Task 2.2

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

namespace HttpProxy
{
    class Program
    {
        static readonly List<string> maliciousPatterns = new List<string>
        {
            "SQLmap",
            "MaliciousHeader",
            "cmd=",
            "exec",
            "/etc/passwd",
            "base64",
            "select+from"
        };

        static void Main(string[] args)
        {
            int port = 8888;
            TcpListener listener = new TcpListener(IPAddress.Any, port);

            listener.Start();
            Console.WriteLine($"[+] Прокси-сервер запущен на порту {port}");

            while (true)
            {
                TcpClient client = listener.AcceptTcpClient();
                ThreadPool.QueueUserWorkItem(HandleClient, client);
            }
        }

        static void HandleClient(object obj)
        {
            TcpClient client = obj as TcpClient;

            try
            {
                NetworkStream clientStream = client.GetStream();
                StreamReader reader = new StreamReader(clientStream);
                StreamWriter writer = new StreamWriter(clientStream) { AutoFlush = true };

                string requestLine = reader.ReadLine();
                if (string.IsNullOrEmpty(requestLine)) return;

                Console.WriteLine($"\n[>] Запрос: {requestLine}");

                StringBuilder headers = new StringBuilder();
                string line;

                while (!string.IsNullOrEmpty(line = reader.ReadLine()))
                {
                    headers.AppendLine(line);
                }

                string fullRequest = requestLine + "\n" + headers.ToString();

                foreach (string pattern in maliciousPatterns)
                {
                    if (fullRequest.IndexOf(pattern, StringComparison.OrdinalIgnoreCase) >= 0)
                    {
                        Console.ForegroundColor = ConsoleColor.Red;
                        Console.WriteLine($"[!] Обнаружена угроза: {pattern}");
                        Console.ResetColor();

                        string forbiddenResponse = "HTTP/1.1 403 Forbidden\r\nContent-Length: 0\r\n\r\n";
                        byte[] forbiddenBytes = Encoding.ASCII.GetBytes(forbiddenResponse);
                        clientStream.Write(forbiddenBytes, 0, forbiddenBytes.Length);

                        client.Close();
                        return;
                    }
                }

                string[] tokens = requestLine.Split(' ');

                if (tokens.Length < 2)
                {
                    client.Close();
                    return;
                }

                string method = tokens[0];
                string url = tokens[1];

                string hostLine = headers.ToString().Split(new[] { "Host: " }, StringSplitOptions.None)[1];
                string host = hostLine.Split('\n')[0].Trim();

                Uri uri = new Uri(url.StartsWith("http") ? url : "http://" + host + url);
                int port = uri.Port == -1 ? 80 : uri.Port;

                TcpClient server = new TcpClient(uri.Host, port);
                NetworkStream serverStream = server.GetStream();

                StreamWriter serverWriter = new StreamWriter(serverStream) { AutoFlush = true };
                serverWriter.WriteLine(requestLine);
                serverWriter.Write(headers.ToString() + "\r\n");

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

                while ((bytesRead = serverStream.Read(buffer, 0, buffer.Length)) > 0)
                {
                    clientStream.Write(buffer, 0, bytesRead);
                }

                client.Close();
                server.Close();
            }
            catch (Exception ex)
            {
                Console.WriteLine($"[!] Ошибка: {ex.Message}");
                client?.Close();
            }
        }
    }
}