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readdiscreteinputsrequest.go
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/
readdiscreteinputsrequest.go
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package packet
import (
"encoding/binary"
"fmt"
"math"
"math/rand"
)
// ReadDiscreteInputsRequestTCP is TCP Request for Read Discrete Inputs (FC=02)
//
// Example packet: 0x81 0x80 0x00 0x00 0x00 0x06 0x10 0x02 0x00 0x6B 0x00 0x03
// 0x81 0x80 - transaction id (0,1)
// 0x00 0x00 - protocol id (2,3)
// 0x00 0x06 - number of bytes in the message (PDU = ProtocolDataUnit) to follow (4,5)
// 0x10 - unit id (6)
// 0x02 - function code (7)
// 0x00 0x6B - start address (8,9)
// 0x00 0x03 - discrete inputs quantity to return (10,11)
type ReadDiscreteInputsRequestTCP struct {
MBAPHeader
ReadDiscreteInputsRequest
}
// ReadDiscreteInputsRequestRTU is RTU Request for Read Discrete Inputs (FC=02)
//
// Example packet: 0x10 0x02 0x00 0x6B 0x00 0x03 0x4a 0x96
// 0x10 - unit id (0)
// 0x02 - function code (1)
// 0x00 0x6B - start address (2,3)
// 0x00 0x03 - discrete inputs quantity to return (4,5)
// 0x4a 0x96 - CRC16 (6,7)
type ReadDiscreteInputsRequestRTU struct {
ReadDiscreteInputsRequest
}
// ReadDiscreteInputsRequest is Request for Read Discrete Inputs (FC=02)
type ReadDiscreteInputsRequest struct {
UnitID uint8
StartAddress uint16
Quantity uint16
}
// NewReadDiscreteInputsRequestTCP creates new instance of Read Discrete Inputs TCP request
func NewReadDiscreteInputsRequestTCP(unitID uint8, startAddress uint16, quantity uint16) (*ReadDiscreteInputsRequestTCP, error) {
if quantity == 0 || quantity > 2000 {
// 2000 coils is due that in response data size field is 1 byte so max 250*8=2000 coils can be returned
return nil, fmt.Errorf("quantity is out of range (1-2000): %v", quantity)
}
return &ReadDiscreteInputsRequestTCP{
MBAPHeader: MBAPHeader{
TransactionID: uint16(1 + rand.Intn(65534)),
ProtocolID: 0,
},
ReadDiscreteInputsRequest: ReadDiscreteInputsRequest{
UnitID: unitID,
// function code is added by Bytes()
StartAddress: startAddress,
Quantity: quantity,
},
}, nil
}
// Bytes returns ReadDiscreteInputsRequestTCP packet as bytes form
func (r ReadDiscreteInputsRequestTCP) Bytes() []byte {
length := uint16(6)
result := make([]byte, tcpMBAPHeaderLen+length)
r.MBAPHeader.bytes(result[0:6], length)
r.ReadDiscreteInputsRequest.bytes(result[6:12])
return result
}
// ExpectedResponseLength returns length of bytes that valid response to this request would be
func (r ReadDiscreteInputsRequestTCP) ExpectedResponseLength() int {
// response = 6 header len + 1 unitid + 1 fc + 1 coil byte count + N data len (1-256)
return 6 + 3 + r.coilByteLength()
}
// ParseReadDiscreteInputsRequestTCP parses given bytes into ReadDiscreteInputsRequestTCP
func ParseReadDiscreteInputsRequestTCP(data []byte) (*ReadDiscreteInputsRequestTCP, error) {
header, err := ParseMBAPHeader(data)
if err != nil {
return nil, err
}
unitID := data[6]
if data[7] != FunctionReadDiscreteInputs {
tmpErr := NewErrorParseTCP(ErrIllegalFunction, "received function code in packet is not 0x02")
tmpErr.Packet.TransactionID = header.TransactionID
tmpErr.Packet.UnitID = unitID
tmpErr.Packet.Function = FunctionReadDiscreteInputs
return nil, tmpErr
}
quantity := binary.BigEndian.Uint16(data[10:12])
if !(quantity >= 1 && quantity <= 125) { // 0x0001 to 0x007D
