Add support for Ascii over UDP client

asciiudpclient.go

@@ -0,0 +1,102 @@
+// Copyright 2014 Quoc-Viet Nguyen. All rights reserved.
+// This software may be modified and distributed under the terms
+// of the BSD license. See the LICENSE file for details.
+
+package modbus
+
+import (
+	"fmt"
+	"log"
+	"net"
+	"sync"
+	"time"
+)
+
+const (
+	udpTimeout = 10 * time.Second
+)
+
+// ASCIIClientHandler implements Packager and Transporter interface.
+type ASCIIUDPClientHandler struct {
+	asciiPackager
+	asciiUdpTransporter
+}
+
+// NewASCIIClientHandler allocates and initializes a ASCIIClientHandler.
+// The address format is ip:port
+func NewASCIIUDPClientHandler(address string, slaveId int) *ASCIIUDPClientHandler {
+	handler := &ASCIIUDPClientHandler{}
+	handler.Address = address
+	handler.SlaveId = byte(slaveId)
+	handler.Timeout = udpTimeout
+	return handler
+}
+
+// ASCIIClient creates ASCII client with default handler and given connect string.
+func ASCIIUDPClient(address string, slaveId int) Client {
+	handler := NewASCIIUDPClientHandler(address, slaveId)
+	return NewClient(handler)
+}
+
+
+func (mb *asciiUdpTransporter) logf(format string, v ...interface{}) {
+	if mb.Logger != nil {
+		mb.Logger.Printf(format, v...)
+	}
+}
+
+
+// asciiUdpTransporter implements Transporter interface.
+type asciiUdpTransporter struct {
+	// Connect string
+	Address string
+	// Connect & Read timeout
+	Timeout time.Duration
+	// Transmission logger
+	Logger *log.Logger
+
+	// UDP "connection"
+	mu           sync.Mutex
+	conn         *net.UDPConn
+}
+
+func (mb *asciiUdpTransporter) Send(aduRequest []byte) (aduResponse []byte, err error) {
+	mb.mu.Lock()
+	defer mb.mu.Unlock()
+
+	// Make sure port is connected
+	if err = mb.connect(); err != nil {
+		return
+	}
+
+	// Send the request
+	mb.logf("modbus: sending %q\n", aduRequest)
+	if _, err = mb.conn.Write(aduRequest); err != nil {
+		return
+	}
+	// Get the response
+	var length int
+	data := make([]byte, asciiMaxSize)
+	mb.conn.SetDeadline(time.Now().Add(mb.Timeout))
+	length, _, err = mb.conn.ReadFromUDP(data)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	aduResponse = data[0:length]
+	mb.logf("modbus: received %q\n", aduResponse)
+	return
+}
+
+
+func (mb *asciiUdpTransporter) connect() error {
+	if mb.conn == nil {
+		s, err := net.ResolveUDPAddr("udp4", mb.Address)
+		conn, err := net.DialUDP("udp4", nil, s)
+		if err != nil {
+			return err
+		}
+		mb.conn = conn
+	}
+	return nil
+}