# SimpleHttpProxyConsole 簡易端口轉發

C# (.net framework 4.5)

using System;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading.Tasks;

class Program {
    private const string SERVER_IP = "***.***.***.***"; // 目標伺服器的 IP
    private const string CHL_IP = "***.***.***.***";    // 本地 (也就是跳板) 的 IP
    private const int SERVER_A_PORT = 62000;            // 目標伺服器的 Port
    private const int LOCAL_PORT = 62000;               // 本地代理伺服器的 Port

    static async Task Main(string[] args) {
        TcpListener listener = new TcpListener(IPAddress.Any, LOCAL_PORT);
        listener.Start();
        Console.WriteLine($"Proxy server is running on port {LOCAL_PORT}...");

        while (true) {
            TcpClient client = await listener.AcceptTcpClientAsync();
            _ = Task.Run(() => HandleClientAsync(client)); // 每個連線分別處理
        }
    }

    private static async Task HandleClientAsync(TcpClient client) {
        using (client) {
            byte[] buffer = new byte[8192]; // 合理的緩衝區大小
            NetworkStream clientStream = client.GetStream();

            try {
                // 讀取用戶端的 HTTP 請求
                int bytesRead = await clientStream.ReadAsync(buffer, 0, buffer.Length);
                if (bytesRead <= 0) {
                    return; // 用戶端關閉連線
                }

                string clientRequest = Encoding.UTF8.GetString(buffer, 0, bytesRead);
                Console.WriteLine("Client Request Received:");
                Console.WriteLine(clientRequest);

                // 創建與目標伺服器的連線
                using (TcpClient server = new TcpClient(SERVER_IP, SERVER_A_PORT))
                using (NetworkStream serverStream = server.GetStream()) {
                    // 轉發用戶端請求到目標伺服器
                    await serverStream.WriteAsync(buffer, 0, bytesRead);

                    // 接收目標伺服器的回應
                    using (MemoryStream responseStream = new MemoryStream()) {
                        int bytesFromServer;
                        while ((bytesFromServer = await serverStream.ReadAsync(buffer, 0, buffer.Length)) > 0) {
                            responseStream.Write(buffer, 0, bytesFromServer);
                        }

                        // 處理目標伺服器的回應
                        byte[] serverResponseBytes = responseStream.ToArray();
                        string serverResponse = Encoding.UTF8.GetString(serverResponseBytes);

                        Console.WriteLine("Server Response Received:");
                        Console.WriteLine(serverResponse);

                        // 替換 IP 地址
                        if (serverResponse.Contains(SERVER_IP)) {
                            serverResponse = serverResponse.Replace(SERVER_IP, CHL_IP);
                            serverResponseBytes = Encoding.UTF8.GetBytes(serverResponse);
                        }

                        // 回傳處理後的回應給用戶端
                        await clientStream.WriteAsync(serverResponseBytes, 0, serverResponseBytes.Length);
                    }
                }
            }
            catch (Exception ex) {
                Console.WriteLine($"Error: {ex.Message}");
            }
        }
    }
}