Phase 3 PR 21 — Modbus TCP driver: first native-protocol greenfield for v2. New src/Driver.Modbus project with ModbusDriver implementing IDriver + ITagDiscovery + IReadable + IWritable. Validates the driver-agnostic abstractions (IAddressSpaceBuilder, DriverAttributeInfo, DataValueSnapshot, WriteRequest/WriteResult) generalize beyond Galaxy — nothing Galaxy-specific is used here. ModbusDriverOptions carries Host/Port/UnitId/Timeout + a pre-declared tag list (Modbus has no discovery protocol — tags are configuration). IModbusTransport abstracts the socket layer so tests swap in-memory fakes; concrete ModbusTcpTransport speaks the MBAP ADU (TxId + Protocol=0 + Length + UnitId + PDU) over TcpClient, serializes requests through a semaphore for single-flight in-order responses, validates the response TxId matches, surfaces server exception PDUs as ModbusException with function code + exception code. DiscoverAsync streams one folder per driver with a BaseDataVariable per tag + DriverAttributeInfo that flags writable tags as SecurityClassification.Operate vs ViewOnly for read-only regions. ReadAsync routes per-tag by ModbusRegion: FC01 for Coils, FC02 for DiscreteInputs, FC03 for HoldingRegisters, FC04 for InputRegisters; register values decoded through System.Buffers.Binary.BinaryPrimitives (BigEndian for single-register Int16/UInt16 + two-register Int32/UInt32/Float32 per standard modbus word-swap conventions). WriteAsync uses FC05 (Write Single Coil with 0xFF00/0x0000 encoding) for booleans, FC06 (Write Single Register) for 16-bit types, FC16 (Write Multiple Registers) for 32-bit types. Unknown tag → BadNodeIdUnknown; write to InputRegister or DiscreteInput or Writable=false tag → BadNotWritable; exception during transport → BadInternalError + driver health Degraded. Subscriptions + Historian + Alarms deliberately out of scope — Modbus has no push model (subscribe would be a polling overlay, additive PR) and no history/alarm semantics at the protocol level. Tests (9 new ModbusDriverTests): InitializeAsync connects + populates the tag map + sets health=Healthy; Read Int16 from HoldingRegister returns BigEndian value; Read Float32 spans two registers BigEndian (IEEE 754 single for 25.5f round-trips exactly); Read Coil returns boolean from the bit-packed response; unknown tag name returns BadNodeIdUnknown without an exception; Write UInt16 round-trips via FC06; Write Float32 uses FC16 (two-register write verified by decoding back through the fake register bank); Write to InputRegister returns BadNotWritable; Discover streams one folder + one variable per tag with correct DriverDataType mapping (Int16/Int32→Int32, UInt16/UInt32→Int32, Float32→Float32, Bool→Boolean). FakeTransport simulates a 256-register/256-coil bank + implements the 7 function codes the driver uses. slnx updated with the new src + tests entries. Full solution post-add: 0 errors, 189 tests pass (9 Modbus + 180 pre-existing). IDriver abstraction validated against a fundamentally different protocol — Modbus TCP has no AlarmExtension, no ScanState, no IPC boundary, no historian, no LDAP — and the same builder/reader/writer contract plugged straight in. Future PRs on this driver: ISubscribable via a polling loop, IHostConnectivityProbe for dead-device detection, PLC-specific data-type extensions (Int64/BCD/string-in-registers).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
2026-04-18 11:55:21 -04:00
parent 52791952dd
commit 058c3dddd3
8 changed files with 789 additions and 0 deletions
--- a/src/ZB.MOM.WW.OtOpcUa.Driver.Modbus/ModbusTcpTransport.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Driver.Modbus/ModbusTcpTransport.cs
@@ -0,0 +1,113 @@
+using System.Net.Sockets;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus;
+
+/// <summary>
+///     Concrete Modbus TCP transport. Wraps a single <see cref="TcpClient"/> and serializes
+///     requests so at most one transaction is in-flight at a time — Modbus servers typically
+///     support concurrent transactions, but the single-flight model keeps the wire trace
+///     easy to diagnose and avoids interleaved-response correlation bugs.
