How to VBA callback function when XMLHTTP onTimeOut?

Question

I'm trying get xml data from webserver to excel, then I wrote a sendRequest function to call in excel

=sendRequest("http://abb.com/index.php?id=111")

When web-server having trouble, cannot connect or cannot find, excel is not responding, it was horrible! To avoid it, i think we should set timeOut. These are my function:

Function sendRequest(Url)
    'Call service
    Set XMLHTTP = CreateObject("Msxml2.ServerXMLHTTP.6.0")

    'Timeout values are in milli-seconds
    lResolve = 10 * 1000
    lConnect = 10 * 1000
    lSend = 10 * 1000
    lReceive = 15 * 1000 'waiting time to receive data from server
    XMLHTTP.setTimeOuts lResolve, lConnect, lSend, lReceive

    XMLHTTP.OnTimeOut = OnTimeOutMessage 'callback function

    XMLHTTP.Open "GET", Url, False

    On Error Resume Next
    XMLHTTP.Send
    On Error GoTo 0

    sendRequest = (XMLHTTP.responseText)
End Function

Private Function OnTimeOutMessage()
    'Application.Caller.Value = "Server error: request time-out"
    MsgBox ("Server error: request time-out")
End Function

Normally, when XMLHTTP's timeout occurs, event OnTimeOutMessage will be executed (reference #1, #2). But as in my test, OnTimeOutMessage is executed right at the beginning of sendRequest()

How to use callback function when Msxml2.ServerXMLHTTP.6.0 request is time-out?

Thank for your help!

Solution

The line;

XMLHTTP.OnTimeOut = OnTimeOutMessage

Is not a method assignment; rather it immediately executes OnTimeOutMessage() (and assigns its useless return value to OnTimeOut).

The equivalent line in JavaScript as per your example link correctly assigns a Function object to OnTimeOut for subsequent invokation - this is not supported by VBA.

Instead, you could trap the timeout error raised after .send or use early binding, WithEvents, & inline event handlers.