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asciiclient.go
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asciiclient.go
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package modbus
import (
"encoding/hex"
"fmt"
)
// protocol frame: asciiStart + ( slaveID + functionCode + data + lrc ) + CR + LF.
const (
asciiStart = ":"
asciiEnd = "\r\n"
hexTable = "0123456789ABCDEF"
)
// ASCIIClientProvider implements ClientProvider interface.
type ASCIIClientProvider struct {
serialPort
logger
*pool
}
// check ASCIIClientProvider implements the interface ClientProvider underlying method.
var _ ClientProvider = (*ASCIIClientProvider)(nil)
// request pool, all ASCII client use this pool.
var asciiPool = newPool(asciiCharacterMaxSize)
// NewASCIIClientProvider allocates and initializes a ASCIIClientProvider.
// it will use default /dev/ttyS0 19200 8 1 N and timeout 1000.
func NewASCIIClientProvider(opts ...ClientProviderOption) *ASCIIClientProvider {
p := &ASCIIClientProvider{
logger: newLogger("modbusASCIIMaster => "),
pool: asciiPool,
}
p.autoReconnect = SerialDefaultAutoReconnect
for _, opt := range opts {
opt(p)
}
return p
}
// encode slaveID & PDU to a ASCII frame,return adu
// Start : 1 char
// slaveID : 2 chars
// ---- data Unit ----
// Function : 2 chars
// Data : 0 up to 2x252 chars
// ---- checksum ----
// LRC : 2 chars
// End : 2 chars
func (sf *protocolFrame) encodeASCIIFrame(slaveID byte, pdu ProtocolDataUnit) ([]byte, error) {
length := len(pdu.Data) + 3
if length > asciiAduMaxSize {
return nil, fmt.Errorf("modbus: length of data '%v' must not be bigger than '%v'", length, asciiAduMaxSize)
}
// Exclude the beginning colon and terminating CRLF pair characters
lrcVal := new(LRC).
Reset().
Push(slaveID).Push(pdu.FuncCode).Push(pdu.Data...).
Value()
// real ascii frame to send,
// including asciiStart + ( slaveID + functionCode + data + lrc ) + CRLF
frame := sf.adu[: 0 : length*2+3]
frame = append(frame, []byte(asciiStart)...) // the beginning colon characters
// the real adu
frame = append(frame,
hexTable[slaveID>>4], hexTable[slaveID&0x0f], // slave ID
hexTable[pdu.FuncCode>>4], hexTable[pdu.FuncCode&0x0f]) // pdu funcCode
for _, v := range pdu.Data {
frame = append(frame, hexTable[v>>4], hexTable[v&0x0f]) // pdu data
}
frame = append(frame, hexTable[lrcVal>>4], hexTable[lrcVal&0x0f]) // lrc value
// terminating CRLF characters
return append(frame, []byte(asciiEnd)...), nil
}
// decode extracts slaveID & PDU from ASCII frame and verify LRC.
func decodeASCIIFrame(adu []byte) (uint8, []byte, error) {
if len(adu) < asciiAduMinSize+6 { // Minimum size (including address, function and LRC)
return 0, nil, fmt.Errorf("modbus: response length '%v' does not meet minimum '%v'", len(adu), 9)
}
switch {
case len(adu)%2 != 1: // Length excluding colon must be an even number
return 0, nil, fmt.Errorf("modbus: response length '%v' is not an even number", len(adu)-1)
case string(adu[0:len(asciiStart)]) != asciiStart: // First char must be a colons
return 0, nil, fmt.Errorf("modbus: response frame '%x'... is not started with '%x'",
string(adu[0:len(asciiStart)]), asciiStart)
case string(adu[len(adu)-len(asciiEnd):]) != asciiEnd: // 2 last chars must be \r\n
return 0, nil, fmt.Errorf("modbus: response frame ...'%x' is not ended with '%x'",
string(adu[len(adu)-len(asciiEnd):]), asciiEnd)
}
// real adu pass Start and CRLF
dat := adu[1 : len(adu)-2]
buf := make([]byte, hex.DecodedLen(len(dat)))
length, err := hex.Decode(buf, dat)
if err != nil {
return 0, nil, err
}
// Calculate checksum
lrcVal := new(LRC).Reset().Push(buf[:length-1]...).Value()
if buf[length-1] != lrcVal { // LRC
return 0, nil, fmt.Errorf("modbus: response lrc '%x' does not match expected '%x'", buf[length-1], lrcVal)
}
return buf[0], buf[1 : length-1], nil
}
// Send request to the remote server,it implements on SendRawFrame.
func (sf *ASCIIClientProvider) Send(slaveID byte, request ProtocolDataUnit) (ProtocolDataUnit, error) {
var response ProtocolDataUnit
frame := sf.pool.get()
defer sf.pool.put(frame)
aduRequest, err := frame.encodeASCIIFrame(slaveID, request)
if err != nil {
return response, err
}
aduResponse, err := sf.SendRawFrame(aduRequest)
if err != nil {
return response, err
}
rspSlaveID, pdu, err := decodeASCIIFrame(aduResponse)
if err != nil {
return response, err
}
response = ProtocolDataUnit{pdu[0], pdu[1:]}
if err = verify(slaveID, rspSlaveID, request, response); err != nil {
return response, err
}
return response, nil
}
// SendPdu send pdu request to the remote server.
func (sf *ASCIIClientProvider) SendPdu(slaveID byte, pduRequest []byte) ([]byte, error) {
if len(pduRequest) < pduMinSize || len(pduRequest) > pduMaxSize {
return nil, fmt.Errorf("modbus: pdu size '%v' must not be between '%v' and '%v'",
len(pduRequest), pduMinSize, pduMaxSize)
}
frame := sf.pool.get()
defer sf.pool.put(frame)
request := ProtocolDataUnit{pduRequest[0], pduRequest[1:]}
aduRequest, err := frame.encodeASCIIFrame(slaveID, request)
if err != nil {
return nil, err
}
aduResponse, err := sf.SendRawFrame(aduRequest)
if err != nil {
return nil, err
}
rspSlaveID, pdu, err := decodeASCIIFrame(aduResponse)
if err != nil {
return nil, err
}
response := ProtocolDataUnit{pdu[0], pdu[1:]}
if err = verify(slaveID, rspSlaveID, request, response); err != nil {
return nil, err
}
return pdu, nil
}
// SendRawFrame send Adu frame.
func (sf *ASCIIClientProvider) SendRawFrame(aduRequest []byte) (aduResponse []byte, err error) {
sf.mu.Lock()
defer sf.mu.Unlock()
// check port is connected
if !sf.isConnected() {
return nil, ErrClosedConnection
}
// Send the request
sf.Debug("sending [% x]", aduRequest)
var tryCnt byte
for {
_, err = sf.port.Write(aduRequest)
if err == nil { // success
break
}
if sf.autoReconnect == 0 {
return
}
for {
err = sf.connect()
if err == nil {
break
}
tryCnt++
if tryCnt >= sf.autoReconnect {
return
}
}
}
// Get the response
var n int
var data [asciiCharacterMaxSize]byte
length := 0
for {
if n, err = sf.port.Read(data[length:]); err != nil {
return
}
length += n
if length >= asciiCharacterMaxSize || n == 0 {
break
}
// Expect end of frame in the data received
if length > asciiAduMinSize {
if string(data[length-len(asciiEnd):length]) == asciiEnd {
break
}
}
}
aduResponse = data[:length]
sf.Debug("received [% x]", aduResponse)
return aduResponse, nil
}