RabbitMQ EventingBasicConsumer lose messages

Question

I'm developing an application for messaging using Rabbit MQ. I use EventingBasicConsumer, Exchange and QueueBind. For test i run my application for receaving messages and then turn my ethernet controller off. After i turn it on receaving messges start again, but about 500 messages was lost. My code:

private void DoWork()
    {
        try
        {
            var connection = ConnectionFactory.CreateConnection();
            IModel model = connection.CreateModel();

            // Configure the Quality of service for the model. Below is how what each setting means.
            // BasicQos(0="Dont send me a new message untill I’ve finshed",  1= "Send me one message at a time", false ="Apply to this Model only")
            model.BasicQos(0, 1, false);

            model.ExchangeDeclare(Options.RabbitConnectionOptions.Exchange, RabbitConstants.ExchangeType, RabbitConstants.ExchangeDurable, RabbitConstants.ExchangeAutoDelete);
            var queueDeclareOk = model.QueueDeclare("SomeSubsruberQueue3", RabbitConstants.QueueDurable, RabbitConstants.QueueExclusive, RabbitConstants.ExchangeAutoDelete);


            var queueName = queueDeclareOk.QueueName;

            foreach (var optionsBindingKey in Options.BindingKeys)
            {
                Logger.Debug($"QueueBind for {nameof(optionsBindingKey)}={optionsBindingKey}");
                model.QueueBind(queueName, Options.RabbitConnectionOptions.Exchange, optionsBindingKey);
            }


            var consumer = new EventingBasicConsumer(model);

            consumer.Received += (ch, ea) =>
            {
                try
                {
                    var body = ea.Body;
                    var message = Encoding.UTF8.GetString(body);
                    var routingKey = ea.RoutingKey;
                    var messageToLog = $" [x] Received '{routingKey}':'{message}'";                        

                    Logger.Info(messageToLog);
                    Console.WriteLine($"receavedCount={++receavedCount}");

                }
                catch (Exception e)
                {
                    Console.WriteLine(e);
                    throw;
                }
            };

            model.BasicConsume(queueName, RabbitConstants.QueueAutoAck, consumer);
        }
        catch (Exception e)
        {
            Logger.Error(e);
            Console.WriteLine(e);
            throw;
        }
    }

How can i prevent loosing messages?

P.s. here the log, shows lost messages. "Id" is sequential, so u can see, that massages with id's from 926 to 1299 was lost

2017-02-14 10:52:01.4916 <Root><Subscribers><Subscriber Id="922" Name="1c" />
2017-02-14 10:52:01.4916 <Root><Subscribers><Subscriber Id="923" Name="1c" />
2017-02-14 10:52:01.4916 <Root><Subscribers><Subscriber Id="924" Name="1c" />
2017-02-14 10:52:01.5056 <Root><Subscribers><Subscriber Id="925" Name="1c" />
2017-02-14 10:52:22.5606 <Root><Subscribers><Subscriber Id="1300" Name="1c" />
2017-02-14 10:52:22.5606 <Root><Subscribers><Subscriber Id="1301" Name="1c" />
2017-02-14 10:52:22.5676 <Root><Subscribers><Subscriber Id="1302" Name="1c" />
2017-02-14 10:52:22.6046 <Root><Subscribers><Subscriber Id="1303" Name="1c" />

UPD:

if i modify:

model.BasicConsume(queueName,true, consumer);

to

model.BasicConsume(queueName,false, consumer);

and use explicit ASK

((EventingBasicConsumer)ch).Model.BasicAck(ea.DeliveryTag, false);

i have very strange behaviour:

2017-02-14 13:06:35.9835| DeliveryTag=23, <Subscriber Id="778" Name="1c" /> 
2017-02-14 13:06:36.0295| DeliveryTag=24, <Subscriber Id="779" Name="1c" /> 
2017-02-14 13:06:57.3285| DeliveryTag=26, <Subscriber Id="782" Name="1c" /> 
2017-02-14 13:06:57.3755| DeliveryTag=27, <Subscriber Id="783" Name="1c" />

There is no DeliveryTag=25 !

Answer 1

Ок, thanks Emil Vikström, i must use explicit ASK:

model.BasicConsume(queueName,false, consumer);

and do ask after processing message:

((EventingBasicConsumer)ch).Model.BasicAck(ea.DeliveryTag, false);

Other question about lost message: rabbitMq reordering message when returning it to queue. So its not los, its just will receaved later

Answer 2

Don't use auto-ACK. Read a message, do whatever you want to do with it, then ACK explicitly when you are done with it.