mbproxy: initial commit through Phase 9 (TxId multiplexing)
Adds the mbproxy service end-to-end. Phases 00-08 implement the production-ready single-listener / 1:1-backend transparent Modbus TCP proxy with bidirectional BCD rewriting for the ~54-PLC DL205/DL260 fleet. Phase 9 replaces the connection layer with a single backend socket per PLC plus MBAP TxId rewriting, lifting the H2-ECOM100's 4-concurrent-client cap as an operational ceiling. Phase 9 additions of note: - PlcMultiplexer + UpstreamPipe + TxIdAllocator + CorrelationMap - InFlightRequest with IReadOnlyList<InterestedParty> (load-bearing for Phase 10 read coalescing — do not collapse to a single field) - Per-request watchdog: surfaces Modbus exception 0x0B to upstream on BackendRequestTimeoutMs, defending against lost responses, dead-PLC paths, and pymodbus 3.13.0's concurrent-multiplexed- request bug (its ServerRequestHandler.last_pdu state race) - Status DTO + HTML gain inFlight / maxInFlight / txIdWraps / disconnectCascades / queueDepth (Tier 1.6 in docs/kpi.md) Tests: 263 unit + 38 E2E. Multiplexer correctness under truly concurrent backend traffic is proved against a stub backend in PlcMultiplexerTests; MultiplexerE2ETests paces requests so pymodbus 3.13's single-PDU framer stays in known-good mode. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Joseph Doherty
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using System.Text.Json;
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using Microsoft.AspNetCore.Builder;
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using Microsoft.AspNetCore.Hosting;
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using Microsoft.AspNetCore.Http;
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using Microsoft.Extensions.Options;
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using Mbproxy.Options;
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namespace Mbproxy.Admin;
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/// <summary>
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/// Hosted service that owns the Kestrel-backed admin HTTP endpoint.
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///
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/// <para>Lifecycle:</para>
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/// <list type="bullet">
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/// <item><see cref="StartAsync"/> builds a <see cref="WebApplication"/> bound to
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/// <c>Mbproxy.AdminPort</c> and starts it non-blocking.</item>
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/// <item>If the bind fails (port in use, etc.), logs <c>mbproxy.admin.bind.failed</c>
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/// at Error and continues — the proxy listeners are unaffected.</item>
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/// <item>If <c>AdminPort</c> changes via hot-reload, the current app is stopped and a
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/// new one is started on the new port. Other config changes are ignored here.</item>
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/// <item><see cref="StopAsync"/> shuts down the current Kestrel app with a 2 s deadline.</item>
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/// </list>
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///
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/// <para>Routes: exactly two — <c>GET /</c> (HTML) and <c>GET /status.json</c> (JSON).</para>
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/// </summary>
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internal sealed partial class AdminEndpointHost : IHostedService, IAsyncDisposable
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{
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private readonly IOptionsMonitor<MbproxyOptions> _optionsMonitor;
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private readonly StatusSnapshotBuilder _builder;
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private readonly ILoggerFactory _loggerFactory;
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private readonly ILogger<AdminEndpointHost> _logger;
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// The currently-running Kestrel app; null when stopped or when bind failed.
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private WebApplication? _app;
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// Protects concurrent Start/Stop calls (hot-reload + StopAsync racing).
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private readonly SemaphoreSlim _lock = new(1, 1);
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// Current configured port — used to detect changes on hot-reload.
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private int _currentPort;
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// Subscription token for IOptionsMonitor.OnChange.
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private IDisposable? _optionsChangeRegistration;
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public AdminEndpointHost(
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IOptionsMonitor<MbproxyOptions> optionsMonitor,
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StatusSnapshotBuilder builder,
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ILoggerFactory loggerFactory)
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{
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_optionsMonitor = optionsMonitor;
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_builder = builder;
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_loggerFactory = loggerFactory;
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_logger = loggerFactory.CreateLogger<AdminEndpointHost>();
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}
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public async Task StartAsync(CancellationToken cancellationToken)
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{
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_currentPort = _optionsMonitor.CurrentValue.AdminPort;
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await StartAppAsync(_currentPort, cancellationToken).ConfigureAwait(false);
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// Subscribe to config changes: if AdminPort changes, re-bind.
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_optionsChangeRegistration = _optionsMonitor.OnChange(opts =>
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{
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int newPort = opts.AdminPort;
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if (newPort == _currentPort) return; // Only care about AdminPort changes.
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// Fire-and-forget: re-bind is async; we can't await in OnChange.
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_ = Task.Run(async () =>
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{
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await _lock.WaitAsync().ConfigureAwait(false);
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try
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{
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if (newPort == _currentPort) return; // double-check under lock
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// Stop the old app.
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await StopCurrentAppAsync().ConfigureAwait(false);
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_currentPort = newPort;
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// Start on the new port.
