Re: [Twisted-Python] Looking for some advice debugging issue with transport.write calls

self.in_send_message seems like a potential source of bugs (can't see it being set to False on all branches here) and is also likely unnecessary. General advice: 1. Simplify, simplify, simplify. 2. Unit tests (see https://twistedmatrix.com/documents/current/core/howto/trial.html).