PHP setCookie inside Curl Progress Function

Currently I have a progress function Curl is using to write the current progress to a txt file. From there I have Jquery doing an ajax GET to get the current progress of the download. This all is working properly but I want to move from using a file to using a cookie and then have jquery read that cookie instead of working with actual files. Right now I modified the progress callback function to use setcookie but I am seeing an issue that is breaking things on the jquery end of things. I see where the cookie is being set but it doesn't get updated again until the progress is 100. So basically the progress cookie jumps from 0 to 100 percent and is not representative of the actual progress. Here is that function as it is now (you can see in the commented code where I was writing to a file:

function progressCallback($resource, $download_size, $downloaded_size, $upload_size, $uploaded_size)
{
    global $workingDir;
    static $previousProgress = 0;

    if ($download_size == 0) {
        $progress = 0;
    } else {
        $progress = round($downloaded_size * 100 / $download_size);
        if ($progress > $previousProgress) {
            $previousProgress = $progress;
            //$fp = fopen($workingDir.'progress.txt', 'w');
            //fputs($fp, "$progress");
            //fclose($fp);
            setcookie('progressPercent', $progress, 0, '/', '', 0, 0);
        }
    }
}

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