Parsing requests returns errors that can be sent as bytes

packet/error.go

@@ -5,74 +5,121 @@ import (
  "fmt"
 )
 
+// ErrCode is enumeration for response error codes
+type ErrCode uint8
+
+const (
+ // ErrUnknown is catchall error code
+ ErrUnknown = 0
+ // ErrIllegalFunction is The function code received in the query is not an allowable action for the server.
+ // This may be because the function code is only applicable to newer devices, and was not implemented in the
+ // unit selected. It could also indicate that the server is in the wrong state to process a request of this
+ // type, for example because it is unconfigured and is being asked to return register values.
+ // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 48
+ ErrIllegalFunction = 1
+ // ErrIllegalDataAddress is The data address received in the query is not an allowable address for the server.
+ // More specifically, the combination of reference number and transfer length is invalid. For a controller with 100
+ // registers, the PDU addresses the first register as 0, and the last one as 99. If a request is submitted with a
+ // starting register address of 96 and a quantity of registers of 4, then this request will successfully
+ // operate (address-wise at least) on registers 96, 97, 98, 99. If a request is submitted with a starting
+ // register address of 96 and a quantity of registers of 5, then this request will fail with Exception
+ // Code 0x02 “Illegal Data Address” since it attempts to operate on registers 96, 97, 98, 99 and 100, and
+ // there is no register with address 100.
+ // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 48
+ ErrIllegalDataAddress = 2
+ // ErrIllegalDataValue is A value contained in the query data field is not an allowable value for server.
+ // This indicates a fault in the structure of the remainder of a complex request, such as that the implied length
+ // is incorrect. It specifically does NOT mean that a data item submitted for storage in a register has a value
+ // outside the expectation of the application program, since the MODBUS protocol is unaware of the significance of
+ // any particular value of any particular register.
+ // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 48
+ ErrIllegalDataValue = 3
+ // ErrServerFailure is An unrecoverable error occurred while the server was attempting to perform the requested action.
+ // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 48
+ ErrServerFailure = 4
+ // ErrAcknowledge is Specialized use in conjunction with programming commands. The server has accepted the request
+ // and is processing it, but a long duration of time will be required to do so. This response is returned to prevent
+ // a timeout error from occurring in the client. The client can next issue a Poll Program Complete message to
+ // determine if processing is completed.
+ // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 48
+ ErrAcknowledge = 5
+ // ErrServerBusy is Specialized use in conjunction with programming commands. The server is engaged in processing a
+ // long duration program command. The client should retransmit the message later when the server is free.
+ // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 48
+ ErrServerBusy = 6
+ // ErrMemoryParityError is Specialized use in conjunction with function codes 20 and 21 and reference type 6, to
+ // indicate that the extended file area failed to pass a consistency check.
+ // The server attempted to read record file, but detected a parity error in the memory. The client can retry
+ // the request, but service may be required on the server device.
+ // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 48
+ ErrMemoryParityError = 8
+ // ErrGatewayPathUnavailable is Specialized use in conjunction with gateways, indicates that the gateway was unable
+ // to allocate an internal communication path from the input port to the output port for processing the request.
+ // Usually means that the gateway is misconfigured or overloaded.
+ // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 49
+ ErrGatewayPathUnavailable = 10
+ // ErrGatewayTargetedDeviceResponse is Specialized use in conjunction with gateways, indicates that no response was
+ // obtained from the target device. Usually means that the device is not present on the network.
+ // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 49
+ ErrGatewayTargetedDeviceResponse = 11
+)
+
 func errorText(code uint8) string {
  switch code {
