chore: update `bytes` dependency to git master (#1796)

Tokio will track changes to bytes until 0.5 is released.

12 files changed, 47 insertions, 287 deletions

diff --git a/tokio/Cargo.toml b/tokio/Cargo.toml
index 9364ea82..0619a50f 100644
--- a/tokio/Cargo.toml
+++ b/tokio/Cargo.toml
@@ -91,8 +91,7 @@ uds = ["io-driver", "mio-uds", "libc"]
 [dependencies]
 tokio-macros = { version = "=0.2.0-alpha.6", optional = true, path = "../tokio-macros" }
 
-bytes = "0.4"
-iovec = "0.1"
+bytes = { git = "https://github.com/tokio-rs/bytes" }
 pin-project-lite = "0.1.1"
 
 # Everything else is optional...
diff --git a/tokio/src/io/async_read.rs b/tokio/src/io/async_read.rs
index 974cf346..d7e703d4 100644
--- a/tokio/src/io/async_read.rs
+++ b/tokio/src/io/async_read.rs
@@ -1,5 +1,6 @@
 use bytes::BufMut;
 use std::io;
+use std::mem::MaybeUninit;
 use std::ops::DerefMut;
 use std::pin::Pin;
 use std::task::{Context, Poll};
@@ -63,9 +64,9 @@ pub trait AsyncRead {
     ///
     /// [`io::Read`]: std::io::Read
     /// [`poll_read_buf`]: #method.poll_read_buf
-    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [u8]) -> bool {
+    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [MaybeUninit<u8>]) -> bool {
         for x in buf {
-            *x = 0;
+            *x.as_mut_ptr() = 0;
         }
 
         true
@@ -109,6 +110,9 @@ pub trait AsyncRead {
 
                 self.prepare_uninitialized_buffer(b);
 
+                // Convert to `&mut [u8]`
+                let b = &mut *(b as *mut [MaybeUninit<u8>] as *mut [u8]);
+
                 ready!(self.poll_read(cx, b))?
             };
 
@@ -120,7 +124,7 @@ pub trait AsyncRead {
 
 macro_rules! deref_async_read {
     () => {
-        unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [u8]) -> bool {
+        unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [MaybeUninit<u8>]) -> bool {
             (**self).prepare_uninitialized_buffer(buf)
         }
 
@@ -145,7 +149,7 @@ where
     P: DerefMut + Unpin,
     P::Target: AsyncRead,
 {
-    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [u8]) -> bool {
+    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [MaybeUninit<u8>]) -> bool {
         (**self).prepare_uninitialized_buffer(buf)
     }
 
@@ -159,7 +163,7 @@ where
 }
 
 impl AsyncRead for &[u8] {
-    unsafe fn prepare_uninitialized_buffer(&self, _buf: &mut [u8]) -> bool {
+    unsafe fn prepare_uninitialized_buffer(&self, _buf: &mut [MaybeUninit<u8>]) -> bool {
         false
     }
 
@@ -173,7 +177,7 @@ impl AsyncRead for &[u8] {
 }
 
 impl<T: AsRef<[u8]> + Unpin> AsyncRead for io::Cursor<T> {
-    unsafe fn prepare_uninitialized_buffer(&self, _buf: &mut [u8]) -> bool {
+    unsafe fn prepare_uninitialized_buffer(&self, _buf: &mut [MaybeUninit<u8>]) -> bool {
         false
     }
 
diff --git a/tokio/src/io/util/buf_reader.rs b/tokio/src/io/util/buf_reader.rs
index 46caa1fa..5cf2c179 100644
--- a/tokio/src/io/util/buf_reader.rs
+++ b/tokio/src/io/util/buf_reader.rs
@@ -3,6 +3,7 @@ use crate::io::{AsyncBufRead, AsyncRead, AsyncWrite};
 
