A signal handler cannot be a method on an object

[todddialpad]

Describe the bug

If I try and register a method on an object as a signal handler, an exception is thrown because it is not possible to set an attribute on a bound method

    self.add_signal(self.after_routing, 'http.routing.after')
  File "sanic/lib/python3.7/site-packages/sanic/mixins/signals.py", line 77, in add_signal
    handler
  File "sanic/lib/python3.7/site-packages/sanic/mixins/signals.py", line 57, in decorator
    self._apply_signal(future_signal)
  File "sanic/lib/python3.7/site-packages/sanic/app.py", line 420, in _apply_signal
    return self.signal_router.add(*signal)
  File "sanic/lib/python3.7/site-packages/sanic/signals.py", line 222, in add
    handler.__requirements__ = condition  # type: ignore
AttributeError: 'method' object has no attribute '__requirements__'

Code snippet

import sanic

class MyApp(sanic.Sanic):
  def __init__(self, *args, **kwargs):
    super().__init__(*args, **kwargs)
    self.add_signal(self.after_routing, 'http.routing.after')

  def after_routing(self, request, route, kwargs, handler):
    pass

app = MyApp(name='method_signal_handler')

Expected behavior

I would expect the bound method to be registered, and then called when the signal is dispatched.

Environment (please complete the following information):

• OS: MacOS
• Sanic Version: 22.9

Additional context

[Tronic]

Added code tags for readability.

[ChihweiLHBird]

I looked into it and found this was because method object doesn't support being injected arbitrary variables. I would like to purpose saving the conditions and triggers in dict instead of the handler (function) object. One part that confused me is that __trigger__ saved in the function object seems never used. What do you guys think about this solution? @ahopkins @Tronic @sanic-org/framework

[ahopkins]

Yes, that is correct. IIRC, there is not a great way to pass this info. I'd have to look. Happy to hear a proposal.

[ChihweiLHBird]

Yes, that is correct. IIRC, there is not a great way to pass this info. I'd have to look. Happy to hear a proposal.

How do you think about the draft? #2608