- case 1:
- // The function code received in the query is not an allowable action for the server. This may be
- // because the function code is only applicable to newer devices, and was not implemented in the
- // unit selected. It could also indicate that the server is in the wrong state to process a request of this
- // type, for example because it is unconfigured and is being asked to return register values.
- // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 48
+ case ErrIllegalFunction:
  return "Illegal function"
- case 2:
- // The data address received in the query is not an allowable address for the server. More specifically,
- // the combination of reference number and transfer length is invalid. For a controller with 100 registers,
- // the PDU addresses the first register as 0, and the last one as 99. If a request is submitted with a
- // starting register address of 96 and a quantity of registers of 4, then this request will successfully
- // operate (address-wise at least) on registers 96, 97, 98, 99. If a request is submitted with a starting
- // register address of 96 and a quantity of registers of 5, then this request will fail with Exception
- // Code 0x02 “Illegal Data Address” since it attempts to operate on registers 96, 97, 98, 99 and 100, and
- // there is no register with address 100.
- // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 48
+ case ErrIllegalDataAddress:
  return "Illegal data address"
- case 3:
- // A value contained in the query data field is not an allowable value for server. This indicates a fault in
- // the structure of the remainder of a complex request, such as that the implied length is incorrect.
- // It specifically does NOT mean that a data item submitted for storage in a register has a value outside
- // the expectation of the application program, since the MODBUS protocol is unaware of the significance of any
- // particular value of any particular register.
- // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 48
+ case ErrIllegalDataValue:
  return "Illegal data value"
- case 4:
- // An unrecoverable error occurred while the server was attempting to perform the requested action.
- // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 48
+ case ErrServerFailure:
  return "Server failure"
- case 5:
- // Specialized use in conjunction with programming commands.
- // The server has accepted the request and is processing it, but a long duration of time will be required to
- // do so. This response is returned to prevent a timeout error from occurring in the client. The client can
- // next issue a Poll Program Complete message to determine if processing is completed.
- // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 48
+ case ErrAcknowledge:
  return "Acknowledge"
- case 6:
- // Specialized use in conjunction with programming commands.
- // The server is engaged in processing a long duration program command. The client should retransmit the
- // message later when the server is free.
- // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 48
+ case ErrServerBusy:
  return "Server busy"
- case 8:
- // Specialized use in conjunction with function codes 20 and 21 and reference type 6, to indicate that the
- // extended file area failed to pass a consistency check.
- // The server attempted to read record file, but detected a parity error in the memory. The client can retry
- // the request, but service may be required on the server device.
- // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 48
+ case ErrMemoryParityError:
  return "Memory parity error"
- case 10:
- // Specialized use in conjunction with gateways, indicates that the gateway was unable to allocate an internal
- // communication path from the input port to the output port for processing the request. Usually means that
- // the gateway is misconfigured or overloaded.
- // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 49
+ case ErrGatewayPathUnavailable:
  return "Gateway path unavailable"
- case 11:
- // Specialized use in conjunction with gateways, indicates that no response was obtained from the target device.
- // Usually means that the device is not present on the network.
- // Quote from: `MODBUS Application Protocol Specification V1.1b3`, page 49
+ case ErrGatewayTargetedDeviceResponse:
  return "Gateway targeted device failed to respond"
+ case ErrUnknown:
+ fallthrough
  default:
  return fmt.Sprintf("Unknown error code: %v", code)
  }
 }
 
