1 // SPDX-License-Identifier: GPL-2.0
3 //! String representations.
5 use alloc::alloc::AllocError;
7 use core::fmt::{self, Write};
8 use core::ops::{self, Deref, Index};
12 error::{code::*, Error},
15 /// Byte string without UTF-8 validity guarantee.
17 pub struct BStr([u8]);
20 /// Returns the length of this string.
22 pub const fn len(&self) -> usize {
26 /// Returns `true` if the string is empty.
28 pub const fn is_empty(&self) -> bool {
32 /// Creates a [`BStr`] from a `[u8]`.
34 pub const fn from_bytes(bytes: &[u8]) -> &Self {
35 // SAFETY: `BStr` is transparent to `[u8]`.
36 unsafe { &*(bytes as *const [u8] as *const BStr) }
40 impl fmt::Display for BStr {
41 /// Formats printable ASCII characters, escaping the rest.
44 /// # use kernel::{fmt, b_str, str::{BStr, CString}};
45 /// let ascii = b_str!("Hello, BStr!");
46 /// let s = CString::try_from_fmt(fmt!("{}", ascii)).unwrap();
47 /// assert_eq!(s.as_bytes(), "Hello, BStr!".as_bytes());
49 /// let non_ascii = b_str!("🦀");
50 /// let s = CString::try_from_fmt(fmt!("{}", non_ascii)).unwrap();
51 /// assert_eq!(s.as_bytes(), "\\xf0\\x9f\\xa6\\x80".as_bytes());
53 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
56 // Common escape codes.
57 b'\t' => f.write_str("\\t")?,
58 b'\n' => f.write_str("\\n")?,
59 b'\r' => f.write_str("\\r")?,
60 // Printable characters.
61 0x20..=0x7e => f.write_char(b as char)?,
62 _ => write!(f, "\\x{:02x}", b)?,
69 impl fmt::Debug for BStr {
70 /// Formats printable ASCII characters with a double quote on either end,
71 /// escaping the rest.
74 /// # use kernel::{fmt, b_str, str::{BStr, CString}};
75 /// // Embedded double quotes are escaped.
76 /// let ascii = b_str!("Hello, \"BStr\"!");
77 /// let s = CString::try_from_fmt(fmt!("{:?}", ascii)).unwrap();
78 /// assert_eq!(s.as_bytes(), "\"Hello, \\\"BStr\\\"!\"".as_bytes());
80 /// let non_ascii = b_str!("😺");
81 /// let s = CString::try_from_fmt(fmt!("{:?}", non_ascii)).unwrap();
82 /// assert_eq!(s.as_bytes(), "\"\\xf0\\x9f\\x98\\xba\"".as_bytes());
84 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
88 // Common escape codes.
89 b'\t' => f.write_str("\\t")?,
90 b'\n' => f.write_str("\\n")?,
91 b'\r' => f.write_str("\\r")?,
92 // String escape characters.
93 b'\"' => f.write_str("\\\"")?,
94 b'\\' => f.write_str("\\\\")?,
95 // Printable characters.
96 0x20..=0x7e => f.write_char(b as char)?,
97 _ => write!(f, "\\x{:02x}", b)?,
104 impl Deref for BStr {
108 fn deref(&self) -> &Self::Target {
113 /// Creates a new [`BStr`] from a string literal.
115 /// `b_str!` converts the supplied string literal to byte string, so non-ASCII
116 /// characters can be included.
121 /// # use kernel::b_str;
122 /// # use kernel::str::BStr;
123 /// const MY_BSTR: &BStr = b_str!("My awesome BStr!");
128 const S: &'static str = $str;
129 const C: &'static $crate::str::BStr = $crate::str::BStr::from_bytes(S.as_bytes());
134 /// Possible errors when using conversion functions in [`CStr`].
135 #[derive(Debug, Clone, Copy)]
136 pub enum CStrConvertError {
137 /// Supplied bytes contain an interior `NUL`.