 use pin_project_lite::pin_project;
 use std::io::{self, Read};
+use std::mem::MaybeUninit;
 use std::pin::Pin;
 use std::task::{Context, Poll};
 use std::{cmp, fmt};
@@ -45,7 +46,12 @@ impl<R: AsyncRead> BufReader<R> {
         unsafe {
             let mut buffer = Vec::with_capacity(capacity);
             buffer.set_len(capacity);
-            inner.prepare_uninitialized_buffer(&mut buffer);
+
+            {
+                // Convert to MaybeUninit
+                let b = &mut *(&mut buffer[..] as *mut [u8] as *mut [MaybeUninit<u8>]);
+                inner.prepare_uninitialized_buffer(b);
+            }
             Self {
                 inner,
                 buf: buffer.into_boxed_slice(),
@@ -120,7 +126,7 @@ impl<R: AsyncRead> AsyncRead for BufReader<R> {
     }
 
     // we can't skip unconditionally because of the large buffer case in read.
-    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [u8]) -> bool {
+    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [MaybeUninit<u8>]) -> bool {
         self.inner.prepare_uninitialized_buffer(buf)
     }
 }
diff --git a/tokio/src/io/util/buf_stream.rs b/tokio/src/io/util/buf_stream.rs
index 7ff1d3f4..a1676c29 100644
--- a/tokio/src/io/util/buf_stream.rs
+++ b/tokio/src/io/util/buf_stream.rs
@@ -2,11 +2,10 @@ use crate::io::util::{BufReader, BufWriter};
 use crate::io::{AsyncBufRead, AsyncRead, AsyncWrite};
 
 use pin_project_lite::pin_project;
-use std::io::{self};
-use std::{
-    pin::Pin,
-    task::{Context, Poll},
-};
+use std::io;
+use std::mem::MaybeUninit;
+use std::pin::Pin;
+use std::task::{Context, Poll};
 
 pin_project! {
     /// Wraps a type that is [`AsyncWrite`] and [`AsyncRead`], and buffers its input and output.
@@ -126,7 +125,7 @@ impl<RW: AsyncRead + AsyncWrite> AsyncRead for BufStream<RW> {
     }
 
     // we can't skip unconditionally because of the large buffer case in read.
-    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [u8]) -> bool {
+    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [MaybeUninit<u8>]) -> bool {
         self.inner.prepare_uninitialized_buffer(buf)
     }
 }
diff --git a/tokio/src/io/util/buf_writer.rs b/tokio/src/io/util/buf_writer.rs
index 5c98bd82..e7ae57a0 100644
--- a/tokio/src/io/util/buf_writer.rs
+++ b/tokio/src/io/util/buf_writer.rs
@@ -4,6 +4,7 @@ use crate::io::{AsyncBufRead, AsyncRead, AsyncWrite};
 use pin_project_lite::pin_project;
 use std::fmt;
 use std::io::{self, Write};
+use std::mem::MaybeUninit;
 use std::pin::Pin;
 use std::task::{Context, Poll};
 
@@ -152,7 +153,7 @@ impl<W: AsyncWrite + AsyncRead> AsyncRead for BufWriter<W> {
     }
 
     // we can't skip unconditionally because of the large buffer case in read.
-    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [u8]) -> bool {
+    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [MaybeUninit<u8>]) -> bool {
         self.get_ref().prepare_uninitialized_buffer(buf)
     }
 }
diff --git a/tokio/src/io/util/read_to_end.rs b/tokio/src/io/util/read_to_end.rs
index 36eba5bb..0cd91f84 100644
--- a/tokio/src/io/util/read_to_end.rs
+++ b/tokio/src/io/util/read_to_end.rs
@@ -2,6 +2,7 @@ use crate::io::AsyncRead;
 
 use std::future::Future;
 use std::io;
+use std::mem::MaybeUninit;
 use std::pin::Pin;
 use std::task::{Context, Poll};
 
