How to set up CORS or OPTIONS for Rocket.rs

Question

I\'ve got a backend running rocket.rs which my flutter web app sends a request to, but it can\'t get past the OPTIONS response.

I have tried adding CORS (rocket_cors) t

Answer 1

In order for a server to provide an external API it needs to be able to deal with Cross Origin Resource Sharing (CORS). CORS is an HTTP-header based mechanism that allows a server to indicate which origins (domain, protocol, or port) that a browser should permit loading of resources.

You can create a fairing to handle CORS globally for your app. For example, the following will allow GET, POST, PATCH, or OPTIONS requests from any origin:

use rocket::{Request, Response};
use rocket::fairing::{Fairing, Info, Kind};
use rocket::http::Header;

pub struct CORS();

impl Fairing for CORS {
    fn info(&self) -> Info {
        Info {
            name: "Add CORS headers to requests",
            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"));
    }
}

You just have to attach the fairing like this:

rocket::ignite().attach(CORS())

You can learn more about CORS Response headers here

Answer 2

Lambda Fairy's comment answered it for me.
I put it all in the GET Handler:

#[get("/")]
fn get_handler<'a>() -> Response<'a> {
    let mut res = Response::new();
    res.set_status(Status::new(200, "No Content"));
    res.adjoin_header(ContentType::Plain);
    res.adjoin_raw_header("Access-Control-Allow-Methods", "POST, GET, OPTIONS");
    res.adjoin_raw_header("Access-Control-Allow-Origin", "*");
    res.adjoin_raw_header("Access-Control-Allow-Credentials", "true");
    res.adjoin_raw_header("Access-Control-Allow-Headers", "Content-Type");
    res.set_sized_body(Cursor::new("Response")); 
    res