What is Middlewares in aiogram?

Question

Python

For a long time I just can’t understand what Middleware is, what they are for, where and when they are used. Please explain in detail, can you throw off another link with examples

Answer 1

In general, Middlewares is a layer called automatically after a request and before it is processed by the server. Can be used, for example, for logging or adding a payload.
An example from the docs that adds a counter value to the data of each message

from aiogram import BaseMiddleware
from aiogram.types import Message


class CounterMiddleware(BaseMiddleware):
    def __init__(self) -> None:
        self.counter = 0

    async def __call__(
        self,
        handler: Callable, Awaitable[Any]],
        event: Message,
        data: Dict[str, Any]
    ) -> Any:
        self.counter += 1
        data['counter'] = self.counter
        return await handler(event, data)