TCP communication-VBForums
Results 1 to 6 of 6

Thread: TCP communication

  1. #1

    Thread Starter
    Addicted Member
    Join Date
    Mar 2016
    Posts
    247

    TCP communication

    Hi,
    I have TCPIP connection using TCPclient and TCPlistener in a seperate thread.
    It works fine if I allways open a new client after each roundtrip (sending /recieving or recieving /sending).
    I wonder how I could keep the connection open and constantly exchange data.
    server side
    Code:
    while true
     While not server.pending
     end while
    
     dim client as TcpClient = server.AcceptTcpClient()
     Dim stream as NetworkStream = client.GetStream()
     ...get the data  and send out new data in msg...
     stream.Write(msg.0,msg.Length)
     client.Close()
    end while
    Client
    Code:
    Dim client As New TcpClient(IP,Port)
    dim stream as NetworkStream= client.GetStream()
    ..prepare data...
    stream.write(data,0,data.Length)
    'Get the requested data
    While Not stream.DataAvailble
     Sleep(200)
    End While
    While stream.DataAvailable
       Dim bytes As Int32 = stream.Read(readbuffer, 0, readbuffer.Length)
       responseData += System.Text.Encoding.ASCII.GetString(readbuffer, 0, bytes) 
    End While
    
    stream.Close():client.Close()
    client = New TcpClient(IP,Port)
    data = System.Text.Encoding.ASCII.GetBytes("some Text")
    stream=client.getStream()
    stream.write(data,0,data.Length)

  2. #2
    Sinecure devotee
    Join Date
    Aug 2013
    Location
    Southern Tier NY
    Posts
    4,169

    Re: TCP communication

    I would suggest not closing the clients.

  3. #3

    Thread Starter
    Addicted Member
    Join Date
    Mar 2016
    Posts
    247

    Re: TCP communication

    I have tried it. But this does not seem to send the data. It looks like the connection had been closed, although the networkstream.canwrite and client.connected returned true.

  4. #4
    .NUT jmcilhinney's Avatar
    Join Date
    May 2005
    Location
    Sydney, Australia
    Posts
    97,669

    Re: TCP communication

    Rather than using synchronous methods on a dedicated thread, I would suggest using the asynchronous methods built into the types you're using. If you follow the CodeBank link in my signature below, you'll find a thread on Asynchronous TCP that demonstrates those methods.
    Why is my data not saved to my database? | MSDN Data Walkthroughs
    VBForums Database Development FAQ
    My CodeBank Submissions: VB | C#
    My Blog: Data Among Multiple Forms (3 parts)
    Beginner Tutorials: VB | C# | SQL

  5. #5
    Sinecure devotee
    Join Date
    Aug 2013
    Location
    Southern Tier NY
    Posts
    4,169

    Re: TCP communication

    jmcilhinney is probably correct in that you should use asynchronous methods to implement your interfaces, although I find synchronous reads on background threads easier to write myself. Probably because I haven't tried using the asynchronous method enough.

    As a quick example, I just wrote this code which ping-pongs a random sized small message (10 to 100 bytes) between two threads over TCP within the same executable (which sounds like what you may have been experimenting with?).

    No controls needed on the form. Run from the IDE and it prints out to the Immediate window, (or Output window depending on IDE configuration).
    Example output:
    Code:
    Client sent the first message to kick things off. Sent 65 bytes
    Server received 65 bytes
    Server sent 49 bytes
    Client received 49 bytes
    Client sent 64 bytes
    Server received 64 bytes
    Server sent 94 bytes
    Client received 94 bytes
    Client sent 73 bytes
    Server received 73 bytes
    'etc....
    The receive and send code of the client is mostly the same as the receive and send code of the server.
    Code:
    Imports System.Net.Sockets
    Imports System.Net
    Imports System.Threading
    
    Public Class Form1
      'Server
      Private ServerListenThread As Threading.Thread = New Threading.Thread(AddressOf Listener)
      Private exiting As Boolean
      Private ServerPort As Integer
    
      'Client
      Private TcpClientReceiverThread As New Threading.Thread(AddressOf ClientReceiverThread)
    
    
      Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        ServerListenThread.IsBackground = True
        ServerListenThread.Start()
    
        TcpClientReceiverThread.IsBackground = True
        TcpClientReceiverThread.Start()
      End Sub
    
    #Region "Server"
      Private Sub Listener()
        Dim server As TcpListener
        Dim nStream As NetworkStream = Nothing
    
        Dim bLen(3) As Byte  'the len of the message being sent or received
        Dim outData(100) As Byte
        Dim inData(100) As Byte
    
        Dim iLen As Int32
        Dim rand As New Random
    
        'some random data to send from
        For i As Integer = 0 To 100
          outData(i) = CByte(rand.Next(1, 255))
        Next
    
        server = New TcpListener(IPAddress.Any, 0)  'create a TCP server with a system assigned port
        server.Start()
        ServerPort = CType(server.LocalEndpoint, IPEndPoint).Port 'save the assigned port for reference
    
