1 files changed, 78 insertions, 75 deletions

diff --git a/src/io/util/read_to_end.rs b/src/io/util/read_to_end.rs
index a2cd99b..a974625 100644
--- a/src/io/util/read_to_end.rs
+++ b/src/io/util/read_to_end.rs
@@ -1,92 +1,105 @@
-use crate::io::AsyncRead;
+use crate::io::{AsyncRead, ReadBuf};
 
+use pin_project_lite::pin_project;
 use std::future::Future;
 use std::io;
-use std::mem::MaybeUninit;
+use std::marker::PhantomPinned;
+use std::mem::{self, MaybeUninit};
 use std::pin::Pin;
 use std::task::{Context, Poll};
 
-#[derive(Debug)]
-#[must_use = "futures do nothing unless you `.await` or poll them"]
-#[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
-pub struct ReadToEnd<'a, R: ?Sized> {
-    reader: &'a mut R,
-    buf: &'a mut Vec<u8>,
-    start_len: usize,
+pin_project! {
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct ReadToEnd<'a, R: ?Sized> {
+        reader: &'a mut R,
+        buf: &'a mut Vec<u8>,
+        // The number of bytes appended to buf. This can be less than buf.len() if
+        // the buffer was not empty when the operation was started.
+        read: usize,
+        // Make this future `!Unpin` for compatibility with async trait methods.
+        #[pin]
+        _pin: PhantomPinned,
+    }
 }
 
-pub(crate) fn read_to_end<'a, R>(reader: &'a mut R, buf: &'a mut Vec<u8>) -> ReadToEnd<'a, R>
+pub(crate) fn read_to_end<'a, R>(reader: &'a mut R, buffer: &'a mut Vec<u8>) -> ReadToEnd<'a, R>
 where
     R: AsyncRead + Unpin + ?Sized,
 {
-    let start_len = buf.len();
     ReadToEnd {
         reader,
-        buf,
-        start_len,
+        buf: buffer,
+        read: 0,
+        _pin: PhantomPinned,
     }
 }
 
-struct Guard<'a> {
-    buf: &'a mut Vec<u8>,
-    len: usize,
-}
-
-impl Drop for Guard<'_> {
-    fn drop(&mut self) {
-        unsafe {
-            self.buf.set_len(self.len);
+pub(super) fn read_to_end_internal<R: AsyncRead + ?Sized>(
+    buf: &mut Vec<u8>,
+    mut reader: Pin<&mut R>,
+    num_read: &mut usize,
+    cx: &mut Context<'_>,
+) -> Poll<io::Result<usize>> {
+    loop {
+        // safety: The caller promised to prepare the buffer.
+        let ret = ready!(poll_read_to_end(buf, reader.as_mut(), cx));
+        match ret {
+            Err(err) => return Poll::Ready(Err(err)),
+            Ok(0) => return Poll::Ready(Ok(mem::replace(num_read, 0))),
+            Ok(num) => {
+                *num_read += num;
+            }
         }
     }
 }
 
-// This uses an adaptive system to extend the vector when it fills. We want to
-// avoid paying to allocate and zero a huge chunk of memory if the reader only
-// has 4 bytes while still making large reads if the reader does have a ton
-// of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
-// time is 4,500 times (!) slower than this if the reader has a very small
-// amount of data to return.
-//
-// Because we're extending the buffer with uninitialized data for trusted
-// readers, we need to make sure to truncate that if any of this panics.
-pub(super) fn read_to_end_internal<R: AsyncRead + ?Sized>(
-    mut rd: Pin<&mut R>,
-    cx: &mut Context<'_>,
+/// Tries to read from the provided AsyncRead.
+///
+/// The length of the buffer is increased by the number of bytes read.
+fn poll_read_to_end<R: AsyncRead + ?Sized>(
     buf: &mut Vec<u8>,
-    start_len: usize,
+    read: Pin<&mut R>,
+    cx: &mut Context<'_>,
 ) -> Poll<io::Result<usize>> {
-    let mut g = Guard {
-        len: buf.len(),
-        buf,
-    };
-    let ret;
-    loop {
-        if g.len == g.buf.len() {
-            unsafe {
-                g.buf.reserve(32);
-                let capacity = g.buf.capacity();
-                g.buf.set_len(capacity);
+    // This uses an adaptive system to extend the vector when it fills. We want to
+    // avoid paying to allocate and zero a huge chunk of memory if the reader only
+    // has 4 bytes while still making large reads if the reader does have a ton
+    // of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
+    // time is 4,500 times (!) slower than this if the reader has a very small
+    // amount of data to return.
+    reserve(buf, 32);
 
-                let b = &mut *(&mut g.buf[g.len..] as *mut [u8] as *mut [MaybeUninit<u8>]);
+    let mut unused_capacity = ReadBuf::uninit(get_unused_capacity(buf));
 
-                rd.prepare_uninitialized_buffer(b);
-            }
-        }
+    ready!(read.poll_read(cx, &mut unused_capacity))?;
 
-        match ready!(rd.as_mut().poll_read(cx, &mut g.buf[g.len..])) {
-            Ok(0) => {
-                ret = Poll::Ready(Ok(g.len - start_len));
-                break;
-            }
-            Ok(n) => g.len += n,
-            Err(e) => {
-                ret = Poll::Ready(Err(e));
-                break;
-            }
-        }
+    let n = unused_capacity.filled().len();
+    let new_len = buf.len() + n;
+
+    // This should no longer even be possible in safe Rust. An implementor
+    // would need to have unsafely *replaced* the buffer inside `ReadBuf`,
+    // which... yolo?
+    assert!(new_len <= buf.capacity());
+    unsafe {
+        buf.set_len(new_len);
     }
+    Poll::Ready(Ok(n))
+}
 
-    ret
+/// Allocates more memory and ensures that the unused capacity is prepared for use
+/// with the `AsyncRead`.
+fn reserve(buf: &mut Vec<u8>, bytes: usize) {
+    if buf.capacity() - buf.len() >= bytes {
+        return;
+    }
+    buf.reserve(bytes);
+}
+
+/// Returns the unused capacity of the provided vector.
+fn get_unused_capacity(buf: &mut Vec<u8>) -> &mut [MaybeUninit<u8>] {
+    let uninit = bytes::BufMut::bytes_mut(buf);
+    unsafe { &mut *(uninit as *mut _ as *mut [MaybeUninit<u8>]) }
 }
 
 impl<A> Future for ReadToEnd<'_, A>
@@ -95,19 +108,9 @@ where
 {
     type Output = io::Result<usize>;
 
-    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        let this = &mut *self;
-        read_to_end_internal(Pin::new(&mut this.reader), cx, this.buf, this.start_len)
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let me = self.project();
 
-    #[test]
-    fn assert_unpin() {
-        use std::marker::PhantomPinned;
-        crate::is_unpin::<ReadToEnd<'_, PhantomPinned>>();
+        read_to_end_internal(me.buf, Pin::new(*me.reader), me.read, cx)
     }
 }