76 lines
1.8 KiB
Rust
76 lines
1.8 KiB
Rust
use crate::Stream;
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use core::cmp;
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use core::fmt;
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use core::pin::Pin;
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use core::task::{Context, Poll};
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use pin_project_lite::pin_project;
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pin_project! {
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/// Stream for the [`take`](super::StreamExt::take) method.
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#[must_use = "streams do nothing unless polled"]
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pub struct Take<St> {
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#[pin]
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stream: St,
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remaining: usize,
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}
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}
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impl<St> fmt::Debug for Take<St>
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where
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St: fmt::Debug,
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{
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.debug_struct("Take")
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.field("stream", &self.stream)
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.finish()
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}
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}
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impl<St> Take<St> {
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pub(super) fn new(stream: St, remaining: usize) -> Self {
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Self { stream, remaining }
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}
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}
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impl<St> Stream for Take<St>
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where
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St: Stream,
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{
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type Item = St::Item;
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fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
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if *self.as_mut().project().remaining > 0 {
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self.as_mut().project().stream.poll_next(cx).map(|ready| {
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match &ready {
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Some(_) => {
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*self.as_mut().project().remaining -= 1;
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}
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None => {
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*self.as_mut().project().remaining = 0;
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}
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}
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ready
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})
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} else {
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Poll::Ready(None)
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}
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}
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fn size_hint(&self) -> (usize, Option<usize>) {
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if self.remaining == 0 {
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return (0, Some(0));
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}
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let (lower, upper) = self.stream.size_hint();
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let lower = cmp::min(lower, self.remaining as usize);
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let upper = match upper {
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Some(x) if x < self.remaining as usize => Some(x),
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_ => Some(self.remaining as usize),
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};
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(lower, upper)
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}
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}
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