Implementing FromRequestParts with Generic State

[theBeardA]

Summary

Hey Team, I'm trying to implement FromRequestParts for a struct when the state has generics. not sure if that is possible but I have tried few ways but it dont seem to work

I have these other state for different routes. each of that state having implementation for FromRef for AppState

pub struct OtherState {
    pub app_state: AppState<MyRepo>,
    // other fields...
}

impl FromRef<OtherState> for AppState<MyRepo> {
    fn from_ref(state: &OtherState) -> Self {
        state.app_state.clone()
    }
}

pub struct AppState<R: MigrationRepo> {
    pub pool: Pool,
    pub repository: R
}

The issue arises here when I try to add generic here in AppState

impl<S> FromRequestParts<S> for Claims
where
    AppState: FromRef<S>,
    S: Send + Sync,
{
    type Rejection = ApiError;

    async fn from_request_parts(parts: &mut Parts, state: &S) -> Result<Self, Self::Rejection> {
    .....
    }

axum version

0.7.5

[mladedav]

Shouldn't you write AppState<MyRepo>: FromRef<S>,?

Also please post the error you're getting, it makes it easier to help you.

[theBeardA]

Hey @mladedav. thanks for response. MyRepo is trait and not a concrete type here. so with this, we would get the error the size for values of type (dyn MyRepo + 'static) cannot be known at compilation time.

And I tried this but seems wrong due to error or if I am missing something. the error here is the type parameter P is not constrained by the impl trait, self type, or predicates unconstrained type parameter

impl<S, P> FromRequestParts<S> for Claims
where
    AppState<P>: FromRef<S>,
    S: Send + Sync,
    P: MyRepo,
{ ...

[mladedav]

In your original question you wrote

pub struct OtherState {
    pub app_state: AppState<MyRepo>,
    // other fields...
}

which is something you couldn't do since 2021 if MyRepo is in fact a trait. And in this last version AppState is in fact generic while the code you posted originally did not have generics in the bound.

So please paste the code you tried (or link a playground) and the error you got from the compiler.

But the simplest thing would be to make Claims generic over P if possible. Or just don't make the impl generic and just implement FromRequestParts<OtherState>.

[theBeardA]

my bad. thanks for clarification.
please ignore the orignal code and I will now paste a more clearer code. also can't make Claims generic over anything or it wont really do anything in my case.

use axum::extract::{FromRef, FromRequestParts};
use axum::http::request::Parts;
use rest::api::errors::ApiError;


#[derive(Clone)]
pub struct Config;

pub struct Claims;


// traits
pub trait PermissionRepository: Clone {
    fn get_permissions_by_role(&self, role_id: &str) -> Vec<String>;
    // ... more methods
}
pub trait UserRepository: Clone {
    fn get(&self, user_id: &str) -> String;
    // ... more methods
}


// states
#[derive(Clone)]
pub struct AppState<P: PermissionRepository> {
    pub config: Config,
    pub permission_repository: P,
}

pub struct UserState<T: UserRepository, P: PermissionRepository> {
    pub app_state: AppState<P>,
    pub user_repository: T,
}
pub struct PermissionScopesState<T: UserRepository, P: PermissionRepository> {
    pub app_state: AppState<P>,
    pub user_repository: T,
    pub scopes: Vec<String>,
}


// from refs impl
impl<T: UserRepository, P: PermissionRepository> FromRef<PermissionScopesState<T, P>>
    for AppState<P>
{
    fn from_ref(input: &PermissionScopesState<T, P>) -> Self {
        input.app_state.clone()
    }
}

impl<T: UserRepository, P: PermissionRepository> FromRef<PermissionScopesState<T, P>> for UserState<T, P>
{
    fn from_ref(input: &PermissionScopesState<T, P>) -> Self {
        Self {
            app_state: input.app_state.clone(),
            user_repository: input.user_repository.clone(),
        }
    }
}


// from request parts

impl<S, P> FromRequestParts<S> for Claims
where
    AppState<P>: FromRef<S>,
    S: Send + Sync,
    P: PermissionRepository,
{
    type Rejection = ApiError;

    async fn from_request_parts(parts: &mut Parts, state: &S) -> Result<Self, Self::Rejection> {
        println!("from request parts");
        todo!()
    }
}

this is what I am trying to achieve
what I currently have is permission_repository is not part of AppState, and is inside PermissionScopesState. but the problem with that is that it is pretty verbose to initialize permission repo in each router with along with scopes. so I was thinking to move it to AppState to initialize it once and pass it with AppState but it seems like it is not possible. also note, UserState is not required in all routers so keeping it separate is ok