src/libstd/ffi/c_str.rs

   1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use ascii;
  12 use borrow::{Cow, Borrow};
  13 use cmp::Ordering;
  14 use error::Error;
  15 use fmt::{self, Write};
  16 use io;
  17 use libc;
  18 use mem;
  19 use memchr;
  20 use ops;
  21 use os::raw::c_char;
  22 use ptr;
  23 use slice;
  24 use str::{self, Utf8Error};
  25
  26 /// A type representing an owned C-compatible string
  27 ///
  28 /// This type serves the primary purpose of being able to safely generate a
  29 /// C-compatible string from a Rust byte slice or vector. An instance of this
  30 /// type is a static guarantee that the underlying bytes contain no interior 0
  31 /// bytes and the final byte is 0.
  32 ///
  33 /// A `CString` is created from either a byte slice or a byte vector. After
  34 /// being created, a `CString` predominately inherits all of its methods from
  35 /// the `Deref` implementation to `[c_char]`. Note that the underlying array
  36 /// is represented as an array of `c_char` as opposed to `u8`. A `u8` slice
  37 /// can be obtained with the `as_bytes` method.  Slices produced from a `CString`
  38 /// do *not* contain the trailing nul terminator unless otherwise specified.
  39 ///
  40 /// # Examples
  41 ///
  42 /// ```no_run
  43 /// # fn main() {
  44 /// use std::ffi::CString;
  45 /// use std::os::raw::c_char;
  46 ///
  47 /// extern {
  48 ///     fn my_printer(s: *const c_char);
  49 /// }
  50 ///
  51 /// let c_to_print = CString::new("Hello, world!").unwrap();
  52 /// unsafe {
  53 ///     my_printer(c_to_print.as_ptr());
  54 /// }
  55 /// # }
  56 /// ```
  57 ///
  58 /// # Safety
  59 ///
  60 /// `CString` is intended for working with traditional C-style strings
  61 /// (a sequence of non-null bytes terminated by a single null byte); the
  62 /// primary use case for these kinds of strings is interoperating with C-like
  63 /// code. Often you will need to transfer ownership to/from that external
  64 /// code. It is strongly recommended that you thoroughly read through the
  65 /// documentation of `CString` before use, as improper ownership management
  66 /// of `CString` instances can lead to invalid memory accesses, memory leaks,
  67 /// and other memory errors.
  68
  69 #[derive(PartialEq, PartialOrd, Eq, Ord, Hash, Clone)]
  70 #[stable(feature = "rust1", since = "1.0.0")]
  71 pub struct CString {
  72     // Invariant 1: the slice ends with a zero byte and has a length of at least one.
  73     // Invariant 2: the slice contains only one zero byte.
  74     // Improper usage of unsafe function can break Invariant 2, but not Invariant 1.
  75     inner: Box<[u8]>,
  76 }
  77
  78 /// Representation of a borrowed C string.
  79 ///
  80 /// This dynamically sized type is only safely constructed via a borrowed
  81 /// version of an instance of `CString`. This type can be constructed from a raw
  82 /// C string as well and represents a C string borrowed from another location.
  83 ///
  84 /// Note that this structure is **not** `repr(C)` and is not recommended to be
  85 /// placed in the signatures of FFI functions. Instead safe wrappers of FFI
  86 /// functions may leverage the unsafe `from_ptr` constructor to provide a safe
  87 /// interface to other consumers.