140 /// Supplied bytes are not terminated by `NUL`.
144 impl From<CStrConvertError> for Error {
146 fn from(_: CStrConvertError) -> Error {
151 /// A string that is guaranteed to have exactly one `NUL` byte, which is at the
154 /// Used for interoperability with kernel APIs that take C strings.
156 pub struct CStr([u8]);
159 /// Returns the length of this string excluding `NUL`.
161 pub const fn len(&self) -> usize {
162 self.len_with_nul() - 1
165 /// Returns the length of this string with `NUL`.
167 pub const fn len_with_nul(&self) -> usize {
168 // SAFETY: This is one of the invariant of `CStr`.
169 // We add a `unreachable_unchecked` here to hint the optimizer that
170 // the value returned from this function is non-zero.
171 if self.0.is_empty() {
172 unsafe { core::hint::unreachable_unchecked() };
177 /// Returns `true` if the string only includes `NUL`.
179 pub const fn is_empty(&self) -> bool {
183 /// Wraps a raw C string pointer.
187 /// `ptr` must be a valid pointer to a `NUL`-terminated C string, and it must
188 /// last at least `'a`. When `CStr` is alive, the memory pointed by `ptr`
189 /// must not be mutated.
191 pub unsafe fn from_char_ptr<'a>(ptr: *const core::ffi::c_char) -> &'a Self {
192 // SAFETY: The safety precondition guarantees `ptr` is a valid pointer
193 // to a `NUL`-terminated C string.
194 let len = unsafe { bindings::strlen(ptr) } + 1;
195 // SAFETY: Lifetime guaranteed by the safety precondition.
196 let bytes = unsafe { core::slice::from_raw_parts(ptr as _, len as _) };
197 // SAFETY: As `len` is returned by `strlen`, `bytes` does not contain interior `NUL`.
198 // As we have added 1 to `len`, the last byte is known to be `NUL`.
199 unsafe { Self::from_bytes_with_nul_unchecked(bytes) }
202 /// Creates a [`CStr`] from a `[u8]`.
204 /// The provided slice must be `NUL`-terminated, does not contain any
205 /// interior `NUL` bytes.
206 pub const fn from_bytes_with_nul(bytes: &[u8]) -> Result<&Self, CStrConvertError> {
207 if bytes.is_empty() {
208 return Err(CStrConvertError::NotNulTerminated);
210 if bytes[bytes.len() - 1] != 0 {
211 return Err(CStrConvertError::NotNulTerminated);
214 // `i + 1 < bytes.len()` allows LLVM to optimize away bounds checking,
215 // while it couldn't optimize away bounds checks for `i < bytes.len() - 1`.
216 while i + 1 < bytes.len() {
218 return Err(CStrConvertError::InteriorNul);
222 // SAFETY: We just checked that all properties hold.
223 Ok(unsafe { Self::from_bytes_with_nul_unchecked(bytes) })
226 /// Creates a [`CStr`] from a `[u8]` without performing any additional
231 /// `bytes` *must* end with a `NUL` byte, and should only have a single
232 /// `NUL` byte (or the string will be truncated).
234 pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
235 // SAFETY: Properties of `bytes` guaranteed by the safety precondition.
236 unsafe { core::mem::transmute(bytes) }
239 /// Returns a C pointer to the string.
241 pub const fn as_char_ptr(&self) -> *const core::ffi::c_char {
245 /// Convert the string to a byte slice without the trailing `NUL` byte.
247 pub fn as_bytes(&self) -> &[u8] {
248 &self.0[..self.len()]
251 /// Convert the string to a byte slice containing the trailing `NUL` byte.
253 pub const fn as_bytes_with_nul(&self) -> &[u8] {
257 /// Yields a [`&str`] slice if the [`CStr`] contains valid UTF-8.
259 /// If the contents of the [`CStr`] are valid UTF-8 data, this
260 /// function will return the corresponding [`&str`] slice. Otherwise,
261 /// it will return an error with details of where UTF-8 validation failed.
