Programming Jabber

jabber:iq:oob

We’ve already seen a form of the oob—“Out-Of-Band”—namespace in action, in the imaginary conversation in Chapter 1, where jabber:x:oob was used to pass information about a third-party file location, in the form of a Uniform Resource Locator (URL). The word “band” here refers to the bandwidth, or connection, between the client and the server. The point of an out-of-band connection is that it’s independent of that client-to-server connection (it typically is a connection from one client directly to another), and so doesn’t impact the traffic or bandwidth on that connection. This makes sense when you consider that out-of-band connections are typically used for exchanging large volumes of data, such as binary files.

The jabber:iq:oob namespace is used for pretty much the same thing, except that its usage describes a very simple handshake between two Jabber clients to exchange a file between themselves. (Yes, real peer-to-peer for the purists.) The exchange is made using HTTP. Typically, the client sending the file will start listening for HTTP requests only at the beginning of the transfer process and stop listening at the end of the transfer process. The handshake is used to coordinate the process.

Note

It’s worth pointing out here that HTTP-based peer-to-peer transfers are at the mercy of firewalls, Network Address Translation (NAT) mechanisms, and so on. There is some work underway to build a proxy mechanism—the Proxy Accept Socket Service (PASS). Details can be ...