Programming Jabber

Other Differences Between Client and Component Programming

There are many differences between programming a component and programming a client. We’re already aware of many of the major ones, described earlier in Section 9.3.1.1. There are, however, also more subtle differences that we need to bear in mind.

Components, unlike clients, do not connect to the JSM. They connect as a peer of the JSM. This means not only that they cannot partake of IM features made available by JSM’s modules (see Section 4.4.4 for a list of these modules) but also that they must do more for themselves. This isn’t as bad as it seems. Take store and forward, for example, a feature provided by the JSM’s mod_offline module. While a message sent to a component won’t be stored and forwarded if that component is not connected, a message sent from a component to a client will get stored and forwarded if the client is offline, because the message will be routed to the JSM (as specified by the [ hostname ] in the address), which can decide what action to take. Messages can be passed directly to the client if the user is online or can be stored and forwarded later when they’re back online.

When constructing an element as a client, we should not specify a from attribute before it is sent; this is added by the JSM as it arrives to prevent JID spoofing. If a component does not connect through the JSM, no “from-stamping” takes place; the component itself must stamp the element with a from attribute.

The addressing ...