266 /// # use kernel::str::CStr;
267 /// let cstr = CStr::from_bytes_with_nul(b"foo\0").unwrap();
268 /// assert_eq!(cstr.to_str(), Ok("foo"));
271 pub fn to_str(&self) -> Result<&str, core::str::Utf8Error> {
272 core::str::from_utf8(self.as_bytes())
275 /// Unsafely convert this [`CStr`] into a [`&str`], without checking for
280 /// The contents must be valid UTF-8.
285 /// # use kernel::c_str;
286 /// # use kernel::str::CStr;
287 /// let bar = c_str!("ツ");
288 /// // SAFETY: String literals are guaranteed to be valid UTF-8
289 /// // by the Rust compiler.
290 /// assert_eq!(unsafe { bar.as_str_unchecked() }, "ツ");
293 pub unsafe fn as_str_unchecked(&self) -> &str {
294 unsafe { core::str::from_utf8_unchecked(self.as_bytes()) }
297 /// Convert this [`CStr`] into a [`CString`] by allocating memory and
298 /// copying over the string data.
299 pub fn to_cstring(&self) -> Result<CString, AllocError> {
300 CString::try_from(self)
304 impl fmt::Display for CStr {
305 /// Formats printable ASCII characters, escaping the rest.
308 /// # use kernel::c_str;
309 /// # use kernel::fmt;
310 /// # use kernel::str::CStr;
311 /// # use kernel::str::CString;
312 /// let penguin = c_str!("🐧");
313 /// let s = CString::try_from_fmt(fmt!("{}", penguin)).unwrap();
314 /// assert_eq!(s.as_bytes_with_nul(), "\\xf0\\x9f\\x90\\xa7\0".as_bytes());
316 /// let ascii = c_str!("so \"cool\"");
317 /// let s = CString::try_from_fmt(fmt!("{}", ascii)).unwrap();
318 /// assert_eq!(s.as_bytes_with_nul(), "so \"cool\"\0".as_bytes());
320 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
321 for &c in self.as_bytes() {
322 if (0x20..0x7f).contains(&c) {
323 // Printable character.
324 f.write_char(c as char)?;
326 write!(f, "\\x{:02x}", c)?;
333 impl fmt::Debug for CStr {
334 /// Formats printable ASCII characters with a double quote on either end, escaping the rest.
337 /// # use kernel::c_str;
338 /// # use kernel::fmt;
339 /// # use kernel::str::CStr;
340 /// # use kernel::str::CString;
341 /// let penguin = c_str!("🐧");
342 /// let s = CString::try_from_fmt(fmt!("{:?}", penguin)).unwrap();
343 /// assert_eq!(s.as_bytes_with_nul(), "\"\\xf0\\x9f\\x90\\xa7\"\0".as_bytes());
345 /// // Embedded double quotes are escaped.
346 /// let ascii = c_str!("so \"cool\"");
347 /// let s = CString::try_from_fmt(fmt!("{:?}", ascii)).unwrap();
348 /// assert_eq!(s.as_bytes_with_nul(), "\"so \\\"cool\\\"\"\0".as_bytes());
350 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
352 for &c in self.as_bytes() {
354 // Printable characters.
355 b'\"' => f.write_str("\\\"")?,
356 0x20..=0x7e => f.write_char(c as char)?,
357 _ => write!(f, "\\x{:02x}", c)?,
364 impl AsRef<BStr> for CStr {
366 fn as_ref(&self) -> &BStr {
367 BStr::from_bytes(self.as_bytes())
371 impl Deref for CStr {
375 fn deref(&self) -> &Self::Target {
380 impl Index<ops::RangeFrom<usize>> for CStr {
384 fn index(&self, index: ops::RangeFrom<usize>) -> &Self::Output {
385 // Delegate bounds checking to slice.
386 // Assign to _ to mute clippy's unnecessary operation warning.