@@ -64,7 +65,10 @@ pub(super) fn read_to_end_internal<R: AsyncRead + ?Sized>(
                 g.buf.reserve(32);
                 let capacity = g.buf.capacity();
                 g.buf.set_len(capacity);
-                rd.prepare_uninitialized_buffer(&mut g.buf[g.len..]);
+
+                let b = &mut *(&mut g.buf[g.len..] as *mut [u8] as *mut [MaybeUninit<u8>]);
+
+                rd.prepare_uninitialized_buffer(b);
             }
         }
 
diff --git a/tokio/src/io/util/take.rs b/tokio/src/io/util/take.rs
index 86403853..18332603 100644
--- a/tokio/src/io/util/take.rs
+++ b/tokio/src/io/util/take.rs
@@ -1,6 +1,7 @@
 use crate::io::{AsyncBufRead, AsyncRead};
 
 use pin_project_lite::pin_project;
+use std::mem::MaybeUninit;
 use std::pin::Pin;
 use std::task::{Context, Poll};
 use std::{cmp, io};
@@ -74,7 +75,7 @@ impl<R: AsyncRead> Take<R> {
 }
 
 impl<R: AsyncRead> AsyncRead for Take<R> {
-    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [u8]) -> bool {
+    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [MaybeUninit<u8>]) -> bool {
         self.inner.prepare_uninitialized_buffer(buf)
     }
 
diff --git a/tokio/src/net/tcp/split.rs b/tokio/src/net/tcp/split.rs
index 07c7c3ff..2b337c08 100644
--- a/tokio/src/net/tcp/split.rs
+++ b/tokio/src/net/tcp/split.rs
@@ -11,8 +11,8 @@
 use crate::io::{AsyncRead, AsyncWrite};
 use crate::net::TcpStream;
 
-use bytes::{Buf, BufMut};
 use std::io;
+use std::mem::MaybeUninit;
 use std::net::Shutdown;
 use std::pin::Pin;
 use std::task::{Context, Poll};
@@ -33,7 +33,7 @@ pub(crate) fn split(stream: &mut TcpStream) -> (ReadHalf<'_>, WriteHalf<'_>) {
 }
 
 impl AsyncRead for ReadHalf<'_> {
-    unsafe fn prepare_uninitialized_buffer(&self, _: &mut [u8]) -> bool {
+    unsafe fn prepare_uninitialized_buffer(&self, _: &mut [MaybeUninit<u8>]) -> bool {
         false
     }
 
@@ -44,14 +44,6 @@ impl AsyncRead for ReadHalf<'_> {
     ) -> Poll<io::Result<usize>> {
         self.0.poll_read_priv(cx, buf)
     }
-
-    fn poll_read_buf<B: BufMut>(
-        self: Pin<&mut Self>,
-        cx: &mut Context<'_>,
-        buf: &mut B,
-    ) -> Poll<io::Result<usize>> {
-        self.0.poll_read_buf_priv(cx, buf)
-    }
 }
 
 impl AsyncWrite for WriteHalf<'_> {
@@ -73,14 +65,6 @@ impl AsyncWrite for WriteHalf<'_> {
     fn poll_shutdown(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
         self.0.shutdown(Shutdown::Write).into()
     }
-
-    fn poll_write_buf<B: Buf>(
-        self: Pin<&mut Self>,
-        cx: &mut Context<'_>,
-        buf: &mut B,
-    ) -> Poll<io::Result<usize>> {
-        self.0.poll_write_buf_priv(cx, buf)
-    }
 }
 
 impl AsRef<TcpStream> for ReadHalf<'_> {
diff --git a/tokio/src/net/tcp/stream.rs b/tokio/src/net/tcp/stream.rs
index b73114b4..34d3a493 100644
--- a/tokio/src/net/tcp/stream.rs
+++ b/tokio/src/net/tcp/stream.rs
@@ -3,11 +3,10 @@ use crate::io::{AsyncRead, AsyncWrite, PollEvented};
 use crate::net::tcp::split::{split, ReadHalf, WriteHalf};
 use crate::net::ToSocketAddrs;
 
