自定义读取接口&自定义写入接口
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@@ -9,23 +9,23 @@ import (
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)
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const (
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maxTCPFrameLength int = 260
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mbapHeaderLength int = 7
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maxTCPFrameLength int = 260
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mbapHeaderLength int = 7
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)
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type tcpTransport struct {
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logger *logger
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socket net.Conn
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timeout time.Duration
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lastTxnId uint16
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logger *logger
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socket net.Conn
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timeout time.Duration
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lastTxnId uint16
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}
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// Returns a new TCP transport.
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func newTCPTransport(socket net.Conn, timeout time.Duration, customLogger *log.Logger) (tt *tcpTransport) {
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tt = &tcpTransport{
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socket: socket,
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timeout: timeout,
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logger: newLogger(fmt.Sprintf("tcp-transport(%s)", socket.RemoteAddr()), customLogger),
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socket: socket,
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timeout: timeout,
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logger: newLogger(fmt.Sprintf("tcp-transport(%s)", socket.RemoteAddr()), customLogger),
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}
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return
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@@ -33,7 +33,7 @@ func newTCPTransport(socket net.Conn, timeout time.Duration, customLogger *log.L
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// Closes the underlying tcp socket.
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func (tt *tcpTransport) Close() (err error) {
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err = tt.socket.Close()
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err = tt.socket.Close()
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return
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}
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@@ -41,7 +41,7 @@ func (tt *tcpTransport) Close() (err error) {
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// Runs a request across the socket and returns a response.
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func (tt *tcpTransport) ExecuteRequest(req *pdu) (res *pdu, err error) {
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// set an i/o deadline on the socket (read and write)
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err = tt.socket.SetDeadline(time.Now().Add(tt.timeout))
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err = tt.socket.SetDeadline(time.Now().Add(tt.timeout))
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if err != nil {
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return
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}
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@@ -49,7 +49,7 @@ func (tt *tcpTransport) ExecuteRequest(req *pdu) (res *pdu, err error) {
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// increase the transaction ID counter
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tt.lastTxnId++
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_, err = tt.socket.Write(tt.assembleMBAPFrame(tt.lastTxnId, req))
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_, err = tt.socket.Write(tt.assembleMBAPFrame(tt.lastTxnId, req))
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if err != nil {
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return
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}
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@@ -59,30 +59,34 @@ func (tt *tcpTransport) ExecuteRequest(req *pdu) (res *pdu, err error) {
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return
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}
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func (tt *tcpTransport) ExecuteRequestWithRes(req *pdu) (res *pdu, err error) {
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return nil, nil
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}
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// Reads a request from the socket.
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func (tt *tcpTransport) ReadRequest() (req *pdu, err error) {
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var txnId uint16
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var txnId uint16
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// set an i/o deadline on the socket (read and write)
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err = tt.socket.SetDeadline(time.Now().Add(tt.timeout))
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err = tt.socket.SetDeadline(time.Now().Add(tt.timeout))
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if err != nil {
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return
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}
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req, txnId, err = tt.readMBAPFrame()
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req, txnId, err = tt.readMBAPFrame()
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if err != nil {
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return
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}
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// store the incoming transaction id
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tt.lastTxnId = txnId
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tt.lastTxnId = txnId
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return
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}
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// Writes a response to the socket.
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func (tt *tcpTransport) WriteResponse(res *pdu) (err error) {
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_, err = tt.socket.Write(tt.assembleMBAPFrame(tt.lastTxnId, res))
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_, err = tt.socket.Write(tt.assembleMBAPFrame(tt.lastTxnId, res))
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if err != nil {
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return
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}
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@@ -93,11 +97,11 @@ func (tt *tcpTransport) WriteResponse(res *pdu) (err error) {
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// Reads as many MBAP+modbus frames as necessary until either the response
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// matching tt.lastTxnId is received or an error occurs.
