futures_util/io/
read_line.rs

1use super::read_until::read_until_internal;
2use futures_core::future::Future;
3use futures_core::ready;
4use futures_core::task::{Context, Poll};
5use futures_io::AsyncBufRead;
6use std::io;
7use std::mem;
8use std::pin::Pin;
9use std::str;
10use std::string::String;
11use std::vec::Vec;
12
13/// Future for the [`read_line`](super::AsyncBufReadExt::read_line) method.
14#[derive(Debug)]
15#[must_use = "futures do nothing unless you `.await` or poll them"]
16pub struct ReadLine<'a, R: ?Sized> {
17    reader: &'a mut R,
18    buf: &'a mut String,
19    bytes: Vec<u8>,
20    read: usize,
21    finished: bool,
22}
23
24impl<R: ?Sized + Unpin> Unpin for ReadLine<'_, R> {}
25
26impl<'a, R: AsyncBufRead + ?Sized + Unpin> ReadLine<'a, R> {
27    pub(super) fn new(reader: &'a mut R, buf: &'a mut String) -> Self {
28        Self { reader, bytes: mem::take(buf).into_bytes(), buf, read: 0, finished: false }
29    }
30}
31
32pub(super) fn read_line_internal<R: AsyncBufRead + ?Sized>(
33    reader: Pin<&mut R>,
34    cx: &mut Context<'_>,
35    buf: &mut String,
36    bytes: &mut Vec<u8>,
37    read: &mut usize,
38) -> Poll<io::Result<usize>> {
39    let mut ret = ready!(read_until_internal(reader, cx, b'\n', bytes, read));
40    if str::from_utf8(&bytes[bytes.len() - *read..bytes.len()]).is_err() {
41        bytes.truncate(bytes.len() - *read);
42        if ret.is_ok() {
43            ret = Err(io::Error::new(
44                io::ErrorKind::InvalidData,
45                "stream did not contain valid UTF-8",
46            ));
47        }
48    }
49    *read = 0;
50    // Safety: `bytes` is valid UTF-8 because it was taken from a String
51    // and the newly read bytes are either valid UTF-8 or have been removed.
52    mem::swap(unsafe { buf.as_mut_vec() }, bytes);
53    Poll::Ready(ret)
54}
55
56impl<R: AsyncBufRead + ?Sized + Unpin> Future for ReadLine<'_, R> {
57    type Output = io::Result<usize>;
58
59    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
60        let Self { reader, buf, bytes, read, finished: _ } = &mut *self;
61        let ret = ready!(read_line_internal(Pin::new(reader), cx, buf, bytes, read));
62        self.finished = true;
63        Poll::Ready(ret)
64    }
65}
66
67impl<R: ?Sized> Drop for ReadLine<'_, R> {
68    fn drop(&mut self) {
69        // restore old string contents
70        if !self.finished {
71            self.bytes.truncate(self.bytes.len() - self.read);
72            // Safety: `bytes` is valid UTF-8 because it was taken from a String
73            // and the newly read bytes have been removed.
74            mem::swap(unsafe { self.buf.as_mut_vec() }, &mut self.bytes);
75        }
76    }
77}
futures_util/io/read_line.rs

futures_util/io/
read_line.rs
