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use crate::ascii;
use crate::cmp::Ordering;
use crate::ffi::c_char;
use crate::fmt::{self, Write};
use crate::ops;
use crate::slice;
use crate::slice::memchr;
use crate::str;
/// 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 <code>&[[u8]]</code>
/// slice, or unsafely from a raw `*const c_char`. It can then be
/// converted to a Rust <code>&[str]</code> by performing UTF-8 validation, or
/// into an owned `CString`.
///
/// `&CStr` is to `CString` as <code>&[str]</code> 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 [`CStr::from_ptr`] constructor to provide
/// a safe interface to other consumers.
///
/// # Examples
///
/// Inspecting a foreign C string:
///
/// ```ignore (extern-declaration)
/// use std::ffi::CStr;
/// use std::os::raw::c_char;
///
/// extern "C" { fn my_string() -> *const c_char; }
///
/// unsafe {
/// let slice = CStr::from_ptr(my_string());
/// println!("string buffer size without nul terminator: {}", slice.to_bytes().len());
/// }
/// ```
///
/// Passing a Rust-originating C string:
///
/// ```ignore (extern-declaration)
/// use std::ffi::{CString, CStr};
/// use std::os::raw::c_char;
///
/// fn work(data: &CStr) {
/// extern "C" { fn work_with(data: *const c_char); }
///
/// unsafe { work_with(data.as_ptr()) }
/// }
///
/// let s = CString::new("data data data data").expect("CString::new failed");
/// work(&s);
/// ```
///
/// Converting a foreign C string into a Rust `String`:
///
/// ```ignore (extern-declaration)
/// use std::ffi::CStr;
/// use std::os::raw::c_char;
///
/// extern "C" { fn my_string() -> *const c_char; }
///
/// fn my_string_safe() -> String {
/// unsafe {
/// CStr::from_ptr(my_string()).to_string_lossy().into_owned()
/// }
/// }
///
/// println!("string: {}", my_string_safe());
/// ```
///
/// [str]: prim@str "str"
#[derive(Hash)]
#[cfg_attr(not(test), rustc_diagnostic_item = "CStr")]
#[stable(feature = "core_c_str", since = "1.64.0")]
#[rustc_has_incoherent_inherent_impls]
// FIXME:
// `fn from` in `impl From<&CStr> for Box<CStr>` current implementation relies
// on `CStr` being layout-compatible with `[u8]`.
// When attribute privacy is implemented, `CStr` should be annotated as `#[repr(transparent)]`.
// Anyway, `CStr` representation and layout are considered implementation detail, are
// not documented and must not be relied upon.
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 a nul byte was not in the expected position.
///
/// The slice used to create a [`CStr`] must have one and only one nul byte,
/// positioned at the end.
///
/// This error is created by the [`CStr::from_bytes_with_nul`] method.
/// See its documentation for more.
///
/// # Examples
///
/// ```
/// use std::ffi::{CStr, FromBytesWithNulError};
///
/// let _: FromBytesWithNulError = CStr::from_bytes_with_nul(b"f\0oo").unwrap_err();
/// ```
#[derive(Clone, PartialEq, Eq, Debug)]
#[stable(feature = "core_c_str", since = "1.64.0")]
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 }
}
#[doc(hidden)]
#[unstable(feature = "cstr_internals", issue = "none")]
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",
}
}
}
/// An error indicating that no nul byte was present.
///
/// A slice used to create a [`CStr`] must contain a nul byte somewhere
/// within the slice.
///
/// This error is created by the [`CStr::from_bytes_until_nul`] method.
///
#[derive(Clone, PartialEq, Eq, Debug)]
#[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")]
pub struct FromBytesUntilNulError(());
#[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")]
impl fmt::Display for FromBytesUntilNulError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "data provided does not contain a nul")
}
}
#[stable(feature = "cstr_debug", since = "1.3.0")]
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, "\"")
}
}
#[stable(feature = "cstr_default", since = "1.10.0")]
impl Default for &CStr {
fn default() -> Self {
const SLICE: &[c_char] = &[0];
// SAFETY: `SLICE` is indeed pointing to a valid nul-terminated string.
unsafe { CStr::from_ptr(SLICE.as_ptr()) }
}
}
#[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
impl fmt::Display for FromBytesWithNulError {
#[allow(deprecated, deprecated_in_future)]
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(())
}
}
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.
///
/// # Safety
///
/// * The memory pointed to by `ptr` must contain a valid nul terminator at the
/// end of the string.
///
/// * `ptr` must be [valid] for reads of bytes up to and including the null terminator.
/// This means in particular:
///
/// * The entire memory range of this `CStr` must be contained within a single allocated object!
/// * `ptr` must be non-null even for a zero-length cstr.
///
/// * The memory referenced by the returned `CStr` must not be mutated for
/// the duration of lifetime `'a`.
///
/// > **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.
