sgx_libc/src/c_str.rs

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License..

/// A type representing an owned, C-compatible, nul-terminated string with no nul bytes in the
/// middle.
///
/// This type serves the purpose of being able to safely generate a
/// C-compatible string from a Rust byte slice or vector. An instance of this
/// type is a static guarantee that the underlying bytes contain no interior 0
/// bytes ("nul characters") and that the final byte is 0 ("nul terminator").
///
use sgx_types::c_char;
use crate::memchr;
use crate::ascii;

use core::ops;
use core::cmp::Ordering;
use core::mem;
use core::ptr;
use core::fmt::{self, Write};
use core::num::NonZeroU8;
use alloc::boxed::Box;
use alloc::borrow::{Cow, Borrow, ToOwned};
use alloc::vec::Vec;
use alloc::string::String;
use alloc::slice;
use alloc::rc::Rc;
use alloc::sync::Arc;

use alloc::str::{self, Utf8Error};

/// A type representing an owned C-compatible string
///
#[derive(PartialEq, PartialOrd, Eq, Ord, Hash, Clone)]
pub struct CString {
    // Invariant 1: the slice ends with a zero byte and has a length of at least one.
    // Invariant 2: the slice contains only one zero byte.
    // Improper usage of unsafe function can break Invariant 2, but not Invariant 1.
    inner: Box<[u8]>,
}

/// Representation of a borrowed C string.
///
/// This type represents a borrowed reference to a nul-terminated
/// array of bytes. It can be constructed safely from a `&[`[`u8`]`]`
/// slice, or unsafely from a raw `*const c_char`. It can then be
/// converted to a Rust [`&str`] by performing UTF-8 validation, or
/// into an owned [`CString`].
///
/// `&CStr` is to [`CString`] as [`&str`] is to [`String`]: the former
/// in each pair are borrowed references; the latter are owned
/// strings.
///
/// Note that this structure is **not** `repr(C)` and is not recommended to be
/// placed in the signatures of FFI functions. Instead, safe wrappers of FFI
/// functions may leverage the unsafe [`from_ptr`] constructor to provide a safe
/// interface to other consumers.
///
#[derive(Hash)]
pub struct CStr {
    // FIXME: this should not be represented with a DST slice but rather with
    //        just a raw `c_char` along with some form of marker to make
    //        this an unsized type. Essentially `sizeof(&CStr)` should be the
    //        same as `sizeof(&c_char)` but `CStr` should be an unsized type.
    inner: [c_char],
}

/// An error indicating that an interior nul byte was found.
///
/// While Rust strings may contain nul bytes in the middle, C strings
/// can't, as that byte would effectively truncate the string.
///
/// This error is created by the [`new`][`CString::new`] method on
/// [`CString`]. See its documentation for more.
///
/// [`CString`]: struct.CString.html
/// [`CString::new`]: struct.CString.html#method.new
///
#[derive(Clone, PartialEq, Eq, Debug)]
pub struct NulError(usize, Vec<u8>);

impl fmt::Display for NulError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "nul byte found in provided data at position: {}", self.0)
    }
}

/// An error indicating that a nul byte was not in the expected position.
///
/// The slice used to create a [`CStr`] must have one and only one nul
/// byte at the end of the slice.
///
/// This error is created by the
/// [`from_bytes_with_nul`][`CStr::from_bytes_with_nul`] method on
/// [`CStr`]. See its documentation for more.
///
/// [`CStr`]: struct.CStr.html
/// [`CStr::from_bytes_with_nul`]: struct.CStr.html#method.from_bytes_with_nul
///
#[derive(Clone, PartialEq, Eq, Debug)]
pub struct FromBytesWithNulError {
    kind: FromBytesWithNulErrorKind,
}

