aerosol/src/axum.rs

//! Integration with the `axum` web framework.
//!
//! Provies the `Dep` and `Obtain` axum extractors for easily accessing
//! resources from within route handlers.
//!
//! To make use of these extractors, your application state must either be
//! an `Aerosol`, or you must implement `FromRef<YourState>` for `Aerosol`.

use std::any::type_name;

use async_trait::async_trait;
use axum::{
    extract::{FromRef, FromRequestParts},
    http::{request::Parts, StatusCode},
    response::{IntoResponse, Response},
};

use crate::{Aerosol, AsyncConstructibleResource, ConstructibleResource, Resource};

/// Type of axum Rejection returned when a resource cannot be acquired
#[derive(Debug, thiserror::Error)]
pub enum DependencyError {
    /// Tried to get a resource which did not exist. Use `Obtain(..)` if you want aerosol to
    /// try to construct the resource on demand.
    #[error("Resource `{name}` does not exist")]
    DoesNotExist {
        /// Name of the resource type
        name: &'static str,
    },
    /// Tried and failed to construct a resource.
    #[error("Failed to construct `{name}`: {source}")]
    FailedToConstruct {
        /// Name of the resource type
        name: &'static str,
        /// Error returned by the resource constructor
        #[source]
        source: anyhow::Error,
    },
}

impl IntoResponse for DependencyError {
    fn into_response(self) -> Response {
        tracing::error!("{}", self);
        StatusCode::INTERNAL_SERVER_ERROR.into_response()
    }
}

impl DependencyError {
    pub(crate) fn does_not_exist<T>() -> Self {
        Self::DoesNotExist {
            name: type_name::<T>(),
        }
    }
    pub(crate) fn failed_to_construct<T>(error: impl Into<anyhow::Error>) -> Self {
        Self::FailedToConstruct {
            name: type_name::<T>(),
            source: error.into(),
        }
    }
}

/// Get an already-existing resource from the state. Equivalent to calling `Aerosol::try_get_async`.
pub struct Dep<T: Resource>(pub T);

#[async_trait]
impl<T: ConstructibleResource, S: Send + Sync> FromRequestParts<S> for Dep<T>
where
    Aerosol: FromRef<S>,
{
    type Rejection = DependencyError;

    async fn from_request_parts(_parts: &mut Parts, state: &S) -> Result<Self, Self::Rejection> {
        Aerosol::from_ref(state)
            .try_get_async()
            .await
            .map(Self)
            .ok_or_else(DependencyError::does_not_exist::<T>)
    }
}

/// Get a resource from the state, or construct it if it doesn't exist. Equivalent to calling `Aerosol::try_obtain_async`.
pub struct Obtain<T: AsyncConstructibleResource>(pub T);

#[async_trait]
impl<T: AsyncConstructibleResource, S: Send + Sync> FromRequestParts<S> for Obtain<T>
where
    Aerosol: FromRef<S>,
{
    type Rejection = DependencyError;

    async fn from_request_parts(_parts: &mut Parts, state: &S) -> Result<Self, Self::Rejection> {
        Aerosol::from_ref(state)
            .try_obtain_async()
            .await
            .map(Self)
            .map_err(DependencyError::failed_to_construct::<T>)
    }
}