testing for Internet connection

Alex Tweedly alex at tweedly.net
Sun Dec 19 07:04:14 EST 2004

At 02:01 19/12/2004 -0800, Chipp Walters wrote:

>Hi Richard,
>I've found this to work well:
>function isConnectedToInternet pURL
>   if pURL is empty then put "http://www.google.com" into pURL
>   get URL pURL

There is a potential problem with this approach, which can be avoided by 
using numeric IP addresses rather than host names.  Using a host name will 
cause the Rev app to block for 10-30 seconds while it waits for a DNS 
response (see BZ 2117 for details -  Mark W.'s solution is a non-blocking ping)

This problem happens to me all the time, because I use my laptop connected 
to an ethernet which connects to the internet through another computer 
using a dial-up line, and the dial-up is often disconnected. Laptop thinks 
it has a connection (the ethernet is up) and thinks it has DNS servers it 
can reach (because the main computer acts as a DNS proxy) - but when it 
queries a host name, it is blocked until the DNS response times out.

>if your user is not connected, they will probably get an 'invalid host'
>answer. Testing against google seems always to work for me. I figure, if
>they can't get to google, then they can't get to my server.

Google has been the target of a number of DoS attacks, so there have been 
at least two occasions when large parts of the net couldn't get an answer 
from Google, but could have done from you.

-- Alex.

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