92 lines
2.9 KiB
Rust
92 lines
2.9 KiB
Rust
use futures_core::future::Future;
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use futures_core::ready;
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use futures_core::task::{Context, Poll};
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use futures_io::AsyncRead;
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use std::io;
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use std::pin::Pin;
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use std::vec::Vec;
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/// Future for the [`read_to_end`](super::AsyncReadExt::read_to_end) method.
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#[derive(Debug)]
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#[must_use = "futures do nothing unless you `.await` or poll them"]
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pub struct ReadToEnd<'a, R: ?Sized> {
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reader: &'a mut R,
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buf: &'a mut Vec<u8>,
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start_len: usize,
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}
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impl<R: ?Sized + Unpin> Unpin for ReadToEnd<'_, R> {}
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impl<'a, R: AsyncRead + ?Sized + Unpin> ReadToEnd<'a, R> {
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pub(super) fn new(reader: &'a mut R, buf: &'a mut Vec<u8>) -> Self {
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let start_len = buf.len();
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Self { reader, buf, start_len }
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}
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}
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struct Guard<'a> {
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buf: &'a mut Vec<u8>,
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len: usize,
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}
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impl Drop for Guard<'_> {
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fn drop(&mut self) {
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unsafe {
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self.buf.set_len(self.len);
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}
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}
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}
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// This uses an adaptive system to extend the vector when it fills. We want to
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// avoid paying to allocate and zero a huge chunk of memory if the reader only
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// has 4 bytes while still making large reads if the reader does have a ton
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// of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
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// time is 4,500 times (!) slower than this if the reader has a very small
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// amount of data to return.
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//
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// Because we're extending the buffer with uninitialized data for trusted
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// readers, we need to make sure to truncate that if any of this panics.
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pub(super) fn read_to_end_internal<R: AsyncRead + ?Sized>(
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mut rd: Pin<&mut R>,
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cx: &mut Context<'_>,
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buf: &mut Vec<u8>,
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start_len: usize,
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) -> Poll<io::Result<usize>> {
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let mut g = Guard { len: buf.len(), buf };
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loop {
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if g.len == g.buf.len() {
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unsafe {
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g.buf.reserve(32);
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let capacity = g.buf.capacity();
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g.buf.set_len(capacity);
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super::initialize(&rd, &mut g.buf[g.len..]);
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}
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}
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let buf = &mut g.buf[g.len..];
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match ready!(rd.as_mut().poll_read(cx, buf)) {
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Ok(0) => return Poll::Ready(Ok(g.len - start_len)),
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Ok(n) => {
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// We can't allow bogus values from read. If it is too large, the returned vec could have its length
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// set past its capacity, or if it overflows the vec could be shortened which could create an invalid
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// string if this is called via read_to_string.
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assert!(n <= buf.len());
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g.len += n;
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}
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Err(e) => return Poll::Ready(Err(e)),
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}
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}
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}
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impl<A> Future for ReadToEnd<'_, A>
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where
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A: AsyncRead + ?Sized + Unpin,
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{
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type Output = io::Result<usize>;
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fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
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let this = &mut *self;
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read_to_end_internal(Pin::new(&mut this.reader), cx, this.buf, this.start_len)
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}
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}
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