process_incoming_message
Description:
Process a message after it's received.
If the payload isn't changed the given payload is just returned, otherwise [method@GLib.Bytes.unref] is called on the given
payload and a new [struct@GLib.Bytes] is returned with the new data.
Extensions using reserved bits of the header will reset them in header.
Parameters:
| this | |
| header |
the message header |
| payload |
the payload data |
Returns:
|
the message payload data, or null in case of error |