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Delivery Log Middleware

The middleware is an IEventMiddleware registered via EventPublisherBuilder.Use<T>(). It sits in the publisher pipeline and records every publish attempt.

How It Works​

On every publish call, the middleware:

  1. Captures start time — Uses IEventSystemTime.UtcNow as the start time
  2. Reads attempt number — From EventContext (initializes to 2 on first call, returns 1)
  3. Executes pipeline — Calls next(context)
  4. Records outcome:
    • On success: Outcome = Succeeded
    • On exception: Outcome = Failed, captures error details, re-throws exception
  5. Writes record — Constructs EventDeliveryRecord and calls IEventPublishDeliveryLog.RecordAsync()

Key Characteristics​

CharacteristicDescription
Never swallows exceptions — The middleware always re-throws publish failures
Storage failures are logged — If the log write itself fails, the exception is logged and swallowed
Uses time abstraction — IEventSystemTime instead of DateTimeOffset.UtcNow for testability
Tracks attempt number — Via EventContext for retry scenarios

Time Abstraction​

Using IEventSystemTime instead of direct DateTimeOffset.UtcNow calls makes timestamps deterministic in tests:

public class FrozenSystemTime : IEventSystemTime
{
    public DateTimeOffset UtcNow { get; } = new DateTimeOffset(2025, 6, 1, 12, 0, 0, TimeSpan.Zero);
}

// In tests:
services.AddSingleton<IEventSystemTime, FrozenSystemTime>();

Registration​

builder.Services
    .AddEventPublisher()
    .AddDeliveryLog(log => log.UseInMemory());

The middleware is automatically added to the publisher pipeline when you call AddDeliveryLog().