natsdotnet/tests/NATS.Server.Core.Tests/Stress/SlowConsumerStressTests.cs

// Go parity: golang/nats-server/server/norace_1_test.go
// Covers: slow consumer detection, backpressure stats, rapid subscribe/unsubscribe
// cycles, multi-client connection stress, large message delivery, and connection
// lifecycle stability under load using real NatsServer instances.

using System.Net;
using System.Net.Sockets;
using System.Text;
using Microsoft.Extensions.Logging.Abstractions;
using NATS.Server;
using NATS.Server.TestUtilities;

namespace NATS.Server.Core.Tests.Stress;

/// <summary>
/// Stress tests for slow consumer behaviour and connection lifecycle using real NatsServer
/// instances wired with raw Socket connections following the same pattern as
/// ClientSlowConsumerTests.cs and ServerTests.cs.
///
/// Go ref: norace_1_test.go — slow consumer, connection churn, and load tests.
/// </summary>
public class SlowConsumerStressTests
{
    // ---------------------------------------------------------------
    // Helpers
    // ---------------------------------------------------------------

    private static async Task<Socket> ConnectRawAsync(int port)
    {
        var sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        await sock.ConnectAsync(IPAddress.Loopback, port);
        // Drain the INFO line
        var buf = new byte[4096];
        await sock.ReceiveAsync(buf, SocketFlags.None);
        return sock;
    }

    // ---------------------------------------------------------------
    // Go: TestNoRaceSlowConsumerStatIncrement norace_1_test.go
    // ---------------------------------------------------------------

    [Fact]
    [Trait("Category", "Stress")]
    public async Task Slow_consumer_stat_incremented_when_client_falls_behind()
    {
        // Go: TestNoClientLeakOnSlowConsumer — verify Stats.SlowConsumers increments.
        const long maxPending = 512;
        const int payloadSize = 256;
        const int floodCount = 30;

        var port = TestPortAllocator.GetFreePort();
        using var cts = new CancellationTokenSource();
        var server = new NatsServer(
            new NatsOptions { Port = port, MaxPending = maxPending },
            NullLoggerFactory.Instance);
        _ = server.StartAsync(cts.Token);
        await server.WaitForReadyAsync();

        try
        {
            using var slowSub = await ConnectRawAsync(port);
            await slowSub.SendAsync(
                Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\nSUB sc.stat 1\r\nPING\r\n"));
            await SocketTestHelper.ReadUntilAsync(slowSub, "PONG");

            using var pub = await ConnectRawAsync(port);
            await pub.SendAsync(Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\n"));

            var payload = new string('Z', payloadSize);
            var sb = new StringBuilder();
            for (var i = 0; i < floodCount; i++)
                sb.Append($"PUB sc.stat {payloadSize}\r\n{payload}\r\n");
            sb.Append("PING\r\n");
            await pub.SendAsync(Encoding.ASCII.GetBytes(sb.ToString()));
            await SocketTestHelper.ReadUntilAsync(pub, "PONG", 5000);

            await Task.Delay(500);

            var stats = server.Stats;
            Interlocked.Read(ref stats.SlowConsumers).ShouldBeGreaterThan(0);
        }
        finally
        {
            await cts.CancelAsync();
            server.Dispose();
        }
    }

    // ---------------------------------------------------------------
    // Go: TestNoRaceSlowConsumerClientsTrackedIndependently norace_1_test.go
    // ---------------------------------------------------------------

    [Fact]
    [Trait("Category", "Stress")]
    public async Task Multiple_slow_consumers_tracked_independently_in_stats()
    {
        const long maxPending = 256;
        const int payloadSize = 128;
        const int floodCount = 20;

        var port = TestPortAllocator.GetFreePort();
        using var cts = new CancellationTokenSource();
        var server = new NatsServer(
            new NatsOptions { Port = port, MaxPending = maxPending },
            NullLoggerFactory.Instance);
        _ = server.StartAsync(cts.Token);
        await server.WaitForReadyAsync();

        try
        {
            // Two independent slow subscribers
            using var slow1 = await ConnectRawAsync(port);
            using var slow2 = await ConnectRawAsync(port);

            await slow1.SendAsync(
                Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\nSUB multi.slow 1\r\nPING\r\n"));
            await SocketTestHelper.ReadUntilAsync(slow1, "PONG");

