io: remove poll_{read,write}_buf from traits (#2882)

These functions have object safety issues. It also has been decided to
avoid vectored operations on the I/O traits. A later PR will bring back
vectored operations on specific types that support them.

Refs: #2879, #2716

tokio-util/src/codec/framed_impl.rs

@@ -118,6 +118,8 @@ where
     type Item = Result<U::Item, U::Error>;
 
     fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        use crate::util::poll_read_buf;
+
         let mut pinned = self.project();
         let state: &mut ReadFrame = pinned.state.borrow_mut();
         loop {
@@ -148,7 +150,7 @@ where
             // got room for at least one byte to read to ensure that we don't
             // get a spurious 0 that looks like EOF
             state.buffer.reserve(1);
-            let bytect = match pinned.inner.as_mut().poll_read_buf(cx, &mut state.buffer)? {
+            let bytect = match poll_read_buf(cx, pinned.inner.as_mut(), &mut state.buffer)? {
                 Poll::Ready(ct) => ct,
                 Poll::Pending => return Poll::Pending,
             };

tokio-util/src/io/reader_stream.rs

@@ -70,6 +70,8 @@ impl<R: AsyncRead> ReaderStream<R> {
 impl<R: AsyncRead> Stream for ReaderStream<R> {
     type Item = std::io::Result<Bytes>;
     fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        use crate::util::poll_read_buf;
+
         let mut this = self.as_mut().project();
 
         let reader = match this.reader.as_pin_mut() {
@@ -81,7 +83,7 @@ impl<R: AsyncRead> Stream for ReaderStream<R> {
             this.buf.reserve(CAPACITY);
         }
 
-        match reader.poll_read_buf(cx, &mut this.buf) {
+        match poll_read_buf(cx, reader, &mut this.buf) {
             Poll::Pending => Poll::Pending,
             Poll::Ready(Err(err)) => {
                 self.project().reader.set(None);

tokio-util/src/io/stream_reader.rs

@@ -1,4 +1,4 @@
-use bytes::{Buf, BufMut};
+use bytes::Buf;
 use futures_core::stream::Stream;
 use pin_project_lite::pin_project;
 use std::io;
@@ -119,29 +119,6 @@ where
         self.consume(len);
         Poll::Ready(Ok(()))
     }
-    fn poll_read_buf<BM: BufMut>(
-        mut self: Pin<&mut Self>,
-        cx: &mut Context<'_>,
-        buf: &mut BM,
-    ) -> Poll<io::Result<usize>>
-    where
-        Self: Sized,
-    {
-        if !buf.has_remaining_mut() {
-            return Poll::Ready(Ok(0));
-        }
-
-        let inner_buf = match self.as_mut().poll_fill_buf(cx) {
-            Poll::Ready(Ok(buf)) => buf,
-            Poll::Ready(Err(err)) => return Poll::Ready(Err(err)),
-            Poll::Pending => return Poll::Pending,
-        };
-        let len = std::cmp::min(inner_buf.len(), buf.remaining_mut());
-        buf.put_slice(&inner_buf[..len]);
-
-        self.consume(len);
-        Poll::Ready(Ok(len))
-    }
 }
 
 impl<S, B, E> AsyncBufRead for StreamReader<S, B>

tokio-util/src/lib.rs

@@ -52,3 +52,37 @@ pub mod context;
 pub mod sync;
 
 pub mod either;
+
+#[cfg(any(feature = "io", feature = "codec"))]
+mod util {
+    use tokio::io::{AsyncRead, ReadBuf};
+
+    use bytes::BufMut;
+    use futures_core::ready;
+    use std::io;
+    use std::pin::Pin;
+    use std::task::{Context, Poll};
+
+    pub(crate) fn poll_read_buf<T: AsyncRead>(
+        cx: &mut Context<'_>,
+        io: Pin<&mut T>,
+        buf: &mut impl BufMut,
+    ) -> Poll<io::Result<usize>> {
+        if !buf.has_remaining_mut() {
+            return Poll::Ready(Ok(0));
+        }
+
+        let orig = buf.bytes_mut().as_ptr() as *const u8;
+        let mut b = ReadBuf::uninit(buf.bytes_mut());
+
+        ready!(io.poll_read(cx, &mut b))?;
+        let n = b.filled().len();
+
+        // Safety: we can assume `n` bytes were read, since they are in`filled`.
+        assert_eq!(orig, b.filled().as_ptr());
+        unsafe {
+            buf.advance_mut(n);
+        }
+        Poll::Ready(Ok(n))
+    }
+}