[Qt-interest] how to detect interenet connection ? or that the internet is down

[Arnold Krille]

On Sunday 11 April 2010 14:32:14 Meir Yanovich wrote:
> im developing desktop application that using internet heavlly , but now i
> need to develop mechanizem
> to detect that the internet connection is down , that mean i can't connect
> to the internet
> what is the best way to implement  such mechanism ?

This question is raised regularly on this list, mostly by developers who 
aren't admins...

The result of each of these discussions:

The only way of "checking" for internet-connection is actually trying to do 
what you are after and have proper error-handling.

Detecting a gateway by upnp is fine as long as there is a gateway to detect via 
upnp. If there isn't you are in trouble.
Checking whether the computer has a valid public ip is asking for trouble in 
almost all private and corporate networks.
Pinging google doesn't necessarily mean that your stuff is working too (unless 
pinging google is the purpose of your app).
Resolving a host-name to ip-address doesn't mean that the machine is allowed 
to send and receive data for the task you are after.

And even if one of the above methods work and your initial real request works 
too, you still need proper error-handling in case the connection fails later 
on. So just do what you want to do and deal with the errors and timeouts like 
you are supposed to be. There is no other reliable way of determining whether 
your stuff will work.

Arnold
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