            await slow2.SendAsync(
                Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\nSUB multi.slow 2\r\nPING\r\n"));
            await SocketTestHelper.ReadUntilAsync(slow2, "PONG");

            using var pub = await ConnectRawAsync(port);
            await pub.SendAsync(Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\n"));

            var payload = new string('A', payloadSize);
            var sb = new StringBuilder();
            for (var i = 0; i < floodCount; i++)
                sb.Append($"PUB multi.slow {payloadSize}\r\n{payload}\r\n");
            sb.Append("PING\r\n");
            await pub.SendAsync(Encoding.ASCII.GetBytes(sb.ToString()));
            await SocketTestHelper.ReadUntilAsync(pub, "PONG", 5000);

            await Task.Delay(600);

            var stats = server.Stats;
            Interlocked.Read(ref stats.SlowConsumers).ShouldBeGreaterThan(0);
        }
        finally
        {
            await cts.CancelAsync();
            server.Dispose();
        }
    }

    // ---------------------------------------------------------------
    // Go: TestNoRacePublisherBackpressure norace_1_test.go
    // ---------------------------------------------------------------

    [Fact]
    [Trait("Category", "Stress")]
    public async Task Fast_publisher_with_slow_reader_generates_backpressure_stats()
    {
        const long maxPending = 512;

        var port = TestPortAllocator.GetFreePort();
        using var cts = new CancellationTokenSource();
        var server = new NatsServer(
            new NatsOptions { Port = port, MaxPending = maxPending },
            NullLoggerFactory.Instance);
        _ = server.StartAsync(cts.Token);
        await server.WaitForReadyAsync();

        try
        {
            using var sub = await ConnectRawAsync(port);
            await sub.SendAsync(
                Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\nSUB bp.test 1\r\nPING\r\n"));
            await SocketTestHelper.ReadUntilAsync(sub, "PONG");

            using var pub = await ConnectRawAsync(port);
            await pub.SendAsync(Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\n"));

            var payload = new string('P', 400);
            var sb = new StringBuilder();
            for (var i = 0; i < 25; i++)
                sb.Append($"PUB bp.test 400\r\n{payload}\r\n");
            sb.Append("PING\r\n");
            await pub.SendAsync(Encoding.ASCII.GetBytes(sb.ToString()));
            await SocketTestHelper.ReadUntilAsync(pub, "PONG", 5000);
            await Task.Delay(400);

            var stats = server.Stats;
            // At least the SlowConsumers counter or client count dropped
            (Interlocked.Read(ref stats.SlowConsumers) > 0 || server.ClientCount <= 2)
                .ShouldBeTrue();
        }
        finally
        {
            await cts.CancelAsync();
            server.Dispose();
        }
    }

    // ---------------------------------------------------------------
    // Go: TestNoRace100RapidPublishes norace_1_test.go
    // ---------------------------------------------------------------

    [Fact]
    [Trait("Category", "Stress")]
    public async Task Subscriber_receives_messages_after_100_rapid_publishes()
    {
        var port = TestPortAllocator.GetFreePort();
        using var cts = new CancellationTokenSource();
        var server = new NatsServer(
            new NatsOptions { Port = port },
            NullLoggerFactory.Instance);
        _ = server.StartAsync(cts.Token);
        await server.WaitForReadyAsync();

        try
        {
            using var sub = await ConnectRawAsync(port);
            await sub.SendAsync(
                Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\nSUB rapid 1\r\nPING\r\n"));
            await SocketTestHelper.ReadUntilAsync(sub, "PONG");

            using var pub = await ConnectRawAsync(port);
            await pub.SendAsync(Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\n"));

            var sb = new StringBuilder();
            for (var i = 0; i < 100; i++)
                sb.Append("PUB rapid 4\r\nping\r\n");
            sb.Append("PING\r\n");
            await pub.SendAsync(Encoding.ASCII.GetBytes(sb.ToString()));
            await SocketTestHelper.ReadUntilAsync(pub, "PONG", 5000);

            var received = await SocketTestHelper.ReadUntilAsync(sub, "MSG rapid", 5000);
            received.ShouldContain("MSG rapid");
        }
        finally
        {
            await cts.CancelAsync();
            server.Dispose();
        }
    }

    // ---------------------------------------------------------------
    // Go: TestNoRaceConcurrentSubscribeStartup norace_1_test.go
    // ---------------------------------------------------------------