-use bytes::{Buf, BufMut};
-use iovec::IoVec;
 use std::convert::TryFrom;
 use std::fmt;
 use std::io::{self, Read, Write};
+use std::mem::MaybeUninit;
 use std::net::{self, Shutdown, SocketAddr};
 use std::pin::Pin;
 use std::task::{Context, Poll};
@@ -601,70 +600,6 @@ impl TcpStream {
         }
     }
 
-    pub(crate) fn poll_read_buf_priv<B: BufMut>(
-        &self,
-        cx: &mut Context<'_>,
-        buf: &mut B,
-    ) -> Poll<io::Result<usize>> {
-        ready!(self.io.poll_read_ready(cx, mio::Ready::readable()))?;
-
-        let r = unsafe {
-            // The `IoVec` type can't have a 0-length size, so we create a bunch
-            // of dummy versions on the stack with 1 length which we'll quickly
-            // overwrite.
-            let b1: &mut [u8] = &mut [0];
-            let b2: &mut [u8] = &mut [0];
-            let b3: &mut [u8] = &mut [0];
-            let b4: &mut [u8] = &mut [0];
-            let b5: &mut [u8] = &mut [0];
-            let b6: &mut [u8] = &mut [0];
-            let b7: &mut [u8] = &mut [0];
-            let b8: &mut [u8] = &mut [0];
-            let b9: &mut [u8] = &mut [0];
-            let b10: &mut [u8] = &mut [0];
-            let b11: &mut [u8] = &mut [0];
-            let b12: &mut [u8] = &mut [0];
-            let b13: &mut [u8] = &mut [0];
-            let b14: &mut [u8] = &mut [0];
-            let b15: &mut [u8] = &mut [0];
-            let b16: &mut [u8] = &mut [0];
-            let mut bufs: [&mut IoVec; 16] = [
-                b1.into(),
-                b2.into(),
-                b3.into(),
-                b4.into(),
-                b5.into(),
-                b6.into(),
-                b7.into(),
-                b8.into(),
-                b9.into(),
-                b10.into(),
-                b11.into(),
-                b12.into(),
-                b13.into(),
-                b14.into(),
-                b15.into(),
-                b16.into(),
-            ];
-            let n = buf.bytes_vec_mut(&mut bufs);
-            self.io.get_ref().read_bufs(&mut bufs[..n])
-        };
-
-        match r {
-            Ok(n) => {
-                unsafe {
-                    buf.advance_mut(n);
-                }
-                Poll::Ready(Ok(n))
-            }
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                self.io.clear_read_ready(cx, mio::Ready::readable())?;
-                Poll::Pending
-            }
-            Err(e) => Poll::Ready(Err(e)),
-        }
-    }
-
     pub(crate) fn poll_write_priv(
         &self,
         cx: &mut Context<'_>,
@@ -680,36 +615,6 @@ impl TcpStream {
             x => Poll::Ready(x),
         }
     }
-
-    pub(crate) fn poll_write_buf_priv<B: Buf>(
-        &self,
-        cx: &mut Context<'_>,
-        buf: &mut B,
-    ) -> Poll<io::Result<usize>> {
-        ready!(self.io.poll_write_ready(cx))?;
-
-        let r = {
-            // The `IoVec` type can't have a zero-length size, so create a dummy
-            // version from a 1-length slice which we'll overwrite with the
-            // `bytes_vec` method.
-            static DUMMY: &[u8] = &[0];
-            let iovec = <&IoVec>::from(DUMMY);
-            let mut bufs = [iovec; 64];
-            let n = buf.bytes_vec(&mut bufs);
-            self.io.get_ref().write_bufs(&bufs[..n])
-        };
-        match r {
-            Ok(n) => {
-                buf.advance(n);
-                Poll::Ready(Ok(n))
-            }
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                self.io.clear_write_ready(cx)?;
-                Poll::Pending
-            }
-            Err(e) => Poll::Ready(Err(e)),
-        }
-    }
 }
 
 impl TryFrom<TcpStream> for mio::net::TcpStream {
@@ -741,7 +646,7 @@ impl TryFrom<net::TcpStream> for TcpStream {
 // ===== impl Read / Write =====
 
 impl AsyncRead for TcpStream {
-    unsafe fn prepare_uninitialized_buffer(&self, _: &mut [u8]) -> bool {
+    unsafe fn prepare_uninitialized_buffer(&self, _: &mut [MaybeUninit<u8>]) -> bool {
         false
     }
 
