Header only retrieval in php via curl - php

Question

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?

Answer 1

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.

Answer 2

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)

Answer 3

(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.

Answer 4

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.

Answer 5

Here is my implementation using CURLOPT_HEADER, then parsing the output string into a map:
function http_headers($url){
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_NOBODY, true);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HEADER, true);
$headers = curl_exec($ch);
curl_close($ch);
$data = [];
$headers = explode(PHP_EOL, $headers);
foreach ($headers as $row) {
$parts = explode(':', $row);
if (count($parts) === 2) {
$data[trim($parts[0])] = trim($parts[1]);
}
}
return $data;
};
Sample usage:
$headers = http_headers('https://i.ytimg.com/vi_webp/g-dKXOlsf98/hqdefault.webp');
print_r($headers);
Array
(
['Content-Type'] => 'image/webp'
['ETag'] => '1453807629'
['X-Content-Type-Options'] => 'nosniff'
['Server'] => 'sffe'
['Content-Length'] => 32958
['X-XSS-Protection'] => '1; mode=block'
['Age'] => 11
['Cache-Control'] => 'public, max-age=7200'
)

Answer 6

You need to add
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
to return the header instead of printing it.
Whether returning only the headers is lighter on the server depends on the script that's running, but usually it will be.
I think you also want "filetime" instead of "datetime".