Add scheduled delivery to the Mocha in-memory transport

src/Mocha/src/Mocha.Transport.InMemory/MessageBusBuilderExtensions.cs

@@ -1,4 +1,10 @@
-namespace Mocha.Transport.InMemory;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
+using Microsoft.Extensions.Logging;
+using Mocha.Scheduling;
+using Mocha.Transport.InMemory.Scheduling;
+
+namespace Mocha.Transport.InMemory;
 
 /// <summary>
 /// Extension methods for registering the in-memory messaging transport on an <see cref="IMessageBusHostBuilder"/>.
@@ -19,6 +25,27 @@ public static IMessageBusHostBuilder AddInMemory(
 
         busBuilder.ConfigureMessageBus(b => b.AddTransport(transport));
 
+        busBuilder.Services.TryAddSingleton(
+            static sp => new InMemoryTransportScheduledMessageStore(sp.GetTimeProvider()));
+
+        busBuilder.Services.AddSingleton(
+            new ScheduledMessageStoreRegistration(
+                transport,
+                InMemoryTransportScheduledMessageStore.TokenPrefix,
+                static sp => sp.GetRequiredService<InMemoryTransportScheduledMessageStore>()));
+
+        busBuilder.Services.TryAddSingleton(
+            static sp => new InMemoryScheduledMessageWorker(
+                sp,
+                sp.GetRequiredService<IMessagingRuntime>(),
+                sp.GetRequiredService<IMessagingPools>(),
+                sp.GetRequiredService<InMemoryTransportScheduledMessageStore>(),
+                sp.GetTimeProvider(),
+                sp.GetRequiredService<ILogger<InMemoryScheduledMessageWorker>>()));
+
+        busBuilder.Services.AddHostedService(
+            static sp => sp.GetRequiredService<InMemoryScheduledMessageWorker>());
+
         return busBuilder;
     }
 

src/Mocha/src/Mocha.Transport.InMemory/Mocha.Transport.InMemory.csproj

@@ -6,6 +6,7 @@
   <ItemGroup>
     <ProjectReference Include="..\Mocha.Abstractions\Mocha.Abstractions.csproj" />
     <ProjectReference Include="..\Mocha\Mocha.csproj" />
+    <ProjectReference Include="..\Mocha.Outbox\Mocha.Outbox.csproj" />
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.AspNetCore.WebUtilities" />

src/Mocha/src/Mocha.Transport.InMemory/Scheduling/InMemoryScheduledMessageWorker.cs

