feat(probe): TwinCAT Test-Connect does an ADS ReadState (degrade-guarded)
This commit is contained in:
Joseph Doherty
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// Unit tests for TwinCATDriverProbe — the degrade-guarded ADS ReadState Test-Connect probe.
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//
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// Coverage here is the set of outcomes that are *deterministic on a CI/dev box with no TwinCAT
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// runtime*: invalid JSON, missing host/port, an unreachable TCP target, and — the crux — the
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// DEGRADE path. On this box there is no AMS router, so once the TCP preflight succeeds against a
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// reachable listener the managed ADS client cannot initialise (it throws a "Check for a running
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// TwinCAT router instance!" server exception, NOT an ADS device rejection). The probe MUST treat
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// that as "TCP reachability only" (Ok=true) so it never regresses below the old TCP-only probe.
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//
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// The two paths that REQUIRE a live ADS target are LIVE-VERIFY DEFERRED (no TwinCAT runtime on the
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// rig): (a) the happy "ADS state: Run/Config/Stop" path (Ok=true with the AdsState name), and
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// (b) the route/auth-reject RED path (a reachable router that refuses the route, surfaced as an
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// AdsErrorException carrying a TargetPortNotFound / route AdsErrorCode → Ok=false with the
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// "check the target's ADS route table" message). Those are exercised against a real TwinCAT XAR /
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// remote runtime, out of scope for this unit suite.
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using System.Net;
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using System.Net.Sockets;
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using Shouldly;
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using Xunit;
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namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests;
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[Trait("Category", "Unit")]
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public sealed class TwinCATDriverProbeTests
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{
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private static readonly TwinCATDriverProbe Probe = new();
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// -------------------------------------------------------------------------
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// 1. Invalid JSON
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// -------------------------------------------------------------------------
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/// <summary>Invalid JSON returns Ok=false with a message containing "invalid".</summary>
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[Fact]
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public async Task InvalidJson_Returns_OkFalse_WithInvalidMessage()
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{
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var result = await Probe.ProbeAsync(
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"not-valid-json{{{",
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TimeSpan.FromSeconds(3),
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TestContext.Current.CancellationToken);
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result.Ok.ShouldBeFalse();
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result.Message.ShouldNotBeNull();
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result.Message!.ToLowerInvariant().ShouldContain("invalid");
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result.Latency.ShouldBeNull();
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}
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// -------------------------------------------------------------------------
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// 2. Config with no device / no host
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// -------------------------------------------------------------------------
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/// <summary>An empty Devices list returns Ok=false with a "no host/port" message.</summary>
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[Fact]
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public async Task NoDevices_Returns_OkFalse_WithNoHostPortMessage()
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{
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var result = await Probe.ProbeAsync(
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"{\"devices\":[]}",
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TimeSpan.FromSeconds(3),
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TestContext.Current.CancellationToken);
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result.Ok.ShouldBeFalse();
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result.Message.ShouldNotBeNull();
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result.Message!.ShouldContain("no host/port");
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result.Latency.ShouldBeNull();
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}
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/// <summary>
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/// A first device with a malformed (non-<c>ads://</c>) host address returns Ok=false with a
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/// "no host/port" message because <see cref="TwinCATAmsAddress.TryParse"/> returns null.
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/// </summary>
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[Fact]
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public async Task MalformedHostAddress_Returns_OkFalse_WithNoHostPortMessage()
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{
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var result = await Probe.ProbeAsync(
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"{\"devices\":[{\"hostAddress\":\"not-an-ads-url\"}]}",
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TimeSpan.FromSeconds(3),
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TestContext.Current.CancellationToken);
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result.Ok.ShouldBeFalse();
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result.Message.ShouldNotBeNull();
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result.Message!.ShouldContain("no host/port");
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result.Latency.ShouldBeNull();
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}
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// -------------------------------------------------------------------------
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// 3. Unreachable target — TCP preflight fails first
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// -------------------------------------------------------------------------
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/// <summary>
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/// A closed port causes the TCP preflight <c>ConnectAsync</c> to throw
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/// <see cref="SocketException"/>; the probe returns Ok=false with "Connect failed".
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/// The port is reserved then released so the OS refuses the connection immediately.
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/// </summary>
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[Fact]
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public async Task ClosedPort_Returns_OkFalse_WithConnectFailedMessage()
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{
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// Reserve an ephemeral port then release it so the port is definitely closed.
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var reserved = new TcpListener(IPAddress.Loopback, 0);
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reserved.Start();
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var port = ((IPEndPoint)reserved.LocalEndpoint).Port;
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reserved.Stop();
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// 127.0.0.1 as the first four AMS-Net-ID octets → the probe's TCP target is 127.0.0.1.
