1 files changed, 263 insertions, 0 deletions
diff --git a/third_party/rust/futures-util/src/io/buf_reader.rs b/third_party/rust/futures-util/src/io/buf_reader.rs
new file mode 100644
index 0000000000..0334a9f081
--- /dev/null
+++ b/third_party/rust/futures-util/src/io/buf_reader.rs
@@ -0,0 +1,263 @@
+use super::DEFAULT_BUF_SIZE;
+use futures_core::future::Future;
+use futures_core::ready;
+use futures_core::task::{Context, Poll};
+use futures_io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, IoSliceMut, SeekFrom};
+use pin_project_lite::pin_project;
+use std::io::{self, Read};
+use std::pin::Pin;
+use std::{cmp, fmt};
+
+pin_project! {
+    /// The `BufReader` struct adds buffering to any reader.
+    ///
+    /// It can be excessively inefficient to work directly with a [`AsyncRead`]
+    /// instance. A `BufReader` performs large, infrequent reads on the underlying
+    /// [`AsyncRead`] and maintains an in-memory buffer of the results.
+    ///
+    /// `BufReader` can improve the speed of programs that make *small* and
+    /// *repeated* read calls to the same file or network socket. It does not
+    /// help when reading very large amounts at once, or reading just one or a few
+    /// times. It also provides no advantage when reading from a source that is
+    /// already in memory, like a `Vec<u8>`.
+    ///
+    /// When the `BufReader` is dropped, the contents of its buffer will be
+    /// discarded. Creating multiple instances of a `BufReader` on the same
+    /// stream can cause data loss.
+    ///
+    /// [`AsyncRead`]: futures_io::AsyncRead
+    ///
+    // TODO: Examples
+    pub struct BufReader<R> {
+        #[pin]
+        inner: R,
+        buffer: Box<[u8]>,
+        pos: usize,
+        cap: usize,
+    }
+}
+
+impl<R: AsyncRead> BufReader<R> {
+    /// Creates a new `BufReader` with a default buffer capacity. The default is currently 8 KB,
+    /// but may change in the future.
+    pub fn new(inner: R) -> Self {
+        Self::with_capacity(DEFAULT_BUF_SIZE, inner)
+    }
+
+    /// Creates a new `BufReader` with the specified buffer capacity.
+    pub fn with_capacity(capacity: usize, inner: R) -> Self {
+        unsafe {
+            let mut buffer = Vec::with_capacity(capacity);
+            buffer.set_len(capacity);
+            super::initialize(&inner, &mut buffer);
+            Self { inner, buffer: buffer.into_boxed_slice(), pos: 0, cap: 0 }
+        }
+    }
+
+    delegate_access_inner!(inner, R, ());
+
+    /// Returns a reference to the internally buffered data.
+    ///
+    /// Unlike `fill_buf`, this will not attempt to fill the buffer if it is empty.
+    pub fn buffer(&self) -> &[u8] {
+        &self.buffer[self.pos..self.cap]
+    }
+
+    /// Invalidates all data in the internal buffer.
+    #[inline]
+    fn discard_buffer(self: Pin<&mut Self>) {
+        let this = self.project();
+        *this.pos = 0;
+        *this.cap = 0;
+    }
+}
+
+impl<R: AsyncRead + AsyncSeek> BufReader<R> {
+    /// Seeks relative to the current position. If the new position lies within the buffer,
+    /// the buffer will not be flushed, allowing for more efficient seeks.
+    /// This method does not return the location of the underlying reader, so the caller
+    /// must track this information themselves if it is required.
+    pub fn seek_relative(self: Pin<&mut Self>, offset: i64) -> SeeKRelative<'_, R> {
+        SeeKRelative { inner: self, offset, first: true }
+    }
+
+    /// Attempts to seek relative to the current position. If the new position lies within the buffer,
+    /// the buffer will not be flushed, allowing for more efficient seeks.
+    /// This method does not return the location of the underlying reader, so the caller
+    /// must track this information themselves if it is required.
+    pub fn poll_seek_relative(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        offset: i64,
+    ) -> Poll<io::Result<()>> {
+        let pos = self.pos as u64;
+        if offset < 0 {
+            if let Some(new_pos) = pos.checked_sub((-offset) as u64) {
+                *self.project().pos = new_pos as usize;
+                return Poll::Ready(Ok(()));
+            }
+        } else if let Some(new_pos) = pos.checked_add(offset as u64) {
+            if new_pos <= self.cap as u64 {
+                *self.project().pos = new_pos as usize;
+                return Poll::Ready(Ok(()));
+            }
+        }
+        self.poll_seek(cx, SeekFrom::Current(offset)).map(|res| res.map(|_| ()))
+    }
+}
+
+impl<R: AsyncRead> AsyncRead for BufReader<R> {
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut [u8],
+    ) -> Poll<io::Result<usize>> {
+        // If we don't have any buffered data and we're doing a massive read
+        // (larger than our internal buffer), bypass our internal buffer
+        // entirely.
