Heartbeat messages cause slow consumer

[Yerken Tussupbekov]

Observed behavior

When a subscription with heartbeat enabled has been running for a while ( few days) it is eventually guaranteed to lead to a slow consumer exception. I believe the reason for this is that every heartbeat received increases the pending message count and that never gets decremented. Eventually it will exceed the pending message limit and when a new (non heartbeat) message is received it will throw slow consumer exception

Expected behavior

Subscription can stay alive as long as it wants without leading to a slow consumer exception

Server and client version

Client v.1.0.4 (but I believe the problem exists in current version as well)
Server v.2.9.16

Host environment

No response

Steps to reproduce

Create a subscription e.g.

        var options = PushSubscribeOptions.Builder()
            .WithStream(_clientContext.PersistentStreamName)
            .WithPendingMessageLimit(10)
            .WithConfiguration(
                ConsumerConfiguration.Builder()
                    .WithIdleHeartbeat(6000)
                    .Build())
            .Build(); 
            ...
        js.PushSubscribeAsync(subject: SubjectName, handler: Handler, autoAck: true, options);

Wait couple of minutes and then push a message into the jetstream and see AsyncErrorEventHandler being triggered with Slow Consumer exception

[Yerken Tussupbekov]

Maybe something like this would be a good fix:

main...ideahitme-github:nats.net:patch-1

[Scott Fauerbach]

@ideahitme-github I think I should not count heartbeats at all. Take a look at this. https://github.com/nats-io/nats.net/pull/881/files
Heartbeat messages get a false from this

BeforeChannelAddCheck.Invoke(msg)

so I'm not going to even count them.

[Yerken Tussupbekov]

that works too. Thanks @scottf