application to listen and send

[CCrawshaw]

Hi,
I'm trying to create an application to send and receive strings to an ip address.
I have the send part working okay, but as soon as I try to receive strings, it locks the application until it receives one.

Currently, the receiving part is done on a button click, but ideally I would like to have it going on permanently in the background, and still be able to send strings on a button click.

The local ip address is 10.0.0.14, remote is 10.0.0.25 on port 4000. The code I currently have:

Imports System.Net.Sockets
Imports System.Text

Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

    End Sub
    Public Sub startListener()
        Dim f As Integer = 0
        Dim temp As Integer
        Dim ipaddress(3) As Byte
        ipaddress(0) = 10
        ipaddress(1) = 0
        ipaddress(2) = 0
        ipaddress(3) = 14
        Dim opensock As New Net.Sockets.TcpListener(New Net.IPAddress(ipaddress), 4000)
        Try
            opensock.Start()
        Catch ex As System.Net.Sockets.SocketException
            TextBox1.Text = ex.NativeErrorCode
        End Try
        TextBox1.Text = "Connected"

        Dim tcpClient As TcpClient = opensock.AcceptTcpClient()

        'While f < 5
        TextBox1.Text = "Inside loop"
        Dim networkStream As NetworkStream = tcpClient.GetStream()
        Dim bytes(tcpClient.ReceiveBufferSize) As Byte
        networkStream.Read(bytes, 0, CInt(tcpClient.ReceiveBufferSize))
        Dim returndata As String = Encoding.ASCII.GetString(bytes)
        TextBox1.Text = "Server Waiting..."
        TextBox1.Text = "String received: " & returndata

        temp = 40 - (40 * CInt("&H" & (returndata.Substring(12, 2))) / 255)
        templabel.Text = temp

        TextBox1.Text = "temp is: " & temp
        'End While
        TextBox1.Text = "temp is: " & temp & "Loop Closed"
        'opensock.EndAcceptSocket()
        'opensock.EndAcceptTcpClient()

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

        Dim opensock As New System.Net.Sockets.TcpClient
        Dim swon As String = "A55A6B0550000000FFFBDE0030C8" 'switch on
        Dim swoff As String = "A55A6B0570000000FFFBDE0030E8" 'switch off
        Dim but0 As String = "A55A6B0500000000FFFBDE002066" 'button release

        opensock.Connect("10.0.0.25", 4000)
        Console.WriteLine("connected")

        Dim networkStream As NetworkStream = opensock.GetStream()

        If networkStream.CanWrite And networkStream.CanRead Then
            'SWITCH ON:
            Dim sendBytes As [Byte]() = Encoding.ASCII.GetBytes(swon)
            networkStream.Write(sendBytes, 0, sendBytes.Length)
            ' Read the NetworkStream into a byte buffer.
            Dim bytes(opensock.ReceiveBufferSize) As Byte
            networkStream.Read(bytes, 0, CInt(opensock.ReceiveBufferSize))
            ' Output the data received from the host to the console.
            Dim returndata As String = Encoding.ASCII.GetString(bytes)

            'BUTTON RELEASE:
            sendBytes = Encoding.ASCII.GetBytes(but0)
            networkStream.Write(sendBytes, 0, sendBytes.Length)
            ' Read the NetworkStream into a byte buffer.
            networkStream.Read(bytes, 0, CInt(opensock.ReceiveBufferSize))
            ' Output the data received from the host to the console.
            returndata = Encoding.ASCII.GetString(bytes)
            opensock.Close()
        End If
    End Sub


    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click

        Dim opensock As New System.Net.Sockets.TcpClient
        Dim swon As String = "A55A6B0550000000FFFBDE0030C8" 'switch on
        Dim swoff As String = "A55A6B0570000000FFFBDE0030E8" 'switch off
        Dim but0 As String = "A55A6B0500000000FFFBDE002066" 'button release

        opensock.Connect("10.0.0.25", 4000)
        Console.WriteLine("connected")

        Dim networkStream As NetworkStream = opensock.GetStream()

        If networkStream.CanWrite And networkStream.CanRead Then
            'SWITCH OFF:
            Dim sendBytes As [Byte]() = Encoding.ASCII.GetBytes(swoff)
            networkStream.Write(sendBytes, 0, sendBytes.Length)
            ' Read the NetworkStream into a byte buffer.
            Dim bytes(opensock.ReceiveBufferSize) As Byte
            networkStream.Read(bytes, 0, CInt(opensock.ReceiveBufferSize))
            ' Output the data received from the host to the console.
            Dim returndata As String = Encoding.ASCII.GetString(bytes)