+        if self.pos == self.cap && buf.len() >= self.buffer.len() {
+            let res = ready!(self.as_mut().project().inner.poll_read(cx, buf));
+            self.discard_buffer();
+            return Poll::Ready(res);
+        }
+        let mut rem = ready!(self.as_mut().poll_fill_buf(cx))?;
+        let nread = rem.read(buf)?;
+        self.consume(nread);
+        Poll::Ready(Ok(nread))
+    }
+
+    fn poll_read_vectored(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &mut [IoSliceMut<'_>],
+    ) -> Poll<io::Result<usize>> {
+        let total_len = bufs.iter().map(|b| b.len()).sum::<usize>();
+        if self.pos == self.cap && total_len >= self.buffer.len() {
+            let res = ready!(self.as_mut().project().inner.poll_read_vectored(cx, bufs));
+            self.discard_buffer();
+            return Poll::Ready(res);
+        }
+        let mut rem = ready!(self.as_mut().poll_fill_buf(cx))?;
+        let nread = rem.read_vectored(bufs)?;
+        self.consume(nread);
+        Poll::Ready(Ok(nread))
+    }
+}
+
+impl<R: AsyncRead> AsyncBufRead for BufReader<R> {
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        let this = self.project();
+
+        // If we've reached the end of our internal buffer then we need to fetch
+        // some more data from the underlying reader.
+        // Branch using `>=` instead of the more correct `==`
+        // to tell the compiler that the pos..cap slice is always valid.
+        if *this.pos >= *this.cap {
+            debug_assert!(*this.pos == *this.cap);
+            *this.cap = ready!(this.inner.poll_read(cx, this.buffer))?;
+            *this.pos = 0;
+        }
+        Poll::Ready(Ok(&this.buffer[*this.pos..*this.cap]))
+    }
+
+    fn consume(self: Pin<&mut Self>, amt: usize) {
+        *self.project().pos = cmp::min(self.pos + amt, self.cap);
+    }
+}
+
+impl<R: AsyncWrite> AsyncWrite for BufReader<R> {
+    delegate_async_write!(inner);
+}
+
+impl<R: fmt::Debug> fmt::Debug for BufReader<R> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("BufReader")
+            .field("reader", &self.inner)
+            .field("buffer", &format_args!("{}/{}", self.cap - self.pos, self.buffer.len()))
+            .finish()
+    }
+}
+
+impl<R: AsyncRead + AsyncSeek> AsyncSeek for BufReader<R> {
+    /// Seek to an offset, in bytes, in the underlying reader.
+    ///
+    /// The position used for seeking with `SeekFrom::Current(_)` is the
+    /// position the underlying reader would be at if the `BufReader` had no
+    /// internal buffer.
+    ///
+    /// Seeking always discards the internal buffer, even if the seek position
+    /// would otherwise fall within it. This guarantees that calling
+    /// `.into_inner()` immediately after a seek yields the underlying reader
+    /// at the same position.
+    ///
+    /// To seek without discarding the internal buffer, use
+    /// [`BufReader::seek_relative`](BufReader::seek_relative) or
+    /// [`BufReader::poll_seek_relative`](BufReader::poll_seek_relative).
+    ///
+    /// See [`AsyncSeek`](futures_io::AsyncSeek) for more details.
+    ///
+    /// Note: In the edge case where you're seeking with `SeekFrom::Current(n)`
+    /// where `n` minus the internal buffer length overflows an `i64`, two
+    /// seeks will be performed instead of one. If the second seek returns
+    /// `Err`, the underlying reader will be left at the same position it would
+    /// have if you called `seek` with `SeekFrom::Current(0)`.
+    fn poll_seek(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        pos: SeekFrom,
+    ) -> Poll<io::Result<u64>> {
+        let result: u64;
+        if let SeekFrom::Current(n) = pos {
+            let remainder = (self.cap - self.pos) as i64;
+            // it should be safe to assume that remainder fits within an i64 as the alternative
+            // means we managed to allocate 8 exbibytes and that's absurd.
+            // But it's not out of the realm of possibility for some weird underlying reader to
+            // support seeking by i64::min_value() so we need to handle underflow when subtracting
+            // remainder.
+            if let Some(offset) = n.checked_sub(remainder) {
+                result =
+                    ready!(self.as_mut().project().inner.poll_seek(cx, SeekFrom::Current(offset)))?;
+            } else {
+                // seek backwards by our remainder, and then by the offset
+                ready!(self.as_mut().project().inner.poll_seek(cx, SeekFrom::Current(-remainder)))?;
+                self.as_mut().discard_buffer();
+                result = ready!(self.as_mut().project().inner.poll_seek(cx, SeekFrom::Current(n)))?;
+            }
+        } else {
+            // Seeking with Start/End doesn't care about our buffer length.
+            result = ready!(self.as_mut().project().inner.poll_seek(cx, pos))?;
+        }
+        self.discard_buffer();
+        Poll::Ready(Ok(result))
+    }
+}
+
+/// Future for the [`BufReader::seek_relative`](self::BufReader::seek_relative) method.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless polled"]
+pub struct SeeKRelative<'a, R> {
+    inner: Pin<&'a mut BufReader<R>>,
+    offset: i64,
+    first: bool,
+}
+
+impl<R> Future for SeeKRelative<'_, R>
+where
+    R: AsyncRead + AsyncSeek,
+{
+    type Output = io::Result<()>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let offset = self.offset;
+        if self.first {
+            self.first = false;
+            self.inner.as_mut().poll_seek_relative(cx, offset)
+        } else {
+            self.inner
+                .as_mut()
+                .as_mut()
+                .poll_seek(cx, SeekFrom::Current(offset))
+                .map(|res| res.map(|_| ()))
+        }
+    }
+}