  88 ///
  89 /// # Examples
  90 ///
  91 /// Inspecting a foreign C string
  92 ///
  93 /// ```no_run
  94 /// use std::ffi::CStr;
  95 /// use std::os::raw::c_char;
  96 ///
  97 /// extern { fn my_string() -> *const c_char; }
  98 ///
  99 /// unsafe {
 100 ///     let slice = CStr::from_ptr(my_string());
 101 ///     println!("string length: {}", slice.to_bytes().len());
 102 /// }
 103 /// ```
 104 ///
 105 /// Passing a Rust-originating C string
 106 ///
 107 /// ```no_run
 108 /// use std::ffi::{CString, CStr};
 109 /// use std::os::raw::c_char;
 110 ///
 111 /// fn work(data: &CStr) {
 112 ///     extern { fn work_with(data: *const c_char); }
 113 ///
 114 ///     unsafe { work_with(data.as_ptr()) }
 115 /// }
 116 ///
 117 /// let s = CString::new("data data data data").unwrap();
 118 /// work(&s);
 119 /// ```
 120 ///
 121 /// Converting a foreign C string into a Rust `String`
 122 ///
 123 /// ```no_run
 124 /// use std::ffi::CStr;
 125 /// use std::os::raw::c_char;
 126 ///
 127 /// extern { fn my_string() -> *const c_char; }
 128 ///
 129 /// fn my_string_safe() -> String {
 130 ///     unsafe {
 131 ///         CStr::from_ptr(my_string()).to_string_lossy().into_owned()
 132 ///     }
 133 /// }
 134 ///
 135 /// println!("string: {}", my_string_safe());
 136 /// ```
 137 #[derive(Hash)]
 138 #[stable(feature = "rust1", since = "1.0.0")]
 139 pub struct CStr {
 140     // FIXME: this should not be represented with a DST slice but rather with
 141     //        just a raw `c_char` along with some form of marker to make
 142     //        this an unsized type. Essentially `sizeof(&CStr)` should be the
 143     //        same as `sizeof(&c_char)` but `CStr` should be an unsized type.
 144     inner: [c_char]
 145 }
 146
 147 /// An error returned from `CString::new` to indicate that a nul byte was found
 148 /// in the vector provided.
 149 #[derive(Clone, PartialEq, Eq, Debug)]
 150 #[stable(feature = "rust1", since = "1.0.0")]
 151 pub struct NulError(usize, Vec<u8>);
 152
 153 /// An error returned from `CStr::from_bytes_with_nul` to indicate that a nul
 154 /// byte was found too early in the slice provided or one wasn't found at all.
 155 #[derive(Clone, PartialEq, Eq, Debug)]
 156 #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
 157 pub struct FromBytesWithNulError { _a: () }
 158
 159 /// An error returned from `CString::into_string` to indicate that a UTF-8 error
 160 /// was encountered during the conversion.
 161 #[derive(Clone, PartialEq, Eq, Debug)]
 162 #[stable(feature = "cstring_into", since = "1.7.0")]
 163 pub struct IntoStringError {
 164     inner: CString,
 165     error: Utf8Error,
 166 }
 167
 168 impl CString {
 169     /// Creates a new C-compatible string from a container of bytes.
 170     ///
 171     /// This method will consume the provided data and use the underlying bytes
 172     /// to construct a new string, ensuring that there is a trailing 0 byte.
 173     ///
 174     /// # Examples
 175     ///
 176     /// ```no_run
 177     /// use std::ffi::CString;
 178     /// use std::os::raw::c_char;
 179     ///
 180     /// extern { fn puts(s: *const c_char); }
 181     ///
 182     /// let to_print = CString::new("Hello!").unwrap();
 183     /// unsafe {
 184     ///     puts(to_print.as_ptr());
 185     /// }
 186     /// ```
 187     ///
 188     /// # Errors
 189     ///
 190     /// This function will return an error if the bytes yielded contain an
 191     /// internal 0 byte. The error returned will contain the bytes as well as
 192     /// the position of the nul byte.
 193     #[stable(feature = "rust1", since = "1.0.0")]
 194     pub fn new<T: Into<Vec<u8>>>(t: T) -> Result<CString, NulError> {
 195         Self::_new(t.into())
 196     }
 197
 198     fn _new(bytes: Vec<u8>) -> Result<CString, NulError> {
 199         match memchr::memchr(0, &bytes) {
 200             Some(i) => Err(NulError(i, bytes)),
 201             None => Ok(unsafe { CString::from_vec_unchecked(bytes) }),
 202         }
 203     }
 204
 205     /// Creates a C-compatible string from a byte vector without checking for
 206     /// interior 0 bytes.
 207     ///
 208     /// This method is equivalent to `new` except that no runtime assertion
 209     /// is made that `v` contains no 0 bytes, and it requires an actual
 210     /// byte vector, not anything that can be converted to one with Into.
