add broadband stream extensions

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

src/core/utils/stream/wideband.rs

@@ -0,0 +1,84 @@
+//! Wideband stream combinator extensions to futures::Stream
+#![allow(clippy::type_complexity)]
+
+use std::convert::identity;
+
+use futures::{
+	stream::{Stream, StreamExt},
+	Future,
+};
+
+use super::ReadyExt;
+
+const WIDTH: usize = 32;
+
+/// Concurrency extensions to augment futures::StreamExt. wideband_ combinators
+/// produce in-order.
+pub trait WidebandExt<Item>
+where
+	Self: Stream<Item = Item> + Send + Sized,
+{
+	/// Concurrent filter_map(); ordered results
+	fn widen_filter_map<F, Fut, U, N>(self, n: N, f: F) -> impl Stream<Item = U> + Send
+	where
+		N: Into<Option<usize>>,
+		F: Fn(Item) -> Fut + Send,
+		Fut: Future<Output = Option<U>> + Send,
+		U: Send;
+
+	fn widen_then<F, Fut, U, N>(self, n: N, f: F) -> impl Stream<Item = U> + Send
+	where
+		N: Into<Option<usize>>,
+		F: Fn(Item) -> Fut + Send,
+		Fut: Future<Output = U> + Send,
+		U: Send;
+
+	#[inline]
+	fn wide_filter_map<F, Fut, U>(self, f: F) -> impl Stream<Item = U> + Send
+	where
+		F: Fn(Item) -> Fut + Send,
+		Fut: Future<Output = Option<U>> + Send,
+		U: Send,
+	{
+		self.widen_filter_map(None, f)
+	}
+
+	#[inline]
+	fn wide_then<F, Fut, U>(self, f: F) -> impl Stream<Item = U> + Send
+	where
+		F: Fn(Item) -> Fut + Send,
+		Fut: Future<Output = U> + Send,
+		U: Send,
+	{
+		self.widen_then(None, f)
+	}
+}
+
+impl<Item, S> WidebandExt<Item> for S
+where
+	S: Stream<Item = Item> + Send + Sized,
+{
+	#[inline]
+	fn widen_filter_map<F, Fut, U, N>(self, n: N, f: F) -> impl Stream<Item = U> + Send
+	where
+		N: Into<Option<usize>>,
+		F: Fn(Item) -> Fut + Send,
+		Fut: Future<Output = Option<U>> + Send,
+		U: Send,
+	{
+		self.map(f)
+			.buffered(n.into().unwrap_or(WIDTH))
+			.ready_filter_map(identity)
+	}
+
+	#[inline]
+	fn widen_then<F, Fut, U, N>(self, n: N, f: F) -> impl Stream<Item = U> + Send
+	where
+		N: Into<Option<usize>>,
+		F: Fn(Item) -> Fut + Send,
+		Fut: Future<Output = U> + Send,
+		U: Send,
+	{
+		self.map(f).buffered(n.into().unwrap_or(WIDTH))
+	}
+}