C# asynchronous socket client

using System;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using System.Text;
 
// State object for receiving data from remote device.
public class StateObject
{
    // Client socket.
    public Socket workSocket = null;
    // Size of receive buffer.
    public const int BufferSize = 256;
    // Receive buffer.
    public byte[] buffer = new byte[BufferSize];
    // Received data string.
    public StringBuilder sb = new StringBuilder();
}
 
public class AsynchronousClient
{
 
    // ManualResetEvent instances signal completion.
    private static ManualResetEvent connectDone = new ManualResetEvent(false);
    private static ManualResetEvent sendDone = new ManualResetEvent(false);
    private static ManualResetEvent receiveDone = new ManualResetEvent(false);
 
    // The response from the remote device.
    private static String response = String.Empty;
 
    private static void StartClient()
    {
        // Connect to a remote device.
        try
        {
 
            int port = 25;
            IPHostEntry ipHostInfo = Dns.GetHostEntry("mail.watlow.com");
            IPAddress ipAddress = ipHostInfo.AddressList[0];
 
            //int port = 4000;
            //IPAddress ipAddress = IPAddress.Parse("10.5.48.225");
 
            IPEndPoint remoteEP = new IPEndPoint(ipAddress, port);
 
            // Create a TCP/IP socket.
            Socket client = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
 
            // Connect to the remote endpoint.
            client.BeginConnect(remoteEP, new AsyncCallback(ConnectCallback), client);
            connectDone.WaitOne();
 
            //Receive(client);
            //receiveDone.WaitOne();
            //Console.WriteLine("Response received : {0}", response);
 
            // Send test data to the remote device.
            Send(client, "HELO");
            sendDone.WaitOne();
 
            // Receive the response from the remote device.
            Receive(client);
            receiveDone.WaitOne();
 
            // Write the response to the console.
            Console.WriteLine("Response received : {0}", response);
 
            // Release the socket.
            Console.ReadLine();
            client.Shutdown(SocketShutdown.Both);
            client.Close();
 
        }
        catch (Exception e)
        {
            Console.WriteLine(e.ToString());
        }
    }
 
    private static void ConnectCallback(IAsyncResult ar)
    {
        try
        {
            // Retrieve the socket from the state object.
            Socket client = (Socket)ar.AsyncState;
 
            // Complete the connection.
            client.EndConnect(ar);
 
            Console.WriteLine("Socket connected to {0}", client.RemoteEndPoint.ToString());
 
            // Signal that the connection has been made.
            connectDone.Set();
        }
        catch (Exception e)
        {
            Console.WriteLine(e.ToString());
        }
    }
 
    private static void Receive(Socket client)
    {
        try
        {
            // Create the state object.
            StateObject state = new StateObject();
            state.workSocket = client;
            // Begin receiving the data from the remote device.
            client.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0, new AsyncCallback(ReceiveCallback), state);
        }
        catch (Exception e)
        {
            Console.WriteLine(e.ToString());
        }
    }
 
    private static void ReceiveCallback(IAsyncResult ar)
    {
        try
        {
            // Retrieve the state object and the client socket 
            // from the asynchronous state object.
            StateObject state = (StateObject)ar.AsyncState;
            Socket client = state.workSocket;
 
            // Read data from the remote device.
            int bytesRead = client.EndReceive(ar);
            Console.WriteLine("Read data from the remote device.");
            if (bytesRead > 0)
            {
                // There might be more data, so store the data received so far.
                state.sb.Append(Encoding.ASCII.GetString(state.buffer, 0, bytesRead));
                Console.WriteLine(state.sb);
 
                // Get the rest of the data.
                client.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0, new AsyncCallback(ReceiveCallback), state);
                Console.WriteLine("Code hangs here");
            }
            else
            {
                // All the data has arrived; put it in response.
                if (state.sb.Length > 1)
                {
                    response = state.sb.ToString();
                }
                // Signal that all bytes have been received.
                receiveDone.Set();
            }
        }
        catch (Exception e)
        {
            Console.WriteLine(e.ToString());
        }
    }
 
    private static void Send(Socket client, String data)
    {
        // Convert the string data to byte data using ASCII encoding.
        byte[] byteData = Encoding.ASCII.GetBytes(data);
 
        // Begin sending the data to the remote device.
        client.BeginSend(byteData, 0, byteData.Length, 0, new AsyncCallback(SendCallback), client);
    }
 
    private static void SendCallback(IAsyncResult ar)
    {
        try
        {
            // Retrieve the socket from the state object.
            Socket client = (Socket)ar.AsyncState;
 
            // Complete sending the data to the remote device.
            int bytesSent = client.EndSend(ar);
            Console.WriteLine("Sent {0} bytes to server.", bytesSent);
 
            // Signal that all bytes have been sent.
            sendDone.Set();
        }
        catch (Exception e)
        {
            Console.WriteLine(e.ToString());
        }
    }
 
    public static int Main(String[] args)
    {
        StartClient();
        return 0;
    }
}
                                              

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