split-stream-by

This repo is for a rust crate that offers a futures::Stream extension trait which allows for splitting a Stream into two streams using a predicate function thats checked on each Stream::Item.

use split_stream_by::SplitStreamByExt;

let incoming_stream = futures::stream::iter([0,1,2,3,4,5]);
let (mut even_stream, mut odd_stream) = incoming_stream.split_by(|&n| n % 2 == 0);

tokio::spawn(async move {
	while let Some(even_number) = even_stream.next().await {
		println!("Even {}",even_number);
	}
});

while let Some(odd_number) = odd_stream.next().await {
	println!("Odd {}",odd_number);
}

A more advanced usage uses split_by_map which allows for extracting values while splitting

use split_stream_by::{Either,SplitStreamByExt};

struct Request {
	//...
}

struct Response {
	//...
}

enum Message {
	Request(Request),
	Response(Response)
}

let incoming_stream = futures::stream::iter([
	Message::Request(Request {}),
	Message::Response(Response {}),
	Message::Response(Response {}),
]);
let (mut request_stream, mut response_stream) = incoming_stream.split_by_map(|item| match item {
	Message::Request(req) => Either::Left(req),
	Message::Response(res) => Either::Right(res),
});

tokio::spawn(async move {
	while let Some(request) = request_stream.next().await {
		// ...
	}
});

while let Some(response) = response_stream.next().await {
	// ...
}

In its current implementation, it only buffers up to one element in the scenario where the stream that requests the next item is not the one that matches the predicate. In the future, this might be changed to be configurable using a const generic parameter