Merge pull request torvalds#533 from mdaverde/ml/cstr

rust: add `to_str` and `as_str_unchecked` to `CStr`

rust/kernel/str.rs

@@ -167,6 +167,46 @@ impl CStr {
     pub const fn as_bytes_with_nul(&self) -> &[u8] {
         &self.0
     }
+
+    /// Yields a [`&str`] slice if the [`CStr`] contains valid UTF-8.
+    ///
+    /// If the contents of the [`CStr`] are valid UTF-8 data, this
+    /// function will return the corresponding [`&str`] slice. Otherwise,
+    /// it will return an error with details of where UTF-8 validation failed.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use kernel::str::CStr;
+    /// let cstr = CStr::from_bytes_with_nul(b"foo\0").unwrap();
+    /// assert_eq!(cstr.to_str(), Ok("foo"));
+    /// ```
+    #[inline]
+    pub fn to_str(&self) -> Result<&str, core::str::Utf8Error> {
+        core::str::from_utf8(self.as_bytes())
+    }
+
+    /// Unsafely convert this [`CStr`] into a [`&str`], without checking for
+    /// valid UTF-8.
+    ///
+    /// # Safety
+    ///
+    /// The contents must be valid UTF-8.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use kernel::c_str;
+    /// # use kernel::str::CStr;
+    /// // SAFETY: String literals are guaranteed to be valid UTF-8
+    /// // by the Rust compiler.
+    /// let bar = c_str!("ツ");
+    /// assert_eq!(unsafe { bar.as_str_unchecked() }, "ツ");
+    /// ```
+    #[inline]
+    pub unsafe fn as_str_unchecked(&self) -> &str {
+        unsafe { core::str::from_utf8_unchecked(self.as_bytes()) }
+    }
 }
 
 impl AsRef<BStr> for CStr {
@@ -251,3 +291,32 @@ macro_rules! c_str {
         C
     }};
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_cstr_to_str() {
+        let good_bytes = b"\xf0\x9f\xa6\x80\0";
+        let checked_cstr = CStr::from_bytes_with_nul(good_bytes).unwrap();
+        let checked_str = checked_cstr.to_str().unwrap();
+        assert_eq!(checked_str, "🦀");
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_cstr_to_str_panic() {
+        let bad_bytes = b"\xc3\x28\0";
+        let checked_cstr = CStr::from_bytes_with_nul(bad_bytes).unwrap();
+        checked_cstr.to_str().unwrap();
+    }
+
+    #[test]
+    fn test_cstr_as_str_unchecked() {
+        let good_bytes = b"\xf0\x9f\x90\xA7\0";
+        let checked_cstr = CStr::from_bytes_with_nul(good_bytes).unwrap();
+        let unchecked_str = unsafe { checked_cstr.as_str_unchecked() };
+        assert_eq!(unchecked_str, "🐧");
+    }
+}