            'BUTTON RELEASE:
            sendBytes = Encoding.ASCII.GetBytes(but0)
            networkStream.Write(sendBytes, 0, sendBytes.Length)
            ' Read the NetworkStream into a byte buffer.
            networkStream.Read(bytes, 0, CInt(opensock.ReceiveBufferSize))
            ' Output the data received from the host to the console.
            returndata = Encoding.ASCII.GetString(bytes)
            opensock.Close()
        End If
    End Sub

    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        Me.startListener()
    End Sub
End Class

Any help or a pointer in the right direction would be greatly appreciated.

Cheers,
Chris

 

[CCrawshaw]

listening application

Hi, this is a slight repost, but as I can get no further with my previous question, I'll re-ask it having gone back a few steps.

I'm trying to create an application to listen on a certain ip address and port. Every so often a string will be sent to the ip address which I need to work with. I have got this working so dar, but only in that the application locks up until the string is received, where as I need it listening in the background so I can get the application to do other things.

I think I have a lack of understanding somewhere, if someone could point me in the right direction to look I'd be very grateful.

I have searched the net a lot, but only seem to find the standard listeners which I'm recreating.

Cheers,
Chris

Imports System.Net.Sockets
Imports System.Text

Public Class templistener
    Dim ipaddress(3) As Byte
        

    Dim msg As String = "0000000000000000000000000000"
    Dim t As Integer = "00"
    Dim returndata As String = msg
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        createListener()
    End Sub
    Public Sub createListener()
        ipaddress(0) = 10
        ipaddress(1) = 0
        ipaddress(2) = 0
        ipaddress(3) = 14
        Dim opensock As New Net.Sockets.TcpListener(New Net.IPAddress(ipaddress), 4000)


        Try
            opensock.Start()
        Catch ex As System.Net.Sockets.SocketException
            mess.Text = "cannot start connection"
        End Try

             Dim tcpClient As TcpClient = opensock.AcceptTcpClient()


            mess.Text = "connected"
            comm.Text = msg


            Dim networkStream As NetworkStream = tcpClient.GetStream()
            If networkStream.CanWrite And networkStream.CanRead Then
                mess.Text = "Can read and write"
                Dim bytes(tcpClient.ReceiveBufferSize) As Byte
            networkStream.Read(bytes, 0, CInt(tcpClient.ReceiveBufferSize))
                returndata = Encoding.ASCII.GetString(bytes)

                comm.Text = returndata
                mess.Text = "data received"
                'Console.WriteLine(("TCP Server returned: " + returndata))
            Else
                returndata = msg
            End If

        t = 40 - (40 * CInt("&H" & (returndata.Substring(12, 2))) / 255)
        temp.Text = t
    End Sub


End Class

 

[JohnH]

You need to research multi-threading, to avoid tying up the UI thread long-running/blocking calls must be performed on a secondary thread.

 

[CCrawshaw]

Hi,
Many thanks for that. I now have my application listening in the background, and also it doesn't stop listening as I have added a while true.
My next question is, I now need to add the ability to send strings to the remote ip address on a button click as well as receiving them.
To do this, I assume that when the button is clicked, I need to stop the background worker, open the tcpclient, send the string then restart the background_worker.
Is this correct?

Cheers,
Chris

P.S. I've attached a text file of my code rather than fill the page with 150 lines of code!

 

[JohnH]

How is the communication protocol defined?

 

[CCrawshaw]

Do you mean whether it's TCP/IP or UDP?
The remote unit is currently set to TCP, but I can change it to UDP if it would make things simpler. I left it as TCP as I have never used UDP before.

 

[JohnH]

No, I mean how is the communication you engage supposed to take place? The protocol defines how you are supposed to behave during socket connection.

 

[CCrawshaw]

Ok, the application needs to be able to send and receive 28 characters string to and from the remote unit defined by an ip address and port.

 

[CCrawshaw]

Does that answer your question? I'm still not 100% sure what you're asking.

Cheers,
Chris

 

[JohnH]

I don't understand what that is supposed to mean. Anyway, you can write to the NetworkStream from your button handler while at the same time having a blocking Read receive operation on 'listen' thread, you just need to provide access to the TcpClient/NetworkStream, as in assign it a class field.