def _validate_crlf(self, msg):
        lines = iter(msg.splitlines(True))
        for header in lines:
            if header == CRLF:
                break
            assert header.endswith(CRLF), repr(header)
        else:
            assert 0, f'CRLF between headers and body not found in {msg!r}'
        body = ''.join(lines)
        assert CRLF not in body
        return body