db.rs

impl<'a, 'r> FromRequest<'a, 'r> for DB {
    type Error = ();

    fn from_request(request: &'a Request<'r>) -> request::Outcome<DB, ()> {
        let pool = match <State<r2d2::Pool> as FromRequest>::from_request(request) {
            Outcome::Success(pool) => pool,
            Outcome::Failure(e) => return Outcome::Failure(e),
            Outcome::Forward(_) => return Outcome::Forward(()),
        };

        match pool.get() {
            Ok(conn) => Outcome::Success(DB(conn)),
            Err(_) => Outcome::Failure((Status::ServiceUnavailable, ()))
        }
    }
}