Code shared from the Rust Playground

playground.rs

extern crate futures;

use futures::stream::Stream;
use futures::TryStreamExt;
use futures::{Sink, SinkExt};

// We take a <u64, u32> stream+sink and want to convert it to <u128, u64>
pub fn convert_sink_stream(
    connection: impl Stream<Item = Result<u64, u32>> + Sink<u64, Error = u32>,
) -> impl Stream<Item = Result<u128, u64>> + Sink<u128, Error = u64>
    {
    connection
        .err_into::<u64>()
        .sink_err_into::<u64>()
        .map_ok(|x|u128::from(x))
        .with(|x| {
            let y = u128::from(x);
            futures::future::ok(y)
        })
}