C# Socket 編程實戰：手工構造 HTTP GET 請求與響應解析

核心代碼

public string DoSocketGet(string server)
{
    Encoding ascii = Encoding.ASCII;
    string request = $"GET / HTTP/1.1\r\nHost: {server}\r\nConnection: Close\r\n\r\n";
    byte[] sendBytes = ascii.GetBytes(request);
    byte[] recvBuffer = new byte[256];
    string response = null;

    // 解析 IP
    IPAddress ip = Dns.GetHostAddresses(server)[0];
    IPEndPoint endPoint = new IPEndPoint(ip, 80);

    // 創建 TCP Socket
    using (Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
    {
        socket.Connect(endPoint);
        if (!socket.Connected)
            return "Unable to connect to host";

        // 發送請求
        socket.Send(sendBytes, sendBytes.Length, SocketFlags.None);

        // 接收響應循環
        int bytes = socket.Receive(recvBuffer, recvBuffer.Length, SocketFlags.None);
        response = $"Default HTML page on {server}:\r\n";
        response += ascii.GetString(recvBuffer, 0, bytes);

        while (bytes > 0)
        {
            bytes = socket.Receive(recvBuffer, recvBuffer.Length, SocketFlags.None);
            response += ascii.GetString(recvBuffer, 0, bytes);
        }
    }
    return response;
}

關鍵步驟解析

HTTP 協議要點

• 請求行：GET / HTTP/1.1
• Host 頭：HTTP/1.1 必須，支持虛擬主機
• Connection: Close：告知服務端響應後關閉連接，客戶端才能靠 Receive 返回 0 判斷結束
• 雙 CRLF (\r\n\r\n) 結束請求頭

改進建議

• 使用 HttpWebRequest/HttpClient 替代手工 Socket（生產環境）
• 支持 HTTPS：需 SslStream 包裝 Socket 進行 TLS 握手
• 異步模式：BeginSend/EndSend、BeginReceive/EndReceive 或 SendAsync/ReceiveAsync
• 完整響應解析：分離狀態行、頭部、實體體，處理 Chunked、Content-Length、Gzip 等
• 緩衝區動態擴展：List 或 MemoryStream 避免固定 256 字節截斷

錯誤處理

try
{
    // ... socket operations
}
catch (SocketException ex) when (ex.SocketErrorCode == SocketError.ConnectionRefused)
{
    return "Connection refused";
}
catch (SocketException ex)
{
    return $"Socket error: {ex.Message}";
}
catch (Exception ex)
{
    return $"General error: {ex.Message}";
}