php - Portable and safe way to get PATH_INFO

Question

I'm seeking a portable way to receive the (handy) $_SERVER['PATH_INFO'] variable.

After reading a while, it turns out PATH_INFO is originated from CGI/1.1, and my not always be present in all configuration.

What is the best (mostly security-wise) way to get that variable - apart from extracting it manually (security concern).

Answer 1

Well, I'm (almost) sure that without making use of the $_SERVER superglobal keys, providing a alternative way to figure out PATH_INFO is just impossible, that being said lets first list all of the $_SERVER keys that we may possibly use:

• 'PHP_SELF'
• 'QUERY_STRING'
• 'SCRIPT_FILENAME'
• 'PATH_TRANSLATED'
• 'SCRIPT_NAME'
• 'REQUEST_URI'
• 'PATH_INFO'
• 'ORIG_PATH_INFO'

We obviously need to ignore the last two. Now we should (I don't know this for a fact, I'm just assuming because you said so) filter all the keys that exist in the link you provided (which BTW is offline ATM), that leaves us with the following keys:

• 'PHP_SELF'
• 'SCRIPT_FILENAME'
• 'REQUEST_URI'

Regarding your comment to Anthonys answer:

You are just juggling variables now. SCRIPT_FILENAME is a part of the CGI spec. It will not be available if PATH_INFO is unavailable. As for REQUEST_URI, it's apache's mod_rewrite specific. – LiraNuna

I'm running LightTPD/1.4.20-1 (Win32) with PHP 5.3.0 as CGI, cgi.fix_pathinfo = 1 and $_SERVER['REQUEST_URI'] is very available to me, I also remember using that same variable back in the days when no one used mod_rewrite so my honest humble guess is that you're plain wrong in this point. Regarding the SCRIPT_FILENAME key I'm unable to test that one out ATM. Still, if we close our eyes really hard and believe that you're right that leaves us with only one variable:

• 'PHP_SELF'

I'm not trying in being harsh here (and I still believe that there are more solutions) but if PHP_SELF is the only key you want us to work with (assuming there are no impositions on PHP_SELF itself) there is only one solution left:

function PATH_INFO()
{
 if (array_key_exists('PATH_INFO', $_SERVER) === true)
 {
  return $_SERVER['PATH_INFO'];
 }

 $whatToUse = basename(__FILE__); // see below

 return substr($_SERVER['PHP_SELF'], strpos($_SERVER['PHP_SELF'], $whatToUse) + strlen($whatToUse));
}

This function should work, however there may be some problems using the __FILE__ constant since it returns the path to the file where the __FILE__ constant is declared and not the path to the requested PHP script, so that's why the $whatToUse is there for: sou you can replace it with 'SCRIPT_FILENAME' or if you really believe in what you are saying, just use '.php'.

You should also read this regarding why not to use PHP_SELF.

If this doesn't work for you, I'm sorry but I can think of anything else.

EDIT - Some more reading for you:

• Drupal request_uri() (why do they keep saying REQUEST_URI is Apache specific?)
• PHP_SELF vs PATH_INFO vs SCRIPT_NAME vs REQUEST_URI