From ca7eef71853e1e83bcaa663ebed2aab713a1e167 Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <n.nethercote@gmail.com>
Date: Thu, 12 Oct 2023 10:49:32 +1100
Subject: [PATCH 1/3] Inline `Bytes::next` and `Bytes::size_hint`.

This greatly increases its speed.
---
 library/std/src/io/mod.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index c93bf0202523a..547c184a5c280 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -2778,6 +2778,7 @@ pub struct Bytes<R> {
 impl<R: Read> Iterator for Bytes<R> {
     type Item = Result<u8>;
 
+    #[inline]
     fn next(&mut self) -> Option<Result<u8>> {
         let mut byte = 0;
         loop {
@@ -2790,6 +2791,7 @@ impl<R: Read> Iterator for Bytes<R> {
         }
     }
 
+    #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
         SizeHint::size_hint(&self.inner)
     }

From 69ad06fad505b39158d5c7e576ffbe2bcc6a7c9e Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <n.nethercote@gmail.com>
Date: Thu, 12 Oct 2023 11:25:29 +1100
Subject: [PATCH 2/3] Add `Bytes::byte` field.

We can reuse this in `next`, avoiding the need to zero-initialize a
local variable every time, for a small speed win.
---
 library/std/src/io/mod.rs | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index 547c184a5c280..ce36ba7ca9e3f 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -1000,7 +1000,7 @@ pub trait Read {
     where
         Self: Sized,
     {
-        Bytes { inner: self }
+        Bytes { inner: self, byte: 0 }
     }
 
     /// Creates an adapter which will chain this stream with another.
@@ -2772,6 +2772,7 @@ impl<T> SizeHint for Take<T> {
 #[derive(Debug)]
 pub struct Bytes<R> {
     inner: R,
+    byte: u8,
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -2780,11 +2781,10 @@ impl<R: Read> Iterator for Bytes<R> {
 
     #[inline]
     fn next(&mut self) -> Option<Result<u8>> {
-        let mut byte = 0;
         loop {
-            return match self.inner.read(slice::from_mut(&mut byte)) {
+            return match self.inner.read(slice::from_mut(&mut self.byte)) {
                 Ok(0) => None,
-                Ok(..) => Some(Ok(byte)),
+                Ok(..) => Some(Ok(self.byte)),
                 Err(ref e) if e.is_interrupted() => continue,
                 Err(e) => Some(Err(e)),
             };

From ed2a5871bb41e58b466818109bdae8eb04ea6fb1 Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <n.nethercote@gmail.com>
Date: Thu, 12 Oct 2023 21:50:28 +1100
Subject: [PATCH 3/3] Use `read_exact` in `Bytes::next`.

This is much faster.
---
 library/std/src/io/mod.rs | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index ce36ba7ca9e3f..3c5fa84b87f5b 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -2781,13 +2781,10 @@ impl<R: Read> Iterator for Bytes<R> {
 
     #[inline]
     fn next(&mut self) -> Option<Result<u8>> {
-        loop {
-            return match self.inner.read(slice::from_mut(&mut self.byte)) {
-                Ok(0) => None,
-                Ok(..) => Some(Ok(self.byte)),
-                Err(ref e) if e.is_interrupted() => continue,
-                Err(e) => Some(Err(e)),
-            };
+        match self.inner.read_exact(slice::from_mut(&mut self.byte)) {
+            Ok(()) => Some(Ok(self.byte)),
+            Err(e) if e.kind() == ErrorKind::UnexpectedEof => None,
+            Err(e) => Some(Err(e)),
         }
     }