 211     ///
 212     /// # Examples
 213     ///
 214     /// ```
 215     /// use std::ffi::CString;
 216     ///
 217     /// let raw = b"foo".to_vec();
 218     /// unsafe {
 219     ///     let c_string = CString::from_vec_unchecked(raw);
 220     /// }
 221     /// ```
 222     #[stable(feature = "rust1", since = "1.0.0")]
 223     pub unsafe fn from_vec_unchecked(mut v: Vec<u8>) -> CString {
 224         v.reserve_exact(1);
 225         v.push(0);
 226         CString { inner: v.into_boxed_slice() }
 227     }
 228
 229     /// Retakes ownership of a `CString` that was transferred to C.
 230     ///
 231     /// Additionally, the length of the string will be recalculated from the pointer.
 232     ///
 233     /// # Safety
 234     ///
 235     /// This should only ever be called with a pointer that was earlier
 236     /// obtained by calling `into_raw` on a `CString`. Other usage (e.g. trying to take
 237     /// ownership of a string that was allocated by foreign code) is likely to lead
 238     /// to undefined behavior or allocator corruption.
 239     #[stable(feature = "cstr_memory", since = "1.4.0")]
 240     pub unsafe fn from_raw(ptr: *mut c_char) -> CString {
 241         let len = libc::strlen(ptr) + 1; // Including the NUL byte
 242         let slice = slice::from_raw_parts(ptr, len as usize);
 243         CString { inner: mem::transmute(slice) }
 244     }
 245
 246     /// Transfers ownership of the string to a C caller.
 247     ///
 248     /// The pointer must be returned to Rust and reconstituted using
 249     /// `from_raw` to be properly deallocated. Specifically, one
 250     /// should *not* use the standard C `free` function to deallocate
 251     /// this string.
 252     ///
 253     /// Failure to call `from_raw` will lead to a memory leak.
 254     #[stable(feature = "cstr_memory", since = "1.4.0")]
 255     pub fn into_raw(self) -> *mut c_char {
 256         Box::into_raw(self.into_inner()) as *mut c_char
 257     }
 258
 259     /// Converts the `CString` into a `String` if it contains valid Unicode data.
 260     ///
 261     /// On failure, ownership of the original `CString` is returned.
 262     #[stable(feature = "cstring_into", since = "1.7.0")]
 263     pub fn into_string(self) -> Result<String, IntoStringError> {
 264         String::from_utf8(self.into_bytes())
 265             .map_err(|e| IntoStringError {
 266                 error: e.utf8_error(),
 267                 inner: unsafe { CString::from_vec_unchecked(e.into_bytes()) },
 268             })
 269     }
 270
 271     /// Returns the underlying byte buffer.
 272     ///
 273     /// The returned buffer does **not** contain the trailing nul separator and
 274     /// it is guaranteed to not have any interior nul bytes.
 275     #[stable(feature = "cstring_into", since = "1.7.0")]
 276     pub fn into_bytes(self) -> Vec<u8> {
 277         let mut vec = self.into_inner().into_vec();
 278         let _nul = vec.pop();
 279         debug_assert_eq!(_nul, Some(0u8));
 280         vec
 281     }
 282
 283     /// Equivalent to the `into_bytes` function except that the returned vector
 284     /// includes the trailing nul byte.
 285     #[stable(feature = "cstring_into", since = "1.7.0")]
 286     pub fn into_bytes_with_nul(self) -> Vec<u8> {
 287         self.into_inner().into_vec()
 288     }
 289
 290     /// Returns the contents of this `CString` as a slice of bytes.
 291     ///
 292     /// The returned slice does **not** contain the trailing nul separator and
 293     /// it is guaranteed to not have any interior nul bytes.
 294     #[stable(feature = "rust1", since = "1.0.0")]
 295     pub fn as_bytes(&self) -> &[u8] {
 296         &self.inner[..self.inner.len() - 1]
 297     }
 298
 299     /// Equivalent to the `as_bytes` function except that the returned slice
 300     /// includes the trailing nul byte.
 301     #[stable(feature = "rust1", since = "1.0.0")]
 302     pub fn as_bytes_with_nul(&self) -> &[u8] {
 303         &self.inner
 304     }
 305
 306     // Bypass "move out of struct which implements `Drop` trait" restriction.
 307     fn into_inner(self) -> Box<[u8]> {
 308         unsafe {
 309             let result = ptr::read(&self.inner);
 310             mem::forget(self);
 311             result
 312         }
 313     }
 314 }
 315
 316 // Turns this `CString` into an empty string to prevent
 317 // memory unsafe code from working by accident. Inline
 318 // to prevent LLVM from optimizing it away in debug builds.
