rust - 在 actix-web 服务器和异步闭包之间共享状态

Question

我想定期获取数据(使用异步 reqwest)，然后使用 actix-web 作为服务器在 http 端点上提供数据。 (我有一个具有固定格式的数据源，我希望由需要不同格式的服务读取该数据源，因此我需要转换数据。) 我尝试将 actix 概念与 Rust 书中的线程共享状态示例结合起来，但我不明白该错误或如何解决它。 这是我尽可能缩小的代码:

use actix_web::{get, http, web, App, HttpResponse, HttpServer, Responder};
use std::sync::{Arc, Mutex};
use tokio::time::{sleep, Duration};

struct AppState {
    status: String,
}

#[get("/")]
async fn index(data: web::Data<Mutex<AppState>>) -> impl Responder {
    let state = data.lock().unwrap();
    HttpResponse::Ok()
        .insert_header(http::header::ContentType::plaintext())
        .body(state.status.to_owned())
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    let status_string = get_state().await.unwrap();
    let app_data = Arc::new(Mutex::new(web::Data::new(AppState {
        status: status_string,
    })));

    let app_data1 = Arc::clone(&app_data);
    actix_web::rt::spawn(async move {
        loop {
            println!("I get executed every 2-ish seconds!");
            sleep(Duration::from_millis(2000)).await;

            let res = get_state().await;
            let mut app_data = app_data1.lock().unwrap();
            // Edit 2: this line is not accepted by the compiler
            // Edit 2: *app_data.status = res.unwrap();
            // Edit 2: but this line is accepted
            *app_data = web::Data::new(AppState { status: res });
        }
    });

    let app_data2 = Arc::clone(&app_data);
    // Edit 2: but I get an error here now
    HttpServer::new(move || App::new().app_data(app_data2).service(index))
        .bind(("127.0.0.1", 9090))?
        .run()
        .await
}

async fn get_state() -> Result<String, Box<dyn std::error::Error>> {
    let client = reqwest::Client::new().get("http://ipecho.net/plain".to_string());
    let status = client.send().await?.text().await?;
    println!("got status: {status}");

    Ok(status)
}

但我收到以下错误:

error[E0308]: mismatched types
  --> src/main.rs:33:32
   |
33 |             *app_data.status = res.unwrap();
   |             ----------------   ^^^^^^^^^^^^ expected `str`, found struct `String`
   |             |
   |             expected due to the type of this binding

error[E0277]: the size for values of type `str` cannot be known at compilation time
  --> src/main.rs:33:13
   |
33 |             *app_data.status = res.unwrap();
   |             ^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
   |
   = help: the trait `std::marker::Sized` is not implemented for `str`
   = note: the left-hand-side of an assignment must have a statically known size

Some errors have detailed explanations: E0277, E0308.
For more information about an error, try `rustc --explain E0277`.

为什么我突然得到一个str？有没有简单的解决办法或者我解决这个问题的方法是错误的？ 编辑:也许删除*是正确的方法，正如Peter Hall所建议的那样，但这给了我以下错误:

error[E0594]: cannot assign to data in an `Arc`
  --> src/main.rs:33:13
   |
33 |             app_data.status = res.unwrap();
   |             ^^^^^^^^^^^^^^^ cannot assign
   |
   = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `Arc<AppState>`

error[E0507]: cannot move out of `app_data2`, a captured variable in an `Fn` closure
  --> src/main.rs:38:49
   |
37 |     let app_data2 = Arc::clone(&app_data);
   |         --------- captured outer variable
38 |     HttpServer::new(move || App::new().app_data(app_data2).service(index))
   |                     -------                     ^^^^^^^^^ move occurs because `app_data2` has type `Arc<std::sync::Mutex<Data<AppState>>>`, which does not implement the `Copy` trait
   |                     |
   |                     captured by this `Fn` closure

Some errors have detailed explanations: E0507, E0594.
For more information about an error, try `rustc --explain E0507`.

编辑 2: 我现在收到以下错误(上面用“编辑 2”注释的代码更改):

error[E0507]: cannot move out of `app_data2`, a captured variable in an `Fn` closure
  --> src/main.rs:46:49
   |
45 |     let app_data2 = app_data.clone();
   |         --------- captured outer variable
46 |     HttpServer::new(move || App::new().app_data(app_data2).service(index))
   |                     -------                     ^^^^^^^^^ move occurs because `app_data2` has type `Arc<Mutex<Data<AppState>>>`, which does not implement the `Copy` trait
   |                     |
   |                     captured by this `Fn` closure

For more information about this error, try `rustc --explain E0507`.

我的Cargo.toml依赖项:

[dependencies]
actix-web = "4.2.1"
reqwest = "0.11.12"
tokio = "1.21.2"

Answer 1

异步/同步解决方案

我没有使用 reqwest 进行异步获取，而是使用同步箱 minreq (我在大量搜索后找到的)解决方案。我还选择不使用 #[actix_web::main] 宏，而是在主函数末尾显式启动运行时。

use actix_web::{get, http, rt, web, App, HttpResponse, HttpServer, Responder};
use std::sync::{Arc, Mutex};
use std::thread;
use std::time::Duration;

struct AppState {
    status: String,
}

#[get("/")]
async fn index(data: web::Data<Arc<Mutex<AppState>>>) -> impl Responder {
    let state = &data.lock().unwrap();
    HttpResponse::Ok()
        .insert_header(http::header::ContentType::plaintext())
        .body(state.status.clone())
}

fn main() -> std::io::Result<()> {
    let status_string = get_state().unwrap();
    let app_data = Arc::new(Mutex::new(AppState {
        status: status_string,
    }));

    let app_data1 = Arc::clone(&app_data);
    thread::spawn(move || loop {
        thread::sleep(Duration::from_millis(2000));
        let res = get_state().unwrap();
        let mut app_data = app_data1.lock().unwrap();
        *app_data = AppState { status: res };
    });

    rt::System::new().block_on(
        HttpServer::new(move || {
            App::new()
                .app_data(web::Data::new(app_data.clone()))
                .service(index)
        })
        .bind(("127.0.0.1", 9090))?
        .run(),
    )
}

fn get_state() -> Result<String, Box<dyn std::error::Error>> {
    let resp = minreq::get("http://ipecho.net/plain").send().unwrap();
    let state = resp.as_str().unwrap();
    Ok(state.to_string())
}