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1// SPDX-License-Identifier: GPL-2.0
2
3//! String representations.
4
5use alloc::alloc::AllocError;
6use alloc::vec::Vec;
7use core::fmt::{self, Write};
8use core::ops::{self, Deref, Index};
9
10use crate::{
11 bindings,
12 error::{code::*, Error},
13};
14
15/// Byte string without UTF-8 validity guarantee.
16///
17/// `BStr` is simply an alias to `[u8]`, but has a more evident semantical meaning.
18pub type BStr = [u8];
19
20/// Creates a new [`BStr`] from a string literal.
21///
22/// `b_str!` converts the supplied string literal to byte string, so non-ASCII
23/// characters can be included.
24///
25/// # Examples
26///
27/// ```
28/// # use kernel::b_str;
29/// # use kernel::str::BStr;
30/// const MY_BSTR: &BStr = b_str!("My awesome BStr!");
31/// ```
32#[macro_export]
33macro_rules! b_str {
34 ($str:literal) => {{
35 const S: &'static str = $str;
36 const C: &'static $crate::str::BStr = S.as_bytes();
37 C
38 }};
39}
40
41/// Possible errors when using conversion functions in [`CStr`].
42#[derive(Debug, Clone, Copy)]
43pub enum CStrConvertError {
44 /// Supplied bytes contain an interior `NUL`.
45 InteriorNul,
46
47 /// Supplied bytes are not terminated by `NUL`.
48 NotNulTerminated,
49}
50
51impl From<CStrConvertError> for Error {
52 #[inline]
53 fn from(_: CStrConvertError) -> Error {
54 EINVAL
55 }
56}
57
58/// A string that is guaranteed to have exactly one `NUL` byte, which is at the
59/// end.
60///
61/// Used for interoperability with kernel APIs that take C strings.
62#[repr(transparent)]
63pub struct CStr([u8]);
64
65impl CStr {
66 /// Returns the length of this string excluding `NUL`.
67 #[inline]
68 pub const fn len(&self) -> usize {
69 self.len_with_nul() - 1
70 }
71
72 /// Returns the length of this string with `NUL`.
73 #[inline]
74 pub const fn len_with_nul(&self) -> usize {
75 // SAFETY: This is one of the invariant of `CStr`.
76 // We add a `unreachable_unchecked` here to hint the optimizer that
77 // the value returned from this function is non-zero.
78 if self.0.is_empty() {
79 unsafe { core::hint::unreachable_unchecked() };
80 }
81 self.0.len()
82 }
83
84 /// Returns `true` if the string only includes `NUL`.
85 #[inline]
86 pub const fn is_empty(&self) -> bool {
87 self.len() == 0
88 }
89
90 /// Wraps a raw C string pointer.
91 ///
92 /// # Safety
93 ///
94 /// `ptr` must be a valid pointer to a `NUL`-terminated C string, and it must
95 /// last at least `'a`. When `CStr` is alive, the memory pointed by `ptr`
96 /// must not be mutated.
97 #[inline]
98 pub unsafe fn from_char_ptr<'a>(ptr: *const core::ffi::c_char) -> &'a Self {
99 // SAFETY: The safety precondition guarantees `ptr` is a valid pointer
100 // to a `NUL`-terminated C string.
101 let len = unsafe { bindings::strlen(ptr) } + 1;
102 // SAFETY: Lifetime guaranteed by the safety precondition.
103 let bytes = unsafe { core::slice::from_raw_parts(ptr as _, len as _) };
104 // SAFETY: As `len` is returned by `strlen`, `bytes` does not contain interior `NUL`.
105 // As we have added 1 to `len`, the last byte is known to be `NUL`.
106 unsafe { Self::from_bytes_with_nul_unchecked(bytes) }
107 }
108
109 /// Creates a [`CStr`] from a `[u8]`.
110 ///
111 /// The provided slice must be `NUL`-terminated, does not contain any
112 /// interior `NUL` bytes.
113 pub const fn from_bytes_with_nul(bytes: &[u8]) -> Result<&Self, CStrConvertError> {
114 if bytes.is_empty() {
115 return Err(CStrConvertError::NotNulTerminated);
116 }
117 if bytes[bytes.len() - 1] != 0 {
118 return Err(CStrConvertError::NotNulTerminated);
119 }
120 let mut i = 0;
121 // `i + 1 < bytes.len()` allows LLVM to optimize away bounds checking,
122 // while it couldn't optimize away bounds checks for `i < bytes.len() - 1`.
