Application state access from an Actix web application middleware

Question

I have a simple middleware intended to access the application's global state to perform validation of the authentication token:

use actix_web;
use actix_web::HttpMessage;

pub struct Authenticator;

impl<S> actix_web::middleware::Middleware<S> for Authenticator {
    fn start(
        &self,
        request: &mut actix_web::HttpRequest<S>,
    ) -> actix_web::Result<actix_web::middleware::Started> {
        //let _state = request.state() as &::application::State;
        match request.headers().get("Authentication") {
            Some(_) => Ok(actix_web::middleware::Started::Done),
            None => Err(::view::error(
                "No authentication header provided",
                actix_web::http::StatusCode::FORBIDDEN,
            )),
        }
    }
}

The commented string shows how I tried to get the state. I have tried many ways actually. What is the best way of doing such stuff?

I thought about adding a reference to needed data (e.g. Arc'd RwLock) to the Authenticator structure and constructing it with the reference when I register my middlewares.

I am still not good with trait stuff, but there must be a clean way of casting the S type to my application-defined State structure:

pub struct State {
    pub database: actix::Addr<actix::Syn, ::database::Actor>,
    pub cache: ::std::sync::Arc<::cache::Cache>,
    pub sessions: ::std::sync::Arc<::session::Storage>,
}

Answer 1

Use your state instead of S:

impl actix_web::middleware::Middleware<::Application::State> for Authenticator {
}

By the way, middleware can have state too.