wwtools/mbproxy/tests/Mbproxy.Tests/Proxy/Multiplexing/InFlightByKeyMapTests.cs

using System.Net;
using System.Net.Sockets;
using Mbproxy.Proxy.Multiplexing;
using Microsoft.Extensions.Logging.Abstractions;
using Shouldly;
using Xunit;

namespace Mbproxy.Tests.Proxy.Multiplexing;

/// <summary>
/// Unit tests for the Phase-10 <see cref="InFlightByKeyMap"/>. Covers the atomic
/// attach-or-create primitive (load-bearing concurrency invariant), the per-entry
/// max-parties cap (load-shedding safety valve), and concurrent attach correctness.
/// </summary>
[Trait("Category", "Unit")]
public sealed class InFlightByKeyMapTests
{
    private static UpstreamPipe MakePipe()
    {
        // The map only retains references to InterestedParty; it never reads pipe state.
        // A connected loopback socket satisfies the constructor contract.
        var listener = new TcpListener(IPAddress.Loopback, 0);
        listener.Start();
        var c = new TcpClient();
        c.Connect(IPAddress.Loopback, ((IPEndPoint)listener.LocalEndpoint).Port);
        var s = listener.AcceptSocket();
        listener.Stop();
        return new UpstreamPipe(s, "PLC1", NullLogger.Instance);
    }

    private static InFlightRequest MakeRequest(InterestedParty party, byte fc = 0x03,
        ushort start = 100, ushort qty = 1, byte unit = 1)
    {
        // The factory uses a mutable List<InterestedParty> so the map can append on attach.
        var list = new List<InterestedParty>(capacity: 1) { party };
        return new InFlightRequest(
            UnitId:           unit,
            Fc:               fc,
            StartAddress:     start,
            Qty:              qty,
            InterestedParties: list,
            SentAtUtc:        DateTimeOffset.UtcNow);
    }

    [Fact]
    public async Task AttachOrCreate_NewKey_CallsFactory_WasNewTrue()
    {
        var pipe = MakePipe();
        try
        {
            var map = new InFlightByKeyMap();
            var key = new CoalescingKey(1, 0x03, 100, 1);
            var party = new InterestedParty(pipe, OriginalTxId: 0x1234);

            int factoryCalls = 0;
            map.AttachOrCreate(
                key, party,
                factory: () => { factoryCalls++; return MakeRequest(party); },
                maxParties: 32,
                out var req, out bool wasNew);

            wasNew.ShouldBeTrue("a brand-new key must take the create branch");
            factoryCalls.ShouldBe(1, "the factory must be called exactly once");
            req.ShouldNotBeNull();
            req.InterestedParties.Count.ShouldBe(1);
            map.Count.ShouldBe(1);
        }
        finally
        {
            await pipe.DisposeAsync();
        }
    }

    [Fact]
    public async Task AttachOrCreate_ExistingKey_AppendsParty_WasNewFalse()
    {
        var pipeA = MakePipe();
        var pipeB = MakePipe();
        try
        {
            var map = new InFlightByKeyMap();
            var key = new CoalescingKey(1, 0x03, 100, 1);

            var partyA = new InterestedParty(pipeA, OriginalTxId: 0x1111);
            var partyB = new InterestedParty(pipeB, OriginalTxId: 0x2222);

            int factoryCalls = 0;
            map.AttachOrCreate(key, partyA,
                factory: () => { factoryCalls++; return MakeRequest(partyA); },
                maxParties: 32, out var first, out bool firstWasNew);

            map.AttachOrCreate(key, partyB,
                factory: () => { factoryCalls++; return MakeRequest(partyB); },
                maxParties: 32, out var second, out bool secondWasNew);

            firstWasNew.ShouldBeTrue();
            secondWasNew.ShouldBeFalse("the second attach must coalesce onto the first");
            factoryCalls.ShouldBe(1, "the factory must only fire on the create branch");
            second.ShouldBeSameAs(first, "both attaches must return the same InFlightRequest reference");
            second.InterestedParties.Count.ShouldBe(2, "the second party must be appended in place");
            second.InterestedParties[0].OriginalTxId.ShouldBe((ushort)0x1111);
            second.InterestedParties[1].OriginalTxId.ShouldBe((ushort)0x2222);
        }
        finally
        {
            await pipeA.DisposeAsync();
            await pipeB.DisposeAsync();
        }
    }

    [Fact]
    public async Task AttachOrCreate_ExistingKey_AtMaxParties_CreatesFreshEntry_NotAppend()
    {
        var pipeA = MakePipe();
        var pipeB = MakePipe();
        var pipeC = MakePipe();
        try
        {
            var map = new InFlightByKeyMap();
            var key = new CoalescingKey(1, 0x03, 100, 1);

            var partyA = new InterestedParty(pipeA, OriginalTxId: 0xAAAA);
            var partyB = new InterestedParty(pipeB, OriginalTxId: 0xBBBB);
            var partyC = new InterestedParty(pipeC, OriginalTxId: 0xCCCC);