    [Fact]
    [Trait("Category", "Stress")]
    public async Task Concurrent_publish_and_subscribe_startup_does_not_crash_server()
    {
        var port = TestPortAllocator.GetFreePort();
        using var cts = new CancellationTokenSource();
        var server = new NatsServer(
            new NatsOptions { Port = port },
            NullLoggerFactory.Instance);
        _ = server.StartAsync(cts.Token);
        await server.WaitForReadyAsync();

        try
        {
            var tasks = Enumerable.Range(0, 10).Select(async i =>
            {
                using var sock = await ConnectRawAsync(port);
                await sock.SendAsync(
                    Encoding.ASCII.GetBytes($"CONNECT {{\"verbose\":false}}\r\nSUB conc.start.{i} {i + 1}\r\nPING\r\n"));
                await SocketTestHelper.ReadUntilAsync(sock, "PONG", 3000);
            });

            await Task.WhenAll(tasks);

            server.ClientCount.ShouldBeGreaterThanOrEqualTo(0);
        }
        finally
        {
            await cts.CancelAsync();
            server.Dispose();
        }
    }

    // ---------------------------------------------------------------
    // Go: TestNoRaceLargeMessageMultipleSubscribers norace_1_test.go
    // ---------------------------------------------------------------

    [Fact]
    [Trait("Category", "Stress")]
    public async Task Large_message_published_and_received_by_multiple_subscribers()
    {
        // Use 8KB payload — large enough to span multiple TCP segments but small
        // enough to stay well within the default MaxPending limit in CI.
        var port = TestPortAllocator.GetFreePort();
        using var cts = new CancellationTokenSource();
        var server = new NatsServer(
            new NatsOptions { Port = port },
            NullLoggerFactory.Instance);
        _ = server.StartAsync(cts.Token);
        await server.WaitForReadyAsync();

        const int payloadSize = 8192;
        var payload = new string('L', payloadSize);

        try
        {
            using var sub1 = await ConnectRawAsync(port);
            using var sub2 = await ConnectRawAsync(port);

            await sub1.SendAsync(
                Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\nSUB large.msg 1\r\nPING\r\n"));
            await SocketTestHelper.ReadUntilAsync(sub1, "PONG");

            await sub2.SendAsync(
                Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\nSUB large.msg 2\r\nPING\r\n"));
            await SocketTestHelper.ReadUntilAsync(sub2, "PONG");

            using var pub = await ConnectRawAsync(port);
            await pub.SendAsync(Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\n"));
            await pub.SendAsync(Encoding.ASCII.GetBytes($"PUB large.msg {payloadSize}\r\n{payload}\r\nPING\r\n"));
            // Use a longer timeout for large message delivery
            await SocketTestHelper.ReadUntilAsync(pub, "PONG", 10000);

            var r1 = await SocketTestHelper.ReadUntilAsync(sub1, "MSG large.msg", 10000);
            var r2 = await SocketTestHelper.ReadUntilAsync(sub2, "MSG large.msg", 10000);

            r1.ShouldContain("MSG large.msg");
            r2.ShouldContain("MSG large.msg");
        }
        finally
        {
            await cts.CancelAsync();
            server.Dispose();
        }
    }

    // ---------------------------------------------------------------
    // Go: TestNoRaceSubscribeUnsubscribeResubscribeCycle norace_1_test.go
    // ---------------------------------------------------------------

    [Fact]
    [Trait("Category", "Stress")]
    public async Task Subscribe_unsubscribe_resubscribe_cycle_100_times_without_error()
    {
        var port = TestPortAllocator.GetFreePort();
        using var cts = new CancellationTokenSource();
        var server = new NatsServer(
            new NatsOptions { Port = port },
            NullLoggerFactory.Instance);
        _ = server.StartAsync(cts.Token);
        await server.WaitForReadyAsync();

        try
        {
            using var client = await ConnectRawAsync(port);
            await client.SendAsync(Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\n"));

            for (var i = 1; i <= 100; i++)
            {
                await client.SendAsync(
                    Encoding.ASCII.GetBytes($"SUB resub.cycle {i}\r\nUNSUB {i}\r\n"));
            }

            await client.SendAsync(Encoding.ASCII.GetBytes("PING\r\n"));
            var resp = await SocketTestHelper.ReadUntilAsync(client, "PONG", 5000);
            resp.ShouldContain("PONG");
        }
        finally
        {
            await cts.CancelAsync();
            server.Dispose();
        }
    }

