How to return an early response from an actix-web middleware?

Question

My clients authorize through a token in the Authorization header which needs to be checked for each request. If this header is missing or I cannot find a corresponding user, I want to return the HTTP code Unauthorized, else I want to handle the request normally.

Currently I have a lot of duplicate code because I am checking for this header in every request handler. The actix docs suggest in the very first paragraph that it is possible to halt request processing to return a response early. How can this be achieved?

Since I have not found an example that implements this behavior I tried to come up with my own middleware function, but it won't compile.

I have already boxed the return values in order to overcome the problem of returning two different types (ServiceResponse and Map), so the problem asked in How do I conditionally return different types of futures? is not the issue. It is more that I do not know which types with which trait implementations are exactly required as return value for this wrap_fn function. The ones I have right now do not work.

App::new()
    .wrap(Cors::new().allowed_origin("http://localhost:8080"))
    .register_data(state.clone())
    .service(
        web::scope("/routing")
            .wrap_fn(|req, srv| {
                let unauth: Box<dyn IntoFuture<Item = ServiceResponse>> = Box::new(ServiceResponse::new(req.into_parts().0, HttpResponse::Unauthorized().finish()));
                let auth_header = req.headers().get("Authorization");
                match auth_header {
                    None => unauth,
                    Some(value) => {
                        let token = value.to_str().unwrap();
                        let mut users = state.users.lock().unwrap();
                        let user_state = users.iter_mut().find(|x| x.auth.token == token);
                        match user_state {
                            None => unauth,
                            Some(user) => {
                                Box::new(srv.call(req).map(|res| res))
                            }
                        }
                    }
                }
            })
            .route("/closest", web::get().to(routing::find_closest))
            .route("/fsp", web::post().to(routing::fsp))
            .route("/preference", web::get().to(routing::get_preference))
            .route("/preference", web::post().to(routing::set_preference))
            .route("/find_preference", web::post().to(routing::find_preference))
            .route("/reset", web::post().to(routing::reset_data)),
    )
    .bind("0.0.0.0:8000")
    .expect("Can not bind to port 8000")
    .run()
    .expect("Could not start sever");

There are two errors that I am getting upon compiling.

1.

error[E0191]: the value of the associated types `Future` (from the trait `futures::future::IntoFuture`), `Error` (from the trait `futures::future::IntoFuture`) must be specified
  --> src/server/mod.rs:36:41
   |
36 |                         let unauth: Box<dyn IntoFuture<Item = ServiceResponse>> =
   |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |                                         |
   |                                         associated type `Future` must be specified
   |                                         associated type `Error` must be specified

2.

error[E0277]: the trait bound `dyn futures::future::IntoFuture<Item = actix_web::service::ServiceResponse>: futures::future::Future` is not satisfied
  --> src/server/mod.rs:35:22
   |
35 |                     .wrap_fn(|req, srv| {
   |                      ^^^^^^^ the trait `futures::future::Future` is not implemented for `dyn futures::future::IntoFuture<Item = actix_web::service::ServiceResponse>`
   |
   = note: required because of the requirements on the impl of `futures::future::Future` for `std::boxed::Box<dyn futures::future::IntoFuture<Item = actix_web::service::ServiceResponse>>`

Answer 1

You can create your own type, Authorized, implement FromRequest for it and define Authorized as an argument in the handlers that should be checked for authorization.

Simplified example:

use actix_web::dev::Payload;
use actix_web::error::ErrorUnauthorized;
use actix_web::{web, App, Error, FromRequest, HttpRequest, HttpResponse, HttpServer};

fn main() {
    HttpServer::new(move || App::new().route("/", web::to(index)))
        .bind("127.0.0.1:3000")
        .expect("Can not bind to '127.0.0.1:3000'")
        .run()
        .unwrap();
}

fn index(_: Authorized) -> HttpResponse {
    HttpResponse::Ok().body("authorized")
}

struct Authorized;

impl FromRequest for Authorized {
    type Error = Error;
    type Future = Result<Self, Error>;
    type Config = ();

    fn from_request(req: &HttpRequest, _: &mut Payload) -> Self::Future {
        if is_authorized(req) {
            Ok(Authorized)
        } else {
            Err(ErrorUnauthorized("not authorized"))?
        }
    }
}

fn is_authorized(req: &HttpRequest) -> bool {
    if let Some(value) = req.headers().get("authorized") {
        // actual implementation that checks header here
        dbg!(value);
        true
    } else {
        false
    }
}

This code yields:

$ curl localhost:3000
not authorized⏎
$ curl localhost:3000 -H 'Authorized: i am root'
authorized⏎

You could probably do something in the same lines with middlewares, but I have not got my head around the middleware abstraction. Also, you might want to provide useful information to the handlers, like username:

struct Authorized {
    username: String
}

Answer 2

I'm kind of late to the party but the best way to do this from within Actix middleware is using futures::future::Either. You can see how it's used here: https://github.com/actix/examples/blob/master/middleware/middleware/src/redirect.rs.

The left hand side of Either will be a Future which passes the response to the next stage in the chain. The right hand side will be a response (usually HttpResponse) if you wish to return the response early.