def pre_request(self, request_headers: dict):
        """Called just before the HTTP request is sent.

        Might alter `request_headers`.

        """
        # Ask the server not to encode the content so that we can resume, etc.
        request_headers['Accept-Encoding'] = 'identity'
        if self._resume:
            bytes_have = os.path.getsize(self._output_file.name)
            if bytes_have:
                # Set ``Range`` header to resume the download
                # TODO: Use "If-Range: mtime" to make sure it's fresh?
                request_headers['Range'] = f'bytes={bytes_have}-'
                self._resumed_from = bytes_have
Called just before the HTTP request is sent.

        Might alter `request_headers`.

        
httpie/downloads.py