 319 #[stable(feature = "cstring_drop", since = "1.13.0")]
 320 impl Drop for CString {
 321     #[inline]
 322     fn drop(&mut self) {
 323         unsafe { *self.inner.get_unchecked_mut(0) = 0; }
 324     }
 325 }
 326
 327 #[stable(feature = "rust1", since = "1.0.0")]
 328 impl ops::Deref for CString {
 329     type Target = CStr;
 330
 331     fn deref(&self) -> &CStr {
 332         unsafe { mem::transmute(self.as_bytes_with_nul()) }
 333     }
 334 }
 335
 336 #[stable(feature = "rust1", since = "1.0.0")]
 337 impl fmt::Debug for CString {
 338     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 339         fmt::Debug::fmt(&**self, f)
 340     }
 341 }
 342
 343 #[stable(feature = "cstring_into", since = "1.7.0")]
 344 impl From<CString> for Vec<u8> {
 345     fn from(s: CString) -> Vec<u8> {
 346         s.into_bytes()
 347     }
 348 }
 349
 350 #[stable(feature = "cstr_debug", since = "1.3.0")]
 351 impl fmt::Debug for CStr {
 352     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 353         write!(f, "\"")?;
 354         for byte in self.to_bytes().iter().flat_map(|&b| ascii::escape_default(b)) {
 355             f.write_char(byte as char)?;
 356         }
 357         write!(f, "\"")
 358     }
 359 }
 360
 361 #[stable(feature = "cstr_default", since = "1.10.0")]
 362 impl<'a> Default for &'a CStr {
 363     fn default() -> &'a CStr {
 364         static SLICE: &'static [c_char] = &[0];
 365         unsafe { CStr::from_ptr(SLICE.as_ptr()) }
 366     }
 367 }
 368
 369 #[stable(feature = "cstr_default", since = "1.10.0")]
 370 impl Default for CString {
 371     /// Creates an empty `CString`.
 372     fn default() -> CString {
 373         let a: &CStr = Default::default();
 374         a.to_owned()
 375     }
 376 }
 377
 378 #[stable(feature = "cstr_borrow", since = "1.3.0")]
 379 impl Borrow<CStr> for CString {
 380     fn borrow(&self) -> &CStr { self }
 381 }
 382
 383 impl NulError {
 384     /// Returns the position of the nul byte in the slice that was provided to
 385     /// `CString::new`.
 386     ///
 387     /// # Examples
 388     ///
 389     /// ```
 390     /// use std::ffi::CString;
 391     ///
 392     /// let nul_error = CString::new("foo\0bar").unwrap_err();
 393     /// assert_eq!(nul_error.nul_position(), 3);
 394     ///
 395     /// let nul_error = CString::new("foo bar\0").unwrap_err();
 396     /// assert_eq!(nul_error.nul_position(), 7);
 397     /// ```
 398     #[stable(feature = "rust1", since = "1.0.0")]
 399     pub fn nul_position(&self) -> usize { self.0 }
 400
 401     /// Consumes this error, returning the underlying vector of bytes which
 402     /// generated the error in the first place.
 403     ///
 404     /// # Examples
 405     ///
 406     /// ```
 407     /// use std::ffi::CString;
 408     ///
 409     /// let nul_error = CString::new("foo\0bar").unwrap_err();
 410     /// assert_eq!(nul_error.into_vec(), b"foo\0bar");
 411     /// ```
 412     #[stable(feature = "rust1", since = "1.0.0")]
 413     pub fn into_vec(self) -> Vec<u8> { self.1 }
 414 }
 415
 416 #[stable(feature = "rust1", since = "1.0.0")]
 417 impl Error for NulError {
 418     fn description(&self) -> &str { "nul byte found in data" }
 419 }
 420
 421 #[stable(feature = "rust1", since = "1.0.0")]
 422 impl fmt::Display for NulError {
 423     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 424         write!(f, "nul byte found in provided data at position: {}", self.0)
 425     }
 426 }
 427
 428 #[stable(feature = "rust1", since = "1.0.0")]
 429 impl From<NulError> for io::Error {
 430     fn from(_: NulError) -> io::Error {
 431         io::Error::new(io::ErrorKind::InvalidInput,
 432                        "data provided contains a nul byte")
 433     }
 434 }
 435
 436 impl IntoStringError {
 437     /// Consumes this error, returning original `CString` which generated the
 438     /// error.
