Checking for internet connection.
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From: Daniel Brown on 21 Dec 2009 12:27 On Sat, Dec 19, 2009 at 19:13, Angus Mann <angusmann(a)pobox.com> wrote: > Hi all. > > I'w writing a PHP app that is designed to run over a LAN, so internet > connection for the server is not really essential. Some users may > deliberately not connect it to the internet as a security precaution. > > But I'd like the app to make use of an internet connection if it exists to > check for an update, and notify the user. > > Is there a simple way for a PHP script to check if it has an internet > connection? If it's running on Linux, this will work. For other OS'es, you may have to tweak it a bit. <?php $ip = '24.254.254.1'; // This is a bogus address. Replace it with yours. exec('ping -c 1 -w 3 '.$ip,$ret,$err); if($err) die('Internet connection unavailable.'); ?> This executes a system call to the PING utility, which then sends a single packet with a deadline of 3 seconds to the address. If it causes anything but a 0 return on STDERR, it dies with the message "Internet connection unavailable." Don't use name-based lookups unless you absolutely have to in this case. There are more points of failure and bottlenecking, which can make your code run really slow or fail completely. -- </Daniel P. Brown> daniel.brown(a)parasane.net || danbrown(a)php.net http://www.parasane.net/ || http://www.pilotpig.net/ Looking for hosting or dedicated servers? Ask me how we can fit your budget!
From: Andy Shellam on 21 Dec 2009 14:40 > > Both at home and at work there are caching DNS on the LAN. So a DNS > request may come back with a valid IP address when the WAN connection is > down. I still won't be able to connect to the remote site. Dig an external server - e.g. dig @a.root-servers.net google.co.uk If your net is down the query will fail even if the reply is cached locally, because you're specifically requesting a response from a.root-servers.net.
From: Stuart Dallas on 22 Dec 2009 08:39 On 21 Dec 2009, at 19:40, Andy Shellam wrote: >> >> Both at home and at work there are caching DNS on the LAN. So a DNS >> request may come back with a valid IP address when the WAN connection is >> down. I still won't be able to connect to the remote site. > > Dig an external server - e.g. dig @a.root-servers.net google.co.uk > > If your net is down the query will fail even if the reply is cached locally, because you're specifically requesting a response from a.root-servers.net. I'm confused... what's the problem with just trying to hit the update server? If you can then you check for updates, if not then you, erm, don't. Simples, no? -Stuart -- http://stut.net/
From: "Bob McConnell" on 22 Dec 2009 08:27 From: Andy Shellam >> >> Both at home and at work there are caching DNS on the LAN. So a DNS >> request may come back with a valid IP address when the WAN connection is >> down. I still won't be able to connect to the remote site. > > Dig an external server - e.g. dig @a.root-servers.net google.co.uk > > If your net is down the query will fail even if the reply is > cached locally, because you're specifically requesting a response > from a.root-servers.net. What means dig? I can't find it in the function index of the online manual. Bob McConnell
From: Ashley Sheridan on 22 Dec 2009 09:22
On Tue, 2009-12-22 at 08:27 -0500, Bob McConnell wrote: > From: Andy Shellam > > >> > >> Both at home and at work there are caching DNS on the LAN. So a DNS > >> request may come back with a valid IP address when the WAN connection > is > >> down. I still won't be able to connect to the remote site. > > > > Dig an external server - e.g. dig @a.root-servers.net google.co.uk > > > > If your net is down the query will fail even if the reply is > > cached locally, because you're specifically requesting a response > > from a.root-servers.net. > > What means dig? I can't find it in the function index of the online > manual. > > Bob McConnell > It's not a PHP thing, it's a network thing (Domain Information Groper) http://en.wikipedia.org/wiki/Domain_Information_Groper Thanks, Ash http://www.ashleysheridan.co.uk |