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func (tt *tcpTransport) readResponse() (res *pdu, err error) {
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var txnId uint16
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var txnId uint16
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for {
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// grab a frame
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res, txnId, err = tt.readMBAPFrame()
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res, txnId, err = tt.readMBAPFrame()
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// ignore unknown protocol identifiers
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if err == ErrUnknownProtocolId {
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@@ -111,9 +115,9 @@ func (tt *tcpTransport) readResponse() (res *pdu, err error) {
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// ignore unknown transaction identifiers
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if tt.lastTxnId != txnId {
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tt.logger.Warningf("received unexpected transaction id " +
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"(expected 0x%04x, received 0x%04x)",
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tt.lastTxnId, txnId)
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tt.logger.Warningf("received unexpected transaction id "+
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"(expected 0x%04x, received 0x%04x)",
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tt.lastTxnId, txnId)
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continue
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}
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@@ -125,33 +129,33 @@ func (tt *tcpTransport) readResponse() (res *pdu, err error) {
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// Reads an entire frame (MBAP header + modbus PDU) from the socket.
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func (tt *tcpTransport) readMBAPFrame() (p *pdu, txnId uint16, err error) {
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var rxbuf []byte
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var bytesNeeded int
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var protocolId uint16
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var unitId uint8
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var rxbuf []byte
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var bytesNeeded int
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var protocolId uint16
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var unitId uint8
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// read the MBAP header
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rxbuf = make([]byte, mbapHeaderLength)
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_, err = io.ReadFull(tt.socket, rxbuf)
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rxbuf = make([]byte, mbapHeaderLength)
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_, err = io.ReadFull(tt.socket, rxbuf)
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if err != nil {
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return
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}
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// decode the transaction identifier
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txnId = bytesToUint16(BIG_ENDIAN, rxbuf[0:2])
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txnId = bytesToUint16(BIG_ENDIAN, rxbuf[0:2])
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// decode the protocol identifier
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protocolId = bytesToUint16(BIG_ENDIAN, rxbuf[2:4])
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protocolId = bytesToUint16(BIG_ENDIAN, rxbuf[2:4])
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// store the source unit id
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unitId = rxbuf[6]
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unitId = rxbuf[6]
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// determine how many more bytes we need to read
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bytesNeeded = int(bytesToUint16(BIG_ENDIAN, rxbuf[4:6]))
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bytesNeeded = int(bytesToUint16(BIG_ENDIAN, rxbuf[4:6]))
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// the byte count includes the unit ID field, which we already have
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bytesNeeded--
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// never read more than the max allowed frame length
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if bytesNeeded + mbapHeaderLength > maxTCPFrameLength {
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if bytesNeeded+mbapHeaderLength > maxTCPFrameLength {
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err = ErrProtocolError
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return
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}
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@@ -163,8 +167,8 @@ func (tt *tcpTransport) readMBAPFrame() (p *pdu, txnId uint16, err error) {
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}
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// read the PDU
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rxbuf = make([]byte, bytesNeeded)
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_, err = io.ReadFull(tt.socket, rxbuf)
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rxbuf = make([]byte, bytesNeeded)
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_, err = io.ReadFull(tt.socket, rxbuf)
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if err != nil {
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return
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}
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@@ -178,9 +182,9 @@ func (tt *tcpTransport) readMBAPFrame() (p *pdu, txnId uint16, err error) {
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// store unit id, function code and payload in the PDU object
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p = &pdu{
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unitId: unitId,
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functionCode: rxbuf[0],
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payload: rxbuf[1:],
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unitId: unitId,
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functionCode: rxbuf[0],
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payload: rxbuf[1:],
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}
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return
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@@ -189,17 +193,17 @@ func (tt *tcpTransport) readMBAPFrame() (p *pdu, txnId uint16, err error) {
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// Turns a PDU into an MBAP frame (MBAP header + PDU) and returns it as bytes.
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func (tt *tcpTransport) assembleMBAPFrame(txnId uint16, p *pdu) (payload []byte) {
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// transaction identifier
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payload = uint16ToBytes(BIG_ENDIAN, txnId)
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payload = uint16ToBytes(BIG_ENDIAN, txnId)
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// protocol identifier (always 0x0000)
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payload = append(payload, 0x00, 0x00)
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payload = append(payload, 0x00, 0x00)
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// length (covers unit identifier + function code + payload fields)
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payload = append(payload, uint16ToBytes(BIG_ENDIAN, uint16(2 + len(p.payload)))...)
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payload = append(payload, uint16ToBytes(BIG_ENDIAN, uint16(2+len(p.payload)))...)
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// unit identifier
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payload = append(payload, p.unitId)
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payload = append(payload, p.unitId)
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// function code
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payload = append(payload, p.functionCode)
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payload = append(payload, p.functionCode)
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// payload
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payload = append(payload, p.payload...)
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payload = append(payload, p.payload...)
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return
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}
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