first init

udp.go

@@ -0,0 +1,102 @@
+package modbus
+
+import (
+	"net"
+	"time"
+)
+
+// udpSockWrapper wraps a net.UDPConn (UDP socket) to
+// allow transports to consume data off the network socket on
+// a byte per byte basis rather than datagram by datagram.
+type udpSockWrapper struct {
+	leftoverCount int
+	rxbuf         []byte
+	sock          *net.UDPConn
+}
+
+func newUDPSockWrapper(sock net.Conn) (usw *udpSockWrapper) {
+	usw = &udpSockWrapper{
+		rxbuf: make([]byte, maxTCPFrameLength),
+		sock:  sock.(*net.UDPConn),
+	}
+
+	return
+}
+
+func (usw *udpSockWrapper) Read(buf []byte) (rlen int, err error) {
+	var copied int
+
+	if usw.leftoverCount > 0 {
+		// if we're holding onto any bytes from a previous datagram,
+		// use them to satisfy the read (potentially partially)
+		copied = copy(buf, usw.rxbuf[0:usw.leftoverCount])
+
+		if usw.leftoverCount > copied {
+			// move any leftover bytes to the beginning of the buffer
+			copy(usw.rxbuf, usw.rxbuf[copied:usw.leftoverCount])
+		}
+		// make a note of how many leftover bytes we have in the buffer
+		usw.leftoverCount -= copied
+	} else {
+		// read up to maxTCPFrameLength bytes from the socket
+		rlen, err = usw.sock.Read(usw.rxbuf)
+		if err != nil {
+			return
+		}
+		// copy as many bytes as possible to satisfy the read
+		copied = copy(buf, usw.rxbuf[0:rlen])
+
+		if rlen > copied {
+			// move any leftover bytes to the beginning of the buffer
+			copy(usw.rxbuf, usw.rxbuf[copied:rlen])
+		}
+		// make a note of how many leftover bytes we have in the buffer
+		usw.leftoverCount = rlen - copied
+	}
+
+	rlen = copied
+
+	return
+}
+
+func (usw *udpSockWrapper) Close() (err error) {
+	err = usw.sock.Close()
+
+	return
+}
+
+func (usw *udpSockWrapper) Write(buf []byte) (wlen int, err error) {
+	wlen, err = usw.sock.Write(buf)
+
+	return
+}
+
+func (usw *udpSockWrapper) SetDeadline(deadline time.Time) (err error) {
+	err = usw.sock.SetDeadline(deadline)
+
+	return
+}
+
+func (usw *udpSockWrapper) SetReadDeadline(deadline time.Time) (err error) {
+	err = usw.sock.SetReadDeadline(deadline)
+
+	return
+}
+
+func (usw *udpSockWrapper) SetWriteDeadline(deadline time.Time) (err error) {
+	err = usw.sock.SetWriteDeadline(deadline)
+
+	return
+}
+
+func (usw *udpSockWrapper) LocalAddr() (addr net.Addr) {
+	addr = usw.sock.LocalAddr()
+
+	return
+}
+
+func (usw *udpSockWrapper) RemoteAddr() (addr net.Addr) {
+	addr = usw.sock.RemoteAddr()
+
+	return
+}