 439     #[stable(feature = "cstring_into", since = "1.7.0")]
 440     pub fn into_cstring(self) -> CString {
 441         self.inner
 442     }
 443
 444     /// Access the underlying UTF-8 error that was the cause of this error.
 445     #[stable(feature = "cstring_into", since = "1.7.0")]
 446     pub fn utf8_error(&self) -> Utf8Error {
 447         self.error
 448     }
 449 }
 450
 451 #[stable(feature = "cstring_into", since = "1.7.0")]
 452 impl Error for IntoStringError {
 453     fn description(&self) -> &str {
 454         "C string contained non-utf8 bytes"
 455     }
 456
 457     fn cause(&self) -> Option<&Error> {
 458         Some(&self.error)
 459     }
 460 }
 461
 462 #[stable(feature = "cstring_into", since = "1.7.0")]
 463 impl fmt::Display for IntoStringError {
 464     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 465         self.description().fmt(f)
 466     }
 467 }
 468
 469 impl CStr {
 470     /// Casts a raw C string to a safe C string wrapper.
 471     ///
 472     /// This function will cast the provided `ptr` to the `CStr` wrapper which
 473     /// allows inspection and interoperation of non-owned C strings. This method
 474     /// is unsafe for a number of reasons:
 475     ///
 476     /// * There is no guarantee to the validity of `ptr`
 477     /// * The returned lifetime is not guaranteed to be the actual lifetime of
 478     ///   `ptr`
 479     /// * There is no guarantee that the memory pointed to by `ptr` contains a
 480     ///   valid nul terminator byte at the end of the string.
 481     ///
 482     /// > **Note**: This operation is intended to be a 0-cost cast but it is
 483     /// > currently implemented with an up-front calculation of the length of
 484     /// > the string. This is not guaranteed to always be the case.
 485     ///
 486     /// # Examples
 487     ///
 488     /// ```no_run
 489     /// # fn main() {
 490     /// use std::ffi::CStr;
 491     /// use std::os::raw::c_char;
 492     ///
 493     /// extern {
 494     ///     fn my_string() -> *const c_char;
 495     /// }
 496     ///
 497     /// unsafe {
 498     ///     let slice = CStr::from_ptr(my_string());
 499     ///     println!("string returned: {}", slice.to_str().unwrap());
 500     /// }
 501     /// # }
 502     /// ```
 503     #[stable(feature = "rust1", since = "1.0.0")]
 504     pub unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr {
 505         let len = libc::strlen(ptr);
 506         mem::transmute(slice::from_raw_parts(ptr, len as usize + 1))
 507     }
 508
 509     /// Creates a C string wrapper from a byte slice.
 510     ///
 511     /// This function will cast the provided `bytes` to a `CStr` wrapper after
 512     /// ensuring that it is null terminated and does not contain any interior
 513     /// nul bytes.
 514     ///
 515     /// # Examples
 516     ///
 517     /// ```
 518     /// use std::ffi::CStr;
 519     ///
 520     /// let cstr = CStr::from_bytes_with_nul(b"hello\0");
 521     /// assert!(cstr.is_ok());
 522     /// ```
 523     #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
 524     pub fn from_bytes_with_nul(bytes: &[u8])
 525                                -> Result<&CStr, FromBytesWithNulError> {
 526         if bytes.is_empty() || memchr::memchr(0, &bytes) != Some(bytes.len() - 1) {
 527             Err(FromBytesWithNulError { _a: () })
 528         } else {
 529             Ok(unsafe { Self::from_bytes_with_nul_unchecked(bytes) })
 530         }
 531     }
 532
 533     /// Unsafely creates a C string wrapper from a byte slice.
 534     ///
 535     /// This function will cast the provided `bytes` to a `CStr` wrapper without
 536     /// performing any sanity checks. The provided slice must be null terminated
 537     /// and not contain any interior nul bytes.
