<?xml version='1.0' encoding='UTF-8'?> <!DOCTYPE xep SYSTEM 'xep.dtd' [ <!ENTITY % ents SYSTEM 'xep.ent'> %ents; ]> <?xml-stylesheet type='text/xsl' href='xep.xsl'?> <xep> <header> <title>Component Connections</title> <abstract>This document specifies a standards-track XMPP protocol extension that enables server components to connect to XMPP servers.</abstract> &LEGALNOTICE; <number>0225</number> <status>Deferred</status> <type>Standards Track</type> <sig>Standards</sig> <approver>Council</approver> <dependencies> <spec>XMPP Core</spec> </dependencies> <supersedes/> <supersededby/> <shortname>component</shortname> &stpeter; <revision> <version>0.2</version> <date>2008-10-06</date> <initials>psa</initials> <remark><p>Modified namespace to incorporate namespace versioning; clarified that the value of the <hostname/> element can be either <domain> or <domain/resource>.</p></remark> </revision> <revision> <version>0.1</version> <date>2007-08-08</date> <initials>psa</initials> <remark><p>Initial published version.</p></remark> </revision> <revision> <version>0.0.1</version> <date>2007-07-31</date> <initials>psa</initials> <remark><p>First draft.</p></remark> </revision> </header> <section1 topic='Introduction' anchor='intro'> <p>&xep0114; 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:</p> <ul> <li>It does not support Transport Layer Security (TLS; see &rfc5246;) for channel encryption.</li> <li>It does not support the Simple Authentication and Security Layer (SASL; see &rfc4422;) for authentication.</li> <li>It does not enable a component to bind multiple hostnames to one stream (as, for example, a client can bind multiple resource identifiers).</li> <li>It multiplies namespaces beyond necessity, adding the "jabber:component:accept" and "jabber:component:connect" namespaces to "jabber:client" and "jabber:server".</li> </ul> <p>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.</p> </section1> <section1 topic='Requirements' anchor='reqs'> <p>This document addresses the following requirements:</p> <ol> <li>Support Transport Layer Security for channel encryption.</li> <li>Support the Simple Authentication and Security Layer for authentication.</li> <li>Enable a component to bind multiple hostnames to one stream.</li> <li>Use one of the existing default namespaces for XML streams between components and servers.</li> </ol> </section1> <section1 topic='Stream Establishment' anchor='stream'> <p>XML streams are established between a component and a server exactly as they are between a client and a server as specified in &xmppcore;, with the following exceptions:</p> <ol> <li>The 'from' address of the initial stream header SHOULD be the "default" hostname of the component.</li> <li>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.</li> <li>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.</li> </ol> </section1> <section1 topic='Hostname Binding' anchor='bind'> <p>The protocol defined in <cite>XEP-0114</cite> 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.</p> <p>If a server offers component binding over a stream, it MUST advertise a feature of "urn:xmpp:component:0".</p> <example caption='Stream Feature'><![CDATA[ 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> ]]></example> <p>In order to bind a hostname, the component sends a bind request to the server.</p> <example caption='Bind Request'><![CDATA[ C: <iq id='bind_1' type='set'> <bind xmlns='urn:xmpp:component:0'> <hostname>chat.example.com</hostname> </bind> </iq> ]]></example> <p>If the hostname can be bound, the server MUST return an IQ-result specifying the exact hostname that was bound.</p> <example caption='Bind Result'><![CDATA[ S: <iq id='bind_1' type='result'> <bind xmlns='urn:xmpp:component:0'> <hostname>chat.example.com</hostname> </bind> </iq> ]]></example> <p>If the hostname cannot be bound, the server MUST return an IQ-error, which SHOULD be &badrequest;, &conflict;, ¬allowed;, or &constraint;, just as with client resource binding as specified in <cite>RFC 3920</cite>.</p> <p>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.</p> <p>A component can send a subsequent bind request to bind another hostname (a server MUST support binding of multiple hostnames).</p> <example caption='Another Bind Request'><![CDATA[ C: <iq id='bind_2' type='set'> <bind xmlns='urn:xmpp:component:0'> <hostname>foo.example.com</hostname> </bind> </iq> ]]></example> <p>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;).</p> <p>A component can also unbind a resource that has already been bound (a server MUST support unbinding).</p> <example caption='Unbind Request'><![CDATA[ C: <iq id='unbind_1' type='set'> <unbind xmlns='urn:xmpp:component:0'> <hostname>foo.example.com</hostname> </unbind> </iq> ]]></example> <p>If the hostname can be unbound, the server MUST return an IQ-result.</p> <example caption='Unbind Result'><![CDATA[ S: <iq id='unbind_1' type='result'/> ]]></example> </section1> <section1 topic='Security Considerations' anchor='security'> <p>This protocol improves upon the earlier component protocol defined in <cite>XEP-0114</cite> 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.</p> </section1> <section1 topic='IANA Considerations' anchor='iana'> <p>This document requires no interaction with &IANA;.</p> </section1> <section1 topic='XMPP Registrar Considerations' anchor='registrar'> <section2 topic='Protocol Namespaces' anchor='registrar-ns'> <p>This specification defines the following XML namespace:</p> <ul> <li>urn:xmpp:component:0</li> </ul> <p>Upon advancement of this specification from a status of Experimental to a status of Draft, the ®ISTRAR; shall add the foregoing namespace to the registry located at &NAMESPACES;, as described in Section 4 of &xep0053;.</p> </section2> <section2 topic='Protocol Versioning' anchor='registrar-versioning'> &NSVER; </section2> </section1> <section1 topic='XML Schema' anchor='schema'> <code><![CDATA[ <?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> ]]></code> </section1> </xep>