123 while i + 1 < bytes.len() {
124 if bytes[i] == 0 {
125 return Err(CStrConvertError::InteriorNul);
126 }
127 i += 1;
128 }
129 // SAFETY: We just checked that all properties hold.
130 Ok(unsafe { Self::from_bytes_with_nul_unchecked(bytes) })
131 }
132
133 /// Creates a [`CStr`] from a `[u8]` without performing any additional
134 /// checks.
135 ///
136 /// # Safety
137 ///
138 /// `bytes` *must* end with a `NUL` byte, and should only have a single
139 /// `NUL` byte (or the string will be truncated).
140 #[inline]
141 pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
142 // SAFETY: Properties of `bytes` guaranteed by the safety precondition.
143 unsafe { core::mem::transmute(bytes) }
144 }
145
146 /// Returns a C pointer to the string.
147 #[inline]
148 pub const fn as_char_ptr(&self) -> *const core::ffi::c_char {
149 self.0.as_ptr() as _
150 }
151
152 /// Convert the string to a byte slice without the trailing 0 byte.
153 #[inline]
154 pub fn as_bytes(&self) -> &[u8] {
155 &self.0[..self.len()]
156 }
157
158 /// Convert the string to a byte slice containing the trailing 0 byte.
159 #[inline]
160 pub const fn as_bytes_with_nul(&self) -> &[u8] {
161 &self.0
162 }
163
164 /// Yields a [`&str`] slice if the [`CStr`] contains valid UTF-8.
165 ///
166 /// If the contents of the [`CStr`] are valid UTF-8 data, this
167 /// function will return the corresponding [`&str`] slice. Otherwise,
168 /// it will return an error with details of where UTF-8 validation failed.
169 ///
170 /// # Examples
171 ///
172 /// ```
173 /// # use kernel::str::CStr;
174 /// let cstr = CStr::from_bytes_with_nul(b"foo\0").unwrap();
175 /// assert_eq!(cstr.to_str(), Ok("foo"));
176 /// ```
177 #[inline]
178 pub fn to_str(&self) -> Result<&str, core::str::Utf8Error> {
179 core::str::from_utf8(self.as_bytes())
180 }
181
182 /// Unsafely convert this [`CStr`] into a [`&str`], without checking for
183 /// valid UTF-8.
184 ///
185 /// # Safety
186 ///
187 /// The contents must be valid UTF-8.
188 ///
189 /// # Examples
190 ///
191 /// ```
192 /// # use kernel::c_str;
193 /// # use kernel::str::CStr;
194 /// // SAFETY: String literals are guaranteed to be valid UTF-8
195 /// // by the Rust compiler.
196 /// let bar = c_str!("ツ");
197 /// assert_eq!(unsafe { bar.as_str_unchecked() }, "ツ");
198 /// ```
199 #[inline]
200 pub unsafe fn as_str_unchecked(&self) -> &str {
201 unsafe { core::str::from_utf8_unchecked(self.as_bytes()) }
202 }
203
204 /// Convert this [`CStr`] into a [`CString`] by allocating memory and
205 /// copying over the string data.
206 pub fn to_cstring(&self) -> Result<CString, AllocError> {
207 CString::try_from(self)
208 }
209}
210
211impl fmt::Display for CStr {
212 /// Formats printable ASCII characters, escaping the rest.
213 ///
214 /// ```
215 /// # use kernel::c_str;
216 /// # use kernel::fmt;
217 /// # use kernel::str::CStr;
218 /// # use kernel::str::CString;
219 /// let penguin = c_str!("🐧");
220 /// let s = CString::try_from_fmt(fmt!("{}", penguin)).unwrap();
221 /// assert_eq!(s.as_bytes_with_nul(), "\\xf0\\x9f\\x90\\xa7\0".as_bytes());
222 ///
223 /// let ascii = c_str!("so \"cool\"");
224 /// let s = CString::try_from_fmt(fmt!("{}", ascii)).unwrap();
225 /// assert_eq!(s.as_bytes_with_nul(), "so \"cool\"\0".as_bytes());
226 /// ```
227 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
228 for &c in self.as_bytes() {
229 if (0x20..0x7f).contains(&c) {
230 // Printable character.
231 f.write_char(c as char)?;
232 } else {
233 write!(f, "\\x{:02x}", c)?;
234 }
235 }
236 Ok(())
237 }
238}
239
240impl fmt::Debug for CStr {
241 /// Formats printable ASCII characters with a double quote on either end, escaping the rest.
