natsdotnet/tests/NATS.Server.JetStream.Tests/JetStream/Consumers/MaxDeliveriesTests.cs

// Go: consumer.go maxDeliver config — max delivery enforcement and advisory generation
using NATS.Server.JetStream.Consumers;

namespace NATS.Server.JetStream.Tests.JetStream.Consumers;

public class MaxDeliveriesTests
{
    // Test 1: MaxDeliver=0 means unlimited; many redeliveries do not terminate
    [Fact]
    public void MaxDeliver_zero_means_unlimited()
    {
        // Go: consumer.go — maxDeliver=0 disables the limit entirely
        var ack = new AckProcessor();
        ack.MaxDeliver = 0;
        ack.Register(1, ackWaitMs: 5000);

        for (var i = 0; i < 100; i++)
            ack.ScheduleRedelivery(1, delayMs: 1);

        ack.PendingCount.ShouldBe(1);
        ack.ExceededCount.ShouldBe(0);
        ack.TerminatedCount.ShouldBe(0);
    }

    // Test 2: MaxDeliver=3 terminates on the 4th redelivery attempt
    [Fact]
    public void MaxDeliver_terminates_when_exceeded()
    {
        // Go: consumer.go — maxDeliver enforced in ScheduleRedelivery; Deliveries > maxDeliver → terminate
        var ack = new AckProcessor();
        ack.MaxDeliver = 3;
        ack.Register(1, ackWaitMs: 5000);

        // Deliveries starts at 1 after Register; three more bumps → Deliveries reaches 4
        ack.ScheduleRedelivery(1, delayMs: 1); // Deliveries = 2 (ok)
        ack.ScheduleRedelivery(1, delayMs: 1); // Deliveries = 3 (ok, at limit)
        ack.ScheduleRedelivery(1, delayMs: 1); // Deliveries = 4 (exceeded)

        ack.PendingCount.ShouldBe(0);
        ack.TerminatedCount.ShouldBe(1);
    }

    // Test 3: Exceeded sequence is added to the exceeded list
    [Fact]
    public void Exceeded_sequence_added_to_list()
    {
        // Go: consumer.go — exceeded sequences collected for advisory events
        var ack = new AckProcessor();
        ack.MaxDeliver = 1;
        ack.Register(1, ackWaitMs: 5000);

        // Deliveries starts at 1; next call makes it 2 which exceeds maxDeliver=1
        ack.ScheduleRedelivery(1, delayMs: 1);

        ack.ExceededCount.ShouldBe(1);
        ack.GetExceededSequences().ShouldContain((ulong)1);
    }

    // Test 4: DrainExceeded clears the list after returning sequences
    [Fact]
    public void DrainExceeded_clears_list()
    {
        // Go: consumer.go — drain after sending advisories to avoid duplicate events
        var ack = new AckProcessor();
        ack.MaxDeliver = 1;
        ack.Register(1, ackWaitMs: 5000);
        ack.ScheduleRedelivery(1, delayMs: 1);

        ack.ExceededCount.ShouldBe(1);

        ack.DrainExceeded();

        ack.ExceededCount.ShouldBe(0);
        ack.GetExceededSequences().ShouldBeEmpty();
    }

    // Test 5: Exceeded sequence is moved to the terminated set
    [Fact]
    public void Exceeded_message_is_terminated()
    {
        // Go: consumer.go — exceeded sequence enters terminated set; cannot be redelivered
        var ack = new AckProcessor();
        ack.MaxDeliver = 2;
        ack.Register(1, ackWaitMs: 5000);

        ack.ScheduleRedelivery(1, delayMs: 1); // Deliveries = 2 (at limit)
        ack.ScheduleRedelivery(1, delayMs: 1); // Deliveries = 3 (exceeded)

        // Sequence removed from pending and not redeliverable
        ack.PendingCount.ShouldBe(0);
        ack.TerminatedCount.ShouldBe(1);
    }

