BUG: Winsock Control run-time error 10054 in DataArrival event for UDP (260018)

SYMPTOMS

A run-time error occurs when you use network communications on a Windows 2000-based computer with a Winsock Control that uses User Datagram Protocol (UDP), and the Protocol property of the control is set as sckUDPProtocol.

If a SendData request is sent to a RemoteHost that is not listening on the RemotePort, the DataArrival event fires and indicates that 1 byte of data is available. When you call the GetData method to retrieve that data, the following Microsoft Visual Basic run-time error occurs:

'10054' - "The connection is reset by remote side".

Normally, you can capture the error by using the Error event of the Winsock Control. However, even when the Error event is present for the control, the Error event never fires and a run-time error message box displays.

CAUSE

When a UDP packet is sent to a remote computer and that computer is not listening on the port specified, the Internet Control Message Protocol (ICMP) reports this as an ICMP Port Unreachable error, which is then translated to the Windows 2000 Winsock control as error 10054.

The Winsock Control incorrectly handles the error, causing it to pass to the Visual Basic run-time where the error is subsequently caught and displayed.

RESOLUTION

To work around this problem, use the Microsoft Visual Basic Standard Error Handling mechanism to catch the error. This workaround is illustrated in the following code snippet:

Private Sub Winsock1_DataArrival(ByVal bytesTotal As Long)
   Dim szData As String

   On Error Resume Next
   Winsock1.GetData szData
   If Err Then 
      ' handle the error here
   End if
End Sub

Use the On Error method around the GetData method of the Winsock Control to capture the error.

MORE INFORMATION

Steps to reproduce the behavior

Create a new project.
Add the Winsock Control to the project.
Place a Winsock Control on the form.

Add the following code in the Load event of the form:

Private Sub Form_Load()
  Winsock1.Protocol = sckUDPProtocol
  Winsock1.RemoteHost = "localhost"
  Winsock1.RemotePort = 8377	' pick port that is not listening
  Winsock1.SendData "Hello World!"
End Sub

Private Sub Winsock1_DataArrival(ByVal bytesTotal As Long)
  Dim szData As String
  Winsock1.GetData szData       ' error occurs here.
End Sub

Private Sub Winsock1_Error(ByVal Number As Integer, Description As String, ByVal Scode As Long, ByVal Source As String, ByVal HelpFile As String, ByVal HelpContext As Long, CancelDisplay As Boolean)
  CancelDisplay = True
  MsgBox "Error"
End Sub

If you run this code on a Windows 2000-based computer, the Winsock1_Error handler is never called even though a Winsock Control error occurred.

The Visual Basic error handler is able to trap and handle the error if you use the work around described in the "Resolution" section.

NOTE: The run-time error does not occur if you run the same code on a Microsoft Windows 98-based computer or a Microsoft Windows NT-based computer.

REFERENCES

For more information, click the following article numbers to view the articles in the Microsoft Knowledge Base:

245442 Winsock ignores ICMP Port Unreachable control messages

244751 Winsock Control does not fire Error Event in all cases

263823 WinSock Recvfrom() now returns WSAECONNRESET instead of blocking or timing out