Remote Zip Extraction > Can't seem to get this to the finish line

The purpose of this code is to grab an update.zip file from a remote server, unzip it and save it to a local directory, updating, overwriting or creating the updated files.

I've almost got a non cURL version of this working, but I'd rather use this开发者_运维知识库 version. The first problem I have is that the path to the tmp folder is incorrect. I need a better method of sniffing that out (temporarily hardcoded)...

The 2nd problem is that the code's not working, but its not throwing an error. Its executing the $x branch but no zip extraction is taking place.

require('../../../wp-blog-header.php'); //enables wp security check and ABSPATH

    $payload = file_get_contents('http://myserver.com/upgrade.zip'); //grab the file from the remote server
    $target = ABSPATH .'wp-content/themes/mytheme/'; // this is the destination for the unzipped files

openZip($payload); 

function openZip($file_to_open, $debug = false) { 
    global $target;
    $file = ABSPATH . '/tmp/'.md5($file_to_open).'.zip'; //this should be home/myfolder/tmp but ABSPATH is giving the wrong path to the tmp directory.
    $client = curl_init($file_to_open);
    curl_setopt($client, CURLOPT_RETURNTRANSFER, 1);  
    $fileData = curl_exec($client);

    file_put_contents($file, $fileData);

    $zip = new ZipArchive();  
    $x = $zip->open($file);  
    if($x === true) {  //this is true, but no zip extraction?
        $zip->extractTo($target);  
        $zip->close();  

        unlink($file);  
    } else {
        if($debug !== true) {
            unlink($file);
        }  
        die("There was a problem. Please try again!");  
    }  
}

The most likely cause here is that you're not actually writing the zip file data in your file_put_contents() call inside openZip. If you pass a zero-length file to $zip->open(), it will happily go about its way returning (bool)true, even though you obviously will not be able to extract anything from it. See this example.