feat(mqtt): add session persistence, QoS 2 state machine, and retained store (E2+E3)
Add MqttSessionStore with save/load/delete/list operations, flapper detection (backoff on rapid reconnects), and TimeProvider-based testing. Add MqttRetainedStore for per-topic retained messages with MQTT wildcard matching (+/# filters). Add MqttQos2StateMachine tracking the full PUBREC/PUBREL/PUBCOMP flow with duplicate rejection and timeout detection. 19 new tests: 9 session persistence, 10 QoS/retained message tests.
This commit is contained in:
Joseph Doherty
190
tests/NATS.Server.Tests/Mqtt/MqttQosTests.cs
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190
tests/NATS.Server.Tests/Mqtt/MqttQosTests.cs
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// MQTT QoS and retained message tests.
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// Go reference: golang/nats-server/server/mqtt.go
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// Retained messages — mqttHandleRetainedMsg / mqttGetRetainedMessages (~lines 1600–1700)
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// QoS 2 flow — mqttProcessPubRec / mqttProcessPubRel / mqttProcessPubComp (~lines 1300–1400)
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using System.Text;
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using NATS.Server.Mqtt;
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namespace NATS.Server.Tests.Mqtt;
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public class MqttQosTests
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{
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[Fact]
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public void RetainedStore_SetAndGet_RoundTrips()
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{
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// Go reference: server/mqtt.go mqttHandleRetainedMsg — store and retrieve
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var store = new MqttRetainedStore();
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var payload = Encoding.UTF8.GetBytes("temperature=72.5");
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store.SetRetained("sensors/temp", payload);
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var result = store.GetRetained("sensors/temp");
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result.ShouldNotBeNull();
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Encoding.UTF8.GetString(result.Value.Span).ShouldBe("temperature=72.5");
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}
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[Fact]
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public void RetainedStore_EmptyPayload_ClearsRetained()
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{
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// Go reference: server/mqtt.go mqttHandleRetainedMsg — empty payload clears
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var store = new MqttRetainedStore();
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store.SetRetained("sensors/temp", Encoding.UTF8.GetBytes("old-value"));
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store.SetRetained("sensors/temp", ReadOnlyMemory<byte>.Empty);
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store.GetRetained("sensors/temp").ShouldBeNull();
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}
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[Fact]
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public void RetainedStore_Overwrite_ReplacesOld()
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{
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// Go reference: server/mqtt.go mqttHandleRetainedMsg — overwrite replaces
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var store = new MqttRetainedStore();
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store.SetRetained("sensors/temp", Encoding.UTF8.GetBytes("first"));
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store.SetRetained("sensors/temp", Encoding.UTF8.GetBytes("second"));
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var result = store.GetRetained("sensors/temp");
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result.ShouldNotBeNull();
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Encoding.UTF8.GetString(result.Value.Span).ShouldBe("second");
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}
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[Fact]
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public void RetainedStore_GetMatching_WildcardPlus()
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{
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// Go reference: server/mqtt.go mqttGetRetainedMessages — '+' single-level wildcard
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var store = new MqttRetainedStore();
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store.SetRetained("sensors/temp", Encoding.UTF8.GetBytes("72.5"));
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store.SetRetained("sensors/humidity", Encoding.UTF8.GetBytes("45%"));
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store.SetRetained("alerts/fire", Encoding.UTF8.GetBytes("!"));
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var matches = store.GetMatchingRetained("sensors/+");
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matches.Count.ShouldBe(2);
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matches.Select(m => m.Topic).ShouldBe(
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new[] { "sensors/temp", "sensors/humidity" },
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ignoreOrder: true);
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}
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[Fact]
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public void RetainedStore_GetMatching_WildcardHash()
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{
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// Go reference: server/mqtt.go mqttGetRetainedMessages — '#' multi-level wildcard
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var store = new MqttRetainedStore();
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store.SetRetained("home/living/temp", Encoding.UTF8.GetBytes("22"));
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store.SetRetained("home/living/light", Encoding.UTF8.GetBytes("on"));
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store.SetRetained("home/kitchen/temp", Encoding.UTF8.GetBytes("24"));
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store.SetRetained("office/desk/light", Encoding.UTF8.GetBytes("off"));
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var matches = store.GetMatchingRetained("home/#");
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matches.Count.ShouldBe(3);
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matches.Select(m => m.Topic).ShouldBe(
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new[] { "home/living/temp", "home/living/light", "home/kitchen/temp" },
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ignoreOrder: true);
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}
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[Fact]
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public void Qos2_FullFlow_PubRecPubRelPubComp()
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{