#[derive(Clone, PartialEq, Eq, Debug)]
enum FromBytesWithNulErrorKind {
    InteriorNul(usize),
    NotNulTerminated,
}

impl FromBytesWithNulError {
    fn interior_nul(pos: usize) -> FromBytesWithNulError {
        FromBytesWithNulError { kind: FromBytesWithNulErrorKind::InteriorNul(pos) }
    }
    fn not_nul_terminated() -> FromBytesWithNulError {
        FromBytesWithNulError { kind: FromBytesWithNulErrorKind::NotNulTerminated }
    }

    pub fn __description(&self) -> &str {
        match self.kind {
            FromBytesWithNulErrorKind::InteriorNul(..) => {
                "data provided contains an interior nul byte"
            }
            FromBytesWithNulErrorKind::NotNulTerminated => "data provided is not nul terminated",
        }
    }
}

impl fmt::Display for FromBytesWithNulError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(self.__description())?;
        if let FromBytesWithNulErrorKind::InteriorNul(pos) = self.kind {
            write!(f, " at byte pos {}", pos)?;
        }
        Ok(())
    }
}

/// An error indicating invalid UTF-8 when converting a [`CString`] into a [`String`].
///
/// `CString` is just a wrapper over a buffer of bytes with a nul
/// terminator; [`into_string`][`CString::into_string`] performs UTF-8
/// validation on those bytes and may return this error.
///
/// This `struct` is created by the
/// [`into_string`][`CString::into_string`] method on [`CString`]. See
/// its documentation for more.
///
/// [`String`]: ../string/struct.String.html
/// [`CString`]: struct.CString.html
/// [`CString::into_string`]: struct.CString.html#method.into_string
#[derive(Clone, PartialEq, Eq, Debug)]
pub struct IntoStringError {
    inner: CString,
    error: Utf8Error,
}

impl IntoStringError {
    pub fn __description(&self) -> &str {
        "C string contained non-utf8 bytes"
    }

    pub fn __source(&self) -> &Utf8Error {
        &self.error
    }
}

impl fmt::Display for IntoStringError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.__description().fmt(f)
    }
}


impl CString {
    /// Creates a new C-compatible string from a container of bytes.
    ///
    /// This function will consume the provided data and use the
    /// underlying bytes to construct a new string, ensuring that
    /// there is a trailing 0 byte. This trailing 0 byte will be
    /// appended by this function; the provided data should *not*
    /// contain any 0 bytes in it.
    ///
    pub fn new<T: Into<Vec<u8>>>(t: T) -> Result<CString, NulError> {
        trait SpecIntoVec {
            fn into_vec(self) -> Vec<u8>;
        }
        impl<T: Into<Vec<u8>>> SpecIntoVec for T {
            default fn into_vec(self) -> Vec<u8> {
                self.into()
            }
        }
        // Specialization for avoiding reallocation.
        impl SpecIntoVec for &'_ [u8] {
            fn into_vec(self) -> Vec<u8> {
                let mut v = Vec::with_capacity(self.len() + 1);
                v.extend(self);
                v
            }
        }
        impl SpecIntoVec for &'_ str {
            fn into_vec(self) -> Vec<u8> {
                let mut v = Vec::with_capacity(self.len() + 1);
                v.extend(self.as_bytes());
                v
            }
        }

        Self::_new(SpecIntoVec::into_vec(t))
    }

    fn _new(bytes: Vec<u8>) -> Result<CString, NulError> {
        match memchr::memchr(0, &bytes) {
            Some(i) => Err(NulError(i, bytes)),
            None => Ok(unsafe { CString::from_vec_unchecked(bytes) }),
        }
    }

    /// Creates a C-compatible string by consuming a byte vector,
    /// without checking for interior 0 bytes.
    ///
    /// This method is equivalent to [`new`] except that no runtime assertion
    /// is made that `v` contains no 0 bytes, and it requires an actual
    /// byte vector, not anything that can be converted to one with Into.
    ///
    /// [`new`]: #method.new
    ///
    pub unsafe fn from_vec_unchecked(mut v: Vec<u8>) -> CString {
        v.reserve_exact(1);
        v.push(0);
        CString { inner: v.into_boxed_slice() }
    }