@@ -0,0 +1,217 @@
+using System.Diagnostics;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.ObjectPool;
+using Mocha.Middlewares;
+using Mocha.Outbox;
+using Mocha.Scheduling;
+using Mocha.Threading;
+
+namespace Mocha.Transport.InMemory.Scheduling;
+
+/// <summary>
+/// A hosted background worker that drains due entries from the in-memory scheduled message store and
+/// dispatches them through the normal endpoint pipeline. It sleeps on the store's dedicated signal
+/// until the next entry is due.
+/// </summary>
+internal sealed class InMemoryScheduledMessageWorker(
+    IServiceProvider services,
+    IMessagingRuntime runtime,
+    IMessagingPools pools,
+    InMemoryTransportScheduledMessageStore store,
+    TimeProvider timeProvider,
+    ILogger<InMemoryScheduledMessageWorker> logger)
+    : IHostedService, IAsyncDisposable
+{
+    private readonly ObjectPool<DispatchContext> _contextPool = pools.DispatchContext;
+
+#if NET9_0_OR_GREATER
+    private readonly Lock _lock = new();
+#else
+    private readonly object _lock = new();
+#endif
+    private ContinuousTask? _task;
+
+    public Task StartAsync(CancellationToken cancellationToken)
+    {
+        lock (_lock)
+        {
+            if (_task is not null)
+            {
+                return Task.CompletedTask;
+            }
+
+            _task = new ContinuousTask(ProcessAsync);
+        }
+
+        return Task.CompletedTask;
+    }
+
+    public async Task StopAsync(CancellationToken cancellationToken)
+    {
+        ContinuousTask? task;
+
+        lock (_lock)
+        {
+            task = _task;
+            _task = null;
+        }
+
+        if (task is not null)
+        {
+            await task.DisposeAsync();
+        }
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        await StopAsync(CancellationToken.None);
+    }
+
+    private async Task ProcessAsync(CancellationToken cancellationToken)
+    {
+        while (!cancellationToken.IsCancellationRequested)
+        {
+            try
+            {
+                var now = timeProvider.GetUtcNow();
+
+                if (store.TryTakeDue(now, out var entry))
+                {
+                    await DispatchAsync(entry, cancellationToken);
+
+                    continue;
+                }
+
+                var wakeTime = store.NextDueTime() ?? DateTimeOffset.MaxValue;
+
+                await store.Signal.WaitUntilAsync(wakeTime, cancellationToken);
+            }
+            catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
+            {
+                // Normal shutdown.
+            }
+        }
+    }
+
+    private async Task DispatchAsync(ScheduledEntry entry, CancellationToken cancellationToken)
+    {
+        var envelope = entry.Envelope;
+        var messageType = GetMessageType(envelope.MessageType);
+        var isReply = envelope.Headers?.IsReply() ?? false;
+        var endpoint = isReply
+            ? GetReplyDispatchEndpoint(envelope.DestinationAddress)
+            : GetDispatchEndpoint(envelope.DestinationAddress);
+
+        if (messageType is null || endpoint is null)
+        {
+            logger.CouldNotResolveScheduledMessage(entry.Id);
+
+            return;
+        }
+
+        Activity? activity = null;
+        var traceparent = envelope.Headers?.Get(MessageHeaders.Traceparent);
+
+        if (!string.IsNullOrEmpty(traceparent))
+        {
+            var tracestate = envelope.Headers?.Get(MessageHeaders.Tracestate);
+            if (ActivityContext.TryParse(traceparent, tracestate, out var parentContext))
+            {
+                activity = OpenTelemetry.Source.CreateActivity(
+                    "scheduler send",
+                    ActivityKind.Client,
+                    parentContext);
+
+                activity?.SetMessageId(envelope.MessageId);
+
+                activity?.Start();
+            }
+        }
+
+        var context = _contextPool.Get();
+        try
+        {
+            await using var scope = services.CreateAsyncScope();
+
+            context.Initialize(scope.ServiceProvider, endpoint, runtime, messageType, cancellationToken);
+            context.SkipScheduler();
+            context.SkipOutbox();
+            context.Envelope = envelope;
+
+            await endpoint.ExecuteAsync(context);
+        }
+        catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
+        {
+            // The worker is shutting down; the in-flight message is lost (in-memory is non-durable).
+        }
+        catch (Exception ex)
+        {
+            logger.ScheduledMessageDispatchFailed(entry.Id, ex);
+        }
+        finally
+        {
+            _contextPool.Return(context);
+            activity?.Dispose();
+        }
+    }
+
+    private MessageType? GetMessageType(string? messageType)
+    {
+        try
+        {
+            return messageType is null ? null : runtime.Messages.GetMessageType(messageType);
+        }
+        catch
+        {
+            return null;
+        }
+    }
+
+    private DispatchEndpoint? GetReplyDispatchEndpoint(string? destinationAddress)
+    {
+        try
+        {
+            if (!Uri.TryCreate(destinationAddress, UriKind.Absolute, out var uri))
+            {
+                return null;
+            }
+
+            return runtime.GetTransport(uri)?.ReplyDispatchEndpoint;
+        }
+        catch
+        {
+            return null;
+        }
+    }
+
+    private DispatchEndpoint? GetDispatchEndpoint(string? destinationAddress)
+    {
+        try
+        {
+            if (destinationAddress is null || !Uri.TryCreate(destinationAddress, UriKind.Absolute, out var uri))
+            {
+                return null;
+            }
+
+            return runtime.GetDispatchEndpoint(uri);
+        }
+        catch
+        {
+            return null;
+        }
+    }
+}
+
+internal static partial class InMemorySchedulerLogs
+{
+    [LoggerMessage(
+        1,
+        LogLevel.Critical,
+        "Could not resolve the message type or endpoint for scheduled message {Id}. Message dropped.")]
+    public static partial void CouldNotResolveScheduledMessage(this ILogger logger, Guid id);
+
+    [LoggerMessage(2, LogLevel.Error, "Failed to dispatch scheduled message {Id}. Message dropped.")]
+    public static partial void ScheduledMessageDispatchFailed(this ILogger logger, Guid id, Exception exception);
+}