[2005] TCP socket server example?

[Mathiaslylo]

I'd like a TCP socket server example. I need it, and I haven't been able to find it anywhere. Only a few useless samples.

[Atheist]

The MSDN 101 Samples has a pretty good example.
Anyways, heres one Ive made for you:

Dim listener As Net.Sockets.TcpListener
    Dim listenThread As Threading.Thread
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        listener = New Net.Sockets.TcpListener(Net.IPAddress.Any, 32111)
        listener.Start()
        listenThread = New Threading.Thread(AddressOf DoListen)
        listenThread.IsBackground = True
        listenThread.Start()
    End Sub
 
    Private Sub DoListen()
        'This is the sub that does all the actual "listening". Its an endless loop that calls the AcceptTcpClient method over and over.
        'If there is no connecting TcpClient, it will raise an exception but we will ignore this by catching it in a try statement and doing nothing with it.
        'On the other hand, If a client has connected, it proceeds to the next line and a streamreader reads the incoming stream and shows it in a messagebox.
        Dim sr As IO.StreamReader
        Do
            Try
                Dim client As Net.Sockets.TcpClient = listener.AcceptTcpClient
                sr = New IO.StreamReader(client.GetStream)
                MessageBox.Show(sr.ReadToEnd)
                sr.Close()
            Catch
            End Try
        Loop
    End Sub

Ive just put some badly written explanations in the DoListen sub, I think you can figure the rest out

[Mathiaslylo]

The MSDN 101 Samples has a pretty good example.
Anyways, heres one Ive made for you:

Dim listener As Net.Sockets.TcpListener
    Dim listenThread As Threading.Thread
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        listener = New Net.Sockets.TcpListener(Net.IPAddress.Any, 32111)
        listener.Start()
        listenThread = New Threading.Thread(AddressOf DoListen)
        listenThread.IsBackground = True
        listenThread.Start()
    End Sub
 
    Private Sub DoListen()
        'This is the sub that does all the actual "listening". Its an endless loop that calls the AcceptTcpClient method over and over.
        'If there is no connecting TcpClient, it will raise an exception but we will ignore this by catching it in a try statement and doing nothing with it.
        'On the other hand, If a client has connected, it proceeds to the next line and a streamreader reads the incoming stream and shows it in a messagebox.
        Dim sr As IO.StreamReader
        Do
            Try
                Dim client As Net.Sockets.TcpClient = listener.AcceptTcpClient
                sr = New IO.StreamReader(client.GetStream)
                MessageBox.Show(sr.ReadToEnd)
                sr.Close()
            Catch
            End Try
        Loop
    End Sub

Ive just put some badly written explanations in the DoListen sub, I think you can figure the rest out

Uuuuh! Good job! However, how to make it multi client compatible?

[Atheist]

It is multiclient compatible.
Alot of clients can send data to the server at the same time.

[Mathiaslylo]

It is multiclient compatible.
Alot of clients can send data to the server at the same time.

Yes, but what I mean, is that how to make the server be able to reply to a specific client of all the clients connected?

[Atheist]

Aha. Wait 1 sec rewriting example...

[Mathiaslylo]

Aha. Wait 1 sec rewriting example...

Nice. Thanks.

[Atheist]

Dim listener As Net.Sockets.TcpListener
    Dim listenThread As Threading.Thread
    Dim Clients As New Dictionary(Of String, Net.Sockets.TcpClient)
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        listener = New Net.Sockets.TcpListener(Net.IPAddress.Any, 32111)
        listener.Start()
        listenThread = New Threading.Thread(AddressOf DoListen)
        listenThread.IsBackground = True
        listenThread.Start()
    End Sub
 
    Private Sub DoListen()
        'This is the sub that does all the actual "listening". Its an endless loop that calls the AcceptTcpClient method over and over.
        'If there is no connecting TcpClient, it will raise an exception but we will ignore this by catching it in a try statement and doing nothing with it.
        'If a client has connected it proceeds to the next line and a streamreader reads the incoming stream and shows it in a messagebox.
        Dim sr As IO.StreamReader
        Do
            Try
                Dim client As Net.Sockets.TcpClient = listener.AcceptTcpClient
                sr = New IO.StreamReader(client.GetStream)
                If sr.ReadToEnd = "Register" Then
                    Clients.Add("Mr Bean", client)
                End If
                sr.Close()
            Catch
            End Try
        Loop
    End Sub
 
