Problems with data received thru socket

[Jesper Stocholm]

I am using the example [1] as the basis for an application I am
currently writing. The setup consists of two applications (client and
server) that talk to each other thru TCP.

I have no problems with sending information back and forth, but I have
problems _containing_ the data sent from the client to the server.

In the class I instantiate/declare a StringBuilder to collect the
data as it comes thru the socket

private StringBuilder _sb = new StringBuilder();

For each byte I read I append this byte to _sb, but somehow only
the initial byte is appended to _sb - all other bytes are somehow
lost. I also add all bytes to a listBox, so I have verified that the
data from the client is actually received by my application.

I have tried to display the data arriving (in this case the string
"test") with

System.String szData = new System.String(chars);
MessageBox.Show("szData:" + szData + "\n" + "somestring");

The result is this:

szData:t
szData:e
szData:s
szData:t

Whereas I would expext:

szData:t
somestring
szData:e
somestring
szData:s
somestring
szData:t
somestring

So somehow the data is "disapearing" for me.

Can you tell me why?
The relevant code on the server is this:

public void OnDataReceived(IAsyncResult asyn)
{
try
{
CSocketPacket theSockId = (CSocketPacket)asyn.AsyncState ;
//end receive...
int iRx = 0 ;
iRx = theSockId.thisSocket.EndReceive (asyn);
char[] chars = new char[iRx + 1];
System.Text.Decoder d = System.Text.Encoding.UTF8.GetDecoder();
int charLen = d.GetChars(theSockId.dataBuffer,0, iRx, chars, 0);
System.String szData = new System.String(chars);
listBox1.Items.Add(DateTime.Now.ToString() + "\t" + szData);
_sb.Append(szData); // this line is causing problems
WaitForData(m_socWorker );
}
catch (ObjectDisposedException )
{
System.Diagnostics.Debugger.Log(0,"1","\nOnDataRec eived: Socket has been closed\n");
}
catch(SocketException se)
{
MessageBox.Show (se.Message );
}
}

public void WaitForData(System.Net.Sockets.Socket soc)
{
try
{
if ( pfnWorkerCallBack == null )
{
pfnWorkerCallBack = new AsyncCallback (OnDataReceived);
}
CSocketPacket theSocPkt = new CSocketPacket ();
theSocPkt.thisSocket = soc;
// now start to listen for any data...
soc .BeginReceive (theSocPkt.dataBuffer ,0,theSocPkt.dataBuffer.Length ,SocketFlags.None,pfnWorkerCallBack,theSocPkt);
}
catch(SocketException se)
{
MessageBox.Show (se.Message );
}
}
thanks,
[1] http://www.developerfusion.com/show/3997

--
Jesper Stocholm
Copenhagen, Denmark