XEP-0225: Component Connections

1. Introduction¶

Jabber Component Protocol (XEP-0114) [1] defines a protocol that enables a server component to connect to an XMPP server. However, there are a number of perceived limitations with that protocol:

• It does not support Transport Layer Security (TLS; see RFC 5246 [2]) for channel encryption.
• It does not support the Simple Authentication and Security Layer (SASL; see RFC 4422 [3]) for authentication.
• It does not enable a component to bind multiple hostnames to one stream (as, for example, a client can bind multiple resource identifiers).
• It multiplies namespaces beyond necessity, adding the "jabber:component:accept" and "jabber:component:connect" namespaces to "jabber:client" and "jabber:server".

This document specifies a standards-track protocol that addresses the basic requirements for component connections. In the future, additional documents may specify more advanced features on top of the protocol defined herein.

2. Requirements¶

This document addresses the following requirements:

1. Support Transport Layer Security for channel encryption.
2. Support the Simple Authentication and Security Layer for authentication.
3. Enable a component to bind multiple hostnames to one stream.
4. Use one of the existing default namespaces for XML streams between components and servers.

3. Stream Establishment¶

XML streams are established between a component and a server exactly as they are between a client and a server as specified in XMPP Core [4], with the following exceptions:

1. The 'from' address of the initial stream header SHOULD be the "default" hostname of the component.
2. The JID asserted by the end entity (in this case a component) during STARTTLS negotiation and SASL negotiation MUST be of the form <domain> in conformance with the definition of a domain identifier from XMPP Core.
3. If a "simple user name" is included in accordance with the chosen SASL mechanism, it MUST be of the form <domain> in conformance with the definition of a domain identifier from XMPP Core.

4. Hostname Binding¶

The protocol defined in Jabber Component Protocol (XEP-0114) [1] depended on use of the 'to' address in the stream header to specify the hostname of the component. By contrast, client-to-server connections use stream establishment is followed by binding of a resource to the stream (in fact multiple resources can be bound to the stream). This protocol emulates client-to-server connections by using a hostname binding process that is similar to the resource binding process specified in XMPP Core.

If a server offers component binding over a stream, it MUST advertise a feature of "urn:xmpp:component:0".

S: <stream:stream
       from='example.com'
       id='gPybzaOzBmaADgxKXu9UClbprp0='
       to='chat.example.com'
       version='1.0'
       xml:lang='en'
       xmlns='jabber:client'
       xmlns:stream='http://etherx.jabber.org/streams'>

S: <stream:features>
     <bind xmlns='urn:xmpp:component:0'>
       <required/>
     </bind>
   </stream:features>

In order to bind a hostname, the component sends a bind request to the server.

C: <iq id='bind_1' type='set'>
     <bind xmlns='urn:xmpp:component:0'>
       <hostname>chat.example.com</hostname>
     </bind>
   </iq>

If the hostname can be bound, the server MUST return an IQ-result specifying the exact hostname that was bound.

S: <iq id='bind_1' type='result'>
     <bind xmlns='urn:xmpp:component:0'>
       <hostname>chat.example.com</hostname>
     </bind>
   </iq>

If the hostname cannot be bound, the server MUST return an IQ-error, which SHOULD be <bad-request/>, <conflict/>, <not-allowed/>, or <resource-constraint/>, just as with client resource binding as specified in RFC 3920 [5].

Note: Although the JID asserted during STARTTLS and SASL negotiation MUST be of the form <domain> (i.e., an XMPP domain identifier), the <hostname/> element MAY be of the form <domain/resource>. This form can be used for application-specific functionality (e.g., load balancing), but such functionality is out of scope for this specification.

A component can send a subsequent bind request to bind another hostname (a server MUST support binding of multiple hostnames).

C: <iq id='bind_2' type='set'>
     <bind xmlns='urn:xmpp:component:0'>
       <hostname>foo.example.com</hostname>
     </bind>
   </iq>

If the server cannot process the bind request (e.g., because the component has already bound the desired hostname), the server MUST return an IQ-error (e.g., <conflict/>).

A component can also unbind a resource that has already been bound (a server MUST support unbinding).

C: <iq id='unbind_1' type='set'>
     <unbind xmlns='urn:xmpp:component:0'>
       <hostname>foo.example.com</hostname>
     </unbind>
   </iq>

If the hostname can be unbound, the server MUST return an IQ-result.

S: <iq id='unbind_1' type='result'/>

5. Security Considerations¶

This protocol improves upon the earlier component protocol defined in Jabber Component Protocol (XEP-0114) [1] by specifying the use of Transport Layer Security (TLS) for channel encryption and the Simple Authentication and Security Layer (SASL) for authentication. Because this protocol re-uses the XML stream establishment processes defined in XMPP Core, the security considerations from RFC 3920 and RFC 6120 apply to this protocol as well.

6. IANA Considerations¶

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

7. XMPP Registrar Considerations¶

8. XML Schema¶

<?xml version='1.0' encoding='UTF-8'?>

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='urn:xmpp:component:0'
    xmlns='urn:xmpp:component:0'
    elementFormDefault='qualified'>

  <xs:element name='bind'>
    <xs:complexType>
      <xs:sequence>
        <xs:choice minOccurs='0' maxOccurs='1'>
          <xs:element name='hostname' type='xs:string'/>
        </xs:choice>
        <xs:element name='required'
                    minOccurs='0'
                    maxOccurs='1'
                    type='empty'/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

  <xs:element name='unbind'>
    <xs:complexType>
      <xs:sequence minOccurs='0'>
        <xs:element name='hostname' type='xs:string'/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

</xs:schema>

Appendices

Appendix A: Document Information¶

Series

XEP

Number

0225

Publisher

XMPP Standards Foundation

Status

Deferred

Type

Standards Track

Version

0.2

Last Updated

2008-10-06

Approving Body

XMPP Council

Dependencies

XMPP Core

Supersedes

None

Superseded By

None

Short Name

component

Source Control

HTML

This document in other formats: XML  PDF

Appendix B: Author Information¶

Peter Saint-Andre

Email

stpeter@stpeter.im

JabberID

stpeter@jabber.org

URI

https://stpeter.im/

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 0.2 (2008-10-06)¶

   Modified namespace to incorporate namespace versioning; clarified that the value of the <hostname/> element can be either <domain> or <domain/resource>.

   psa
2. Version 0.1 (2007-08-08)¶

   Initial published version.

   psa
3. Version 0.0.1 (2007-07-31)¶

   First draft.

   psa

Appendix I: Bib(La)TeX Entry

@report{saint-andre2007component,
  title = {Component Connections},
  author = {Saint-Andre, Peter},
  type = {XEP},
  number = {0225},
  version = {0.2},
  institution = {XMPP Standards Foundation},
  url = {https://xmpp.org/extensions/xep-0225.html},
  date = {2007-07-31/2008-10-06},
}

END