Introduction
This is a attempt to answer few of the questions regarding Asynchronous socket programming using C#. I have been working in the socket programming domain using C/C++. This will be an attempt to do the similar thing using C#.
This article speaks about the creation of TCP/IP socket and use of this connection between applications. The Client-Server architecture can be local or distributed over the network. We will discuss a different aspect of a client-server architecture, which uses some thing different than a conventional threads.
A Client-Server architecture
The architecture used here is simple, it has a server that listens for clients to connect.
There is sequence in which the client can connect to the running server. Server should be "Listening" before a connection is made to client.
Though the .NET concept of sockets is used for many applications like WebServices and Remoting, the major advantage is that the low level socket is done for programmer. Hence no need to use direct sockets. This is not true though, while interfacing to other non .NET systems sockets.
The server listens for clients to connect. When a connection is made, the server will accept the connection and return a acknowledgement. There should be some way to detect the loss of a connection in system. This can be a "Polling type acrchitecture" or a "event based architecture"
1. Using Polling
System.Net.Sockets provides provides a class TcpListener. This class has a method to listen for client connections and process them.
The following code shows the use of the TcpListener class :
private Socket Myclient = null;
//Create a listener
TcpListener listener = new TcpListener( PortNumber );
//Start listener
listener.Start();
//Listen in a loop
while(true)
{
byte [] MyBuff = new byte[127];
if( listener.Pending() )
{
//Accept the connection
Myclient = listener.AcceptSocket();
//Send acknowledgment.
Myclient.Send(/* data to be send*/);
}
else
{
//Wait for the request
Thread.Sleep( 100 );
}
}
2. Using socket events
The event based method is more suitable than the polling method in the applications like Chat servers.
First identify the name and address of the server:
//Get the local m/c name and address
IPAddress [] aryAddr = null;
string HostName = Dns.GetHostName();
IPHostEntry ipEntry = Dns.GetHostByName( HostName );
aryAddr = ipEntry.AddressList;
Using the address id bind the listener to the same address. The following shows this binding and listing. Also add an event handler which is pointing to all connection requests.
This will reduce the overhead of polling.
//You can use "C:\WinNT\System32\drivers\etc\Services" to find out the port numbers.
int nPort = /*any port which is available*/;
// Create the listener socket
Socket listener = new Socket( AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp );
listener.Bind( new IPEndPoint( aryLocalAddr[0], nPort ) );
listener.Listen( 10 );
// Setup a callback routine for connection notification.
listener.BeginAccept( new AsyncCallback( /*method name*/), listener );
Now write a routine which will be active, when connection is requested by client.
(This is the method which will be passed in the above code line instead of /*method name*/)
Socket Myclient;
public void OnConnect( IAsyncResult ar )
{
Socket listener = (Socket)ar.AsyncState;
Myclient = listener.EndAccept( ar );
Myclient.Send(/* data to be send*/ );
listener.BeginAccept( new AsyncCallback( OnConnect ), listener );
}
The client side code is fairly simple,
What we have to do is:
1. Create a socket
2. Connect a socket
3. Call BeginReceive
4. Fire Connection Accepted event.
5. Send the data
6. Close the socket :)
Summary
Though it is simple to use Sockets it requires a good amount of coding.
The above article is just a over view of the concepts that can be used while having your own Cleint-Srerver application. (While writing this article, have taken help from various sources, and mainly MSDN.)
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| Author: Satish Ramahnujan 19 Aug 2004 | Member Level: Bronze Points : 0 |
Was helpful and good. As the article mentions, there is a quite a bit of coding there. As it is in C# found it difficult to use it in VB.net.
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| Author: James 08 Dec 2008 | Member Level: Bronze Points : 1 |
Very nice article. Exactly what one needs for implementing a listener socket in C# if they haven't done it in that language before, except... might want to update it to include the namespaces.
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