    /// Retakes ownership of a `CString` that was transferred to C via [`into_raw`].
    ///
    /// Additionally, the length of the string will be recalculated from the pointer.
    ///
    /// # Safety
    ///
    /// This should only ever be called with a pointer that was earlier
    /// obtained by calling [`into_raw`] on a `CString`. Other usage (e.g., trying to take
    /// ownership of a string that was allocated by foreign code) is likely to lead
    /// to undefined behavior or allocator corruption.
    ///
    /// > **Note:** If you need to borrow a string that was allocated by
    /// > foreign code, use [`CStr`]. If you need to take ownership of
    /// > a string that was allocated by foreign code, you will need to
    /// > make your own provisions for freeing it appropriately, likely
    /// > with the foreign code's API to do that.
    ///
    /// [`into_raw`]: #method.into_raw
    /// [`CStr`]: struct.CStr.html
    ///
    pub unsafe fn from_raw(ptr: *mut c_char) -> CString {
        let len = crate::strlen(ptr) + 1; // Including the NUL byte
        let slice = slice::from_raw_parts_mut(ptr, len as usize);
        CString { inner: Box::from_raw(slice as *mut [c_char] as *mut [u8]) }
    }

    /// Consumes the `CString` and transfers ownership of the string to a C caller.
    ///
    /// The pointer which this function returns must be returned to Rust and reconstituted using
    /// [`from_raw`] to be properly deallocated. Specifically, one
    /// should *not* use the standard C `free()` function to deallocate
    /// this string.
    ///
    /// Failure to call [`from_raw`] will lead to a memory leak.
    ///
    /// [`from_raw`]: #method.from_raw
    ///
    #[inline]
    pub fn into_raw(self) -> *mut c_char {
        Box::into_raw(self.into_inner()) as *mut c_char
    }

    /// Converts the `CString` into a [`String`] if it contains valid UTF-8 data.
    ///
    /// On failure, ownership of the original `CString` is returned.
    ///
    /// [`String`]: ../string/struct.String.html
    ///
    pub fn into_string(self) -> Result<String, IntoStringError> {
        String::from_utf8(self.into_bytes()).map_err(|e| IntoStringError {
            error: e.utf8_error(),
            inner: unsafe { CString::from_vec_unchecked(e.into_bytes()) },
        })
    }

    /// Consumes the `CString` and returns the underlying byte buffer.
    ///
    /// The returned buffer does **not** contain the trailing nul
    /// terminator, and it is guaranteed to not have any interior nul
    /// bytes.
    ///
    pub fn into_bytes(self) -> Vec<u8> {
        let mut vec = self.into_inner().into_vec();
        let _nul = vec.pop();
        debug_assert_eq!(_nul, Some(0u8));
        vec
    }

    /// Equivalent to the [`into_bytes`] function except that the returned vector
    /// includes the trailing nul terminator.
    ///
    /// [`into_bytes`]: #method.into_bytes
    ///
    pub fn into_bytes_with_nul(self) -> Vec<u8> {
        self.into_inner().into_vec()
    }

    /// Returns the contents of this `CString` as a slice of bytes.
    ///
    /// The returned slice does **not** contain the trailing nul
    /// terminator, and it is guaranteed to not have any interior nul
    /// bytes. If you need the nul terminator, use
    /// [`as_bytes_with_nul`] instead.
    ///
    /// [`as_bytes_with_nul`]: #method.as_bytes_with_nul
    ///
    #[inline]
    pub fn as_bytes(&self) -> &[u8] {
        &self.inner[..self.inner.len() - 1]
    }

    /// Equivalent to the [`as_bytes`] function except that the returned slice
    /// includes the trailing nul terminator.
    #[inline]
    pub fn as_bytes_with_nul(&self) -> &[u8] {
        &self.inner
    }

    /// Extracts a [`CStr`] slice containing the entire string.
    #[inline]
    pub fn as_c_str(&self) -> &CStr {
        &*self
    }

