Task1.2

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

namespace Task1_2
{
    public class Program
    {
        static void Main(string[] args)
        {
            int port = 8080;
            TcpListener listener = new TcpListener(IPAddress.Any, port);
            listener.Start();
            Console.WriteLine($"[+] Прокси-сервер запущен на порту {port}...");

            while (true)
            {
                TcpClient client = listener.AcceptTcpClient();
                Thread thread = new Thread(() => HandleClient(client));
                thread.Start();
            }
        }

        private static readonly List<string> MaliciousPatterns = new List<string>
        {
            "SQLmap",
            "MaliciousHeader",
            "/etc/passwd",
            "cmd.exe",
            "union select"
        };

        private static void HandleClient(TcpClient client)
        {
            using (client)
            {
                try
                {
                    NetworkStream clientStream = client.GetStream();
                    byte[] buffer = new byte[8192];
                    int bytesRead = clientStream.Read(buffer, 0, buffer.Length);

                    if (bytesRead == 0)
                    {
                        return;
                    }

                    string requestText = Encoding.UTF8.GetString(buffer, 0, bytesRead);
                    Console.WriteLine($"[>] Запрос от клиента:\n{requestText.Split('\n')[0]}");

                    if (IsMalicious(requestText))
                    {
                        Console.WriteLine("[!] Подозрительный запрос заблокирован!");
                        string forbiddenResponse = "HTTP/1.1 403 Forbidden\r\nContent-Length: 0\r\n\r\n";
                        byte[] responseBytes = Encoding.UTF8.GetBytes(forbiddenResponse);
                        clientStream.Write(responseBytes, 0, responseBytes.Length);
                        return;
                    }

                    ForwardRequest(requestText, clientStream);
                }
                catch (Exception ex)
                {
                    Console.WriteLine($"[x] Ошибка: {ex.Message}");
                }
            }
        }

        private static bool IsMalicious(string request)
        {
            request = request.ToLower();

            foreach (var pattern in MaliciousPatterns)
            {
                if (request.Contains(pattern.ToLower()))
                {
                    return true;
                }
            }

            return false;
        }

        private static void ForwardRequest(string requestText, NetworkStream clientStream)
        {
            try
            {
                string[] lines = requestText.Split(new[] { "\r\n", "\n" }, StringSplitOptions.None);
                string hostLine = Array.Find(lines, line => line.StartsWith("Host:", StringComparison.OrdinalIgnoreCase));

                if (hostLine == null)
                {
                    Console.WriteLine("[!] Не удалось определить хост.");
                    return;
                }

                string host = hostLine.Substring(6).Trim();
                int port = 80;

                using (TcpClient server = new TcpClient(host, port))
                using (NetworkStream serverStream = server.GetStream())
                {
                    byte[] requestBytes = Encoding.UTF8.GetBytes(requestText);
                    serverStream.Write(requestBytes, 0, requestBytes.Length);

                    byte[] buffer = new byte[8192];
                    int bytesRead;

                    while ((bytesRead = serverStream.Read(buffer, 0, buffer.Length)) > 0)
                    {
                        clientStream.Write(buffer, 0, bytesRead);
                    }
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine($"[x] Ошибка при пересылке запроса: {ex.Message}");
            }
        }
    }
}