Csharp/C Sharp/Network/Web Proxy Server

Implements a multi-threaded Web proxy server

<source lang="csharp"> /* 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);
       }
   }

}

      </source>