    /// Converts this `CString` into a boxed [`CStr`].
    ///
    /// [`CStr`]: struct.CStr.html
    ///
    pub fn into_boxed_c_str(self) -> Box<CStr> {
        unsafe { Box::from_raw(Box::into_raw(self.into_inner()) as *mut CStr) }
    }

    /// Bypass "move out of struct which implements [`Drop`] trait" restriction.
    ///
    /// [`Drop`]: ../ops/trait.Drop.html
    fn into_inner(self) -> Box<[u8]> {
        // Rationale: `mem::forget(self)` invalidates the previous call to `ptr::read(&self.inner)`
        // so we use `ManuallyDrop` to ensure `self` is not dropped.
        // Then we can return the box directly without invalidating it.
        // See https://github.com/rust-lang/rust/issues/62553.
        let this = mem::ManuallyDrop::new(self);
        unsafe { ptr::read(&this.inner) }
    }
}

// Turns this `CString` into an empty string to prevent
// memory-unsafe code from working by accident. Inline
// to prevent LLVM from optimizing it away in debug builds.
impl Drop for CString {
    #[inline]
    fn drop(&mut self) {
        unsafe {
            *self.inner.get_unchecked_mut(0) = 0;
        }
    }
}

impl ops::Deref for CString {
    type Target = CStr;

    #[inline]
    fn deref(&self) -> &CStr {
        unsafe { CStr::from_bytes_with_nul_unchecked(self.as_bytes_with_nul()) }
    }
}

impl fmt::Debug for CString {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Debug::fmt(&**self, f)
    }
}

impl From<CString> for Vec<u8> {
    /// Converts a [`CString`] into a [`Vec`]`<u8>`.
    ///
    /// The conversion consumes the [`CString`], and removes the terminating NUL byte.
    ///
    /// [`Vec`]: ../vec/struct.Vec.html
    /// [`CString`]: ../ffi/struct.CString.html
    #[inline]
    fn from(s: CString) -> Vec<u8> {
        s.into_bytes()
    }
}

impl fmt::Debug for CStr {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "\"")?;
        for byte in self.to_bytes().iter().flat_map(|&b| ascii::escape_default(b)) {
            f.write_char(byte as char)?;
        }
        write!(f, "\"")
    }
}

impl Default for &CStr {
    fn default() -> Self {
        const SLICE: &[c_char] = &[0];
        unsafe { CStr::from_ptr(SLICE.as_ptr()) }
    }
}

impl Default for CString {
    /// Creates an empty `CString`.
    fn default() -> CString {
        let a: &CStr = Default::default();
        a.to_owned()
    }
}

impl Borrow<CStr> for CString {
    #[inline]
    fn borrow(&self) -> &CStr {
        self
    }
}

impl<'a> From<Cow<'a, CStr>> for CString {
    #[inline]
    fn from(s: Cow<'a, CStr>) -> Self {
        s.into_owned()
    }
}

impl From<&CStr> for Box<CStr> {
    fn from(s: &CStr) -> Box<CStr> {
        let boxed: Box<[u8]> = Box::from(s.to_bytes_with_nul());
        unsafe { Box::from_raw(Box::into_raw(boxed) as *mut CStr) }
    }
}

impl From<Box<CStr>> for CString {
    /// Converts a [`Box`]`<CStr>` into a [`CString`] without copying or allocating.
    ///
    /// [`Box`]: ../boxed/struct.Box.html
    /// [`CString`]: ../ffi/struct.CString.html
    #[inline]
    fn from(s: Box<CStr>) -> CString {
        s.into_c_string()
    }
}

