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

Tokio will track changes to bytes until 0.5 is released.

26 files changed, 101 insertions, 331 deletions

diff --git a/examples/Cargo.toml b/examples/Cargo.toml
index 782a16cb..ed273590 100644
--- a/examples/Cargo.toml
+++ b/examples/Cargo.toml
@@ -8,7 +8,7 @@ edition = "2018"
 tokio = { version = "=0.2.0-alpha.6", path = "../tokio" }
 tokio-util = { version = "=0.2.0-alpha.6", path = "../tokio-util" }
 
-bytes = "0.4.12"
+bytes = { git = "https://github.com/tokio-rs/bytes" }
 futures = "0.3.0"
 
 [[example]]
diff --git a/tokio-test/Cargo.toml b/tokio-test/Cargo.toml
index 60cb3e50..b1ac4de1 100644
--- a/tokio-test/Cargo.toml
+++ b/tokio-test/Cargo.toml
@@ -22,7 +22,7 @@ categories = ["asynchronous", "testing"]
 [dependencies]
 tokio = { version = "=0.2.0-alpha.6", path = "../tokio", features = ["test-util"] }
 
-bytes = "0.4"
+bytes = { git = "https://github.com/tokio-rs/bytes" }
 futures-core = "0.3.0"
 
 [dev-dependencies]
diff --git a/tokio-tls/src/lib.rs b/tokio-tls/src/lib.rs
index de29b244..3a36ceaa 100644
--- a/tokio-tls/src/lib.rs
+++ b/tokio-tls/src/lib.rs
@@ -35,6 +35,7 @@ use std::fmt;
 use std::future::Future;
 use std::io::{self, Read, Write};
 use std::marker::Unpin;
+use std::mem::MaybeUninit;
 use std::pin::Pin;
 use std::ptr::null_mut;
 use std::task::{Context, Poll};
@@ -182,7 +183,7 @@ impl<S> AsyncRead for TlsStream<S>
 where
     S: AsyncRead + AsyncWrite + Unpin,
 {
-    unsafe fn prepare_uninitialized_buffer(&self, _: &mut [u8]) -> bool {
+    unsafe fn prepare_uninitialized_buffer(&self, _: &mut [MaybeUninit<u8>]) -> bool {
         // Note that this does not forward to `S` because the buffer is
         // unconditionally filled in by OpenSSL, not the actual object `S`.
         // We're decrypting bytes from `S` into the buffer above!
diff --git a/tokio-util/Cargo.toml b/tokio-util/Cargo.toml
index c857c839..8e5542be 100644
--- a/tokio-util/Cargo.toml
+++ b/tokio-util/Cargo.toml
@@ -22,7 +22,7 @@ categories = ["asynchronous"]
 [dependencies]
 tokio = { version = "=0.2.0-alpha.6", path = "../tokio" }
 
-bytes = "0.4.7"
+bytes = { git = "https://github.com/tokio-rs/bytes" }
 futures-core = "0.3.0"
 futures-sink = "0.3.0"
 log = "0.4"
diff --git a/tokio-util/src/codec/framed.rs b/tokio-util/src/codec/framed.rs
index 62403d56..0c5ef9f6 100644
--- a/tokio-util/src/codec/framed.rs
+++ b/tokio-util/src/codec/framed.rs
@@ -11,6 +11,7 @@ use futures_sink::Sink;
 use pin_project_lite::pin_project;
 use std::fmt;
 use std::io::{self, BufRead, Read, Write};
+use std::mem::MaybeUninit;
 use std::pin::Pin;
 use std::task::{Context, Poll};
 