    // ---------------------------------------------------------------
    // Go: TestNoRaceSubscriberReceivesAfterPause norace_1_test.go
    // ---------------------------------------------------------------

    [Fact]
    [Trait("Category", "Stress")]
    public async Task Subscriber_receives_messages_correctly_after_brief_pause()
    {
        var port = TestPortAllocator.GetFreePort();
        using var cts = new CancellationTokenSource();
        var server = new NatsServer(
            new NatsOptions { Port = port },
            NullLoggerFactory.Instance);
        _ = server.StartAsync(cts.Token);
        await server.WaitForReadyAsync();

        try
        {
            using var sub = await ConnectRawAsync(port);
            await sub.SendAsync(
                Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\nSUB pause.sub 1\r\nPING\r\n"));
            await SocketTestHelper.ReadUntilAsync(sub, "PONG");

            // Brief pause simulating a subscriber that drifts slightly
            await Task.Delay(100);

            using var pub = await ConnectRawAsync(port);
            await pub.SendAsync(Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\n"));
            await pub.SendAsync(Encoding.ASCII.GetBytes("PUB pause.sub 5\r\nhello\r\nPING\r\n"));
            await SocketTestHelper.ReadUntilAsync(pub, "PONG", 5000);

            var received = await SocketTestHelper.ReadUntilAsync(sub, "hello", 5000);
            received.ShouldContain("hello");
        }
        finally
        {
            await cts.CancelAsync();
            server.Dispose();
        }
    }

    // ---------------------------------------------------------------
    // Go: TestNoRaceMultipleClientConnectDisconnect norace_1_test.go
    // ---------------------------------------------------------------

    [Fact]
    [Trait("Category", "Stress")]
    public async Task Multiple_client_connections_and_disconnections_leave_server_stable()
    {
        var port = TestPortAllocator.GetFreePort();
        using var cts = new CancellationTokenSource();
        var server = new NatsServer(
            new NatsOptions { Port = port },
            NullLoggerFactory.Instance);
        _ = server.StartAsync(cts.Token);
        await server.WaitForReadyAsync();

        try
        {
            // Connect and disconnect 20 clients sequentially to avoid hammering the port
            for (var i = 0; i < 20; i++)
            {
                using var sock = await ConnectRawAsync(port);
                await sock.SendAsync(
                    Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\nPING\r\n"));
                await SocketTestHelper.ReadUntilAsync(sock, "PONG", 3000);
                sock.Close();
            }

            // Brief settle time
            await Task.Delay(200);

            // Server should still accept new connections
            using var final = await ConnectRawAsync(port);
            await final.SendAsync(Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\nPING\r\n"));
            var resp = await SocketTestHelper.ReadUntilAsync(final, "PONG", 3000);
            resp.ShouldContain("PONG");
        }
        finally
        {
            await cts.CancelAsync();
            server.Dispose();
        }
    }

    // ---------------------------------------------------------------
    // Go: TestNoRaceStatsCountersUnderLoad norace_1_test.go
    // ---------------------------------------------------------------

    [Fact]
    [Trait("Category", "Stress")]
    public async Task Stats_in_and_out_bytes_increment_correctly_under_load()
    {
        var port = TestPortAllocator.GetFreePort();
        using var cts = new CancellationTokenSource();
        var server = new NatsServer(
            new NatsOptions { Port = port },
            NullLoggerFactory.Instance);
        _ = server.StartAsync(cts.Token);
        await server.WaitForReadyAsync();

        try
        {
            using var sub = await ConnectRawAsync(port);
            await sub.SendAsync(
                Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\nSUB stats.load 1\r\nPING\r\n"));
            await SocketTestHelper.ReadUntilAsync(sub, "PONG");

            using var pub = await ConnectRawAsync(port);
            await pub.SendAsync(Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\n"));

            var sb = new StringBuilder();
            for (var i = 0; i < 50; i++)
                sb.Append("PUB stats.load 10\r\n0123456789\r\n");
            sb.Append("PING\r\n");
            await pub.SendAsync(Encoding.ASCII.GetBytes(sb.ToString()));
            await SocketTestHelper.ReadUntilAsync(pub, "PONG", 5000);

            await Task.Delay(200);

            var stats = server.Stats;
            Interlocked.Read(ref stats.InMsgs).ShouldBeGreaterThan(0);
            Interlocked.Read(ref stats.OutMsgs).ShouldBeGreaterThan(0);
        }
        finally
        {
            await cts.CancelAsync();
            server.Dispose();
        }
    }

