php how to detect the extension of a file - php

Question

I'm using curl to download different files (e.g .doc, .jpg, jpeg , docx etc) from a webmail so I would like to know how find this extension because the link that I'm using(e.g example.com/file=3838438) basically outputs the file content but there is no file extension specified in the link.

Answer 1

You probably want the MIME types, not the extension (which is unreliable). The MIME type is a portable way to identify the file type. Examples are image/jpeg and text/html.
First, check whether that site tells you the mime type in the HTTP response. You want to look for the Content-Type header.
If that isn't useful, you can use finfo_file or finfo_buffer to guess mime types. These are available from PECL, or in PHP 5.3 and later.
In older versions of PHP, you can use mime_content_type.

Answer 2

If you're in a Un*x hosted environment, you can call exec('file ' . $file_path, $result) to have the system do an analysis of the file. Check $result for it's answer.
It will have something like:
Filename: ASCII text
Filename: PDF document, version 1.3
etc.

Answer 3

If you don't have to use curl, here is how you could do it using straight PHP.
Note: It is possible to set headers, credentials etc. while using fopen() to fetch URL's using the HTTP context options.
<?php
class DownloadWithExtension
{
// array for caching mimetypes
public $mimetypes = array();
// create mimetype cache when instantiated
public function __construct() {
// iterate through /etc/mime.types and create a hash with
// mime-types as keys and the first extension as the value.
foreach(preg_grep('/(^#)|(^\s+$)/',
file('/etc/mime.types'), PREG_GREP_INVERT) as $line) {
$minfo = preg_split('/\t+/', $line);
if (count($minfo) > 1) {
$this->mimetypes[$minfo[0]] = trim(array_shift(explode(' ', $minfo[1])));
}
}
}
// download $url and save as $prefix while automatically
// determining appropriate extension.
// #param $url - URL to download
// #param $prefix - Filename to save to (without extension)
// #return filename used
public function get($url, $prefix) {
$mimetype = NULL;
$filename = NULL;
$src = fopen($url, 'r');
if (! $src) {
throw new Exception('Failed to open: ' . $url);
}
$meta = stream_get_meta_data($src);
foreach($meta['wrapper_data'] as $header){
if (preg_match('/^content-type: ([^\s]+)/i', $header, &$matches)) {
$mimetype = $matches[1];
break;
}
}
$extension = #$this->mimetypes[$mimetype];
// default to .bin if the mime-type could not be determined
$filename = sprintf('%s.%s', $prefix, $extension ? $extension : 'bin');
$dst = fopen($filename, 'w');
if (! ($dst && stream_copy_to_stream($src, $dst) &&
fclose($src) && fclose($dst))) {
throw new Exception('An error occurred while saving the file!');
}
return $filename;
}
}
$d = new DownloadWithExtension();
$url = 'http://example.com?file=3838438';
$filename = $d->get($url, '/tmp/myfile');
print(sprintf("Saved %s as %s\n", $url, $filename));