如何在Actix-web 3.3.2版本中正确实现类似SayHi的简单中间件

核心改动说明 #

原有文档示例是针对更早的Actix-web 2.x版本编写，3.x版本中Transform trait新增了第二个泛型参数用于指定请求类型，补上该参数即可解决编译报错。

完整可运行代码 #

1. Cargo.toml 依赖配置 #

[dependencies]
actix-web = "3.3.2"
actix-service = "1.0.6"
futures = "0.3"

2. 中间件实现代码 #

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;

// 补全Transform的第二个泛型参数ServiceRequest即可解决模板参数缺失报错
impl<S, B> Transform<S, ServiceRequest> 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<ServiceRequest> 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)
        })
    }
}

3. 中间件挂载示例 #

use actix_web::{App, HttpServer, web};

async fn index() -> &'static str {
    "Hello World"
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    HttpServer::new(|| {
        App::new()
            // 挂载自定义中间件
            .wrap(SayHi)
            .route("/", web::get().to(index))
    })
    .bind(("127.0.0.1", 8080))?
    .run()
    .await
}

运行服务后访问本地8080端口即可在控制台看到中间件打印的日志。

内容的提问来源于stack exchange，提问作者Matt