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How to detect a blocked address from php

so here is my problem; we are trying to configure facebook like the twitter button on our website’s twitter button, but this makes browsers not respond when facebook and twitter are blocked on their computers. so what I would like to do is to determine if facebook or twitter are blocked, and then remove the buttons for these computers, and also allow all others to download them.

is this possible in php or in javascript?

I could not find testing information if the link is blocked or not.

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You can put two hidden images on your page, and then add similar buttons on the fly.
Something like this should work:

<img style="display:none;" onload="user_can_access_facebook()" onerror="no_access_to_facebook()" src="http://static.ak.fbcdn.net/rsrc.php/v1/yp/r/kk8dc2UJYJ4.png" />

If the javascript function user_can_access_facebook() should add a similar button to the DOM.

(http://static.ak.fbcdn.net/rsrc.php/v1/yp/r/kk8dc2UJYJ4.png is the URL of the Facebook logo on the login page. It may not be a static link, so you might need to find another static resource to check.)

For twitter you have to do the same.

Edit:
I put together a small POC:

 <html> <head> <script language="javascript" type="text/javascript"> function user_can_access(sitename) { var siteDiv = document.getElementById(sitename + '_access'); siteDiv.innerText = "You have access to " + sitename; } function no_access(sitename) { var siteDiv = document.getElementById(sitename + '_access'); siteDiv.innerText = "You do NOT have access to " + sitename; } </script> </head> <body> <img src="http://static.ak.fbcdn.net/rsrc.php/v1/yp/r/kk8dc2UJYJ4.png" onload="user_can_access('Facebook')" onerror="no_access('Facebook')" style="display:none;" /> <img src="http://support.twitter.com/images/twitter-logo-no-bird.png" onload="user_can_access('Twitter')" onerror="no_access('Twitter')" style="display:none;" /> <div id="Facebook_access"></div> <div id="Twitter_access"></div> </body> </html>

To try locally, simply block access to the corresponding domain above (static.ak.fbcdn.net and support.twitter.com).
As stated above, you may need to find other resources that are static for verification. If the URLs for images change to facebook and twitter, you should also change them in your code.

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You can try downloading Javascript img or another resource from twitter / facebook and see if it really loads, and then ask AJAX to tell the server that it is not working.

But as far as PHP is concerned, there is no way to determine what connections the client machine can make.

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To manage this in PHP, you will need to first determine if they have access using the JavaScript image method on the download page, and then do a javascript redirect

 document.location="/index.php?TwitterBlocked=true";

Based on the get parameter, you can then insert the code to display the buttons.

However, this whole approach is ugly. The button code provided by these social sites is used on the Internet, and if you download them as the very last bit of JavaScript when downloading a document, you should not have performance on your site.

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