    Private Function SendToUser(ByVal user As String, ByVal data As String) As Boolean
        If Clients.ContainsKey(user) Then
            Dim sw As New IO.StreamWriter(Clients.Item(user).GetStream)
            sw.Write(data)
            sw.Flush()
            sw.Close()
            Return True
        Else
            Return False
        End If
    End Function

In this example, if a client sends "Register" to the server, the server adds the client to a Dictionary along with a unique string that identifies it (altough in this case, the string will not be unique, but you will need to change that). And the SendToUser function pretty much speaks for itself.

[Mathiaslylo]

Dim listener As Net.Sockets.TcpListener
    Dim listenThread As Threading.Thread
    Dim Clients As New Dictionary(Of String, Net.Sockets.TcpClient)
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        listener = New Net.Sockets.TcpListener(Net.IPAddress.Any, 32111)
        listener.Start()
        listenThread = New Threading.Thread(AddressOf DoListen)
        listenThread.IsBackground = True
        listenThread.Start()
    End Sub
 
    Private Sub DoListen()
        'This is the sub that does all the actual "listening". Its an endless loop that calls the AcceptTcpClient method over and over.
        'If there is no connecting TcpClient, it will raise an exception but we will ignore this by catching it in a try statement and doing nothing with it.
        'If a client has connected it proceeds to the next line and a streamreader reads the incoming stream and shows it in a messagebox.
        Dim sr As IO.StreamReader
        Do
            Try
                Dim client As Net.Sockets.TcpClient = listener.AcceptTcpClient
                sr = New IO.StreamReader(client.GetStream)
                If sr.ReadToEnd = "Register" Then
                    Clients.Add("Mr Bean", client)
                End If
                sr.Close()
            Catch
            End Try
        Loop
    End Sub
 
    Private Function SendToUser(ByVal user As String, ByVal data As String) As Boolean
        If Clients.ContainsKey(user) Then
            Dim sw As New IO.StreamWriter(Clients.Item(user).GetStream)
            sw.Write(data)
            sw.Flush()
            sw.Close()
            Return True
        Else
            Return False
        End If
    End Function

In this example, if a client sends "Register" to the server, the server adds the client to a Dictionary along with a unique string that identifies it (altough in this case, the string will not be unique, but you will need to change that). And the SendToUser function pretty much speaks for itself.

Very impressive! You keep surprising me!

Now, what if I want to send data to all clients connected?

[Atheist]

You would do something like this:

Private Sub SendToAll(ByVal data As String)
        Dim sw As IO.StreamWriter
        For Each c As Net.Sockets.TcpClient In Clients.Values
            sw = New IO.StreamWriter(c.GetStream)
            sw.Write(data)
            sw.Flush()
            sw.Close()
        Next
    End Sub

[Mathiaslylo]

You would do something like this:

Private Sub SendToAll(ByVal data As String)
        Dim sw As IO.StreamWriter
        For Each c As Net.Sockets.TcpClient In Clients.Values
            sw = New IO.StreamWriter(c.GetStream)
            sw.Write(data)
            sw.Flush()
            sw.Close()
        Next
    End Sub

That's great! I'll test that tomorrow, and reply with my rating from 1 to 10, among with any problems I might experience. Thanks for it! It seems suitable! +REP!

[Mathiaslylo]

That's great! I'll test that tomorrow, and reply with my rating from 1 to 10, among with any problems I might experience. Thanks for it! It seems suitable! +REP!

So what if I want the code to have some kind of event that triggers when one of the clients receive data?

[Atheist]

Each client is using a System.Net.Sockets.TcpClient, you will need to read its stream continouesly to find whenever something is incoming.