@@ -261,7 +262,7 @@ impl<T: BufRead, U> BufRead for Fuse<T, U> {
 }
 
 impl<T: AsyncRead, U> AsyncRead for Fuse<T, U> {
-    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [u8]) -> bool {
+    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [MaybeUninit<u8>]) -> bool {
         self.io.prepare_uninitialized_buffer(buf)
     }
 
diff --git a/tokio-util/src/codec/framed_write.rs b/tokio-util/src/codec/framed_write.rs
index 4296e993..9aed7ea3 100644
--- a/tokio-util/src/codec/framed_write.rs
+++ b/tokio-util/src/codec/framed_write.rs
@@ -11,6 +11,7 @@ use log::trace;
 use pin_project_lite::pin_project;
 use std::fmt;
 use std::io::{self, BufRead, Read};
+use std::mem::MaybeUninit;
 use std::pin::Pin;
 use std::task::{Context, Poll};
 
@@ -284,7 +285,7 @@ impl<T: BufRead> BufRead for FramedWrite2<T> {
 }
 
 impl<T: AsyncRead> AsyncRead for FramedWrite2<T> {
-    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-util/src/codec/length_delimited.rs b/tokio-util/src/codec/length_delimited.rs
index b36b6aa7..01ba2aec 100644
--- a/tokio-util/src/codec/length_delimited.rs
+++ b/tokio-util/src/codec/length_delimited.rs
@@ -345,7 +345,7 @@ use crate::codec::{Decoder, Encoder, Framed, FramedRead, FramedWrite};
 
 use tokio::io::{AsyncRead, AsyncWrite};
 
-use bytes::{Buf, BufMut, Bytes, BytesMut, IntoBuf};
+use bytes::{Buf, BufMut, Bytes, BytesMut};
 use std::error::Error as StdError;
 use std::io::{self, Cursor};
 use std::{cmp, fmt};
@@ -457,7 +457,7 @@ impl LengthDelimitedCodec {
 
             // match endianess
             let n = if self.builder.length_field_is_big_endian {
-                src.get_uint_be(field_len)
+                src.get_uint(field_len)
             } else {
                 src.get_uint_le(field_len)
             };
@@ -551,7 +551,7 @@ impl Encoder for LengthDelimitedCodec {
     type Error = io::Error;
 
     fn encode(&mut self, data: Bytes, dst: &mut BytesMut) -> Result<(), io::Error> {
-        let n = (&data).into_buf().remaining();
+        let n = (&data).remaining();
 
         if n > self.builder.max_frame_len {
             return Err(io::Error::new(
@@ -579,7 +579,7 @@ impl Encoder for LengthDelimitedCodec {
         dst.reserve(self.builder.length_field_len + n);
 
         if self.builder.length_field_is_big_endian {
-            dst.put_uint_be(n as u64, self.builder.length_field_len);
+            dst.put_uint(n as u64, self.builder.length_field_len);
         } else {
             dst.put_uint_le(n as u64, self.builder.length_field_len);
         }
diff --git a/tokio-util/src/codec/lines_codec.rs b/tokio-util/src/codec/lines_codec.rs
index bca69723..8029956f 100644
--- a/tokio-util/src/codec/lines_codec.rs
+++ b/tokio-util/src/codec/lines_codec.rs
@@ -1,7 +1,7 @@
 use crate::codec::decoder::Decoder;
 use crate::codec::encoder::Encoder;
 
-use bytes::{BufMut, BytesMut};
+use bytes::{Buf, BufMut, BytesMut};
 use std::{cmp, fmt, io, str, usize};
 
 /// A simple `Codec` implementation that splits up data into lines.
@@ -168,7 +168,7 @@ impl Decoder for LinesCodec {
                 if buf.is_empty() || buf == &b"\r"[..] {
                     None
                 } else {
-                    let line = buf.take();
+                    let line = buf.split_to(buf.len());
                     let line = without_carriage_return(&line);
                     let line = utf8(line)?;
                     self.next_index = 0;
@@ -185,7 +185,7 @@ impl Encoder for LinesCodec {
 
