The interface for a user-defined node consists of:
- A set of implementation functions that provide the functionality of the
user-defined node. These functions are invoked by the message broker. The
implementation functions are mandatory, and if they are not supplied by the
developer, an exception is thrown at runtime.
- A set of utility functions that create resources in the message broker,
or request a service of the broker. These utility functions are invoked by
a user-defined node.
Most of the utilities are shared by any type of node, however there are
a few that are specific to input nodes. These are marked in the text.