Programming Jabber

The Opening Tag

Earlier, we said that the opening document tag was used by the client to “announce its intentions.” The following is a typical opening document tag from a Jabber client that has made a socket connection to port 5222 on the Jabber server jabber.org:

<stream:stream
    xmlns:stream="http://etherx.jabber.org/streams"
    to="jabber.org"
    xmlns="jabber:client">

There are four parts to this opening tag:

The <stream:stream> tag

Every streaming Jabber XML document must start, and end, with a <stream:stream> tag, qualified with the stream namespace.

The stream namespace declaration

xmlns:stream="http://etherx.jabber.org/streams"

The declaration of the stream namespace also comes in the opening stream tag. It refers to a URL (http://etherx.jabber.org/streams), which is a fixed value and serves to uniquely identify the stream namespace used in the XML document, rooted with <stream/>, that is, streamed over a Jabber connection.

The namespace qualifies only the tags that are prefixed stream:. Apart from stream, there is one other tag name used in these documents that is qualified by this namespace, and that is error. The <stream:error/> tag is used to convey Jabber XML stream connection errors, such as premature disconnection, invalid namespace specifications, incomplete root tag definitions, a timeout while waiting for authentication to follow the root tag exchange, and so on.

The to attribute

to="jabber.org"

There is a to attribute that specifies to which Jabber server the ...