How do I pass state to the async interceptor function?

[Falmarri]

For example, I want to access a database. I can't figure out how to pass the database into the function. I've tried implementing the AsyncInterceptor, but ran into the fact that the associated type is a future, and I can't figure out how to name the future because of rust-lang/rust#63063

    type Future = impl futures_core::Future<Output=Result<Request<()>, Status>>;

    async fn call(&mut self, request: Request<()>) -> Result<Request<()>, Status> {`
        todo!()
    }
}

doesn't work. I've also tried type Future = Box<dyn futures_core::Future<Output=Result<Request<()>, Status>> + Unpin>; but ran into

   = note: expected signature `fn(&mut MyService, tonic::Request<_>) -> Box<(dyn futures_core::Future<Output = Result<tonic::Request<()>, tonic::Status>> + Unpin + 'static)>`
              found signature `fn(&mut MyService, tonic::Request<_>) -> impl futures_core::Future<Output = Result<tonic::Request<()>, tonic::Status>>`

[isaaguilar]

This worked for me:

#[derive(Clone)]
pub struct MyAuthInterceptor {
    pub db: Pool<Postgres>,
}

impl AsyncInterceptor for MyAuthInterceptor {
    type Future = Pin<Box<dyn Future<Output = Result<Request<()>, Status>> + Send + 'static>>;

    fn call(&mut self, request: Request<()>) -> Self::Future {
        let fut = self.authenticate(request);
        Box::pin(fut)
    }
}

impl MyAuthInterceptor {
    pub fn new(db: Pool<Postgres>) -> Self {
        Self { db }
    }

    pub fn authenticate(
        &self,
        request: Request<()>,
    ) -> impl Future<Output = Result<Request<()>, Status>> + Send + 'static {
        let db = self.db.clone(); // Clone the database pool
        let metadata = request.metadata().clone(); // Clone the request metadata
        async move {
            // Now we can use db inside the async block
            //  match sqlx::query("...").fetch_one(db).await {
            //     Ok(_) => {}
            //     Err(_) => {}
            // }
            Ok(request)
        }
    }
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Setup stuff like `svc` and `address`
    let db = PgPoolOptions::new().max_connections(5).connect(&dsn).await?;
    let auth_service = MyAuthInterceptor::new(db);
    Server::builder()
        .layer(async_interceptor(auth_service)) // <----- Add the async interceptor here
        .add_service(svc)
        .serve(address)
        .await?;
}