tower/util/boxed/sync.rs
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use crate::ServiceExt;
use tower_layer::{layer_fn, LayerFn};
use tower_service::Service;
use sync_wrapper::SyncWrapper;
use std::fmt;
use std::{
future::Future,
pin::Pin,
task::{Context, Poll},
};
/// A boxed `Service + Send` trait object.
///
/// [`BoxService`] turns a service into a trait object, allowing the response
/// future type to be dynamic. This type requires both the service and the
/// response future to be [`Send`].
///
/// If you need a boxed [`Service`] that implements [`Clone`] consider using
/// [`BoxCloneService`](crate::util::BoxCloneService).
///
/// Dynamically dispatched [`Service`] objects allow for erasing the underlying
/// [`Service`] type and using the `Service` instances as opaque handles. This can
/// be useful when the service instance cannot be explicitly named for whatever
/// reason.
///
/// # Examples
///
/// ```
/// use futures_util::future::ready;
/// # use tower_service::Service;
/// # use tower::util::{BoxService, service_fn};
/// // Respond to requests using a closure, but closures cannot be named...
/// # pub fn main() {
/// let svc = service_fn(|mut request: String| {
/// request.push_str(" response");
/// ready(Ok(request))
/// });
///
/// let service: BoxService<String, String, ()> = BoxService::new(svc);
/// # drop(service);
/// }
/// ```
///
/// [`Service`]: crate::Service
/// [`Rc`]: std::rc::Rc
pub struct BoxService<T, U, E> {
inner:
SyncWrapper<Box<dyn Service<T, Response = U, Error = E, Future = BoxFuture<U, E>> + Send>>,
}
/// A boxed `Future + Send` trait object.
///
/// This type alias represents a boxed future that is [`Send`] and can be moved
/// across threads.
type BoxFuture<T, E> = Pin<Box<dyn Future<Output = Result<T, E>> + Send>>;
impl<T, U, E> BoxService<T, U, E> {
#[allow(missing_docs)]
pub fn new<S>(inner: S) -> Self
where
S: Service<T, Response = U, Error = E> + Send + 'static,
S::Future: Send + 'static,
{
// rust can't infer the type
let inner: Box<dyn Service<T, Response = U, Error = E, Future = BoxFuture<U, E>> + Send> =
Box::new(inner.map_future(|f: S::Future| Box::pin(f) as _));
let inner = SyncWrapper::new(inner);
BoxService { inner }
}
/// Returns a [`Layer`] for wrapping a [`Service`] in a [`BoxService`]
/// middleware.
///
/// [`Layer`]: crate::Layer
pub fn layer<S>() -> LayerFn<fn(S) -> Self>
where
S: Service<T, Response = U, Error = E> + Send + 'static,
S::Future: Send + 'static,
{
layer_fn(Self::new)
}
}
impl<T, U, E> Service<T> for BoxService<T, U, E> {
type Response = U;
type Error = E;
type Future = BoxFuture<U, E>;
fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), E>> {
self.inner.get_mut().poll_ready(cx)
}
fn call(&mut self, request: T) -> BoxFuture<U, E> {
self.inner.get_mut().call(request)
}
}
impl<T, U, E> fmt::Debug for BoxService<T, U, E> {
fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
fmt.debug_struct("BoxService").finish()
}
}
#[test]
fn is_sync() {
fn assert_sync<T: Sync>() {}
assert_sync::<BoxService<(), (), ()>>();
}