Moving the newResponseWriter factory to ChannelTransport and Transport

NewResponseWriter was moved to ChannelTransport and Transport  to keep
tchannel handler's constructor parameters consisent with the pattern in
which these parameters come from the fields of ChannelTransport and
ChannelTransport.

transport/tchannel/channel_transport.go

@@ -82,12 +82,13 @@ func (options transportOptions) newChannelTransport() *ChannelTransport {
 		logger = zap.NewNop()
 	}
 	return &ChannelTransport{
-		once:            lifecycle.NewOnce(),
-		ch:              options.ch,
-		addr:            options.addr,
-		tracer:          options.tracer,
-		logger:          logger.Named("tchannel"),
-		originalHeaders: options.originalHeaders,
+		once:              lifecycle.NewOnce(),
+		ch:                options.ch,
+		addr:              options.addr,
+		tracer:            options.tracer,
+		logger:            logger.Named("tchannel"),
+		originalHeaders:   options.originalHeaders,
+		newResponseWriter: newHandlerWriter,
 	}
 }
 
@@ -96,15 +97,15 @@ func (options transportOptions) newChannelTransport() *ChannelTransport {
 // If you have a YARPC peer.Chooser, use the unqualified tchannel.Transport
 // instead.
 type ChannelTransport struct {
-	ch              Channel
-	name            string
-	addr            string
-	tracer          opentracing.Tracer
-	logger          *zap.Logger
-	router          transport.Router
-	originalHeaders bool
-
-	once *lifecycle.Once
+	once              *lifecycle.Once
+	ch                Channel
+	name              string
+	addr              string
+	tracer            opentracing.Tracer
+	logger            *zap.Logger
+	router            transport.Router
+	originalHeaders   bool
+	newResponseWriter func(inboundCallResponse, tchannel.Format, headerCase) responseWriter
 }
 
 // Channel returns the underlying TChannel "Channel" instance.
@@ -139,7 +140,7 @@ func (t *ChannelTransport) start() error {
 		for s := range services {
 			sc := t.ch.GetSubChannel(s)
 			existing := sc.GetHandlers()
-			sc.SetHandler(handler{existing: existing, router: t.router, tracer: t.tracer, logger: t.logger, newResponseWriter: newHandlerWriter})
+			sc.SetHandler(handler{existing: existing, router: t.router, tracer: t.tracer, logger: t.logger, newResponseWriter: t.newResponseWriter})
 		}
 	}
 

transport/tchannel/transport.go

@@ -52,13 +52,14 @@ type Transport struct {
 	lock sync.Mutex
 	once *lifecycle.Once
 
-	ch       *tchannel.Channel
-	router   transport.Router
-	tracer   opentracing.Tracer
-	logger   *zap.Logger
-	name     string
-	addr     string
-	listener net.Listener
+	ch                *tchannel.Channel
+	router            transport.Router
+	tracer            opentracing.Tracer
+	logger            *zap.Logger
+	name              string
+	addr              string
+	listener          net.Listener
+	newResponseWriter func(inboundCallResponse, tchannel.Format, headerCase) responseWriter
 
 	connTimeout            time.Duration
 	initialConnRetryDelay  time.Duration
@@ -111,6 +112,7 @@ func (o transportOptions) newTransport() *Transport {
 		tracer:              o.tracer,
 		logger:              logger,
 		headerCase:          headerCase,
+		newResponseWriter:   newHandlerWriter,
 	}
 }
 
@@ -202,7 +204,7 @@ func (t *Transport) start() error {
 			tracer:            t.tracer,
 			headerCase:        t.headerCase,
 			logger:            t.logger,
-			newResponseWriter: newHandlerWriter,
+			newResponseWriter: t.newResponseWriter,
 		},
 		OnPeerStatusChanged: t.onPeerStatusChanged,
 	}