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Interface TopicControl

Topic control feature.

Provides methods to change and update the topic tree stored on the server.


// Get a reference to topic control feature
var topics = session.topics;


  • TopicControl




  • Add a topic to the server at a specific path. This returns a Result.

    The path should be a string. To express hierarchies, / can be used as a delimiter. This allows topics to be nested and grouped below each other. For example, session.topics.add('foo/bar'); creates the topic bar . A topic is not created at foo by this method.

    Each topic has a particular type, which constrains the kind of values that the topic will allow. This type can either be explicitly provided, or included as part of a TopicSpecification.

    Adding from topic type

    To directly specify the type of topic to create, provide a string path and a TopicType. Topics specified in this way are created with default topic properties, as described in TopicSpecification.

    Adding from topic specification

    TopicSpecifications allows the creation of topics of a particular type, along with additional properties that determine how the topic operates. For instance, you may wish to specify that a topic will validate values before publishing, or that it will only publish values instead of deltas.

    Operation results

    If the topic was added, or a topic already exists with the same path and specification, the operation will succeed. If there is a problem with adding the topic then the result will be rejected with an error.

    If any sessions have already subscribed to the same path that a topic is created for, they will receive a subscription event once the topic is added, and a value event with the initial value (if supplied).

    If the session is closed when calling this method, the returned result will be rejected.


    If the operation fails a TopicAddFailReason is provided. Adding a topic may fail because the session has insufficient permissions; a topic already exists at the specified path; or certain mandatory TopicSpecification properties were missing


    // Create a topic with a Topic Type
    session.topics.add('foo/binary', diffusion.topics.TopicType.BINARY);


    // Create a topic with a TopicSpecification
    const TopicSpecification = diffusion.topics.TopicSpecification;
    var specification = new TopicSpecification(diffusion.topics.TopicType.JSON, {
        TopicSpecification.VALIDATE_VALUES : "true"
    session.topics.add('foo/json', specification);


    // Handle the add topic result
    session.topics.add('foo/bob', diffusion.topics.TopicType.JSON).then(function(result) {
        if (result.added) {
            console.log('Topic added');
        } else {
            console.log('A compatible topic already exists');
    }, function(error) {
        console.log('Topic add failed: ', error);


    Returns Result<TopicAddResult>

    a Result for this operation


  • Register a MissingTopicHandler to handle requests for a branch of the topic tree.

    The provided handler is called when a client subscribes using a topic selector that matches no existing topics. This allows a control client session to be notified when another session requests a topic that does not exist.

    A control client can register multiple handlers, but may only register a single handler for a given topic path. See MissingTopicHandler.onRegister. A handler will only be called for topic selectors with a path prefix that starts with or is equal to topicPath . If the path prefix matches multiple handlers, the one registered for the most specific (longest) topic path will be called.

    If the session is closed or the handler could not be registered, the returned Result will call its failure callback, and the handler's MissingTopicHandler.onClose or MissingTopicHandler.onError method will be called.


    Returns Result<void>

    a Result for this registration


  • Remove one or more topics at the server.

    The topics to remove will depend upon the nature of the topic selector specified. If the selector does not have descendant pattern qualifiers (i.e. / or //), only those topics that exist at paths indicated by the selector will be removed and not their descendants. If a single / qualifier is specified, all descendants of the matching topic paths will be removed. If // is specified, all branches of the topic tree that match the selector (i.e topics at the selected paths and all descendants of the selected paths) will be removed.

    This function can take any number of arguments. Each argument can be a string or a TopicSelector. Alternatively, an array of strings and TopicSelectors can be passed as a single argument. At least one valid selector has to be specified.


    // Remove the topic at 'foo/bar', leaving descendants


    // Remove the topic at 'foo/bar' and all descendants


    • selector: Array<string | TopicSelector>

      the selector specifying the topics to remove

    Returns Result<TopicRemovalResult>

    a Result resolving to a TopicRemovalResult

  • Parameters

    Returns Result<TopicRemovalResult>