+/// </summary>
+public sealed class ModbusTcpTransport : IModbusTransport
+{
+    private readonly string _host;
+    private readonly int _port;
+    private readonly TimeSpan _timeout;
+    private readonly SemaphoreSlim _gate = new(1, 1);
+    private TcpClient? _client;
+    private NetworkStream? _stream;
+    private ushort _nextTx;
+    private bool _disposed;
+
+    public ModbusTcpTransport(string host, int port, TimeSpan timeout)
+    {
+        _host = host;
+        _port = port;
+        _timeout = timeout;
+    }
+
+    public async Task ConnectAsync(CancellationToken ct)
+    {
+        _client = new TcpClient();
+        using var cts = CancellationTokenSource.CreateLinkedTokenSource(ct);
+        cts.CancelAfter(_timeout);
+        await _client.ConnectAsync(_host, _port, cts.Token).ConfigureAwait(false);
+        _stream = _client.GetStream();
+    }
+
+    public async Task<byte[]> SendAsync(byte unitId, byte[] pdu, CancellationToken ct)
+    {
+        if (_disposed) throw new ObjectDisposedException(nameof(ModbusTcpTransport));
+        if (_stream is null) throw new InvalidOperationException("Transport not connected");
+
+        await _gate.WaitAsync(ct).ConfigureAwait(false);
+        try
+        {
+            var txId = ++_nextTx;
+
+            // MBAP: [TxId(2)][Proto=0(2)][Length(2)][UnitId(1)] + PDU
+            var adu = new byte[7 + pdu.Length];
+            adu[0] = (byte)(txId >> 8);
+            adu[1] = (byte)(txId & 0xFF);
+            // protocol id already zero
+            var len = (ushort)(1 + pdu.Length); // unit id + pdu
+            adu[4] = (byte)(len >> 8);
+            adu[5] = (byte)(len & 0xFF);
+            adu[6] = unitId;
+            Buffer.BlockCopy(pdu, 0, adu, 7, pdu.Length);
+
+            using var cts = CancellationTokenSource.CreateLinkedTokenSource(ct);
+            cts.CancelAfter(_timeout);
+            await _stream.WriteAsync(adu.AsMemory(), cts.Token).ConfigureAwait(false);
+            await _stream.FlushAsync(cts.Token).ConfigureAwait(false);
+
+            var header = new byte[7];
+            await ReadExactlyAsync(_stream, header, cts.Token).ConfigureAwait(false);
+            var respTxId = (ushort)((header[0] << 8) | header[1]);
+            if (respTxId != txId)
+                throw new InvalidDataException($"Modbus TxId mismatch: expected {txId} got {respTxId}");
+            var respLen = (ushort)((header[4] << 8) | header[5]);
+            if (respLen < 1) throw new InvalidDataException($"Modbus response length too small: {respLen}");
+            var respPdu = new byte[respLen - 1];
+            await ReadExactlyAsync(_stream, respPdu, cts.Token).ConfigureAwait(false);
+
+            // Exception PDU: function code has high bit set.
+            if ((respPdu[0] & 0x80) != 0)
+            {
+                var fc = (byte)(respPdu[0] & 0x7F);
+                var ex = respPdu[1];
+                throw new ModbusException(fc, ex, $"Modbus exception fc={fc} code={ex}");
+            }
+
+            return respPdu;
+        }
+        finally
+        {
+            _gate.Release();
+        }
+    }
+
+    private static async Task ReadExactlyAsync(Stream s, byte[] buf, CancellationToken ct)
+    {
+        var read = 0;
+        while (read < buf.Length)
+        {
+            var n = await s.ReadAsync(buf.AsMemory(read), ct).ConfigureAwait(false);
+            if (n == 0) throw new EndOfStreamException("Modbus socket closed mid-response");
+            read += n;
+        }
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        if (_disposed) return;
+        _disposed = true;
+        try
+        {
+            if (_stream is not null) await _stream.DisposeAsync().ConfigureAwait(false);
+        }
+        catch { /* best-effort */ }
+        _client?.Dispose();
+        _gate.Dispose();
+    }
+}