387 let _ = &self.as_bytes()[index.start..];
388 // SAFETY: We just checked the bounds.
389 unsafe { Self::from_bytes_with_nul_unchecked(&self.0[index.start..]) }
393 impl Index<ops::RangeFull> for CStr {
397 fn index(&self, _index: ops::RangeFull) -> &Self::Output {
405 // Marker trait for index types that can be forward to `BStr`.
406 pub trait CStrIndex {}
408 impl CStrIndex for usize {}
409 impl CStrIndex for ops::Range<usize> {}
410 impl CStrIndex for ops::RangeInclusive<usize> {}
411 impl CStrIndex for ops::RangeToInclusive<usize> {}
414 impl<Idx> Index<Idx> for CStr
416 Idx: private::CStrIndex,
419 type Output = <BStr as Index<Idx>>::Output;
422 fn index(&self, index: Idx) -> &Self::Output {
423 &self.as_ref()[index]
427 /// Creates a new [`CStr`] from a string literal.
429 /// The string literal should not contain any `NUL` bytes.
434 /// # use kernel::c_str;
435 /// # use kernel::str::CStr;
436 /// const MY_CSTR: &CStr = c_str!("My awesome CStr!");
441 const S: &str = concat!($str, "\0");
442 const C: &$crate::str::CStr = match $crate::str::CStr::from_bytes_with_nul(S.as_bytes()) {
444 Err(_) => panic!("string contains interior NUL"),
455 const ALL_ASCII_CHARS: &'static str =
456 "\\x01\\x02\\x03\\x04\\x05\\x06\\x07\\x08\\x09\\x0a\\x0b\\x0c\\x0d\\x0e\\x0f\
457 \\x10\\x11\\x12\\x13\\x14\\x15\\x16\\x17\\x18\\x19\\x1a\\x1b\\x1c\\x1d\\x1e\\x1f \
458 !\"#$%&'()*+,-./0123456789:;<=>?@\
459 ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\\x7f\
460 \\x80\\x81\\x82\\x83\\x84\\x85\\x86\\x87\\x88\\x89\\x8a\\x8b\\x8c\\x8d\\x8e\\x8f\
461 \\x90\\x91\\x92\\x93\\x94\\x95\\x96\\x97\\x98\\x99\\x9a\\x9b\\x9c\\x9d\\x9e\\x9f\
462 \\xa0\\xa1\\xa2\\xa3\\xa4\\xa5\\xa6\\xa7\\xa8\\xa9\\xaa\\xab\\xac\\xad\\xae\\xaf\
463 \\xb0\\xb1\\xb2\\xb3\\xb4\\xb5\\xb6\\xb7\\xb8\\xb9\\xba\\xbb\\xbc\\xbd\\xbe\\xbf\
464 \\xc0\\xc1\\xc2\\xc3\\xc4\\xc5\\xc6\\xc7\\xc8\\xc9\\xca\\xcb\\xcc\\xcd\\xce\\xcf\
465 \\xd0\\xd1\\xd2\\xd3\\xd4\\xd5\\xd6\\xd7\\xd8\\xd9\\xda\\xdb\\xdc\\xdd\\xde\\xdf\
466 \\xe0\\xe1\\xe2\\xe3\\xe4\\xe5\\xe6\\xe7\\xe8\\xe9\\xea\\xeb\\xec\\xed\\xee\\xef\
467 \\xf0\\xf1\\xf2\\xf3\\xf4\\xf5\\xf6\\xf7\\xf8\\xf9\\xfa\\xfb\\xfc\\xfd\\xfe\\xff";
470 fn test_cstr_to_str() {
471 let good_bytes = b"\xf0\x9f\xa6\x80\0";
472 let checked_cstr = CStr::from_bytes_with_nul(good_bytes).unwrap();
473 let checked_str = checked_cstr.to_str().unwrap();
474 assert_eq!(checked_str, "🦀");
479 fn test_cstr_to_str_panic() {
480 let bad_bytes = b"\xc3\x28\0";
481 let checked_cstr = CStr::from_bytes_with_nul(bad_bytes).unwrap();
482 checked_cstr.to_str().unwrap();
486 fn test_cstr_as_str_unchecked() {
487 let good_bytes = b"\xf0\x9f\x90\xA7\0";
488 let checked_cstr = CStr::from_bytes_with_nul(good_bytes).unwrap();
489 let unchecked_str = unsafe { checked_cstr.as_str_unchecked() };
490 assert_eq!(unchecked_str, "🐧");
