baseimage-tutorial-framework/src/event_handlers/stateful_event_handler.py

import json

from event_handler_base import EventHandlerBase


class StatefulEventHandler(EventHandlerBase):
    def __init__(self, anchor, event_handler_function, zmq_context=None):
        super().__init__(anchor, zmq_context)
        self.event_handler_function = event_handler_function
        self.generator = None
        self.subscribe('reset')

        def event_handler_callback(msg_parts):
            anchor, message = msg_parts
            if anchor == b'reset':
                self.reset()
                return
            data_json = json.loads(message)
            if self.generator is None:
                self.generator = self.event_handler_function(data_json, self)
            try:
                response_anchor, response_data = next(self.generator)
            except StopIteration:
                self.reset()
                return
            self.subscribe(response_anchor)
            response_data = json.dumps({
                'anchor': response_anchor,
                'data': response_data,
            })
            response = [r.encode('utf-8') for r in (response_anchor, response_data)]
            self.zmq_push_socket.send_multipart(response)

        self.zmq_sub_stream.on_recv(event_handler_callback)

    def unsubscribe_all(self):
        super().unsubscribe_all()
        self.subscribe('reset')

    def reset(self):
        self.generator = None
        self.unsubscribe_all()
        self.subscribe(self.anchor)