 538     ///
 539     /// # Examples
 540     ///
 541     /// ```
 542     /// use std::ffi::{CStr, CString};
 543     ///
 544     /// unsafe {
 545     ///     let cstring = CString::new("hello").unwrap();
 546     ///     let cstr = CStr::from_bytes_with_nul_unchecked(cstring.to_bytes_with_nul());
 547     ///     assert_eq!(cstr, &*cstring);
 548     /// }
 549     /// ```
 550     #[stable(feature = "cstr_from_bytes", since = "1.10.0")]
 551     pub unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
 552         mem::transmute(bytes)
 553     }
 554
 555     /// Returns the inner pointer to this C string.
 556     ///
 557     /// The returned pointer will be valid for as long as `self` is and points
 558     /// to a contiguous region of memory terminated with a 0 byte to represent
 559     /// the end of the string.
 560     ///
 561     /// **WARNING**
 562     ///
 563     /// It is your responsibility to make sure that the underlying memory is not
 564     /// freed too early. For example, the following code will cause undefined
 565     /// behaviour when `ptr` is used inside the `unsafe` block:
 566     ///
 567     /// ```no_run
 568     /// use std::ffi::{CString};
 569     ///
 570     /// let ptr = CString::new("Hello").unwrap().as_ptr();
 571     /// unsafe {
 572     ///     // `ptr` is dangling
 573     ///     *ptr;
 574     /// }
 575     /// ```
 576     ///
 577     /// This happens because the pointer returned by `as_ptr` does not carry any
 578     /// lifetime information and the string is deallocated immediately after
 579     /// the `CString::new("Hello").unwrap().as_ptr()` expression is evaluated.
 580     /// To fix the problem, bind the string to a local variable:
 581     ///
 582     /// ```no_run
 583     /// use std::ffi::{CString};
 584     ///
 585     /// let hello = CString::new("Hello").unwrap();
 586     /// let ptr = hello.as_ptr();
 587     /// unsafe {
 588     ///     // `ptr` is valid because `hello` is in scope
 589     ///     *ptr;
 590     /// }
 591     /// ```
 592     #[stable(feature = "rust1", since = "1.0.0")]
 593     pub fn as_ptr(&self) -> *const c_char {
 594         self.inner.as_ptr()
 595     }
 596
 597     /// Converts this C string to a byte slice.
 598     ///
 599     /// This function will calculate the length of this string (which normally
 600     /// requires a linear amount of work to be done) and then return the
 601     /// resulting slice of `u8` elements.
 602     ///
 603     /// The returned slice will **not** contain the trailing nul that this C
 604     /// string has.
 605     ///
 606     /// > **Note**: This method is currently implemented as a 0-cost cast, but
 607     /// > it is planned to alter its definition in the future to perform the
 608     /// > length calculation whenever this method is called.
 609     #[stable(feature = "rust1", since = "1.0.0")]
 610     pub fn to_bytes(&self) -> &[u8] {
 611         let bytes = self.to_bytes_with_nul();
 612         &bytes[..bytes.len() - 1]
 613     }
 614
 615     /// Converts this C string to a byte slice containing the trailing 0 byte.
 616     ///
 617     /// This function is the equivalent of `to_bytes` except that it will retain
 618     /// the trailing nul instead of chopping it off.
 619     ///
 620     /// > **Note**: This method is currently implemented as a 0-cost cast, but
 621     /// > it is planned to alter its definition in the future to perform the
 622     /// > length calculation whenever this method is called.
 623     #[stable(feature = "rust1", since = "1.0.0")]
 624     pub fn to_bytes_with_nul(&self) -> &[u8] {
 625         unsafe { mem::transmute(&self.inner) }
 626     }
 627
 628     /// Yields a `&str` slice if the `CStr` contains valid UTF-8.
 629     ///
 630     /// This function will calculate the length of this string and check for
 631     /// UTF-8 validity, and then return the `&str` if it's valid.
 632     ///
 633     /// > **Note**: This method is currently implemented to check for validity
 634     /// > after a 0-cost cast, but it is planned to alter its definition in the
 635     /// > future to perform the length calculation in addition to the UTF-8
 636     /// > check whenever this method is called.
