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

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Control.CheckForIllegalCrossThreadCalls = False
        Dim Th As New Threading.Thread(AddressOf Ascolta)
        Th.SetApartmentState(Threading.ApartmentState.STA)
        Th.Start()

    End Sub

    Sub Ascolta()

        Dim server As TcpListener
        server = Nothing
        Try

            'Imposta la porta
            Dim port As Int32 = 2000
            Dim localAddr As IPAddress = IPAddress.Parse("000.000.00.0")
        
            server = New TcpListener(localAddr, port)

            ''Avvia l'apertura della porta "2000"
            server.Start()

            ' Buffer per la lettura dei dati
            Dim bytes(1024) As Byte
            Dim data As String = Nothing

            ' Avvio il ciclo per la connessione
            While True

                TextBox1.Text += "Attendo la connessione..." & vbCrLf

                'Accetto la connessione
                Dim client As TcpClient = server.AcceptTcpClient()

                TextBox1.Text += "Connesso!" & vbCrLf

                data = Nothing

                'Oggetto canale per la ricezione e l'invio
                Dim stream As NetworkStream = client.GetStream()

                Dim i As Int32

                'Ricevo i dati inviati dal client
                i = stream.Read(bytes, 0, bytes.Length)

                While (i <> 0)

                    'Converto i dati da bytes a ASCII.
                    data = System.Text.Encoding.ASCII.GetString(bytes, 0, i)
                    TextBox1.Text += "Ricevuti: " & data & vbCrLf

                    'Analisi dei dati inviati dal client
                    data = data.ToUpper()
                    Dim msg As Byte() = System.Text.Encoding.ASCII.GetBytes(data)

                    'Invio la risposta al client
                    stream.Write(msg, 0, msg.Length)
                    TextBox1.Text += "Inviato: " & data & vbCrLf
                    i = stream.Read(bytes, 0, bytes.Length)

                End While

                'Chiudo la connessione
                client.Close()

            End While

        Catch ex As SocketException

            TextBox1.Text += "SocketException: " & vbCrLf

        Finally

            server.Stop()

        End Try
    End Sub

End Class