///
/// # Caveat
///
/// The lifetime for the returned slice is inferred from its usage. To prevent accidental misuse,
/// it's suggested to tie the lifetime to whichever source lifetime is safe in the context,
/// such as by providing a helper function taking the lifetime of a host value for the slice,
/// or by explicit annotation.
///
/// # Examples
///
/// ```ignore (extern-declaration)
/// # fn main() {
/// use std::ffi::CStr;
/// use std::os::raw::c_char;
///
/// extern "C" {
/// fn my_string() -> *const c_char;
/// }
///
/// unsafe {
/// let slice = CStr::from_ptr(my_string());
/// println!("string returned: {}", slice.to_str().unwrap());
/// }
/// # }
/// ```
///
/// [valid]: core::ptr#safety
#[inline]
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr {
// SAFETY: The caller has provided a pointer that points to a valid C
// string with a NUL terminator of size less than `isize::MAX`, whose
// content remain valid and doesn't change for the lifetime of the
// returned `CStr`.
//
// Thus computing the length is fine (a NUL byte exists), the call to
// from_raw_parts is safe because we know the length is at most `isize::MAX`, meaning
// the call to `from_bytes_with_nul_unchecked` is correct.
//
// The cast from c_char to u8 is ok because a c_char is always one byte.
unsafe {
extern "C" {
/// Provided by libc or compiler_builtins.
fn strlen(s: *const c_char) -> usize;
}
let len = 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 method will create a `CStr` from any byte slice that contains at
/// least one nul byte. The caller does not need to know or specify where
/// the nul byte is located.
///
/// If the first byte is a nul character, this method will return an
/// empty `CStr`. If multiple nul characters are present, the `CStr` will
/// end at the first one.
///
/// If the slice only has a single nul byte at the end, this method is
/// equivalent to [`CStr::from_bytes_with_nul`].
///
/// # Examples
/// ```
/// #![feature(cstr_from_bytes_until_nul)]
///
/// use std::ffi::CStr;
///
/// let mut buffer = [0u8; 16];
/// unsafe {
/// // Here we might call an unsafe C function that writes a string
/// // into the buffer.
/// let buf_ptr = buffer.as_mut_ptr();
/// buf_ptr.write_bytes(b'A', 8);
/// }
/// // Attempt to extract a C nul-terminated string from the buffer.
/// let c_str = CStr::from_bytes_until_nul(&buffer[..]).unwrap();
/// assert_eq!(c_str.to_str().unwrap(), "AAAAAAAA");
/// ```
///
#[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")]
pub fn from_bytes_until_nul(bytes: &[u8]) -> Result<&CStr, FromBytesUntilNulError> {
let nul_pos = memchr::memchr(0, bytes);
match nul_pos {
Some(nul_pos) => {
let subslice = &bytes[..nul_pos + 1];
// SAFETY: We know there is a nul byte at nul_pos, so this slice
// (ending at the nul byte) is a well-formed C string.
Ok(unsafe { CStr::from_bytes_with_nul_unchecked(subslice) })
}
None => Err(FromBytesUntilNulError(())),
}
}
/// 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.
///
/// If the nul byte may not be at the end,
/// [`CStr::from_bytes_until_nul`] can be used instead.
///
/// # Examples
///
/// ```
/// use std::ffi::CStr;
///
/// let cstr = CStr::from_bytes_with_nul(b"hello\0");
/// assert!(cstr.is_ok());
/// ```
///
/// Creating a `CStr` without a trailing nul terminator is an error:
///
/// ```
/// use std::ffi::CStr;
///
/// let cstr = CStr::from_bytes_with_nul(b"hello");
/// assert!(cstr.is_err());
/// ```
///
/// Creating a `CStr` with an interior nul byte is an error:
///
/// ```
/// use std::ffi::CStr;
///
/// let cstr = CStr::from_bytes_with_nul(b"he\0llo\0");
/// assert!(cstr.is_err());
/// ```
#[stable(feature = "cstr_from_bytes", since = "1.10.0")]
pub fn from_bytes_with_nul(bytes: &[u8]) -> Result<&Self, FromBytesWithNulError> {
let nul_pos = memchr::memchr(0, bytes);
match nul_pos {
Some(nul_pos) if nul_pos + 1 == bytes.len() => {
// SAFETY: We know there is only one nul byte, at the end
// of the byte slice.
Ok(unsafe { Self::from_bytes_with_nul_unchecked(bytes) })
}
Some(nul_pos) => Err(FromBytesWithNulError::interior_nul(nul_pos)),
None => 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.
///
/// # Safety
/// The provided slice **must** be nul-terminated and not contain any interior
/// nul bytes.
