natsdotnet/tests/NATS.Server.Tests/ClientTests.cs

using System.IO.Pipelines;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Text.Json;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using NATS.Server;
using NATS.Server.Auth;
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,
        };

        var authService = AuthService.Build(new NatsOptions());
        _natsClient = new NatsClient(1, _serverSocket, new NatsOptions(), serverInfo, authService, null, NullLogger.Instance);
    }

    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);

        response.ShouldStartWith("INFO ");
        response.ShouldContain("server_id");
        response.ShouldContain("\r\n");

        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);

        response.ShouldContain("PONG\r\n");

        await _cts.CancelAsync();
    }

    [Fact]
    public async Task Client_SendErrAsync_writes_correct_wire_format()
    {
        var runTask = _natsClient.RunAsync(_cts.Token);

        // Read INFO first
        var buf = new byte[4096];
        using var readCts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
        await _clientSocket.ReceiveAsync(buf, SocketFlags.None, readCts.Token);

        // Trigger SendErrAsync
        await _natsClient.SendErrAsync("Invalid Subject");

        var n = await _clientSocket.ReceiveAsync(buf, SocketFlags.None, readCts.Token);
        var response = Encoding.ASCII.GetString(buf, 0, n);

        response.ShouldBe("-ERR 'Invalid Subject'\r\n");

        await _cts.CancelAsync();
    }

    [Fact]
    public async Task Client_SendErrAndCloseAsync_sends_error_then_disconnects()
    {
        var runTask = _natsClient.RunAsync(_cts.Token);

        // Read INFO first
        var buf = new byte[4096];
        using var readCts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
        await _clientSocket.ReceiveAsync(buf, SocketFlags.None, readCts.Token);

        // Trigger SendErrAndCloseAsync
        await _natsClient.SendErrAndCloseAsync("maximum connections exceeded");

        var n = await _clientSocket.ReceiveAsync(buf, SocketFlags.None, readCts.Token);
        var response = Encoding.ASCII.GetString(buf, 0, n);

        response.ShouldBe("-ERR 'maximum connections exceeded'\r\n");

        // Connection should be closed — next read returns 0
        n = await _clientSocket.ReceiveAsync(buf, SocketFlags.None, readCts.Token);
        n.ShouldBe(0);
    }
}