impl From<Vec<NonZeroU8>> for CString {
    /// Converts a [`Vec`]`<`[`NonZeroU8`]`>` into a [`CString`] without
    /// copying nor checking for inner null bytes.
    ///
    /// [`CString`]: ../ffi/struct.CString.html
    /// [`NonZeroU8`]: ../num/struct.NonZeroU8.html
    /// [`Vec`]: ../vec/struct.Vec.html
    #[inline]
    fn from(v: Vec<NonZeroU8>) -> CString {
        unsafe {
            // Transmute `Vec<NonZeroU8>` to `Vec<u8>`.
            let v: Vec<u8> = {
                // Safety:
                //   - transmuting between `NonZeroU8` and `u8` is sound;
                //   - `alloc::Layout<NonZeroU8> == alloc::Layout<u8>`.
                let (ptr, len, cap): (*mut NonZeroU8, _, _) = Vec::into_raw_parts(v);
                Vec::from_raw_parts(ptr.cast::<u8>(), len, cap)
            };
            // Safety: `v` cannot contain null bytes, given the type-level
            // invariant of `NonZeroU8`.
            CString::from_vec_unchecked(v)
        }
    }
}

impl Clone for Box<CStr> {
    #[inline]
    fn clone(&self) -> Self {
        (**self).into()
    }
}

impl From<CString> for Box<CStr> {
    /// Converts a [`CString`] into a [`Box`]`<CStr>` without copying or allocating.
    ///
    /// [`CString`]: ../ffi/struct.CString.html
    /// [`Box`]: ../boxed/struct.Box.html
    #[inline]
    fn from(s: CString) -> Box<CStr> {
        s.into_boxed_c_str()
    }
}

impl<'a> From<CString> for Cow<'a, CStr> {
    #[inline]
    fn from(s: CString) -> Cow<'a, CStr> {
        Cow::Owned(s)
    }
}

impl<'a> From<&'a CStr> for Cow<'a, CStr> {
    #[inline]
    fn from(s: &'a CStr) -> Cow<'a, CStr> {
        Cow::Borrowed(s)
    }
}

impl<'a> From<&'a CString> for Cow<'a, CStr> {
    #[inline]
    fn from(s: &'a CString) -> Cow<'a, CStr> {
        Cow::Borrowed(s.as_c_str())
    }
}

impl From<CString> for Arc<CStr> {
    /// Converts a [`CString`] into a [`Arc`]`<CStr>` without copying or allocating.
    ///
    /// [`CString`]: ../ffi/struct.CString.html
    /// [`Arc`]: ../sync/struct.Arc.html
    #[inline]
    fn from(s: CString) -> Arc<CStr> {
        let arc: Arc<[u8]> = Arc::from(s.into_inner());
        unsafe { Arc::from_raw(Arc::into_raw(arc) as *const CStr) }
    }
}

impl From<&CStr> for Arc<CStr> {
    #[inline]
    fn from(s: &CStr) -> Arc<CStr> {
        let arc: Arc<[u8]> = Arc::from(s.to_bytes_with_nul());
        unsafe { Arc::from_raw(Arc::into_raw(arc) as *const CStr) }
    }
}

impl From<CString> for Rc<CStr> {
    /// Converts a [`CString`] into a [`Rc`]`<CStr>` without copying or allocating.
    ///
    /// [`CString`]: ../ffi/struct.CString.html
    /// [`Rc`]: ../rc/struct.Rc.html
    #[inline]
    fn from(s: CString) -> Rc<CStr> {
        let rc: Rc<[u8]> = Rc::from(s.into_inner());
        unsafe { Rc::from_raw(Rc::into_raw(rc) as *const CStr) }
    }
}

impl From<&CStr> for Rc<CStr> {
    #[inline]
    fn from(s: &CStr) -> Rc<CStr> {
        let rc: Rc<[u8]> = Rc::from(s.to_bytes_with_nul());
        unsafe { Rc::from_raw(Rc::into_raw(rc) as *const CStr) }
    }
}

impl Default for Box<CStr> {
    fn default() -> Box<CStr> {
        let boxed: Box<[u8]> = Box::from([0]);
        unsafe { Box::from_raw(Box::into_raw(boxed) as *mut CStr) }
    }
}

impl NulError {
    /// Returns the position of the nul byte in the slice that caused
    /// [`CString::new`] to fail.
    ///
    /// [`CString::new`]: struct.CString.html#method.new
    ///
    pub fn nul_position(&self) -> usize {
        self.0
    }

