Programming Jabber

The from attribute

The from attribute is fairly straightforward; it normally serves to confirm to the client that the requested logical host is available. For example:

from="jabber.org"

If the host is available, the value of the from attribute from the server will match the value of the to attribute from the client. However, in some circumstances, the value can be different. The value sent in the from attribute is a redirection, or respecification, of the logical host by which the Jabber server (or more specifically the JSM component within the Jabber server) is actually known.

Logical host aliases can be defined in the Jabber server’s configuration to “convert” a hostname specified in the incoming to attribute. The <alias/> tag, which is used to define these logical host aliases, is described in Section 4.6 in Chapter 4. But how are these hostname conversions used? Here’s an example.

Let’s say that you’re running a Jabber server on an internal network that doesn’t have an available DNS server. The host where the Jabber server runs is called apollo, and its IP address is 192.168.1.4. Some people will connect to the host via the hostname because they have it defined in a local /etc/hosts file; others will connect via the IP address. Normally, the hostname (or IP address) specified in the connection parameters given to a Jabber client will be:

• Used to build the socket connection to the Jabber server.

• Specified in the to attribute in the opening XML stream to specify the logical ...