additional futures extension utils

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/utils/future/ext_ext.rs

@@ -0,0 +1,34 @@
+//! Extended external extensions to futures::FutureExt
+
+use std::marker::Unpin;
+
+use futures::{future, future::Select, Future};
+
+/// This interface is not necessarily complete; feel free to add as-needed.
+pub trait ExtExt<T>
+where
+	Self: Future<Output = T> + Send,
+{
+	fn until<A, B, F>(self, f: F) -> Select<A, B>
+	where
+		Self: Sized,
+		F: FnOnce() -> B,
+		A: Future<Output = T> + From<Self> + Send + Unpin,
+		B: Future<Output = ()> + Send + Unpin;
+}
+
+impl<T, Fut> ExtExt<T> for Fut
+where
+	Fut: Future<Output = T> + Send,
+{
+	#[inline]
+	fn until<A, B, F>(self, f: F) -> Select<A, B>
+	where
+		Self: Sized,
+		F: FnOnce() -> B,
+		A: Future<Output = T> + From<Self> + Send + Unpin,
+		B: Future<Output = ()> + Send + Unpin,
+	{
+		future::select(self.into(), f())
+	}
+}