    /// Consumes this error, returning the underlying vector of bytes which
    /// generated the error in the first place.
    ///
    pub fn into_vec(self) -> Vec<u8> {
        self.1
    }
}

impl IntoStringError {
    /// Consumes this error, returning original [`CString`] which generated the
    /// error.
    ///
    /// [`CString`]: struct.CString.html
    pub fn into_cstring(self) -> CString {
        self.inner
    }

    /// Access the underlying UTF-8 error that was the cause of this error.
    pub fn utf8_error(&self) -> Utf8Error {
        self.error
    }
}

impl CStr {
    /// Wraps a raw C string with a safe C string wrapper.
    ///
    /// This function will wrap the provided `ptr` with a `CStr` wrapper, which
    /// allows inspection and interoperation of non-owned C strings. The total
    /// size of the raw C string must be smaller than `isize::MAX` **bytes**
    /// in memory due to calling the `slice::from_raw_parts` function.
    /// This method is unsafe for a number of reasons:
    ///
    /// * There is no guarantee to the validity of `ptr`.
    /// * The returned lifetime is not guaranteed to be the actual lifetime of
    ///   `ptr`.
    /// * There is no guarantee that the memory pointed to by `ptr` contains a
    ///   valid nul terminator byte at the end of the string.
    /// * It is not guaranteed that the memory pointed by `ptr` won't change
    ///   before the `CStr` has been destroyed.
    ///
    /// > **Note**: This operation is intended to be a 0-cost cast but it is
    /// > currently implemented with an up-front calculation of the length of
    /// > the string. This is not guaranteed to always be the case.
    ///
    pub unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr {
        let len = crate::strlen(ptr);
        let ptr = ptr as *const u8;
        CStr::from_bytes_with_nul_unchecked(slice::from_raw_parts(ptr, len as usize + 1))
    }

    /// Creates a C string wrapper from a byte slice.
    ///
    /// This function will cast the provided `bytes` to a `CStr`
    /// wrapper after ensuring that the byte slice is nul-terminated
    /// and does not contain any interior nul bytes.
    ///
    pub fn from_bytes_with_nul(bytes: &[u8]) -> Result<&CStr, FromBytesWithNulError> {
        let nul_pos = memchr::memchr(0, bytes);
        if let Some(nul_pos) = nul_pos {
            if nul_pos + 1 != bytes.len() {
                return Err(FromBytesWithNulError::interior_nul(nul_pos));
            }
            Ok(unsafe { CStr::from_bytes_with_nul_unchecked(bytes) })
        } else {
            Err(FromBytesWithNulError::not_nul_terminated())
        }
    }

    /// Unsafely creates a C string wrapper from a byte slice.
    ///
    /// This function will cast the provided `bytes` to a `CStr` wrapper without
    /// performing any sanity checks. The provided slice **must** be nul-terminated
    /// and not contain any interior nul bytes.
    ///
    #[inline]
    pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
        &*(bytes as *const [u8] as *const CStr)
    }

    /// Returns the inner pointer to this C string.
    ///
    /// The returned pointer will be valid for as long as `self` is, and points
    /// to a contiguous region of memory terminated with a 0 byte to represent
    /// the end of the string.
    ///
    #[inline]
    pub const fn as_ptr(&self) -> *const c_char {
        self.inner.as_ptr()
    }

    /// Converts this C string to a byte slice.
    ///
    /// The returned slice will **not** contain the trailing nul terminator that this C
    /// string has.
    ///
    /// > **Note**: This method is currently implemented as a constant-time
    /// > cast, but it is planned to alter its definition in the future to
    /// > perform the length calculation whenever this method is called.
    ///
    #[inline]
    pub fn to_bytes(&self) -> &[u8] {
        let bytes = self.to_bytes_with_nul();
        &bytes[..bytes.len() - 1]
    }

