmpp:http:upload:0'
    filename='très cool.jpg'
    size='23456'
    content-type='image/jpeg' />
  <error type='wait'>
    <resource-constraint xmlns='urn:ietf:params:xml:ns:xmpp-stanzas' />
    <text xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>Quota reached. You can only upload 5 files in 5 minutes</text>
    <retry xmlns='urn:xmpp:http:upload:0'
      stamp='2017-12-03T23:42:05Z' />
  </error>
</iq>

<iq from='upload.montague.tld'
    id='step_03'
    to='romeo@montague.tld/garden'
    type='error'>
  <request xmlns='urn:xmpp:http:upload:0'
     filename='très cool.jpg'
     size='23456'
     content-type='image/jpeg' />
  <error type='auth'>
    <forbidden xmlns='urn:ietf:params:xml:ns:xmpp-stanzas' />
    <text xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>Only premium members are allowed to upload files</text>
  </error>
</iq>

6. Upload¶

The actual upload of the file happens via HTTP-PUT and is out of scope of this document. The upload service MUST reject the file upload if the Content-Length does not match the size of the slot request. The service SHOULD reject the file if the Content-Type has been specified beforehand and does not match. The service MAY assume application/octet-stream as a Content-Type if it the client did not specify a Content-Type at all.

In addition to the Content-Length and Content-Type header the client MUST include all allowed headers that came with the slot assignment.

There is no further XMPP communication required between the upload service and the client. A HTTP status Code of 201 means that the server is now ready to serve the file via the provided GET URL. If the upload fails for whatever reasons the client MAY request a new slot.

7. Implementation Notes¶

The upload service SHOULD choose an appropriate timeout for the validity of the PUT URL. Since there is no reason for a client to wait between requesting the slot and starting the upload, relatively low timeout values of around 300s are RECOMMENDED.

To make HTTP Upload work in web clients (including those hosted on a different domain) the upload service SHOULD set appropriate CORS-Headers. The exact headers and values are out of scope of this document but may include: Access-Control-Allow-Origin, Access-Control-Allow-Methods and Access-Control-Allow-Headers. For HTTP upload services that use custom Authorization or Cookie request header the CORS-Header Access-Control-Allow-Credentials might also be of importance.

Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: OPTIONS, HEAD, GET, PUT
Access-Control-Allow-Headers: Authorization, Content-Type
Access-Control-Allow-Credentials: true

Clients SHOULD NOT interpret headers and treat them as opaque.

8. Security Considerations¶

Content-Security-Policy: default-src 'none'; frame-ancestors 'none';

9. IANA Considerations¶

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

10. XMPP Registrar Considerations¶

11. XML Schema¶

<xml version="1.0" encoding="utf8">
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
    targetNamespace="urn:xmpp:http:upload:0"
    xmlns="urn:xmpp:http:upload:0">
  <xs:element name="request">
    <xs:complexType>
      <xs:attribute name="filename" type="xs:string" use="required"/>
      <xs:attribute name="size" type="xs:positiveInteger" use="required"/>
      <xs:attribute name="content-type" type="xs:string" use="optional"/>
    </xs:complexType>
  </xs:element>
  <xs:element name="slot">
    <xs:complexType>
     <xs:sequence>
       <xs:element name="put" minOccurs="1" maxOccurs="1">
         <xs:complexType>
           <xs:attribute name="url" type="xs:string" use="required"/>
           <xs:sequence>
             <xs:element name="header" minOccurs="0" maxOccurs="unbounded" type="xs:string">
               <xs:complexType>
                 <xs:attribute name="name" use="required">
                   <xs:simpleType>
                     <xs:restriction base="xs:string">
                       <xs:enumeration value="Authorization"/>
                       <xs:enumeration value="Cookie"/>
                       <xs:enumeration value="Expires"/>
                     </xs:restriction>
                   </xs:simpleType>
                 </xs:attribute>
               </xs:complexType>
             </xs:element>
           </xs:sequence>
         </xs:complexType>
       </xs:element>
       <xs:element name="get" minOccurs="1" maxOccurs="1">
         <xs:complexType>
           <xs:attribute name="url" type="xs:string" use="required"/>
         </xs:complexType>
       </xs:element>
     </xs:sequence>
    </xs:complexType>
  </xs:element>
  <xs:element name="file-too-large">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="max-file-size" type="xs:positiveInteger" minOccurs="0" maxOccurs="1"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
  <xs:element name="retry">
    <xs:complexType>
      <xs:attribute name="stamp" type="xs:string" use="required"/>
    </xs:complexType>
  </xs:element>
</xs:schema>

