fastapi 通过 中间件修改request body

开发过程中遇到的一个问题：就是想要修改request中的请求体，具体代码如下

class CustomMiddleware:
   def __init__(self, app):
       self.app = app

   async def __call__(self, scope, receive, send):
       if scope["type"] != "http":
           await self.app(scope, receive, send)
           return

       async def modify_body():
           message = await receive()
           assert message["type"] == "http.request"

           body: bytes = message.get("body", b"")
           body: str = body.decode()
           data = json.loads(body)
           data["value"] = "456"

           message["body"] = json.dumps(data).encode()
           return message

       await self.app(scope, modify_body, send)


app.add_middleware(CustomMiddleware)

recive 是一个异步函数