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use std::{
cell::Cell,
fmt,
future::{ready, Future, Ready},
rc::Rc,
};
use actix_web::{dev, error, Error, FromRequest, HttpRequest};
use futures_core::future::LocalBoxFuture;
use tokio::sync::OnceCell;
use tracing::debug;
pub struct LazyData<T> {
inner: Rc<LazyDataInner<T>>,
}
struct LazyDataInner<T> {
cell: OnceCell<T>,
fut: Cell<Option<LocalBoxFuture<'static, T>>>,
}
impl<T> Clone for LazyData<T> {
fn clone(&self) -> Self {
Self {
inner: self.inner.clone(),
}
}
}
impl<T: fmt::Debug> fmt::Debug for LazyData<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Lazy")
.field("cell", &self.inner.cell)
.field("fut", &"..")
.finish()
}
}
impl<T> LazyData<T> {
pub fn new<F, Fut>(init: F) -> LazyData<T>
where
F: FnOnce() -> Fut,
Fut: Future<Output = T> + 'static,
{
Self {
inner: Rc::new(LazyDataInner {
cell: OnceCell::new(),
fut: Cell::new(Some(Box::pin(init()))),
}),
}
}
pub async fn get(&self) -> &T {
self.inner
.cell
.get_or_init(|| async move {
match self.inner.fut.take() {
Some(fut) => fut.await,
None => panic!("LazyData instance has previously been poisoned"),
}
})
.await
}
}
impl<T: 'static> FromRequest for LazyData<T> {
type Error = Error;
type Future = Ready<Result<Self, Error>>;
#[inline]
fn from_request(req: &HttpRequest, _: &mut dev::Payload) -> Self::Future {
if let Some(lazy) = req.app_data::<LazyData<T>>() {
ready(Ok(lazy.clone()))
} else {
debug!(
"Failed to extract `LazyData<{}>` for `{}` handler. For the Data extractor to work \
correctly, wrap the data with `LazyData::new()` and pass it to `App::app_data()`. \
Ensure that types align in both the set and retrieve calls.",
core::any::type_name::<T>(),
req.match_name().unwrap_or_else(|| req.path())
);
ready(Err(error::ErrorInternalServerError(
"Requested application data is not configured correctly. \
View/enable debug logs for more details.",
)))
}
}
}
#[cfg(test)]
mod tests {
use std::time::Duration;
use actix_web::{
http::StatusCode,
test::{call_service, init_service, TestRequest},
web, App, HttpResponse,
};
use super::*;
#[actix_web::test]
async fn lazy_data() {
let app = init_service(
App::new()
.app_data(LazyData::new(|| async { 10usize }))
.service(web::resource("/").to(|_: LazyData<usize>| HttpResponse::Ok())),
)
.await;
let req = TestRequest::default().to_request();
let resp = call_service(&app, req).await;
assert_eq!(resp.status(), StatusCode::OK);
let app = init_service(
App::new()
.app_data(LazyData::new(|| async {
actix_web::rt::time::sleep(Duration::from_millis(40)).await;
10usize
}))
.service(web::resource("/").to(|_: LazyData<usize>| HttpResponse::Ok())),
)
.await;
let req = TestRequest::default().to_request();
let resp = call_service(&app, req).await;
assert_eq!(resp.status(), StatusCode::OK);
let app = init_service(
App::new()
.app_data(LazyData::new(|| async { 10u32 }))
.service(web::resource("/").to(|_: LazyData<usize>| HttpResponse::Ok())),
)
.await;
let req = TestRequest::default().to_request();
let resp = call_service(&app, req).await;
assert_eq!(resp.status(), StatusCode::INTERNAL_SERVER_ERROR);
}
#[actix_web::test]
async fn lazy_data_web_block() {
let app = init_service(
App::new()
.app_data(LazyData::new(|| async {
web::block(|| std::thread::sleep(Duration::from_millis(40)))
.await
.unwrap();
10usize
}))
.service(web::resource("/").to(|_: LazyData<usize>| HttpResponse::Ok())),
)
.await;
let req = TestRequest::default().to_request();
let resp = call_service(&app, req).await;
assert_eq!(resp.status(), StatusCode::OK);
}
}