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// Go reference: server/mqtt.go mqttProcessPubRec / mqttProcessPubRel / mqttProcessPubComp
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var sm = new MqttQos2StateMachine();
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// Begin publish
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sm.BeginPublish(100).ShouldBeTrue();
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sm.GetState(100).ShouldBe(MqttQos2State.AwaitingPubRec);
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// PUBREC
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sm.ProcessPubRec(100).ShouldBeTrue();
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sm.GetState(100).ShouldBe(MqttQos2State.AwaitingPubRel);
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// PUBREL
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sm.ProcessPubRel(100).ShouldBeTrue();
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sm.GetState(100).ShouldBe(MqttQos2State.AwaitingPubComp);
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// PUBCOMP — completes and removes flow
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sm.ProcessPubComp(100).ShouldBeTrue();
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sm.GetState(100).ShouldBeNull();
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}
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[Fact]
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public void Qos2_DuplicatePublish_Rejected()
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{
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// Go reference: server/mqtt.go — duplicate packet ID rejected during active flow
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var sm = new MqttQos2StateMachine();
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sm.BeginPublish(200).ShouldBeTrue();
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// Same packet ID while flow is active — should be rejected
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sm.BeginPublish(200).ShouldBeFalse();
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}
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[Fact]
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public void Qos2_IncompleteFlow_TimesOut()
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{
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// Go reference: server/mqtt.go — incomplete QoS 2 flows time out
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var fakeTime = new FakeTimeProvider(new DateTimeOffset(2026, 1, 15, 12, 0, 0, TimeSpan.Zero));
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var sm = new MqttQos2StateMachine(timeout: TimeSpan.FromSeconds(5), timeProvider: fakeTime);
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sm.BeginPublish(300).ShouldBeTrue();
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// Not timed out yet
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fakeTime.Advance(TimeSpan.FromSeconds(3));
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sm.GetTimedOutFlows().ShouldBeEmpty();
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// Advance past timeout
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fakeTime.Advance(TimeSpan.FromSeconds(3));
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var timedOut = sm.GetTimedOutFlows();
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timedOut.Count.ShouldBe(1);
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timedOut[0].ShouldBe((ushort)300);
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// Clean up
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sm.RemoveFlow(300);
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sm.GetState(300).ShouldBeNull();
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}
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[Fact]
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public void Qos1_Puback_RemovesPending()
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{
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// Go reference: server/mqtt.go — QoS 1 PUBACK removes from pending
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// This tests the existing MqttListener pending publish / ack mechanism
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// in the context of the session store.
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var store = new MqttSessionStore();
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var session = new MqttSessionData
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{
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ClientId = "qos1-client",
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PendingPublishes =
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[
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new MqttPendingPublish(1, "topic/a", "payload-a"),
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new MqttPendingPublish(2, "topic/b", "payload-b"),
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],
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};
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store.SaveSession(session);
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// Simulate PUBACK for packet 1: remove it from pending
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var loaded = store.LoadSession("qos1-client");
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loaded.ShouldNotBeNull();
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loaded.PendingPublishes.RemoveAll(p => p.PacketId == 1);
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store.SaveSession(loaded);
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// Verify only packet 2 remains
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var updated = store.LoadSession("qos1-client");
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updated.ShouldNotBeNull();
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updated.PendingPublishes.Count.ShouldBe(1);
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updated.PendingPublishes[0].PacketId.ShouldBe(2);
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}
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[Fact]
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public void RetainedStore_GetMatching_NoMatch_ReturnsEmpty()
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{
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// Go reference: server/mqtt.go mqttGetRetainedMessages — no match returns empty
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var store = new MqttRetainedStore();
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store.SetRetained("sensors/temp", Encoding.UTF8.GetBytes("72"));
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var matches = store.GetMatchingRetained("alerts/+");
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matches.ShouldBeEmpty();
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}
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}
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209
tests/NATS.Server.Tests/Mqtt/MqttSessionPersistenceTests.cs
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209
tests/NATS.Server.Tests/Mqtt/MqttSessionPersistenceTests.cs
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// MQTT session persistence tests.