494 fn test_cstr_display() {
495 let hello_world = CStr::from_bytes_with_nul(b"hello, world!\0").unwrap();
496 assert_eq!(format!("{}", hello_world), "hello, world!");
497 let non_printables = CStr::from_bytes_with_nul(b"\x01\x09\x0a\0").unwrap();
498 assert_eq!(format!("{}", non_printables), "\\x01\\x09\\x0a");
499 let non_ascii = CStr::from_bytes_with_nul(b"d\xe9j\xe0 vu\0").unwrap();
500 assert_eq!(format!("{}", non_ascii), "d\\xe9j\\xe0 vu");
501 let good_bytes = CStr::from_bytes_with_nul(b"\xf0\x9f\xa6\x80\0").unwrap();
502 assert_eq!(format!("{}", good_bytes), "\\xf0\\x9f\\xa6\\x80");
506 fn test_cstr_display_all_bytes() {
507 let mut bytes: [u8; 256] = [0; 256];
508 // fill `bytes` with [1..=255] + [0]
509 for i in u8::MIN..=u8::MAX {
510 bytes[i as usize] = i.wrapping_add(1);
512 let cstr = CStr::from_bytes_with_nul(&bytes).unwrap();
513 assert_eq!(format!("{}", cstr), ALL_ASCII_CHARS);
517 fn test_cstr_debug() {
518 let hello_world = CStr::from_bytes_with_nul(b"hello, world!\0").unwrap();
519 assert_eq!(format!("{:?}", hello_world), "\"hello, world!\"");
520 let non_printables = CStr::from_bytes_with_nul(b"\x01\x09\x0a\0").unwrap();
521 assert_eq!(format!("{:?}", non_printables), "\"\\x01\\x09\\x0a\"");
522 let non_ascii = CStr::from_bytes_with_nul(b"d\xe9j\xe0 vu\0").unwrap();
523 assert_eq!(format!("{:?}", non_ascii), "\"d\\xe9j\\xe0 vu\"");
524 let good_bytes = CStr::from_bytes_with_nul(b"\xf0\x9f\xa6\x80\0").unwrap();
525 assert_eq!(format!("{:?}", good_bytes), "\"\\xf0\\x9f\\xa6\\x80\"");
529 fn test_bstr_display() {
530 let hello_world = BStr::from_bytes(b"hello, world!");
531 assert_eq!(format!("{}", hello_world), "hello, world!");
532 let escapes = BStr::from_bytes(b"_\t_\n_\r_\\_\'_\"_");
533 assert_eq!(format!("{}", escapes), "_\\t_\\n_\\r_\\_'_\"_");
534 let others = BStr::from_bytes(b"\x01");
535 assert_eq!(format!("{}", others), "\\x01");
536 let non_ascii = BStr::from_bytes(b"d\xe9j\xe0 vu");
537 assert_eq!(format!("{}", non_ascii), "d\\xe9j\\xe0 vu");
538 let good_bytes = BStr::from_bytes(b"\xf0\x9f\xa6\x80");
539 assert_eq!(format!("{}", good_bytes), "\\xf0\\x9f\\xa6\\x80");
543 fn test_bstr_debug() {
544 let hello_world = BStr::from_bytes(b"hello, world!");
545 assert_eq!(format!("{:?}", hello_world), "\"hello, world!\"");
546 let escapes = BStr::from_bytes(b"_\t_\n_\r_\\_\'_\"_");
547 assert_eq!(format!("{:?}", escapes), "\"_\\t_\\n_\\r_\\\\_'_\\\"_\"");
548 let others = BStr::from_bytes(b"\x01");
549 assert_eq!(format!("{:?}", others), "\"\\x01\"");
550 let non_ascii = BStr::from_bytes(b"d\xe9j\xe0 vu");
551 assert_eq!(format!("{:?}", non_ascii), "\"d\\xe9j\\xe0 vu\"");
552 let good_bytes = BStr::from_bytes(b"\xf0\x9f\xa6\x80");
553 assert_eq!(format!("{:?}", good_bytes), "\"\\xf0\\x9f\\xa6\\x80\"");
557 /// Allows formatting of [`fmt::Arguments`] into a raw buffer.
