我一直在尝试根据Actix-web文档中列出的示例编译SayHi中间件：https://actix.rs/docs/middleware/。问题是在最新版本的Actix-web（3.3.2）和Rust（1.55）中，这段代码无法编译，模板缺少参数（大概是因为请求类型已经移动到它们？），即使我将请求类型移动到正确的位置，其他内容也会中断。
如何在最新版本的actix-web中实现像SayHi这样的简单中间件？
我是Rust的新手，所以如果我遗漏了一些明显的东西，请告诉我，但我已经在这两天了，我似乎无法找到或制作任何代码，成功地在最新版本中创建一个简单的actix-web中间件。
这是截至2021年10月16日的actix文档中的示例代码：

use std::pin::Pin;
use std::task::{Context, Poll};

use actix_service::{Service, Transform};
use actix_web::{dev::ServiceRequest, dev::ServiceResponse, Error};
use futures::future::{ok, Ready};
use futures::Future;

pub struct SayHi;

impl<S, B> Transform<S> for SayHi
where
    S: Service<Request = ServiceRequest, Response = ServiceResponse<B>, Error = Error>,
    S::Future: 'static,
    B: 'static,
{
    type Request = ServiceRequest;
    type Response = ServiceResponse<B>;
    type Error = Error;
    type InitError = ();
    type Transform = SayHiMiddleware<S>;
    type Future = Ready<Result<Self::Transform, Self::InitError>>;

    fn new_transform(&self, service: S) -> Self::Future {
        ok(SayHiMiddleware { service })
    }
}

pub struct SayHiMiddleware<S> {
    service: S,
}

impl<S, B> Service for SayHiMiddleware<S>
where
    S: Service<Request = ServiceRequest, Response = ServiceResponse<B>, Error = Error>,
    S::Future: 'static,
    B: 'static,
{
    type Request = ServiceRequest;
    type Response = ServiceResponse<B>;
    type Error = Error;
    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>>>>;

    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        self.service.poll_ready(cx)
    }

    fn call(&mut self, req: ServiceRequest) -> Self::Future {
        println!("Hi from start. You requested: {}", req.path());

        let fut = self.service.call(req);

        Box::pin(async move {
            let res = fut.await?;

            println!("Hi from response");
            Ok(res)
        })
    }
}