def _next_header(self, session, options=None):
"""Provide next FIX message header."""
state = session.state
header = FixMessage()
header.set(FLD_SENDER_COMP_ID, session.get_conf('sender_comp_id'))
header.set(FLD_TARGET_COMP_ID, session.get_conf('target_comp_id'))
if options is None:
header.set(FLD_MSG_SEQNUM, state.send_seqno)
else:
if options.get(FLD_MSG_SEQNUM, int) is None:
header.set(FLD_MSG_SEQNUM, state.send_seqno)
# merge options
header.join(options)
header.set(FLD_SENDING_TIME, utc_timestamp())
return header
