From b07c1f7f4d46f083725a03f85a3c6cd3447267ae Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Beno=C3=AEt=20du=20Garreau?= <bdgdlm@outlook.com>
Date: Wed, 13 Mar 2024 15:09:39 +0100
Subject: [PATCH 1/3] Improve several `Read` implementations

---
 library/std/src/io/cursor.rs | 21 +++++++++++++++++++++
 library/std/src/io/impls.rs  |  4 +++-
 library/std/src/process.rs   |  4 ++++
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/library/std/src/io/cursor.rs b/library/std/src/io/cursor.rs
index 49dde828c1f..c4e97fc45ff 100644
--- a/library/std/src/io/cursor.rs
+++ b/library/std/src/io/cursor.rs
@@ -364,6 +364,27 @@ where
         self.pos += n as u64;
         Ok(())
     }
+
+    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
+        let content = self.remaining_slice();
+        let len = content.len();
+        buf.try_reserve(len)?;
+        buf.extend_from_slice(content);
+        self.pos += len as u64;
+
+        Ok(len)
+    }
+
+    fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
+        let content =
+            crate::str::from_utf8(self.remaining_slice()).map_err(|_| io::Error::INVALID_UTF8)?;
+        let len = content.len();
+        buf.try_reserve(len)?;
+        buf.push_str(content);
+        self.pos += len as u64;
+
+        Ok(len)
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/library/std/src/io/impls.rs b/library/std/src/io/impls.rs
index dd7e0725176..9f9ee4af5c8 100644
--- a/library/std/src/io/impls.rs
+++ b/library/std/src/io/impls.rs
@@ -329,8 +329,9 @@ impl Read for &[u8] {
     #[inline]
     fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
         let content = str::from_utf8(self).map_err(|_| io::Error::INVALID_UTF8)?;
-        buf.push_str(content);
         let len = self.len();
+        buf.try_reserve(len)?;
+        buf.push_str(content);
         *self = &self[len..];
         Ok(len)
     }
@@ -478,6 +479,7 @@ impl<A: Allocator> Read for VecDeque<u8, A> {
         let len = self.len();
         let content = self.make_contiguous();
         let string = str::from_utf8(content).map_err(|_| io::Error::INVALID_UTF8)?;
+        buf.try_reserve(len)?;
         buf.push_str(string);
         self.clear();
         Ok(len)
diff --git a/library/std/src/process.rs b/library/std/src/process.rs
index 69cc61b30ef..ab282135d1a 100644
--- a/library/std/src/process.rs
+++ b/library/std/src/process.rs
@@ -486,6 +486,10 @@ impl Read for ChildStderr {
     fn is_read_vectored(&self) -> bool {
         self.inner.is_read_vectored()
     }
+
+    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
+        self.inner.read_to_end(buf)
+    }
 }
 
 impl AsInner<AnonPipe> for ChildStderr {

From 23211b638a78bc7b3e69b8e8cdd25abebeb0f7ea Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Beno=C3=AEt=20du=20Garreau?= <bdgdlm@outlook.com>
Date: Thu, 14 Mar 2024 11:20:59 +0100
Subject: [PATCH 2/3] `VecDeque::read_to_string`: avoid making the slices
 contiguous

---
 library/std/src/io/impls.rs | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/library/std/src/io/impls.rs b/library/std/src/io/impls.rs
index 9f9ee4af5c8..46f04c7cd39 100644
--- a/library/std/src/io/impls.rs
+++ b/library/std/src/io/impls.rs
@@ -474,15 +474,8 @@ impl<A: Allocator> Read for VecDeque<u8, A> {
 
     #[inline]
     fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
-        // We have to use a single contiguous slice because the `VecDequeue` might be split in the
-        // middle of an UTF-8 character.
-        let len = self.len();
-        let content = self.make_contiguous();
-        let string = str::from_utf8(content).map_err(|_| io::Error::INVALID_UTF8)?;
-        buf.try_reserve(len)?;
-        buf.push_str(string);
-        self.clear();
-        Ok(len)
+        // SAFETY: We only append to the buffer
+        unsafe { io::append_to_string(buf, |buf| self.read_to_end(buf)) }
     }
 }
 

From 2e3ee230220cc81b159d99d833cba46c667e3321 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Beno=C3=AEt=20du=20Garreau?= <bdgdlm@outlook.com>
Date: Wed, 10 Apr 2024 19:16:31 +0200
Subject: [PATCH 3/3] Avoid panicking branch in `append_to_string`

---
 library/std/src/io/mod.rs | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index 98973a43e1d..450fa43ebea 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -384,7 +384,10 @@ where
 {
     let mut g = Guard { len: buf.len(), buf: buf.as_mut_vec() };
     let ret = f(g.buf);
-    if str::from_utf8(&g.buf[g.len..]).is_err() {
+
+    // SAFETY: the caller promises to only append data to `buf`
+    let appended = g.buf.get_unchecked(g.len..);
+    if str::from_utf8(appended).is_err() {
         ret.and_then(|_| Err(Error::INVALID_UTF8))
     } else {
         g.len = g.buf.len();