     fn encode(&mut self, line: String, buf: &mut BytesMut) -> Result<(), LinesCodecError> {
         buf.reserve(line.len() + 1);
-        buf.put(line);
+        buf.put(line.as_bytes());
         buf.put_u8(b'\n');
         Ok(())
     }
diff --git a/tokio-util/src/udp/frame.rs b/tokio-util/src/udp/frame.rs
index 4a8c3c0b..d37b20cd 100644
--- a/tokio-util/src/udp/frame.rs
+++ b/tokio-util/src/udp/frame.rs
@@ -47,7 +47,14 @@ impl<C: Decoder + Unpin> Stream for UdpFramed<C> {
 
         let (_n, addr) = unsafe {
             // Read into the buffer without having to initialize the memory.
-            let res = ready!(Pin::new(&mut pin.socket).poll_recv_from(cx, pin.rd.bytes_mut()));
+            //
+            // safety: we know tokio::net::UdpSocket never reads from the memory
+            // during a recv
+            let res = {
+                let bytes = &mut *(pin.rd.bytes_mut() as *mut _ as *mut [u8]);
+                ready!(Pin::new(&mut pin.socket).poll_recv_from(cx, bytes))
+            };
+
             let (n, addr) = res?;
             pin.rd.advance_mut(n);
             (n, addr)
diff --git a/tokio-util/tests/codecs.rs b/tokio-util/tests/codecs.rs
index 4709854a..d1212866 100644
--- a/tokio-util/tests/codecs.rs
+++ b/tokio-util/tests/codecs.rs
@@ -45,14 +45,14 @@ fn lines_decoder() {
     let mut codec = LinesCodec::new();
     let buf = &mut BytesMut::new();
     buf.reserve(200);
-    buf.put("line 1\nline 2\r\nline 3\n\r\n\r");
+    buf.put_slice(b"line 1\nline 2\r\nline 3\n\r\n\r");
     assert_eq!("line 1", codec.decode(buf).unwrap().unwrap());
     assert_eq!("line 2", codec.decode(buf).unwrap().unwrap());
     assert_eq!("line 3", codec.decode(buf).unwrap().unwrap());
     assert_eq!("", codec.decode(buf).unwrap().unwrap());
     assert_eq!(None, codec.decode(buf).unwrap());
     assert_eq!(None, codec.decode_eof(buf).unwrap());
-    buf.put("k");
+    buf.put_slice(b"k");
     assert_eq!(None, codec.decode(buf).unwrap());
     assert_eq!("\rk", codec.decode_eof(buf).unwrap().unwrap());
     assert_eq!(None, codec.decode(buf).unwrap());
@@ -67,7 +67,7 @@ fn lines_decoder_max_length() {
     let buf = &mut BytesMut::new();
 
     buf.reserve(200);
-    buf.put("line 1 is too long\nline 2\nline 3\r\nline 4\n\r\n\r");
+    buf.put_slice(b"line 1 is too long\nline 2\nline 3\r\nline 4\n\r\n\r");
 
     assert!(codec.decode(buf).is_err());
 
@@ -102,7 +102,7 @@ fn lines_decoder_max_length() {
 
     assert_eq!(None, codec.decode(buf).unwrap());
     assert_eq!(None, codec.decode_eof(buf).unwrap());
-    buf.put("k");
+    buf.put_slice(b"k");
     assert_eq!(None, codec.decode(buf).unwrap());
 
     let line = codec.decode_eof(buf).unwrap().unwrap();
@@ -119,7 +119,7 @@ fn lines_decoder_max_length() {
 
     // Line that's one character too long. This could cause an out of bounds
     // error if we peek at the next characters using slice indexing.
-    buf.put("aaabbbc");
+    buf.put_slice(b"aaabbbc");
     assert!(codec.decode(buf).is_err());
 }
 
