From 84542d22a71cb486b0f79cf3bfd7a264b688030c Mon Sep 17 00:00:00 2001
From: klensy <klensy@users.noreply.github.com>
Date: Sun, 28 Mar 2021 19:34:38 +0300
Subject: [PATCH 1/2] ffi::c_str added tests for empty strings

---
 library/std/src/ffi/c_str/tests.rs | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/library/std/src/ffi/c_str/tests.rs b/library/std/src/ffi/c_str/tests.rs
index 4dff3df63a8b6..4f7ba9ad43756 100644
--- a/library/std/src/ffi/c_str/tests.rs
+++ b/library/std/src/ffi/c_str/tests.rs
@@ -193,3 +193,19 @@ fn cstr_index_from_empty() {
     let cstr = CStr::from_bytes_with_nul(original).unwrap();
     let _ = &cstr[original.len()..];
 }
+
+#[test]
+fn c_string_from_empty_string() {
+    let original = "";
+    let cstring = CString::new(original).unwrap();
+    assert_eq!(original.as_bytes(), cstring.as_bytes());
+    assert_eq!([b'\0'], cstring.as_bytes_with_nul());
+}
+
+#[test]
+fn c_str_from_empty_string() {
+    let original = b"\0";
+    let cstr = CStr::from_bytes_with_nul(original).unwrap();
+    assert_eq!([] as [u8; 0], cstr.to_bytes());
+    assert_eq!([b'\0'], cstr.to_bytes_with_nul());
+}

From a0ff4612f21e312362a3ffbec0a104b9937d700b Mon Sep 17 00:00:00 2001
From: klensy <klensy@users.noreply.github.com>
Date: Sun, 28 Mar 2021 19:55:09 +0300
Subject: [PATCH 2/2] ffi::c_str smaller as_bytes

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

diff --git a/library/std/src/ffi/c_str.rs b/library/std/src/ffi/c_str.rs
index 687ed61b95961..ed4950c57a627 100644
--- a/library/std/src/ffi/c_str.rs
+++ b/library/std/src/ffi/c_str.rs
@@ -613,7 +613,8 @@ impl CString {
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn as_bytes(&self) -> &[u8] {
-        &self.inner[..self.inner.len() - 1]
+        // SAFETY: CString has a length at least 1
+        unsafe { self.inner.get_unchecked(..self.inner.len() - 1) }
     }
 
     /// Equivalent to [`CString::as_bytes()`] except that the
@@ -1322,7 +1323,8 @@ impl CStr {
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn to_bytes(&self) -> &[u8] {
         let bytes = self.to_bytes_with_nul();
-        &bytes[..bytes.len() - 1]
+        // SAFETY: to_bytes_with_nul returns slice with length at least 1
+        unsafe { bytes.get_unchecked(..bytes.len() - 1) }
     }
 
     /// Converts this C string to a byte slice containing the trailing 0 byte.