如何編寫自定義 FastAPI 中間件 class

Question

I have read FastAPI's documentation about middlewares (specifically, the middleware tutorial , the CORS middleware section and the advanced middleware guide), but couldn't find a concrete example of how to write a middleware class which you can add using the add_middleware function (in與使用裝飾器添加的基本中間件 function 相比）在此站點上也沒有。

我更喜歡在基於應用的裝飾器上使用add_middleware的原因是，我想在共享庫中編寫一個中間件，供幾個不同的項目使用，因此我不能將它綁定到特定的FastAPI實例。

所以我的問題是：你是怎么做到的？

Answer 1

由於 FastAPI 實際上是下面的Starlette ，因此您可以使用BaseHTTPMiddleware來實現中間件 class（您可能也想看看這篇文章）。 下面給出了相同方法的兩個變體，其中add_middleware() function 用於添加中間件 class。

選項1

中間件.py

from fastapi import Request

class MyMiddleware:
    def __init__(
            self,
            some_attribute: str,
    ):
        self.some_attribute = some_attribute

    async def __call__(self, request: Request, call_next):
        # do something with the request object
        content_type = request.headers.get('Content-Type')
        print(content_type)
        
        # process the request and get the response    
        response = await call_next(request)
        
        return response

應用程序.py

from fastapi import FastAPI
from middleware import MyMiddleware
from starlette.middleware.base import BaseHTTPMiddleware

app = FastAPI()
my_middleware = MyMiddleware(some_attribute="some_attribute_here_if_needed")
app.add_middleware(BaseHTTPMiddleware, dispatch=my_middleware)

選項 2

中間件.py

from fastapi import Request
from starlette.middleware.base import BaseHTTPMiddleware

class MyMiddleware(BaseHTTPMiddleware):
    def __init__(
            self,
            app,
            some_attribute: str,
    ):
        super().__init__(app)
        self.some_attribute = some_attribute

    async def dispatch(self, request: Request, call_next):
        # do something with the request object, for example
        content_type = request.headers.get('Content-Type')
        print(content_type)
        
        # process the request and get the response    
        response = await call_next(request)
        
        return response

應用程序.py

from fastapi import FastAPI
from middleware import MyMiddleware

app = FastAPI()
app.add_middleware(MyMiddleware, some_attribute="some_attribute_here_if_needed")

Answer 2

@Error - Syntactical Remorse 引發的BaseHTTPMiddleware 錯誤的一個潛在解決方法是對中間件定義使用部分並使用函數式方法，這似乎至少對我有用：

中間件.py

from typing import Any, Callable, Coroutine
from fastapi import Response


async def my_middleware(request: Request, call_next: Callable, some_attribute: Any) -> Response:
    request.state.attr = some_attribute  # Do what you need with your attribute
    return await call_next(request)

應用程序.py

from functools import partial
from fastapi import FastAPI
from middleware import my_middleware


app = FastAPI()

my_custom_middleware: partial[Coroutine[Any, Any, Any]] = partial(my_middleware, some_attribute="my-app")

app.middleware("http")(my_custom_middlware)