Azure Function App Azure Service Bus trigger triggers twice

问题

I'm using Azure Function Apps with a service bus trigger to read a service bus and do stuff with the contents of the service bus message. The service bus receives a JSON serialized object and then I de-serialize the JSON message back to the object in the Function App. However, for some reason whenever something gets sent to the service bus, the trigger fires twice with one being the JSON message and one being a message containing text "Service Bus Message".

I have no idea what causes the second message, so what I came up with is just de-serializing the service bus message and when it fails with the "Service Bus Message", I'll just catch the exception and ignore it. However, I don't think this is the right way to handle this issue and actual errors in JSON de-serialization will be ignored. What is the correct way to handle the second message?

Example code:

using Newtonsoft.Json;

public static void Run(string myQueueItem, ILogger log, out SendGridMessage mailMessage)
{
    MyClass myObject = null;
    try
    {
        myObject = JsonConvert.DeserializeObject<MyClass>(myQueueItem);
        // do stuff
    }
    catch (JsonException je)
    {
        // ignore this exception
    }
    catch (Exception e)
    {
        // handle the other exceptions and send an alert
    }
}

Edit: One thing I did leave out in the original post is that I do have a SendGrid output too. I don't see why that would have any effect on the trigger which is why I left it out. However, I'm adding it now just in case it might be the cause for some weird reason.

Edit 2: Added full working code that highlights the issue

// Sender
using System;
using System.Text;
using System.Threading.Tasks;
using Microsoft.Azure.ServiceBus;
using Newtonsoft.Json;

namespace myapp
{
    class Program
    {
        static void Main(string[] args) => MainAsync().GetAwaiter().GetResult();

        static async Task MainAsync()
        {
            string serviceBusConnectionString = "<your servicebus connectionstring>";
            string queueName = "<your queue name>";
            IQueueClient queueClient = new QueueClient(serviceBusConnectionString, queueName);
            string messageBody = JsonConvert.SerializeObject(new Test());
            var message = new Message(Encoding.UTF8.GetBytes(messageBody));
            await queueClient.SendAsync(message);
            await queueClient.CloseAsync();
        }

        class Test
        {
            public string Text { get; set; } = "test";
        }
    }
}

// Receiver
#r "Newtonsoft.Json"

using System;
using System.Threading.Tasks;
using Newtonsoft.Json;

public static void Run(string myQueueItem, ILogger log)
{
    try
    {
        Test test = JsonConvert.DeserializeObject<Test>(myQueueItem);
        log.LogInformation($"C# ServiceBus queue trigger function processed message: {test.Text}");
    }
    catch (Exception e)
    {
        log.LogInformation($"Exception: {e.Message}");
    }
}

class Test
{
    public string Text { get; set; } = "test";
}

Result:

2019-11-04T08:38:10.544 [Information] Executing 'Functions.test' (Reason='This function was programmatically called via the host APIs.', Id=06e10006-baa6-430f-b5db-9a5eae5c154c)
2019-11-04T08:38:10.659 [Information] Exception: Unexpected character encountered while parsing value: S. Path '', line 0, position 0. // This here is caused by "Service bus message"
2019-11-04T08:38:10.659 [Information] Executed 'Functions.test' (Succeeded, Id=06e10006-baa6-430f-b5db-9a5eae5c154c)
2019-11-04T08:39:02.582 [Information] Executing 'Functions.test' (Reason='New ServiceBus message detected on 'test'.', Id=5d7622a7-cc8d-44c9-8720-626fdbb8cabb)
2019-11-04T08:39:02.583 [Information] Trigger Details: MessageId: 13bba779fd524fa1a0098acd6634aded, DeliveryCount: 1, EnqueuedTime: 11/4/2019 8:39:02 AM, LockedUntil: 11/4/2019 8:39:07 AM
2019-11-04T08:39:02.584 [Information] C# ServiceBus queue trigger function processed message: test // This here is the actual message
2019-11-04T08:39:02.584 [Information] Executed 'Functions.test' (Succeeded, Id=5d7622a7-cc8d-44c9-8720-626fdbb8cabb)

回答1:

Based on my test, the trigger will not be triggered twice.

namespace ServiceBusTrigger
{
    public static class Function1
    {
        [FunctionName("Function1")]
        public static void Run([ServiceBusTrigger("myqueue", Connection = "ServiceBusConnection")]string myQueueItem, ILogger log)
        {
            log.LogInformation($"C# ServiceBus queue trigger function processed message: {myQueueItem}");

            var myMessage = JsonConvert.DeserializeObject<MyMessage>(myQueueItem);

            log.LogInformation($"ID: {myMessage.id}\tContent:{myMessage.content}");
        }
    }
}

Send a message manually, and get the following output:


Pause Clear Expand

2019-11-04T08:18:56.837 [Information] Executing 'Function1' (Reason='New ServiceBus message detected on 'myqueue'.', Id=7fb37483-b9a3-4c19-baa3-235b419bb585)
2019-11-04T08:18:56.837 [Information] Trigger Details: MessageId: c00a8e41-d883-4620-992f-6b9b4fdae320, DeliveryCount: 1, EnqueuedTime: 11/4/2019 8:18:56 AM, LockedUntil: 11/4/2019 8:19:26 AM
2019-11-04T08:18:56.838 [Information] C# ServiceBus queue trigger function processed message: {"id":"1","content":"abc"}
2019-11-04T08:18:56.838 [Information] ID: 1 Content:abc
2019-11-04T08:18:56.839 [Information] Executed 'Function1' (Succeeded, Id=7fb37483-b9a3-4c19-baa3-235b419bb585)

So, could you please check your service bus producer to see if any additional message was sent.

Of you can just stop your function app, send a message manually and check on the portal:

If everything was fine, then there should only be 1 active message.

Update

来源：https://stackoverflow.com/questions/58656425/azure-function-app-azure-service-bus-trigger-triggers-twice

标签

azure

servicebus

azure-function-app