#
actix_service/
macros.rs

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    /// An implementation of [`poll_ready`]() that always signals readiness.
    ///
    /// This should only be used for basic leaf services that have no concept of un-readiness.
    /// For wrapper or other service types, use [`forward_ready!`] for simple cases or write a bespoke
    /// `poll_ready` implementation.
    ///
    /// [`poll_ready`]: crate::Service::poll_ready
    ///
    /// # Examples
    /// ```no_run
    /// use actix_service::Service;
    /// use futures_util::future::{ready, Ready};
    ///
    /// struct IdentityService;
    ///
    /// impl Service<u32> for IdentityService {
    ///     type Response = u32;
    ///     type Error = ();
    ///     type Future = Ready<Result<Self::Response, Self::Error>>;
    ///
    ///     actix_service::always_ready!();
    ///
    ///     fn call(&self, req: u32) -> Self::Future {
    ///         ready(Ok(req))
    ///     }
    /// }
    /// ```
    ///
    /// [`forward_ready!`]: crate::forward_ready
    #[macro_export]
    macro_rules! always_ready {
        () => {
            #[inline]
            fn poll_ready(
                &self,
                _: &mut ::core::task::Context<'_>,
            ) -> ::core::task::Poll<Result<(), Self::Error>> {
                ::core::task::Poll::Ready(Ok(()))
            }
        };
    }

    /// An implementation of [`poll_ready`] that forwards readiness checks to a
    /// named struct field.
    ///
    /// Tuple structs are not supported.
    ///
    /// [`poll_ready`]: crate::Service::poll_ready
    ///
    /// # Examples
    /// ```no_run
    /// use actix_service::Service;
    /// use futures_util::future::{ready, Ready};
    ///
    /// struct WrapperService<S> {
    ///     inner: S,
    /// }
    ///
    /// impl<S> Service<()> for WrapperService<S>
    /// where
    ///     S: Service<()>,
    /// {
    ///     type Response = S::Response;
    ///     type Error = S::Error;
    ///     type Future = S::Future;
    ///
    ///     actix_service::forward_ready!(inner);
    ///
    ///     fn call(&self, req: ()) -> Self::Future {
    ///         self.inner.call(req)
    ///     }
    /// }
    /// ```
    #[macro_export]
    macro_rules! forward_ready {
        ($field:ident) => {
            #[inline]
            fn poll_ready(
                &self,
                cx: &mut ::core::task::Context<'_>,
            ) -> ::core::task::Poll<Result<(), Self::Error>> {
                self.$field
                    .poll_ready(cx)
                    .map_err(::core::convert::Into::into)
            }
        };
    }

    #[cfg(test)]
    mod tests {
        use core::{
            cell::Cell,
            convert::Infallible,
            task::{self, Context, Poll},
        };

        use futures_util::{
            future::{ready, Ready},
            task::noop_waker,
        };

        use crate::Service;

        struct IdentityService;

        impl Service<u32> for IdentityService {
            type Response = u32;
            type Error = Infallible;
            type Future = Ready<Result<Self::Response, Self::Error>>;

            always_ready!();

            fn call(&self, req: u32) -> Self::Future {
                ready(Ok(req))
            }
        }

        struct CountdownService(Cell<u32>);

        impl Service<()> for CountdownService {
            type Response = ();
            type Error = Infallible;
            type Future = Ready<Result<Self::Response, Self::Error>>;

            fn poll_ready(&self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
                let count = self.0.get();

                if count == 0 {
                    Poll::Ready(Ok(()))
                } else {
                    self.0.set(count - 1);
                    cx.waker().wake_by_ref();
                    Poll::Pending
                }
            }

            fn call(&self, _: ()) -> Self::Future {
                ready(Ok(()))
            }
        }

        struct WrapperService<S> {
            inner: S,
        }

        impl<S> Service<()> for WrapperService<S>
        where
            S: Service<()>,
        {
            type Response = S::Response;
            type Error = S::Error;
            type Future = S::Future;

            forward_ready!(inner);

            fn call(&self, _: ()) -> Self::Future {
                self.inner.call(())
            }
        }

        #[test]
        fn test_always_ready_macro() {
            let waker = noop_waker();
            let mut cx = task::Context::from_waker(&waker);

            let svc = IdentityService;

            assert!(svc.poll_ready(&mut cx).is_ready());
            assert!(svc.poll_ready(&mut cx).is_ready());
            assert!(svc.poll_ready(&mut cx).is_ready());
        }

        #[test]
        fn test_forward_ready_macro() {
            let waker = noop_waker();
            let mut cx = task::Context::from_waker(&waker);

            let svc = WrapperService {
                inner: CountdownService(Cell::new(3)),
            };

            assert!(svc.poll_ready(&mut cx).is_pending());
            assert!(svc.poll_ready(&mut cx).is_pending());
            assert!(svc.poll_ready(&mut cx).is_pending());
            assert!(svc.poll_ready(&mut cx).is_ready());
        }
    }