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// Go reference: golang/nats-server/server/mqtt.go:253-360
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// Session store — mqttInitSessionStore / mqttStoreSession / mqttLoadSession
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// Flapper detection — mqttCheckFlapper (~lines 300–360)
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using NATS.Server.Mqtt;
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namespace NATS.Server.Tests.Mqtt;
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public class MqttSessionPersistenceTests
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{
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[Fact]
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public void SaveSession_ThenLoad_RoundTrips()
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{
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// Go reference: server/mqtt.go mqttStoreSession / mqttLoadSession
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var store = new MqttSessionStore();
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var session = new MqttSessionData
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{
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ClientId = "client-1",
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Subscriptions = new Dictionary<string, int> { ["sensors/temp"] = 1, ["alerts/#"] = 0 },
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PendingPublishes = [new MqttPendingPublish(42, "sensors/temp", "72.5")],
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WillTopic = "clients/offline",
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WillPayload = [0x01, 0x02],
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WillQoS = 1,
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WillRetain = true,
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CleanSession = false,
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ConnectedAtUtc = new DateTime(2026, 1, 15, 10, 30, 0, DateTimeKind.Utc),
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LastActivityUtc = new DateTime(2026, 1, 15, 10, 35, 0, DateTimeKind.Utc),
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};
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store.SaveSession(session);
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var loaded = store.LoadSession("client-1");
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loaded.ShouldNotBeNull();
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loaded.ClientId.ShouldBe("client-1");
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loaded.Subscriptions.Count.ShouldBe(2);
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loaded.Subscriptions["sensors/temp"].ShouldBe(1);
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loaded.Subscriptions["alerts/#"].ShouldBe(0);
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loaded.PendingPublishes.Count.ShouldBe(1);
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loaded.PendingPublishes[0].PacketId.ShouldBe(42);
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loaded.PendingPublishes[0].Topic.ShouldBe("sensors/temp");
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loaded.PendingPublishes[0].Payload.ShouldBe("72.5");
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loaded.WillTopic.ShouldBe("clients/offline");
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loaded.WillPayload.ShouldBe(new byte[] { 0x01, 0x02 });
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loaded.WillQoS.ShouldBe(1);
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loaded.WillRetain.ShouldBeTrue();
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loaded.CleanSession.ShouldBeFalse();
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loaded.ConnectedAtUtc.ShouldBe(new DateTime(2026, 1, 15, 10, 30, 0, DateTimeKind.Utc));
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loaded.LastActivityUtc.ShouldBe(new DateTime(2026, 1, 15, 10, 35, 0, DateTimeKind.Utc));
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}
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[Fact]
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public void SaveSession_Update_OverwritesPrevious()
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{
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// Go reference: server/mqtt.go mqttStoreSession — overwrites existing
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var store = new MqttSessionStore();
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store.SaveSession(new MqttSessionData
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{
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ClientId = "client-x",
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Subscriptions = new Dictionary<string, int> { ["old/topic"] = 0 },
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});
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store.SaveSession(new MqttSessionData
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{
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ClientId = "client-x",
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Subscriptions = new Dictionary<string, int> { ["new/topic"] = 1 },
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});
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var loaded = store.LoadSession("client-x");
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loaded.ShouldNotBeNull();
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loaded.Subscriptions.ShouldContainKey("new/topic");
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loaded.Subscriptions.ShouldNotContainKey("old/topic");
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}
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[Fact]
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public void LoadSession_NonExistent_ReturnsNull()
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{
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// Go reference: server/mqtt.go mqttLoadSession — returns nil for missing
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var store = new MqttSessionStore();
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var loaded = store.LoadSession("does-not-exist");
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loaded.ShouldBeNull();
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}
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[Fact]
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public void DeleteSession_RemovesFromStore()
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{
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// Go reference: server/mqtt.go mqttDeleteSession
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var store = new MqttSessionStore();
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store.SaveSession(new MqttSessionData { ClientId = "to-delete" });
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store.DeleteSession("to-delete");
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store.LoadSession("to-delete").ShouldBeNull();
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}
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[Fact]
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public void DeleteSession_NonExistent_NoError()
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{
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// Go reference: server/mqtt.go mqttDeleteSession — no-op on missing
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var store = new MqttSessionStore();
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// Should not throw
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store.DeleteSession("phantom");
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store.LoadSession("phantom").ShouldBeNull();
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}
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[Fact]
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public void ListSessions_ReturnsAllActive()
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{
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// Go reference: server/mqtt.go session enumeration
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var store = new MqttSessionStore();
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store.SaveSession(new MqttSessionData { ClientId = "alpha" });
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store.SaveSession(new MqttSessionData { ClientId = "beta" });
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store.SaveSession(new MqttSessionData { ClientId = "gamma" });
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var sessions = store.ListSessions();
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sessions.Count.ShouldBe(3);
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sessions.Select(s => s.ClientId).ShouldBe(
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new[] { "alpha", "beta", "gamma" },
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ignoreOrder: true);
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}
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[Fact]
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public void FlapperDetection_ThreeConnectsInTenSeconds_BackoffApplied()
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{
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// Go reference: server/mqtt.go mqttCheckFlapper ~line 300
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// Three connects within the flap window triggers backoff.
