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IQ or Message? XMPP message stanzas provide a “fire-and-forget” transport that is best used for human-readable text, alerts, notifications, and whenever you don’t need assurance that the content was truly delivered. IQ stanzas provide a more reliable transport that is optimized for a structured exchange of data, typically non-human-readable data. ) Using the values of the IQ stanza’s type, we can generate a fairly structured IQ interaction between two entities, as shown in Figure 2-5. lit" type="get"> Communication Primitives | 21 Figure 2-5.

In an online music service)? Maybe. But XMPP developers tend to be conservative about the payloads they include in a presence stanza. One exception is capabilities information—data about what XMPP features and extensions a device supports. Because there are a lot of XMPP features and extensions, and because users want to know when, for example, a friend has plugged in a video camera and can now engage in a video chat, it’s helpful to dynamically publish capabilities data in presence. We discuss this usage in depth in Chapter 5.

A higher-priority resource is more likely to receive a message sent to the account’s bare JID. A resource with a negative priority will never receive such a message (although it will receive a message sent directly to that resource). The latter is useful for network-enabling a device that doesn’t intercept human-oriented chat messages. tld/TV"> -1 36 | Chapter 3: Presence Directed Presence The presence notifications we’ve looked at so far have been broadcast—that is, they are sent to everyone in your roster (you indicate that you want a presence notification to be broadcast by leaving off the to address).