CORS Fairing in Rocket Causing Lifetime Errors

Question

I'm trying to add a CORS policy to my rocket API. I've tried a couple ways but the closest (I think) and most straightforward way so far has been to add a custom Fairing that sets the CORS headers in the on_response hook. I've been using the Fairings implementation guide and this answer to a similar question, but I am running into complaints about lifetimes.

This is the on_response hook.

fn on_response(&self, request: &Request, response: &mut Response) {
    response.set_header(Header::new("Access-Control-Allow-Origin", "*"));
    response.set_header(Header::new("Access-Control-Allow-Methods", "POST, GET, PATCH, OPTIONS"));
    response.set_header(Header::new("Access-Control-Allow-Headers", "*"));
    response.set_header(Header::new("Access-Control-Allow-Credentials", "true"));
}

Running cargo run yields the following error:

error[E0195]: lifetime parameters or bounds on method `on_response` do not match the trait declaration
  --> src/main.rs:16:19
   |
16 |     fn on_response(&self, request: &Request, response: &mut Response) {
   |                   ^ lifetimes do not match method in trait

Is there a way to resolve the lifetime complaints?

Also of interest would be an idiomatic way to set CORS in Rocket (I've looked at rocket_cors but following the examples creates a bunch of version headaches regarding having to use nightly builds, but maybe I missed a more straightforward way?).

Here's the full code:

Main.rs:

use rocket::http::Header;
use rocket::{Request, Response};
use rocket::fairing::{Fairing, Info, Kind};
#[macro_use] extern crate rocket;

pub struct CORS;

impl Fairing for CORS {
    fn info(&self) -> Info {
        Info {
            name: "Add CORS headers to responses",
            kind: Kind::Response
        }
    }

    fn on_response(&self, request: &Request, response: &mut Response) {
        response.set_header(Header::new("Access-Control-Allow-Origin", "*"));
        response.set_header(Header::new("Access-Control-Allow-Methods", "POST, GET, PATCH, OPTIONS"));
        response.set_header(Header::new("Access-Control-Allow-Headers", "*"));
        response.set_header(Header::new("Access-Control-Allow-Credentials", "true"));
    }
}

#[get("/")]
fn index() -> &'static str {
    "Hello, world!"
}

#[launch]
fn rocket() -> _ {
    rocket::build()
        .attach(CORS)
        .mount("/", routes![index])
}

cargo.toml

[package]
name = "my_project"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
rocket = "0.5.0-rc.1"
rocket_cors = "0.5.2"

It's hard to answer your question because it doesn't include a [MRE]. We can't tell what crates (and their versions), types, traits, fields, etc. are present in the code. It would make it easier for us to help you if you try to reproduce your error on the [Rust Playground](https://play.rust-lang.org) if possible, otherwise in a brand new Cargo project, then [edit] your question to include the additional info. There are [Rust-specific MRE tips](//stackoverflow.com/tags/rust/info) you can use to reduce your original code for posting here. Thanks! — Shepmaster, Dec 21 '21 at 17:51
@Shepmaster I added the entire main and cargo to the question. — BWStearns, Dec 21 '21 at 17:57

score 0 · Accepted Answer · answered Dec 22 '21 at 23:04

In 0.5.0 Fairing implementations need async traits.

#[rocket::async_trait]
impl Fairing for CORS {
    fn info(&self) -> Info {
        Info {
            name: "Add CORS headers to responses",
            kind: Kind::Response
        }
    }

    async fn on_response<'r>(&self, _request: &'r Request<'_>, response: &mut Response<'r>) {
        response.set_header(Header::new("Access-Control-Allow-Origin", "*"));
        response.set_header(Header::new("Access-Control-Allow-Methods", "POST, GET, PATCH, OPTIONS"));
        response.set_header(Header::new("Access-Control-Allow-Headers", "*"));
        response.set_header(Header::new("Access-Control-Allow-Credentials", "true"));
    }
}

(thanks @TimY for the comment over here)

CORS Fairing in Rocket Causing Lifetime Errors

1 Answers1