How to use a generic session with Actix and Paperclip?

Question

I've created a server using Actix Web which has authentication support. Now I want to add an OpenAPI Specification using paperclip.

Normally you only have to add #[derive(Apiv2Security)] to the struct which represents the session of an authorized user. In my case this does not seem to do the trick because of some indirection: The app_data contains a generic Context type which defines what storage should be used (for example a database or an in memory store). The Context has an associated type which specifies the type of session it can load. The code looks something like this:

use actix_http::Payload;
use actix_web::{App, FromRequest, HttpRequest, HttpServer};
use paperclip::actix::{api_v2_operation, web, Apiv2Security, OpenApiExt};
use serde::{Deserialize, Serialize};
use std::convert::Infallible;
use std::future::{ready, Ready};

trait Context {
    type Session: Session;
    fn session_by_id(&self, session_id: usize) -> Self::Session;
}

#[derive(Clone)]
struct InMemoryContext;

impl Context for InMemoryContext {
    type Session = SimpleSession;

    fn session_by_id(&self, session_id: usize) -> Self::Session {
        SimpleSession {
            id: session_id
        }
    }
}

pub trait Session {
    fn id(&self) -> usize;
}

#[derive(Clone, Deserialize, Serialize, Apiv2Security)]
#[openapi(
    apiKey,
    in = "header",
    name = "Authorization",
    description = "Use format 'Bearer TOKEN'"
)]
pub struct SimpleSession {
    id: usize,
}

impl Session for SimpleSession {
    fn id(&self) -> usize {
        self.id
    }
}

impl FromRequest for SimpleSession {
    type Error = Infallible;
    type Future = Ready<Result<Self, Self::Error>>;

    fn from_request(req: &HttpRequest, payload: &mut Payload) -> Self::Future {
        let ctx = req
            .app_data::<web::Data<InMemoryContext>>()
            .expect("InMemoryContext must be available")
            .get_ref()
            .clone();
        ready(Ok(ctx.session_by_id(42)))
    }
}

#[api_v2_operation]
async fn hello_world_handler<C: Context>(session: C::Session) -> web::Json<usize> {
    web::Json(session.id())
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    HttpServer::new(|| {
        App::new()
            .app_data(web::Data::new(InMemoryContext {}))
            .wrap_api()
            .route(
                "/hello",
                web::get().to(hello_world_handler::<InMemoryContext>),
            )
            .with_json_spec_at("/api/spec/v2")
            .build()
    })
    .bind(("127.0.0.1", 8080))?
    .run()
    .await
}

The compiler throws errors because it cannot find the methods generated by the derive macro:

error[E0599]: no function or associated item named `update_parameter` found for associated type `<C as Context>::Session` in the current scope
  --> src/main.rs:61:1
   |
61 | #[api_v2_operation]
   | ^^^^^^^^^^^^^^^^^^^ function or associated item not found in `<C as Context>::Session`
   |
   = note: this error originates in the attribute macro `api_v2_operation` (in Nightly builds, run with -Z macro-backtrace for more info)

Do you know how to get this working?

Answer 1

I found out that a trait was missing on Context::Session. The solution is to add paperclip::actix::OperationModifier:

trait Context {
    type Session: Session + OperationModifier;
    fn session_by_id(&self, session_id: usize) -> Self::Session;
}