feat(tooling): add standalone rendezvous test client (#25)

src/FinalFactory.Rendezvous.TestClient/DirectEchoProtocol.cs

@@ -0,0 +1,130 @@
+using System.Security.Cryptography;
+using System.Text;
+using LiteNetLib;
+using LiteNetLib.Utils;
+
+namespace FinalFactory.Rendezvous.TestClient;
+
+internal sealed class DirectEchoProtocol : IDisposable
+{
+    private const string PingPrefix = "rv1-ping:";
+    private const string EchoPrefix = "rv1-echo:";
+    private const string AckPrefix = "rv1-ack:";
+    private const string DonePrefix = "rv1-done:";
+    private readonly EventBasedNetListener _events;
+    private readonly bool _host;
+    private readonly Dictionary<NetPeer, string> _hostNonces = [];
+    private readonly TaskCompletionSource<bool> _completed = new(
+        TaskCreationOptions.RunContinuationsAsynchronously);
+    private string? _nonce;
+    private bool _disposed;
+
+    internal DirectEchoProtocol(EventBasedNetListener events, bool host)
+    {
+        _events = events ?? throw new ArgumentNullException(nameof(events));
+        _host = host;
+        _events.NetworkReceiveEvent += OnReceive;
+        _events.PeerDisconnectedEvent += OnPeerDisconnected;
+    }
+
+    internal Task Completion => _completed.Task;
+    internal int PendingHostExchangeCount => _hostNonces.Count;
+    internal event Action<NetPeer>? ExchangeCompleted;
+
+    internal void BeginJoin(NetPeer peer)
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        if (_host || _nonce is not null)
+        {
+            throw new InvalidOperationException("The direct echo exchange is already active.");
+        }
+
+        _nonce = Convert.ToHexString(RandomNumberGenerator.GetBytes(16)).ToLowerInvariant();
+        Send(peer, PingPrefix + _nonce);
+    }
+
+    public void Dispose()
+    {
+        if (_disposed)
+        {
+            return;
+        }
+        _events.NetworkReceiveEvent -= OnReceive;
+        _events.PeerDisconnectedEvent -= OnPeerDisconnected;
+        _hostNonces.Clear();
+        _disposed = true;
+    }
+
+    private void OnReceive(
+        NetPeer peer,
+        NetPacketReader reader,
+        byte channel,
+        DeliveryMethod deliveryMethod)
+    {
+        try
+        {
+            ReadOnlySpan<byte> payload = reader.GetRemainingBytesSpan();
+            if (payload.Length is < 9 or > 64)
+            {
+                return;
+            }
+            string message = Encoding.ASCII.GetString(payload);
+            if (_host && TryNonce(message, PingPrefix, out string? pingNonce))
+            {
+                _hostNonces[peer] = pingNonce!;
+                Send(peer, EchoPrefix + pingNonce);
+            }
+            else if (_host
+                     && _hostNonces.TryGetValue(peer, out string? hostNonce)
+                     && string.Equals(message, AckPrefix + hostNonce, StringComparison.Ordinal))
+            {
+                _hostNonces.Remove(peer);
+                Send(peer, DonePrefix + hostNonce);
+                ExchangeCompleted?.Invoke(peer);
+                _completed.TrySetResult(true);
+            }
+            else if (!_host
+                     && _nonce is not null
+                     && string.Equals(message, EchoPrefix + _nonce, StringComparison.Ordinal))
+            {
+                Send(peer, AckPrefix + _nonce);
+            }
+            else if (!_host
+                     && _nonce is not null
+                     && string.Equals(message, DonePrefix + _nonce, StringComparison.Ordinal))
+            {
+                ExchangeCompleted?.Invoke(peer);
+                _completed.TrySetResult(true);
+            }
+        }
+        finally
+        {
+            reader.Recycle();
+        }
+    }
+
+    private static bool TryNonce(string message, string prefix, out string? nonce)
+    {
+        nonce = null;
+        if (!message.StartsWith(prefix, StringComparison.Ordinal)
+            || message.Length != prefix.Length + 32)
+        {
+            return false;
+        }
+        string candidate = message[prefix.Length..];
+        if (!candidate.All(static character => character is >= '0' and <= '9'
+                or >= 'a' and <= 'f'))
+        {
+            return false;
+        }
+        nonce = candidate;
+        return true;
+    }
+
+    private static void Send(NetPeer peer, string message) => peer.Send(
+        Encoding.ASCII.GetBytes(message),
+        DeliveryMethod.ReliableOrdered);
+
+    private void OnPeerDisconnected(NetPeer peer, DisconnectInfo disconnectInfo) =>
+        _hostNonces.Remove(peer);
+}