Source code
Revision control
Copy as Markdown
Other Tools
use crate::io::util::read_until::read_until_internal;
use crate::io::AsyncBufRead;
use pin_project_lite::pin_project;
use std::future::Future;
use std::io;
use std::marker::PhantomPinned;
use std::mem;
use std::pin::Pin;
use std::string::FromUtf8Error;
use std::task::{Context, Poll};
pin_project! {
/// Future for the [`read_line`](crate::io::AsyncBufReadExt::read_line) method.
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct ReadLine<'a, R: ?Sized> {
reader: &'a mut R,
// This is the buffer we were provided. It will be replaced with an empty string
// while reading to postpone utf-8 handling until after reading.
output: &'a mut String,
// The actual allocation of the string is moved into this vector instead.
buf: Vec<u8>,
// The number of bytes appended to buf. This can be less than buf.len() if
// the buffer was not empty when the operation was started.
read: usize,
// Make this future `!Unpin` for compatibility with async trait methods.
#[pin]
_pin: PhantomPinned,
}
}
pub(crate) fn read_line<'a, R>(reader: &'a mut R, string: &'a mut String) -> ReadLine<'a, R>
where
R: AsyncBufRead + ?Sized + Unpin,
{
ReadLine {
reader,
buf: mem::take(string).into_bytes(),
output: string,
read: 0,
_pin: PhantomPinned,
}
}
fn put_back_original_data(output: &mut String, mut vector: Vec<u8>, num_bytes_read: usize) {
let original_len = vector.len() - num_bytes_read;
vector.truncate(original_len);
*output = String::from_utf8(vector).expect("The original data must be valid utf-8.");
}
/// This handles the various failure cases and puts the string back into `output`.
///
/// The `truncate_on_io_error` bool is necessary because `read_to_string` and `read_line`
/// disagree on what should happen when an IO error occurs.
pub(super) fn finish_string_read(
io_res: io::Result<usize>,
utf8_res: Result<String, FromUtf8Error>,
read: usize,
output: &mut String,
truncate_on_io_error: bool,
) -> Poll<io::Result<usize>> {
match (io_res, utf8_res) {
(Ok(num_bytes), Ok(string)) => {
debug_assert_eq!(read, 0);
*output = string;
Poll::Ready(Ok(num_bytes))
}
(Err(io_err), Ok(string)) => {
*output = string;
if truncate_on_io_error {
let original_len = output.len() - read;
output.truncate(original_len);
}
Poll::Ready(Err(io_err))
}
(Ok(num_bytes), Err(utf8_err)) => {
debug_assert_eq!(read, 0);
put_back_original_data(output, utf8_err.into_bytes(), num_bytes);
Poll::Ready(Err(io::Error::new(
io::ErrorKind::InvalidData,
"stream did not contain valid UTF-8",
)))
}
(Err(io_err), Err(utf8_err)) => {
put_back_original_data(output, utf8_err.into_bytes(), read);
Poll::Ready(Err(io_err))
}
}
}
pub(super) fn read_line_internal<R: AsyncBufRead + ?Sized>(
reader: Pin<&mut R>,
cx: &mut Context<'_>,
output: &mut String,
buf: &mut Vec<u8>,
read: &mut usize,
) -> Poll<io::Result<usize>> {
let io_res = ready!(read_until_internal(reader, cx, b'\n', buf, read));
let utf8_res = String::from_utf8(mem::take(buf));
// At this point both buf and output are empty. The allocation is in utf8_res.
debug_assert!(buf.is_empty());
debug_assert!(output.is_empty());
finish_string_read(io_res, utf8_res, *read, output, false)
}
impl<R: AsyncBufRead + ?Sized + Unpin> Future for ReadLine<'_, R> {
type Output = io::Result<usize>;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let me = self.project();
read_line_internal(Pin::new(*me.reader), cx, me.output, me.buf, me.read)
}
}