@@ -752,14 +657,6 @@ impl AsyncRead for TcpStream {
     ) -> Poll<io::Result<usize>> {
         self.poll_read_priv(cx, buf)
     }
-
-    fn poll_read_buf<B: BufMut>(
-        self: Pin<&mut Self>,
-        cx: &mut Context<'_>,
-        buf: &mut B,
-    ) -> Poll<io::Result<usize>> {
-        self.poll_read_buf_priv(cx, buf)
-    }
 }
 
 impl AsyncWrite for TcpStream {
@@ -781,14 +678,6 @@ impl AsyncWrite for TcpStream {
         self.shutdown(std::net::Shutdown::Write)?;
         Poll::Ready(Ok(()))
     }
-
-    fn poll_write_buf<B: Buf>(
-        self: Pin<&mut Self>,
-        cx: &mut Context<'_>,
-        buf: &mut B,
-    ) -> Poll<io::Result<usize>> {
-        self.poll_write_buf_priv(cx, buf)
-    }
 }
 
 impl fmt::Debug for TcpStream {
diff --git a/tokio/src/net/unix/split.rs b/tokio/src/net/unix/split.rs
index f9bb7e9a..9b9fa5ee 100644
--- a/tokio/src/net/unix/split.rs
+++ b/tokio/src/net/unix/split.rs
@@ -11,8 +11,8 @@
 use crate::io::{AsyncRead, AsyncWrite};
 use crate::net::UnixStream;
 
-use bytes::{Buf, BufMut};
 use std::io;
+use std::mem::MaybeUninit;
 use std::net::Shutdown;
 use std::pin::Pin;
 use std::task::{Context, Poll};
@@ -30,7 +30,7 @@ pub(crate) fn split(stream: &mut UnixStream) -> (ReadHalf<'_>, WriteHalf<'_>) {
 }
 
 impl AsyncRead for ReadHalf<'_> {
-    unsafe fn prepare_uninitialized_buffer(&self, _: &mut [u8]) -> bool {
+    unsafe fn prepare_uninitialized_buffer(&self, _: &mut [MaybeUninit<u8>]) -> bool {
         false
     }
 
@@ -41,14 +41,6 @@ impl AsyncRead for ReadHalf<'_> {
     ) -> Poll<io::Result<usize>> {
         self.0.poll_read_priv(cx, buf)
     }
-
-    fn poll_read_buf<B: BufMut>(
-        self: Pin<&mut Self>,
-        cx: &mut Context<'_>,
-        buf: &mut B,
-    ) -> Poll<io::Result<usize>> {
-        self.0.poll_read_buf_priv(cx, buf)
-    }
 }
 
 impl AsyncWrite for WriteHalf<'_> {
@@ -67,14 +59,6 @@ impl AsyncWrite for WriteHalf<'_> {
     fn poll_shutdown(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
         self.0.shutdown(Shutdown::Write).into()
     }
-
-    fn poll_write_buf<B: Buf>(
-        self: Pin<&mut Self>,
-        cx: &mut Context<'_>,
-        buf: &mut B,
-    ) -> Poll<io::Result<usize>> {
-        self.0.poll_write_buf_priv(cx, buf)
-    }
 }
 
 impl AsRef<UnixStream> for ReadHalf<'_> {
diff --git a/tokio/src/net/unix/stream.rs b/tokio/src/net/unix/stream.rs
index 7a226994..a430fa17 100644
--- a/tokio/src/net/unix/stream.rs
+++ b/tokio/src/net/unix/stream.rs
@@ -3,11 +3,10 @@ use crate::io::{AsyncRead, AsyncWrite, PollEvented};
 use crate::net::unix::split::{split, ReadHalf, WriteHalf};
 use crate::net::unix::ucred::{self, UCred};
 
