Share state between actix-web server and async closure - rust

Question

I want to periodically fetch data (using asynchronous reqwest), which is then served at an http endpoint using actix-web as a server.
(I have a data source that has a fixed format, that I want to have read by a service that require a different format, so I need to transform the data.)
I've tried to combine actix concepts with the thread sharing state example from the Rust book, but I don't understand the error or how to solve it.
This is the code minified as much as I was able:
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)
}
But I get the following error:
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`.
Why do I suddenly get a str? Is there an easy fix or is my approach to solving this wrong?
Edit: Maybe removing the * is the right way to go, as Peter Hall suggests, but that gives me the following error instead:
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`.
Edit 2: I now get the following error (code changes commented with 'Edit 2' above):
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`.
My Cargo.toml dependencies:
[dependencies]
actix-web = "4.2.1"
reqwest = "0.11.12"
tokio = "1.21.2"

Answer 1

async solution
I had my types mixed up a bit, having the app state as Arc<Mutex<T>> seemed to be the way to go, maybe it would be better with Arc<RwLock<T>>.
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<Arc<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(AppState {
status: status_string,
}));
let app_data1 = app_data.clone();
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.unwrap();
let mut app_data = app_data1.lock().unwrap();
*app_data = AppState { status: res };
}
});
HttpServer::new(move || {
App::new()
.app_data(web::Data::new(app_data.clone()))
.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)
}

Answer 2

async/sync solution
Instead of doing the async get with reqwest I have a solution with the synchronous crate minreq (that I found after a lot of searching). I also chose to not use the #[actix_web::main] macro, and instead start the runtime explicitly at the end of my main function.
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())
}