Private client As Net.Sockets.TcpClient
Private readBuffer(255) As Byte
 
Private Sub Button1_Click(...)
client = New Net.Sockets.TcpClient("somewhere", 0)
client.GetStream.BeginRead(readBuffer, 0, 255, AddressOf DoRead, Nothing)
End Sub

And then you will need a subroutine just like on the server:

Private Sub DoRead(ByVal ar As IAsyncResult)
Try
    'EndRead returns the number of bytes that were recieved, so we will need to check so that something was recieved
    Dim TotalBytes As Integer = client.GetStream.EndRead(ar)
    If TotalBytes  > 0
        Dim strMessage As String = System.Text.Encoding.ASCII.GetString(readBuffer, 0, TotalBytes)
       
        'Here is the place to do whatever you want with the incoming message: strMessage
    
        'Calling this method again is important, it begins the read again.
        client.GetStream.BeginRead(readBuffer, 0, 255, AddressOf DoRead, Nothing)
Catch e As Exception
    MessageBox.Show(e.Message)
End Try
End Sub

[Mathiaslylo]

Each client is using a System.Net.Sockets.TcpClient, you will need to read its stream continouesly to find whenever something is incoming.

Private client As Net.Sockets.TcpClient
Private readBuffer(255) As Byte
 
Private Sub Button1_Click(...)
client = New Net.Sockets.TcpClient("somewhere", 0)
client.GetStream.BeginRead(readBuffer, 0, 255, AddressOf DoRead, Nothing)
End Sub

And then you will need a subroutine just like on the server:

Private Sub DoRead(ByVal ar As IAsyncResult)
Try
    'EndRead returns the number of bytes that were recieved, so we will need to check so that something was recieved
    Dim TotalBytes As Integer = client.GetStream.EndRead(ar)
    If TotalBytes  > 0
        Dim strMessage As String = System.Text.Encoding.ASCII.GetString(readBuffer, 0, TotalBytes)
       
        'Here is the place to do whatever you want with the incoming message: strMessage
    
        'Calling this method again is important, it begins the read again.
        client.GetStream.BeginRead(readBuffer, 0, 255, AddressOf DoRead, Nothing)
Catch e As Exception
    MessageBox.Show(e.Message)
End Try
End Sub

Okay, so how do I know which client reads the data and receives it?

[Atheist]

I dont really understand what you mean. All the code I posted in my last post should go in the client application. You would know who recieves the data because you would know who you sent the data too

[Mathiaslylo]

I dont really understand what you mean. All the code I posted in my last post should go in the client application. You would know who recieves the data because you would know who you sent the data too

I'm sorry I was misunderstood. I'll try to explain in another way. In the DoRead sub, I would like it from there to also return the actual name of the client you add when you use

Clients.Add("Mr Bean", client)

[Atheist]

Aha, you would require the client to send his username along with the "Register" keyword.
I know that this technique was used in the MSDN example, lets say the client wants to send two things at once, both the "Register" keyword and his name, he would then send this:

"Register|Mr Bean"

to the server. When the server recieves this string, it splits it on each | character, and evaluates the first part (Which should always be the 'keyword'). Heres how the DoListen sub would look:

Private Sub DoListen()
        'This is the sub that does all the actual "listening". Its an endless loop that calls the AcceptTcpClient method over and over.
        'If there is no connecting TcpClient, it will raise an exception but we will ignore this by catching it in a try statement and doing nothing with it.
        'If a client has connected it proceeds to the next line and a streamreader reads the incoming stream and shows it in a messagebox.
        Dim sr As IO.StreamReader
        Do
            Try
                Dim client As Net.Sockets.TcpClient = listener.AcceptTcpClient
                sr = New IO.StreamReader(client.GetStream)
                'We split the incoming string by each | character, giving us an array of string elements where the first element is the 'Keyword'
                Dim Data() As String = sr.ReadToEnd.Split("|"c)
                sr.Close()
                Select Case Data(0)
                    Case "Register"
                        'Data(0) was Register, so we know that the next element will be the name of the client
                        If Not Clients.ContainsKey(Data(1))
                            Clients.Add(Data(1), client)
                        End If
                End Select
            Catch
            End Try
        Loop
    End Sub

[Mathiaslylo]

