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Thread: Getting simultaneous messages from different clients - TCP/IP communication

  1. #1

    Thread Starter
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    Oct 2017
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    6

    Getting simultaneous messages from different clients - TCP/IP communication

    Hi! Please, can anyone help me? I'm doing a test by creating a chat program that receives data from multiple clients. Everything is working well. My problem is that when two clients send messages at the same time, I just get the message from one of the clients. Is there a way to get incoming messages at the same time sorted by order of arrival?

    below, part of the Server code.


    Code:
    Public Sub LISTEN()
            Dim CLIENT As New NEWCLIENT
            While True
                Try
                    CLIENT.SOCKETCLIENT = SERVER.AcceptSocket
                    CLIENTIP = CLIENT.SOCKETCLIENT.RemoteEndPoint
                    CLIENT.THREADCLIENT = New Thread(AddressOf READ)
                    CLIENTS.Add(CLIENTIP, CLIENT)
                    NEWCONEXION(CLIENTIP)
                    CLIENT.THREADCLIENT.Start()
                Catch ex As Exception
                End Try
            End While
        End Sub
    
        Public Sub READ()
            Dim CLIENT As New NEWCLIENT
            Dim DATA() As Byte
            Dim IP As IPEndPoint = CLIENTIP
            CLIENT = CLIENTS(IP)
            While True
                If CLIENT.SOCKETCLIENT.Connected Then
                    DATA = New Byte(1024) {}
                    Try
                        If CLIENT.SOCKETCLIENT.Receive(DATA, DATA.Length, 0) > 0 Then
                            CLIENT.MSG = Encoding.UTF7.GetString(DATA)
                            CLIENTS(IP) = CLIENT
    
                            Datareceived(IP)
    
    
                        Else
    
                            Exit While
                        End If
                    Catch ex As Exception
    
                        Exit While
                    End Try
                End If
            End While
            Call ENDTHREAD(IP)
        End Sub
    
    Private Sub DATARECEIVED(ByVal IDTerminal As IPEndPoint)
    ListBox1.Items.Add(DATARECEIVED)
    End Sub

  2. #2
    You don't want to know.
    Join Date
    Aug 2010
    Posts
    4,269

    Re: Getting simultaneous messages from different clients - TCP/IP communication

    Wow. This coding style is very archaic. Please consider looking at the examples on MSDN and adopting a style like them. TYPING IN ALL CAPS MAKES IT VERY DIFFICULT TO READ. THERE ARE PSYCHOLOGICAL STUDIES THAT PROVE IT. AndAlternatingCapsMakeItEasier TOPICKOUTWORDSIFTHEREARENOSPACES. I know it's Visual "BASIC", but I think we've moved on from all-caps.

    I can't answer definitively, because I don't know what the type "NEWCLIENT" is. If you don't show me the types your code uses, I can't make a good assertation of where problems lie.

    This bit is very bad:
    Code:
    Catch ex As Exception
    End Try
    Your program throws exceptions to tell you something went wrong. This code says, "If something goes wrong, don't bother me". So if something is going wrong with the message you "aren't receiving", you've politely asked your program to shove it. That means it's probably happening and you don't know. The error message would be useful when it comes to understanding what is happening.

    I can't make much progress. Your code looks like pseudocode because you aren't using any types I'm familiar with, and you're also making decisions that don't make any sense from an expert perspective. For example:
    Code:
    If CLIENT.SOCKETCLIENT.Receive(DATA, DATA.Length, 0) > 0 Then
    If this is any Socket.Receive() I'm familiar with, the function is returning how many bytes it read. That may be only 10 or 15 bytes, but the array 'DATA' is 1024 bytes. So you're supposed to make sure you only try to decode that many bytes. But then:
    Code:
    CLIENT.MSG = Encoding.UTF7.GetString(DATA)
    UTF7 is a very, very strange encoding. Almost no one uses it. Why did you choose this encoding?

    That little bit of code, if written with familiar APIs, should look something like this:
    Code:
    Try
        Dim bytesRead = clientInfo.Client.Receive(buffer, buffer.Length, 0)
        If bytesRead > 0 Then
            Dim message As String = Encoding.UTF8.GetString(buffer, bytesRead, 0)
            clientInfo.Message = message
            ...
    Like above, you don't do anything reasonable if this throws an exception, so you don't have a clue if it's working. Never, ever, ever write a "Catch ex As Exception" if you aren't logging or displaying what the exception does.

    TL;DR:

    Don't try to write your own chat client just yet. There are hundreds of tutorials online with examples. Download one of them, study it, and try transcribing it so you can learn how it works. After you've played with a few tutorials for a few days, try this again and see if it isn't easier.

    Also, seriously. Lose the all-caps. I almost decided to ignore this thread because of it.
    This answer is wrong. You should be using TableAdapter and Dictionaries instead.

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