Lifetime issue with Actix Web - rust

Question

I'm implementing middleware with Actix-web and having an issue with lifetime that I couldn't figure out.
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();
}
The error that I get is the following,
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...
As for what I understand, I am passing cache_addr as a reference to with_tus function. Inside each closure in route, addr is also a reference.
I don't understand why the compiler said the lifetime cannot outlive the anonymous lifetime #1. From what I can tell is that cache_addr's lifetime still outlives the closure. The lifetime should cover up until system.run() line. Can someone enlighten me?
Edit:
I updated the code above to MCVE (at least to a point that it is simple enough to copy the whole code and run cargo build while still preserving the same error message). I can't run it on rust-playground. It doesn't support actix crate at this point. I tried reducing it further but it's giving me a different error. Sorry, I am pretty new to Rust.
My questions are twofold, one I like to understand what's the error telling me. Second, I like to know how to properly do this with actix thus why the sample code is dependent on actix.

Answer 1

Look at the 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 generic depends on T and R that in turn have 'static lifetime requirement.
Your closure captures an &Addr<CacheActor> that it is not valid for 'static lifetime and this generates the error.
A possibility that I see is to use the App "State", directly from the docs:
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.
In this case should be something like:
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();
}