 637     #[stable(feature = "cstr_to_str", since = "1.4.0")]
 638     pub fn to_str(&self) -> Result<&str, str::Utf8Error> {
 639         // NB: When CStr is changed to perform the length check in .to_bytes()
 640         // instead of in from_ptr(), it may be worth considering if this should
 641         // be rewritten to do the UTF-8 check inline with the length calculation
 642         // instead of doing it afterwards.
 643         str::from_utf8(self.to_bytes())
 644     }
 645
 646     /// Converts a `CStr` into a `Cow<str>`.
 647     ///
 648     /// This function will calculate the length of this string (which normally
 649     /// requires a linear amount of work to be done) and then return the
 650     /// resulting slice as a `Cow<str>`, replacing any invalid UTF-8 sequences
 651     /// with `U+FFFD REPLACEMENT CHARACTER`.
 652     ///
 653     /// > **Note**: This method is currently implemented to check for validity
 654     /// > after a 0-cost cast, but it is planned to alter its definition in the
 655     /// > future to perform the length calculation in addition to the UTF-8
 656     /// > check whenever this method is called.
 657     #[stable(feature = "cstr_to_str", since = "1.4.0")]
 658     pub fn to_string_lossy(&self) -> Cow<str> {
 659         String::from_utf8_lossy(self.to_bytes())
 660     }
 661 }
 662
 663 #[stable(feature = "rust1", since = "1.0.0")]
 664 impl PartialEq for CStr {
 665     fn eq(&self, other: &CStr) -> bool {
 666         self.to_bytes().eq(other.to_bytes())
 667     }
 668 }
 669 #[stable(feature = "rust1", since = "1.0.0")]
 670 impl Eq for CStr {}
 671 #[stable(feature = "rust1", since = "1.0.0")]
 672 impl PartialOrd for CStr {
 673     fn partial_cmp(&self, other: &CStr) -> Option<Ordering> {
 674         self.to_bytes().partial_cmp(&other.to_bytes())
 675     }
 676 }
 677 #[stable(feature = "rust1", since = "1.0.0")]
 678 impl Ord for CStr {
 679     fn cmp(&self, other: &CStr) -> Ordering {
 680         self.to_bytes().cmp(&other.to_bytes())
 681     }
 682 }
 683
 684 #[stable(feature = "cstr_borrow", since = "1.3.0")]
 685 impl ToOwned for CStr {
 686     type Owned = CString;
 687
 688     fn to_owned(&self) -> CString {
 689         CString { inner: self.to_bytes_with_nul().to_vec().into_boxed_slice() }
 690     }
 691 }
 692
 693 #[stable(feature = "cstring_asref", since = "1.7.0")]
 694 impl<'a> From<&'a CStr> for CString {
 695     fn from(s: &'a CStr) -> CString {
 696         s.to_owned()
 697     }
 698 }
 699
 700 #[stable(feature = "cstring_asref", since = "1.7.0")]
 701 impl ops::Index<ops::RangeFull> for CString {
 702     type Output = CStr;
 703
 704     #[inline]
 705     fn index(&self, _index: ops::RangeFull) -> &CStr {
 706         self
 707     }
 708 }
 709
 710 #[stable(feature = "cstring_asref", since = "1.7.0")]
 711 impl AsRef<CStr> for CStr {
 712     fn as_ref(&self) -> &CStr {
 713         self
 714     }
 715 }
 716
 717 #[stable(feature = "cstring_asref", since = "1.7.0")]
 718 impl AsRef<CStr> for CString {
 719     fn as_ref(&self) -> &CStr {
 720         self
 721     }
 722 }
 723
 724 #[cfg(test)]
 725 mod tests {
 726     use super::*;
 727     use os::raw::c_char;
 728     use borrow::Cow::{Borrowed, Owned};
 729     use hash::{Hash, Hasher};
 730     use collections::hash_map::DefaultHasher;
 731
 732     #[test]
 733     fn c_to_rust() {
 734         let data = b"123\0";
 735         let ptr = data.as_ptr() as *const c_char;
 736         unsafe {
 737             assert_eq!(CStr::from_ptr(ptr).to_bytes(), b"123");
 738             assert_eq!(CStr::from_ptr(ptr).to_bytes_with_nul(), b"123\0");
 739         }
 740     }
 741
