Restoring messages from database - rebus

Question

I am thinking of a way to manage failed messages in Rebus.
In my second level retry strategy I want to save the message and exception details into the database so that I can later review the error details and decide whether to resend the message to the be reprocessed or ignore and delete.
In the handler I am capturing details as follows:
public async Task Handle(IFailed<StudentCreated> failedMessage)
{
//Logic to Defer Message with rebus_defer_count not shown
DictionarySerializer dictionarySerializer = new
DictionarySerializer();
ObjectSerializer objectSerializer = new ObjectSerializer();
string headers =
dictionarySerializer.SerializeToString(failedMessage.Headers);
string message =
objectSerializer.SerializeToString(failedMessage.Message);
Exception lastException= failedMessage.Exceptions.Last();
string exception = objectSerializer.SerializeToString(lastException);
//Logic to save the message and error details in the database not shown
}
This will enable me to save the message and error details into the database where I can create a dashboard to view the messages and resolve them as I wish rather than in the broker queue such as RabbitMQ.
Now my question is how can I return them to the handler where the error was raised using the information provided in the headers?
What is the best way to do it with REBUS provided I have all the details from the Failed Message as shown in my code snippet?
Regards

Answer 1

What you're trying to achieve will be much easier if you make a small change to your application. You see, Rebus already has a built-in service in place for handling failed messages called IErrorHandler.
You can register your own error handler like this:
Configure.With(...)
.(...)
.Options(o => o.Register<IErrorHandler>(c => new MyCustomErrorHandler()))
.Start();
thus replacing the default error handler (which btw. is PoisonQueueErrorHandler)
The error handler gets to handle the message in the form of the raw TransportMessage (i.e. simply headers and a byte[]) when all retries have failed, so this is the perfect place to save the message to your database.
If you then look here, you can see how Rebus' default error handler adds its own queue name as the rbs2-source-queue header, meaning that the message can later be sent back to that queue.
With this information, it should be fairly easy to write some code that inspects the message for its source queue and sends a RabbitMQ message to that queue.
This will only work if the re-delivery service has access to the RabbitMQ instance where all of your Rebus endpoints are running, of course. It's less straightforward, if you want to implement this in a general way: E.g. if you were using Fleet Manager, each Rebus instance would use a long-polling protocol to query the server for commands, which enables Fleet Manager to tell any Rebus instance to e.g. send a previously failed message to any queue it has access to.