php - Opening downloaded zip file creates cpgz file?

Question

If I make the url for a zip file the href of a link and click the link, my zip file gets downloaded and opening it gets the contents as I expect.

Here's that HTML:

<a href="http://mysite.com/uploads/my-archive.zip">download zip</a>

The problem is I'd like the link to point to my application such that I could determine whether the user is authorized to access this zip file.

so I'd like my HTML to be this:

 <a href="/canDownload">download zip</a> 

and my PHP for the /canDownload page:

//business logic to determine if user can download

if($yesCanDownload){

$archive='https://mysite.com/uploads/my-archive.zip';
header("Content-Type: application/zip");
header("Content-Disposition: attachment; filename=".basename($archive));
header("Content-Length: ".filesize($archive));
ob_clean();
flush();
echo readfile("$archive");
}   

So, I think the problem has to do with the header() code but i've tried a bunch of things related to that based on various google and other SO suggestions and none work.

If you answer my question, it is likely you can answer this question too: Zipped file with PHP results in cpgz file after extraction

Answer 1

The answer in my case was that there was an empty line being output before readfile().

So i added:

ob_end_clean();

readfile($filename);

But you should probably search for the place where this line is being output in your code.