592 lines
18 KiB
Rust
592 lines
18 KiB
Rust
// SPDX-License-Identifier: GPL-2.0
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//! String representations.
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use alloc::vec::Vec;
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use core::fmt::{self, Write};
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use core::ops::{self, Deref, Index};
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use crate::{
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bindings,
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error::{code::*, Error},
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};
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/// Byte string without UTF-8 validity guarantee.
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///
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/// `BStr` is simply an alias to `[u8]`, but has a more evident semantical meaning.
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pub type BStr = [u8];
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/// Creates a new [`BStr`] from a string literal.
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///
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/// `b_str!` converts the supplied string literal to byte string, so non-ASCII
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/// characters can be included.
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///
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/// # Examples
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///
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/// ```
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/// # use kernel::b_str;
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/// # use kernel::str::BStr;
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/// const MY_BSTR: &BStr = b_str!("My awesome BStr!");
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/// ```
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#[macro_export]
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macro_rules! b_str {
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($str:literal) => {{
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const S: &'static str = $str;
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const C: &'static $crate::str::BStr = S.as_bytes();
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C
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}};
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}
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/// Possible errors when using conversion functions in [`CStr`].
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#[derive(Debug, Clone, Copy)]
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pub enum CStrConvertError {
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/// Supplied bytes contain an interior `NUL`.
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InteriorNul,
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/// Supplied bytes are not terminated by `NUL`.
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NotNulTerminated,
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}
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impl From<CStrConvertError> for Error {
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#[inline]
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fn from(_: CStrConvertError) -> Error {
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EINVAL
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}
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}
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/// A string that is guaranteed to have exactly one `NUL` byte, which is at the
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/// end.
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///
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/// Used for interoperability with kernel APIs that take C strings.
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#[repr(transparent)]
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pub struct CStr([u8]);
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impl CStr {
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/// Returns the length of this string excluding `NUL`.
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#[inline]
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pub const fn len(&self) -> usize {
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self.len_with_nul() - 1
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}
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/// Returns the length of this string with `NUL`.
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#[inline]
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pub const fn len_with_nul(&self) -> usize {
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// SAFETY: This is one of the invariant of `CStr`.
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// We add a `unreachable_unchecked` here to hint the optimizer that
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// the value returned from this function is non-zero.
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if self.0.is_empty() {
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unsafe { core::hint::unreachable_unchecked() };
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}
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self.0.len()
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}
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/// Returns `true` if the string only includes `NUL`.
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#[inline]
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pub const fn is_empty(&self) -> bool {
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self.len() == 0
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}
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/// Wraps a raw C string pointer.
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///
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/// # Safety
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///
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/// `ptr` must be a valid pointer to a `NUL`-terminated C string, and it must
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/// last at least `'a`. When `CStr` is alive, the memory pointed by `ptr`
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/// must not be mutated.
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#[inline]
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pub unsafe fn from_char_ptr<'a>(ptr: *const core::ffi::c_char) -> &'a Self {
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// SAFETY: The safety precondition guarantees `ptr` is a valid pointer
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// to a `NUL`-terminated C string.
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let len = unsafe { bindings::strlen(ptr) } + 1;
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// SAFETY: Lifetime guaranteed by the safety precondition.
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let bytes = unsafe { core::slice::from_raw_parts(ptr as _, len as _) };
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// SAFETY: As `len` is returned by `strlen`, `bytes` does not contain interior `NUL`.
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// As we have added 1 to `len`, the last byte is known to be `NUL`.
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unsafe { Self::from_bytes_with_nul_unchecked(bytes) }
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}
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/// Creates a [`CStr`] from a `[u8]`.
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///
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/// The provided slice must be `NUL`-terminated, does not contain any
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/// interior `NUL` bytes.
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pub const fn from_bytes_with_nul(bytes: &[u8]) -> Result<&Self, CStrConvertError> {
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if bytes.is_empty() {
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return Err(CStrConvertError::NotNulTerminated);
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}
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if bytes[bytes.len() - 1] != 0 {
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return Err(CStrConvertError::NotNulTerminated);
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}
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let mut i = 0;
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// `i + 1 < bytes.len()` allows LLVM to optimize away bounds checking,
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// while it couldn't optimize away bounds checks for `i < bytes.len() - 1`.
