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Synchronous Server Socket Example

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.

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 StartListening()
        ' 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.
        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.
                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
        
        Catch e As Exception
            Console.WriteLine(e.ToString())
        End Try
        
        Console.WriteLine(ControlChars.Cr + "Press ENTER to continue...")
        Console.Read()
    End Sub 'StartListening
    
    ' Entry point that delegates to C-style main Private Function.
    Public Overloads Shared Sub Main()
        System.Environment.ExitCode = _
            Main(System.Environment.GetCommandLineArgs())
    End Sub
    
    
    Overloads Public Shared Function Main(args() As [String]) As Integer
        StartListening()
        Return 0
    End Function 'Main
End Class 'SynchronousSocketListener

[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;
    }
}

See Also

Synchronous Client Socket Example | Using a Synchronous Server Socket | Socket Code Examples

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