Appendices

Appendix A: Document Information¶

Series

XEP

Number

0363

Publisher

XMPP Standards Foundation

Status

Stable

Type

Standards Track

Version

1.1.0

Last Updated

2022-01-04

Approving Body

XMPP Council

Dependencies

XMPP Core, XEP-0030, XEP-0128

Supersedes

None

Superseded By

None

Short Name

NOT_YET_ASSIGNED

Source Control

HTML

This document in other formats: XML  PDF

Appendix B: Author Information¶

Daniel Gultsch

Email

daniel@gultsch.de

JabberID

daniel@gultsch.de

Appendix C: Legal Notices¶

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¶

Appendix H: Revision History¶

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

1. Version 1.1.0 (2022-01-04)¶
   • Filename size in bytes.
   • Headers MUST be included in the PUT request.
   • Headers considered opaque.
   • Servers may want to sign headers, in security implications.
   • Allow header case insensitivity, multiple times the same header, and preserve the order in the HTTP request.
   egp, mb
2. Version 1.0.0 (2020-02-11)¶
   Accepted as Draft standard by the XMPP Council. Voted on 2020-01-29.
   XEP Editor (jsc)
3. Version 0.10.0 (2020-01-20)¶
   • Remove statement about access control from Requirements. (Statement about long randomized file names had been moved to Security Considerations earlier.)
   • Add section about IP address leak to Security Considerations.
   dg
4. Version 0.9.0 (2018-12-18)¶
   • Divided Security Considerations into multiple sub sections and added information about properly isolating the HTTP Upload service
   • Added schema
   • Added example for CORS header
   dg
5. Version 0.8.0 (2018-12-10)¶
   • Added implementation notes regarding CORS headers for use of HTTP Upload in web clients.
   • Increase recommended timeout value for PUT URLs to better suit mobile connections
   dg
6. Version 0.7.0 (2018-05-30)¶
   • Changed not-allowed error to forbidden as this is more appropriate according to RFC 6120 [1]
   dg
7. Version 0.6.0 (2018-04-21)¶
   • Handling of non ASCII characters in URL
   • Removed normative language from first paragraph of the security considerations.
   dg
8. Version 0.5.0 (2018-02-15)¶
   • Allow only a specific set of HTTP headers to be included in the request
   • Removed some inappropriate use of normative language
   dg
9. Version 0.4.0 (2017-12-03)¶
   • Added <retry/> element to error response
   • Extend Security Considerations
   dg
10. Version 0.3.1 (2017-04-21)¶

    Fixed example

    dg
11. Version 0.3.0 (2017-02-01)¶

    Slight syntax changes and added ability to provide additional HTTP header fields on slot assignment.

    dg
12. Version 0.2.5 (2017-01-08)¶

    Merge typo fixes suggested by an unnamed user.

    XEP Editor: ssw
13. Version 0.2.4 (2016-10-28)¶

    Fix TLS reference

    dg (XEP Editor: ssw)
14. Version 0.2.3 (2016-07-11)¶

    Typo fixes

    wjt (XEP Editor: ssw)
15. Version 0.2.2 (2016-03-30)¶

    Typo fix

    ssw
16. Version 0.2.1 (2016-03-16)¶

    Minor dependency and citation fixes (fs).

    XEP Editor (ssw)
17. Version 0.2 (2016-03-07)¶

    Announce maximum file size by means of Service Discovery Extensions (XEP-0128) [2]

    dg
18. Version 0.1.2 (2016-02-16)¶

    Fix typo of discovery (Philipp Hancke).

    XEP Editor (mam)
19. Version 0.1.1 (2016-01-05)¶

    Fix invalid XML in examples (tpa).

    XEP Editor (ssw)
20. Version 0.1 (2015-08-27)¶

    Initial published version approved by the XMPP Council.

    XEP Editor (mam)
21. Version 0.0.1 (2015-07-25)¶

    First draft.

    dg

Appendix I: Bib(La)TeX Entry

@report{gultsch2015xep0363,
  title = {HTTP File Upload},
  author = {Gultsch, Daniel},
  type = {XEP},
  number = {0363},
  version = {1.1.0},
  institution = {XMPP Standards Foundation},
  url = {https://xmpp.org/extensions/xep-0363.html},
  date = {2015-07-25/2022-01-04},
}

END