+// NewErrorParseTCP creates new instance of parsing error that can be sent to the client
+func NewErrorParseTCP(code uint8, message string) *ErrorParseTCP {
+ return &ErrorParseTCP{
+ Message: message,
+ Packet: ErrorResponseTCP{
+ TransactionID: 0,
+ UnitID: 0,
+ Function: 0,
+ Code: code,
+ },
+ }
+}
+
+// ErrorParseTCP is parsing error that can be sent to the client
+type ErrorParseTCP struct {
+ Message string
+ Packet ErrorResponseTCP
+}
+
+// Error translates error code to error message.
+func (e ErrorParseTCP) Error() string {
+ return e.Message
+}
+
+// Bytes returns ErrorParseTCP packet as bytes form
+func (e ErrorParseTCP) Bytes() []byte {
+ return e.Packet.Bytes()
+}
+
 // ErrorResponseTCP is TCP error response send by server to client
 type ErrorResponseTCP struct {
  TransactionID uint16
@@ -105,6 +152,34 @@ func (re ErrorResponseTCP) FunctionCode() uint8 {
  return re.Function
 }
 
+// NewErrorParseRTU creates new instance of parsing error that can be sent to the client
+func NewErrorParseRTU(code uint8, message string) *ErrorParseRTU {
+ return &ErrorParseRTU{
+ Message: message,
+ Packet: ErrorResponseRTU{
+ UnitID: 0,
+ Function: 0,
+ Code: code,
+ },
+ }
+}
+
+// ErrorParseRTU is parsing error that can be sent to the client
+type ErrorParseRTU struct {
+ Message string
+ Packet ErrorResponseRTU
+}
+
+// Error translates error code to error message.
+func (e ErrorParseRTU) Error() string {
+ return e.Message
+}
+
+// Bytes returns ErrorParseRTU packet as bytes form
+func (e ErrorParseRTU) Bytes() []byte {
+ return e.Packet.Bytes()
+}
+
 // ErrorResponseRTU is RTU error response send by server to client
 type ErrorResponseRTU struct {
  UnitID uint8

packet/packet.go

@@ -61,17 +61,17 @@ func (h MBAPHeader) bytes(dst []byte, length uint16) {
 // ParseMBAPHeader parses MBAPHeader from given bytes
 func ParseMBAPHeader(data []byte) (MBAPHeader, error) {
  if len(data) < 6 {
- return MBAPHeader{}, errors.New("data to short to contain MBAPHeader")
+ return MBAPHeader{}, NewErrorParseTCP(ErrServerFailure, "data to short to contain MBAPHeader")
  }
  if data[2] != 0x0 || data[3] != 0x00 {
- return MBAPHeader{}, errors.New("invalid protocol id")
+ return MBAPHeader{}, NewErrorParseTCP(ErrServerFailure, "invalid protocol id")
  }
  pduLen := binary.BigEndian.Uint16(data[4:6])
  if pduLen == 0 {
- return MBAPHeader{}, errors.New("pdu length in header not be 0")
+ return MBAPHeader{}, NewErrorParseTCP(ErrServerFailure, "pdu length in header can not be 0")
  }
  if len(data) != 6+int(pduLen) {
- return MBAPHeader{}, errors.New("packet length does not match length in header")
+ return MBAPHeader{}, NewErrorParseTCP(ErrServerFailure, "packet length does not match length in header")
  }
  return MBAPHeader{
  TransactionID: binary.BigEndian.Uint16(data[0:2]),

packet/packet_test.go

@@ -47,9 +47,9 @@ func TestParseMBAPHeader(t *testing.T) {
  expectError: "invalid protocol id",
  },
  {
- name: "nok, pdu length in header not be 0",
+ name: "nok, pdu length in header can not be 0",
  when: []byte{0x81, 0x80, 0x00, 0x00, 0x00, 0x00},
- expectError: "pdu length in header not be 0",
+ expectError: "pdu length in header can not be 0",
  },
  {
  name: "nok, packet length does not match length in header",