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var configJson = $"{{\"devices\":[{{\"hostAddress\":\"ads://127.0.0.1.1.1:{port}\"}}]}}";
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using var cts = CancellationTokenSource.CreateLinkedTokenSource(
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TestContext.Current.CancellationToken);
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cts.CancelAfter(TimeSpan.FromSeconds(5));
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var result = await Probe.ProbeAsync(
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configJson,
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TimeSpan.FromSeconds(3),
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cts.Token);
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result.Ok.ShouldBeFalse();
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result.Message.ShouldNotBeNull();
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// Either a fast SocketException ("Connect failed") or, if the OS stalls, a timeout.
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var lower = result.Message!.ToLowerInvariant();
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(lower.Contains("connect failed") || lower.Contains("timed out")).ShouldBeTrue(
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$"Expected 'Connect failed' or 'timed out' but got: {result.Message}");
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result.Latency.ShouldBeNull();
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}
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/// <summary>
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/// A target on a non-routable IP (192.0.2.1 — TEST-NET-1, RFC 5737) with a short
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/// cancellation window times out (or fails fast on EHOSTUNREACH) at the TCP preflight.
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/// </summary>
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[Fact]
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public async Task BlackHoleTarget_Returns_OkFalse_WithTimedOutOrConnectFailed()
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{
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using var cts = CancellationTokenSource.CreateLinkedTokenSource(
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TestContext.Current.CancellationToken);
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cts.CancelAfter(TimeSpan.FromSeconds(1));
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var configJson = "{\"devices\":[{\"hostAddress\":\"ads://192.0.2.1.1.1:851\"}]}";
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var result = await Probe.ProbeAsync(
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configJson,
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TimeSpan.FromSeconds(1),
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cts.Token);
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result.Ok.ShouldBeFalse();
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result.Message.ShouldNotBeNull();
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var lower = result.Message!.ToLowerInvariant();
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(lower.Contains("timed out") || lower.Contains("connect failed")).ShouldBeTrue(
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$"Expected 'timed out' or 'Connect failed' but got: {result.Message}");
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result.Latency.ShouldBeNull();
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}
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// -------------------------------------------------------------------------
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// 4. DEGRADE path — TCP reachable, but the ADS handshake can't be attempted here
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// -------------------------------------------------------------------------
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/// <summary>
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/// The crux. A reachable TCP listener satisfies the preflight, but on this box (no TwinCAT
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/// AMS router) the managed ADS client cannot establish a session — <c>AdsClient.Connect</c>
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/// throws an environment/router exception (NOT an ADS device rejection). The probe MUST
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/// DEGRADE: <c>Ok=true</c> with the "TCP reachability only" note, never a false RED. This
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/// guarantees the new probe never reports worse than the old TCP-only probe on a host with
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/// no ADS runtime.
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/// </summary>
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[Fact]
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public async Task ReachableTcp_NoAdsRuntime_Degrades_To_OkTrue_WithTcpOnlyNote()
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{
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// Stand up a real TCP listener and accept (then drop) connections so the preflight
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// ConnectAsync succeeds. We never speak ADS — the ADS handshake is what must degrade.
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var listener = new TcpListener(IPAddress.Loopback, 0);
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listener.Start();
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var port = ((IPEndPoint)listener.LocalEndpoint).Port;
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using var acceptCts = CancellationTokenSource.CreateLinkedTokenSource(
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TestContext.Current.CancellationToken);
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var acceptLoop = Task.Run(async () =>
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{
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try
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{
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while (true)
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{
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var client = await listener.AcceptTcpClientAsync(acceptCts.Token);
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// Hold the socket briefly so the preflight sees a clean accept, then close.
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_ = Task.Run(async () =>
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{
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await Task.Delay(200);
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client.Dispose();
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});
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}
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}
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catch (OperationCanceledException) { /* accept cancelled — expected on teardown */ }
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catch (ObjectDisposedException) { /* listener stopped — expected on teardown */ }
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catch (SocketException) { /* listener stopped — expected on teardown */ }
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});
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try
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{
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var configJson = $"{{\"devices\":[{{\"hostAddress\":\"ads://127.0.0.1.1.1:{port}\"}}]}}";
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using var cts = CancellationTokenSource.CreateLinkedTokenSource(
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TestContext.Current.CancellationToken);
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cts.CancelAfter(TimeSpan.FromSeconds(10));
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var result = await Probe.ProbeAsync(
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configJson,
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TimeSpan.FromSeconds(3),
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cts.Token);
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// DEGRADE guard: must be Ok=true (never worse than TCP-only), with the explicit note
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// and a latency. If on some box AdsClient instead threw synchronously at construction,
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// the probe still degrades the same way — this assertion holds either way.
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result.Ok.ShouldBeTrue(
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$"Degrade guard violated — probe returned a worse-than-TCP result: {result.Message}");
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result.Message.ShouldNotBeNull();
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result.Message!.ShouldContain("ADS handshake unavailable on this host");
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result.Message!.ShouldContain("TCP reachability only");
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result.Latency.ShouldNotBeNull();
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}
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finally
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{
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await acceptCts.CancelAsync();
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listener.Stop();
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try { await acceptLoop; } catch { /* ignore teardown races */ }
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}
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}
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}
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