Socket Programming

[deva]

Hi,

We are developing an utility using Socket programming, we face few issues here, we would
like to take your inputs to resolve these errors.

Firstly, We want to transfer a string data from the client to server, to do this we
follow the logic given below.

Sub SendData()
Dim objTCPClient As New TcpClient()
Dim objStream As Stream
Dim bytMessage(1000) As Byte
Dim strMessage as string = "Sample Message"

objTCPClient = New TcpClient()
objTCPClient.Connect(strContactIPAddr, strContactPortNumber)

objStream = objTCPClient.GetStream()
bytMessage = System.Text.Encoding.ASCII.GetBytes(strMessage)

objStream.Write(bytMessage, 0, Len(strMessage))

objTCPClient.Close()
objTCPClient = Nothing
End Sub

when we execute the above piece of code, it sends the data to the server application
which has been listening for request at a particular ip address and port. When we verified
the string data received from the socket's input stream, we get "Sample Message as the
received text, we would like to know why the ending " (double quotes) is missing here.

Secondly, from the server application, we have a sub routine called Listener,
which is invoked periodically using Timer object from System.Threading namespace. Inside
this subroutine, we used ListenerObject.AcceptSocket() to receive the data sent from
various systems. Here, we are trying to load windows form instances dynamically based upon
the client which sent the data. This subroutine receives data from various client systems

properly, but the form which we are opening from this procedure comes to the foreground, but we

could not set focus to this form and use it in the normal way. It is constantly blocked by some

process. The code snippet used for the above process is given below for your reference.

In a module file, we have the public variables as mentioned below.

Public objTcpListener As TcpListener
Public objTimer As System.Threading.Timer

From a form load event, we execute the code given below.

objTcpListener = New TcpListener(strPortNumber)
objTcpListener.Start()

objTimer = New Timer(New TimerCallback(AddressOf Listener), Nothing, 0, 1000)


Sub Listener()
Dim objSocket As Socket
Dim bytMessage(1000) As Byte

objSocket = objTcpListener.AcceptSocket()
objSocket.Receive(bytMessage)
strMessage = Encoding.ASCII.GetString(bytMessage)

Dim obj_frm_Message as new frmMessage
obj_frm_Message.lblMessage = strMessage
obj_frm_Message.Show()
obj_frm_Message.Focus()

objSocket.Close()
Application.DoEvents()
End Sub

As we mentioned earlier, we could execute the logic given above successfully, it pops up
the new window with the message sent by the tcp client application, but we could not set
focus to the window which is poped up, it is constantly blocked by some system process and
we could not do any operation with those windows.

When we close the main window, all the windows opened through Listenr sub routine get
closed.

Can you give us your inputs to resolve the above mentioned issues, we look forward
for your replies, thank you.

Regards,
Deva.

[StormJason]

1st problem:

The symbol " disappear because the receive byte buffer you define is 1000 bytes while your message is less than that so the remaining space will fill with hex 0x00. The solution is that after you convert the bytes array to text, try to remove those 0x00 by using TRIM.

At Server Side:

objSocket.Receive(bytMessage)
strMessage = Encoding.ASCII.GetString(bytMessage) strMessage.Trim("")

another way to do it is to re dimension your bytes array at the client side to the size exactly same with the character you need to sent so that there won't sent extra 0x00 to server side.

At Client Side:

redim bytMessage(strMessage.Length-1)
bytMessage = System.Text.Encoding.ASCII.GetBytes(strMessage)

objStream.Write(bytMessage, 0, Len(strMessage))


2nd problem:

Still not clear about the problem you are facing.... do you mean that the windows had poped up..,.but the application hangs..or you mean other things?

[deva]

Hi Jason,

Thank you for the reply, we believe that the details provided here would help you to identify our problem and enable you to tell us why it behaves so.

We are developing an utility using Socket programming, we face a problem here, we would like to take your inputs to resolve these errors.

We have written a server application which listens for data from multiple clients. The same application is capable of sending messages to other clients, especially to the client
from whom it received the message. To take care of this requirement, we placed the TCPListener in a subroutine and executed this subroutine using timer object from
System.Threading namespace. This particular subroutine is invoked periodiacally say once in four seconds or once in five seconds throug this timer object.

From this subroutine, we used TCPListener object's AcceptSocket method to receive data from other clients. Now, after receiving a message from a client, we want to load a form
dynamically by displaying the message we received.

This subroutine receives data from various client systems properly, but the windows form which we are opening from this procedure comes to the foreground, but we could not set focus to this

form and use it in the normal way. It is constantly blocked by some system process. This form is hangling and we could not do operation using this.

We have loaded another form before we listen for requests from clients, we are able to use this form in the normal way. It tells us that the application does not hang-up, just the form we loaded through listener procedure is blocked. We have provided the
code snippet below for your reference.

In a module file, we have the public variables as mentioned below.

Public objTcpListener As TcpListener
Public objTimer As System.Threading.Timer

From a form load event, we execute the code given below.

objTcpListener = New TcpListener(strPortNumber)
objTcpListener.Start()

objTimer = New Timer(New TimerCallback(AddressOf Listener), Nothing, 0, 1000)


Sub Listener()
Dim objSocket As Socket
Dim bytMessage(1000) As Byte

objSocket = objTcpListener.AcceptSocket()
objSocket.Receive(bytMessage)
strMessage = Encoding.ASCII.GetString(bytMessage)

Dim obj_frm_Message as new frmMessage
obj_frm_Message.lblMessage = strMessage
obj_frm_Message.Show()
obj_frm_Message.Focus()

objSocket.Close()
Application.DoEvents()
End Sub

As we mentioned earlier, we could execute the logic given above successfully, it pops up the new window with the message sent by the tcp client application, but we could not set focus to the window which is poped up, it is constantly blocked by some system process and we could not do any operation with this window.

Can you give us your inputs to resolve the above mentioned issues, we look forward for your replies, thank you.

Regards,
Deva.