242 ///
243 /// ```
244 /// # use kernel::c_str;
245 /// # use kernel::fmt;
246 /// # use kernel::str::CStr;
247 /// # use kernel::str::CString;
248 /// let penguin = c_str!("🐧");
249 /// let s = CString::try_from_fmt(fmt!("{:?}", penguin)).unwrap();
250 /// assert_eq!(s.as_bytes_with_nul(), "\"\\xf0\\x9f\\x90\\xa7\"\0".as_bytes());
251 ///
252 /// // Embedded double quotes are escaped.
253 /// let ascii = c_str!("so \"cool\"");
254 /// let s = CString::try_from_fmt(fmt!("{:?}", ascii)).unwrap();
255 /// assert_eq!(s.as_bytes_with_nul(), "\"so \\\"cool\\\"\"\0".as_bytes());
256 /// ```
257 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
258 f.write_str("\"")?;
259 for &c in self.as_bytes() {
260 match c {
261 // Printable characters.
262 b'\"' => f.write_str("\\\"")?,
263 0x20..=0x7e => f.write_char(c as char)?,
264 _ => write!(f, "\\x{:02x}", c)?,
265 }
266 }
267 f.write_str("\"")
268 }
269}
270
271impl AsRef<BStr> for CStr {
272 #[inline]
273 fn as_ref(&self) -> &BStr {
274 self.as_bytes()
275 }
276}
277
278impl Deref for CStr {
279 type Target = BStr;
280
281 #[inline]
282 fn deref(&self) -> &Self::Target {
283 self.as_bytes()
284 }
285}
286
287impl Index<ops::RangeFrom<usize>> for CStr {
288 type Output = CStr;
289
290 #[inline]
291 fn index(&self, index: ops::RangeFrom<usize>) -> &Self::Output {
292 // Delegate bounds checking to slice.
293 // Assign to _ to mute clippy's unnecessary operation warning.
294 let _ = &self.as_bytes()[index.start..];
295 // SAFETY: We just checked the bounds.
296 unsafe { Self::from_bytes_with_nul_unchecked(&self.0[index.start..]) }
297 }
298}
299
300impl Index<ops::RangeFull> for CStr {
301 type Output = CStr;
302
303 #[inline]
304 fn index(&self, _index: ops::RangeFull) -> &Self::Output {
305 self
306 }
307}
308
309mod private {
310 use core::ops;
311
312 // Marker trait for index types that can be forward to `BStr`.
313 pub trait CStrIndex {}
314
315 impl CStrIndex for usize {}
316 impl CStrIndex for ops::Range<usize> {}
317 impl CStrIndex for ops::RangeInclusive<usize> {}
318 impl CStrIndex for ops::RangeToInclusive<usize> {}
319}
320
321impl<Idx> Index<Idx> for CStr
322where
323 Idx: private::CStrIndex,
324 BStr: Index<Idx>,
325{
326 type Output = <BStr as Index<Idx>>::Output;
327
328 #[inline]
329 fn index(&self, index: Idx) -> &Self::Output {
330 &self.as_bytes()[index]
331 }
332}
333
334/// Creates a new [`CStr`] from a string literal.
335///
336/// The string literal should not contain any `NUL` bytes.
337///
338/// # Examples
339///
340/// ```
341/// # use kernel::c_str;
342/// # use kernel::str::CStr;
343/// const MY_CSTR: &CStr = c_str!("My awesome CStr!");
344/// ```
345#[macro_export]
346macro_rules! c_str {
347 ($str:expr) => {{
348 const S: &str = concat!($str, "\0");
349 const C: &$crate::str::CStr = match $crate::str::CStr::from_bytes_with_nul(S.as_bytes()) {
350 Ok(v) => v,
351 Err(_) => panic!("string contains interior NUL"),
352 };
353 C
354 }};
355}
356
357#[cfg(test)]
358mod tests {
359 use super::*;
360
361 #[test]
362 fn test_cstr_to_str() {
363 let good_bytes = b"\xf0\x9f\xa6\x80\0";
364 let checked_cstr = CStr::from_bytes_with_nul(good_bytes).unwrap();
365 let checked_str = checked_cstr.to_str().unwrap();
366 assert_eq!(checked_str, "🦀");
367 }
368
369 #[test]
370 #[should_panic]
371 fn test_cstr_to_str_panic() {
372 let bad_bytes = b"\xc3\x28\0";
373 let checked_cstr = CStr::from_bytes_with_nul(bad_bytes).unwrap();
374 checked_cstr.to_str().unwrap();
375 }
376
377 #[test]
378 fn test_cstr_as_str_unchecked() {
379 let good_bytes = b"\xf0\x9f\x90\xA7\0";
380 let checked_cstr = CStr::from_bytes_with_nul(good_bytes).unwrap();
381 let unchecked_str = unsafe { checked_cstr.as_str_unchecked() };
382 assert_eq!(unchecked_str, "🐧");
383 }
384}
385
386/// Allows formatting of [`fmt::Arguments`] into a raw buffer.
