fix(mtconnect): an Agent refusal of /current is a reply, not a comms fault

Health contract: an MTConnectError document (NO_DEVICE, INVALID_REQUEST, ...) is the Agent answering. The parsers now mark such an InvalidDataException (MTConnectXml.IsAgentRefusal - the type is sealed, so a Data marker, every other handler unchanged); ReadAsync reports the batch Bad but does not degrade the read path, advances LastSuccessfulRead, clears a prior read degradation and warns once per distinct refusal. An unparseable answer stays a comms fault. Refs #743 Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT
2026-10-22 16:03:38 -04:00
parent d67634cc4f
commit ac01c88c0e
7 changed files with 137 additions and 4 deletions
@@ -159,4 +159,73 @@ public sealed class MTConnectReadPathTests
            await driver.ShutdownAsync(CancellationToken.None);
        }
    }
+
+    private const string NoDeviceError =
+        """
+        <?xml version="1.0" encoding="UTF-8"?>
+        <MTConnectError xmlns="urn:mtconnect.org:MTConnectError:1.3">
+          <Header creationTime="2026-10-22T12:00:00Z" sender="stub-agent" instanceId="1" version="1.3.0.12" bufferSize="1"/>
+          <Errors><Error errorCode="NO_DEVICE">Could not find the device 'VMC-9'</Error></Errors>
+        </MTConnectError>
+        """;
+
+    private static Exception ParseFailure(string xml)
+    {
+        try
+        {
+            MTConnectStreamsParser.Parse(xml);
+        }
+        catch (Exception ex)
+        {
+            return ex;
+        }
+
+        throw new InvalidOperationException("expected the parse to fail");
+    }
+
+    /// <summary>
+    ///     Health contract: an MTConnectError answer to /current is the Agent REFUSING (it answered) — the batch is Bad,
+    ///     but health is restored / kept Healthy with the stamp advanced, and the refusal is logged once, not per read.
+    /// </summary>
+    [Fact]
+    public async Task An_agent_refusal_of_current_is_a_reply_not_a_comms_fault()
+    {
+        var logger = new RecordingDriverLogger();
+        var client = CannedAgentClient.FromFixtures();
+        var driver = new MTConnectDriver(Opts(), "mt-refusal", _ => client, logger);
+        await driver.InitializeAsync("{}", Ct);
+        try
+        {
+            // A comms fault first, so the refusal has a Degraded to restore.
+            client.CurrentFailure = new HttpRequestException("connection refused");
+            await driver.ReadAsync(["dev1_pos"], Ct);
+            driver.GetHealth().State.ShouldBe(DriverState.Degraded, "positive control: a comms fault does degrade");
+            var stamp = driver.GetHealth().LastSuccessfulRead.ShouldNotBeNull();
+
+            var refusal = ParseFailure(NoDeviceError);
+            MTConnectXml.IsAgentRefusal(refusal).ShouldBeTrue();
+            client.CurrentFailure = refusal;
+            var deadline = DateTime.UtcNow + TimeSpan.FromSeconds(5);
+            while (DateTime.UtcNow <= stamp && DateTime.UtcNow < deadline) await Task.Yield();
+
+            var first = await driver.ReadAsync(["dev1_pos"], Ct);
+            await driver.ReadAsync(["dev1_pos"], Ct);
+
+            first.Single().StatusCode.ShouldBe(0x80050000u, "the batch is still Bad");
+            var h = driver.GetHealth();
+            h.State.ShouldBe(DriverState.Healthy);
+            h.LastSuccessfulRead.ShouldNotBeNull().ShouldBeGreaterThan(stamp);
+            logger.WarningsSnapshot().Count(w => w.Contains("NO_DEVICE")).ShouldBe(1, "a persistent refusal warns once");
+        }
+        finally
+        {
+            client.CurrentFailure = null;
+            await driver.ShutdownAsync(CancellationToken.None);
+        }
+    }
+
+    /// <summary>An answer that is not an MTConnect document at all is NOT marked a refusal (it stays a comms fault).</summary>
+    [Fact]
+    public void A_garbage_answer_is_not_an_agent_refusal() =>
+        MTConnectXml.IsAgentRefusal(ParseFailure("<html><body>proxy error</body></html>")).ShouldBeFalse();
 }