Revert "remove unnecessary use of unsafe in read_from_io"

This reverts commit da237611cb.

src/server/utils.rs

@@ -1,5 +1,5 @@
 use bytes::{BufMut, BytesMut};
-use futures::Poll;
+use futures::{Async, Poll};
 use std::io;
 
 use super::IoStream;
@@ -10,8 +10,22 @@ const HW_BUFFER_SIZE: usize = 32_768;
 pub fn read_from_io<T: IoStream>(
     io: &mut T, buf: &mut BytesMut,
 ) -> Poll<usize, io::Error> {
-    if buf.remaining_mut() < LW_BUFFER_SIZE {
-        buf.reserve(HW_BUFFER_SIZE);
+    unsafe {
+        if buf.remaining_mut() < LW_BUFFER_SIZE {
+            buf.reserve(HW_BUFFER_SIZE);
+        }
+        match io.read(buf.bytes_mut()) {
+            Ok(n) => {
+                buf.advance_mut(n);
+                Ok(Async::Ready(n))
+            }
+            Err(e) => {
+                if e.kind() == io::ErrorKind::WouldBlock {
+                    Ok(Async::NotReady)
+                } else {
+                    Err(e)
+                }
+            }
+        }
     }
-    io.read_buf(buf)
 }