Imports System
Imports System.Net
Imports System.Net.Sockets
Imports System.Text
Imports System.Threading
' State object for reading client data asynchronously
Public Class StateObject
' Client socket.
Public workSocket As Socket = Nothing
' Size of receive buffer.
Public Const BufferSize As Integer = 1024
' Receive buffer.
Public buffer(BufferSize) As Byte
' Received data string.
Public sb As New StringBuilder
End Class 'StateObject
Public Class AsynchronousSocketListener
' Incoming data from the client.
Public Shared data As String = Nothing
' Thread signal.
Public Shared allDone As New ManualResetEvent(False)
Public Sub New()
End Sub 'New
Public Shared Sub StartListening()
' Data buffer for incoming data.
Dim bytes() As Byte = New [Byte](1024) {}
' Establish the local endpoint for the socket.
' The DNS name of the computer
' running the listener is "host.contoso.com".
Dim ipHostInfo As IPHostEntry = Dns.Resolve(Dns.GetHostName())
Dim ipAddress As IPAddress = ipHostInfo.AddressList(0)
Dim localEndPoint As New IPEndPoint(ipAddress, 11000)
' Intializes 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(100)
While True
' Set the event to nonsignaled state.
allDone.Reset()
' Start an asynchronous socket to listen for connections.
Console.WriteLine("Waiting for a connection...")
listener.BeginAccept(New AsyncCallback(AddressOf AcceptCallback), _
listener)
' Wait until a connection is made before continuing.
allDone.WaitOne()
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
Public Shared Sub AcceptCallback(ByVal ar As IAsyncResult)
' Signal the main thread to continue.
allDone.Set()
' Get the socket that handles the client request.
Dim listener As Socket = CType(ar.AsyncState, Socket)
Dim handler As Socket = listener.EndAccept(ar)
' Create the state object.
Dim state As New StateObject
state.workSocket = handler
handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0, _
New AsyncCallback(AddressOf ReadCallback), state)
End Sub 'AcceptCallback
Public Shared Sub ReadCallback(ByVal ar As IAsyncResult)
Dim content As [String] = [String].Empty
' Retrieve the state object and the handler socket
' from the asynchronous state object.
Dim state As StateObject = CType(ar.AsyncState, StateObject)
Dim handler As Socket = state.workSocket
' Read data from client socket.
Dim bytesRead As Integer = handler.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))
' Check for end-of-file tag. If it is not there, read
' more data.
content = state.sb.ToString()
If content.IndexOf("<EOF>") > -1 Then
' All the data has been read from the
' client. Display it on the console.
Console.WriteLine("Read {0} bytes from socket. " + _
ControlChars.Cr + " Data : {1}", content.Length, content)
' Echo the data back to the client.
Send(handler, content)
Else
' Not all data received. Get more.
handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, _
0, New AsyncCallback(AddressOf ReadCallback), state)
End If
End If
End Sub 'ReadCallback
Private Shared Sub Send(ByVal handler As Socket, ByVal 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.
handler.BeginSend(byteData, 0, byteData.Length, 0, _
New AsyncCallback(AddressOf SendCallback), handler)
End Sub 'Send
Private Shared Sub SendCallback(ByVal ar As IAsyncResult)
Try
' Retrieve the socket from the state object.
Dim handler As Socket = CType(ar.AsyncState, Socket)
' Complete sending the data to the remote device.
Dim bytesSent As Integer = handler.EndSend(ar)
Console.WriteLine("Sent {0} bytes to client.", bytesSent)
handler.Shutdown(SocketShutdown.Both)
handler.Close()
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
Public Overloads Shared Function Main(ByVal args() As [String]) As Integer
StartListening()
Return 0
End Function 'Main
End Class 'AsynchronousSocketListener
