refactor: remove leftover from read_initializer feature (#2949)

Author: paolobarbolini

futures-util/src/io/mod.rs

@@ -21,7 +21,7 @@
 use crate::compat::Compat;
 use crate::future::assert_future;
 use crate::stream::assert_stream;
-use std::{pin::Pin, ptr, string::String, vec::Vec};
+use std::{pin::Pin, string::String, vec::Vec};
 
 // Re-export some types from `std::io` so that users don't have to deal
 // with conflicts when `use`ing `futures::io` and `std::io`.
@@ -34,14 +34,6 @@ pub use futures_io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite};
 // https://github.com/rust-lang/rust/blob/master/src/libstd/sys_common/io.rs#L1
 const DEFAULT_BUF_SIZE: usize = 8 * 1024;
 
-/// Initializes a buffer if necessary.
-///
-/// A buffer is currently always initialized.
-#[inline]
-unsafe fn initialize<R: AsyncRead>(_reader: &R, buf: &mut [u8]) {
-    unsafe { ptr::write_bytes(buf.as_mut_ptr(), 0, buf.len()) }
-}
-
 mod allow_std;
 pub use self::allow_std::AllowStdIo;
 

futures-util/src/io/read_to_end.rs

@@ -3,6 +3,7 @@ use futures_core::ready;
 use futures_core::task::{Context, Poll};
 use futures_io::AsyncRead;
 use std::io;
+use std::iter;
 use std::pin::Pin;
 use std::vec::Vec;
 
@@ -55,12 +56,10 @@ pub(super) fn read_to_end_internal<R: AsyncRead + ?Sized>(
     let mut g = Guard { len: buf.len(), buf };
     loop {
         if g.len == g.buf.len() {
-            unsafe {
-                g.buf.reserve(32);
-                let capacity = g.buf.capacity();
-                g.buf.set_len(capacity);
-                super::initialize(&rd, &mut g.buf[g.len..]);
-            }
+            g.buf.reserve(32);
+            let spare_capacity = g.buf.capacity() - g.buf.len();
+            // FIXME: switch to `Vec::resize` once rust-lang/rust#120050 is fixed
+            g.buf.extend(iter::repeat(0).take(spare_capacity));
         }
 
         let buf = &mut g.buf[g.len..];