387///
388/// It does not fail if callers write past the end of the buffer so that they can calculate the
389/// size required to fit everything.
390///
391/// # Invariants
392///
393/// The memory region between `pos` (inclusive) and `end` (exclusive) is valid for writes if `pos`
394/// is less than `end`.
395pub(crate) struct RawFormatter {
396 // Use `usize` to use `saturating_*` functions.
397 beg: usize,
398 pos: usize,
399 end: usize,
400}
401
402impl RawFormatter {
403 /// Creates a new instance of [`RawFormatter`] with an empty buffer.
404 fn new() -> Self {
405 // INVARIANT: The buffer is empty, so the region that needs to be writable is empty.
406 Self {
407 beg: 0,
408 pos: 0,
409 end: 0,
410 }
411 }
412
413 /// Creates a new instance of [`RawFormatter`] with the given buffer pointers.
414 ///
415 /// # Safety
416 ///
417 /// If `pos` is less than `end`, then the region between `pos` (inclusive) and `end`
418 /// (exclusive) must be valid for writes for the lifetime of the returned [`RawFormatter`].
419 pub(crate) unsafe fn from_ptrs(pos: *mut u8, end: *mut u8) -> Self {
420 // INVARIANT: The safety requirements guarantee the type invariants.
421 Self {
422 beg: pos as _,
423 pos: pos as _,
424 end: end as _,
425 }
426 }
427
428 /// Creates a new instance of [`RawFormatter`] with the given buffer.
429 ///
430 /// # Safety
431 ///
432 /// The memory region starting at `buf` and extending for `len` bytes must be valid for writes
433 /// for the lifetime of the returned [`RawFormatter`].
434 pub(crate) unsafe fn from_buffer(buf: *mut u8, len: usize) -> Self {
435 let pos = buf as usize;
436 // INVARIANT: We ensure that `end` is never less then `buf`, and the safety requirements
437 // guarantees that the memory region is valid for writes.
438 Self {
439 pos,
440 beg: pos,
441 end: pos.saturating_add(len),
442 }
443 }
444
445 /// Returns the current insert position.
446 ///
447 /// N.B. It may point to invalid memory.
448 pub(crate) fn pos(&self) -> *mut u8 {
449 self.pos as _
450 }
451
452 /// Return the number of bytes written to the formatter.
453 pub(crate) fn bytes_written(&self) -> usize {
454 self.pos - self.beg
455 }
456}
457
458impl fmt::Write for RawFormatter {
459 fn write_str(&mut self, s: &str) -> fmt::Result {
460 // `pos` value after writing `len` bytes. This does not have to be bounded by `end`, but we
461 // don't want it to wrap around to 0.
462 let pos_new = self.pos.saturating_add(s.len());
463
464 // Amount that we can copy. `saturating_sub` ensures we get 0 if `pos` goes past `end`.
465 let len_to_copy = core::cmp::min(pos_new, self.end).saturating_sub(self.pos);
466
467 if len_to_copy > 0 {
468 // SAFETY: If `len_to_copy` is non-zero, then we know `pos` has not gone past `end`
469 // yet, so it is valid for write per the type invariants.
470 unsafe {
471 core::ptr::copy_nonoverlapping(
472 s.as_bytes().as_ptr(),
473 self.pos as *mut u8,
474 len_to_copy,
475 )
476 };
477 }
478
479 self.pos = pos_new;
480 Ok(())
481 }
482}
483
484/// Allows formatting of [`fmt::Arguments`] into a raw buffer.
485///
486/// Fails if callers attempt to write more than will fit in the buffer.
487pub(crate) struct Formatter(RawFormatter);
488
489impl Formatter {
490 /// Creates a new instance of [`Formatter`] with the given buffer.
491 ///
492 /// # Safety
493 ///
494 /// The memory region starting at `buf` and extending for `len` bytes must be valid for writes
495 /// for the lifetime of the returned [`Formatter`].
496 pub(crate) unsafe fn from_buffer(buf: *mut u8, len: usize) -> Self {
497 // SAFETY: The safety requirements of this function satisfy those of the callee.
