仅在下载完成后执行代码并提取PHP

I have a file to download via curl in PHP about 16Mb, is a zip file,m I want to download and when is finished to download extract it, after extract parse every file inside it.

This is my code:

        $ch2=curl_init();
        curl_setopt($ch2, CURLOPT_URL, $this->URL);
        curl_setopt($ch2, CURLOPT_TIMEOUT, 5040);
        curl_setopt($ch2, CURLOPT_HEADER, 0);
        curl_setopt($ch2, CURLOPT_RETURNTRANSFER, 1);
        curl_setopt($ch2, CURLOPT_POST, 1);
        curl_setopt($ch2, CURLOPT_POSTFIELDS,$this->XMLRequest);
        curl_setopt($ch2, CURLOPT_SSL_VERIFYHOST, 1);
        curl_setopt($ch2, CURLOPT_SSL_VERIFYPEER, FALSE); 
        curl_setopt($ch2, CURLOPT_SSLVERSION, 3); 
        curl_setopt($ch2, CURLOPT_FOLLOWLOCATION, true);

        $httpHeader2 = array(
            "Content-Type: text/xml; charset=UTF-8",
            "Content-Encoding: UTF-8"
        );

        // Execute request, store response and HTTP response code      

        $xml = curl_exec($ch2);
        $this->errno=curl_getinfo( $ch2, CURLINFO_HTTP_CODE );

        curl_close($ch2);

        $file2 = fopen('json_upload/item.zip','w+');
        fwrite($file2, $xml);
        fclose($file2);

        $zip = new ZipArchive;
        echo'<p>json_upload/item.zip</p>';
        $zip->open('json_upload/item.zip', ZIPARCHIVE::CREATE | ZIPARCHIVE::OVERWRITE);
        $zip->extractTo('json_upload/item/');
        $zip->close();

In this mode the file downloaded is 1,6Mb not all and if I try to extract manually return me an error like is damaged.

If I comment the extract code of the zip the file is downloaded completely and if I extract it manually it works fine.

How can I execute the extract of the zip only when the download is complete?
And after how can I execute the parse of each file inside only when the extract command finished?

Thanks

Instead of using fwrite, use file_put_contents()

Replace

$file2 = fopen('json_upload/item.zip','w+');
fwrite($file2, $xml);
fclose($file2);

With

file_put_contents('json_upload/item.zip', $xml);