Imports System.Net.Sockets
Imports System.Text
Class TCPCli
    Shared Sub Main()

        Dim tcpClient As New System.Net.Sockets.TcpClient()
        tcpClient.Connect("127.0.0.1", 8000)
        Dim networkStream As NetworkStream = tcpClient.GetStream()
        If networkStream.CanWrite And networkStream.CanRead Then
            ' Do a simple write.
            Dim sendBytes As [Byte]() = Encoding.ASCII.GetBytes("Is anybody there")
            networkStream.Write(sendBytes, 0, sendBytes.Length)
            ' Read the NetworkStream into a byte buffer.
            Dim bytes(tcpClient.ReceiveBufferSize) As Byte
            networkStream.Read(bytes, 0, CInt(tcpClient.ReceiveBufferSize))
            ' Output the data received from the host to the console.
            Dim returndata As String = Encoding.ASCII.GetString(bytes)
            Console.WriteLine(("Host returned: " + returndata))
        Else
            If Not networkStream.CanRead Then
                Console.WriteLine("cannot not write data to this stream")
                tcpClient.Close()
            Else
                If Not networkStream.CanWrite Then
                    Console.WriteLine("cannot read data from this stream")
                    tcpClient.Close()
                End If
            End If
        End If
        ' pause so user can view the console output
        Console.ReadLine()
    End Sub
End Class

All we're doing here is creating a new TcpClient, calling its Connect method, and then getting access to its underlying NetworkStream via the GetStream() method. We Write our message into the stream (converted to a byte array first) and then Read the response from the server. When done, we close the socket. And now, on the server side:

Imports System.Net.Sockets
Imports System.Text
Class TCPSrv
    Shared Sub Main()
        ' Must listen on correct port- must be same as port client wants to connect on.
        Const portNumber As Integer = 8000
        Dim tcpListener As New TcpListener(portNumber)
        tcpListener.Start()
        Console.WriteLine("Waiting for connection...")
        Try
            'Accept the pending client connection and return 
            'a TcpClient initialized for communication. 
            Dim tcpClient As TcpClient = tcpListener.AcceptTcpClient()
            Console.WriteLine("Connection accepted.")
            ' Get the stream
            Dim networkStream As NetworkStream = tcpClient.GetStream()
            ' Read the stream into a byte array
            Dim bytes(tcpClient.ReceiveBufferSize) As Byte
            networkStream.Read(bytes, 0, CInt(tcpClient.ReceiveBufferSize))
            ' Return the data received from the client to the console.
            Dim clientdata As String = Encoding.ASCII.GetString(bytes)
            Console.WriteLine(("Client sent: " + clientdata))
            Dim responseString As String = "Connected to server."
            Dim sendBytes As [Byte]() = Encoding.ASCII.GetBytes(responseString)
            networkStream.Write(sendBytes, 0, sendBytes.Length)
            Console.WriteLine(("Message Sent /> : " + responseString))
            'Any communication with the remote client using the TcpClient can go here.
            'Close TcpListener and TcpClient.
            tcpClient.Close()
            tcpListener.Stop()
            Console.WriteLine("exit")
            Console.ReadLine()
        Catch e As Exception
            Console.WriteLine(e.ToString())
            Console.ReadLine()
        End Try
    End Sub
   End Class

As can be seen, the server creates a new instance of the TcpListener class on the port, and calls the Start() method. It then calls the AcceptTcpClient() method which returns a TcpClient that you can use to send and receive data. Use TcpClient.GetStream to obtain the underlying NetworkStream of the TcpClient. NetworkStream inherits from Stream, which provides a rich collection of methods and properties for network communications ( If you want greater flexibility than a TcpClient offers, consider using AcceptSocket.).

We do a Read to get the sent data, and we can also call networkStream.Write() to send back a response. That's pretty much it for sending data over TCP sockets in .NET! Its easy, simple, and very extensible. You can download a VB.NET solution with projects for both the Client and the Server (listener) at the link below.

Download the code that accompanies this article