Aha, you would require the client to send his username along with the "Register" keyword.
I know that this technique was used in the MSDN example, lets say the client wants to send two things at once, both the "Register" keyword and his name, he would then send this:

"Register|Mr Bean"

to the server. When the server recieves this string, it splits it on each | character, and evaluates the first part (Which should always be the 'keyword'). Heres how the DoListen sub would look:

Private Sub DoListen()
        'This is the sub that does all the actual "listening". Its an endless loop that calls the AcceptTcpClient method over and over.
        'If there is no connecting TcpClient, it will raise an exception but we will ignore this by catching it in a try statement and doing nothing with it.
        'If a client has connected it proceeds to the next line and a streamreader reads the incoming stream and shows it in a messagebox.
        Dim sr As IO.StreamReader
        Do
            Try
                Dim client As Net.Sockets.TcpClient = listener.AcceptTcpClient
                sr = New IO.StreamReader(client.GetStream)
                'We split the incoming string by each | character, giving us an array of string elements where the first element is the 'Keyword'
                Dim Data() As String = sr.ReadToEnd.Split("|"c)
                sr.Close()
                Select Case Data(0)
                    Case "Register"
                        'Data(0) was Register, so we know that the next element will be the name of the client
                        If Not Clients.ContainsKey(Data(1))
                            Clients.Add(Data(1), client)
                        End If
                End Select
            Catch
            End Try
        Loop
    End Sub

Good job. Now, back to my question. In DoRead, how can I identify the name of the client I am reading from?

[Atheist]

I dont understand the question . DoRead is the subroutine in the client application, it reads its own stream for incoming data. Any incoming data will be from the server.
The clients will not be sending data between eachother, everything goes through the server.

[Mathiaslylo]

I dont understand the question . DoRead is the subroutine in the client application, it reads its own stream for incoming data. Any incoming data will be from the server.
The clients will not be sending data between eachother, everything goes through the server.

Well, I'll try to modify your code to explain.

First, let's say 2 clients are connected. "John", and "Mathy". This sub then occurs, since one of those 2 clients receives data, which causes the "DoRead" sub to be called. However, inside the DoRead sub, how do I know if it was "John" or "Mathy" that received the data?

[Atheist]

Well, I'll try to modify your code to explain.

First, let's say 2 clients are connected. "John", and "Mathy". This sub then occurs, since one of those 2 clients receives data, which causes the "DoRead" sub to be called. However, inside the DoRead sub, how do I know if it was "John" or "Mathy" that received the data?

I take it that John and Mathy are both on their own pc's, then they will be running their own instances of the client application. Two clients will not be sharing the same application, and therefor not the same DoRead subroutine
I hope that answer was clear

[Mathiaslylo]

I take it that John and Mathy are both on their own pc's, then they will be running their own instances of the client application. Two clients will not be sharing the same application, and therefor not the same DoRead subroutine
I hope that answer was clear

Well, it wasn't You see, I still can't determine who is who.
I'd like the function to be modified something like:

Private Sub DoRead(ByVal ar As IAsyncResult, byval User as string)

Where User is the user receiving data?

[Atheist]

So you're saying that there will only be 1 client application that will be used by many users? If so:
Every message that the server sends should consist of atleast two parts: The first part is the 'Keyword' (defines what the message actually is), and the second part should be to which user the message is addressed. Something like this:

"Message|Mr Bean|Go to bed!"

Could be sent from the server, and then evaluated on the client.

[Mathiaslylo]

So you're saying that there will only be 1 client application that will be used by many users? If so:
Every message that the server sends should consist of atleast two parts: The first part is the 'Keyword' (defines what the message actually is), and the second part should be to which user the message is addressed. Something like this:

"Message|Mr Bean|Go to bed!"

Could be sent from the server, and then evaluated on the client.

Ah! Thank you so much !

[Mathiaslylo]

Ah! Thank you so much !

So what about a TCP client then?

[Atheist]

What about it?

[Mathiaslylo]

What about it?

