The protocol used for the connection to the plugin is TCP based. All messages originate in the GUI and are sent to the plugin. The plugin does not send any messages to the GUI. All feedback happens via the netlogger interface.
There are three messages which the GUI can send to the client:
Increment the parallelism level of a transfer
connect send "+parallelism <transfer_id>" <CRLF> close
Decrement the parallelism level of a transfer
connect send "-parallelism <transfer_id>" <CRLF> close
Force a transfer to fail
connect send "fault <transfer_id>" <CRLF> close