This callback is used to generate custom contents published with the add_handler function.
The arguments passed are the same as passed to add_handler. The Publisher will decrease the reference count of the returned buffer after deliving it. It's valid to return null in situations were no contents can be generated.
| publisher |
the Publisher |
| key |
the unique key |
| user_data |
user data set when the signal handler was installed |
|
The Contents buffer for this publication, or null. |