Implement Modbus UDP

README.md

@@ -21,6 +21,7 @@ Bit access:
 # Supported formats
 - TCP
 - Serial (RTU, ASCII)
+- UDP
 
 # Usage
 Basic usage:
@@ -81,6 +82,12 @@ For Modbus RTU, replace the address field and use the `rtu-` arguments in order
 ```sh
 ./modbus-cli -address=rtu:///dev/ttyUSB0 -rtu-baudrate=57600 -rtu-stopbits=2 -rtu-parity=N -rtu-databits=8 ...
 ```
+
+For Modbus UDP, replace the address field with a UDP address.
+```sh
+./modbus-cli --address=udp://127.0.0.1:502 ...
+```
+
 ### Reading Registers
 
 Read 1 register and get raw result

cmd/modbus-cli/main.go

@@ -472,7 +472,13 @@ func newHandler(o option) (modbus.ClientHandler, error) {
 		h.ProtocolRecoveryTimeout = o.tcp.protocolRecoveryTimeout
 		h.Logger = o.logger
 		return h, nil
+	case "udp":
+		h := modbus.NewRTUOverUDPClientHandler(u.Host)
+		h.SlaveID = byte(o.slaveID)
+		h.Logger = o.logger
+		return h, nil
 	}
+
 	return nil, fmt.Errorf("unsupported scheme: %s", u.Scheme)
 }
 

rtu_over_tcp_client.go

@@ -68,23 +68,23 @@ func (mb *rtuTCPTransporter) Send(aduRequest []byte) (aduResponse []byte, err er
 	var n int
 	var n1 int
 	var data [rtuMaxSize]byte
-	//We first read the minimum length and then read either the full package
-	//or the error package, depending on the error status (byte 2 of the response)
+	// We first read the minimum length and then read either the full package
+	// or the error package, depending on the error status (byte 2 of the response)
 	n, err = io.ReadAtLeast(mb.conn, data[:], rtuMinSize)
 	if err != nil {
 		return
 	}
-	//if the function is correct
+	// if the function is correct
 	if data[1] == function {
-		//we read the rest of the bytes
+		// we read the rest of the bytes
 		if n < bytesToRead {
 			if bytesToRead > rtuMinSize && bytesToRead <= rtuMaxSize {
 				n1, err = io.ReadFull(mb.conn, data[n:bytesToRead])
 				n += n1
 			}
 		}
 	} else if data[1] == functionFail {
-		//for error we need to read 5 bytes
+		// for error we need to read 5 bytes
 		if n < rtuExceptionSize {
 			n1, err = io.ReadFull(mb.conn, data[n:rtuExceptionSize])
 		}

