Redirection and server availability using sockets

[srebman]

I have two servers, one hosted and one local. My local server uses dynamic dns and I am trying to write a script on my hosted server that will check to see if my local server is accessible. If it is accessible I would like the script to do a browser redirect to my local server. If the connection can't be made I would like the script to be in the header of an index page on the hosted server or redirect to a valid page one the hosted server. From what I've found on the net it should be possible using socket() but am not sure how to go about it. Is there anyone who can help me with this?

Apache 2
php 5

Thank You.

[thorpe]

You dont need to go to the trouble of using sockets. [man]fopen[/man] should suffice. eg;

if (!fopen("http://yourlocalserver.com/file.php")) {
  echo "unable to access remote host";
}

[srebman]

Thank you that seems like an easier way to go about it. I am having a problem with the if statment not failing when I take down my local server. Here is my script:

<?php

if (!fopen("http://localserver/index.php", "r")) {
    header("location: http://remoteserver/index.php");
} else {
	header("location: http://sub.localserver/");
	 }

fclose("http://localserver/index.php", "r");

?>

Even when I shutdown httpd on the local server so "httpd://localserver/index.php" is unavailable I still get redirected to sub.localserver with an unable to establish connection. Can anyone see what I am doing wrong?

Thank you.

[bradgrafelman]

Try this:

if (! $sock = @fsockopen('localserver', 80, $num, $error, 3))
     header("location: http://remoteserver/index.php");
else {
     fclose($sock);
     header("location: http://sub.localserver/");
}

Note that the '3' (last parameter) in [man]fsockopen/man is the timeout parameter. If it is a local server, it should respond fairly quickly, so I specified a shorter timeout. You may need to adjust this, however.