'Flask-style' decorator-based API

[gertvdijk]

The current API is a bit similar to Starlette's applications.

It would be nice to explore if an (additional) Flask/FastAPI/Click-like API can be offered with decorators hooking up the methods to callbacks and configure other options negotiate flags from parameters to the decorators.

E.g. (pseudocode):

from purepythonmilter import (
    AppendHeader,
    Continue,
    EndOfHeaders,
    Macros,
    PurePythonMilter,
)

my_milter = PurePythonMilter(name="my_milter")

@my_milter.hook_on_end_of_headers(
    manipulations=[AppendHeader],
    macros_needed=[Macros.MTA_QUEUE_ID],
)
async def hook_on_end_of_headers(cmd: EndOfHeaders) -> Continue:
    print(EndOfHeaders.headers)
    print(EndOfHeaders.context.all_macros[Macros.MTA_QUEUE_ID])
    return Continue(
        manipulations=[AppendHeader(headername="Foo", headertext="Bar")]
    )

Challenge is probably to get the strict typing working with decorators.

Still open/unsure:

• ability to connect multiple functions to the same hooks (called in sequence).
• ability to decorate/connect class member methods to carry state yourself.