PHP zip download bug - php

Question

I have a script that lets users download a zip file on request. It works 100% on computer browsers but does not work on Android/mobile browsers, except for Opera (mobile) only.
Here's my script.
$leads = new Packer($zip_name);
$index = 1;
$count = 0;
foreach($cLeads->lastUnitInfo['leads'] as $lead)
{
// build a request string
$export = 'export_lead_'.$index;
$req = $_POST[$export];
// add it to the zip file
if(isset($req) && $req == '1')
{
// debug only
//echo 'adding lead: '.$lead['file_name'].'<br />';
$leads->addLead('leads/'.$lead['file_name'],$lead['item_name']);
$count++;
//echo 'count: '.$count.'<br/>';
}
$index++;
}
// debug
//exit('count: '.$count); // displays same results on all browsers.
// we got anything packed ?
if($count <= 0) //// <-------- BLOCK OF BUG ON MOBILE PHONE
{
if(file_exists($zip_name))
unlink($zip_name); // delete the zip file created.
exit('<h1>Nothing to export</h1>');
} ///// <---------------------- END BLOCK
// download the leads here.
$leads->purge();
exit;
Here's my purge() function
public function purge($zip_name = 'leads.zip')
{
header('Content-type: application/zip');
header('Content-Disposition: attachment; filename="'.$zip_name.'"');
ob_clean();
flush();
readfile($this->zip_name);
// errors will be disabled here
unlink($this->zip_name);
}
On my Android phone, the zip file gets downloaded but contains <h1>Nothing to export</h1> which renders it as an invalid zip file.
So my problem is, How is it that the block only executes on mobile browsers (except Opera) and then continues to download the zip when it should have exited if $count was zero at all?
I debugged it using Fiddler and the requests are all the same but the output is different, why ?
Is this a bug in PHP? Because if you look at my code the function purge() should output errors saying headers have already been sent but it just continues to download the zip file.
Browsers:
Dolphin (+Beta)
FireFox
Default Android browser
Boat Browser
PHP versions tested:
5.3.13 (Production, shared server)
5.1.4
This is driving me nuts now.
#Alix This is the weirdest bug I've ever seen. I don't seriously see any logical errors here. For the script to initiate a download, there actually has to be files added to the zip. Now on my phone, it says no files are added but there's a zip file in the temp folder. Moreover if there are no files added ($count = 0) then the script should terminate (hence the exit() function) with just a message <h1>Nothing to export</h1>. But it goes on to download the zip file (which at this time does not exist, but in the temp folder it does). The zip file ends up being corrupt as it contains <h1>Nothing to export</h1>
Alix wrote:
*> what happens if you comment out the exit call before serving the file?
It says readfile error then purges the zip file in gibberish UNICODE chars. I can tell it's the zip file because it starts with PK and contains the names of images being exported.
Alix wrote:
If this doesn't work, you may wanna change exit('<h1>Nothing to export</h1>'); to exit(var_dump($_REQUEST));, that way you may check for possible bugs in the form submission by inspecting the Zip file.
Interesting. It prints nothing but the cookie and a $_GET parameter only. If I put the code in your suggestion at the beginning on the script and in the block that adds the files to the zip it prints all the $_POST variables.
There's clearly a bug on PHP's part here. It should terminate when exit is called but it doesn't. And mind you this only happens on mobile browsers except Opera. I'm going to cry blood now.

Answer 1

Are you sure the other browsers are setting $_POST[$export] to the correct value?
Also, you should first ob_[end_]clean() and then output the headers, not the other way around:
public function purge($zip_name = 'leads.zip')
{
ob_end_clean();
flush();
header('Content-Type: application/zip');
header('Content-Disposition: attachment; filename="'.$zip_name.'"');
readfile($this->zip_name);
// errors will be disabled here
unlink($this->zip_name);
}
Additionally, you may wanna set these headers:
header('Content-Length: ' . intval(filesize($zip_name)));
header('Content-Transfer-Encoding: binary');
If this doesn't work, you may wanna change exit('<h1>Nothing to export</h1>'); to exit(var_dump($_REQUEST));, that way you may check for possible bugs in the form submission by inspecting the Zip file.