Check for active internet connection

Question

Wrote a small app that accesses a bunch of search websites and puts the results in a word document, which gets run a few hundred times a day.

It saves individual search results in a number of local folders so the next time those words are searched, it grabs them locally instead of loading the website again.

This works fine - even though it's not quick. People are impressed because until a few weeks ago they did this manually by literally loading up six different search websites, searching, and then copying and pasting the results in a word document.

However, our Office's internet is unreliable, and has been down the last half a day. This has meant about 400 bad searches have been saved in the local folders, and inserted into the final documents.

When a person was searching they could tell if the internet was broken and they would do their searches later. Obviously, though, this app can't tell, and because I'm not using APIs or anything, and because I am limited to using the VBA environment (I'm not even allowed MZ tools), I need to find some way to check that the internet is working before continuing with the program flow, without relying on too many references, and preferably without screenscraping for the phrase "404 Page Not Found".

I'm not very familiar with VB, and VBA is ruining me in so many ways, so there's probably some easy way to do this, which is why I'm asking here.

Appreciate any help.

Answer 1

Obviously, your problem has many levels. You should start by defining "connected to the internet", and go on with developing fallback strategies that include not writing invalid files on failure.

As for the "am I connected" question, you can try tapping into the Win32 API:

Private Declare Function InternetGetConnectedState Lib "wininet.dll" _
(ByRef dwflags As Long, ByVal dwReserved As Long ) As Long

Public Function GetInternetConnectedState() As Boolean
  GetInternetConnectedState = InternetGetConnectedState(0&,0&)
End Function

Though depending on your network setup (proxy/NAT/firewall restrictions etc.), Windows might have a different opinion about this than you.

Trying to GET the pages you are interested in, checking on the return status in the HTTP headers (gateway timeout, 404, whatever you expect to happen when it "doen't work) might also be a way to go.

Answer 2

You could use MSXML library & use XMLHttpRequest class to check for things

e.g.

On Error Resume Next
Dim request As MSXML2.XMLHTTP60
request.Open "http://www.google.com"
request.Send
Msgbox request.Status

The status will give you HTTP Status code of what happened to the request. You might have to do some more checks, depending on your scenario.

Hope that helps.