Azure function app, service bus and return service bus

Question

I have an azure function with a service bus input attribute and service bus output attribute set.

This means that whatever I return from this function will be returned to the ‘return’ queue.

However, i want to manually handle some messages as there is no point retrying them I just want to put them straight on the LDQ and carry on.

So i added MessageReceiver as a parameter with lockToken.

All good.

But now, if i handle the message and send to DLQ i have no way ending the function execution gracefully as it is expecting a return. So i throw an exception. But now i have numerous error logs in the output like ‘lock is invalid’.

I tried to set autocomplete to false but then i have a different issue; how do i ensure i can return the message AND log it in a transaction and handle rollback?

Any guidance??

Example:

  public static class Function1
    {
        [FunctionName("Function1")]
        [return: ServiceBus("returnQueueName", Connection = "myConnectionString")]
        public static async System.Threading.Tasks.Task<ReturnMessage> RunAsync([ServiceBusTrigger("mytopic", "mysubscription", Connection = "myConnectionString")]
        string mySbMsg, ILogger log,
            MessageReceiver messageReceiver, string lockToken)
        {
            log.LogInformation($"C# ServiceBus topic trigger function processed message: {mySbMsg}");

            await messageReceiver.DeadLetterAsync(lockToken);

            return new ReturnMessage();
        }
    }

    public class ReturnMessage
    {
        public string Payload { get; set; }
    }

Hopefully you can see that the input queue and output queue are handled by the hosting system - Azure. I like this because it will look after atomcity for me.

But if I include the line:

await messageReceiver.DeadLetterAsync(lockToken);

This will move the current message to the DLQ.

GREAT!!! That's what I want.

But I am now forced to return something OR throw an exception. Is there any way out of this as seeing the error messages is misleading as there is no error to follow.

I think you need to post your code as it's not clear what your problem is. — spodger

Kam Kam · Accepted Answer · 2019-05-05T08:27:17

As far as I can see it appears that you shouldn't use an automatic return service bus binding. Instead, you should manually connect to the return topic/queue and handle the message logistics manually.

Azure function app, service bus and return service bus

1 Answers