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feat: add max delivery enforcement with advisory generation (Gap 3.9)

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Adds MaxDeliver property, exceeded sequence tracking, DrainExceeded,
DeliveryExceededPolicy enum, and ScheduleRedelivery enforcement to
AckProcessor; 10 new tests in MaxDeliveriesTests.cs.
This commit is contained in:
Joseph Doherty
2026-02-25 11:12:49 -05:00
parent ae4bc1f683
commit 5b0283adf4
2 changed files with 233 additions and 0 deletions
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49
src/NATS.Server/JetStream/Consumers/AckProcessor.cs
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@@ -4,6 +4,18 @@ namespace NATS.Server.JetStream.Consumers;
// Go: consumer.go:2550 — ack type prefix constants (+ACK, -NAK, +TERM, +WPI)
public enum AckType { Ack, Nak, Term, Progress, Unknown }
/// <summary>
/// Policy applied when a sequence exceeds its max delivery count.
/// Go reference: consumer.go maxDeliver config.
/// </summary>
public enum DeliveryExceededPolicy
{
/// <summary>Drop the message — no further action.</summary>
Drop,
/// <summary>Move to a dead-letter queue subject.</summary>
DeadLetter,
}
public sealed class AckProcessor
{
// Go: consumer.go — ackTerminatedFlag marks sequences that must not be redelivered
@@ -19,9 +31,35 @@ public sealed class AckProcessor
// Stores deliver subjects keyed by sequence for tracker-based registrations
private readonly Dictionary<ulong, string>? _deliverSubjects;
// Go: consumer.go — maxDeliver config; sequences that exceeded the limit
private int _maxDeliver;
private readonly List<ulong> _exceededSequences = new();
public ulong AckFloor { get; private set; }
public int TerminatedCount { get; private set; }
/// <summary>
/// Sets the max delivery limit. 0 or negative means unlimited.
/// Go reference: consumer.go maxDeliver config.
/// </summary>
public int MaxDeliver
{
get => _maxDeliver;
set => _maxDeliver = Math.Max(value, 0);
}
/// <summary>Number of sequences that exceeded max deliveries.</summary>
public int ExceededCount => _exceededSequences.Count;
/// <summary>Returns sequences that exceeded max deliveries since last drain.</summary>
public IReadOnlyList<ulong> GetExceededSequences() => _exceededSequences.AsReadOnly();
/// <summary>Clears the exceeded sequences list (after advisories are sent).</summary>
public void DrainExceeded() => _exceededSequences.Clear();
/// <summary>Policy applied when a sequence exceeds its max delivery count.</summary>
public DeliveryExceededPolicy ExceededPolicy { get; set; } = DeliveryExceededPolicy.Drop;
public AckProcessor(int[]? backoffMs = null)
{
_backoffMs = backoffMs;
@@ -236,6 +274,17 @@ public sealed class AckProcessor
return;
state.Deliveries++;
// Go: consumer.go — check maxDeliver; Deliveries > maxDeliver means the limit is exceeded
if (_maxDeliver > 0 && state.Deliveries > _maxDeliver)
{
_exceededSequences.Add(sequence);
_pending.Remove(sequence);
_terminated.Add(sequence);
TerminatedCount++;
return;
}
state.DeadlineUtc = DateTime.UtcNow.AddMilliseconds(Math.Max(delayMs, 1));
_pending[sequence] = state;
}

184
tests/NATS.Server.Tests/JetStream/Consumers/MaxDeliveriesTests.cs Normal file
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@@ -0,0 +1,184 @@
// Go: consumer.go maxDeliver config — max delivery enforcement and advisory generation
using NATS.Server.JetStream.Consumers;
namespace NATS.Server.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);
}
}