Interface Topics

Example:

// Produce a fallback value stream for receiving JSON values.
var json = diffusion.datatypes.json();

session.addFallbackStream(json).on('value', function(topic, specification, newValue, oldValue) {
      console.log('New value ', newValue.get());
});

This method will not cause the server to send any topic updates unless already subscribed. This allows the registration of listeners prior to subscribing via Session.select, or to add/remove listeners independently of subscriptions on the server.

The values as specific types, use the Streams will only receive values from topics for which the specified Data Type is compatible.

The first argument of this function can be a string, a TopicSelector, or a non-empty array of strings and TopicSelectors.

Example:

// Produce a value stream for receiving JSON values.
var json = diffusion.datatypes.json();

session.addStream(topic, json).on('value', function(topic, specification, newValue, oldValue) {
      console.log('New value ', newValue.get());
});

Fetching a topic will provide its current value without subscribing this client to that topic. The returned FetchStream will emit value events for each topic that is matched for which a fetch request can be satisfied. Once complete, the FetchStream will be closed.

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.

Example:

// Fetch a topic's value
session.fetch("foo").on('value', function(value, path) {
    console.log("Value for topic '" + path + "' is: " + value);
});

Example:

// Fetch multiple topics, handling possible errors
session.fetch("?foo/bar.*").on({
    value : function(value, path) { ... },
    error : function(error) { ... },
    close : function() { ... }
});

deprecated

since 6.2

Prefer the use of fetchRequest instead. Unlike this method fetchRequest supports additional query constraints, returns type-safe values, and optionally allows topic properties to be retrieved. This will be removed in a future release.

If the request is invoked by calling fetch, the fetch result will provide the paths and types of all of the topics which the session has permission to read.

Usually the query should be restricted to a subset of the topic tree, and should retrieve the topic values and/or properties. This is achieved by applying one or more of the fluent builder methods to produce more refined requests.

Example:

// Create and send a fetch request. Then pass the results to a resultHandler
session.fetchRequest()
       .withValues(diffusion.datatypes.StringDataType)
       .fetch("*A/B//")
       .then(resultHandler);

see

diffusion.topics.FetchRequest

since

6.2

Subscription causes the server to establish a subscription for this session to any topic that matches the specified selector, including topics that are added after the initial call to Session.select.

If the provided selector string does not begin with one of the prefixes defined by TopicSelectors, it will be treated as a direct topic path.

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.

Example:

// Subscribe to a topic foo
session.select("foo").then(function() {
    // Successfully subscribed
}, function(err) {
    // There was an error with subscribing to topic "foo"
});

No more updates will be received from the server for any topics matched by the selector. If no topics exist that match the selector, the server will do nothing.

Each topic that this session is unsubscribed from will cause an unsubscribe event. Any ValueStream objects produced from Session.addStream will remain open, and will continue to emit updates for topics that the session has not been unsubscribed from.

The returned result will resolve normally when the session has been unsubscribed. It will resolve with an error if the session is unable to unsubscribe, for instance due to security constraints.

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.

Example:

// Unsubscribe from a single topic
session.unsubscribe('foo');

Example:

// Unsubscribe from multiple topics
session.unsubscribe('?foo/.*');