Need Help with this Async code

[Terry Olsen]

I'm trying to use Async Socket calls to create a tcp server. It goes into
the listening correctly, but when I connect, it crashes with the following
exception:

An unhandled exception of type 'System.Invalid OperationExcept ion' occurred
in system.dll
Additional information: AcceptCallback
There is no source code available for the current location.

Here's the code. Hopefully someone can help me out.
-----------------------------------------------------------
Private sck As Socket 'Class level

Private Sub btnStart_Click( ByVal sender As System.Object, _
ByVal e As System.EventArg s) Handles btnStart.Click
Dim addr As IPAddress = IPAddress.Parse ("0.0.0.0")
Dim ep As New IPEndPoint(addr , CInt(txtPort.Te xt))
Dim sck As New Socket(AddressF amily.InterNetw ork, _
SocketType.Stre am, ProtocolType.Tc p)
sck.Bind(ep)
sck.Listen(2)
sck.BeginAccept (AddressOf AcceptCallback, Nothing)
lblStatus.Text = "Listening"
End Sub

Private Sub AcceptCallback( ByVal ar As IAsyncResult)
sck.EndAccept(a r) 'I believe this is my problem
Dim bytes(4095) As Byte
sck.BeginReceiv e(bytes, 0, bytes.Length, SocketFlags.Non e, _
AddressOf ReceiveCallback , bytes)
End Sub

Private Sub ReceiveCallback (ByVal ar As IAsyncResult)
Dim bytes() As Byte = CType(ar.AsyncS tate, Byte())
Dim numbytes As Int32 = sck.EndReceive( ar)
If numbytes = 0 Then
Else
End If
End Sub

[Tom Shelton]

On 2005-01-30, Terry Olsen <to******@hotma il.com> wrote:

I'm trying to use Async Socket calls to create a tcp server. It goes into
the listening correctly, but when I connect, it crashes with the following
exception:

An unhandled exception of type 'System.Invalid OperationExcept ion' occurred
in system.dll
Additional information: AcceptCallback
There is no source code available for the current location.

Here's the code. Hopefully someone can help me out.
-----------------------------------------------------------
Private sck As Socket 'Class level

Private Sub btnStart_Click( ByVal sender As System.Object, _
ByVal e As System.EventArg s) Handles btnStart.Click
Dim addr As IPAddress = IPAddress.Parse ("0.0.0.0")
Dim ep As New IPEndPoint(addr , CInt(txtPort.Te xt))
Dim sck As New Socket(AddressF amily.InterNetw ork, _
SocketType.Stre am, ProtocolType.Tc p)
sck.Bind(ep)
sck.Listen(2)
sck.BeginAccept (AddressOf AcceptCallback, Nothing)
lblStatus.Text = "Listening"
End Sub

Private Sub AcceptCallback( ByVal ar As IAsyncResult)
sck.EndAccept(a r) 'I believe this is my problem
Dim bytes(4095) As Byte
sck.BeginReceiv e(bytes, 0, bytes.Length, SocketFlags.Non e, _
AddressOf ReceiveCallback , bytes)
End Sub

Private Sub ReceiveCallback (ByVal ar As IAsyncResult)
Dim bytes() As Byte = CType(ar.AsyncS tate, Byte())
Dim numbytes As Int32 = sck.EndReceive( ar)
If numbytes = 0 Then
Else
End If
End Sub

Terry...

Your trying to read off your server socket. When a socket connection is
accepted, the client is actually connected on a new socket so that the
server socket goes back to listening.

You should really be doing something like:

Private Sub AcceptCallback (ByVal ar As IAsyncResult)
Dim clt As Socket = sck.EndAccept(a r)
...
clt.BeginReciev e (....)
sck.BeginAccept (...)
End Sub

You might try looking through the async socket examples here:
http://msdn.microsoft.com/library/de...consockets.asp

HTH
--
Tom Shelton [MVP]