BasicQos not working as expected

[JanEggers]

Describe the bug

We are using version 6.8.1 of the client and when specifying Basic Qos prefetchCount but the client still pulls in all the messages there are.

Reproduction steps

using System.Reactive.Subjects;
using System.Text.Json;
using RabbitMQ.Client;
using RabbitMQ.Client.Events;


var factory = new ConnectionFactory()
{
    HostName = "localhost",
    UserName = "rabbit",
    Password = "rabbit"
};

var eventCount = 10000;

var consumed = 0;

var tcs = new TaskCompletionSource();
var consumerConnection = factory.CreateConnection();
var consumerModel = consumerConnection.CreateModel();
consumerModel.BasicQos(0, 50, false);
consumerModel.QueueDeclare("test", true, true, false);
consumerModel.QueueBind("test", "amq.topic", "world.*");
var consumer = new EventingBasicConsumer(consumerModel);

consumer.Received += (sender, eventArgs) =>
{
    var body = eventArgs.Body.Span;
    var dto = JsonSerializer.Deserialize<Dto>(body);

    consumed++;

    Thread.Sleep(1000);

    Console.WriteLine(dto.Id);

    if (consumed == eventCount)
    {
        tcs.TrySetResult();
    }
};
consumerModel.BasicConsume("test", true, "", consumer);

var producerConnection = factory.CreateConnection();
var producerModel = producerConnection.CreateModel();


var msgs = Enumerable.Range(1, eventCount)
    .Select(i => Guid.NewGuid())
    .Select(id => new Dto() { Id = id });

foreach (var msg in msgs)
{
    producerModel.BasicPublish("amq.topic", $"world.{msg.Id}", body: JsonSerializer.SerializeToUtf8Bytes(msg));
}

await tcs.Task;


class Dto
{
    public Guid Id { get; set; }
}

here is a screenshot of ConsumerWorkService which buffers all the events and not just 50 as expected.

not yet

Expected behavior

it works

Additional context

No response

[kjnilsson]

Try consumerModel.BasicConsume("test", false, "", consumer);

[lukebakken]

As @kjnilsson points out, you are using automatic acknowledgements, which basically negates prefetch/QoS.