Implement read_buf for a few more types

Implement read_buf for TcpStream, Stdin, StdinLock, ChildStdout,
ChildStderr (and internally for AnonPipe, Handle, Socket), so
that it skips buffer initialization.

The other provided methods like read_to_string and read_to_end are
implemented in terms of read_buf and so benefit from the optimization
as well.

This commit also implements read_vectored and is_read_vectored where
applicable.

1 files changed, 27 insertions, 1 deletions

diff --git a/library/std/src/net/tcp/tests.rs b/library/std/src/net/tcp/tests.rs
index e019bc0b67a..7a3c66e4504 100644
--- a/library/std/src/net/tcp/tests.rs
+++ b/library/std/src/net/tcp/tests.rs
@@ -1,6 +1,7 @@
 use crate::fmt;
 use crate::io::prelude::*;
-use crate::io::{ErrorKind, IoSlice, IoSliceMut};
+use crate::io::{BorrowedBuf, ErrorKind, IoSlice, IoSliceMut};
+use crate::mem::MaybeUninit;
 use crate::net::test::{next_test_ip4, next_test_ip6};
 use crate::net::*;
 use crate::sync::mpsc::channel;
@@ -280,6 +281,31 @@ fn partial_read() {
 }
 
 #[test]
+fn read_buf() {
+    each_ip(&mut |addr| {
+        let srv = t!(TcpListener::bind(&addr));
+        let t = thread::spawn(move || {
+            let mut s = t!(TcpStream::connect(&addr));
+            s.write_all(&[1, 2, 3, 4]).unwrap();
+        });
+
+        let mut s = t!(srv.accept()).0;
+        let mut buf: [MaybeUninit<u8>; 128] = MaybeUninit::uninit_array();
+        let mut buf = BorrowedBuf::from(buf.as_mut_slice());
+        t!(s.read_buf(buf.unfilled()));
+        assert_eq!(buf.filled(), &[1, 2, 3, 4]);
+
+        // FIXME: sgx uses default_read_buf that initializes the buffer.
+        if cfg!(not(target_env = "sgx")) {
+            // TcpStream::read_buf should omit buffer initialization.
+            assert_eq!(buf.init_len(), 4);
+        }
+
+        t.join().ok().expect("thread panicked");
+    })
+}
+
+#[test]
 fn read_vectored() {
     each_ip(&mut |addr| {
         let srv = t!(TcpListener::bind(&addr));