@@ -131,16 +131,16 @@ fn lines_decoder_max_length_underrun() {
     let buf = &mut BytesMut::new();
 
     buf.reserve(200);
-    buf.put("line ");
+    buf.put_slice(b"line ");
     assert_eq!(None, codec.decode(buf).unwrap());
-    buf.put("too l");
+    buf.put_slice(b"too l");
     assert!(codec.decode(buf).is_err());
-    buf.put("ong\n");
+    buf.put_slice(b"ong\n");
     assert_eq!(None, codec.decode(buf).unwrap());
 
-    buf.put("line 2");
+    buf.put_slice(b"line 2");
     assert_eq!(None, codec.decode(buf).unwrap());
-    buf.put("\n");
+    buf.put_slice(b"\n");
     assert_eq!("line 2", codec.decode(buf).unwrap().unwrap());
 }
 
@@ -152,11 +152,11 @@ fn lines_decoder_max_length_bursts() {
     let buf = &mut BytesMut::new();
 
     buf.reserve(200);
-    buf.put("line ");
+    buf.put_slice(b"line ");
     assert_eq!(None, codec.decode(buf).unwrap());
-    buf.put("too l");
+    buf.put_slice(b"too l");
     assert_eq!(None, codec.decode(buf).unwrap());
-    buf.put("ong\n");
+    buf.put_slice(b"ong\n");
     assert!(codec.decode(buf).is_err());
 }
 
@@ -168,9 +168,9 @@ fn lines_decoder_max_length_big_burst() {
     let buf = &mut BytesMut::new();
 
     buf.reserve(200);
-    buf.put("line ");
+    buf.put_slice(b"line ");
     assert_eq!(None, codec.decode(buf).unwrap());
-    buf.put("too long!\n");
+    buf.put_slice(b"too long!\n");
     assert!(codec.decode(buf).is_err());
 }
 
@@ -182,10 +182,10 @@ fn lines_decoder_max_length_newline_between_decodes() {
     let buf = &mut BytesMut::new();
 
     buf.reserve(200);
-    buf.put("hello");
+    buf.put_slice(b"hello");
     assert_eq!(None, codec.decode(buf).unwrap());
 
-    buf.put("\nworld");
+    buf.put_slice(b"\nworld");
     assert_eq!("hello", codec.decode(buf).unwrap().unwrap());
 }
 
@@ -198,9 +198,9 @@ fn lines_decoder_discard_repeat() {
     let buf = &mut BytesMut::new();
 
     buf.reserve(200);
-    buf.put("aa");
+    buf.put_slice(b"aa");
     assert!(codec.decode(buf).is_err());
-    buf.put("a");
+    buf.put_slice(b"a");
     assert!(codec.decode(buf).is_err());
 }
 
diff --git a/tokio-util/tests/framed.rs b/tokio-util/tests/framed.rs
index 25ddf86a..b98df736 100644
--- a/tokio-util/tests/framed.rs
+++ b/tokio-util/tests/framed.rs
@@ -4,7 +4,7 @@ use tokio::prelude::*;
 use tokio_test::assert_ok;
 use tokio_util::codec::{Decoder, Encoder, Framed, FramedParts};
 
-use bytes::{Buf, BufMut, BytesMut, IntoBuf};
+use bytes::{Buf, BufMut, BytesMut};
 use futures::StreamExt;
 use std::io::{self, Read};
 use std::pin::Pin;
@@ -24,7 +24,7 @@ impl Decoder for U32Codec {
             return Ok(None);
         }
 