559 /// It does not fail if callers write past the end of the buffer so that they can calculate the
560 /// size required to fit everything.
564 /// The memory region between `pos` (inclusive) and `end` (exclusive) is valid for writes if `pos`
565 /// is less than `end`.
566 pub(crate) struct RawFormatter {
567 // Use `usize` to use `saturating_*` functions.
574 /// Creates a new instance of [`RawFormatter`] with an empty buffer.
576 // INVARIANT: The buffer is empty, so the region that needs to be writable is empty.
584 /// Creates a new instance of [`RawFormatter`] with the given buffer pointers.
588 /// If `pos` is less than `end`, then the region between `pos` (inclusive) and `end`
589 /// (exclusive) must be valid for writes for the lifetime of the returned [`RawFormatter`].
590 pub(crate) unsafe fn from_ptrs(pos: *mut u8, end: *mut u8) -> Self {
591 // INVARIANT: The safety requirements guarantee the type invariants.
599 /// Creates a new instance of [`RawFormatter`] with the given buffer.
603 /// The memory region starting at `buf` and extending for `len` bytes must be valid for writes
604 /// for the lifetime of the returned [`RawFormatter`].
605 pub(crate) unsafe fn from_buffer(buf: *mut u8, len: usize) -> Self {
606 let pos = buf as usize;
607 // INVARIANT: We ensure that `end` is never less then `buf`, and the safety requirements
608 // guarantees that the memory region is valid for writes.
612 end: pos.saturating_add(len),
616 /// Returns the current insert position.
618 /// N.B. It may point to invalid memory.
619 pub(crate) fn pos(&self) -> *mut u8 {
623 /// Returns the number of bytes written to the formatter.
624 pub(crate) fn bytes_written(&self) -> usize {
629 impl fmt::Write for RawFormatter {
630 fn write_str(&mut self, s: &str) -> fmt::Result {
631 // `pos` value after writing `len` bytes. This does not have to be bounded by `end`, but we
632 // don't want it to wrap around to 0.
633 let pos_new = self.pos.saturating_add(s.len());
635 // Amount that we can copy. `saturating_sub` ensures we get 0 if `pos` goes past `end`.
636 let len_to_copy = core::cmp::min(pos_new, self.end).saturating_sub(self.pos);
639 // SAFETY: If `len_to_copy` is non-zero, then we know `pos` has not gone past `end`
640 // yet, so it is valid for write per the type invariants.
642 core::ptr::copy_nonoverlapping(
643 s.as_bytes().as_ptr(),
655 /// Allows formatting of [`fmt::Arguments`] into a raw buffer.
657 /// Fails if callers attempt to write more than will fit in the buffer.
658 pub(crate) struct Formatter(RawFormatter);
661 /// Creates a new instance of [`Formatter`] with the given buffer.
665 /// The memory region starting at `buf` and extending for `len` bytes must be valid for writes
666 /// for the lifetime of the returned [`Formatter`].
667 pub(crate) unsafe fn from_buffer(buf: *mut u8, len: usize) -> Self {
668 // SAFETY: The safety requirements of this function satisfy those of the callee.
