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refactor(modbus-rtu): distinct CrcMismatch/UnitMismatch desync reasons
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The RTU framer overloaded DesyncReason.TruncatedFrame for three distinct
failures — a genuine short read, a CRC-16 validation failure, and a
CRC-valid reply from the wrong RS-485 slave. Split the latter two into
dedicated CrcMismatch / UnitMismatch enum members so a future .Reason
consumer (metrics, operator diagnostics) can tell a wiring/EMI CRC fault
apart from a mis-addressed multi-drop reply. Behaviour is unchanged — all
three still throw ModbusTransportDesyncException and tear the socket down.

Framing tests now assert the specific Reason on each path.

Follow-up #12 from the Modbus RTU-over-TCP plan.

Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
This commit is contained in:
Joseph Doherty
2026-07-25 15:13:48 -04:00
parent e27eb77187
commit ee12568cab
3 changed files with 24 additions and 8 deletions
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tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ModbusRtuFramingTests.cs
+6 -3
View File
@@ -43,8 +43,9 @@ public sealed class ModbusRtuFramingTests
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>(
var ex = await Should.ThrowAsync<ModbusTransportDesyncException>(
ModbusRtuFraming.ReadResponsePduAsync(s, 0x01, TestContext.Current.CancellationToken));
ex.Reason.ShouldBe(ModbusTransportDesyncException.DesyncReason.CrcMismatch);
}
[Fact]
@@ -63,8 +64,9 @@ public sealed class ModbusRtuFramingTests
// CRC-valid FC03 frame addressed to unit 0x02, but we asked for 0x01 -> unit-mismatch desync.
var frame = ModbusCrc.Append(new byte[] { 0x02, 0x03, 0x02, 0x00, 0x0A });
await using var s = Canned(frame);
await Should.ThrowAsync<ModbusTransportDesyncException>(
var ex = await Should.ThrowAsync<ModbusTransportDesyncException>(
ModbusRtuFraming.ReadResponsePduAsync(s, 0x01, TestContext.Current.CancellationToken));
ex.Reason.ShouldBe(ModbusTransportDesyncException.DesyncReason.UnitMismatch);
}
[Fact]
@@ -86,8 +88,9 @@ public sealed class ModbusRtuFramingTests
var frame = ModbusCrc.Append(new byte[] { 0x01, 0x03, 0x02, 0x00, 0x0A });
var truncated = frame[..4];
await using var s = new DribbleStream(truncated, chunk: 2);
await Should.ThrowAsync<ModbusTransportDesyncException>(
var ex = await Should.ThrowAsync<ModbusTransportDesyncException>(
ModbusRtuFraming.ReadResponsePduAsync(s, 0x01, TestContext.Current.CancellationToken));
ex.Reason.ShouldBe(ModbusTransportDesyncException.DesyncReason.TruncatedFrame);
}
/// <summary>