-        let n = buf.split_to(4).into_buf().get_u32_be();
+        let n = buf.split_to(4).get_u32();
         Ok(Some(n))
     }
 }
@@ -36,7 +36,7 @@ impl Encoder for U32Codec {
     fn encode(&mut self, item: u32, dst: &mut BytesMut) -> io::Result<()> {
         // Reserve space
         dst.reserve(4);
-        dst.put_u32_be(item);
+        dst.put_u32(item);
         Ok(())
     }
 }
@@ -66,7 +66,7 @@ impl AsyncRead for DontReadIntoThis {
 #[tokio::test]
 async fn can_read_from_existing_buf() {
     let mut parts = FramedParts::new(DontReadIntoThis, U32Codec);
-    parts.read_buf = vec![0, 0, 0, 42].into();
+    parts.read_buf = BytesMut::from(&[0, 0, 0, 42][..]);
 
     let mut framed = Framed::from_parts(parts);
     let num = assert_ok!(framed.next().await.unwrap());
@@ -77,7 +77,7 @@ async fn can_read_from_existing_buf() {
 #[test]
 fn external_buf_grows_to_init() {
     let mut parts = FramedParts::new(DontReadIntoThis, U32Codec);
-    parts.read_buf = vec![0, 0, 0, 42].into();
+    parts.read_buf = BytesMut::from(&[0, 0, 0, 42][..]);
 
     let framed = Framed::from_parts(parts);
     let FramedParts { read_buf, .. } = framed.into_parts();
@@ -88,7 +88,7 @@ fn external_buf_grows_to_init() {
 #[test]
 fn external_buf_does_not_shrink() {
     let mut parts = FramedParts::new(DontReadIntoThis, U32Codec);
-    parts.read_buf = vec![0; INITIAL_CAPACITY * 2].into();
+    parts.read_buf = BytesMut::from(&vec![0; INITIAL_CAPACITY * 2][..]);
 
     let framed = Framed::from_parts(parts);
     let FramedParts { read_buf, .. } = framed.into_parts();
diff --git a/tokio-util/tests/framed_read.rs b/tokio-util/tests/framed_read.rs
index 9aa644aa..06caa0a4 100644
--- a/tokio-util/tests/framed_read.rs
+++ b/tokio-util/tests/framed_read.rs
@@ -5,7 +5,7 @@ use tokio_test::assert_ready;
 use tokio_test::task;
 use tokio_util::codec::{Decoder, FramedRead};
 
-use bytes::{Buf, BytesMut, IntoBuf};
+use bytes::{Buf, BytesMut};
 use futures::Stream;
 use std::collections::VecDeque;
 use std::io;
@@ -45,7 +45,7 @@ impl Decoder for U32Decoder {
             return Ok(None);
         }
 
-        let n = buf.split_to(4).into_buf().get_u32_be();
+        let n = buf.split_to(4).get_u32();
         Ok(Some(n))
     }
 }
diff --git a/tokio-util/tests/framed_write.rs b/tokio-util/tests/framed_write.rs
index 9d760766..706e6792 100644
--- a/tokio-util/tests/framed_write.rs
+++ b/tokio-util/tests/framed_write.rs
@@ -35,7 +35,7 @@ impl Encoder for U32Encoder {
     fn encode(&mut self, item: u32, dst: &mut BytesMut) -> io::Result<()> {
         // Reserve space
         dst.reserve(4);
-        dst.put_u32_be(item);
+        dst.put_u32(item);
         Ok(())
     }
 }
@@ -78,7 +78,7 @@ fn write_hits_backpressure() {
 
     for i in 0..=ITER {
         let mut b = BytesMut::with_capacity(4);
-        b.put_u32_be(i as u32);
+        b.put_u32(i as u32);
 
         // Append to the end
         match mock.calls.back_mut().unwrap() {
diff --git a/tokio-util/tests/udp.rs b/tokio-util/tests/udp.rs
index be05dbc4..af8002bd 100644
--- a/tokio-util/tests/udp.rs
+++ b/tokio-util/tests/udp.rs
@@ -73,7 +73,7 @@ impl Encoder for ByteCodec {
 
     fn encode(&mut self, data: Vec<u8>, buf: &mut BytesMut) -> Result<(), io::Error> {
         buf.reserve(data.len());
-        buf.put(data);
+        buf.put_slice(&data);
         Ok(())
     }
 }
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>> {
-