-use bytes::{Buf, BufMut};
-use iovec::IoVec;
 use std::convert::TryFrom;
 use std::fmt;
 use std::io::{self, Read, Write};
+use std::mem::MaybeUninit;
 use std::net::Shutdown;
 use std::os::unix::io::{AsRawFd, RawFd};
 use std::os::unix::net::{self, SocketAddr};
@@ -137,7 +136,7 @@ impl TryFrom<net::UnixStream> for UnixStream {
 }
 
 impl AsyncRead for UnixStream {
-    unsafe fn prepare_uninitialized_buffer(&self, _: &mut [u8]) -> bool {
+    unsafe fn prepare_uninitialized_buffer(&self, _: &mut [MaybeUninit<u8>]) -> bool {
         false
     }
 
@@ -148,14 +147,6 @@ impl AsyncRead for UnixStream {
     ) -> Poll<io::Result<usize>> {
         self.poll_read_priv(cx, buf)
     }
-
-    fn poll_read_buf<B: BufMut>(
-        self: Pin<&mut Self>,
-        cx: &mut Context<'_>,
-        buf: &mut B,
-    ) -> Poll<io::Result<usize>> {
-        self.poll_read_buf_priv(cx, buf)
-    }
 }
 
 impl AsyncWrite for UnixStream {
@@ -174,14 +165,6 @@ impl AsyncWrite for UnixStream {
     fn poll_shutdown(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
         Poll::Ready(Ok(()))
     }
-
-    fn poll_write_buf<B: Buf>(
-        self: Pin<&mut Self>,
-        cx: &mut Context<'_>,
-        buf: &mut B,
-    ) -> Poll<io::Result<usize>> {
-        self.poll_write_buf_priv(cx, buf)
-    }
 }
 
