roundcubemail-plugins-kolab/plugins/kolab_files/lib/kolab_files_observer.php

<?php

/**
 * Observer for HTTP_Request2 implementing saving response body into a file
 */
class kolab_files_observer implements SplObserver
{
    protected $file;
    protected $fp;

    public function set_file($file)
    {
        $this->file = $file;
    }

    public function update(SplSubject $subject): void
    {
        /** @var HTTP_Request2 $subject */
        $event = $subject->getLastEvent();

        switch ($event['name']) {
            case 'receivedHeaders':
                if (!$this->file || !($this->fp = @fopen($this->file, 'wb'))) {
                    throw new Exception("Cannot open target file '{$this->file}'");
                }
                break;

            case 'receivedBodyPart':
            case 'receivedEncodedBodyPart':
                fwrite($this->fp, $event['data']);
                break;

            case 'receivedBody':
                fclose($this->fp);
                break;
        }
    }
}