Attribute detail

These attributes are added to <invoke>:

Name	Required	Type	Default value	Valid values	Description
target	if using a connection type, but never both of those	URI	none	Any value accepted by the type implementation	The connection will be opened there.
targetexpr		Vale expression	none		Evaluates when the <invoke> element is executed, used as if there had been a target attribute with the resulting value.

Moreover, the src attribute is forbidden when using a connection type.

Children

Specific connection types may use children (for example param, jssc:header and content) to specify initialization and authentication data. By default, the only useful children are:

• 0 or more param elements with the location attribute
• 0 or one finalize element

Behavior

The connection is opened when an invoked session would be started, i.e. when its source state becomes active after a macrostep. The connection is closed when the source state is exited (it may also be closed from the other side for any reason).

• If the target is invalid and detected as such immediately, or if the target is unreachable or denied by security restrictions (in fact, for any non-recoverable error raised asynchronously by the underlying implementation), an error.communication.id (where id is the invokeid) is placed into the internal queue and the connection attempt is abandonned. Note that in the case of browser-based implementations, the user may see the exact reason in the JavaScript console, but the interpreter may not have that privilege.
• Otherwise, the connection is virtually open and the implementation must attempt to maintain it as long as the element's source state is active. Following redirections (if allowed), as well as reconnection and recovery attempts should be transparent to the SCXML session. Authentification may be exposed to the SCXML session if necessary.
• If the other side explicitly closes the connection in a way that the protocol understands to be permanent, the interpreter must immediately close the connection on its own side and place a done.invoke.id event in the external queue. It must not reconnect unless the element's source state is re-entered.

While the connection is open:

• If the connection type allows sending, the invokeid (whether specified or generated) preceded by "#_" becomes a valid target for <send> elements with their type attribute set to the type of the connection. Moreover, if the autoforward attribute was present, all events processed by the interpreter must be sent over the connection at the time they are dequeued.
• If the connection type allows receiving, any event received over the connection and destined to the session must be placed into the session's external queue, with its origintype set to the connection type, its origin and its invokeid to the connection's invokeid. Note that a single real connection may be used to dispatch events from the same source to multiple sessions or in response to multiple invoke elements, as long as the implementation pretends to have one virtual connection for every connection-like invoke.
• The event's data payload must be decoded (when receiving) or encoded (when sending) as defined by the connection type, including fallback mechanisms. If it is not possible despite any defined fallbacks, an error.execution.parsefailed must be placed in the internal queue and the event's data field must be left empty.
• If a finalize element is present but empty, and the event data can be parsed as key-value pairs, any names (in the namelist) or locations (in params) specified in the connection and present as properties of the event's data must be updated with the values values in the event's data. If instead the finalize element contains executable content, that content is executed. Either action must occur when the event is dequeued, as usual.

When the invoke element's source state is exited, the connection is closed. When relevant, the other side should be notified according to the actual protocol used. No done event is generated by the interpreter when the connection is closed in this way.

As soon as a connection is closed for whatever reason, the interpreter must not send anymore events over it and it must ignore any further events that it receives from it.

Definition in JSSC

Invoke types in JSSC are represented by properties of the SCxml.invokeTypes object. Adding a new type, whether connection-like or normal invokes, simply means adding a new object. In the case of connection-like types, instead of an instantiate method, the object should have an open method with the same arguments, except that the first argument passed to it will be the target instead of the source.