cURL default GET request isn't recognized by PHP - php

Question

I'm trying to create a simple Web service that has to return various HTTP codes depending on some conditions, mainly the existence of files related to the specific resources requested via URI. However, i'm stuck on a really strange behaviour i keep getting when I try to generate a 404 header via PHP.
The first snippet, that works, is as follows:
$isNotFound = TRUE;
if ($isNotFound) header('HTTP/1.1 404 Not Found');
Using a simple command-line cURL to request the URI behind which this script runs, I get:
$ curl -LI http://www.example.com/
HTTP/1.1 404 Not Found
Date: Wed, 18 Sep 2013 20:57.25 GMT
Server: Apache/2.2.22 (Ubuntu)
X-Powered-By: PHP/5.3.10-1ubuntu3.8
Vary: Accept-Encoding
Connection: clse
Content-Type: text/html
Now, the second take is like this:
$isNotFound = FALSE;
if ($_SERVER['REQUEST_METHOD'] === 'GET') {
$isNotFound = TRUE;
}
if ($isNotFound === TRUE) {
header('HTTP/1.1 404 Not Found');
}
Running cURL again, this time I get this:
$ curl -LI http://www.example.com/
HTTP/1.1 200 OK
Date: ...
The header is the same as the former, except for the code. To check the obvious, I also printed the value of $isNotFound just before the last if, and it was indeed evaluated to TRUE, so the header call with the 404 code should be executed. I also added an exit() inside the last if, and another header() at the end of the script, giving other codes in response (like 302), and the result is always that the header inside the if is ignored.
I managed to make the second script work by explicitly specifying the request method as GET in the cURL call:
$ curl -X GET -LI http://www.example.com/
HTTP/1.1 404 Not Found
Date: ...
I also had the doubt that cURL wasn't using GET as the default method, but printing the $_SERVER array showed that the request method was indeed GET.
So, what is the reason of this strange behaviour? Is cURL's fault when using the implicit GET method, or is something happening inside PHP? Or maybe i'm so tired that i'm missing something trivial?
Thank you guys, and sorry for the long post.

Answer 1

Next time read the manual:
-I, --head
(HTTP/FTP/FILE) Fetch the HTTP-header only! HTTP-servers feature the
command HEAD which this uses to get nothing but the header of a
document. When used on an FTP or FILE file, curl displays the
file size and last modification time only.
(or your webserver log files, or your TCP stream)