Tutorial Synchronous Socket Programming using .NET (For Server)

The following example program creates a server that receives connection requests from clients. The server is built with a synchronous socket, so execution of the server application is suspended while it waits for a connection from a client. The application receives a string from the client, displays the string on the console, and then echoes the string back to the client. The string from the client must contain the string "<EOF>" to signal the end of the message.




Code For VB

Imports System
Imports System.Net
Imports System.Net.Sockets
Imports System.Text
Imports Microsoft.VisualBasic

Public Class SynchronousSocketListener

' Incoming data from the client.
Public Shared data As String = Nothing

Public Shared Sub Main()
' Data buffer for incoming data.
Dim bytes() As Byte = New [Byte](1024) {}

' Establish the local endpoint for the socket.
' Dns.GetHostName returns the name of the 
' host running the application.
Dim ipHostInfo As IPHostEntry = Dns.Resolve(Dns.GetHostName())
Dim ipAddress As IPAddress = ipHostInfo.AddressList(0)
Dim localEndPoint As New IPEndPoint(ipAddress, 11000)

' Create a TCP/IP socket.
Dim listener As New Socket(AddressFamily.InterNetwork, _
SocketType.Stream, ProtocolType.Tcp)

' Bind the socket to the local endpoint and 
' listen for incoming connections.

listener.Bind(localEndPoint)
listener.Listen(10)

' Start listening for connections.
While True
Console.WriteLine("Waiting for a connection...")
' Program is suspended while waiting for an incoming connection.
Dim handler As Socket = listener.Accept()
data = Nothing

' An incoming connection needs to be processed.
While True
bytes = New Byte(1024) {}
Dim bytesRec As Integer = handler.Receive(bytes)
data += Encoding.ASCII.GetString(bytes, 0, bytesRec)
If data.IndexOf("<EOF>") > -1 Then
Exit While
End If
End While
' Show the data on the console.
Console.WriteLine("Text received : {0}", data)
' Echo the data back to the client.
Dim msg As Byte() = Encoding.ASCII.GetBytes(data)
handler.Send(msg)
handler.Shutdown(SocketShutdown.Both)
handler.Close()
End While
End Sub

End Class 'SynchronousSocketListener

Code For C#

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

public class SynchronousSocketListener {

// Incoming data from the client.
public static string data = null;

public static void StartListening() {
// Data buffer for incoming data.
byte[] bytes = new Byte[1024];

// Establish the local endpoint for the socket.
// Dns.GetHostName returns the name of the 
// host running the application.
IPHostEntry ipHostInfo = Dns.Resolve(Dns.GetHostName());
IPAddress ipAddress = ipHostInfo.AddressList[0];
IPEndPoint localEndPoint = new IPEndPoint(ipAddress, 11000);

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

// Bind the socket to the local endpoint and 
// listen for incoming connections.
try {
listener.Bind(localEndPoint);
listener.Listen(10);

// Start listening for connections.
while (true) {
Console.WriteLine("Waiting for a connection...");
// Program is suspended while waiting for an incoming connection.
Socket handler = listener.Accept();
data = null;

// An incoming connection needs to be processed.
while (true) {
bytes = new byte[1024];
int bytesRec = handler.Receive(bytes);
data += Encoding.ASCII.GetString(bytes,0,bytesRec);
if (data.IndexOf("<EOF>") > -1) {
break;
}
}

// Show the data on the console.
Console.WriteLine( "Text received : {0}", data);

// Echo the data back to the client.
byte[] msg = Encoding.ASCII.GetBytes(data);

handler.Send(msg);
handler.Shutdown(SocketShutdown.Both);
handler.Close();
}

} catch (Exception e) {
Console.WriteLine(e.ToString());
}

Console.WriteLine("\nPress ENTER to continue...");
Console.Read();

}

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

Synchronous server sockets suspend the execution of the application until a connection request is received on the socket. Synchronous server sockets are not suitable for applications that make heavy use of the network in their operation, but they can be suitable for simple network applications.

After a Socket is set to listen on an endpoint using the Bind and Listen methods, it is ready to accept incoming connection requests using the Accept method. The application is suspended until a connection request is received when the Accept method is called.

When a connection request is received, Accept returns a new Socket instance that is associated with the connecting client. The following example reads data from the client, displays it on the console, and echoes the data back to the client. The Socket does not specify any messaging protocol, so the string "" marks the end of the message data. It assumes that a Socket named listener has been initialized and bound to an endpoint.

Code For VB

Console.WriteLine("Waiting for a connection...")
Dim handler As Socket = listener.Accept()
Dim data As String = Nothing

While True
bytes = New Byte(1024) {}
Dim bytesRec As Integer = handler.Receive(bytes)
data += Encoding.ASCII.GetString(bytes, 0, bytesRec)
If data.IndexOf("<EOF>") > - 1 Then
Exit While
End If
End While

Console.WriteLine("Text received : {0}", data)

Dim msg As Byte() = Encoding.ASCII.GetBytes(data)
handler.Send(msg)
handler.Shutdown(SocketShutdown.Both)
handler.Close()

Code For C#

Console.WriteLine("Waiting for a connection...");
Socket handler = listener.Accept();
String data = null;

while (true) {
bytes = new byte[1024];
int bytesRec = handler.Receive(bytes);
data += Encoding.ASCII.GetString(bytes,0,bytesRec);
if (data.IndexOf("<EOF>") > -1) {
break;
}
}

Console.WriteLine( "Text received : {0}", data);

byte[] msg = Encoding.ASCII.GetBytes(data);
handler.Send(msg);
handler.Shutdown(SocketShutdown.Both);
handler.Close();

Download project and code here