498 Self(unsafe { RawFormatter::from_buffer(buf, len) })
499 }
500}
501
502impl Deref for Formatter {
503 type Target = RawFormatter;
504
505 fn deref(&self) -> &Self::Target {
506 &self.0
507 }
508}
509
510impl fmt::Write for Formatter {
511 fn write_str(&mut self, s: &str) -> fmt::Result {
512 self.0.write_str(s)?;
513
514 // Fail the request if we go past the end of the buffer.
515 if self.0.pos > self.0.end {
516 Err(fmt::Error)
517 } else {
518 Ok(())
519 }
520 }
521}
522
523/// An owned string that is guaranteed to have exactly one `NUL` byte, which is at the end.
524///
525/// Used for interoperability with kernel APIs that take C strings.
526///
527/// # Invariants
528///
529/// The string is always `NUL`-terminated and contains no other `NUL` bytes.
530///
531/// # Examples
532///
533/// ```
534/// use kernel::{str::CString, fmt};
535///
536/// let s = CString::try_from_fmt(fmt!("{}{}{}", "abc", 10, 20)).unwrap();
537/// assert_eq!(s.as_bytes_with_nul(), "abc1020\0".as_bytes());
538///
539/// let tmp = "testing";
540/// let s = CString::try_from_fmt(fmt!("{tmp}{}", 123)).unwrap();
541/// assert_eq!(s.as_bytes_with_nul(), "testing123\0".as_bytes());
542///
543/// // This fails because it has an embedded `NUL` byte.
544/// let s = CString::try_from_fmt(fmt!("a\0b{}", 123));
545/// assert_eq!(s.is_ok(), false);
546/// ```
547pub struct CString {
548 buf: Vec<u8>,
549}
550
551impl CString {
552 /// Creates an instance of [`CString`] from the given formatted arguments.
553 pub fn try_from_fmt(args: fmt::Arguments<'_>) -> Result<Self, Error> {
554 // Calculate the size needed (formatted string plus `NUL` terminator).
555 let mut f = RawFormatter::new();
556 f.write_fmt(args)?;
557 f.write_str("\0")?;
558 let size = f.bytes_written();
559
560 // Allocate a vector with the required number of bytes, and write to it.
561 let mut buf = Vec::try_with_capacity(size)?;
562 // SAFETY: The buffer stored in `buf` is at least of size `size` and is valid for writes.
563 let mut f = unsafe { Formatter::from_buffer(buf.as_mut_ptr(), size) };
564 f.write_fmt(args)?;
565 f.write_str("\0")?;
566
567 // SAFETY: The number of bytes that can be written to `f` is bounded by `size`, which is
568 // `buf`'s capacity. The contents of the buffer have been initialised by writes to `f`.
569 unsafe { buf.set_len(f.bytes_written()) };
570
571 // Check that there are no `NUL` bytes before the end.
572 // SAFETY: The buffer is valid for read because `f.bytes_written()` is bounded by `size`
573 // (which the minimum buffer size) and is non-zero (we wrote at least the `NUL` terminator)
574 // so `f.bytes_written() - 1` doesn't underflow.
575 let ptr = unsafe { bindings::memchr(buf.as_ptr().cast(), 0, (f.bytes_written() - 1) as _) };
576 if !ptr.is_null() {
577 return Err(EINVAL);
578 }
579
580 // INVARIANT: We wrote the `NUL` terminator and checked above that no other `NUL` bytes
581 // exist in the buffer.
582 Ok(Self { buf })
583 }
584}
585
586impl Deref for CString {
587 type Target = CStr;
588
589 fn deref(&self) -> &Self::Target {
590 // SAFETY: The type invariants guarantee that the string is `NUL`-terminated and that no
591 // other `NUL` bytes exist.
592 unsafe { CStr::from_bytes_with_nul_unchecked(self.buf.as_slice()) }
593 }
594}
595
596impl<'a> TryFrom<&'a CStr> for CString {
597 type Error = AllocError;
598
599 fn try_from(cstr: &'a CStr) -> Result<CString, AllocError> {
600 let mut buf = Vec::new();
601
602 buf.try_extend_from_slice(cstr.as_bytes_with_nul())
603 .map_err(|_| AllocError)?;
604
605 // INVARIANT: The `CStr` and `CString` types have the same invariants for
606 // the string data, and we copied it over without changes.
607 Ok(CString { buf })
608 }
609}
610
611impl fmt::Debug for CString {
612 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
613 fmt::Debug::fmt(&**self, f)
614 }
615}
616
617/// A convenience alias for [`core::format_args`].
618#[macro_export]
619macro_rules! fmt {
620 ($($f:tt)*) => ( core::format_args!($($f)*) )
621}