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while i + 1 < bytes.len() {
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if bytes[i] == 0 {
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return Err(CStrConvertError::InteriorNul);
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}
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i += 1;
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}
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// SAFETY: We just checked that all properties hold.
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Ok(unsafe { Self::from_bytes_with_nul_unchecked(bytes) })
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}
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/// Creates a [`CStr`] from a `[u8]` without performing any additional
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/// checks.
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///
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/// # Safety
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///
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/// `bytes` *must* end with a `NUL` byte, and should only have a single
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/// `NUL` byte (or the string will be truncated).
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#[inline]
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pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
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// SAFETY: Properties of `bytes` guaranteed by the safety precondition.
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unsafe { core::mem::transmute(bytes) }
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}
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/// Returns a C pointer to the string.
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#[inline]
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pub const fn as_char_ptr(&self) -> *const core::ffi::c_char {
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self.0.as_ptr() as _
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}
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/// Convert the string to a byte slice without the trailing 0 byte.
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#[inline]
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pub fn as_bytes(&self) -> &[u8] {
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&self.0[..self.len()]
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}
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/// Convert the string to a byte slice containing the trailing 0 byte.
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#[inline]
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pub const fn as_bytes_with_nul(&self) -> &[u8] {
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&self.0
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}
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/// Yields a [`&str`] slice if the [`CStr`] contains valid UTF-8.
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///
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/// If the contents of the [`CStr`] are valid UTF-8 data, this
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/// function will return the corresponding [`&str`] slice. Otherwise,
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/// it will return an error with details of where UTF-8 validation failed.
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///
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/// # Examples
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///
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/// ```
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/// # use kernel::str::CStr;
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/// let cstr = CStr::from_bytes_with_nul(b"foo\0").unwrap();
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/// assert_eq!(cstr.to_str(), Ok("foo"));
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/// ```
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#[inline]
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pub fn to_str(&self) -> Result<&str, core::str::Utf8Error> {
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core::str::from_utf8(self.as_bytes())
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}
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/// Unsafely convert this [`CStr`] into a [`&str`], without checking for
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/// valid UTF-8.
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///
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/// # Safety
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///
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/// The contents must be valid UTF-8.
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///
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/// # Examples
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///
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/// ```
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/// # use kernel::c_str;
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/// # use kernel::str::CStr;
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/// // SAFETY: String literals are guaranteed to be valid UTF-8
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/// // by the Rust compiler.
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/// let bar = c_str!("ツ");
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/// assert_eq!(unsafe { bar.as_str_unchecked() }, "ツ");
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/// ```
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#[inline]
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pub unsafe fn as_str_unchecked(&self) -> &str {
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unsafe { core::str::from_utf8_unchecked(self.as_bytes()) }
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}
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}
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impl fmt::Display for CStr {
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/// Formats printable ASCII characters, escaping the rest.
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///
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/// ```
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/// # use kernel::c_str;
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/// # use kernel::str::CStr;
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/// # use kernel::str::CString;
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/// let penguin = c_str!("🐧");
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/// let s = CString::try_from_fmt(fmt!("{}", penguin)).unwrap();
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/// assert_eq!(s.as_bytes_with_nul(), "\\xf0\\x9f\\x90\\xa7\0".as_bytes());
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///
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/// let ascii = c_str!("so \"cool\"");
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/// let s = CString::try_from_fmt(fmt!("{}", ascii)).unwrap();
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/// assert_eq!(s.as_bytes_with_nul(), "so \"cool\"\0".as_bytes());
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/// ```
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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for &c in self.as_bytes() {
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if (0x20..0x7f).contains(&c) {
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// Printable character.
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f.write_char(c as char)?;
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} else {
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write!(f, "\\x{:02x}", c)?;
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}
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}
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Ok(())
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}
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}
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impl fmt::Debug for CStr {
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/// Formats printable ASCII characters with a double quote on either end, escaping the rest.
