A Handler has no way of changing the underlying connection Deadline, since it has no access to the net.Conn (except by maintaining a map from RemoteAddr to net.Conn via Server.ConnState, but it's more than anyone should need to do). Moreover, it can't implement a timeout itself because the Close method of the ResponseWriter implementation is not documented to unblock concurrent Writes.

This means that if the server has a WriteTimeout, the connection has a definite lifespan, and streaming is impossible. So servers with any streaming endpoints are forced not to implement timeouts at all on the entire Server.

A possible solution might be to expose the net.Conn in the Context. Another could be to allow interface upgrades to the SetDeadline methods on ResponseWriter. Yet another would be to make (*response).Close unblock (*response).Write.