Callback for download once the request has finished.

def _request_finished(self, reply):
        """Callback for download once the request has finished."""
        url = to_text_string(reply.url().toEncoded(), encoding='utf-8')

        if url in self._paths:
            path = self._paths[url]
        if url in self._workers:
            worker = self._workers[url]

        if url in self._head_requests:
            error = reply.error()
#            print(url, error)
            if error:
                logger.error(str(('Head Reply Error:', error)))
                worker.sig_download_finished.emit(url, path)
                worker.sig_finished.emit(worker, path, error)
                return

            self._head_requests.pop(url)
            start_download = not bool(error)
            header_pairs = reply.rawHeaderPairs()
            headers = {}

            for hp in header_pairs:
                headers[to_text_string(hp[0]).lower()] = to_text_string(hp[1])

            total_size = int(headers.get('content-length', 0))

            # Check if file exists
            if os.path.isfile(path):
                file_size = os.path.getsize(path)

                # Check if existing file matches size of requested file
                start_download = file_size != total_size

            if start_download:
                # File sizes dont match, hence download file
                qurl = QUrl(url)
                request = QNetworkRequest(qurl)
                self._get_requests[url] = request
                reply = self._manager.get(request)

                error = reply.error()
                if error:
                    logger.error(str(('Reply Error:', error)))

                reply.downloadProgress.connect(
                    lambda r, t, w=worker: self._progress(r, t, w))
            else:
                # File sizes match, dont download file or error?
                worker.finished = True
                worker.sig_download_finished.emit(url, path)
                worker.sig_finished.emit(worker, path, None)
        elif url in self._get_requests:
            data = reply.readAll()
            self._save(url, path, data)