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await StartAppAsync(newPort, CancellationToken.None).ConfigureAwait(false);
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}
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finally
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{
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_lock.Release();
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}
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});
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});
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}
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public async Task StopAsync(CancellationToken cancellationToken)
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{
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_optionsChangeRegistration?.Dispose();
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_optionsChangeRegistration = null;
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await _lock.WaitAsync(cancellationToken).ConfigureAwait(false);
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try
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{
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await StopCurrentAppAsync().ConfigureAwait(false);
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}
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finally
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{
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_lock.Release();
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}
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}
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// ── Internal helpers ─────────────────────────────────────────────────────
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/// <summary>
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/// Builds and starts a Kestrel <see cref="WebApplication"/> on <paramref name="port"/>.
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/// On bind failure, logs the error and sets <c>_app = null</c> — does NOT throw.
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/// Caller must hold <c>_lock</c> or be in a single-threaded context (StartAsync).
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/// </summary>
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private async Task StartAppAsync(int port, CancellationToken ct)
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{
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try
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{
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// Use CreateSlimBuilder with explicit args (empty) to avoid inheriting
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// process-level environment variables like ASPNETCORE_URLS.
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var builder = WebApplication.CreateSlimBuilder(new WebApplicationOptions
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{
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Args = [],
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});
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// Suppress Kestrel/ASP.NET Core built-in logging; forward to the outer host's
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// logger factory so that admin-endpoint errors appear in the proxy's log stream.
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builder.Logging.ClearProviders();
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builder.Logging.AddProvider(new ForwardingLoggerProvider(_loggerFactory));
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// Explicit Kestrel listen — overrides any ASPNETCORE_URLS that leaked in.
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builder.WebHost.UseKestrel(k =>
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{
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k.Listen(System.Net.IPAddress.Any, port);
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});
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var app = builder.Build();
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// ── Routes ───────────────────────────────────────────────────────
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app.MapGet("/", (HttpContext ctx) =>
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{
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var snapshot = _builder.Build();
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string html = StatusHtmlRenderer.Render(snapshot);
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return Results.Content(html, "text/html; charset=utf-8");
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});
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app.MapGet("/status.json", (HttpContext ctx) =>
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{
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var snapshot = _builder.Build();
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string json = JsonSerializer.Serialize(snapshot, StatusJsonContext.Default.StatusResponse);
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return Results.Content(json, "application/json");
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});
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await app.StartAsync(ct).ConfigureAwait(false);
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_app = app;
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LogAdminStarted(_logger, port);
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}
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catch (Exception ex) when (ex is not OperationCanceledException)
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{
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// Bind failed — log and continue. Proxy listeners are unaffected.
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LogAdminBindFailed(_logger, port, ex.Message);
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_app = null;
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}
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}
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/// <summary>
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/// Stops the current <see cref="WebApplication"/> with a 2 s deadline, then disposes it.
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/// </summary>
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private async Task StopCurrentAppAsync()
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{
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if (_app is null) return;
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var app = _app;
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_app = null;
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try
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{
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using var stopCts = new CancellationTokenSource(TimeSpan.FromSeconds(2));
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await app.StopAsync(stopCts.Token).ConfigureAwait(false);
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}
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catch
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{
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// Best-effort.
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}
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await app.DisposeAsync().ConfigureAwait(false);
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}
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// ── IAsyncDisposable ─────────────────────────────────────────────────────
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public async ValueTask DisposeAsync()
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{
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_optionsChangeRegistration?.Dispose();
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_lock.Dispose();
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if (_app is { } app)
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{
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_app = null;
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await app.DisposeAsync().ConfigureAwait(false);
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}
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}
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// ── Logging ──────────────────────────────────────────────────────────────
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[LoggerMessage(EventId = 70, EventName = "mbproxy.admin.started",
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Level = LogLevel.Information,
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Message = "Admin endpoint started on port {Port}")]
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private static partial void LogAdminStarted(ILogger logger, int port);
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[LoggerMessage(EventId = 71, EventName = "mbproxy.admin.bind.failed",
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Level = LogLevel.Error,
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Message = "Admin endpoint bind failed — admin page will be unavailable: Port={Port} Reason={Reason}")]
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private static partial void LogAdminBindFailed(ILogger logger, int port, string reason);
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// ── Inner logger provider (forwards Kestrel/ASP.NET logs to the proxy's factory) ────
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private sealed class ForwardingLoggerProvider : ILoggerProvider
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{
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private readonly ILoggerFactory _factory;
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public ForwardingLoggerProvider(ILoggerFactory factory) => _factory = factory;
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public ILogger CreateLogger(string categoryName) => _factory.CreateLogger(categoryName);
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public void Dispose() { }
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}
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}
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