如何通过文件的URL找出文件的扩展名？

Question

I am trying to find out what extensions a particular url has, Here is what I am trying to do:

$pathinfo = pathinfo('http://imgur.com/9P54j');
$extension = $pathinfo['extension'];
echo $extension;

The url 'http://imgur.com/9P54j' is actually a url having 9P54j.gif image, and its not evident in the url, how do I extract the extension .gif of the the file '9P54j' ?

Answer 1

That URL is not a URL to the .gf image, but a page that contains the image in its HTML. You will want to parse the HTML for the URL to the image. Try: rightclick on the image in the link you provided above, and click "open image" or "view image" to see the full URL.

Even that URL may not have an extension because the data may be streamed to the user bia PHP. If that's the case, just check the Content-Type header to find out what the extension is.

Answer 2

You can use a regex to extract it, something like this:

$url = 'http://imgur.com/9P54j';
$content = file_get_contents($url);
$explode = explode('/', $url);
preg_match('/http:\/\/i\.imgur\.com\/' . array_pop($explode) . '(\.[A-z]{1,4})/', $content, $matches);
$ext = $matches[1]; // '.gif'

Answer 3

My answer assumes that would like to grab the file's extension from urls that have no extensions in the url itself.

Using pathinfo() will not work as it retrieves the extension using text procession and in the url there is just no extension.

An approach would be to use lower level http functionality that allows to send a http request to the url and fetch the response headers. The response headers should regulary contain the 'Content-Type:' header that shows us the mimetype of the content.

Once having the 'Content-Type' header you could use a translation table and translation mimetype to file extension. This list of supported extensions would of course be limited und there are mimetypes that can translate to more than one extension. In such cases you would have to do further investigations on the files content itself.

As a real php programm would be too large for this answer I'll give just a pseudo code:

<?php

function get_extension_from_mimetype($url) {
    // static translation table. to be extended
    static $translationTable = array (
        'image/jpeg' => 'jpg',
        'text/xml' => 'xml',
        'text/html' => 'html'
    );

    $defaultExtension = 'dat';

    // you'll have to write this method 
    $mimetype = get_mimetype_by_url($url);

    if(isset($translationTable[$mimetype])) {
        $extension = $translationTable[$mimetype];
    } else {
        $extension = $defaultExtension;
    }

    return $extension;
}