        Dim lClient As TcpClient = Nothing
    
        Try
          lClient = server.AcceptTcpClient()
          nStream = lClient.GetStream
          Dim cnt As Integer
          Do Until exiting  'Inner loop where we read the stream
            cnt = nStream.Read(bLen, 0, 4)                     'Read the 4-byte image length into bLen byte array
            iLen = BitConverter.ToInt32(bLen, 0)             'Convert the 4 bytes into a 32-bit integer
            If iLen < 100 Then                               'Simply santity check of the value, don't expect more than 100 bytes
              iLen = nStream.Read(inData, 0, iLen)           '  Read the amount of data we expect to receive
              If Not exiting Then                            '  Make sure the form is still there (close wasn't selected while we were waiting to read)
                Debug.Print("Server received {0} bytes", iLen)
                iLen = rand.Next(10, 100)                    'choose to send 10 to 100 bytes the other direction
                bLen = BitConverter.GetBytes(iLen)           'convert length to four bytes
                nStream.Write(bLen, 0, 4)                    'send length out first
                nStream.Write(outData, 0, iLen)              'followed by the data
                Debug.Print("Server sent {0} bytes", iLen)
              End If
            End If
          Loop
    
        Catch ex As Exception                               'If we get an exception at any point in the process (usually a connection lost or closed)
        Finally
          If nStream IsNot Nothing Then nStream.Dispose()
          If lClient IsNot Nothing Then lClient.Close()
        End Try
    
        server.Stop()
        server = Nothing
      End Sub
    #End Region
    
    #Region "Client"
      Private Sub ClientReceiverThread()
        Dim client As New TcpClient
        Dim nStream As NetworkStream = Nothing
    
        Dim bLen(3) As Byte  'the len of the message being sent or received
        Dim outData(100) As Byte
        Dim inData(100) As Byte
    
        Dim iLen As Int32
        Dim rand As New Random
    
        'some random data to send from
        For i As Integer = 0 To 100
          outData(i) = CByte(rand.Next(1, 255))
        Next
    
        Do While ServerPort = 0     'Wait for Server to tell us what port to connect to
          Thread.Sleep(100)
        Loop
    
        client.Connect(IPAddress.Parse("127.0.0.1"), ServerPort)
    
        If client.Connected Then
          nStream = client.GetStream
    
          Try
            'Send a message to the server to get things started.
            iLen = rand.Next(10, 100)                    'choose to send 10 to 100 bytes to the server
            bLen = BitConverter.GetBytes(iLen)           'convert length to four bytes
            nStream.Write(bLen, 0, 4)                    'send length out first
            nStream.Write(outData, 0, iLen)              'followed by the data
            Debug.Print("Client sent the first message to kick things off. Sent {0} bytes", iLen)
    
            Dim cnt As Integer
            Do Until exiting                                   'Will loop, waiting for server to respond, then sending another message
              cnt = nStream.Read(bLen, 0, 4)                   'Read the 4-byte image length into bLen byte array
              iLen = BitConverter.ToInt32(bLen, 0)             'Convert the 4 bytes into a 32-bit integer
              If iLen < 100 Then                               'Simply santity check of the value, don't expect more than 100 bytes
                iLen = nStream.Read(inData, 0, iLen)           '  Read the amount of data we expect to receive
                If Not exiting Then                            '  Make sure the form is still there (close wasn't selected while we were waiting to read)
                  Debug.Print("Client received {0} bytes", iLen)
                  iLen = rand.Next(10, 100)                    'choose to send 10 to 100 bytes the other direction
                  bLen = BitConverter.GetBytes(iLen)           'convert length to four bytes
                  nStream.Write(bLen, 0, 4)                    'send length out first
                  nStream.Write(outData, 0, iLen)              'followed by the data
                  Debug.Print("Client sent {0} bytes", iLen)
                End If
              End If
            Loop
    
          Catch ex As Exception                               'If we get an exception at any point in the process (usually a connection lost or closed)
          Finally
            If nStream IsNot Nothing Then nStream.Dispose()
            If client IsNot Nothing Then client.Close()
          End Try
    
          client = Nothing
        Else
          Debug.Print("Client didn't connect. Example busted")
        End If
        exiting = True
      End Sub
    
    #End Region
    End Class
    p.s. This code was somewhat pulled form two programs that transferred bitmap data as a png image between two computers, which is why some comments mention "image".
    Last edited by passel; Feb 8th, 2018 at 06:15 PM.

  6. #6

    Thread Starter
    Addicted Member
    Join Date
    Mar 2016
    Posts
    247

    Re: TCP communication

    thanks for this nice example. I think I now better understand the way to program with sockets. It works now!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  



Featured


Click Here to Expand Forum to Full Width