XEP-xxxx: Bidirectional Server-to-Server Connections

2.1 Stream Feature¶

If a server supports bidirectional server-to-server streams, it should inform the connecting entity when returning stream features during the stream negotiation process (both before and after TLS negotiation). This is done by including a <bidi/> element qualified by the 'urn:xmpp:features:bidi' namespace.

<stream:features>
  <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
  <bidi xmlns='urn:xmpp:features:bidi'/>
</stream:features>

If the initiating entity chooses to use TLS, STARTTLS negotiation MUST be completed before enabling bidirectionality.

2.2 Negotiation¶

To enable bidirectional communication, the connecting server sends a <bidi/> element qualified by the 'urn:xmpp:bidi' namespace. This SHOULD be done before either SASL negotiation or Server Dialback (XEP-0220) [3].

C: <bidi xmlns='urn:xmpp:bidi'/>

Note: Since there is no reply to the request, it is possible to pipeline it.

After enabling bidirectionality, the connecting server continues to authenticate via SASL or requests to send stanzas for a domain pair with Server Dialback. The receiving server MUST NOT send stanzas to the peer before it has authenticated via SASL, or the peer's identity has been verified via Server Dialback. Note that the receiving server MUST NOT attempt to verify a dialback key on the same connection where the corresponding request was issued.

Also note that the receiving server MUST only send stanzas for which it has been authenticated - in the case of TLS/SASL based authentication, this is the value of the stream's 'to' attribute, whereas in the case of Server Dialback (XEP-0220) [3] this is the value of the 'to' attribute on any <db:result> element.

Finally, once bidirectionality is enabled, the receiving server MAY initiate Server Dialback (XEP-0220) [3] authentications for other domains it hosts to any domain authenticated to be hosted by the connecting server.

5.1 Protocol Namespaces¶

• 'urn:xmpp:bidi'

5.2 Stream Features¶

• 'urn:xmpp:features:bidi'

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1. RFC 3920: Extensible Messaging and Presence Protocol (XMPP): Core <http://tools.ietf.org/html/rfc3920>.

2. RFC 3920: Extensible Messaging and Presence Protocol (XMPP): Core <http://tools.ietf.org/html/draft-ietf-saintandre-rfc3920bis>.

3. XEP-0220: Server Dialback <https://xmpp.org/extensions/xep-0220.html>.

4. 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/>.