SunshinePHP Developer Conference 2015

Using remote files

As long as allow_url_fopen is enabled in php.ini, you can use HTTP and FTP URLs with most of the functions that take a filename as a parameter. In addition, URLs can be used with the include, include_once, require and require_once statements (since PHP 5.2.0, allow_url_include must be enabled for these). See Supported Protocols and Wrappers for more information about the protocols supported by PHP.

For example, you can use this to open a file on a remote web server, parse the output for the data you want, and then use that data in a database query, or simply to output it in a style matching the rest of your website.

Example #1 Getting the title of a remote page

<?php
$file 
fopen ("http://www.example.com/""r");
if (!
$file) {
    echo 
"<p>Unable to open remote file.\n";
    exit;
}
while (!
feof ($file)) {
    
$line fgets ($file1024);
    
/* This only works if the title and its tags are on one line */
    
if (preg_match ("@\<title\>(.*)\</title\>@i"$line$out)) {
        
$title $out[1];
        break;
    }
}
fclose($file);
?>

You can also write to files on an FTP server (provided that you have connected as a user with the correct access rights). You can only create new files using this method; if you try to overwrite a file that already exists, the fopen() call will fail.

To connect as a user other than 'anonymous', you need to specify the username (and possibly password) within the URL, such as 'ftp://user:password@ftp.example.com/path/to/file'. (You can use the same sort of syntax to access files via HTTP when they require Basic authentication.)

Example #2 Storing data on a remote server

<?php
$file 
fopen ("ftp://ftp.example.com/incoming/outputfile""w");
if (!
$file) {
    echo 
"<p>Unable to open remote file for writing.\n";
    exit;
}
/* Write the data here. */
fwrite ($file$_SERVER['HTTP_USER_AGENT'] . "\n");
fclose ($file);
?>

Note:

You might get the idea from the example above that you can use this technique to write to a remote log file. Unfortunately that would not work because the fopen() call will fail if the remote file already exists. To do distributed logging like that, you should take a look at syslog().

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User Contributed Notes 2 notes

up
4
slva dot web dot sit at gmail dot com
10 months ago
If  allow_url_fopen is disabled in php.ini you can use CURL function for check file exist:

<?php
$ch
= curl_init("http://www.example.com/favicon.ico");

curl_setopt($ch, CURLOPT_NOBODY, true);
curl_exec($ch);
$retcode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
// $retcode >= 400 -> not found, $retcode = 200, found.
curl_close($ch);
?>
up
-13
heck at fas dot harvard dot edu
10 years ago
The previous post is part right, part wrong. It's part right because it's true that the php script will run on the remote server, if it's capable of interpreting php scripts. You can see this by creating this script on a remote machine:
<?php
echo system("hostname");
?>
Then include that in a php file on your local machine. When you view it in a browser, you'll see the hostname of the remote machine.

However, that does not mean there are no security worries here. Just try replacing the previous script with this one:
<?php
echo "<?php system(\"hostname\"); ?>";
?>
I'm guessing you can figure out what that's gonna do.

So yes, remote includes can be a major security problem.
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