    // Test 6: ProcessNak triggers redelivery check through ScheduleRedelivery
    [Fact]
    public void ProcessNak_triggers_redelivery_check()
    {
        // Go: consumer.go — processNak calls ScheduleRedelivery which enforces maxDeliver
        var ack = new AckProcessor();
        ack.MaxDeliver = 2;
        ack.Register(1, ackWaitMs: 5000);

        ack.ProcessNak(1); // Deliveries = 2 (at limit)
        ack.PendingCount.ShouldBe(1);
        ack.ExceededCount.ShouldBe(0);

        ack.ProcessNak(1); // Deliveries = 3 (exceeded)
        ack.PendingCount.ShouldBe(0);
        ack.ExceededCount.ShouldBe(1);
    }

    // Test 7: ScheduleRedelivery enforces max deliver regardless of whether it was called from expiry path
    [Fact]
    public void TryGetExpired_respects_max_deliver()
    {
        // Go: consumer.go — ScheduleRedelivery checks maxDeliver regardless of call site;
        // the expiry redelivery loop calls ScheduleRedelivery so maxDeliver is enforced there too.
        // We verify this by directly calling ScheduleRedelivery after the deadline would have passed,
        // without relying on wall-clock time.
        var ack = new AckProcessor();
        ack.MaxDeliver = 1;
        ack.Register(1, ackWaitMs: 5000);

        // Deliveries starts at 1; calling ScheduleRedelivery makes it 2 which exceeds maxDeliver=1
        // This is exactly what the expiry dispatch loop does: read expired seq, call ScheduleRedelivery
        ack.ScheduleRedelivery(1, delayMs: 1);

        ack.PendingCount.ShouldBe(0);
        ack.ExceededCount.ShouldBe(1);
    }

    // Test 8: MaxDeliver=-1 is treated as unlimited (negative values clamped to 0)
    [Fact]
    public void MaxDeliver_negative_treated_as_unlimited()
    {
        // Go: consumer.go — any non-positive maxDeliver is treated as unlimited
        var ack = new AckProcessor();
        ack.MaxDeliver = -1;
        ack.Register(1, ackWaitMs: 5000);

        for (var i = 0; i < 50; i++)
            ack.ScheduleRedelivery(1, delayMs: 1);

        ack.PendingCount.ShouldBe(1);
        ack.ExceededCount.ShouldBe(0);
        ack.MaxDeliver.ShouldBe(0); // -1 clamped to 0
    }

    // Test 9: ExceededPolicy defaults to Drop
    [Fact]
    public void DeliveryExceededPolicy_defaults_to_drop()
    {
        // Go: consumer.go — default behavior for exceeded messages is to drop them
        var ack = new AckProcessor();

        ack.ExceededPolicy.ShouldBe(DeliveryExceededPolicy.Drop);
    }

    // Test 10: Multiple independent sequences can each exceed max deliveries
    [Fact]
    public void Multiple_sequences_can_exceed()
    {
        // Go: consumer.go — each sequence tracked independently; multiple can exceed in same window
        var ack = new AckProcessor();
        ack.MaxDeliver = 1;
        ack.Register(1, ackWaitMs: 5000);
        ack.Register(2, ackWaitMs: 5000);
        ack.Register(3, ackWaitMs: 5000);

        // Each sequence starts at Deliveries=1; one call makes each exceed maxDeliver=1
        ack.ScheduleRedelivery(1, delayMs: 1);
        ack.ScheduleRedelivery(2, delayMs: 1);
        ack.ScheduleRedelivery(3, delayMs: 1);

        ack.ExceededCount.ShouldBe(3);
        ack.PendingCount.ShouldBe(0);
        ack.TerminatedCount.ShouldBe(3);

        var exceeded = ack.GetExceededSequences();
        exceeded.ShouldContain((ulong)1);
        exceeded.ShouldContain((ulong)2);
        exceeded.ShouldContain((ulong)3);
    }
}