remove futures-util from service deps (#235)

actix-service/src/ready.rs

@@ -0,0 +1,54 @@
+//! When MSRV is 1.48, replace with `core::future::Ready` and `core::future::ready()`.
+
+use core::{
+    future::Future,
+    pin::Pin,
+    task::{Context, Poll},
+};
+
+/// Future for the [`ready`](ready()) function.
+#[derive(Debug, Clone)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Ready<T> {
+    val: Option<T>,
+}
+
+impl<T> Ready<T> {
+    /// Unwraps the value from this immediately ready future.
+    #[inline]
+    pub fn into_inner(mut self) -> T {
+        self.val.take().unwrap()
+    }
+}
+
+impl<T> Unpin for Ready<T> {}
+
+impl<T> Future for Ready<T> {
+    type Output = T;
+
+    #[inline]
+    fn poll(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<T> {
+        let val = self.val.take().expect("Ready can not be polled twice.");
+        Poll::Ready(val)
+    }
+}
+
+/// Creates a future that is immediately ready with a value.
+#[allow(dead_code)]
+pub(crate) fn ready<T>(val: T) -> Ready<T> {
+    Ready { val: Some(val) }
+}
+
+/// Create a future that is immediately ready with a success value.
+#[allow(dead_code)]
+pub(crate) fn ok<T, E>(val: T) -> Ready<Result<T, E>> {
+    Ready { val: Some(Ok(val)) }
+}
+
+/// Create a future that is immediately ready with an error value.
+#[allow(dead_code)]
+pub(crate) fn err<T, E>(err: E) -> Ready<Result<T, E>> {
+    Ready {
+        val: Some(Err(err)),
+    }
+}