Add TcpRpc server and client and split crypto code into multiple classes

Networking/AesPacketCrypto.cs

@@ -0,0 +1,16 @@
+using RemSox.Utils;
+
+namespace RemSox.Networking;
+
+internal class AesPacketCrypto(byte[] key) : IPacketCrypto
+{
+    public byte[] Decrypt(byte[] data)
+    {
+        return AesGcmCrypto.Decrypt(data, key);
+    }
+
+    public byte[] Encrypt(byte[] data)
+    {
+        return AesGcmCrypto.Encrypt(data, key);
+    }
+}

Networking/IPacketCrypto.cs

@@ -0,0 +1,8 @@
+namespace RemSox.Networking;
+
+public interface IPacketCrypto
+{
+    byte[] Encrypt(byte[] data);
+
+    byte[] Decrypt(byte[] data);
+}

Networking/TcpConnection.cs

@@ -0,0 +1,18 @@
+using System.Net.Sockets;
+
+/// <summary>
+/// Simple wrapper around TcpClient to hold connection-scoped resources safely.
+/// </summary>
+public class TcpConnection(TcpClient client) : IDisposable
+{
+    public TcpClient Client { get; } = client;
+    public NetworkStream Stream { get; } = client.GetStream();
+    public SemaphoreSlim SendLock { get; } = new(1, 1);
+
+    public void Dispose()
+    {
+        Stream.Dispose();
+        Client.Dispose();
+        SendLock.Dispose();
+    }
+}

Networking/TcpMessage.cs

@@ -0,0 +1,8 @@
+namespace RemSox.Networking;
+
+public class TcpMessage
+{
+    public string Type { get; set; } = string.Empty;
+    public string RequestId { get; set; } = string.Empty;
+    public byte[] Payload { get; set; } = [];
+}