            // MaxParties = 2 — first attach creates, second appends, third overflows.
            map.AttachOrCreate(key, partyA,
                factory: () => MakeRequest(partyA), maxParties: 2,
                out var first, out _);
            map.AttachOrCreate(key, partyB,
                factory: () => MakeRequest(partyB), maxParties: 2,
                out var second, out _);

            int factoryCalls = 0;
            map.AttachOrCreate(key, partyC,
                factory: () => { factoryCalls++; return MakeRequest(partyC); },
                maxParties: 2,
                out var third, out bool thirdWasNew);

            thirdWasNew.ShouldBeTrue("the third attach must overflow into a fresh entry");
            factoryCalls.ShouldBe(1, "the factory must fire to create the overflow entry");
            third.ShouldNotBeSameAs(first, "the overflow must be a distinct InFlightRequest");
            third.InterestedParties.Count.ShouldBe(1, "the overflow entry starts with only its triggering party");
            first.InterestedParties.Count.ShouldBe(2, "the original entry stays capped at maxParties");
        }
        finally
        {
            await pipeA.DisposeAsync();
            await pipeB.DisposeAsync();
            await pipeC.DisposeAsync();
        }
    }

    [Fact]
    public async Task TryRemove_AfterAttach_AllPartiesPresent_InRetrievedEntry()
    {
        var pipeA = MakePipe();
        var pipeB = MakePipe();
        try
        {
            var map = new InFlightByKeyMap();
            var key = new CoalescingKey(1, 0x03, 100, 1);

            var partyA = new InterestedParty(pipeA, 1);
            var partyB = new InterestedParty(pipeB, 2);

            map.AttachOrCreate(key, partyA, () => MakeRequest(partyA), 32, out _, out _);
            map.AttachOrCreate(key, partyB, () => MakeRequest(partyB), 32, out _, out _);

            bool removed = map.TryRemove(key, out var req);

            removed.ShouldBeTrue();
            req.InterestedParties.Count.ShouldBe(2, "both attached parties must be present in the removed entry");
            map.Count.ShouldBe(0);
        }
        finally
        {
            await pipeA.DisposeAsync();
            await pipeB.DisposeAsync();
        }
    }

    [Fact]
    public void TryRemove_OfMissing_ReturnsFalse()
    {
        var map = new InFlightByKeyMap();
        var key = new CoalescingKey(1, 0x03, 100, 1);

        map.TryRemove(key, out _).ShouldBeFalse("removing a never-attached key must report false");
    }

    [Fact]
    public async Task Concurrent_AttachOrCreate_From_Two_Threads_NoLostParties_AndNoDuplicateEntries()
    {
        // 16 tasks × 500 ops each, all racing on the same key. The map must keep exactly
        // one entry per key (unlimited MaxParties → no overflow). Each successful attach
        // must contribute exactly one party to whatever entry was created/joined.
        //
        // Each task reuses a single UpstreamPipe across its ops — the map only stores the
        // InterestedParty reference; pipe state is irrelevant to the map's invariants.
        // Spinning up 100 × 1000 = 100,000 loopback sockets exhausts the test machine's
        // ephemeral port pool; we use one pipe per task instead.
        const int Tasks = 16;
        const int OpsPerTask = 500;
        const int MaxParties = int.MaxValue;

        var map = new InFlightByKeyMap();
        var key = new CoalescingKey(1, 0x03, 100, 1);
        var pipes = new List<UpstreamPipe>(Tasks);
        for (int i = 0; i < Tasks; i++) pipes.Add(MakePipe());

        long attaches = 0;
        long creates  = 0;

        try
        {
            var work = new Task[Tasks];
            var workCt = TestContext.Current.CancellationToken;
            for (int t = 0; t < Tasks; t++)
            {
                var pipe = pipes[t];
                work[t] = Task.Run(() =>
                {
                    for (int i = 0; i < OpsPerTask; i++)
                    {
                        if (workCt.IsCancellationRequested) return;
                        var party = new InterestedParty(pipe, (ushort)i);
                        map.AttachOrCreate(
                            key, party,
                            factory: () => MakeRequest(party),
                            maxParties: MaxParties,
                            out _, out bool wasNew);
                        if (wasNew) Interlocked.Increment(ref creates);
                        else        Interlocked.Increment(ref attaches);
                    }
                }, workCt);
            }
            await Task.WhenAll(work);

            (creates + attaches).ShouldBe((long)(Tasks * OpsPerTask), "every op must take exactly one branch");
            creates.ShouldBe(1, "all ops share the same key with unlimited MaxParties — exactly one create");

            // The retained entry must contain every attached party.
            bool removed = map.TryRemove(key, out var entry);
            removed.ShouldBeTrue();
            entry.InterestedParties.Count.ShouldBe(Tasks * OpsPerTask,
                "the entry's party list must hold every attached party — no lost parties under race");
            map.Count.ShouldBe(0);
        }
        finally
        {
            foreach (var p in pipes)
                try { await p.DisposeAsync(); } catch { }
        }
    }
}