servertu.go

package mbserver

import (
	"io"

	"github.com/goburrow/serial"
)

// 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) {
	port, err := serial.Open(serialConfig)
	if err != nil {
		s.l.Error("failed to open", "address", serialConfig.Address, "err", err)
	}
	s.ports = append(s.ports, port)

	return err
}

func (s *Server) acceptSerialRequests(port serial.Port) error {
SkipFrameError:
	for {
		select {
		case <-s.closeSignalChan:
			return port.Close()
		default:
			buffer := make([]byte, 512)

			bytesRead, err := port.Read(buffer)
			if err != nil {
				if err != io.EOF {
					s.l.Error("serial read Error", "err", err)
				}
				return err
			}

			if bytesRead != 0 {

				// Set the length of the packet to the number of read bytes.
				packet := buffer[:bytesRead]

				frame, err := NewRTUFrame(packet)
				if err != nil {
					s.l.Error("bad serial frame error", "err", err)
					//The next line prevents RTU server from exiting when it receives a bad frame. Simply discard the erroneous
					//frame and wait for next frame by jumping back to the beginning of the 'for' loop.
					s.l.Warn("Keep the RTU server running!!")
					continue SkipFrameError
					//return
				}

				request := &Request{port, frame}

				s.requestChan <- request
			}
		}
	}
}