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Fix transaction identifier collision #157

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Fix transaction identifier collision #157

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12 changes: 9 additions & 3 deletions src/FluentModbus/Client/ModbusTcpClient.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -219,16 +219,18 @@ protected override Span<byte> TransceiveFrame(byte unitIdentifier, ModbusFunctio

writer.Seek(0, SeekOrigin.Begin);

var requestTransactionIdentifier = GetTransactionIdentifier();

if (BitConverter.IsLittleEndian)
{
writer.WriteReverse(GetTransactionIdentifier()); // 00-01 Transaction Identifier
writer.WriteReverse(requestTransactionIdentifier); // 00-01 Transaction Identifier
writer.WriteReverse((ushort)0); // 02-03 Protocol Identifier
writer.WriteReverse((ushort)(frameLength - 6)); // 04-05 Length
}

else
{
writer.Write(GetTransactionIdentifier()); // 00-01 Transaction Identifier
writer.Write(requestTransactionIdentifier); // 00-01 Transaction Identifier
writer.Write((ushort)0); // 02-03 Protocol Identifier
writer.Write((ushort)(frameLength - 6)); // 04-05 Length
}
Expand Down Expand Up @@ -291,7 +293,11 @@ protected override Span<byte> TransceiveFrame(byte unitIdentifier, ModbusFunctio
if (!isParsed) // read MBAP header only once
{
// read MBAP header
_ = reader.ReadUInt16Reverse(); // 00-01 Transaction Identifier
var responseTransactionIdentifier = reader.ReadUInt16Reverse(); // 00-01 Transaction Identifier
if (requestTransactionIdentifier != responseTransactionIdentifier)
{
throw new ModbusException(ErrorMessage.ModbusClient_InvalidTransactionIdentifier);
}
var protocolIdentifier = reader.ReadUInt16Reverse(); // 02-03 Protocol Identifier
bytesFollowing = reader.ReadUInt16Reverse(); // 04-05 Length
_ = reader.ReadByte(); // 06 Unit Identifier
Expand Down
18 changes: 12 additions & 6 deletions src/FluentModbus/Client/ModbusTcpClientAsync.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -15,24 +15,26 @@ protected override async Task<Memory<byte>> TransceiveFrameAsync(byte unitIdenti
var frameBuffer = _frameBuffer;
var writer = _frameBuffer.Writer;
var reader = _frameBuffer.Reader;

// build request
writer.Seek(7, SeekOrigin.Begin);
extendFrame(writer);
var frameLength = (int)writer.BaseStream.Position;

writer.Seek(0, SeekOrigin.Begin);

var requestTransactionIdentifier = GetTransactionIdentifier();

if (BitConverter.IsLittleEndian)
{
writer.WriteReverse(GetTransactionIdentifier()); // 00-01 Transaction Identifier
writer.WriteReverse(requestTransactionIdentifier); // 00-01 Transaction Identifier
writer.WriteReverse((ushort)0); // 02-03 Protocol Identifier
writer.WriteReverse((ushort)(frameLength - 6)); // 04-05 Length
}

else
{
writer.Write(GetTransactionIdentifier()); // 00-01 Transaction Identifier
writer.Write(requestTransactionIdentifier); // 00-01 Transaction Identifier
writer.Write((ushort)0); // 02-03 Protocol Identifier
writer.Write((ushort)(frameLength - 6)); // 04-05 Length
}
Expand Down Expand Up @@ -95,10 +97,14 @@ protected override async Task<Memory<byte>> TransceiveFrameAsync(byte unitIdenti
if (!isParsed) // read MBAP header only once
{
// read MBAP header
_ = reader.ReadUInt16Reverse(); // 00-01 Transaction Identifier
var responseTransactionIdentifier = reader.ReadUInt16Reverse(); // 00-01 Transaction Identifier
if (requestTransactionIdentifier != responseTransactionIdentifier)
{
throw new ModbusException(ErrorMessage.ModbusClient_InvalidTransactionIdentifier);
}
var protocolIdentifier = reader.ReadUInt16Reverse(); // 02-03 Protocol Identifier
bytesFollowing = reader.ReadUInt16Reverse(); // 04-05 Length
_ = reader.ReadByte(); // 06 Unit Identifier
bytesFollowing = reader.ReadUInt16Reverse(); // 04-05 Length
_ = reader.ReadByte(); // 06 Unit Identifier

if (protocolIdentifier != 0)
throw new ModbusException(ErrorMessage.ModbusClient_InvalidProtocolIdentifier);
Expand Down
9 changes: 9 additions & 0 deletions src/FluentModbus/Resources/ErrorMessage.Designer.cs
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3 changes: 3 additions & 0 deletions src/FluentModbus/Resources/ErrorMessage.resx
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Original file line number Diff line number Diff line change
Expand Up @@ -165,6 +165,9 @@
<data name="ModbusClient_InvalidProtocolIdentifier" xml:space="preserve">
<value>The protocol identifier is invalid.</value>
</data>
<data name="ModbusClient_InvalidTransactionIdentifier" xml:space="preserve">
<value>The transaction identifier is invalid.</value>
</data>
<data name="ModbusClient_InvalidResponseFunctionCode" xml:space="preserve">
<value>The responsed function code is invalid.</value>
</data>
Expand Down