Asynchronous Socket Server Programming for Beginner

It’s a sample Server socket code that code based on MSDN sample code.

That code works asynchronously for send/receive data between client and server. By that code any one can transfer data easily as when he want. Here some string data has been transferred. Before sending string data just it has been converted to byte array and then it has transferred client to server. Now I’m writing code to transfer string data between client and server, but within short time I will write how can transfer huge file data by asynchronous socket.
Now may some one think why we should use Asynchronous socket except synchronous socket? Because using asynchronous socket we can transfer data in different thread and data can transfer more smoothly. If any one try to send large data without any multi-threading model then he will see that when data is transferring then his program looks line ‘crashed’. However, lets describing some portion about that code.

For use socket asynchronously Microsoft has provide very helpful technology in .Net. We just use some inbuilt function with ‘Begin-End’ scenario with three word ‘Accept, Send & Receive’. This functions are:

BeginAccept() – EndAccept()
BeginReceive() – EndReceive()
BeginSend() – EndSend()

These functions when invoke then it create & starts internal thread and starts working with a separate thread and continue working. So it don’t hamper main thread. Also inter-thread communication done by ‘ManualResetEvent’. ManualResetEvent object can handle it with it’s three functions :
Set ()

Also here has used ‘StringBuilder’ for string operation in spite of simple ‘string’ class. Both class does same work, but ‘StringBuilder’ is very fast than ‘string’, but you can use ‘string’ also.

However, the exact codes are as given below, at then end of that code I’m writing my personal some experience. Let’s see:

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

// State object for reading client data asynchronously
public class StateObject
// Client socket.
public Socket workSocket = null;
// Size of receive buffer.
public const int BufferSize = 1024;
// Receive buffer.
public byte[] buffer = new byte[BufferSize];
// Received data string.
public StringBuilder sb = new StringBuilder();

public class AsynchronousSocketListener
// Thread signal.
public static ManualResetEvent allDone = new ManualResetEvent(false);

public AsynchronousSocketListener()

public static void StartListening()
// Temp storage for incoming data.
byte[] recvDataBytes = new Byte[1024];

// Make endpoint for the socket.
//IPAddress serverAdd = Dns.Resolve(“localhost”); – That line was wrong
//’baaelSiljan’ has noticed it and then I’ve modified that line, correct line will be as:
IPHostEntry ipHost = Dns.Resolve(“localhost”);
IPAddress serverAdd = ipHost.AddressList[0];

IPEndPoint ep = new IPEndPoint(serverAdd, 5656);

// Create a TCP/IP socket for listner.
Socket listenerSock = new Socket(AddressFamily.InterNetwork,
SocketType.Stream, ProtocolType.Tcp);

// Bind the socket to the endpoint and wait for listen for incoming connections.

while (true)
// Set the event to nonsignaled state.

// Start an asynchronous socket to listen for connections.
Console.WriteLine(“Waiting for Client…”);
new AsyncCallback(AcceptCallback),

// Wait until a connection is made before continuing.

catch (Exception e)

Console.WriteLine(“\nPress ENTER to continue…”);


public static void AcceptCallback(IAsyncResult ar)
// Signal the main thread to continue.

// Get the socket that handles the client request.
Socket listener = (Socket)ar.AsyncState;
Socket handler = listener.EndAccept(ar);

// Create the state object.
StateObject state = new StateObject();
state.workSocket = handler;
handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
new AsyncCallback(ReadCallback), state);

public static void ReadCallback(IAsyncResult ar)
String content = String.Empty;

// Retrieve the state object and the handler socket
// from the asynchronous state object.
StateObject state = (StateObject)ar.AsyncState;
Socket handler = state.workSocket;

// Read data from the client socket.
int bytesRead = handler.EndReceive(ar);

if (bytesRead > 0)
// There might be more data, so store the data received so far.
state.buffer, 0, bytesRead));

// Check for end-of-file tag. If it is not there, read
// more data.
content =;
if (content.IndexOf(“”) > -1)
// All the data has been read from the
// client. Display it on the console.
Console.WriteLine(“Read {0} bytes from socket. \n Data : {1}”,
content.Length, content);
// Echo the data back to the client.
Send(handler, content);
// Not all data received. Get more.
handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
new AsyncCallback(ReadCallback), state);

private static void Send(Socket handler, 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.
handler.BeginSend(byteData, 0, byteData.Length, 0,
new AsyncCallback(SendCallback), handler);

private static void SendCallback(IAsyncResult ar)
// Retrieve the socket from the state object.
Socket handler = (Socket)ar.AsyncState;

// Complete sending the data to the remote device.
int bytesSent = handler.EndSend(ar);
Console.WriteLine(“Sent {0} bytes to client.”, bytesSent);


catch (Exception e)

public static int Main(String[] args)
return 0;

How that code was?

But always keep in mind here system is using default thread pool which by default handle maximum 25 thread, which may gives problem in large application, but for small application it’s fine. Also it’s using internal multi-threading technology which is comparatively slower than raw threading program. However let’s carry on.