<?php
file_put_contents('progress.txt', '');

if (is_file('progress.txt')) {
    unlink('progress.txt');
}

if (is_file('testfile.iso')) {
    unlink('testfile.iso');
}

$targetFile = fopen('testfile.iso', 'w');

$ch = curl_init('https://speed.hetzner.de/100MB.bin');
curl_setopt($ch, CURLOPT_PROGRESSFUNCTION, 'progressCallback');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_NOPROGRESS, false);
curl_setopt($ch, CURLOPT_FILE, $targetFile);
curl_exec($ch);
fclose($targetFile);

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

    if ($download_size == 0) {
        $progress = 0;
    } else {
        $progress = round($downloaded_size * 100 / $download_size);
    }

    if ($progress > $previousProgress) {
        $previousProgress = $progress;
        // $fp = fopen('progress.txt', 'a');
        $fp = fopen('progress.txt', 'w');
        fputs($fp, "$progress\n");
        fclose($fp);
    }
}