專案目標

使用原始 Socket 建立 HTTP/1.0 伺服器，瀏覽器輸入 https://ip:port 即可看到伺服器當前時間，無需撰寫客戶端程式。適合理解 HTTP 協議本質、嵌入式裝置管理介面、輕量健康檢查端點。

完整原始碼 (Console Application)

using System;
using System.Collections.Generic;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading;

namespace MiniHttpServer
{
    class HttpProcessor
    {
        private readonly Socket _clientSocket;
        private readonly BufferedStream _stream;
        private readonly StreamReader _reader;
        private readonly StreamWriter _writer;

        public HttpProcessor(Socket clientSocket)
        {
            _clientSocket = clientSocket;
            var netStream = new NetworkStream(clientSocket, FileAccess.ReadWrite, ownsSocket: false);
            _stream = new BufferedStream(netStream);
            _reader = new StreamReader(_stream, Encoding.ASCII);
            _writer = new StreamWriter(_stream, Encoding.ASCII) { AutoFlush = true, NewLine = "\r\n" };
        }

        public void Process()
        {
            try
            {
                // 1. 讀取請求行 (只處理第一行：GET / HTTP/1.1)
                string requestLine = _reader.ReadLine();
                if (string.IsNullOrEmpty(requestLine)) return;

                Console.WriteLine($"Request: {requestLine}");

                // 2. 讀取並丟棄標頭 (直到空行)
                while (!string.IsNullOrEmpty(_reader.ReadLine())) { }

                // 3. 回應 HTTP 200 OK + 時間內容
                WriteSuccessResponse();
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Process error: {ex.Message}");
                try { WriteErrorResponse(); } catch { }
            }
            finally
            {
                // 關閉連線 (HTTP/1.0 無 Keep-Alive)
                try { _clientSocket.Shutdown(SocketShutdown.Both); } catch { }
                _clientSocket.Close();
            }
        }

        private void WriteSuccessResponse()
        {
            string time = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss");
            string body = $"
Server Time
{time}
";
            byte[] bodyBytes = Encoding.UTF8.GetBytes(body);

            _writer.WriteLine("HTTP/1.0 200 OK");
            _writer.WriteLine("Server: MiniHttpServer/1.0");
            _writer.WriteLine($"Date: {DateTime.UtcNow:R}"); // RFC 1123
            _writer.WriteLine("Content-Type: text/html; charset=utf-8");
            _writer.WriteLine($"Content-Length: {bodyBytes.Length}");
            _writer.WriteLine("Connection: close");
            _writer.WriteLine(); // 空行分隔標頭與內文
            _writer.Flush();

            _stream.Write(bodyBytes, 0, bodyBytes.Length);
            _stream.Flush();
        }

        private void WriteErrorResponse()
        {
            string body = "
404 Not Found
";
            byte[] bodyBytes = Encoding.UTF8.GetBytes(body);

            _writer.WriteLine("HTTP/1.0 404 Not Found");
            _writer.WriteLine("Content-Type: text/html; charset=utf-8");
            _writer.WriteLine($"Content-Length: {bodyBytes.Length}");
            _writer.WriteLine("Connection: close");
            _writer.WriteLine();
            _writer.Flush();

            _stream.Write(bodyBytes, 0, bodyBytes.Length);
        }
    }

    class HttpServer
    {
        private readonly int _port;
        private readonly IPAddress _bindAddress;
        private Socket _listener;
        private volatile bool _running;

        public HttpServer(int port = 8080, string bindIp = "0.0.0.0")
        {
            _port = port;
            _bindAddress = IPAddress.Parse(bindIp);
        }

        public void Start()
        {
            _listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            _listener.Bind(new IPEndPoint(_bindAddress, _port));
            _listener.Listen(100); // backlog
            _running = true;

            Console.WriteLine($"HTTP Server started on https://{_bindAddress}:{_port}");
            Console.WriteLine("Press Ctrl+C to stop...");

            while (_running)
            {
                try
                {
                    Socket client = _listener.Accept(); // 封鎖等待連線
                    ThreadPool.QueueUserWorkItem(_ => new HttpProcessor(client).Process());
                }
                catch (SocketException ex) when (!_running)
                {
                    break; // 正常停止
                }
                catch (Exception ex)
                {
                    Console.WriteLine($"Accept error: {ex.Message}");
                }
            }
        }

        public void Stop()
        {
            _running = false;
            _listener?.Close();
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            int port = args.Length > 0 ? int.Parse(args[0]) : 8080;
            var server = new HttpServer(port);
            
