I've just been looking through a website's error_log and one of the error's that has been logged a few times is:
[21-Jun-2011 12:24:03] PHP Notice: Undefined index: HTTP_USER_AGENT in /home/ukevents/public_html/lib/toro.php on line 130
The line this pertains to in toro.php is:
private function ipad_request() {
return strstr($_SERVER['HTTP_USER_AGENT'], 'iPad');
}
Is it possible for $_SERVER['HTTP_USER_AGENT'] to not be set by a HTTP request?
Yes, it's possible, this a HTTP header sent (or not sent) by client, and you should not rely on it. From php manual:
Contents of the User-Agent: header from the current request, if there is one
So the correct code would be:
private function ipad_request() {
return isset($_SERVER['HTTP_USER_AGENT']) && strstr($_SERVER['HTTP_USER_AGENT'], 'iPad');
}
Yes. Any browser or user-agent can choose not to send the User-Agent header. If they do not send that header, $_SERVER['HTTP_USER_AGENT'] won't be set.
Use isset() to ensure that $_SERVER['HTTP_USER_AGENT'] is set.
private function ipad_request() {
if(!isset($_SERVER['HTTP_USER_AGENT'])) return false;
return strstr($_SERVER['HTTP_USER_AGENT'], 'iPad') !== false;
}
Yes, it's possible, but it never happens for a regular request.
All browsers do send a browser string in the request, so any request that arrives without one comes from some other program. Even all well-behaving bots send a browser string, so you don't have to be concerned about not showing up in search engines either.
PHP docs says:
'HTTP_USER_AGENT' Contents of the User-Agent: header from the current request, if there is one.
(relevant part italicised) so it would appear it might not always be set.
An example where HTTP_USER_AGENT is undefined is if the request coming from GoDaddy's 404 page handler for your site where you have set the handler to be one of your pages.