669 Self(unsafe { RawFormatter::from_buffer(buf, len) })
673 impl Deref for Formatter {
674 type Target = RawFormatter;
676 fn deref(&self) -> &Self::Target {
681 impl fmt::Write for Formatter {
682 fn write_str(&mut self, s: &str) -> fmt::Result {
683 self.0.write_str(s)?;
685 // Fail the request if we go past the end of the buffer.
686 if self.0.pos > self.0.end {
694 /// An owned string that is guaranteed to have exactly one `NUL` byte, which is at the end.
696 /// Used for interoperability with kernel APIs that take C strings.
700 /// The string is always `NUL`-terminated and contains no other `NUL` bytes.
705 /// use kernel::{str::CString, fmt};
707 /// let s = CString::try_from_fmt(fmt!("{}{}{}", "abc", 10, 20)).unwrap();
708 /// assert_eq!(s.as_bytes_with_nul(), "abc1020\0".as_bytes());
710 /// let tmp = "testing";
711 /// let s = CString::try_from_fmt(fmt!("{tmp}{}", 123)).unwrap();
712 /// assert_eq!(s.as_bytes_with_nul(), "testing123\0".as_bytes());
714 /// // This fails because it has an embedded `NUL` byte.
715 /// let s = CString::try_from_fmt(fmt!("a\0b{}", 123));
716 /// assert_eq!(s.is_ok(), false);
723 /// Creates an instance of [`CString`] from the given formatted arguments.
724 pub fn try_from_fmt(args: fmt::Arguments<'_>) -> Result<Self, Error> {
725 // Calculate the size needed (formatted string plus `NUL` terminator).
726 let mut f = RawFormatter::new();
729 let size = f.bytes_written();
731 // Allocate a vector with the required number of bytes, and write to it.
732 let mut buf = Vec::try_with_capacity(size)?;
733 // SAFETY: The buffer stored in `buf` is at least of size `size` and is valid for writes.
734 let mut f = unsafe { Formatter::from_buffer(buf.as_mut_ptr(), size) };
738 // SAFETY: The number of bytes that can be written to `f` is bounded by `size`, which is
739 // `buf`'s capacity. The contents of the buffer have been initialised by writes to `f`.
740 unsafe { buf.set_len(f.bytes_written()) };
742 // Check that there are no `NUL` bytes before the end.
743 // SAFETY: The buffer is valid for read because `f.bytes_written()` is bounded by `size`
744 // (which the minimum buffer size) and is non-zero (we wrote at least the `NUL` terminator)
745 // so `f.bytes_written() - 1` doesn't underflow.
746 let ptr = unsafe { bindings::memchr(buf.as_ptr().cast(), 0, (f.bytes_written() - 1) as _) };
751 // INVARIANT: We wrote the `NUL` terminator and checked above that no other `NUL` bytes
752 // exist in the buffer.
757 impl Deref for CString {
760 fn deref(&self) -> &Self::Target {
761 // SAFETY: The type invariants guarantee that the string is `NUL`-terminated and that no
762 // other `NUL` bytes exist.
763 unsafe { CStr::from_bytes_with_nul_unchecked(self.buf.as_slice()) }
767 impl<'a> TryFrom<&'a CStr> for CString {
768 type Error = AllocError;
770 fn try_from(cstr: &'a CStr) -> Result<CString, AllocError> {
771 let mut buf = Vec::new();
773 buf.try_extend_from_slice(cstr.as_bytes_with_nul())
774 .map_err(|_| AllocError)?;
776 // INVARIANT: The `CStr` and `CString` types have the same invariants for
777 // the string data, and we copied it over without changes.
782 impl fmt::Debug for CString {
783 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
784 fmt::Debug::fmt(&**self, f)
788 /// A convenience alias for [`core::format_args`].
791 ($($f:tt)*) => ( core::format_args!($($f)*) )