1 files changed, 108 insertions, 0 deletions
diff --git a/tokio/src/io/util/read_to_end.rs b/tokio/src/io/util/read_to_end.rs
new file mode 100644
index 00000000..36eba5bb
--- /dev/null
+++ b/tokio/src/io/util/read_to_end.rs
@@ -0,0 +1,108 @@
+use crate::io::AsyncRead;
+
+use std::future::Future;
+use std::io;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+#[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>,
+    start_len: usize,
+}
+
+pub(crate) fn read_to_end<'a, R>(reader: &'a mut R, buf: &'a mut Vec<u8>) -> ReadToEnd<'a, R>
+where
+    R: AsyncRead + Unpin + ?Sized,
+{
+    let start_len = buf.len();
+    ReadToEnd {
+        reader,
+        buf,
+        start_len,
+    }
+}
+
+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);
+        }
+    }
+}
+
+// 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<'_>,
+    buf: &mut Vec<u8>,
+    start_len: usize,
+) -> 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);
+                rd.prepare_uninitialized_buffer(&mut g.buf[g.len..]);
+            }
+        }
+
+        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;
+            }
+        }
+    }
+
+    ret
+}
+
+impl<A> Future for ReadToEnd<'_, A>
+where
+    A: AsyncRead + ?Sized + Unpin,
+{
+    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::*;
+
+    #[test]
+    fn assert_unpin() {
+        use std::marker::PhantomPinned;
+        crate::is_unpin::<ReadToEnd<'_, PhantomPinned>>();
+    }
+}