Actix Web 的终身问题

Question

我正在使用 Actix-web 实现中间件，但遇到了一个我无法弄清楚的生命周期问题。

extern crate actix_web;

use actix_web::actix::{Actor, Addr, Context, System};
use actix_web::middleware::Middleware;
use actix_web::{http, server, App, HttpRequest, Responder};
use std::collections::HashMap;

pub struct CacheActor {
    caches: HashMap<String, String>,
}

impl CacheActor {
    pub fn new() -> Self {
        CacheActor {
            caches: HashMap::new(),
        }
    }
}

impl Actor for CacheActor {
    type Context = Context<Self>;
}

fn create_resource(req: HttpRequest, addr: &Addr<CacheActor>) -> impl Responder {
    unimplemented!();
    format!("Unimplemented")
}

fn list_resources(req: HttpRequest, addr: &Addr<CacheActor>) -> impl Responder {
    unimplemented!();
    format!("Unimplemented")
}

pub trait TusMiddlewareTrait {
    fn with_tus(self, addr: &Addr<CacheActor>) -> App;
}

impl TusMiddlewareTrait for App {
    fn with_tus(self, addr: &Addr<CacheActor>) -> App {
        self.route("/files", http::Method::GET, |req| list_resources(req, addr))
            .route("/files", http::Method::POST, |req| {
                create_resource(req, addr)
            })
    }
}

fn main() {
    let system = System::new("Example");
    let cache_addr = CacheActor::new().start();

    server::new(|| App::new().with_tus(&cache_addr))
        .bind("127.0.0.1:8080")
        .unwrap()
        .run();

    system.run();
}

我得到的错误如下，

error[E0495]: cannot infer an appropriate lifetime due to conflicting requirements
  --> src/tus/middleware.rs:84:49
   |
84 |             .route("/files", http::Method::GET, |req| list_resources(req, addr))
   |                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: first, the lifetime cannot outlive the anonymous lifetime #1 defined on the method body at 81:5...
  --> src/tus/middleware.rs:81:5
   |
81 | /     fn with_tus(self, addr: &actix::Addr<cache::CacheActor>) -> App {
82 | |         self.middleware(TusMiddleware)
83 | |             .route("/files", http::Method::OPTIONS, tus_information)
84 | |             .route("/files", http::Method::GET, |req| list_resources(req, addr))
...  |
87 | |             })
88 | |     }
   | |_____^
   = note: ...so that the types are compatible:
           expected &&actix::address::Addr<tus::cache::CacheActor>
              found &&actix::address::Addr<tus::cache::CacheActor>
   = note: but, the lifetime must be valid for the static lifetime...

至于我的理解，我将 cache_addr 作为对 with_tus 函数的引用传递。在 route 中的每个闭包内，addr 也是一个引用。

我不明白编译器为什么说the lifetime cannot outlive the anonymous lifetime #1。据我所知，cache_addr 的生命周期仍然超过闭包。生命周期应该覆盖到 system.run() 行。谁能赐教一下？

编辑:

我将上面的代码更新为 MCVE（至少在某种程度上它足够简单，可以复制整个代码和运行 cargo build，同时仍然保留相同的错误消息）。我不能运行在 rust-playground 上。目前它不支持 actix crate。我尝试进一步减少它，但它给了我一个不同的错误。抱歉，我对 Rust 很陌生。

我的问题有两个，一个是我想了解错误告诉我的是什么。其次，我想知道如何使用 actix 正确执行此操作，因此示例代码依赖于 actix.

的原因

Answer 1

看看 App::route signature:

pub fn route<T, F, R>(self, path: &str, method: Method, f: F) -> App<S> 
where
    F: WithFactory<T, S, R>,
    R: Responder + 'static,
    T: FromRequest<S> + 'static,

F 泛型依赖于 T 和 R，后者又具有 'static 生命周期要求。

你的闭包捕获了一个 &Addr<CacheActor> 它在 'static 生命周期内无效，这会产生错误。

我看到的一种可能性是直接从 docs:

使用 App "State"

Application state is shared with all routes and resources within the same application. When using an http actor, state can be accessed with the HttpRequest::state() as read-only, but interior mutability with RefCell can be used to achieve state mutability. State is also available for route matching predicates and middlewares.

在这种情况下应该是这样的：

extern crate actix_web;

use actix_web::actix::{Actor, Addr, Context, System};
use actix_web::{http, server, App, HttpRequest, HttpResponse, Result};
use std::collections::HashMap;
use actix_web::dev::Handler;

#[derive(Clone)]
pub struct CacheActor {
    caches: HashMap<String, String>,
}

impl CacheActor {
    pub fn new() -> Self {
        CacheActor {
            caches: HashMap::new(),
        }
    }
}

impl Actor for CacheActor {
    type Context = Context<Self>;
}

impl<S> Handler<S> for CacheActor {
    type Result = String;

    fn handle(&self, _req: &HttpRequest<S>) -> Self::Result {
        unimplemented!();
    }
}

fn list_resources(req: &HttpRequest<Addr<CacheActor>>) -> Result<HttpResponse> {
    Ok(HttpResponse::Found()
        .header(http::header::LOCATION, format!("hello {}", req.path()))
        .finish())
}

fn main() {
    let system = System::new("Example");

    server::new(|| {
        let cache_addr = CacheActor::new().start();
        App::with_state(cache_addr)
            .resource("/world", |r| r.method(http::Method::GET).f(list_resources))
    })
    .bind("127.0.0.1:8080")
    .unwrap()
    .run();

    system.run();
}

Actix Web 的终身问题

Lifetime issue with Actix Web

rust

lifetime

rust-actix