自定义读取接口&自定义写入接口

rtu_transport.go

@@ -109,6 +109,59 @@ func (rt *rtuTransport) ExecuteRequest(req *pdu) (res *pdu, err error) {
 	return
 }
 
+func (rt *rtuTransport) ExecuteRequestWithRes(req *pdu) (res *pdu, err error) {
+	var ts time.Time
+	var t time.Duration
+	var n int
+
+	// set an i/o deadline on the link
+	err = rt.link.SetDeadline(time.Now().Add(rt.timeout))
+	if err != nil {
+		return
+	}
+
+	// if the line was active less than 3.5 char times ago,
+	// let t3.5 expire before transmitting
+	t = time.Since(rt.lastActivity.Add(rt.t35))
+	if t < 0 {
+		time.Sleep(t * (-1))
+	}
+
+	ts = time.Now()
+
+	// build an RTU ADU out of the request object and
+	// send the final ADU+CRC on the wire
+	n, err = rt.link.Write(rt.assembleRTUFrame(req))
+	if err != nil {
+		return
+	}
+
+	// estimate how long the serial line was busy for.
+	// note that on most platforms, Write() will be buffered and return
+	// immediately rather than block until the buffer is drained
+	rt.lastActivity = ts.Add(time.Duration(n) * rt.t1)
+
+	// observe inter-frame delays
+	time.Sleep(rt.lastActivity.Add(rt.t35).Sub(time.Now()))
+
+	// read the response back from the wire
+	res, err = rt.readRTUFrameWithRes()
+
+	if err == ErrBadCRC || err == ErrProtocolError || err == ErrShortFrame {
+		// wait for and flush any data coming off the link to allow
+		// devices to re-sync
+		time.Sleep(time.Duration(maxRTUFrameLength) * rt.t1)
+		discard(rt.link)
+	}
+
+	// mark the time if we heard anything back
+	if err != ErrRequestTimedOut {
+		rt.lastActivity = time.Now()
+	}
+
+	return
+}
+
 // Reads a request from the rtu link.
 func (rt *rtuTransport) ReadRequest() (req *pdu, err error) {
 	// reading requests from RTU links is currently unsupported
@@ -140,7 +193,7 @@ func (rt *rtuTransport) readRTUFrame() (res *pdu, err error) {
 	var bytesNeeded int
 	var crc crc
 
-	rxbuf = make([]byte, 10243)
+	rxbuf = make([]byte, maxRTUFrameLength)
 
 	// read the serial ADU header: unit id (1 byte), function code (1 byte) and
 	// PDU length/exception code (1 byte)
@@ -198,6 +251,75 @@ func (rt *rtuTransport) readRTUFrame() (res *pdu, err error) {
 	return
 }
 
+func (rt *rtuTransport) readRTUFrameWithRes() (res *pdu, err error) {
+	var rxbuf []byte
+	var byteCount int
+	var bytesNeeded int
+	var crc crc
+
+	rxbuf = make([]byte, 4096)
+
+	// read the serial ADU header: unit id (1 byte), function code (1 byte) and
+	// PDU length/exception code (1 byte)
+	byteCount, err = io.ReadFull(rt.link, rxbuf[0:3])
+	if (byteCount > 0 || err == nil) && byteCount != 3 {
+		err = ErrShortFrame
+		return
+	}
+	if err != nil && err != io.ErrUnexpectedEOF {
+		return
+	}
+
+	// figure out how many further bytes to read
+	bytesNeeded, err = expectedResponseLenth(uint8(rxbuf[1]), uint8(rxbuf[2]))
+	if err != nil {
+		return
+	}
+
+	// we need to read 2 additional bytes of CRC after the payload
+	bytesNeeded += 2
+
+	// never read more than the max allowed frame length
+	if byteCount+bytesNeeded > maxRTUFrameLength {
+		err = ErrProtocolError
+		return
+	}
+
+	byteCount, err = io.ReadFull(rt.link, rxbuf[3:3+bytesNeeded])
+	if err != nil && err != io.ErrUnexpectedEOF {
+		return
+	}
+	if byteCount != bytesNeeded {
+		rt.logger.Warningf("expected %v bytes, received %v", bytesNeeded, byteCount)
+		err = ErrShortFrame
+		return
+	}
+
+	// compute the CRC on the entire frame, excluding the CRC
+	crc.init()
+	crc.add(rxbuf[0 : 3+bytesNeeded-2])
+
+	// compare CRC values
+	if !crc.isEqual(rxbuf[3+bytesNeeded-2], rxbuf[3+bytesNeeded-1]) {
+		err = ErrBadCRC
+		return
+	}
+
+	_, err = io.ReadFull(rt.link, rxbuf[3+bytesNeeded:])
+	if err != nil && err != io.ErrUnexpectedEOF {
+		return
+	}
+
+	res = &pdu{
+		unitId:       rxbuf[0],
+		functionCode: rxbuf[1],
+		// pass the byte count + trailing data as payload, withtout the CRC
+		payload: rxbuf[3+bytesNeeded:],
+	}
+
+	return
+}
+
 // Turns a PDU object into bytes.
 func (rt *rtuTransport) assembleRTUFrame(p *pdu) (adu []byte) {
 	var crc crc