Networking/TcpRpcBase.cs

@@ -0,0 +1,141 @@
+using RemSox.Networking;
+
+using System.Buffers.Binary;
+using System.Collections.Concurrent;
+using System.Diagnostics.CodeAnalysis;
+using System.Net.Sockets;
+using System.Text.Json;
+
+public abstract class TcpRpcBase(IPacketCrypto? crypto = null)
+{
+    protected readonly IPacketCrypto? crypto = crypto;
+    protected readonly Dictionary<string, Func<TcpConnection, TcpMessage, Task>> handlers = [];
+    protected readonly ConcurrentDictionary<string, TaskCompletionSource<byte[]>> pendingRequests = new();
+
+    // Security Guard: Prevent OOM/DoS via oversized length headers (Default: 32MB)
+    protected const int MaxMessageSize = 32 * 1024 * 1024;
+
+    /// <summary>
+    /// Base message registration for handlers tracking the sending connection.
+    /// </summary>
+    [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "Handled via library constraints")]
+    public void ListenTo<T>(string type, Func<TcpConnection, T, Task> handler)
+    {
+        handlers[type] = async (conn, msg) =>
+        {
+            T data = JsonSerializer.Deserialize<T>(msg.Payload)!;
+            await handler(conn, data);
+        };
+    }
+
+    /// <summary>
+    /// Overloaded listener where connection mapping can be ignored (Convenient for Clients).
+    /// </summary>
+    public void ListenTo<T>(string type, Func<T, Task> handler)
+    {
+        ListenTo<T>(type, async (_, data) => await handler(data));
+    }
+
+    [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "Handled via library constraints")]
+    protected async Task SendRaw(TcpConnection conn, TcpMessage msg)
+    {
+        byte[] data = JsonSerializer.SerializeToUtf8Bytes(msg);
+
+        if (crypto is not null)
+        {
+            data = crypto.Encrypt(data);
+        }
+
+        // Allocate a single contiguous frame buffer to prevent inter-thread fragmentation 
+        // and eliminate redundant Socket Write Syscalls.
+        byte[] packet = new byte[4 + data.Length];
+        BinaryPrimitives.WriteInt32LittleEndian(packet, data.Length);
+        Array.Copy(data, 0, packet, 4, data.Length);
+
+        // Enforce sequence safety across multiple threads pushing data out of a singular stream
+        await conn.SendLock.WaitAsync();
+        try
+        {
+            await conn.Stream.WriteAsync(packet);
+        }
+        finally
+        {
+            _ = conn.SendLock.Release();
+        }
+    }
+
+    [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "Handled via library constraints")]
+    protected async Task HandleConnection(TcpConnection conn, CancellationToken token = default)
+    {
+        NetworkStream stream = conn.Stream;
+        byte[] lengthBytes = new byte[4];
+
+        try
+        {
+            while (!token.IsCancellationRequested && conn.Client.Connected)
+            {
+                // 1. Frame Length Read
+                await stream.ReadExactlyAsync(lengthBytes, token);
+                int length = BinaryPrimitives.ReadInt32LittleEndian(lengthBytes);
+
+                // DoS Payload Protection Check
+                if (length is <= 0 or > MaxMessageSize)
+                {
+                    throw new InvalidDataException($"Protocol violation: Received packet length of {length} bytes exceeds limits.");
+                }
+
+                // 2. Body Payload Read
+                byte[] buffer = new byte[length];
+                await stream.ReadExactlyAsync(buffer, token);
+
+                if (crypto is not null)
+                {
+                    buffer = crypto.Decrypt(buffer);
+                }
+
+                TcpMessage? msg = JsonSerializer.Deserialize<TcpMessage>(buffer);
+                if (msg is null)
+                {
+                    continue;
+                }
+
+                // 3. Response Handler Check
+                if (pendingRequests.TryGetValue(msg.RequestId, out TaskCompletionSource<byte[]>? tcs))
+                {
+                    _ = tcs.TrySetResult(msg.Payload);
+                    _ = pendingRequests.TryRemove(msg.RequestId, out _);
+                    continue;
+                }
+
+                // 4. Inbound Router Handler
+                if (handlers.TryGetValue(msg.Type, out Func<TcpConnection, TcpMessage, Task>? handler))
+                {
+                    // Decouple handler execution to the ThreadPool so slow business logic 
+                    // doesn't bottleneck packet processing from the network stream interface.
+                    _ = Task.Run(async () =>
+                    {
+                        try
+                        {
+                            await handler(conn, msg);
+                        }
+                        catch
+                        {
+                            // Operational log placement here for user exceptions inside delegates
+                        }
+                    }, token);
+                }
+            }
+        }
+        catch
+        {
+            // Explicitly handles natural dropping scenarios cleanly
+        }
+        finally
+        {
+            OnConnectionClosed(conn);
+            conn.Dispose();
+        }
+    }
+
+    protected abstract void OnConnectionClosed(TcpConnection conn);
+}

Networking/TcpRpcClient.cs

@@ -0,0 +1,92 @@
+using System.Diagnostics.CodeAnalysis;
+using System.Net.Sockets;
+using System.Text.Json;
+
+namespace RemSox.Networking;
+
+public class TcpRpcClient(IPacketCrypto? crypto = null) : TcpRpcBase(crypto)
+{
+    private TcpConnection? connection;
+
+    public async Task ConnectAsync(string host, int port)
+    {
+        TcpClient client = new();
+        await client.ConnectAsync(host, port);
+
+        connection = new TcpConnection(client);
+
+        // Run network monitoring task loop background-detached
+        _ = HandleConnection(connection);
+    }
+
+    [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "Handled via library constraints")]
+    public async Task<TRes> RequestAsync<TReq, TRes>(string type, TReq request, TimeSpan timeout = default)
+    {
+        if (connection is null)
+        {
+            throw new InvalidOperationException("Client not connected.");
+        }
+
+        if (timeout == default)
+        {
+            timeout = TimeSpan.FromSeconds(30); // Default fallback timeout
+        }
+
+        string requestId = Guid.NewGuid().ToString();
+        TaskCompletionSource<byte[]> tcs = new(TaskCreationOptions.RunContinuationsAsynchronously);
+        pendingRequests[requestId] = tcs;
+
+        try
+        {
+            await SendRaw(connection, new TcpMessage
+            {
+                Type = type,
+                RequestId = requestId,
+                Payload = JsonSerializer.SerializeToUtf8Bytes(request)
+            });
+
+            // Enforce async timeout safety to prevent permanent dictionary leaks on dropped calls
+            using CancellationTokenSource timeoutCts = new(timeout);
+            await using (timeoutCts.Token.Register(() => tcs.TrySetCanceled()))
+            {
+                byte[] responseBytes = await tcs.Task;
+                return JsonSerializer.Deserialize<TRes>(responseBytes)!;
+            }
+        }
+        finally
+        {
+            _ = pendingRequests.TryRemove(requestId, out _);
+        }
+    }
+
+    [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "Handled via library constraints")]
+    public Task SendAsync<T>(string type, T data)
+    {
+        if (connection is null)
+        {
+            throw new InvalidOperationException("Client not connected.");
+        }
+
+        return SendRaw(connection, new TcpMessage
+        {
+            Type = type,
+            RequestId = Guid.NewGuid().ToString(),
+            Payload = JsonSerializer.SerializeToUtf8Bytes(data)
+        });
+    }
+
+    protected override void OnConnectionClosed(TcpConnection conn)
+    {
+        if (connection == conn)
+        {
+            connection = null;
+        }
+
+        // Fail-fast all lingering tasks waiting on an dead connection loop
+        foreach (TaskCompletionSource<byte[]> req in pendingRequests.Values)
+        {
+            _ = req.TrySetException(new SocketException((int)SocketError.ConnectionReset));
+        }
+        pendingRequests.Clear();
+    }
+}

