Header only retrieval in php via curl

Actually I have two questions.

(1) Is there any reduction in processing power or bandwidth used on remote server if I retrieve only headers as opposed to full page retrieval using php and curl?

(2) Since I think, and I might be wrong, that answer to first questions is YES, I am trying to get last modified date or If-Modified-Since header of remote file only in order to compare it with time-date of locally stored data, so I can, in case it has been changed, store it locally. However, my script seems unable to fetch that piece of info, I get NULL, when I run this:

class last_change {

 public last_change;

 function set_last_change() {
  $curl = curl_init();
    curl_setopt($curl, CURLOPT_URL, "http://url/file.xml");
    curl_setopt($curl, CURLOPT_HEADER, true);
    curl_setopt($curl, CURLOPT_FILETIME, true);
    curl_setopt($curl, CURLOPT_NOBODY, true);
  // $header = curl_exec($curl);
  $this -> last_change = curl_getinfo($header);
  curl_close($curl);
 }

 function get_last_change() {
  return $this -> last_change['datetime']; // I have tested with Last-Modified & If-Modified-Since to no avail
 }

}

In case $header = curl_exec($curl) is uncomented, header data is displayed, even if I haven't requested it and is as follows:

HTTP/1.1 200 OK
Date: Fri, 04 Sep 2009 12:15:51 GMT
Server: Apache/2.2.8 (Linux/SUSE)
Last-Modified: Thu, 03 Sep 2009 12:46:54 GMT
ETag: "198054-118c-472abc735ab80"
Accept-Ranges: bytes
Content-Length: 4492
Content-Type: text/xml

Based on that, 'Last-Modified' is returned.

So, what am I doing wrong?

You are passing $header to curl_getinfo(). It should be $curl (the curl handle). You can get just the filetime by passing CURLINFO_FILETIME as the second parameter to curl_getinfo(). (Often the filetime is unavailable, in which case it will be reported as -1).

Your class seems to be wasteful, though, throwing away a lot of information that could be useful. Here's another way it might be done:

class URIInfo 
{
    public $info;
    public $header;
    private $url;

    public function __construct($url)
    {
        $this->url = $url;
        $this->setData();
    }

    public function setData() 
    {
        $curl = curl_init();
        curl_setopt($curl, CURLOPT_URL, $this->url);
        curl_setopt($curl, CURLOPT_FILETIME, true);
        curl_setopt($curl, CURLOPT_NOBODY, true);
        curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($curl, CURLOPT_HEADER, true);
        $this->header = curl_exec($curl);
        $this->info = curl_getinfo($curl);
        curl_close($curl);
    }

    public function getFiletime() 
    {
        return $this->info['filetime'];
    }

    // Other functions can be added to retrieve other information.
}

$uri_info = new URIInfo('http://www.codinghorror.com/blog/');
$filetime = $uri_info->getFiletime();
if ($filetime != -1) {
    echo date('Y-m-d H:i:s', $filetime);
} else {
    echo 'filetime not available';
}

Yes, the load will be lighter on the server, since it's only returning only the HTTP header (responding, after all, to a HEAD request). How much lighter will vary greatly.

Why use CURL for this? There is a PHP-function for that:

$headers=get_headers("http://www.amazingjokes.com/img/2014/530c9613d29bd_CountvonCount.jpg");
print_r($headers);

returns the following:

Array
(
    [0] => HTTP/1.1 200 OK
    [1] => Date: Tue, 11 Mar 2014 22:44:38 GMT
    [2] => Server: Apache
    [3] => Last-Modified: Tue, 25 Feb 2014 14:08:40 GMT
    [4] => ETag: "54e35e8-8873-4f33ba00673f4"
    [5] => Accept-Ranges: bytes
    [6] => Content-Length: 34931
    [7] => Connection: close
    [8] => Content-Type: image/jpeg
)

Should be easy to get the content-type after this.

You could also add the format=1 to get_headers:

$headers=get_headers("http://www.amazingjokes.com/img/2014/530c9613d29bd_CountvonCount.jpg",1);
    print_r($headers);

This will return the following:

Array
(
    [0] => HTTP/1.1 200 OK
    [Date] => Tue, 11 Mar 2014 22:44:38 GMT
    [Server] => Apache
    [Last-Modified] => Tue, 25 Feb 2014 14:08:40 GMT
    [ETag] => "54e35e8-8873-4f33ba00673f4"
    [Accept-Ranges] => bytes
    [Content-Length] => 34931
    [Connection] => close
    [Content-Type] => image/jpeg
)

More reading here (PHP.NET)

(1) Yes. A HEAD request (as you're issuing in this case) is far lighter on the server because it only returns the HTTP headers, as opposed to the headers and content like a standard GET request.

(2) You need to set the CURLOPT_RETURNTRANSFER option to true before you call curl_exec() to have the content returned, as opposed to printed:

curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);

That should also make your class work correctly.

You can set the default stream context:

stream_context_set_default(
    array(
        'http' => array(
            'method' => 'HEAD'
        )
    )
);

Then use:

$headers = get_headers($url,1);

get_headers seems to be more efficient than cURL once get_headers skip steps like trigger authentication routines such as log in prompts or cookies.