pagination.py 文件源码

def decode_cursor(self, request):
        """
        Given a request with a cursor, return a `Cursor` instance.
        """
        # Determine if we have a cursor, and if so then decode it.
        encoded = request.query_params.get(self.cursor_query_param)
        if encoded is None:
            return None

        # The offset in the cursor is used in situations where we have a
        # nearly-unique index. (Eg millisecond precision creation timestamps)
        # We guard against malicious users attempting to cause expensive database
        # queries, by having a hard cap on the maximum possible size of the offset.
        OFFSET_CUTOFF = 1000

        try:
            querystring = b64decode(encoded.encode('ascii')).decode('ascii')
            tokens = urlparse.parse_qs(querystring, keep_blank_values=True)

            offset = tokens.get('o', ['0'])[0]
            offset = _positive_int(offset, cutoff=OFFSET_CUTOFF)

            reverse = tokens.get('r', ['0'])[0]
            reverse = bool(int(reverse))

            position = tokens.get('p', [None])[0]
        except (TypeError, ValueError):
            raise NotFound(self.invalid_cursor_message)

        return Cursor(offset=offset, reverse=reverse, position=position)