// ProxyServer.cs 

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

namespace nsProxyServer
{
    public class ProxyServer
    {
        static public void Main(string[] args)
        {
            int Port = 3125;
            if (args.Length > 0)
            {
                try
                {
                    Port = Convert.ToInt32(args[0]);
                }
                catch
                {
                    Console.WriteLine("Enter a port number:");
                    return;
                }
            }
            try
            {

                TcpListener sockServer = new TcpListener(Port);
                sockServer.Start();
                while (true)
                {

                    Socket socket = sockServer.AcceptSocket();
                    clsProxyConnection proxy = new clsProxyConnection(socket);
                    Thread thrd = new Thread(new ThreadStart(proxy.Run));
                    thrd.Start();

                }
            }
            catch (IOException e)
            {
                Console.WriteLine(e.Message);
            }
        }
    }

    class ProxyConnection
    {
        public ProxyConnection(Socket sockClient)
        {
            m_sockClient = sockClient;
        }
        Socket m_sockClient;
        Byte[] readBuf = new Byte[1024];
        Byte[] buffer = null;
        Encoding ASCII = Encoding.ASCII;

        public void Run()
        {
            string strFromClient = "";
            try
            {

                int bytes = ReadMessage(m_sockClient,
                                         readBuf, ref strFromClient);

                if (bytes == 0)
                    return;

                int index1 = strFromClient.IndexOf(' ');
                int index2 = strFromClient.IndexOf(' ', index1 + 1);
                string strClientConnection =
                      strFromClient.Substring(index1 + 1, index2 - index1);

                if ((index1 < 0) || (index2 < 0))
                {
                    throw (new IOException());
                }

                Console.WriteLine("Connecting to Site " +
                                   strClientConnection);
                Console.WriteLine("Connection from " +
                                   m_sockClient.RemoteEndPoint);

                WebRequest req = (WebRequest)WebRequest.Create
                                                     (strClientConnection);

                WebResponse response = req.GetResponse();
                int BytesRead = 0;
                Byte[] Buffer = new Byte[32];
                int BytesSent = 0;


                Stream ResponseStream = response.GetResponseStream();


                BytesRead = ResponseStream.Read(Buffer, 0, 32);
                StringBuilder strResponse = new StringBuilder("");
                while (BytesRead != 0)
                {

                    strResponse.Append(Encoding.ASCII.GetString(Buffer,
                                        0, BytesRead));
                    m_sockClient.Send(Buffer, BytesRead, 0);
                    BytesSent += BytesRead;

                    BytesRead = ResponseStream.Read(Buffer, 0, 32);
                }
            }
            catch (FileNotFoundException e)
            {
                SendErrorPage(404, "File Not Found", e.Message);
            }
            catch (IOException e)
            {
                SendErrorPage(503, "Service not available", e.Message);
            }
            catch (Exception e)
            {
                SendErrorPage(404, "File Not Found", e.Message);
                Console.WriteLine(e.StackTrace);
                Console.WriteLine(e.Message);
            }
            finally
            {

                if (m_sockClient != null)
                {
                    if (m_sockClient.Connected)
                    {
                        m_sockClient.Close();
                    }
                }
            }

        }
        // Write an error response to the client.
        void SendErrorPage(int status, string strReason, string strText)
        {
            SendMessage(m_sockClient, "HTTP/1.0" + " " + status + " " + strReason + "\r\n");
            SendMessage(m_sockClient, "Content-Type: text/plain" + "\r\n");
            SendMessage(m_sockClient, "Proxy-Connection: close" + "\r\n");
            SendMessage(m_sockClient, "\r\n");
            SendMessage(m_sockClient, status + " " + strReason);
            SendMessage(m_sockClient, strText);
        }

        // Send a string to a socket.
        void SendMessage(Socket sock, string strMessage)
        {
            buffer = new Byte[strMessage.Length + 1];
            int len = ASCII.GetBytes(strMessage.ToCharArray(),
                                      0, strMessage.Length, buffer, 0);
            sock.Send(buffer, len, 0);
        }

        // Read a string from a socket.
        int ReadMessage(Socket sock, byte[] buf, ref string strMessage)
        {
            int iBytes = sock.Receive(buf, 1024, 0);
            strMessage = Encoding.ASCII.GetString(buf);
            return (iBytes);
        }
    }
}