tokio: add AsyncReadExt::read_to_end (#1279)

tokio/src/io/async_read_ext.rs

@@ -1,6 +1,7 @@
 use crate::io::copy::{copy, Copy};
 use crate::io::read::{read, Read};
 use crate::io::read_exact::{read_exact, ReadExact};
+use crate::io::read_to_end::{read_to_end, ReadToEnd};
 
 use tokio_io::{AsyncRead, AsyncWrite};
 
@@ -60,6 +61,14 @@ pub trait AsyncReadExt: AsyncRead {
     {
         read_exact(self, dst)
     }
+
+    /// Read all bytes until EOF in this source, placing them into `dst`.
+    fn read_to_end<'a>(&'a mut self, dst: &'a mut Vec<u8>) -> ReadToEnd<'a, Self>
+    where
+        Self: Unpin,
+    {
+        read_to_end(self, dst)
+    }
 }
 
 impl<R: AsyncRead + ?Sized> AsyncReadExt for R {}

tokio/src/io/mod.rs

@@ -41,6 +41,7 @@ mod async_write_ext;
 mod copy;
 mod read;
 mod read_exact;
+mod read_to_end;
 mod write;
 mod write_all;
 

tokio/src/io/read_to_end.rs

@@ -0,0 +1,99 @@
+use tokio_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,
+}
+
+impl<R: ?Sized + Unpin> Unpin for ReadToEnd<'_, R> {}
+
+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)
+    }
+}

tokio/tests/io_read_to_end.rs

@@ -0,0 +1,40 @@
+#![deny(warnings, rust_2018_idioms)]
+#![feature(async_await)]
+
+use tokio::io::{AsyncRead, AsyncReadExt};
+use tokio_test::assert_ok;
+
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use std::{cmp, io};
+
+#[tokio::test]
+async fn read_to_end() {
+    struct Rd {
+        val: &'static [u8],
+    }
+
+    impl AsyncRead for Rd {
+        fn poll_read(
+            mut self: Pin<&mut Self>,
+            _cx: &mut Context<'_>,
+            buf: &mut [u8],
+        ) -> Poll<io::Result<usize>> {
+            let me = &mut *self;
+            let len = cmp::min(buf.len(), me.val.len());
+
+            buf[..len].copy_from_slice(&me.val[..len]);
+            me.val = &me.val[len..];
+            Poll::Ready(Ok(len))
+        }
+    }
+
+    let mut buf = vec![];
+    let mut rd = Rd {
+        val: b"hello world",
+    };
+
+    let n = assert_ok!(rd.read_to_end(&mut buf).await);
+    assert_eq!(n, 11);
+    assert_eq!(buf[..], b"hello world"[..]);
+}