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I am writing a anti-leeching download script, and my plan is to create a temporary file, which is named by session ID, then after the session expires, the file will be automatically deleted. Is it possible ? And can you give me some tips how to do that in PHP ?
Thanks so much for any reply
671
Ok, so we have the following requirements so far
Let's see. This is not working code, but it should work along these lines:
<?php // download.php
session_start(); // start or resume a session
// always sanitize user input
$fileId = filter_input(INPUT_GET, 'fileId', FILTER_SANITIZE_NUMBER_INT);
$token = filter_input(INPUT_GET, 'token', FILTER_UNSAFE_RAW);
$referer = filter_input(INPUT_SERVER, 'HTTP_REFERER', FILTER_SANITIZE_URL);
$script = filter_input(INPUT_SERVER, 'SCRIPT_NAME', FILTER_SANITIZE_URL);
// mush session_id and fileId into an access token
$secret = 'i can haz salt?';
$expectedToken = md5($secret . session_id() . $fileId);
// check if request came from download.php and has the valid access token
if(($expectedToken === $token) && ($referer === $script)) {
$file = realpath('path/to/files/' . $fileId . '.zip');
if(is_readable($file)) {
session_destroy(); // optional
header(/* stuff */);
fpassthru($file);
exit;
}
}
// if no file was sent, send the page with the download link.
?>
<html ...
<?php printf('a href="/download.php?fileId=%s&token=%s',
$fileId, $expectedToken); ?>
...
</html>
And that's it. No database required. This should cover requirements 1-3. You cannot control speed with PHP, but if you dont destroy the session after sending a file you could write a counter to the session and limit the number of files the user will be sent during a session.
I wholeheartedly agree that this could be solved much more elegantly than with this monkeyform hack, but as proof-of-concept, it should be sufficient.
171
PHP has a function for that name tmpfile. It creates a temporary file and returns a resource. The resource can be used like any other resource.
E.g. the example from the manual:
<?php
$temp = tmpfile();
fwrite($temp, "writing to tempfile");
fseek($temp, 0);
echo fread($temp, 1024);
fclose($temp); // this removes the file
?>
The file is automatically removed when closed (using fclose()), or when the script ends. You can use any file functions on the resource. You can find these here. Hope this will help you?
Another solution would be to create the file in the regular way and use a cronjob to regular check if a session is expired. The expiration date and other session data could be stored in a database. Use the script to query that data and determine if a session is expired. If so, remove it physically from the disk. Make sure to run the script once an hour or so (depending on your timeout).
21
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