RegisterTopic Method

Register a topic name. Returns the topic id mapped to the newly registered topic name.

Syntax

mqttsn.registerTopic(topicName, [callback])

Callback

The 'callback' parameter specifies a function which will be called when the operation completes (or an error is encountered). If the 'callback' parameter is not specified, then the method will block and will not return until the operation completes (or an error is encountered).

The callback for this method is defined as:

function(err, data){ }

'err' is the error that occurred. If there was no error, then 'err' is 'null'.

'data' is the value returned by the method.

'err' has 2 properties which hold detailed information:

err.code
err.message

Remarks

Requests that the gateway establish a new topic id mapping for the TopicName provided. If accepted, the gateway assigns a topic id to the received topic name and returns it. At this point, the client may begin sending messages with this topic id.

Topic Names

Topic names are case-sensitive, must be 1-65535 characters long, and may include any characters except wildcard characters (# and +) and the null character. The / character separates levels within a topic name, which is important in the context of subscribing (see Subscribe for more information).

Keep in mind that using topic names with leading or trailing / characters will cause topic levels with zero-length names to be created. That is, a topic name like /a/b/ consists of the levels '', 'a', 'b', and ''. Depending on the server, multiple successive /s may also cause zero-length levels to be created, or may be treated as a single /.

Topic names that begin with a $ are "system topics", and servers will typically prevent clients from publishing to them.