    /// Converts this C string to a byte slice containing the trailing 0 byte.
    ///
    /// This function is the equivalent of [`to_bytes`] except that it will retain
    /// the trailing nul terminator instead of chopping it off.
    ///
    /// > **Note**: This method is currently implemented as a 0-cost cast, but
    /// > it is planned to alter its definition in the future to perform the
    /// > length calculation whenever this method is called.
    ///
    /// [`to_bytes`]: #method.to_bytes
    ///
    #[inline]
    pub fn to_bytes_with_nul(&self) -> &[u8] {
        unsafe { &*(&self.inner as *const [c_char] as *const [u8]) }
    }

    /// 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.
    ///
    /// [`&str`]: ../primitive.str.html
    ///
    pub fn to_str(&self) -> Result<&str, str::Utf8Error> {
        // N.B., when `CStr` is changed to perform the length check in `.to_bytes()`
        // instead of in `from_ptr()`, it may be worth considering if this should
        // be rewritten to do the UTF-8 check inline with the length calculation
        // instead of doing it afterwards.
        str::from_utf8(self.to_bytes())
    }

    /// Converts a `CStr` into a [`Cow`]`<`[`str`]`>`.
    ///
    /// If the contents of the `CStr` are valid UTF-8 data, this
    /// function will return a [`Cow`]`::`[`Borrowed`]`(`[`&str`]`)`
    /// with the corresponding [`&str`] slice. Otherwise, it will
    /// replace any invalid UTF-8 sequences with
    /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD] and return a
    /// [`Cow`]`::`[`Owned`]`(`[`String`]`)` with the result.
    ///
    /// [`Cow`]: ../borrow/enum.Cow.html
    /// [`Borrowed`]: ../borrow/enum.Cow.html#variant.Borrowed
    /// [`Owned`]: ../borrow/enum.Cow.html#variant.Owned
    /// [`str`]: ../primitive.str.html
    /// [`String`]: ../string/struct.String.html
    /// [U+FFFD]: ../char/constant.REPLACEMENT_CHARACTER.html
    ///
    pub fn to_string_lossy(&self) -> Cow<'_, str> {
        String::from_utf8_lossy(self.to_bytes())
    }

    /// Converts a [`Box`]`<CStr>` into a [`CString`] without copying or allocating.
    ///
    /// [`Box`]: ../boxed/struct.Box.html
    /// [`CString`]: struct.CString.html
    ///
    pub fn into_c_string(self: Box<CStr>) -> CString {
        let raw = Box::into_raw(self) as *mut [u8];
        CString { inner: unsafe { Box::from_raw(raw) } }
    }
}

impl PartialEq for CStr {
    fn eq(&self, other: &CStr) -> bool {
        self.to_bytes().eq(other.to_bytes())
    }
}

impl Eq for CStr {}

impl PartialOrd for CStr {
    fn partial_cmp(&self, other: &CStr) -> Option<Ordering> {
        self.to_bytes().partial_cmp(&other.to_bytes())
    }
}

impl Ord for CStr {
    fn cmp(&self, other: &CStr) -> Ordering {
        self.to_bytes().cmp(&other.to_bytes())
    }
}

impl ToOwned for CStr {
    type Owned = CString;

    fn to_owned(&self) -> CString {
        CString { inner: self.to_bytes_with_nul().into() }
    }

    fn clone_into(&self, target: &mut CString) {
        let mut b = Vec::from(mem::take(&mut target.inner));
        self.to_bytes_with_nul().clone_into(&mut b);
        target.inner = b.into_boxed_slice();
    }
}

impl From<&CStr> for CString {
    fn from(s: &CStr) -> CString {
        s.to_owned()
    }
}

impl ops::Index<ops::RangeFull> for CString {
    type Output = CStr;

    #[inline]
    fn index(&self, _index: ops::RangeFull) -> &CStr {
        self
    }
}

impl AsRef<CStr> for CStr {
    #[inline]
    fn as_ref(&self) -> &CStr {
        self
    }
}

impl AsRef<CStr> for CString {
    #[inline]
    fn as_ref(&self) -> &CStr {
        self
    }
}