RabbitMQ response is been lost in controller

Question

Good evening everyone, I've got a web app written using .NET and a mobile app. I'm sending some values to rabbitMQ server through my web app and this is working fine, i put it in a queue but when the mobile app accepts the request, i don't get the returned value.

Here is my controller

    public async Task<ActionResult> GetCollect(int id)
    {
        int PartnerId = 0;
        bool SentRequest = false;

        try
        {
            SentRequest = await RuleRabbitMQ.SentRequestRule(id);
            if(SentRequest )
            {
                PartnerId = await RuleRabbitMQ.RequestAccepted();
            }
        }
        catch (Exception Ex)
        {

        }
    }

This is my RabbitMQ class

 public class InteractionRabbitMQ
{

    public async Task<bool> SentRequestRule(int id)
    {
        bool ConnectionRabbitMQ = false;
        await Task.Run(() => 
        {
            try
            {
                ConnectionFactory connectionFactory = new ConnectionFactory()
                {
                   //credentials go here
                };

                IConnection connection = connectionFactory.CreateConnection();
                IModel channel = connection.CreateModel();

                channel.QueueDeclare("SolicitacaoSameDay", true, false, false, null);

                string rpcResponseQueue = channel.QueueDeclare().QueueName;

                string correlationId = Guid.NewGuid().ToString();

                IBasicProperties basicProperties = channel.CreateBasicProperties();
                basicProperties.ReplyTo = rpcResponseQueue;
                basicProperties.CorrelationId = correlationId;
                byte[] messageBytes = Encoding.UTF8.GetBytes(string.Concat(" ", id.ToString()));
                channel.BasicPublish("", "SolicitacaoSameDay", basicProperties, messageBytes);

                channel.Close();
                connection.Close();

                if (connection != null)
                {
                    ConnectionRabbitMQ = true;
                }
                else
                {
                    ConnectionRabbitMQ = false;
                }
            }
            catch (Exception Ex)
            {
                throw new ArgumentException($"Thre was a problem with  RabbitMQ server. " +
                    $"Pleaser, contact the support with Error: {Ex.ToString()}");
            }
        });
        return ConnectionRabbitMQ;
    }

    public async Task<int> RequestAccepted()
    {

        bool SearchingPartner= true;
        int PartnerId = 0;

        await Task.Run(() =>
        {
            try
            {
                var connectionFactory = new ConnectionFactory()
                {
                    // credentials
                };

                IConnection connection = connectionFactory.CreateConnection();
                IModel channel = connection.CreateModel();

                channel.BasicQos(0, 1, false);

                var eventingBasicConsumer = new EventingBasicConsumer(channel);


                eventingBasicConsumer.Received += (sender, basicDeliveryEventArgs) =>
                {
                    string Response = Encoding.UTF8.GetString(basicDeliveryEventArgs.Body, 0, basicDeliveryEventArgs.Body.Length);
                    channel.BasicAck(basicDeliveryEventArgs.DeliveryTag, false);
                    if(!string.IsNullOrWhiteSpace(Response))
                    {
                        int Id = Convert.ToInt32(Response);
                        PartnerId = Id > 0 ? Id : 0;
                        SearchingPartner = false;

                    }
                };


                channel.BasicConsume("SolicitacaoAceitaSameDay", false, eventingBasicConsumer);
            }
            catch (Exception Ex)
            {
               // error message
            }
        });
        return PartnerId ;
    }

Answer 1

I am not sure this works, can't build an infrastructure to test this quickly, but - your issue is that the RequestAccepted returns a Task which completes before the Received event is caught by the Rabbit client library.

Syncing the two could possibly resolve the issue, note however that this could potentially make your code waiting very long for (or even - never get) the response.

public Task<int> RequestAccepted()
{
    bool SearchingPartner= true;
    int PartnerId = 0;

    var connectionFactory = new ConnectionFactory()
    {
        // credentials
    };

    IConnection connection = connectionFactory.CreateConnection();
    IModel channel = connection.CreateModel();

    channel.BasicQos(0, 1, false);

    TaskCompletionSource<int> tcs = new TaskCompletionSource<int>();

    var eventingBasicConsumer = new EventingBasicConsumer(channel);
    eventingBasicConsumer.Received += (sender, basicDeliveryEventArgs) =>
    {
         string Response = Encoding.UTF8.GetString(basicDeliveryEventArgs.Body, 0, basicDeliveryEventArgs.Body.Length);
         channel.BasicAck(basicDeliveryEventArgs.DeliveryTag, false);
         if(!string.IsNullOrWhiteSpace(Response))
         {
             int Id = Convert.ToInt32(Response);
             PartnerId = Id > 0 ? Id : 0;
             SearchingPartner = false;

             tcs.SetResult( PartnerId );
         }
    };


    channel.BasicConsume("SolicitacaoAceitaSameDay", false, eventingBasicConsumer);

    return tcs.Task;
}

There are couple of issues with this approach.

First, no error handling. Then, what if the event is sent by the RMQ before the consumer subscribes to it? The consumer will block as it will never receive anything back.

And last, I don't think RMQ consumers are ever intended to be created in every request to your controller and then never disposed. While this could work on your dev box where you create a couple of requests manually, it won't probably ever scale to fix a scenario where dozens/hundreds of concurrent users hit your website and multiple RMQ consumers compete one against the other.

I don't think there is an easy way around it other than completely separate the consumer out of your web app, put it in a System Service or a Hangfire job and let it get responses to all possible requests and from the cache - serve responses to web requests.

This is a pure speculation, though, based on my understanding of what you try to do. I could be wrong here, of course.

Answer 2

byte[] messageBytes = Encoding.UTF8.GetBytes(string.Concat(" ", idColeta.ToString()));

I reckon 'idColeta' is blank.