why do some HTTP headers show up in $_SERVER? Why not $_GET or $_POST ???

[lawrence k]

I noticed this odd PHP function in an article about AJAX and Prototype:

[color=blue]
> http://www.sitepoint.com/article/pai...pt-prototype/2
>
> Prototype adds a custom HTTP header to all its AJAX requests so that your server
> application can detect that it's an AJAX call, rather than a normal call. The header is:
>
> X-Requested-With: XMLHttpRequest
>
> Here's an example PHP function used to detect an AJAX call:
>
> function isAjax() {
> return isset($_SERVER['HTTP_X_REQUEST ED_WITH']) &&
> $_SERVER ['HTTP_X_REQUEST ED_WITH'] == 'XMLHttpRequest ';
> }[/color]


Most of the AJAX calls I've seen are GET or POST, so I expect them to
show up in the $_GET or $_POST arrays. Why would this header show up in
the $_SERVER array?

[nospam@example.com]

Re: why do some HTTP headers show up in $_SERVER? Why not $_GET or $_POST ???


lawrence k wrote:
[color=blue]
> Most of the AJAX calls I've seen are GET or POST, so I expect them to
> show up in the $_GET or $_POST arrays. Why would this header show up in
> the $_SERVER array?[/color]

A HTTP header is not an extra parameter passed via GET or POST. See
http://www.php.net/manual/en/function.header.php.

[John Dunlop]

Re: why do some HTTP headers show up in $_SERVER? Why not $_GET or $_POST ???

lawrence k:
[color=blue]
> Most of the AJAX calls I've seen are GET or POST, so I expect them to
> show up in the $_GET or $_POST arrays. Why would this header show up in
> the $_SERVER array?[/color]

GET and POST are just the names of two methods of sending an HTTP
request, not to be confused with the PHP variables of the same name.
The PHP variable $_GET makes available name=value pairs passed in the
query part of the request-URL (even if the actual method is POST), and
$_POST makes available name=value pairs passed in the body of the
request. $_SERVER, on the other hand, makes available some but not all
of the headers of the request.

http://www.php.net/manual/en/language.variables.predefined.php

HTH.

--
Jock