[BUGFIX] Using headObject to proof that a folder exists does not work in every case

[geldmacher]

If files in the bucket were created by a 3rd party tool and the folder structure is not created explicity beforehand (which is not necesssary because S3 allows a structured filesystem just by prefixes), the headObject method returns a 404, because there is no folder object to fetch meta data from.

We can use listObjects in this case. If it delivers min. 1 object, we can assume that it is a folder.

[GerDner]

The listObjects case does not work, or does not work with API v4.

The following code snipped does work for me.

    /**
     * Checks if a prefix exists
     *
     * @param string $identifier
     * @return bool
     */
    protected function prefixExists($identifier)
    {

        if($this->objectExists($identifier)){
            return true;
        }
        $objects = $this->getListObjects($identifier);

        return $objects['KeyCount'] > 0;
    }