Script running twice?

Question

Okay so I'm trying to make a secure download system where a certain buyer with a specific license number has access to a download which he can download twice before his permission is lifted. In order to do this I've got a 'count' column next to a 'product_id' and 'license_number' column in the same row. The product id and license number are automatically generated and passed onto the buyer when my paypal ipn script confirms it.

Now here's the problem: when they access the download page with the correct variables the count gets updated by +1, but for some reason this sql query is run twice and I get +2 in my database actually. I have already changed it a bit to check the value first and then change accordingly (to see if that fixes the error) but the error still isn't fixed.

I personally think that maybe me calling a file to download makes the script run twice or am I wrong here?

This is the code:

<?php

include ('../storescripts/connect_to_mysql.php');

// Looks first if the post variables have been set

if(!isset($_GET['id']) && ($_GET['lcn'])){

    // Error output
    echo 'The big PHP monster will not accept you into his cave without bringing an offering of variables!';

} else {

    // Set the variables
    $id = $_GET['id'];
    $license_number = $_GET['lcn'];

    // Check if there is such a thing (Yes, aliens) as the given id and license number
    $sql = mysql_query("SELECT * FROM secure_downloads WHERE product_id ='$id' AND license_number ='$license_number' LIMIT 1");

    $result = mysql_num_rows($sql);

    if($result > 0){



        // Now update the download count
        // Check first if the count is 0

        // Make a variable from the count sql   
        $sql_count = mysql_query("SELECT * FROM secure_downloads WHERE product_id='$id' AND license_number='$license_number' LIMIT 1");

        while($row = mysql_fetch_assoc($sql_count)){
                $count = $row['count']; 
            }

        // Check if the count is above two
        if ($count >= 2){
        // Download has already been downloaded 2 times, do not allow download
        echo 'The download limit for this file has been reached.';
        exit();

    } else if ($count = 0) {
        // Everything is alright, start downloading

        // Force the file download
        $file = 'test.jpg';
        // Change the count to 1
        mysql_query("UPDATE secure_downloads SET count=1 WHERE product_id = '$id' AND license_number = '$license_number'");
        readfile($file);
        exit();

        } else if ($count = 1) {

        // Everything is alright, start downloading

        // Force the file download
        $file = 'test.jpg';
        // Change the count to 2
        mysql_query("UPDATE secure_downloads SET count=2 WHERE product_id = '$id' AND license_number = '$license_number'");
        header('Content-Description: File Transfer');
        header('Content-Type: application/octet-stream');
        header('Content-Disposition: attachment; filename='.basename($file));
        header('Content-Transfer-Encoding: binary');
        header('Expires: 0');
        header('Cache-Control: must-revalidate');
        header('Pragma: public');
        header('Content-Length: ' . filesize($file));
        ob_clean();
        flush();
        readfile($file);


    exit();


    }


    } else {


        // It doesn't exist, tell the user either the variables were wrong or the 
        // download limit has been reached
        echo 'Cannot download the file, either the link is wrong or the download limit has been reached';
    }

}

?>

Answer 1

} else if ($count = 0) {

Change that to ==. Looks like you're assigning 0 to the variable count on each loop, which will probably be the cause of your woes.

There's another issue here:

} else if ($count = 1) {

Make sure all of your if statements use == (or ===) to compare, rather than = to assign.

Answer 2

Take a look at the server logs to see if you are actually getting two requests on the download URL? I have seen cases where certain browsers (particularly mobile browsers) actually make a HEAD request before doing the actual GET. If your code cannot differentiate between these two request types, it will execute twice.