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use crate::io::util::read_line::finish_string_read;
use crate::io::util::read_to_end::read_to_end_internal;
use crate::io::AsyncRead;
use pin_project_lite::pin_project;
use std::future::Future;
use std::marker::PhantomPinned;
use std::pin::Pin;
use std::task::{Context, Poll};
use std::{io, mem};
pin_project! {
/// Future for the [`read_to_string`](super::AsyncReadExt::read_to_string) method.
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct ReadToString<'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_to_string<'a, R>(
reader: &'a mut R,
string: &'a mut String,
) -> ReadToString<'a, R>
where
R: AsyncRead + ?Sized + Unpin,
{
let buf = mem::replace(string, String::new()).into_bytes();
ReadToString {
reader,
buf,
output: string,
read: 0,
_pin: PhantomPinned,
}
}
/// # Safety
///
/// Before first calling this method, the unused capacity must have been
/// prepared for use with the provided AsyncRead. This can be done using the
/// `prepare_buffer` function in `read_to_end.rs`.
unsafe fn read_to_string_internal<R: AsyncRead + ?Sized>(
reader: Pin<&mut R>,
output: &mut String,
buf: &mut Vec<u8>,
read: &mut usize,
cx: &mut Context<'_>,
) -> Poll<io::Result<usize>> {
let io_res = ready!(read_to_end_internal(buf, reader, read, cx));
let utf8_res = String::from_utf8(mem::replace(buf, Vec::new()));
// 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, true)
}
impl<A> Future for ReadToString<'_, A>
where
A: AsyncRead + ?Sized + Unpin,
{
type Output = io::Result<usize>;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let me = self.project();
// safety: The constructor of ReadToString called `prepare_buffer`.
unsafe { read_to_string_internal(Pin::new(*me.reader), me.output, me.buf, me.read, cx) }
}
}
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