use futures::{Future, Stream}; // 0.1.28

pub fn take_first<S>(stream: S) -> impl Future<Item = Option<S::Item>, Error = S::Error>
where
    S: Stream,
{
    stream
        .into_future()
        .map(|(maybe_first, _rest_of_the_stream)| maybe_first)
        .map_err(|(err, _rest_of_the_stream)| err)
}