forked from mirror/async-std
87 lines
2.4 KiB
Rust
87 lines
2.4 KiB
Rust
use crate::future::Future;
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use crate::task::{Context, Poll};
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use std::io;
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use std::pin::Pin;
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use futures_io::AsyncRead;
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#[doc(hidden)]
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#[allow(missing_debug_implementations)]
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pub struct ReadToEndFuture<'a, T: Unpin + ?Sized> {
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pub(crate) reader: &'a mut T,
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pub(crate) buf: &'a mut Vec<u8>,
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pub(crate) start_len: usize,
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}
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impl<T: AsyncRead + Unpin + ?Sized> Future for ReadToEndFuture<'_, T> {
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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 Self {
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reader,
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buf,
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start_len,
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} = &mut *self;
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read_to_end_internal(Pin::new(reader), cx, buf, *start_len)
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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 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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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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let mut g = Guard {
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len: buf.len(),
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buf,
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};
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let ret;
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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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rd.initializer().initialize(&mut g.buf[g.len..]);
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}
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}
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match futures_core::ready!(rd.as_mut().poll_read(cx, &mut g.buf[g.len..])) {
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Ok(0) => {
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ret = Poll::Ready(Ok(g.len - start_len));
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break;
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}
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Ok(n) => g.len += n,
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Err(e) => {
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ret = Poll::Ready(Err(e));
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break;
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}
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}
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}
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ret
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}
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