async def _dump_message_field(self, writer, msg, field, fvalue=None):
fname, ftype, params = field[<NUM_LIT:0>], field[<NUM_LIT:1>], field[<NUM_LIT:2>:]<EOL>fvalue = getattr(msg, fname, None) if fvalue is None else fvalue<EOL>await self.dump_field(writer, fvalue, ftype, params)<EOL>
Dumps a message field to the writer. Field is defined by the message field specification.

:param writer:
:param msg:
:param field:
:param fvalue:
:return: