feat: implement NatsClient connection handler with read/write pipeline

tests/NATS.Server.Tests/ClientTests.cs

@@ -0,0 +1,87 @@
+using System.IO.Pipelines;
+using System.Net;
+using System.Net.Sockets;
+using System.Text;
+using System.Text.Json;
+using NATS.Server;
+using NATS.Server.Protocol;
+
+namespace NATS.Server.Tests;
+
+public class ClientTests : IAsyncDisposable
+{
+    private readonly Socket _serverSocket;
+    private readonly Socket _clientSocket;
+    private readonly NatsClient _natsClient;
+    private readonly CancellationTokenSource _cts = new();
+
+    public ClientTests()
+    {
+        // Create connected socket pair via loopback
+        var listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
+        listener.Bind(new IPEndPoint(IPAddress.Loopback, 0));
+        listener.Listen(1);
+        var port = ((IPEndPoint)listener.LocalEndPoint!).Port;
+
+        _clientSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
+        _clientSocket.Connect(IPAddress.Loopback, port);
+        _serverSocket = listener.Accept();
+        listener.Dispose();
+
+        var serverInfo = new ServerInfo
+        {
+            ServerId = "test",
+            ServerName = "test",
+            Version = "0.1.0",
+            Host = "127.0.0.1",
+            Port = 4222,
+        };
+
+        _natsClient = new NatsClient(1, _serverSocket, new NatsOptions(), serverInfo);
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        await _cts.CancelAsync();
+        _natsClient.Dispose();
+        _clientSocket.Dispose();
+    }
+
+    [Fact]
+    public async Task Client_sends_INFO_on_start()
+    {
+        var runTask = _natsClient.RunAsync(_cts.Token);
+
+        // Read from client socket — should get INFO
+        var buf = new byte[4096];
+        var n = await _clientSocket.ReceiveAsync(buf, SocketFlags.None);
+        var response = Encoding.ASCII.GetString(buf, 0, n);
+
+        Assert.StartsWith("INFO ", response);
+        Assert.Contains("server_id", response);
+        Assert.Contains("\r\n", response);
+
+        await _cts.CancelAsync();
+    }
+
+    [Fact]
+    public async Task Client_responds_PONG_to_PING()
+    {
+        var runTask = _natsClient.RunAsync(_cts.Token);
+
+        // Read INFO
+        var buf = new byte[4096];
+        await _clientSocket.ReceiveAsync(buf, SocketFlags.None);
+
+        // Send CONNECT then PING
+        await _clientSocket.SendAsync(Encoding.ASCII.GetBytes("CONNECT {}\r\nPING\r\n"));
+
+        // Read response — should get PONG
+        var n = await _clientSocket.ReceiveAsync(buf, SocketFlags.None);
+        var response = Encoding.ASCII.GetString(buf, 0, n);
+
+        Assert.Contains("PONG\r\n", response);
+
+        await _cts.CancelAsync();
+    }
+}