From eae615dfdd9222a49182e59cc15bd47da1d536b6 Mon Sep 17 00:00:00 2001
From: yukang <moorekang@gmail.com>
Date: Sun, 8 Jan 2023 05:02:04 +0800
Subject: [PATCH 1/2] Remove unnecessary lseek syscall when using std::fs::read

---
 library/std/src/fs.rs | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/library/std/src/fs.rs b/library/std/src/fs.rs
index f357d505fe8..6ddd5c28cc2 100644
--- a/library/std/src/fs.rs
+++ b/library/std/src/fs.rs
@@ -250,7 +250,9 @@ pub fn read<P: AsRef<Path>>(path: P) -> io::Result<Vec<u8>> {
     fn inner(path: &Path) -> io::Result<Vec<u8>> {
         let mut file = File::open(path)?;
         let mut bytes = Vec::new();
-        file.read_to_end(&mut bytes)?;
+        let size = file.metadata().map(|m| m.len()).unwrap_or(0);
+        bytes.reserve(size as usize);
+        io::default_read_to_end(&mut file, &mut bytes)?;
         Ok(bytes)
     }
     inner(path.as_ref())
@@ -289,7 +291,9 @@ pub fn read_to_string<P: AsRef<Path>>(path: P) -> io::Result<String> {
     fn inner(path: &Path) -> io::Result<String> {
         let mut file = File::open(path)?;
         let mut string = String::new();
-        file.read_to_string(&mut string)?;
+        let size = file.metadata().map(|m| m.len()).unwrap_or(0);
+        string.reserve(size as usize);
+        io::default_read_to_string(&mut file, &mut string)?;
         Ok(string)
     }
     inner(path.as_ref())

From f7bc68bb4edd1974f7c4aa6113902132429c00e8 Mon Sep 17 00:00:00 2001
From: yukang <moorekang@gmail.com>
Date: Wed, 11 Jan 2023 00:19:27 +0800
Subject: [PATCH 2/2] use with_capacity in read read_to_string

---
 library/std/src/fs.rs | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/library/std/src/fs.rs b/library/std/src/fs.rs
index 6ddd5c28cc2..5c5ef0b1125 100644
--- a/library/std/src/fs.rs
+++ b/library/std/src/fs.rs
@@ -249,9 +249,8 @@ pub struct DirBuilder {
 pub fn read<P: AsRef<Path>>(path: P) -> io::Result<Vec<u8>> {
     fn inner(path: &Path) -> io::Result<Vec<u8>> {
         let mut file = File::open(path)?;
-        let mut bytes = Vec::new();
         let size = file.metadata().map(|m| m.len()).unwrap_or(0);
-        bytes.reserve(size as usize);
+        let mut bytes = Vec::with_capacity(size as usize);
         io::default_read_to_end(&mut file, &mut bytes)?;
         Ok(bytes)
     }
@@ -290,9 +289,8 @@ pub fn read<P: AsRef<Path>>(path: P) -> io::Result<Vec<u8>> {
 pub fn read_to_string<P: AsRef<Path>>(path: P) -> io::Result<String> {
     fn inner(path: &Path) -> io::Result<String> {
         let mut file = File::open(path)?;
-        let mut string = String::new();
         let size = file.metadata().map(|m| m.len()).unwrap_or(0);
-        string.reserve(size as usize);
+        let mut string = String::with_capacity(size as usize);
         io::default_read_to_string(&mut file, &mut string)?;
         Ok(string)
     }