transport: stop using http.CloseNotifier in handler server (#2697)

internal/transport/handler_server.go

@@ -63,9 +63,6 @@ func NewServerHandlerTransport(w http.ResponseWriter, r *http.Request, stats sta
 	if _, ok := w.(http.Flusher); !ok {
 		return nil, errors.New("gRPC requires a ResponseWriter supporting http.Flusher")
 	}
-	if _, ok := w.(http.CloseNotifier); !ok {
-		return nil, errors.New("gRPC requires a ResponseWriter supporting http.CloseNotifier")
-	}
 
 	st := &serverHandlerTransport{
 		rw:             w,
@@ -308,19 +305,13 @@ func (ht *serverHandlerTransport) HandleStreams(startStream func(*Stream), trace
 		ctx, cancel = context.WithCancel(ctx)
 	}
 
-	// requestOver is closed when either the request's context is done
-	// or the status has been written via WriteStatus.
+	// requestOver is closed when the status has been written via WriteStatus.
 	requestOver := make(chan struct{})
-
-	// clientGone receives a single value if peer is gone, either
-	// because the underlying connection is dead or because the
-	// peer sends an http2 RST_STREAM.
-	clientGone := ht.rw.(http.CloseNotifier).CloseNotify()
 	go func() {
 		select {
 		case <-requestOver:
 		case <-ht.closedCh:
-		case <-clientGone:
+		case <-ht.req.Context().Done():
 		}
 		cancel()
 		ht.Close()

internal/transport/handler_server_test.go

@@ -98,26 +98,6 @@ func TestHandlerTransport_NewServerHandlerTransport(t *testing.T) {
 			},
 			wantErr: "gRPC requires a ResponseWriter supporting http.Flusher",
 		},
-		{
-			name: "not closenotifier",
-			req: &http.Request{
-				ProtoMajor: 2,
-				Method:     "POST",
-				Header: http.Header{
-					"Content-Type": {"application/grpc"},
-				},
-				RequestURI: "/service/foo.bar",
-			},
-			modrw: func(w http.ResponseWriter) http.ResponseWriter {
-				// Return w without its CloseNotify method
-				type onlyFlusher interface {
-					http.ResponseWriter
-					http.Flusher
-				}
-				return struct{ onlyFlusher }{w.(onlyFlusher)}
-			},
-			wantErr: "gRPC requires a ResponseWriter supporting http.CloseNotifier",
-		},
 		{
 			name: "valid",
 			req: &http.Request{