tokio::io::Stdin implements AsyncRead but is not Async

[aep]

Version

tokio 0.1.8
futures 0.1.21

Platform

Linux sdzx 4.18.5-arch1-1-ARCH #1 SMP PREEMPT Fri Aug 24 12:48:58 UTC 2018 x86_64 GNU/Linux

Description

poll_read on tokio::io::Stdin is blocking. that is unexpected and confusing.

extern crate tokio;
#[macro_use]
extern crate futures;

use tokio::io::{AsyncRead,stdin};
use std::io::{Write, stdout};
use futures::{Future, Async};

struct IoBridge<R,W>
where R: AsyncRead,
      W: Write,
{
    r: R,
    w: W,
}


impl<R,W> Future for IoBridge<R,W>
where R: AsyncRead,
      W: Write,
{
    type Item  = ();
    type Error = tokio::io::Error;
    fn poll(&mut self) -> Result<Async<Self::Item>, Self::Error> {
        println!(".");
        let mut buf = [0;1024];
        loop {
            let len = try_ready!(self.r.poll_read(&mut buf));
            println!("<< {}", len);
            if len == 0 {
                return Ok(Async::Ready(()));
            }
            self.w.write(&buf[..len])?;
            self.w.flush()?;
        }
    }
}


fn main() {
    let f = IoBridge{
        r: stdin(),
        w: stdout()
    }.map_err(|e|panic!(e));

    tokio::run(f);
}

note that . is only printed once. the loop will never exit.

[carllerche]

Thanks for the report. Dup of #589.