rtu_over_udp_client.go

@@ -0,0 +1,165 @@
+package modbus
+
+import (
+	"fmt"
+	"io"
+	"net"
+	"sync"
+)
+
+// ErrADURequestLength informs about a wrong ADU request length.
+type ErrADURequestLength int
+
+func (length ErrADURequestLength) Error() string {
+	return fmt.Sprintf("modbus: ADU request length '%d' must not be less than 2", length)
+}
+
+// ErrADUResponseLength informs about a wrong ADU request length.
+type ErrADUResponseLength int
+
+func (length ErrADUResponseLength) Error() string {
+	return fmt.Sprintf("modbus: ADU response length '%d' must not be less than 2", length)
+}
+
+// RTUOverUDPClientHandler implements Packager and Transporter interface.
+type RTUOverUDPClientHandler struct {
+	rtuPackager
+	rtuUDPTransporter
+}
+
+// NewRTUOverUDPClientHandler allocates and initializes a RTUOverUDPClientHandler.
+func NewRTUOverUDPClientHandler(address string) *RTUOverUDPClientHandler {
+	handler := &RTUOverUDPClientHandler{}
+	handler.Address = address
+	return handler
+}
+
+// RTUOverUDPClient creates RTU over UDP client with default handler and given connect string.
+func RTUOverUDPClient(address string) Client {
+	handler := NewRTUOverUDPClientHandler(address)
+	return NewClient(handler)
+}
+
+// rtuUDPTransporter implements Transporter interface.
+type rtuUDPTransporter struct {
+	// Connect string
+	Address string
+	// Transmission logger
+	Logger logger
+
+	// UDP connection
+	mu   sync.Mutex
+	conn net.Conn
+}
+
+// Send sends data to server and ensures adequate response for request type
+func (mb *rtuUDPTransporter) Send(aduRequest []byte) (aduResponse []byte, err error) {
+	mb.mu.Lock()
+	defer mb.mu.Unlock()
+
+	// Check ADU request length
+	if len(aduRequest) < 2 {
+		err = ErrADURequestLength(len(aduRequest))
+		return
+	}
+
+	// Establish a new connection if not connected
+	if err = mb.connect(); err != nil {
+		return
+	}
+
+	// Send the request
+	mb.logf("modbus: send % x\n", aduRequest)
+	if _, err = mb.conn.Write(aduRequest); err != nil {
+		return
+	}
+	function := aduRequest[1]
+	functionFail := aduRequest[1] & 0x80
+	bytesToRead := calculateResponseLength(aduRequest)
+
+	var n int
+	var n1 int
+	var data [rtuMaxSize]byte
+	// We first read the minimum length and then read either the full package
+	// or the error package, depending on the error status (byte 2 of the response)
+	n, err = io.ReadAtLeast(mb.conn, data[:], rtuMinSize)
+	if err != nil {
+		return
+	}
+
+	// Check ADU response length
+	if len(data) < 2 {
+		err = ErrADUResponseLength(len(data))
+		return
+	}
+
+	// if the function is correct
+	if data[1] == function {
+		// we read the rest of the bytes
+		if n < bytesToRead {
+			if bytesToRead > rtuMinSize && bytesToRead <= rtuMaxSize {
+				n1, err = io.ReadFull(mb.conn, data[n:bytesToRead])
+				n += n1
+			}
+		}
+	} else if data[1] == functionFail {
+		// for error we need to read 5 bytes
+		if n < rtuExceptionSize {
+			n1, err = io.ReadFull(mb.conn, data[n:rtuExceptionSize])
+		}
+		n += n1
+	}
+
+	if err != nil {
+		return
+	}
+	aduResponse = data[:n]
+	mb.logf("modbus: recv % x\n", aduResponse)
+	return
+}
+
+func (mb *rtuUDPTransporter) logf(format string, v ...interface{}) {
+	if mb.Logger != nil {
+		mb.Logger.Printf(format, v...)
+	}
+}
+
+// Connect establishes a new connection to the address in Address.
+func (mb *rtuUDPTransporter) Connect() error {
+	mb.mu.Lock()
+	defer mb.mu.Unlock()
+
+	return mb.connect()
+}
+
+// connect establishes a new connection to the address in Address. Caller must hold the mutex before calling this method.
+// Since UDP is connectionless this does little more than setting up the connection object.
+func (mb *rtuUDPTransporter) connect() error {
+	if mb.conn == nil {
+		dialer := net.Dialer{}
+		conn, err := dialer.Dial("udp", mb.Address)
+		if err != nil {
+			return err
+		}
+		mb.conn = conn
+	}
+	return nil
+}
+
+// Close closes current connection.
+func (mb *rtuUDPTransporter) Close() error {
+	mb.mu.Lock()
+	defer mb.mu.Unlock()
+
+	return mb.close()
+}
+
+// close closes current connection. Caller must hold the mutex before calling this method.
+// Since UDP is connectionless this does little more than freeing up the connection object.
+func (mb *rtuUDPTransporter) close() (err error) {
+	if mb.conn != nil {
+		err = mb.conn.Close()
+		mb.conn = nil
+	}
+	return
+}