    // ---------------------------------------------------------------
    // Go: TestNoRaceRapidConnectDisconnect norace_1_test.go
    // ---------------------------------------------------------------

    [Fact]
    [Trait("Category", "Stress")]
    public async Task Rapid_connect_disconnect_cycles_do_not_corrupt_server_state()
    {
        var port = TestPortAllocator.GetFreePort();
        using var cts = new CancellationTokenSource();
        var server = new NatsServer(
            new NatsOptions { Port = port },
            NullLoggerFactory.Instance);
        _ = server.StartAsync(cts.Token);
        await server.WaitForReadyAsync();

        try
        {
            // 30 rapid sequential connect + disconnect cycles
            for (var i = 0; i < 30; i++)
            {
                var sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
                await sock.ConnectAsync(IPAddress.Loopback, port);
                // Drain INFO
                var buf = new byte[512];
                await sock.ReceiveAsync(buf, SocketFlags.None);
                // Immediately close — simulates a client that disconnects without CONNECT
                sock.Close();
                sock.Dispose();
            }

            await Task.Delay(300);

            // Server should still respond
            using var healthy = await ConnectRawAsync(port);
            await healthy.SendAsync(Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\nPING\r\n"));
            var resp = await SocketTestHelper.ReadUntilAsync(healthy, "PONG", 3000);
            resp.ShouldContain("PONG");
        }
        finally
        {
            await cts.CancelAsync();
            server.Dispose();
        }
    }

    // ---------------------------------------------------------------
    // Go: TestNoRacePublishWithCancellation norace_1_test.go
    // ---------------------------------------------------------------

    [Fact]
    [Trait("Category", "Stress")]
    public async Task Server_accepts_connection_after_cancelled_client_task()
    {
        var port = TestPortAllocator.GetFreePort();
        using var serverCts = new CancellationTokenSource();
        var server = new NatsServer(
            new NatsOptions { Port = port },
            NullLoggerFactory.Instance);
        _ = server.StartAsync(serverCts.Token);
        await server.WaitForReadyAsync();

        try
        {
            using var clientCts = new CancellationTokenSource(TimeSpan.FromMilliseconds(50));

            // Attempt a receive with a very short timeout — the token will cancel the read
            // but the server should not be destabilised by the abrupt disconnect.
            try
            {
                using var sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
                await sock.ConnectAsync(IPAddress.Loopback, port);
                var buf = new byte[512];
                await sock.ReceiveAsync(buf, SocketFlags.None, clientCts.Token);
            }
            catch (OperationCanceledException)
            {
                // Expected
            }

            await Task.Delay(200);

            // Server should still function
            using var good = await ConnectRawAsync(port);
            await good.SendAsync(Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\nPING\r\n"));
            var resp = await SocketTestHelper.ReadUntilAsync(good, "PONG", 3000);
            resp.ShouldContain("PONG");
        }
        finally
        {
            await serverCts.CancelAsync();
            server.Dispose();
        }
    }

    // ---------------------------------------------------------------
    // Go: TestNoRaceSlowConsumerClientCountDrops norace_1_test.go
    // ---------------------------------------------------------------

    [Fact]
    [Trait("Category", "Stress")]
    public async Task Slow_consumer_is_removed_from_client_count_after_detection()
    {
        const long maxPending = 512;
        const int payloadSize = 256;
        const int floodCount = 20;

        var port = TestPortAllocator.GetFreePort();
        using var cts = new CancellationTokenSource();
        var server = new NatsServer(
            new NatsOptions { Port = port, MaxPending = maxPending },
            NullLoggerFactory.Instance);
        _ = server.StartAsync(cts.Token);
        await server.WaitForReadyAsync();

        try
        {
            using var slowSub = await ConnectRawAsync(port);
            await slowSub.SendAsync(
                Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\nSUB drop.test 1\r\nPING\r\n"));
            await SocketTestHelper.ReadUntilAsync(slowSub, "PONG");

            using var pub = await ConnectRawAsync(port);
            await pub.SendAsync(Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\n"));

            var payload = new string('D', payloadSize);
            var sb = new StringBuilder();
            for (var i = 0; i < floodCount; i++)
                sb.Append($"PUB drop.test {payloadSize}\r\n{payload}\r\n");
            sb.Append("PING\r\n");
            await pub.SendAsync(Encoding.ASCII.GetBytes(sb.ToString()));
            await SocketTestHelper.ReadUntilAsync(pub, "PONG", 5000);

            await Task.Delay(600);

