avoid ListenRTU to stop accepting requests because of timeouts. add an option to notify of error if acceptSerialRequests exits.

servertu.go

@@ -1,15 +1,33 @@
 package mbserver
 
 import (
+	"errors"
 	"io"
 	"log"
+	"syscall"
+	"time"
 
 	"github.com/goburrow/serial"
 )
 
+type ListenRTUOption func(options *rtuOptions)
+type rtuOptions struct {
+	notifyExit chan error
+}
+
+func NotifyExit(ch chan error) ListenRTUOption {
+	return func(s *rtuOptions) {
+		s.notifyExit = ch
+	}
+}
+
 // ListenRTU starts the Modbus server listening to a serial device.
 // For example:  err := s.ListenRTU(&serial.Config{Address: "/dev/ttyUSB0"})
-func (s *Server) ListenRTU(serialConfig *serial.Config) (err error) {
+func (s *Server) ListenRTU(serialConfig *serial.Config, options ...ListenRTUOption) (err error) {
+	var opts rtuOptions
+	for _, option := range options {
+		option(&opts)
+	}
 	port, err := serial.Open(serialConfig)
 	if err != nil {
 		log.Fatalf("failed to open %s: %v\n", serialConfig.Address, err)
@@ -19,29 +37,39 @@ func (s *Server) ListenRTU(serialConfig *serial.Config) (err error) {
 	s.portsWG.Add(1)
 	go func() {
 		defer s.portsWG.Done()
-		s.acceptSerialRequests(port)
+		err := s.acceptSerialRequests(port)
+		if opts.notifyExit != nil {
+			opts.notifyExit <- err
+		}
 	}()
 
 	return err
 }
 
-func (s *Server) acceptSerialRequests(port serial.Port) {
-	SkipFrameError:
+func (s *Server) acceptSerialRequests(port serial.Port) error {
+SkipFrameError:
 	for {
 		select {
 		case <-s.portsCloseChan:
-			return
+			return nil
 		default:
 		}
 
 		buffer := make([]byte, 512)
 
 		bytesRead, err := port.Read(buffer)
+		if errors.Is(err, serial.ErrTimeout) {
+			continue
+		}
 		if err != nil {
+			if errors.Is(err, serial.ErrTimeout) || errors.Is(err, syscall.EWOULDBLOCK) {
+				time.Sleep(10 * time.Millisecond)
+				continue
+			}
 			if err != io.EOF {
 				log.Printf("serial read error %v\n", err)
 			}
-			return
+			return err
 		}
 
 		if bytesRead != 0 {