Well, I actually need an example of that as well

[Atheist]

Post #13 is all about the clients communication
The only thing I havent shown is how to send data from the client to the server, but it is done exactly like on the server side. Write to the stream using a streamwriter:

Public Sub SendData(ByVal data As String)
            Try
                Dim writer As New IO.StreamWriter(client.GetStream)
                writer.Write(data)
                writer.Flush()
            Catch ex As Exception
                MessageBox.Show("An error occured, are you sure the server is running?.", "Error!", MessageBoxButtons.OK, MessageBoxIcon.Error)
            End Try
    End Sub

[Mathiaslylo]

Post #13 is all about the clients communication
The only thing I havent shown is how to send data from the client to the server, but it is done exactly like on the server side. Write to the stream using a streamwriter:

Public Sub SendData(ByVal data As String)
            Try
                Dim writer As New IO.StreamWriter(client.GetStream)
                writer.Write(data)
                writer.Flush()
            Catch ex As Exception
                MessageBox.Show("An error occured, are you sure the server is running?.", "Error!", MessageBoxButtons.OK, MessageBoxIcon.Error)
            End Try
    End Sub

You're right, but post #13 doesn't show how to connect with a client

[Atheist]

ah.
You connect the client to the server in one of two ways, either you use the Connect method, or you specify a host and a port when you instanciate it:

Dim Client As New System.Net.Sockets.TcpClient
Client.Connect("127.0.0.1", 30320)

or

Dim Client As New System.Net.Sockets.TcpClient("127.0.0.1", 30320)

[Mathiaslylo]

ah.
You connect the client to the server in one of two ways, either you use the Connect method, or you specify a host and a port when you instanciate it:

Dim Client As New System.Net.Sockets.TcpClient
Client.Connect("127.0.0.1", 30320)

or

Dim Client As New System.Net.Sockets.TcpClient("127.0.0.1", 30320)

Now, I bet this is not ascynchronous? There will be a complete freeze, until it connects. Right?

[Atheist]

It will pause the application for a very short while, and if no connection could be established, it will throw an exception.

[Mathiaslylo]

It will pause the application for a very short while, and if no connection could be established, it will throw an exception.

One problem. The codes you sent for sending data from the server to a client, does not work.

[Atheist]

Whats happening? Have you tried stepping through the code?

[Mathiaslylo]

Whats happening? Have you tried stepping through the code?

Well, I re-modified your code a bit, and here's what I've got, which doesn't work. It does not arrive at the client.

Private Function Send(ByVal user As Long, ByVal data As String) As Boolean
Debug.Print("Sending")
If Clients.ContainsKey(user) = True Then
Debug.Print("User has been found")
Dim sw As System.Net.Sockets.NetworkStream = Clients.Item(user).GetStream
Debug.Print("Stream writer created and write property is " & sw.CanWrite.ToString.ToLower)
Dim d() As Byte
d = System.Text.Encoding.ASCII.GetBytes(data)
sw.Write(d, 0, d.Length)
Debug.Print("Sent")
Return True
Else
Return False
End If
End Function

[Mathiaslylo]

Alright, I fixed that. Now, the error is inside my DoListen sub that I also modified from your own. Look at this.

    Public Function FindUsedIndexes() As String()
        Dim Index1 As Long
        Dim Temp As String = "0"
        Debug.Print("Used indexes from 1 to " & Clients.Values.Count)
        For Index1 = 1 To Clients.Values.Count
            On Error Resume Next
            If Not Clients.Item(Index1) Is Nothing Then
                Temp = Temp & "#" & Index1
            End If
        Next
        Debug.Print("Used indexes was " & Temp & "#0")
        Return Split(Temp & "#0", "#")
    End Function
    Public Function FindFreeIndex() As Long
        Dim Index1 As Long
        For Index1 = 1 To 1000
            GoTo StartLoop
NextIndex:
            Return Index1
StartLoop:
            On Error GoTo NextIndex
            If Clients.Item(Index1) Is Nothing Then
                FindFreeIndex = Index1
            End If
        Next
    End Function

