Serving download after form submit w/ validation - php

Question

I have created together a pretty simple Download Code redeemer in .php (thanks to help from here) and am having a hard time trying to figure out what the best way to serve a download is if the validation is successful. Basically -
User enters invalid code -> Page is refreshed with error message.
User enters valid code -> Give download 'Save as' -> refresh page.
At the minute I'm using http://www.zubrag.com/scripts/download.php to serve the file but once it has started downloading, my form refreshes the page but only half loads the content?!
This is the form with the PHP script I did.
<div class="dcrForm">
<p>Have a physical copy of this release? Claim your digital download by entering your Download Code below.</p>
<form action="index.php" method="post">
<input type="text" name="code" class="dcrInput" value="">
<input type="submit" name="harrisSubmit" class="dcrSubmit" value="Submit">
</form>
<?php
include("scripts/dcr_config.php");
$code="";
$log="";
if (isset($_POST['harrisSubmit']))
{
$code=$_POST['code'];
$link = mysql_connect($hostname, $dbusername, $dbpassword);
mysql_select_db("$databasename");
$query = "select count from $harris where code='$code'";
if ($q=mysql_query($query))
if ($r=mysql_fetch_array($q)){
if ($r[0]<3)
{
$subquery="update $tbname set count='".($r[0]+1)."' where code='$code'";
mysql_query($subquery);
?><script>window.location.href="download.php?f=test.txt";</script><?php
}
}
$log="<p>Invalid code. Try Again.</p>";
}
echo $log."";
?>
</div>
Does anyone have an ideas on what the best way to serve the download would be? I know that currently anyone who had the file location could download the file but I'm not sure how I could go about protecting i

Answer 1

I am glad you have made it this far!
If you are going to redirect the user to a download script, that script would need to have some sort of token attached to it as to prevent unauthorized downloads, basically re-verifying the code or token given.
In the above script, instead of outputting the javascript to redirect to the download script you could do this:
<?php
include "scripts/dcr_config.php";
$code = "";
$log = "";
if (isset($_POST['harrisSubmit'])) {
$code = trim($_POST['code']);
$link = mysql_connect ( $hostname, $dbusername, $dbpassword );
mysql_select_db ( "$databasename" );
$code = mysql_real_escape_string($code); // very important! protects against exploits
$query = "select count from $harris where code='$code'";
if ($q = mysql_query ( $query )) {
if ($r = mysql_fetch_array ( $q )) {
if ($r [0] < 3) {
$subquery = "update $tbname set count='" . ($r [0] + 1) . "' where code='$code'";
mysql_query ( $subquery );
$file = '/path/to/protecteddownload.txt';
// send file to browser as a download dialog
// no content can be output prior to these header() calls
header('Content-type: application/octet-stream');
header('Content-Disposition: attachment; filename="file.txt"');
header('Content-Length: ' . filesize($file));
header("Cache-Control: no-cache, must-revalidate"); // HTTP/1.1
header("Expires: Sat, 26 Jul 1997 05:00:00 GMT");
echo file_get_contents($file);
exit; // terminate script
} else {
$log = 'Sorry, this code has already been redeemed.';
}
} else {
$log = 'Invalid download code. Try again.';
}
} else {
// query failed
$log = 'An error occurred validating your code, please try again later.';
}
$log = "<p>Invalid code. Try Again.</p>";
}
?>
<?php if (isset($log) && $log != ''): ?>
<strong class="error"><?php echo $log ?></strong>
<?php endif; ?>
<div class="dcrForm">
<p>Have a physical copy of this release? Claim your digital download by
entering your Download Code below.</p>
<form action="index.php" method="post"><input type="text" name="code"
class="dcrInput" value=""> <input type="submit" name="harrisSubmit"
class="dcrSubmit" value="Submit"></form>
</div>
The download script is probably similar to some of what I have above.
The key thing about this example is that the file you are serving with file_get_contents, is not accessible from the web. You only send it when a valid code is entered.

Answer 2

I have just 1 quick question, how big is this file? Could this be a case that the php timeout is being experienced while reading the file to the browser?
You could play around with the php settings to confirm this (http://php.net/manual/en/function.set-time-limit.php).
Just my 2 cents