Merge pull request 'feat: expose terminal consumer failure hook' (#3) from IT-1033 into main

Reviewed-on: #3

AGENTS.md

@@ -0,0 +1,26 @@
+# HrynCo.RabbitMq Agent Rules
+
+## Git workflow
+
+- Treat `main` as the only default and integration branch for this repository.
+- Start every task branch from the latest `origin/main`.
+- Before creating a task branch, fetch the remote, switch to `main`, and fast-forward it from `origin/main`.
+- Create the task branch only after confirming that local `main` matches `origin/main`.
+- Open pull requests from the task branch into `main`.
+- Do not use `development` as the base or pull-request target for new work in this repository.
+- Do not commit, push, publish a NuGet package, or merge unless the repository owner explicitly requests that step.
+
+Recommended branch preparation:
+
+```text
+git fetch origin
+git switch main
+git pull --ff-only origin main
+git switch -c <task-branch>
+```
+
+## Delivery
+
+- Keep changes focused and backward compatible where practical because this repository produces a shared NuGet package.
+- Run the solution tests before handoff.
+- Use Conventional Commit messages with a lowercase subject and finish the commit body with `Ref: <issue-id>` when an issue exists.

Hrynco.RabbitMq.Tests/RabbitMqConsumerBaseExtensionTests.cs

@@ -57,6 +57,33 @@ public sealed class RabbitMqConsumerBaseExtensionTests
         error.Should().BeNull();
     }
 
+    [Fact]
+    public async Task RetriesExhaustedHook_ReceivesMessageContextAndTerminalException()
+    {
+        var consumer = new TerminalFailureConsumer(CreateOptions());
+        var message = CreateMessage();
+        var exception = new InvalidOperationException("terminal failure");
+
+        await consumer.InvokeRetriesExhaustedAsync(message, Context, exception);
+
+        consumer.FailedMessage.Should().BeSameAs(message);
+        consumer.FailedContext.Should().BeSameAs(Context);
+        consumer.TerminalException.Should().BeSameAs(exception);
+    }
+
+    [Fact]
+    public async Task RetriesExhaustedHook_IsNoOpByDefault()
+    {
+        var consumer = new LegacyConsumer(CreateOptions());
+
+        Func<Task> act = () => consumer.InvokeRetriesExhaustedAsync(
+            CreateMessage(),
+            Context,
+            new InvalidOperationException("terminal failure"));
+
+        await act.Should().NotThrowAsync();
+    }
+
     private static TestMessage CreateMessage() => new()
     {
         CorrelationContext = new CorrelationContext { CorrelationId = "payload-correlation" },
@@ -117,6 +144,51 @@ public sealed class RabbitMqConsumerBaseExtensionTests
         {
             return TryValidateMessage(message, context, out error);
         }
+
+        public Task InvokeRetriesExhaustedAsync(
+            TestMessage message,
+            RabbitMqMessageContext context,
+            Exception exception)
+        {
+            return HandleMessageRetriesExhaustedAsync(
+                message,
+                context,
+                exception,
+                CancellationToken.None);
+        }
+    }
+
+    private sealed class TerminalFailureConsumer(IOptionsMonitor<RabbitMqSettings> options)
+        : RabbitMqConsumerBase<TestMessage, string>(options, NullLogger.Instance)
+    {
+        protected override string QueueName => "messages.test";
+        public TestMessage? FailedMessage { get; private set; }
+        public RabbitMqMessageContext? FailedContext { get; private set; }
+        public Exception? TerminalException { get; private set; }
+
+        protected override Task HandleMessageRetriesExhaustedAsync(
+            TestMessage message,
+            RabbitMqMessageContext context,
+            Exception exception,
+            CancellationToken cancellationToken)
+        {
+            FailedMessage = message;
+            FailedContext = context;
+            TerminalException = exception;
+            return Task.CompletedTask;
+        }
+
+        public Task InvokeRetriesExhaustedAsync(
+            TestMessage message,
+            RabbitMqMessageContext context,
+            Exception exception)
+        {
+            return HandleMessageRetriesExhaustedAsync(
+                message,
+                context,
+                exception,
+                CancellationToken.None);
+        }
     }
 
     private sealed record TestMessage : IRabbitMqMessage<string>

Hrynco.RabbitMq/README.md

@@ -25,3 +25,10 @@ ownership of acknowledgements and retries.
 Override `TryValidateMessage(...)` for application-specific permanent validation.
 Returning `false` nacks the delivery without requeue before retry processing begins.
 Keep validation errors free of credentials and sensitive payload values.
+
+Override `HandleMessageRetriesExhaustedAsync(...)` when a consumer must react once to a
+terminal processing failure, for example by publishing a neutral failure result to the
+requesting client. The hook runs after the final handler exception and before the original
+delivery is nacked without requeue. Hook failures are logged and do not replace the
+original failure or acknowledgement policy. Application shutdown cancellation does not
+invoke the hook.

Hrynco.RabbitMq/RabbitMqConsumerBase.cs

@@ -82,6 +82,20 @@ public abstract class RabbitMqConsumerBase<TMessage, TMessageData> : BackgroundS
         return true;
     }
 
+    /// <summary>
+    /// Handles a terminal processing failure after all message retries are exhausted.
+    /// The default implementation is a no-op. Implementations should avoid throwing;
+    /// failures from this hook are logged and the original message is still nacked.
+    /// </summary>
+    protected virtual Task HandleMessageRetriesExhaustedAsync(
+        TMessage message,
+        RabbitMqMessageContext context,
+        Exception exception,
+        CancellationToken cancellationToken)
+    {
+        return Task.CompletedTask;
+    }
+
     protected override async Task ExecuteAsync(CancellationToken stoppingToken)
     {
         await EnsureConnectionAsync(stoppingToken);
@@ -155,6 +169,10 @@ public abstract class RabbitMqConsumerBase<TMessage, TMessageData> : BackgroundS
                 await _channel!.BasicAckAsync(args.DeliveryTag, multiple: false, cancellationToken: cancellationToken);
                 return;
             }
+            catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
+            {
+                throw;
+            }
             catch (Exception ex) when (attempt < MaxRetries)
             {
                 _logger.LogWarning(ex,
@@ -169,6 +187,23 @@ public abstract class RabbitMqConsumerBase<TMessage, TMessageData> : BackgroundS
                     "All {Max} attempts exhausted for message on queue {Queue} [CorrelationId={CorrelationId}] — nacking without requeue",
                     MaxRetries, QueueName, payloadCorrelationId);
 
+                try
+                {
+                    await HandleMessageRetriesExhaustedAsync(
+                        message,
+                        context,
+                        ex,
+                        cancellationToken);
+                }
+                catch (Exception hookException)
+                {
+                    _logger.LogError(
+                        hookException,
+                        "Terminal failure hook failed for message on queue {Queue} [CorrelationId={CorrelationId}]",
+                        QueueName,
+                        payloadCorrelationId);
+                }
+
                 await NackWithoutRequeueAsync(args.DeliveryTag, cancellationToken);
             }
         }