tmpErr := NewErrorParseTCP(ErrIllegalDataValue, "invalid quantity. valid range 1..125")
tmpErr.Packet.TransactionID = header.TransactionID
tmpErr.Packet.UnitID = unitID
tmpErr.Packet.Function = FunctionReadDiscreteInputs
return nil, tmpErr
}
return &ReadDiscreteInputsRequestTCP{
MBAPHeader: header,
ReadDiscreteInputsRequest: ReadDiscreteInputsRequest{
UnitID: unitID,
// function code = data[7]
StartAddress: binary.BigEndian.Uint16(data[8:10]),
Quantity: quantity,
},
}, nil
}
// NewReadDiscreteInputsRequestRTU creates new instance of Read Discrete Inputs RTU request
func NewReadDiscreteInputsRequestRTU(unitID uint8, startAddress uint16, quantity uint16) (*ReadDiscreteInputsRequestRTU, error) {
if quantity == 0 || quantity > 2000 {
// 2000 coils is due that in response data size field is 1 byte so max 250*8=2000 coils can be returned
return nil, fmt.Errorf("quantity is out of range (1-2000): %v", quantity)
}
return &ReadDiscreteInputsRequestRTU{
ReadDiscreteInputsRequest: ReadDiscreteInputsRequest{
UnitID: unitID,
// function code is added by Bytes()
StartAddress: startAddress,
Quantity: quantity,
},
}, nil
}
// Bytes returns ReadDiscreteInputsRequestRTU packet as bytes form
func (r ReadDiscreteInputsRequestRTU) Bytes() []byte {
result := make([]byte, 6+2)
bytes := r.ReadDiscreteInputsRequest.bytes(result)
crc := CRC16(bytes[:6])
result[6] = uint8(crc)
result[7] = uint8(crc >> 8)
return result
}
// ExpectedResponseLength returns length of bytes that valid response to this request would be
func (r ReadDiscreteInputsRequestRTU) ExpectedResponseLength() int {
// response = 1 UnitID + 1 functionCode + 2 coils byte count + N coils data
return 4 + r.coilByteLength()
}
// ParseReadDiscreteInputsRequestRTU parses given bytes into ReadDiscreteInputsRequestRTU
func ParseReadDiscreteInputsRequestRTU(data []byte) (*ReadDiscreteInputsRequestRTU, error) {
dLen := len(data)
if dLen != 8 && dLen != 6 { // with or without CRC bytes
return nil, NewErrorParseRTU(ErrServerFailure, "invalid data length to be valid packet")
}
unitID := data[0]
if data[1] != FunctionReadDiscreteInputs {
tmpErr := NewErrorParseRTU(ErrIllegalFunction, "received function code in packet is not 0x02")
tmpErr.Packet.UnitID = unitID
tmpErr.Packet.Function = FunctionReadDiscreteInputs
return nil, tmpErr
}
quantity := binary.BigEndian.Uint16(data[4:6])
if !(quantity >= 1 && quantity <= 125) { // 0x0001 to 0x007D
tmpErr := NewErrorParseRTU(ErrIllegalDataValue, "invalid quantity. valid range 1..125")
tmpErr.Packet.UnitID = unitID
tmpErr.Packet.Function = FunctionReadDiscreteInputs
return nil, tmpErr
}
return &ReadDiscreteInputsRequestRTU{
ReadDiscreteInputsRequest: ReadDiscreteInputsRequest{
UnitID: unitID,
// function code = data[1]
StartAddress: binary.BigEndian.Uint16(data[2:4]),
Quantity: quantity,
},
}, nil
}
// FunctionCode returns function code of this request
func (r ReadDiscreteInputsRequest) FunctionCode() uint8 {
return FunctionReadDiscreteInputs
}
func (r ReadDiscreteInputsRequest) coilByteLength() int {
return int(math.Ceil(float64(r.Quantity) / 8))
}
// Bytes returns ReadDiscreteInputsRequest packet as bytes form
func (r ReadDiscreteInputsRequest) Bytes() []byte {
return r.bytes(make([]byte, 6))
}
func (r ReadDiscreteInputsRequest) bytes(bytes []byte) []byte {
putReadRequestBytes(bytes, r.UnitID, FunctionReadDiscreteInputs, r.StartAddress, r.Quantity)
return bytes
}