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///
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/// ```
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/// # use kernel::c_str;
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/// # use kernel::str::CStr;
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/// # use kernel::str::CString;
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/// let penguin = c_str!("🐧");
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/// let s = CString::try_from_fmt(fmt!("{:?}", penguin)).unwrap();
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/// assert_eq!(s.as_bytes_with_nul(), "\"\\xf0\\x9f\\x90\\xa7\"\0".as_bytes());
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///
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/// // Embedded double quotes are escaped.
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/// let ascii = c_str!("so \"cool\"");
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/// let s = CString::try_from_fmt(fmt!("{:?}", ascii)).unwrap();
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/// assert_eq!(s.as_bytes_with_nul(), "\"so \\\"cool\\\"\"\0".as_bytes());
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/// ```
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.write_str("\"")?;
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for &c in self.as_bytes() {
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match c {
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// Printable characters.
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b'\"' => f.write_str("\\\"")?,
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0x20..=0x7e => f.write_char(c as char)?,
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_ => write!(f, "\\x{:02x}", c)?,
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}
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}
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f.write_str("\"")
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}
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}
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impl AsRef<BStr> for CStr {
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#[inline]
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fn as_ref(&self) -> &BStr {
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self.as_bytes()
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}
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}
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impl Deref for CStr {
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type Target = BStr;
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#[inline]
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fn deref(&self) -> &Self::Target {
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self.as_bytes()
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}
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}
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impl Index<ops::RangeFrom<usize>> for CStr {
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type Output = CStr;
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#[inline]
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fn index(&self, index: ops::RangeFrom<usize>) -> &Self::Output {
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// Delegate bounds checking to slice.
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// Assign to _ to mute clippy's unnecessary operation warning.
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let _ = &self.as_bytes()[index.start..];
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// SAFETY: We just checked the bounds.
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unsafe { Self::from_bytes_with_nul_unchecked(&self.0[index.start..]) }
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}
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}
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impl Index<ops::RangeFull> for CStr {
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type Output = CStr;
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#[inline]
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fn index(&self, _index: ops::RangeFull) -> &Self::Output {
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self
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}
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}
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mod private {
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use core::ops;
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// Marker trait for index types that can be forward to `BStr`.
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pub trait CStrIndex {}
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impl CStrIndex for usize {}
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impl CStrIndex for ops::Range<usize> {}
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impl CStrIndex for ops::RangeInclusive<usize> {}
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impl CStrIndex for ops::RangeToInclusive<usize> {}
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}
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impl<Idx> Index<Idx> for CStr
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where
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Idx: private::CStrIndex,
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BStr: Index<Idx>,
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{
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type Output = <BStr as Index<Idx>>::Output;
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#[inline]
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fn index(&self, index: Idx) -> &Self::Output {
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&self.as_bytes()[index]
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}
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}
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/// Creates a new [`CStr`] from a string literal.
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///
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/// The string literal should not contain any `NUL` bytes.
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///
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/// # Examples
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///
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/// ```
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/// # use kernel::c_str;
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/// # use kernel::str::CStr;
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/// const MY_CSTR: &CStr = c_str!("My awesome CStr!");
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/// ```
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#[macro_export]
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macro_rules! c_str {
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($str:expr) => {{
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const S: &str = concat!($str, "\0");
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const C: &$crate::str::CStr = match $crate::str::CStr::from_bytes_with_nul(S.as_bytes()) {
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Ok(v) => v,
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Err(_) => panic!("string contains interior NUL"),
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};
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C
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}};
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_cstr_to_str() {
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let good_bytes = b"\xf0\x9f\xa6\x80\0";
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let checked_cstr = CStr::from_bytes_with_nul(good_bytes).unwrap();
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let checked_str = checked_cstr.to_str().unwrap();
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assert_eq!(checked_str, "🦀");
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}
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#[test]
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#[should_panic]
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fn test_cstr_to_str_panic() {
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let bad_bytes = b"\xc3\x28\0";
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let checked_cstr = CStr::from_bytes_with_nul(bad_bytes).unwrap();
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checked_cstr.to_str().unwrap();
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}
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#[test]
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fn test_cstr_as_str_unchecked() {
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let good_bytes = b"\xf0\x9f\x90\xA7\0";
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let checked_cstr = CStr::from_bytes_with_nul(good_bytes).unwrap();
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let unchecked_str = unsafe { checked_cstr.as_str_unchecked() };
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assert_eq!(unchecked_str, "🐧");
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}
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}
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/// Allows formatting of [`fmt::Arguments`] into a raw buffer.
