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Asynchronous Client Socket Example

The following example program creates a client that connects to a server. The client is built with an asynchronous socket, so execution of the client application is not suspended while the server returns a response. The application sends a string to the server and then displays the string returned by the server on the console.

Imports System
Imports System.Net
Imports System.Net.Sockets
Imports System.Threading
Imports System.Text

' State object for receiving data from remote device.
Public Class StateObject
    ' Client socket.
    Public workSocket As Socket = Nothing 
    ' Size of receive buffer.
    Public BufferSize As Integer = 256
    ' Receive buffer.
    Public buffer(256) As Byte
    ' Received data string.
    Public sb As New StringBuilder()
End Class 'StateObject

Public Class AsynchronousClient
    ' The port number for the remote device.
    Private Shared port As Integer = 11000
    
    ' ManualResetEvent instances signal completion.
    Private Shared connectDone As New ManualResetEvent(False)
    Private Shared sendDone As New ManualResetEvent(False)
    Private Shared receiveDone As New ManualResetEvent(False)
    
    ' The response from the remote device.
    Private Shared response As [String] = [String].Empty
    
    
    Private Shared Sub StartClient()
        ' Connect to a remote device.
        Try
            ' Establish the remote endpoint for the socket.
            ' The name of the
            ' remote device is "host.contoso.com".
            Dim ipHostInfo As IPHostEntry = Dns.Resolve("host.contoso.com")
            Dim ipAddress As IPAddress = ipHostInfo.AddressList(0)
            Dim remoteEP As New IPEndPoint(ipAddress, port)
            
            '  Create a TCP/IP socket.
            Dim client As New Socket(AddressFamily.InterNetwork, _
                SocketType.Stream, ProtocolType.Tcp)
            
            ' Connect to the remote endpoint.
            client.BeginConnect(remoteEP, AddressOf ConnectCallback, client)
            connectDone.WaitOne()
            
            ' Send test data to the remote device.
            Send(client, "This is a test<EOF>")
            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.
            client.Shutdown(SocketShutdown.Both)
            client.Close()
        
        Catch e As Exception
            Console.WriteLine(e.ToString())
        End Try
    End Sub 'StartClient
    
    
    Private Shared Sub ConnectCallback(ar As IAsyncResult)
        Try
            ' Retrieve the socket from the state object.
            Dim client As Socket = CType(ar.AsyncState, Socket)
            
            ' 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 e As Exception
            Console.WriteLine(e.ToString())
        End Try
    End Sub 'ConnectCallback
    
    
    Private Shared Sub Receive(client As Socket)
        Try
            ' Create the state object.
            Dim state As New StateObject()
            state.workSocket = client
            
            ' Begin receiving the data from the remote device.
            client.BeginReceive(state.buffer, 0, state.BufferSize, 0, _
                AddressOf ReceiveCallback, state)
        Catch e As Exception
            Console.WriteLine(e.ToString())
        End Try
    End Sub 'Receive
    
    
    Private Shared Sub ReceiveCallback(ar As IAsyncResult)
        Try
            ' Retrieve the state object and client socket 
            ' from the asynchronous state object.
            Dim state As StateObject = CType(ar.AsyncState, StateObject)
            Dim client As Socket = state.workSocket
            
            ' Read data from the remote device.
            Dim bytesRead As Integer = client.EndReceive(ar)
            
            If bytesRead > 0 Then
                ' There might be more data, so store the data received so far.
                state.sb.Append(Encoding.ASCII.GetString(state.buffer, 0, _
                    bytesRead))
                
                ' Get the rest of the data.
                client.BeginReceive(state.buffer, 0, state.BufferSize, 0, _
                    AddressOf ReceiveCallback, state)
            Else
                ' All the data has arrived; put it in response.
                If state.sb.Length > 1 Then
                    response = state.sb.ToString()
                End If
                ' Signal that all bytes have been received.
                receiveDone.Set()
            End If
        Catch e As Exception
            Console.WriteLine(e.ToString())
        End Try
    End Sub 'ReceiveCallback
    
    
    Private Shared Sub Send(client As Socket, data As [String])
        ' Convert the string data to byte data using ASCII encoding.
        Dim byteData As Byte() = Encoding.ASCII.GetBytes(data)
        
        ' Begin sending the data to the remote device.
        client.BeginSend(byteData, 0, byteData.Length, 0, _
            AddressOf SendCallback, client)
    End Sub 'Send
    
    
    Private Shared Sub SendCallback(ar As IAsyncResult)
        Try
            ' Retrieve the socket from the state object.
            Dim client As Socket = CType(ar.AsyncState, Socket)
            
            ' Complete sending the data to the remote device.
            Dim bytesSent As Integer = client.EndSend(ar)
            Console.WriteLine("Sent {0} bytes to server.", bytesSent)
            
            ' Signal that all bytes have been sent.
            sendDone.Set()
        Catch e As Exception
            Console.WriteLine(e.ToString())
        End Try
    End Sub 'SendCallback
    
    '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
        StartClient()
        Return 0
    End Function 'Main
End Class 'AsynchronousClient

[C#]
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 {
    // The port number for the remote device.
    private const int port = 11000;

    // 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 {
            // Establish the remote endpoint for the socket.
            // The name of the 
            // remote device is "host.contoso.com".
            IPHostEntry ipHostInfo = Dns.Resolve("host.contoso.com");
            IPAddress ipAddress = ipHostInfo.AddressList[0];
            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();

            // Send test data to the remote device.
            Send(client,"This is a test<EOF>");
            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.
            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);

            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));

                // Get the rest of the data.
                client.BeginReceive(state.buffer,0,StateObject.BufferSize,0,
                    new AsyncCallback(ReceiveCallback), state);
            } 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;
    }
}

See Also

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

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