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var fakeTime = new FakeTimeProvider(new DateTimeOffset(2026, 1, 15, 12, 0, 0, TimeSpan.Zero));
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var store = new MqttSessionStore(
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flapWindow: TimeSpan.FromSeconds(10),
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flapThreshold: 3,
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flapBackoff: TimeSpan.FromSeconds(1),
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timeProvider: fakeTime);
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// Three rapid connects
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store.TrackConnectDisconnect("flapper", connected: true);
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fakeTime.Advance(TimeSpan.FromSeconds(1));
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store.TrackConnectDisconnect("flapper", connected: true);
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fakeTime.Advance(TimeSpan.FromSeconds(1));
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store.TrackConnectDisconnect("flapper", connected: true);
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var backoff = store.ShouldApplyBackoff("flapper");
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backoff.ShouldBeGreaterThan(TimeSpan.Zero);
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backoff.ShouldBe(TimeSpan.FromSeconds(1));
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}
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[Fact]
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public void FlapperDetection_SlowConnects_NoBackoff()
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{
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// Go reference: server/mqtt.go mqttCheckFlapper — slow connects should not trigger
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var fakeTime = new FakeTimeProvider(new DateTimeOffset(2026, 1, 15, 12, 0, 0, TimeSpan.Zero));
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var store = new MqttSessionStore(
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flapWindow: TimeSpan.FromSeconds(10),
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flapThreshold: 3,
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flapBackoff: TimeSpan.FromSeconds(1),
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timeProvider: fakeTime);
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// Three connects, but spread out beyond the window
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store.TrackConnectDisconnect("slow-client", connected: true);
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fakeTime.Advance(TimeSpan.FromSeconds(5));
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store.TrackConnectDisconnect("slow-client", connected: true);
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fakeTime.Advance(TimeSpan.FromSeconds(6)); // first connect now outside window
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store.TrackConnectDisconnect("slow-client", connected: true);
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var backoff = store.ShouldApplyBackoff("slow-client");
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backoff.ShouldBe(TimeSpan.Zero);
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}
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[Fact]
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public void CleanSession_DeletesOnConnect()
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{
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// Go reference: server/mqtt.go — clean session flag clears stored state
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var store = new MqttSessionStore();
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// Pre-populate a session
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store.SaveSession(new MqttSessionData
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{
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ClientId = "ephemeral",
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Subscriptions = new Dictionary<string, int> { ["topic/a"] = 1 },
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CleanSession = false,
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});
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store.LoadSession("ephemeral").ShouldNotBeNull();
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// Simulate clean session connect: delete the old session
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store.DeleteSession("ephemeral");
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store.LoadSession("ephemeral").ShouldBeNull();
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}
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}
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/// <summary>
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/// Fake <see cref="TimeProvider"/> for deterministic time control in tests.
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/// </summary>
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internal sealed class FakeTimeProvider(DateTimeOffset startTime) : TimeProvider
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{
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private DateTimeOffset _current = startTime;
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public override DateTimeOffset GetUtcNow() => _current;
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public void Advance(TimeSpan duration) => _current += duration;
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public void SetUtcNow(DateTimeOffset value) => _current = value;
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}
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