read_line panics if an IO error happens in the middle of a line

[blckngm]

Version

tokio 0.2.4

Description

AsyncBufReadExt::read_line panics at

tokio/tokio/src/io/util/read_line.rs

Line 52 in 80abff0

debug_assert_eq!(*read, 0);

if the stream returns an Err in the middle of a line.

Full reproduction:

use std::pin::Pin;
use std::task::{Context, Poll};
use tokio::io::{self, *};

struct MyStream {
    i: u32,
}

impl MyStream {
    fn new() -> Self {
        MyStream { i: 0 }
    }
}

impl AsyncRead for MyStream {
    fn poll_read(
        mut self: Pin<&mut Self>,
        _cx: &mut Context<'_>,
        buf: &mut [u8],
    ) -> Poll<io::Result<usize>> {
        match self.i {
            0 => {
                buf[..5].copy_from_slice(b"hello");
                self.i = 1;
                Poll::Ready(Ok(5))
            }
            1 => Poll::Ready(Err(io::ErrorKind::BrokenPipe.into())),
            _ => unreachable!(),
        }
    }
}

#[tokio::main]
async fn main() -> io::Result<()> {
    let mut stream = BufReader::new(MyStream::new());
    let mut line = String::new();
    stream.read_line(&mut line).await?;
    Ok(())
}

[gparker42]

Looks like this was fixed by #2541.