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///
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/// It does not fail if callers write past the end of the buffer so that they can calculate the
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/// size required to fit everything.
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///
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/// # Invariants
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///
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/// The memory region between `pos` (inclusive) and `end` (exclusive) is valid for writes if `pos`
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/// is less than `end`.
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pub(crate) struct RawFormatter {
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// Use `usize` to use `saturating_*` functions.
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beg: usize,
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pos: usize,
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end: usize,
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}
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impl RawFormatter {
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/// Creates a new instance of [`RawFormatter`] with an empty buffer.
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fn new() -> Self {
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// INVARIANT: The buffer is empty, so the region that needs to be writable is empty.
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Self {
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beg: 0,
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pos: 0,
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end: 0,
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}
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}
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/// Creates a new instance of [`RawFormatter`] with the given buffer pointers.
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///
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/// # Safety
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///
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/// If `pos` is less than `end`, then the region between `pos` (inclusive) and `end`
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/// (exclusive) must be valid for writes for the lifetime of the returned [`RawFormatter`].
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pub(crate) unsafe fn from_ptrs(pos: *mut u8, end: *mut u8) -> Self {
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// INVARIANT: The safety requirements guarantee the type invariants.
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Self {
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beg: pos as _,
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pos: pos as _,
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end: end as _,
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}
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}
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/// Creates a new instance of [`RawFormatter`] with the given buffer.
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///
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/// # Safety
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///
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/// The memory region starting at `buf` and extending for `len` bytes must be valid for writes
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/// for the lifetime of the returned [`RawFormatter`].
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pub(crate) unsafe fn from_buffer(buf: *mut u8, len: usize) -> Self {
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let pos = buf as usize;
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// INVARIANT: We ensure that `end` is never less then `buf`, and the safety requirements
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// guarantees that the memory region is valid for writes.
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Self {
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pos,
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beg: pos,
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end: pos.saturating_add(len),
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}
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}
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/// Returns the current insert position.
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///
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/// N.B. It may point to invalid memory.
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pub(crate) fn pos(&self) -> *mut u8 {
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self.pos as _
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}
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/// Return the number of bytes written to the formatter.
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pub(crate) fn bytes_written(&self) -> usize {
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self.pos - self.beg
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}
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}
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impl fmt::Write for RawFormatter {
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fn write_str(&mut self, s: &str) -> fmt::Result {
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// `pos` value after writing `len` bytes. This does not have to be bounded by `end`, but we
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// don't want it to wrap around to 0.
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let pos_new = self.pos.saturating_add(s.len());
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// Amount that we can copy. `saturating_sub` ensures we get 0 if `pos` goes past `end`.
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let len_to_copy = core::cmp::min(pos_new, self.end).saturating_sub(self.pos);
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if len_to_copy > 0 {
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// SAFETY: If `len_to_copy` is non-zero, then we know `pos` has not gone past `end`
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// yet, so it is valid for write per the type invariants.
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unsafe {
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core::ptr::copy_nonoverlapping(
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s.as_bytes().as_ptr(),
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self.pos as *mut u8,
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len_to_copy,
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)
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};
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}
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self.pos = pos_new;
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Ok(())
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}
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}
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/// Allows formatting of [`fmt::Arguments`] into a raw buffer.
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///
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/// Fails if callers attempt to write more than will fit in the buffer.
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pub(crate) struct Formatter(RawFormatter);
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impl Formatter {
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/// Creates a new instance of [`Formatter`] with the given buffer.
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///
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/// # Safety
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///
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/// The memory region starting at `buf` and extending for `len` bytes must be valid for writes
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/// for the lifetime of the returned [`Formatter`].
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pub(crate) unsafe fn from_buffer(buf: *mut u8, len: usize) -> Self {
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// SAFETY: The safety requirements of this function satisfy those of the callee.