 742     #[test]
 743     fn simple() {
 744         let s = CString::new("1234").unwrap();
 745         assert_eq!(s.as_bytes(), b"1234");
 746         assert_eq!(s.as_bytes_with_nul(), b"1234\0");
 747     }
 748
 749     #[test]
 750     fn build_with_zero1() {
 751         assert!(CString::new(&b"\0"[..]).is_err());
 752     }
 753     #[test]
 754     fn build_with_zero2() {
 755         assert!(CString::new(vec![0]).is_err());
 756     }
 757
 758     #[test]
 759     fn build_with_zero3() {
 760         unsafe {
 761             let s = CString::from_vec_unchecked(vec![0]);
 762             assert_eq!(s.as_bytes(), b"\0");
 763         }
 764     }
 765
 766     #[test]
 767     fn formatted() {
 768         let s = CString::new(&b"abc\x01\x02\n\xE2\x80\xA6\xFF"[..]).unwrap();
 769         assert_eq!(format!("{:?}", s), r#""abc\x01\x02\n\xe2\x80\xa6\xff""#);
 770     }
 771
 772     #[test]
 773     fn borrowed() {
 774         unsafe {
 775             let s = CStr::from_ptr(b"12\0".as_ptr() as *const _);
 776             assert_eq!(s.to_bytes(), b"12");
 777             assert_eq!(s.to_bytes_with_nul(), b"12\0");
 778         }
 779     }
 780
 781     #[test]
 782     fn to_str() {
 783         let data = b"123\xE2\x80\xA6\0";
 784         let ptr = data.as_ptr() as *const c_char;
 785         unsafe {
 786             assert_eq!(CStr::from_ptr(ptr).to_str(), Ok("123…"));
 787             assert_eq!(CStr::from_ptr(ptr).to_string_lossy(), Borrowed("123…"));
 788         }
 789         let data = b"123\xE2\0";
 790         let ptr = data.as_ptr() as *const c_char;
 791         unsafe {
 792             assert!(CStr::from_ptr(ptr).to_str().is_err());
 793             assert_eq!(CStr::from_ptr(ptr).to_string_lossy(), Owned::<str>(format!("123\u{FFFD}")));
 794         }
 795     }
 796
 797     #[test]
 798     fn to_owned() {
 799         let data = b"123\0";
 800         let ptr = data.as_ptr() as *const c_char;
 801
 802         let owned = unsafe { CStr::from_ptr(ptr).to_owned() };
 803         assert_eq!(owned.as_bytes_with_nul(), data);
 804     }
 805
 806     #[test]
 807     fn equal_hash() {
 808         let data = b"123\xE2\xFA\xA6\0";
 809         let ptr = data.as_ptr() as *const c_char;
 810         let cstr: &'static CStr = unsafe { CStr::from_ptr(ptr) };
 811
 812         let mut s = DefaultHasher::new();
 813         cstr.hash(&mut s);
 814         let cstr_hash = s.finish();
 815         let mut s = DefaultHasher::new();
 816         CString::new(&data[..data.len() - 1]).unwrap().hash(&mut s);
 817         let cstring_hash = s.finish();
 818
 819         assert_eq!(cstr_hash, cstring_hash);
 820     }
 821
 822     #[test]
 823     fn from_bytes_with_nul() {
 824         let data = b"123\0";
 825         let cstr = CStr::from_bytes_with_nul(data);
 826         assert_eq!(cstr.map(CStr::to_bytes), Ok(&b"123"[..]));
 827         let cstr = CStr::from_bytes_with_nul(data);
 828         assert_eq!(cstr.map(CStr::to_bytes_with_nul), Ok(&b"123\0"[..]));
 829
 830         unsafe {
 831             let cstr = CStr::from_bytes_with_nul(data);
 832             let cstr_unchecked = CStr::from_bytes_with_nul_unchecked(data);
 833             assert_eq!(cstr, Ok(cstr_unchecked));
 834         }
 835     }
 836
 837     #[test]
 838     fn from_bytes_with_nul_unterminated() {
 839         let data = b"123";
 840         let cstr = CStr::from_bytes_with_nul(data);
 841         assert!(cstr.is_err());
 842     }
 843
 844     #[test]
 845     fn from_bytes_with_nul_interior() {
 846         let data = b"1\023\0";
 847         let cstr = CStr::from_bytes_with_nul(data);
 848         assert!(cstr.is_err());
 849     }
 850 }