Problem in 0.5 with FromRequest trait and Database Fairing

[Harmos274]

General information

Rocket version: 0.5.0-rc.1
OS: Ubuntu 20.04.2 LTS
Cargo version: cargo 1.54.0-nightly (44456677b 2021-06-12)

Problem

Hello, I am trying to migrate my work project from Rocket 0.4 to Rocket 0.5 but I encountered what I would say is a bug but I'm not sure if I am doing this correctly.

I have a custom guard in my API which implement FromRequest. It retrieves the Authorization header in the request header, and valid the token with the help of my database fairing (PostgreSQL) get by request.guard. When I want to retrieve the pool from my database I use the async run() method crated by the database macro of rocket_sync_db_pools. In the lambda passed as argument of the method I do all my token validation operations and return a request::Outcome in consequence.

Expectation

Returning db.run(|pool| {...}) shouldn't be a problem since it returns the same type as defined in from_request.

Reality

The code does not compile and rustc shows an error of lifetime.

Sample

Code:

#[database("db_name")]
pub struct Database(diesel::PgConnection);

/ *** /

pub enum Authenticated {
    Client(OAuth2ClientModel),
    User(UserModel),
}

#[rocket::async_trait]
impl<'r> FromRequest<'r> for Authenticated {
    type Error = ();

    async fn from_request(request: &'r Request<'_>) -> request::Outcome<Self, Self::Error> {
        let keys: Vec<_> = request.headers().get("Authorization").collect();
        let db: Database = try_outcome!(request.guard::<Database>().await);

        db.run(|pool| {
            if keys.len() != 1 {
                return Outcome::Failure((Status::Unauthorized, ()));
            }
            let key: Vec<_> = keys[0].split(' ').collect();

            if key.len() == 2 && is_bearer(&key) {
                let token_value = match uuid::Uuid::parse_str(key[1]) {
                    Ok(uuid) => uuid,
                    Err(_) => {
                        return Outcome::Failure((Status::BadRequest, ()));
                    }
                };
                // fn validate_token(token: Result<OAuth2TokenNullableModel, OAuth2TokenRetrievalError>, p: &PgConnection,) -> request::Outcome<Authenticated, ()>
                return validate_token(retrieve_token_by_value(&token_value, &pool), &pool);
            }
            Outcome::Failure((Status::BadRequest, ()))
        })
        .await
    }

Compilation error:

error[E0495]: cannot infer an appropriate lifetime due to conflicting requirements
  --> src/domains/common/guards/oauth2_token_validator.rs:36:27
   |
36 |     async fn from_request(request: &'r Request<'_>) -> request::Outcome<Self, Self::Error> {
   |                           ^^^^^^^
   |
note: first, the lifetime cannot outlive the lifetime `'r` as defined on the impl at 33:6...
  --> src/domains/common/guards/oauth2_token_validator.rs:33:6
   |
33 | impl<'r> FromRequest<'r> for Authenticated {
   |      ^^
note: ...so that the expression is assignable
  --> src/domains/common/guards/oauth2_token_validator.rs:36:27
   |
36 |     async fn from_request(request: &'r Request<'_>) -> request::Outcome<Self, Self::Error> {
   |                           ^^^^^^^
   = note: expected `&rocket::Request<'life0>`
              found `&'r rocket::Request<'life0>`
   = note: but, the lifetime must be valid for the static lifetime...
note: ...so that the type `[closure@src/domains/common/guards/oauth2_token_validator.rs:41:18: 58:14]` will meet its required lifetime bounds
  --> src/domains/common/guards/oauth2_token_validator.rs:41:14
   |
41 |             .run(|pool| {
   |              ^^^

I don't really understand this error but it wasn't a problem before 0.5, thank you for your consideration.

[jebrosen]

   = note: but, the lifetime must be valid for the static lifetime...
note: ...so that the type `[closure@src/domains/common/guards/oauth2_token_validator.rs:41:18: 58:14]` will meet its required lifetime bounds
  --> src/domains/common/guards/oauth2_token_validator.rs:41:14
   |
41 |             .run(|pool| {
   |              ^^^

The crux of the problem is that the closure passed to run() must be 'static, i.e. capture no borrows unless those are borrows of 'static data. This limitation is related to running non-async (blocking) code inside an asynchronous server.

But, keys borrows data from request, so you get this error. One solution for this case seems fairly simple: do less in the run() call. Everything up to validate_token doesn't need database access, so something like this ought to work:

#[rocket::async_trait]
impl<'r> FromRequest<'r> for Authenticated {
    type Error = ();

    async fn from_request(request: &'r Request<'_>) -> request::Outcome<Self, Self::Error> {
        let keys: Vec<_> = request.headers().get("Authorization").collect();
        let db: Database = try_outcome!(request.guard::<Database>().await);

       if keys.len() != 1 {
           return Outcome::Failure((Status::Unauthorized, ()));
       }
       let key: Vec<_> = keys[0].split(' ').collect();

       if key.len() == 2 && is_bearer(&key) {
           let token_value = match uuid::Uuid::parse_str(key[1]) {
               Ok(uuid) => uuid,
               Err(_) => {
                   return Outcome::Failure((Status::BadRequest, ()));
               }
           };
           // fn validate_token(token: Result<OAuth2TokenNullableModel, OAuth2TokenRetrievalError>, p: &PgConnection,) -> request::Outcome<Authenticated, ()>
           db.run(|connection| validate_token(retrieve_token_by_value(&token_value, &connection), &connection)).await
       }
       Outcome::Failure((Status::BadRequest, ()))
    }
}