packet/readcoilsrequest.go

@@ -2,7 +2,6 @@ package packet
 
 import (
  "encoding/binary"
- "errors"
  "fmt"
  "math"
  "math/rand"
@@ -84,17 +83,26 @@ func ParseReadCoilsRequestTCP(data []byte) (*ReadCoilsRequestTCP, error) {
  if err != nil {
  return nil, err
  }
+ unitID := data[6]
  if data[7] != FunctionReadCoils {
- return nil, errors.New("received function code in packet is not 0x01")
+ tmpErr := NewErrorParseTCP(ErrIllegalFunction, "received function code in packet is not 0x01")
+ tmpErr.Packet.TransactionID = header.TransactionID
+ tmpErr.Packet.UnitID = unitID
+ tmpErr.Packet.Function = FunctionReadCoils
+ return nil, tmpErr
  }
  quantity := binary.BigEndian.Uint16(data[10:12])
  if !(quantity >= 1 && quantity <= 125) { // 0x0001 to 0x007D
- return nil, errors.New("invalid quantity. valid range 1..125")
+ tmpErr := NewErrorParseTCP(ErrIllegalDataValue, "invalid quantity. valid range 1..125")
+ tmpErr.Packet.TransactionID = header.TransactionID
+ tmpErr.Packet.UnitID = unitID
+ tmpErr.Packet.Function = FunctionReadCoils
+ return nil, tmpErr
  }
  return &ReadCoilsRequestTCP{
  MBAPHeader: header,
  ReadCoilsRequest: ReadCoilsRequest{
- UnitID: data[6],
+ UnitID: unitID,
  // function code = data[7]
  StartAddress: binary.BigEndian.Uint16(data[8:10]),
  Quantity: quantity,
@@ -140,18 +148,25 @@ func (r ReadCoilsRequestRTU) ExpectedResponseLength() int {
 func ParseReadCoilsRequestRTU(data []byte) (*ReadCoilsRequestRTU, error) {
  dLen := len(data)
  if dLen != 8 && dLen != 6 { // with or without CRC bytes
- return nil, errors.New("invalid data length to be valid packet")
+ return nil, NewErrorParseRTU(ErrServerFailure, "invalid data length to be valid packet")
  }
+ unitID := data[0]
  if data[1] != FunctionReadCoils {
- return nil, errors.New("received function code in packet is not 0x01")
+ tmpErr := NewErrorParseRTU(ErrIllegalFunction, "received function code in packet is not 0x01")
+ tmpErr.Packet.UnitID = unitID
+ tmpErr.Packet.Function = FunctionReadCoils
+ return nil, tmpErr
  }
  quantity := binary.BigEndian.Uint16(data[4:6])
  if !(quantity >= 1 && quantity <= 125) { // 0x0001 to 0x007D
- return nil, errors.New("invalid quantity. valid range 1..125")
+ tmpErr := NewErrorParseRTU(ErrIllegalDataValue, "invalid quantity. valid range 1..125")
+ tmpErr.Packet.UnitID = unitID
+ tmpErr.Packet.Function = FunctionReadCoils
+ return nil, tmpErr
  }
  return &ReadCoilsRequestRTU{
  ReadCoilsRequest: ReadCoilsRequest{
- UnitID: data[0],
+ UnitID: unitID,
  // function code = data[1]
  StartAddress: binary.BigEndian.Uint16(data[2:4]),
  Quantity: quantity,

packet/readdiscreteinputsrequest.go

@@ -2,7 +2,6 @@ package packet
 
 import (
  "encoding/binary"
- "errors"
  "fmt"
  "math"
  "math/rand"
@@ -84,17 +83,26 @@ func ParseReadDiscreteInputsRequestTCP(data []byte) (*ReadDiscreteInputsRequestT
  if err != nil {
  return nil, err
  }
+ unitID := data[6]
  if data[7] != FunctionReadDiscreteInputs {
- return nil, errors.New("received function code in packet is not 0x02")
+ 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
- return nil, errors.New("invalid quantity. valid range 1..125")
+ 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: data[6],
+ UnitID: unitID,
  // function code = data[7]
  StartAddress: binary.BigEndian.Uint16(data[8:10]),
  Quantity: quantity,
@@ -139,18 +147,25 @@ func (r ReadDiscreteInputsRequestRTU) ExpectedResponseLength() int {
 func ParseReadDiscreteInputsRequestRTU(data []byte) (*ReadDiscreteInputsRequestRTU, error) {
  dLen := len(data)
  if dLen != 8 && dLen != 6 { // with or without CRC bytes
- return nil, errors.New("invalid data length to be valid packet")
+ return nil, NewErrorParseRTU(ErrServerFailure, "invalid data length to be valid packet")
  }
+ unitID := data[0]
  if data[1] != FunctionReadDiscreteInputs {
- return nil, errors.New("received function code in packet is not 0x02")
+ 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
- return nil, errors.New("invalid quantity. valid range 1..125")
+ 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: data[0],
+ UnitID: unitID,
  // function code = data[1]
  StartAddress: binary.BigEndian.Uint16(data[2:4]),
  Quantity: quantity,