abstract and encapsulate the awkward OptionFuture into Stream pattern

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

src/core/utils/future/option_stream.rs

@@ -0,0 +1,25 @@
+use futures::{Future, FutureExt, Stream, StreamExt, future::OptionFuture};
+
+use super::super::IterStream;
+
+pub trait OptionStream<T> {
+	fn stream(self) -> impl Stream<Item = T> + Send;
+}
+
+impl<T, O, S, Fut> OptionStream<T> for OptionFuture<Fut>
+where
+	Fut: Future<Output = (O, S)> + Send,
+	S: Stream<Item = T> + Send,
+	O: IntoIterator<Item = T> + Send,
+	<O as IntoIterator>::IntoIter: Send,
+	T: Send,
+{
+	#[inline]
+	fn stream(self) -> impl Stream<Item = T> + Send {
+		self.map(|opt| opt.map(|(curr, next)| curr.into_iter().stream().chain(next)))
+			.map(Option::into_iter)
+			.map(IterStream::stream)
+			.flatten_stream()
+			.flatten()
+	}
+}