///
/// # Examples
///
/// ```
/// use std::ffi::{CStr, CString};
///
/// unsafe {
/// let cstring = CString::new("hello").expect("CString::new failed");
/// let cstr = CStr::from_bytes_with_nul_unchecked(cstring.to_bytes_with_nul());
/// assert_eq!(cstr, &*cstring);
/// }
/// ```
#[inline]
#[must_use]
#[stable(feature = "cstr_from_bytes", since = "1.10.0")]
#[rustc_const_stable(feature = "const_cstr_unchecked", since = "1.59.0")]
pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
// We're in a const fn, so this is the best we can do
debug_assert!(!bytes.is_empty() && bytes[bytes.len() - 1] == 0);
// SAFETY: Calling an inner function with the same prerequisites.
unsafe { Self::_from_bytes_with_nul_unchecked(bytes) }
}
#[inline]
const unsafe fn _from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
// SAFETY: Casting to CStr is safe because its internal representation
// is a [u8] too (safe only inside std).
// Dereferencing the obtained pointer is safe because it comes from a
// reference. Making a reference is then safe because its lifetime
// is bound by the lifetime of the given `bytes`.
unsafe { &*(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.
///
/// **WARNING**
///
/// The returned pointer is read-only; writing to it (including passing it
/// to C code that writes to it) causes undefined behavior.
///
/// It is your responsibility to make sure that the underlying memory is not
/// freed too early. For example, the following code will cause undefined
/// behavior when `ptr` is used inside the `unsafe` block:
///
/// ```no_run
/// # #![allow(unused_must_use)] #![allow(temporary_cstring_as_ptr)]
/// use std::ffi::CString;
///
/// let ptr = CString::new("Hello").expect("CString::new failed").as_ptr();
/// unsafe {
/// // `ptr` is dangling
/// *ptr;
/// }
/// ```
///
/// This happens because the pointer returned by `as_ptr` does not carry any
/// lifetime information and the `CString` is deallocated immediately after
/// the `CString::new("Hello").expect("CString::new failed").as_ptr()`
/// expression is evaluated.
/// To fix the problem, bind the `CString` to a local variable:
///
/// ```no_run
/// # #![allow(unused_must_use)]
/// use std::ffi::CString;
///
/// let hello = CString::new("Hello").expect("CString::new failed");
/// let ptr = hello.as_ptr();
/// unsafe {
/// // `ptr` is valid because `hello` is in scope
/// *ptr;
/// }
/// ```
///
/// This way, the lifetime of the `CString` in `hello` encompasses
/// the lifetime of `ptr` and the `unsafe` block.
#[inline]
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_str_as_ptr", since = "1.32.0")]
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.
///
/// # Examples
///
/// ```
/// use std::ffi::CStr;
///
/// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
/// assert_eq!(cstr.to_bytes(), b"foo");
/// ```
#[inline]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn to_bytes(&self) -> &[u8] {
let bytes = self.to_bytes_with_nul();
// 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.
///
/// This function is the equivalent of [`CStr::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.
///
/// # Examples
///
/// ```
/// use std::ffi::CStr;
///
/// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
/// assert_eq!(cstr.to_bytes_with_nul(), b"foo\0");
/// ```
#[inline]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn to_bytes_with_nul(&self) -> &[u8] {
// SAFETY: Transmuting a slice of `c_char`s to a slice of `u8`s
// is safe on all supported targets.
unsafe { &*(&self.inner as *const [c_char] as *const [u8]) }
}
/// Yields a <code>&[str]</code> 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 <code>&[str]</code> slice. Otherwise,
/// it will return an error with details of where UTF-8 validation failed.
///
/// [str]: prim@str "str"
///
/// # Examples
///
/// ```
/// use std::ffi::CStr;
///
/// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed");
/// assert_eq!(cstr.to_str(), Ok("foo"));
/// ```
#[stable(feature = "cstr_to_str", since = "1.4.0")]
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())
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl PartialEq for CStr {
fn eq(&self, other: &CStr) -> bool {
self.to_bytes().eq(other.to_bytes())
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Eq for CStr {}
#[stable(feature = "rust1", since = "1.0.0")]
impl PartialOrd for CStr {
fn partial_cmp(&self, other: &CStr) -> Option<Ordering> {
self.to_bytes().partial_cmp(&other.to_bytes())
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Ord for CStr {
fn cmp(&self, other: &CStr) -> Ordering {
self.to_bytes().cmp(&other.to_bytes())
}
}
#[stable(feature = "cstr_range_from", since = "1.47.0")]
impl ops::Index<ops::RangeFrom<usize>> for CStr {
type Output = CStr;
fn index(&self, index: ops::RangeFrom<usize>) -> &CStr {
let bytes = self.to_bytes_with_nul();
// we need to manually check the starting index to account for the null
// byte, since otherwise we could get an empty string that doesn't end
// in a null.
if index.start < bytes.len() {
// SAFETY: Non-empty tail of a valid `CStr` is still a valid `CStr`.
unsafe { CStr::from_bytes_with_nul_unchecked(&bytes[index.start..]) }
} else {
panic!(
"index out of bounds: the len is {} but the index is {}",
bytes.len(),
index.start
);
}
}
}
#[stable(feature = "cstring_asref", since = "1.7.0")]
impl AsRef<CStr> for CStr {
#[inline]
fn as_ref(&self) -> &CStr {
self
}
}