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feat(modbus-rtu): add ModbusRtuFraming (ADU build + FC-aware length-less deframe)

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Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
This commit is contained in:
Joseph Doherty
2026-07-24 13:33:59 -04:00
parent 8d0f60ec51
commit eed6617784
2 changed files with 228 additions and 0 deletions
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tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ModbusRtuFramingTests.cs
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using Shouldly;
using Xunit;
namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests;
public sealed class ModbusRtuFramingTests
{
private static MemoryStream Canned(params byte[] frame) => new(frame);
[Fact]
public void BuildAdu_prefixes_unit_and_appends_crc()
{
var adu = ModbusRtuFraming.BuildAdu(0x01, new byte[] { 0x03, 0x00, 0x00, 0x00, 0x01 });
adu.ShouldBe(new byte[] { 0x01, 0x03, 0x00, 0x00, 0x00, 0x01, 0x84, 0x0A });
}
[Fact]
public async Task ReadResponse_FC03_returns_bare_pdu()
{
// addr=01 fc=03 byteCount=02 data=00 0A + CRC(lo,hi)
var body = new byte[] { 0x01, 0x03, 0x02, 0x00, 0x0A };
var frame = ModbusCrc.Append(body);
await using var s = Canned(frame);
var pdu = await ModbusRtuFraming.ReadResponsePduAsync(s, 0x01, TestContext.Current.CancellationToken);
pdu.ShouldBe(new byte[] { 0x03, 0x02, 0x00, 0x0A }); // fc + byteCount + data, no addr/CRC
}
[Fact]
public async Task ReadResponse_exception_frame_throws_ModbusException()
{
// addr=01 fc=0x83 exc=0x02 + CRC
var frame = ModbusCrc.Append(new byte[] { 0x01, 0x83, 0x02 });
await using var s = Canned(frame);
var ex = await Should.ThrowAsync<ModbusException>(
ModbusRtuFraming.ReadResponsePduAsync(s, 0x01, TestContext.Current.CancellationToken));
ex.FunctionCode.ShouldBe((byte)0x03);
ex.ExceptionCode.ShouldBe((byte)0x02);
}
[Fact]
public async Task ReadResponse_bad_crc_throws_desync()
{
var frame = ModbusCrc.Append(new byte[] { 0x01, 0x03, 0x02, 0x00, 0x0A });
frame[^1] ^= 0xFF; // corrupt CRC high byte
await using var s = Canned(frame);
await Should.ThrowAsync<ModbusTransportDesyncException>(
ModbusRtuFraming.ReadResponsePduAsync(s, 0x01, TestContext.Current.CancellationToken));
}
[Fact]
public async Task ReadResponse_FC06_write_echo_returns_four_byte_pdu()
{
// addr=01 fc=06 addr=00 07 value=00 2A + CRC -> PDU = 06 00 07 00 2A
var frame = ModbusCrc.Append(new byte[] { 0x01, 0x06, 0x00, 0x07, 0x00, 0x2A });
await using var s = Canned(frame);
var pdu = await ModbusRtuFraming.ReadResponsePduAsync(s, 0x01, TestContext.Current.CancellationToken);
pdu.ShouldBe(new byte[] { 0x06, 0x00, 0x07, 0x00, 0x2A });
}
}