rust - 如何在actix-web 2.0中间件中获取web::Data >？

Question

通常，我可以像这样在App上设置数据并从web::Data获取数据:

let pool = sqlx::MySqlPool::connect("mysql://xxx")
    .await
    .expect("Mysql Connect error!");
HttpServer::new(move || {
    // set the data pool: Pool<MySQL>
    App::new()
        .data(pool.clone())
        .service(web::resource("/home").route(web::get().to(get_xxx)))
})
.bind("0.0.0.0:8000")?
.run()
.await;

// get the data: pool: Pool<MySQL> from argument.
pub async fn get_xxx(
    pool: web::Data<Pool<MySql>>,
    path: web::Path<String>,
) -> Result<HttpResponse, Error> {
    let mut pool = pool.clone();
    todo!()
}

如何在中间件中获取 pool: Pool<MySQL>？
这是一个中间件样本:

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

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

pub struct CheckLogin;

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

    fn new_transform(&self, service: S) -> Self::Future {
        ok(CheckLoginMiddleware { service })
    }
}
pub struct CheckLoginMiddleware<S> {
    service: S,
}

use actix_web::http::HeaderValue;
impl<S, B> Service for CheckLoginMiddleware<S>
where
    S: Service<Request = ServiceRequest, Response = ServiceResponse<B>, Error = Error>,
    S::Future: 'static,
{
    type Request = ServiceRequest;
    type Response = ServiceResponse<B>;
    type Error = Error;
    type Future = Either<S::Future, Ready<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 {
        let pool = todo!(); // here! how can I get the pool: Pool<MySQL>
    }
}

我不知道actix-web如何将参数传递给最终的路由函数。

Answer 1

我认为 req.app_data() 是您想要的。

fn call(&mut self, req: ServiceRequest) -> Self::Future {
    let pool = req.app_data::<web::Data<Pool<MySql>>>().unwrap();
    // ...
}

当您调用 App::data()时，actix-web会将给定值存储到内部映射中。关键是它的类型。调用 app_data()时，您尝试从此 map 中获取值(value)。

I don't know how actix-web passes the arguments to the final route function.

最终的路由功能只需调用 <ParamType as FromRequest>::from_request即可获取值。例如，当您尝试获取 web::Data时发生了以下情况:

impl<T: 'static> FromRequest for Data<T> {
    type Config = ();
    type Error = Error;
    type Future = Ready<Result<Self, Error>>;

    #[inline]
    fn from_request(req: &HttpRequest, _: &mut Payload) -> Self::Future {
        if let Some(st) = req.app_data::<Data<T>>() {
            ok(st.clone())
        } else {
            log::debug!(
                "Failed to construct App-level Data extractor. \
                 Request path: {:?}",
                req.path()
            );
            err(ErrorInternalServerError(
                "App data is not configured, to configure use App::data()",
            ))
        }
    }
}

您可以看到 from_request内部的 web::Data从 web::Data<T>获取值(您的 req.app_data()参数)。
顺便说一句，我注意到您正在使用 sqlx，其 Pool实际上内部有一个 Arc。但是 Data里面也有一个 Arc。这是多余的。如果您介意的话，可以定义包装类型 Pool，并为其实现 FromRequest特性。