借值还不够活？

Question

这是的延续，制作了一个新的 Q 以更好地呈现。

我用 Mutex 做了一个最小的 main，但现在 test_for_closure 做了 not live long enough 并且是 dropped here while still borrowed。多么美妙的旅程！ :)

Rust 游乐场link：https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=7bf56545350624e75aafa10524ea59ff

use std::{convert::Infallible, net::SocketAddr};
use std::sync::{Arc, Mutex};

use hyper::{Body, Request, Response, Server, Version};
use hyper::{Method, StatusCode};
use hyper::service::{make_service_fn, service_fn};
// use tokio::sync::Mutex;

#[tokio::main]
use std::{convert::Infallible, net::SocketAddr};
use std::sync::{Arc, Mutex};

use hyper::{Body, Request, Response, Server, Version};
use hyper::service::{make_service_fn, service_fn};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut test: Arc<Mutex<String>> = Arc::new(Mutex::from("Foo".to_string()));
    let mut test_for_closure = Arc::clone(&test);

    let addr = SocketAddr::from(([127, 0, 0, 1], 4321));

    let make_svc = make_service_fn(|_conn| async {
        Ok::<_, Infallible>(service_fn(|req: Request<Body>| async move {
            if req.version() == Version::HTTP_11 {
                let foo = test_for_closure.lock().unwrap();
                Ok(Response::new(Body::from(foo.as_str())))
            } else {
                Err("not HTTP/1.1, abort connection")
            }
        }))
    });

    let server = Server::bind(&addr).serve(make_svc);

    if let Err(e) = server.await {
        eprintln!("server error: {}", e);
    }

    Ok(())
}

如何解决这个问题，考虑到我们最终需要能够在 main 中修改 Arc 的值，但仍然 hyper 在 HTTP 响应中发回“当前”值？

Answer 1

有两个问题，首先，Body 只实现了 From<&'static str>，但是给定的 &str 绑定到 MutexGuard 上的生命周期，因此 Body::from 调用失败并出现生命周期错误。您可以通过 foo.clone().

解决此问题

第二个问题是关于多个嵌套范围的，这需要在 Arc<Mutex<String>> 和 service_fn 闭包上增加 clone() 和 move。以下编译：

use std::sync::{Arc, Mutex};
use std::{convert::Infallible, net::SocketAddr};

use hyper::service::{make_service_fn, service_fn};
use hyper::{Body, Request, Response, Server, Version};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let test: Arc<Mutex<String>> = Arc::new(Mutex::from("Foo".to_string()));

    let addr = SocketAddr::from(([127, 0, 0, 1], 4321));

    let make_svc = make_service_fn(|_conn| {
        let test_for_closure = test.clone();
        let svc_fn = service_fn(move |req: Request<Body>| {
            let test_for_closure = test_for_closure.clone();
            async move {
                if req.version() == Version::HTTP_11 {
                    let foo = test_for_closure.lock().unwrap();
                    Ok(Response::new(Body::from(foo.clone())))
                } else {
                    Err("not HTTP/1.1, abort connection")
                }
            }
        });
        async move { Ok::<_, Infallible>(svc_fn) }
    });

    let server = Server::bind(&addr).serve(make_svc);

    // change the value at will:
    let mut guard = test.lock().unwrap();
    *guard = "Bar".into();
    drop(guard);

    if let Err(e) = server.await {
        eprintln!("server error: {}", e);
    }

    Ok(())
}

Playground

借值还不够活？

Borrowed value does not live enough?

rust

hyper