    Private Sub DoListen()
        Dim sr As IO.StreamReader
        Debug.Print("Going to listen!")
        Do
            Try
                Dim client As Net.Sockets.TcpClient = listener.AcceptTcpClient
                If client.Connected = True Then
                    Debug.Print("A connection has just been accepted")
                    Ccount = FindFreeIndex()
                    Debug.Print("Free index found " & Ccount)
                    Clients.Add(Ccount, client)
                    Debug.Print("Accepted client added")
                    Dim UserList As String = "-None"
                    Dim ChoosenIndex As Integer = -1
                    Dim Index As Long
                    Debug.Print("Entering data collection loop")
                    For Index = 1 To 100
                        If Index = Ccount Then
                            User(Index).Available = 1
                            User(Index).RequestID = Ccount
                            Exit For
                        Else
                            UserList = UserList & "-" & User(Index).Name
                        End If
                    Next
                    Send(Ccount, "A" & Ccount & "-" & Mid(UserList, 2))
                End If
                For Each Cc As String In FindUsedIndexes()
                    If Not CLng(Cc) = 0 Then
                        Debug.Print("Creating stream reader " & Cc)
                        sr = New IO.StreamReader(Clients.Item(CLng(Cc)).GetStream) 'This line returns a System.InvalidOperationException
                        Debug.Print("Reading to end")
                        Dim dat As String = sr.ReadToEnd
                        Debug.Print("Splitting data")
                        Dim Data() As String = Split(dat, "|")
                        Debug.Print("It sent the data " & dat)
                        sr.Close()
                        Received(Data(1), Data(0))
                    End If
                Next
            Catch
            End Try
        Loop
    End Sub

    Private Function Send(ByVal user As Long, ByVal data As String) As Boolean
        Debug.Print("Sending")
        If Clients.ContainsKey(user) = True Then
            Debug.Print("User has been found")
            Dim sw As New IO.StreamWriter(Clients.Item(user).GetStream)
            sw.Write(data)
            sw.Flush()
            sw.Close()
            Debug.Print("Sent")
            Return True
        Else
            Return False
        End If
    End Function

[Atheist]

First off, before I even look at the code more. I just want to say that GoTo and On Error statements should not be used. If you ever end up "needing" to use them, you know youve got a bad code design. And On Error Resume Next is defenitly not recommended as it does not "handle" any errors, it just ignores them.

[Mathiaslylo]

I found the solution for that problem, and I am now trying to create a UDP client as well, by the codes you made for the TCP client. However, it can't receive data. Please let me know what I am doing wrong here:

        Public Sub Connect(ByVal HostName As String, ByVal Port As Integer)
            If Port = 0 Then
                Err.Raise(44, "MathyProductions.Sockets.TCP.Client", "The port to connect to was not set")
            End If
            If HostName = vbNullString Then
                Err.Raise(45, "MathyProductions.Sockets.TCP.Client", "The hostname to connect to was not set")
            End If
            Client.Connect(HostName, Port)
            Client.BeginReceive(AddressOf DoRead, Nothing)
        End Sub
        Private Sub DoRead(ByVal ar As IAsyncResult)
            Try
                MsgBox("Read something?")
                Dim EndPoint As System.Net.IPEndPoint = Nothing
                Dim Bytes As [Byte]()
                Bytes = Client.EndReceive(ar, EndPoint)
                If Not Bytes Is Nothing Then
                    Dim Data As String = System.Text.Encoding.ASCII.GetString(Bytes)
                    If Mid(Data, 1, 2) = "ID" Then
                        ClientIndex = CLng(Mid(Data, 3, 1))
                        If Len(Mid(Data, 4)) > 0 Then
                            RaiseEvent ClientReceived(Mid(Data, 4))
                        Else
                            RaiseEvent ServerConnected()
                        End If
                    Else
                        RaiseEvent ClientReceived(Data)
                    End If
                Else
                    Debug.Print("MathyProductions.Sockets.UDP.Client: Could not download data")
                End If
                Client.BeginReceive(AddressOf DoRead, Nothing)
            Catch e As Exception
                RaiseEvent ClientError(Err.Number, e.Message)
            End Try
        End Sub

[Mathiaslylo]

Anyone?

[Atheist]

You have mixed the code with alot of old VB6 code. You shouldnt do that in VB .Net.
Besides, why have you changed so much of the original code?