natsdotnet/tests/NATS.E2E.Tests/MqttTests.cs

using System.Net;
using System.Net.Sockets;
using System.Text;
using NATS.E2E.Tests.Infrastructure;

namespace NATS.E2E.Tests;

/// <summary>
/// E2E tests for the server's MQTT bridge using the server's line-based MQTT wire protocol.
/// The server exposes a text-framed MQTT protocol (not binary MQTT 3.1.1) on the mqtt port.
/// Wire commands: CONNECT {clientId}, SUB {topic}, PUB {topic} {payload}, PUBQ1 {packetId} {topic} {payload}, ACK {packetId}
/// Wire responses: CONNACK, SUBACK {topic}, MSG {topic} {payload}, PUBACK {packetId}, REDLIVER {packetId} {topic} {payload}
/// </summary>
[Collection("E2E-Mqtt")]
public class MqttTests(MqttServerFixture fixture)
{
    // ---- wire helpers (duplicated per E2E convention, no shared TestHelpers) ----

    private static async Task WriteLineAsync(NetworkStream stream, string line, CancellationToken ct)
    {
        var bytes = Encoding.UTF8.GetBytes(line + "\n");
        await stream.WriteAsync(bytes, ct);
        await stream.FlushAsync(ct);
    }

    private static async Task<string?> ReadLineAsync(NetworkStream stream, CancellationToken ct)
    {
        var bytes = new List<byte>(64);
        var one = new byte[1];
        try
        {
            while (true)
            {
                var read = await stream.ReadAsync(one.AsMemory(0, 1), ct);
                if (read == 0)
                    return null;
                if (one[0] == (byte)'\n')
                    break;
                if (one[0] != (byte)'\r')
                    bytes.Add(one[0]);
            }
        }
        catch (OperationCanceledException)
        {
            return null;
        }

        return Encoding.UTF8.GetString([.. bytes]);
    }

    private static async Task<TcpClient> ConnectMqttClientAsync(int port, string clientId, CancellationToken ct)
    {
        var tcp = new TcpClient();
        await tcp.ConnectAsync(IPAddress.Loopback, port, ct);
        var stream = tcp.GetStream();
        await WriteLineAsync(stream, $"CONNECT {clientId}", ct);
        var connAck = await ReadLineAsync(stream, ct);
        connAck.ShouldBe("CONNACK");
        return tcp;
    }

    // ---- tests ----

    [Fact]
    public async Task Mqtt_PubSub_SameTopicDelivered()
    {
        using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(15));

        // Subscriber connects and subscribes to topic
        using var subTcp = await ConnectMqttClientAsync(fixture.MqttPort, "e2e-sub-1", cts.Token);
        var subStream = subTcp.GetStream();
        await WriteLineAsync(subStream, "SUB e2e/mqtt/test1", cts.Token);
        var subAck = await ReadLineAsync(subStream, cts.Token);
        subAck.ShouldNotBeNull();
        subAck!.ShouldContain("SUBACK");

        // Publisher connects and publishes
        using var pubTcp = await ConnectMqttClientAsync(fixture.MqttPort, "e2e-pub-1", cts.Token);
        var pubStream = pubTcp.GetStream();
        await WriteLineAsync(pubStream, "PUB e2e/mqtt/test1 hello-world", cts.Token);

        // Subscriber receives the message
        var received = new TaskCompletionSource<string>(TaskCreationOptions.RunContinuationsAsynchronously);
        _ = Task.Run(async () =>
        {
            var line = await ReadLineAsync(subStream, cts.Token);
            if (line is not null)
                received.TrySetResult(line);
            else
                received.TrySetCanceled();
        }, cts.Token);

        var msg = await received.Task.WaitAsync(cts.Token);
        msg.ShouldBe("MSG e2e/mqtt/test1 hello-world");
    }

    [Fact]
    public async Task Mqtt_DifferentTopic_NotDelivered()
    {
        using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(15));

        // Subscriber subscribes to topic A
        using var subTcp = await ConnectMqttClientAsync(fixture.MqttPort, "e2e-sub-2", cts.Token);
        var subStream = subTcp.GetStream();
        await WriteLineAsync(subStream, "SUB e2e/mqtt/topicA", cts.Token);
        var subAck = await ReadLineAsync(subStream, cts.Token);
        subAck.ShouldNotBeNull();
        subAck!.ShouldContain("SUBACK");

        // Publisher publishes to topic B (different topic)
        using var pubTcp = await ConnectMqttClientAsync(fixture.MqttPort, "e2e-pub-2", cts.Token);
        var pubStream = pubTcp.GetStream();
        await WriteLineAsync(pubStream, "PUB e2e/mqtt/topicB unrelated-message", cts.Token);

        // Short-timeout read — subscriber should NOT receive anything
        using var shortCts = new CancellationTokenSource(TimeSpan.FromMilliseconds(300));
        var unexpected = await ReadLineAsync(subStream, shortCts.Token);
        unexpected.ShouldBeNull();
    }

    [Fact]
    public async Task Mqtt_Qos1_PubAckReceived_AndDelivered()
    {
        using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(15));

        // Subscriber connects and subscribes
        using var subTcp = await ConnectMqttClientAsync(fixture.MqttPort, "e2e-qos1-sub", cts.Token);
        var subStream = subTcp.GetStream();
        await WriteLineAsync(subStream, "SUB e2e/mqtt/qos1", cts.Token);
        var subAck = await ReadLineAsync(subStream, cts.Token);
        subAck.ShouldNotBeNull();
        subAck!.ShouldContain("SUBACK");

        // Publisher connects and sends QoS 1 publish (PUBQ1 {packetId} {topic} {payload})
        using var pubTcp = await ConnectMqttClientAsync(fixture.MqttPort, "e2e-qos1-pub", cts.Token);
        var pubStream = pubTcp.GetStream();
        await WriteLineAsync(pubStream, "PUBQ1 42 e2e/mqtt/qos1 qos1-message", cts.Token);

        // Publisher receives PUBACK from server
        var pubAck = await ReadLineAsync(pubStream, cts.Token);
        pubAck.ShouldBe("PUBACK 42");

        // Subscriber receives the message
        var received = new TaskCompletionSource<string>(TaskCreationOptions.RunContinuationsAsynchronously);
        _ = Task.Run(async () =>
        {
            var line = await ReadLineAsync(subStream, cts.Token);
            if (line is not null)
                received.TrySetResult(line);
            else
                received.TrySetCanceled();
        }, cts.Token);

        var msg = await received.Task.WaitAsync(cts.Token);
        msg.ShouldBe("MSG e2e/mqtt/qos1 qos1-message");
    }
}