update error handling in tcp call hander

main.go

@@ -223,7 +223,7 @@ func main() {
 			}(conn)
 		}(l)
 	} else {
-		log.Println("Error creating echo server: %v\n", err)
+		log.Printf("Error creating echo server: %v\n", err)
 	}
 
 	sigs := make(chan os.Signal, 1)

tcp-connection.go

@@ -174,7 +174,7 @@ func (l *GenericListener) HandleConnection(conn net.Conn) {
 	case frame := <-ch:
 		err := l.HandleFrame(conn, &frame)
 		if err != nil {
-			log.Fatalf("Error handling frame: %v\n", err)
+			log.Fatalf("Error in handler: %v\n", err)
 		}
 	case <-time.After(MaxCallDuration):
 		close(ch)
@@ -194,7 +194,8 @@ func (l *GenericListener) HandleFrame(conn net.Conn, frame *FrameWithPayload) er
 			defer close(resultChan)
 			err := handler(frame, resultChan)
 			if err != nil {
-				log.Fatalf("Error handling frame: %v\n", err)
+				resultChan <- MakeFrameWithPayload(frame.Type, 500, []byte(err.Error()))
+				log.Printf("Handler returned error: %s", err)
 			}
 			result := <-resultChan
 			err = SendFrame(conn, &result)

tcp-connection_test.go

@@ -21,7 +21,7 @@ func TestGenericConnection(t *testing.T) {
 		return nil
 	})
 	listener.AddHandler(3, func(input *FrameWithPayload, resultChan chan<- FrameWithPayload) error {
-		return fmt.Errorf("Error")
+		return fmt.Errorf("Error in custom handler")
 	})
 	r, err := conn.Call(1, datta)
 	if err != nil {