            Console.CancelKeyPress += (s, e) => { e.Cancel = true; server.Stop(); };
            
            server.Start();
        }
    }
}

核心流程圖解

[瀏覽器] ── TCP 連線 (三次交手) ──→ [Socket.Accept()]
    │                                      │
    │  GET / HTTP/1.1\r\n                  │
    │  Host: localhost:8080\r\n            │  StreamReader.ReadLine()
    │  User-Agent: ...\r\n                 │  (讀取請求行)
    │  \r\n                                │  (讀取並丟棄標頭)
    │                                     ▼
    │  HTTP/1.0 200 OK\r\n               StreamWriter.WriteLine()
    │  Content-Type: text/html\r\n       (寫入狀態行、標頭)
    │  Content-Length: 123\r\n           │
    │  \r\n                               │  (空行)
    │  ...時間...            │  Stream.Write(bodyBytes)
    │                                     │
    ◄── TCP 關閉 (四次揮手) ─────────────┘  Socket.Shutdown/Close

關鍵技術細節

1. HTTP 協議最小實作要素

• 狀態行：HTTP/1.0 200 OK (版本、狀態碼、原因片語)
• 必要標頭：Content-Type (MIME + charset)、Content-Length (內文位元組數)
• 空行分隔：標頭結束必須有 \r\n\r\n
• 內文：HTML/JSON/純文字等
• Connection: close：HTTP/1.0 預設短連線，回應後主動關閉

2. Socket 非同步改良 (.NET 4.5+)

// 使用 AcceptAsync + ReceiveAsync/SendAsync (SocketAsyncEventArgs) 或
// 更簡單：TcpListener + NetworkStream (參考前文 TCP 時間伺服器)
// 真實生產環境建議用 Kestrel (ASP.NET Core) 或成熟庫

3. 多執行緒模型

• ThreadPool.QueueUserWorkItem：每請求一執行緒池工作項，簡單但高併發下執行緒耗盡
• 改良：SemaphoreSlim 限制併發數、或完整非同步 I/O

4. 繫結 IP 位址選擇

• 0.0.0.0 (IPAddress.Any)：監聽所有網卡介面 (預設)
• 127.0.0.1 (IPAddress.Loopback)：僅本機存取 (安全)
• 特定 LAN IP：僅接受內網請求

功能擴充範例

支援路由：不同路徑回應不同內容

private void Process()
{
    string requestLine = _reader.ReadLine(); // "GET /time HTTP/1.1"
    if (string.IsNullOrEmpty(requestLine)) return;

    string[] parts = requestLine.Split(' ');
    if (parts.Length < 2) return;
    string path = parts[1]; // "/time"

    // 讀取標頭
    while (!string.IsNullOrEmpty(_reader.ReadLine())) { }

    // 簡單路由
    switch (path)
    {
        case "/":
        case "/time":
            WriteHtml($"
Server Time
{DateTime.Now:yyyy-MM-dd HH:mm:ss}
");
            break;
        case "/json":
            WriteJson(new { time = DateTime.UtcNow.ToString("o"), server = "MiniHttpServer" });
            break;
        case "/health":
            WritePlain("OK");
            break;
        default:
            WriteErrorResponse();
            break;
    }
}

private void WriteJson(object obj)
{
    string json = System.Text.Json.JsonSerializer.Serialize(obj);
    byte[] bytes = Encoding.UTF8.GetBytes(json);
    WriteHeaders("application/json", bytes.Length);
    _stream.Write(bytes, 0, bytes.Length);
}

private void WriteHtml(string html)
{
    string full = $"{html}";
    byte[] bytes = Encoding.UTF8.GetBytes(full);
    WriteHeaders("text/html; charset=utf-8", bytes.Length);
    _stream.Write(bytes, 0, bytes.Length);
}

private void WriteHeaders(string contentType, int contentLength)
{
    _writer.WriteLine("HTTP/1.0 200 OK");
    _writer.WriteLine($"Content-Type: {contentType}");
    _writer.WriteLine($"Content-Length: {contentLength}");
    _writer.WriteLine("Connection: close");
    _writer.WriteLine();
    _writer.Flush();
}

測試與驗證

1. 編譯執行：dotnet run 或 VS F5
2. 瀏覽器開啟：https://localhost:8080
3. 命令列測試：

   curl -v https://localhost:8080
   curl https://localhost:8080/json
   curl https://localhost:8080/health

4. 網路抓包 (Wireshark) 觀察 HTTP 封包結構

安全性考量 (若對外暴露)

• 輸入驗證：嚴格解析請求行，防止緩衝區溢位、路徑遍歷
• 速率限制：SemaphoreSlim 或 Token Bucket 限制每 IP QPS
• 標頭注入防護：使用者輸入不直接拼接至回應標頭
• HTTPS：生產環境必須用 SslStream + 有效憑證
• 請求大小限制：避免大 POST 佔用記憶體

結語

從零實作 HTTP 伺服器能深入理解「請求-回應」模型、TCP 流與應用層協議的邊界、標頭與內文分隔、編碼與 Content-Length 的關係。雖然生產環境絕不建議手寫 (請用 Kestrel/NGINX/IIS)，但這個練習是網路程式設計進階的必經之路，也是面試常考核心。