 impl UnixStream {
@@ -212,70 +195,6 @@ impl UnixStream {
         }
     }
 
-    pub(crate) fn poll_read_buf_priv<B: BufMut>(
-        &self,
-        cx: &mut Context<'_>,
-        buf: &mut B,
-    ) -> Poll<io::Result<usize>> {
-        ready!(self.io.poll_read_ready(cx, mio::Ready::readable()))?;
-
-        let r = unsafe {
-            // The `IoVec` type can't have a 0-length size, so we create a bunch
-            // of dummy versions on the stack with 1 length which we'll quickly
-            // overwrite.
-            let b1: &mut [u8] = &mut [0];
-            let b2: &mut [u8] = &mut [0];
-            let b3: &mut [u8] = &mut [0];
-            let b4: &mut [u8] = &mut [0];
-            let b5: &mut [u8] = &mut [0];
-            let b6: &mut [u8] = &mut [0];
-            let b7: &mut [u8] = &mut [0];
-            let b8: &mut [u8] = &mut [0];
-            let b9: &mut [u8] = &mut [0];
-            let b10: &mut [u8] = &mut [0];
-            let b11: &mut [u8] = &mut [0];
-            let b12: &mut [u8] = &mut [0];
-            let b13: &mut [u8] = &mut [0];
-            let b14: &mut [u8] = &mut [0];
-            let b15: &mut [u8] = &mut [0];
-            let b16: &mut [u8] = &mut [0];
-            let mut bufs: [&mut IoVec; 16] = [
-                b1.into(),
-                b2.into(),
-                b3.into(),
-                b4.into(),
-                b5.into(),
-                b6.into(),
-                b7.into(),
-                b8.into(),
-                b9.into(),
-                b10.into(),
-                b11.into(),
-                b12.into(),
-                b13.into(),
-                b14.into(),
-                b15.into(),
-                b16.into(),
-            ];
-            let n = buf.bytes_vec_mut(&mut bufs);
-            self.io.get_ref().read_bufs(&mut bufs[..n])
-        };
-
-        match r {
-            Ok(n) => {
-                unsafe {
-                    buf.advance_mut(n);
-                }
-                Poll::Ready(Ok(n))
-            }
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                self.io.clear_read_ready(cx, mio::Ready::readable())?;
-                Poll::Pending
-            }
-            Err(e) => Poll::Ready(Err(e)),
-        }
-    }
-
     pub(crate) fn poll_write_priv(
         &self,
         cx: &mut Context<'_>,
@@ -291,36 +210,6 @@ impl UnixStream {
             x => Poll::Ready(x),
         }
     }
-
-    pub(crate) fn poll_write_buf_priv<B: Buf>(
-        &self,
-        cx: &mut Context<'_>,
-        buf: &mut B,
-    ) -> Poll<io::Result<usize>> {
-        ready!(self.io.poll_write_ready(cx))?;
-
-        let r = {
-            // The `IoVec` type can't have a zero-length size, so create a dummy
-            // version from a 1-length slice which we'll overwrite with the
-            // `bytes_vec` method.
-            static DUMMY: &[u8] = &[0];
-            let iovec = <&IoVec>::from(DUMMY);
-            let mut bufs = [iovec; 64];
-            let n = buf.bytes_vec(&mut bufs);
-            self.io.get_ref().write_bufs(&bufs[..n])
-        };
-        match r {
-            Ok(n) => {
-                buf.advance(n);
-                Poll::Ready(Ok(n))
-            }
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
-                self.io.clear_write_ready(cx)?;
-                Poll::Pending
-            }
-            Err(e) => Poll::Ready(Err(e)),
-        }
-    }
 }
 
 impl fmt::Debug for UnixStream {
diff --git a/tokio/tests/io_async_read.rs b/tokio/tests/io_async_read.rs
index 007e5403..0b9509e1 100644
--- a/tokio/tests/io_async_read.rs
+++ b/tokio/tests/io_async_read.rs
@@ -4,6 +4,7 @@ use tokio_test::{assert_ready_err, assert_ready_ok};
 
 use bytes::{BufMut, BytesMut};
 use std::io;
+use std::mem::MaybeUninit;
 use std::pin::Pin;
 use std::task::{Context, Poll};
 
@@ -75,12 +76,10 @@ fn read_buf_no_capacity() {
         }
     }
 
-    // Can't create BytesMut w/ zero capacity, so fill it up
-    let mut buf = BytesMut::with_capacity(64);
-    buf.put(&[0; 64][..]);
+    let mut buf = [0u8; 0];
 
     task::spawn(Rd).enter(|cx, rd| {
-        let n = assert_ready_ok!(rd.poll_read_buf(cx, &mut buf));
+        let n = assert_ready_ok!(rd.poll_read_buf(cx, &mut &mut buf[..]));
         assert_eq!(0, n);
     });
 }
@@ -116,7 +115,7 @@ fn read_buf_uninitialized_ok() {
     struct Rd;
 
     impl AsyncRead for Rd {
-        unsafe fn prepare_uninitialized_buffer(&self, _: &mut [u8]) -> bool {
+        unsafe fn prepare_uninitialized_buffer(&self, _: &mut [MaybeUninit<u8>]) -> bool {
             false
         }
 
@@ -134,7 +133,8 @@ fn read_buf_uninitialized_ok() {
     let mut buf = BytesMut::with_capacity(64);
 
     unsafe {
-        buf.bytes_mut()[0..11].copy_from_slice(b"hello world");
+        let b: &mut [u8] = std::mem::transmute(buf.bytes_mut());
+        b[0..11].copy_from_slice(b"hello world");
     }
 
     task::spawn(Rd).enter(|cx, rd| {