1 files changed, 125 insertions, 0 deletions
diff --git a/third_party/rust/futures-util/src/io/take.rs b/third_party/rust/futures-util/src/io/take.rs
new file mode 100644
index 0000000000..2c494804d9
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/take.rs
@@ -0,0 +1,125 @@
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::{AsyncBufRead, AsyncRead};
+use pin_project_lite::pin_project;
+use std::pin::Pin;
+use std::{cmp, io};
+
+pin_project! {
+    /// Reader for the [`take`](super::AsyncReadExt::take) method.
+    #[derive(Debug)]
+    #[must_use = "readers do nothing unless you `.await` or poll them"]
+    pub struct Take<R> {
+        #[pin]
+        inner: R,
+        limit: u64,
+    }
+}
+
+impl<R: AsyncRead> Take<R> {
+    pub(super) fn new(inner: R, limit: u64) -> Self {
+        Self { inner, limit }
+    }
+
+    /// Returns the remaining number of bytes that can be
+    /// read before this instance will return EOF.
+    ///
+    /// # Note
+    ///
+    /// This instance may reach `EOF` after reading fewer bytes than indicated by
+    /// this method if the underlying [`AsyncRead`] instance reaches EOF.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{AsyncReadExt, Cursor};
+    ///
+    /// let reader = Cursor::new(&b"12345678"[..]);
+    /// let mut buffer = [0; 2];
+    ///
+    /// let mut take = reader.take(4);
+    /// let n = take.read(&mut buffer).await?;
+    ///
+    /// assert_eq!(take.limit(), 2);
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    pub fn limit(&self) -> u64 {
+        self.limit
+    }
+
+    /// Sets the number of bytes that can be read before this instance will
+    /// return EOF. This is the same as constructing a new `Take` instance, so
+    /// the amount of bytes read and the previous limit value don't matter when
+    /// calling this method.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::io::{AsyncReadExt, Cursor};
+    ///
+    /// let reader = Cursor::new(&b"12345678"[..]);
+    /// let mut buffer = [0; 4];
+    ///
+    /// let mut take = reader.take(4);
+    /// let n = take.read(&mut buffer).await?;
+    ///
+    /// assert_eq!(n, 4);
+    /// assert_eq!(take.limit(), 0);
+    ///
+    /// take.set_limit(10);
+    /// let n = take.read(&mut buffer).await?;
+    /// assert_eq!(n, 4);
+    ///
+    /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
+    /// ```
+    pub fn set_limit(&mut self, limit: u64) {
+        self.limit = limit
+    }
+
+    delegate_access_inner!(inner, R, ());
+}
+
+impl<R: AsyncRead> AsyncRead for Take<R> {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut [u8],
+    ) -> Poll<Result<usize, io::Error>> {
+        let this = self.project();
+
+        if *this.limit == 0 {
+            return Poll::Ready(Ok(0));
+        }
+
+        let max = cmp::min(buf.len() as u64, *this.limit) as usize;
+        let n = ready!(this.inner.poll_read(cx, &mut buf[..max]))?;
+        *this.limit -= n as u64;
+        Poll::Ready(Ok(n))
+    }
+}
+
+impl<R: AsyncBufRead> AsyncBufRead for Take<R> {
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        let this = self.project();
+
+        // Don't call into inner reader at all at EOF because it may still block
+        if *this.limit == 0 {
+            return Poll::Ready(Ok(&[]));
+        }
+
+        let buf = ready!(this.inner.poll_fill_buf(cx)?);
+        let cap = cmp::min(buf.len() as u64, *this.limit) as usize;
+        Poll::Ready(Ok(&buf[..cap]))
+    }
+
+    fn consume(self: Pin<&mut Self>, amt: usize) {
+        let this = self.project();
+
+        // Don't let callers reset the limit by passing an overlarge value
+        let amt = cmp::min(amt as u64, *this.limit) as usize;
+        *this.limit -= amt as u64;
+        this.inner.consume(amt);
+    }
+}