Csharp/C Sharp/Network/Web Proxy Server

Implements a multi-threaded Web proxy server

/*
C# Programming Tips & Techniques
by Charles Wright, Kris Jamsa
Publisher: Osborne/McGraw-Hill (December 28, 2001)
ISBN: 0072193794
*/
// Proxy.cs -- Implements a multi-threaded Web proxy server
//
//             Compile this program with the following command line:
//                 C:>csc Proxy.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 ("Please enter a port number.");
                    return;
                }
            }
            try
            {
                // Create a listener for the proxy port
                TcpListener sockServer = new TcpListener (Port);
                sockServer.Start ();
                while (true)
                {
                    // Accept connections on the proxy port.
                    Socket socket = sockServer.AcceptSocket ();
                    
                    // When AcceptSocket returns, it means there is a connection. Create
                    // an instance of the proxy server class and start a thread running.
                    clsProxyConnection proxy = new clsProxyConnection (socket);
                    Thread thrd = new Thread (new ThreadStart (proxy.Run));
                    thrd.Start ();
                    // While the thread is running, the main program thread will loop around
                    // and listen for the next connection request.
                }
            }
            catch (IOException e)
            {
                Console.WriteLine (e.Message);
            }
        }
    }
    class clsProxyConnection
    {
        public clsProxyConnection (Socket sockClient)
        {
            m_sockClient = sockClient;
        }
        Socket m_sockClient; //, m_sockServer;
        Byte [] readBuf = new Byte [1024];
        Byte [] buffer = null;
        Encoding ASCII = Encoding.ASCII;
        public void Run ()
        {
            string strFromClient = "";
            try
            {
                // Read the incoming text on the socket/
                int bytes = ReadMessage (m_sockClient,
                                         readBuf, ref strFromClient);
                // If it"s empty, it"s an error, so just return.
                // This will termiate the thread.
                if (bytes == 0)
                    return;
                // Get the URL for the connection. The client browser sends a GET command
                // followed by a space, then the URL, then and identifer for the HTTP version.
                // Extract the URL as the string betweeen the spaces.
                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 ());
                }
                // Write a messsage that we are connecting.
                Console.WriteLine ("Connecting to Site " +
                                   strClientConnection);
                Console.WriteLine ("Connection from " +
                                   m_sockClient.RemoteEndPoint);
                // Create a WebRequest object.
                WebRequest req = (WebRequest) WebRequest.Create
                                                     (strClientConnection);
                // Get the response from the Web site.
                WebResponse response = req.GetResponse ();
                int BytesRead = 0;
                Byte [] Buffer = new Byte[32];
                int BytesSent = 0;
                
                // Create a response stream object.
                Stream ResponseStream = response.GetResponseStream();
                
                // Read the response into a buffer.
                BytesRead = ResponseStream.Read(Buffer,0,32);
                StringBuilder strResponse = new StringBuilder("");
                while (BytesRead != 0)
                {
                    // Pass the response back to the client
                    strResponse.Append(Encoding.ASCII.GetString(Buffer,
                                        0, BytesRead));
                    m_sockClient.Send(Buffer, BytesRead, 0);
                    BytesSent += BytesRead;
                    // Read the next part of the response
                    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
            {
                // Disconnect and close the socket.
                if (m_sockClient != null)
                {
                    if (m_sockClient.Connected)
                    {
                        m_sockClient.Close ();
                    }
                }
            }
            // Returning from this method will terminate the thread.
        }
        // 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);
        }
    }
}