Networking/TcpRpcServer.cs

@@ -0,0 +1,94 @@
+using System.Collections.Concurrent;
+using System.Diagnostics.CodeAnalysis;
+using System.Net;
+using System.Net.Sockets;
+using System.Text.Json;
+
+namespace RemSox.Networking;
+
+public class TcpRpcServer(IPacketCrypto? crypto = null) : TcpRpcBase(crypto)
+{
+    // Fix: Using ConcurrentDictionary to prevent collection errors during structural additions/prunings
+    private readonly ConcurrentDictionary<TcpConnection, byte> connections = new();
+    private TcpListener? listener;
+    private CancellationTokenSource? cts;
+
+    public async Task StartAsync(int port, CancellationToken token = default)
+    {
+        cts = CancellationTokenSource.CreateLinkedTokenSource(token);
+
+        listener = new TcpListener(IPAddress.Any, port);
+        listener.Start();
+
+        try
+        {
+            while (!cts.IsCancellationRequested)
+            {
+                TcpClient client = await listener.AcceptTcpClientAsync(cts.Token);
+
+                TcpConnection conn = new(client);
+                _ = connections.TryAdd(conn, 0);
+
+                _ = HandleConnection(conn, cts.Token);
+            }
+        }
+        catch (OperationCanceledException)
+        {
+            // Expected shutdown scenario
+        }
+    }
+
+    public void Stop()
+    {
+        cts?.Cancel();
+        listener?.Stop();
+
+        foreach (TcpConnection c in connections.Keys)
+        {
+            c.Dispose();
+        }
+
+        connections.Clear();
+    }
+
+    [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "Handled via library constraints")]
+    public void RespondTo<TReq, TRes>(string type, Func<TReq, Task<TRes>> handler)
+    {
+        handlers[type] = async (conn, msg) =>
+        {
+            TReq req = JsonSerializer.Deserialize<TReq>(msg.Payload)!;
+            TRes res = await handler(req);
+
+            await SendRaw(conn, new TcpMessage
+            {
+                Type = type,
+                RequestId = msg.RequestId,
+                Payload = JsonSerializer.SerializeToUtf8Bytes(res)
+            });
+        };
+    }
+
+    [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "Handled via library constraints")]
+    public Task SendToAll<T>(string type, T data)
+    {
+        byte[] payloadBytes = JsonSerializer.SerializeToUtf8Bytes(data);
+        List<Task> sendTasks = [];
+
+        foreach (TcpConnection conn in connections.Keys)
+        {
+            sendTasks.Add(SendRaw(conn, new TcpMessage
+            {
+                Type = type,
+                RequestId = Guid.NewGuid().ToString(),
+                Payload = payloadBytes
+            }));
+        }
+
+        return Task.WhenAll(sendTasks);
+    }
+
+    protected override void OnConnectionClosed(TcpConnection conn)
+    {
+        _ = connections.TryRemove(conn, out _);
+    }
+}