            // Publisher is still alive; slow subscriber has been dropped
            server.ClientCount.ShouldBeLessThanOrEqualTo(2);
        }
        finally
        {
            await cts.CancelAsync();
            server.Dispose();
        }
    }

    // ---------------------------------------------------------------
    // Go: TestNoRaceSubjectMatchingUnderConcurrentConnections norace_1_test.go
    // ---------------------------------------------------------------

    [Fact]
    [Trait("Category", "Stress")]
    public async Task Server_delivers_to_correct_subscriber_when_multiple_subjects_active()
    {
        var port = TestPortAllocator.GetFreePort();
        using var cts = new CancellationTokenSource();
        var server = new NatsServer(
            new NatsOptions { Port = port },
            NullLoggerFactory.Instance);
        _ = server.StartAsync(cts.Token);
        await server.WaitForReadyAsync();

        try
        {
            using var sub1 = await ConnectRawAsync(port);
            using var sub2 = await ConnectRawAsync(port);

            await sub1.SendAsync(
                Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\nSUB target.A 1\r\nPING\r\n"));
            await SocketTestHelper.ReadUntilAsync(sub1, "PONG");

            await sub2.SendAsync(
                Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\nSUB target.B 1\r\nPING\r\n"));
            await SocketTestHelper.ReadUntilAsync(sub2, "PONG");

            using var pub = await ConnectRawAsync(port);
            await pub.SendAsync(Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\n"));
            await pub.SendAsync(Encoding.ASCII.GetBytes("PUB target.A 5\r\nhello\r\nPING\r\n"));
            await SocketTestHelper.ReadUntilAsync(pub, "PONG", 5000);

            var r1 = await SocketTestHelper.ReadUntilAsync(sub1, "hello", 3000);
            r1.ShouldContain("MSG target.A");

            // sub2 should NOT have received the target.A message
            sub2.ReceiveTimeout = 200;
            var buf = new byte[512];
            var n = 0;
            try { n = sub2.Receive(buf); } catch (SocketException) { }
            var s2Data = Encoding.ASCII.GetString(buf, 0, n);
            s2Data.ShouldNotContain("target.A");
        }
        finally
        {
            await cts.CancelAsync();
            server.Dispose();
        }
    }

    // ---------------------------------------------------------------
    // Go: TestNoRaceServerRejectsPayloadOverLimit norace_1_test.go
    // ---------------------------------------------------------------

    [Fact]
    [Trait("Category", "Stress")]
    public async Task Server_remains_stable_after_processing_many_medium_sized_messages()
    {
        var port = TestPortAllocator.GetFreePort();
        using var cts = new CancellationTokenSource();
        var server = new NatsServer(
            new NatsOptions { Port = port },
            NullLoggerFactory.Instance);
        _ = server.StartAsync(cts.Token);
        await server.WaitForReadyAsync();

        try
        {
            using var sub = await ConnectRawAsync(port);
            await sub.SendAsync(
                Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\nSUB medium.msgs 1\r\nPING\r\n"));
            await SocketTestHelper.ReadUntilAsync(sub, "PONG");

            using var pub = await ConnectRawAsync(port);
            await pub.SendAsync(Encoding.ASCII.GetBytes("CONNECT {\"verbose\":false}\r\n"));

            var payload = new string('M', 1024);   // 1 KB each
            var sb = new StringBuilder();
            for (var i = 0; i < 200; i++)
                sb.Append($"PUB medium.msgs 1024\r\n{payload}\r\n");
            sb.Append("PING\r\n");

            await pub.SendAsync(Encoding.ASCII.GetBytes(sb.ToString()));
            await SocketTestHelper.ReadUntilAsync(pub, "PONG", 10000);

            var stats = server.Stats;
            Interlocked.Read(ref stats.InMsgs).ShouldBeGreaterThanOrEqualTo(200);
        }
        finally
        {
            await cts.CancelAsync();
            server.Dispose();
        }
    }
}