tower/util/boxed/
sync.rs

1use crate::ServiceExt;
2use tower_layer::{layer_fn, LayerFn};
3use tower_service::Service;
4
5use sync_wrapper::SyncWrapper;
6
7use std::fmt;
8use std::{
9    future::Future,
10    pin::Pin,
11    task::{Context, Poll},
12};
13
14/// A boxed `Service + Send` trait object.
15///
16/// [`BoxService`] turns a service into a trait object, allowing the response
17/// future type to be dynamic. This type requires both the service and the
18/// response future to be [`Send`].
19///
20/// If you need a boxed [`Service`] that implements [`Clone`] consider using
21/// [`BoxCloneService`](crate::util::BoxCloneService).
22///
23/// Dynamically dispatched [`Service`] objects allow for erasing the underlying
24/// [`Service`] type and using the `Service` instances as opaque handles. This can
25/// be useful when the service instance cannot be explicitly named for whatever
26/// reason.
27///
28/// # Examples
29///
30/// ```
31/// use futures_util::future::ready;
32/// # use tower_service::Service;
33/// # use tower::util::{BoxService, service_fn};
34/// // Respond to requests using a closure, but closures cannot be named...
35/// # pub fn main() {
36/// let svc = service_fn(|mut request: String| {
37///     request.push_str(" response");
38///     ready(Ok(request))
39/// });
40///
41/// let service: BoxService<String, String, ()> = BoxService::new(svc);
42/// # drop(service);
43/// }
44/// ```
45///
46/// [`Service`]: crate::Service
47/// [`Rc`]: std::rc::Rc
48pub struct BoxService<T, U, E> {
49    inner:
50        SyncWrapper<Box<dyn Service<T, Response = U, Error = E, Future = BoxFuture<U, E>> + Send>>,
51}
52
53/// A boxed `Future + Send` trait object.
54///
55/// This type alias represents a boxed future that is [`Send`] and can be moved
56/// across threads.
57type BoxFuture<T, E> = Pin<Box<dyn Future<Output = Result<T, E>> + Send>>;
58
59impl<T, U, E> BoxService<T, U, E> {
60    #[allow(missing_docs)]
61    pub fn new<S>(inner: S) -> Self
62    where
63        S: Service<T, Response = U, Error = E> + Send + 'static,
64        S::Future: Send + 'static,
65    {
66        // rust can't infer the type
67        let inner: Box<dyn Service<T, Response = U, Error = E, Future = BoxFuture<U, E>> + Send> =
68            Box::new(inner.map_future(|f: S::Future| Box::pin(f) as _));
69        let inner = SyncWrapper::new(inner);
70        BoxService { inner }
71    }
72
73    /// Returns a [`Layer`] for wrapping a [`Service`] in a [`BoxService`]
74    /// middleware.
75    ///
76    /// [`Layer`]: crate::Layer
77    pub fn layer<S>() -> LayerFn<fn(S) -> Self>
78    where
79        S: Service<T, Response = U, Error = E> + Send + 'static,
80        S::Future: Send + 'static,
81    {
82        layer_fn(Self::new)
83    }
84}
85
86impl<T, U, E> Service<T> for BoxService<T, U, E> {
87    type Response = U;
88    type Error = E;
89    type Future = BoxFuture<U, E>;
90
91    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), E>> {
92        self.inner.get_mut().poll_ready(cx)
93    }
94
95    fn call(&mut self, request: T) -> BoxFuture<U, E> {
96        self.inner.get_mut().call(request)
97    }
98}
99
100impl<T, U, E> fmt::Debug for BoxService<T, U, E> {
101    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
102        fmt.debug_struct("BoxService").finish()
103    }
104}
105
106#[test]
107fn is_sync() {
108    fn assert_sync<T: Sync>() {}
109
110    assert_sync::<BoxService<(), (), ()>>();
111}
tower/util/boxed/sync.rs

tower/util/boxed/
sync.rs
