Accepts RpcRequestEnvelope and responds with an RpcResponseEnvelope to target.
FramedStringProtocol is used to support stream based messaging (e.
Spawned to listen to the server's response to an RpcRequest.
This crazy amount of indecipherable boilerplate is how we turn a simple Actor into a Flow, without any backpressure, specifically for use in akka-http WebSocket (but could be used elsewhere with caution).