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Self(unsafe { RawFormatter::from_buffer(buf, len) })
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}
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}
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impl Deref for Formatter {
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type Target = RawFormatter;
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fn deref(&self) -> &Self::Target {
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&self.0
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}
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}
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impl fmt::Write for Formatter {
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fn write_str(&mut self, s: &str) -> fmt::Result {
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self.0.write_str(s)?;
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// Fail the request if we go past the end of the buffer.
|
|
if self.0.pos > self.0.end {
|
|
Err(fmt::Error)
|
|
} else {
|
|
Ok(())
|
|
}
|
|
}
|
|
}
|
|
|
|
/// An owned string that is guaranteed to have exactly one `NUL` byte, which is at the end.
|
|
///
|
|
/// Used for interoperability with kernel APIs that take C strings.
|
|
///
|
|
/// # Invariants
|
|
///
|
|
/// The string is always `NUL`-terminated and contains no other `NUL` bytes.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use kernel::str::CString;
|
|
///
|
|
/// let s = CString::try_from_fmt(fmt!("{}{}{}", "abc", 10, 20)).unwrap();
|
|
/// assert_eq!(s.as_bytes_with_nul(), "abc1020\0".as_bytes());
|
|
///
|
|
/// let tmp = "testing";
|
|
/// let s = CString::try_from_fmt(fmt!("{tmp}{}", 123)).unwrap();
|
|
/// assert_eq!(s.as_bytes_with_nul(), "testing123\0".as_bytes());
|
|
///
|
|
/// // This fails because it has an embedded `NUL` byte.
|
|
/// let s = CString::try_from_fmt(fmt!("a\0b{}", 123));
|
|
/// assert_eq!(s.is_ok(), false);
|
|
/// ```
|
|
pub struct CString {
|
|
buf: Vec<u8>,
|
|
}
|
|
|
|
impl CString {
|
|
/// Creates an instance of [`CString`] from the given formatted arguments.
|
|
pub fn try_from_fmt(args: fmt::Arguments<'_>) -> Result<Self, Error> {
|
|
// Calculate the size needed (formatted string plus `NUL` terminator).
|
|
let mut f = RawFormatter::new();
|
|
f.write_fmt(args)?;
|
|
f.write_str("\0")?;
|
|
let size = f.bytes_written();
|
|
|
|
// Allocate a vector with the required number of bytes, and write to it.
|
|
let mut buf = Vec::try_with_capacity(size)?;
|
|
// SAFETY: The buffer stored in `buf` is at least of size `size` and is valid for writes.
|
|
let mut f = unsafe { Formatter::from_buffer(buf.as_mut_ptr(), size) };
|
|
f.write_fmt(args)?;
|
|
f.write_str("\0")?;
|
|
|
|
// SAFETY: The number of bytes that can be written to `f` is bounded by `size`, which is
|
|
// `buf`'s capacity. The contents of the buffer have been initialised by writes to `f`.
|
|
unsafe { buf.set_len(f.bytes_written()) };
|
|
|
|
// Check that there are no `NUL` bytes before the end.
|
|
// SAFETY: The buffer is valid for read because `f.bytes_written()` is bounded by `size`
|
|
// (which the minimum buffer size) and is non-zero (we wrote at least the `NUL` terminator)
|
|
// so `f.bytes_written() - 1` doesn't underflow.
|
|
let ptr = unsafe { bindings::memchr(buf.as_ptr().cast(), 0, (f.bytes_written() - 1) as _) };
|
|
if !ptr.is_null() {
|
|
return Err(EINVAL);
|
|
}
|
|
|
|
// INVARIANT: We wrote the `NUL` terminator and checked above that no other `NUL` bytes
|
|
// exist in the buffer.
|
|
Ok(Self { buf })
|
|
}
|
|
}
|
|
|
|
impl Deref for CString {
|
|
type Target = CStr;
|
|
|
|
fn deref(&self) -> &Self::Target {
|
|
// SAFETY: The type invariants guarantee that the string is `NUL`-terminated and that no
|
|
// other `NUL` bytes exist.
|
|
unsafe { CStr::from_bytes_with_nul_unchecked(self.buf.as_slice()) }
|
|
}
|
|
}
|
|
|
|
/// A convenience alias for [`core::format_args`].
|
|
#[macro_export]
|
|
macro_rules! fmt {
|
|
($($f:tt)*) => ( core::format_args!($($f)*) )
|
|
}
|