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Diffstat (limited to 'library/core/src/ffi/c_str.rs')
| -rw-r--r-- | library/core/src/ffi/c_str.rs | 608 |
1 files changed, 608 insertions, 0 deletions
diff --git a/library/core/src/ffi/c_str.rs b/library/core/src/ffi/c_str.rs new file mode 100644 index 000000000..82e63a7fe --- /dev/null +++ b/library/core/src/ffi/c_str.rs @@ -0,0 +1,608 @@ +use crate::ascii; +use crate::cmp::Ordering; +use crate::ffi::c_char; +use crate::fmt::{self, Write}; +use crate::intrinsics; +use crate::ops; +use crate::slice; +use crate::slice::memchr; +use crate::str; + +/// Representation of a borrowed C string. +/// +/// This type represents a borrowed reference to a nul-terminated +/// array of bytes. It can be constructed safely from a <code>&[[u8]]</code> +/// slice, or unsafely from a raw `*const c_char`. It can then be +/// converted to a Rust <code>&[str]</code> by performing UTF-8 validation, or +/// into an owned `CString`. +/// +/// `&CStr` is to `CString` as <code>&[str]</code> is to `String`: the former +/// in each pair are borrowed references; the latter are owned +/// strings. +/// +/// Note that this structure is **not** `repr(C)` and is not recommended to be +/// placed in the signatures of FFI functions. Instead, safe wrappers of FFI +/// functions may leverage the unsafe [`CStr::from_ptr`] constructor to provide +/// a safe interface to other consumers. +/// +/// # Examples +/// +/// Inspecting a foreign C string: +/// +/// ```ignore (extern-declaration) +/// use std::ffi::CStr; +/// use std::os::raw::c_char; +/// +/// extern "C" { fn my_string() -> *const c_char; } +/// +/// unsafe { +/// let slice = CStr::from_ptr(my_string()); +/// println!("string buffer size without nul terminator: {}", slice.to_bytes().len()); +/// } +/// ``` +/// +/// Passing a Rust-originating C string: +/// +/// ```ignore (extern-declaration) +/// use std::ffi::{CString, CStr}; +/// use std::os::raw::c_char; +/// +/// fn work(data: &CStr) { +/// extern "C" { fn work_with(data: *const c_char); } +/// +/// unsafe { work_with(data.as_ptr()) } +/// } +/// +/// let s = CString::new("data data data data").expect("CString::new failed"); +/// work(&s); +/// ``` +/// +/// Converting a foreign C string into a Rust `String`: +/// +/// ```ignore (extern-declaration) +/// use std::ffi::CStr; +/// use std::os::raw::c_char; +/// +/// extern "C" { fn my_string() -> *const c_char; } +/// +/// fn my_string_safe() -> String { +/// let cstr = unsafe { CStr::from_ptr(my_string()) }; +/// // Get copy-on-write Cow<'_, str>, then guarantee a freshly-owned String allocation +/// String::from_utf8_lossy(cstr.to_bytes()).to_string() +/// } +/// +/// println!("string: {}", my_string_safe()); +/// ``` +/// +/// [str]: prim@str "str" +#[derive(Hash)] +#[cfg_attr(not(test), rustc_diagnostic_item = "CStr")] +#[stable(feature = "core_c_str", since = "1.64.0")] +#[rustc_has_incoherent_inherent_impls] +// FIXME: +// `fn from` in `impl From<&CStr> for Box<CStr>` current implementation relies +// on `CStr` being layout-compatible with `[u8]`. +// When attribute privacy is implemented, `CStr` should be annotated as `#[repr(transparent)]`. +// Anyway, `CStr` representation and layout are considered implementation detail, are +// not documented and must not be relied upon. +pub struct CStr { + // FIXME: this should not be represented with a DST slice but rather with + // just a raw `c_char` along with some form of marker to make + // this an unsized type. Essentially `sizeof(&CStr)` should be the + // same as `sizeof(&c_char)` but `CStr` should be an unsized type. + inner: [c_char], +} + +/// An error indicating that a nul byte was not in the expected position. +/// +/// The slice used to create a [`CStr`] must have one and only one nul byte, +/// positioned at the end. +/// +/// This error is created by the [`CStr::from_bytes_with_nul`] method. +/// See its documentation for more. +/// +/// # Examples +/// +/// ``` +/// use std::ffi::{CStr, FromBytesWithNulError}; +/// +/// let _: FromBytesWithNulError = CStr::from_bytes_with_nul(b"f\0oo").unwrap_err(); +/// ``` +#[derive(Clone, PartialEq, Eq, Debug)] +#[stable(feature = "core_c_str", since = "1.64.0")] +pub struct FromBytesWithNulError { + kind: FromBytesWithNulErrorKind, +} + +#[derive(Clone, PartialEq, Eq, Debug)] +enum FromBytesWithNulErrorKind { + InteriorNul(usize), + NotNulTerminated, +} + +impl FromBytesWithNulError { + fn interior_nul(pos: usize) -> FromBytesWithNulError { + FromBytesWithNulError { kind: FromBytesWithNulErrorKind::InteriorNul(pos) } + } + fn not_nul_terminated() -> FromBytesWithNulError { + FromBytesWithNulError { kind: FromBytesWithNulErrorKind::NotNulTerminated } + } + + #[doc(hidden)] + #[unstable(feature = "cstr_internals", issue = "none")] + pub fn __description(&self) -> &str { + match self.kind { + FromBytesWithNulErrorKind::InteriorNul(..) => { + "data provided contains an interior nul byte" + } + FromBytesWithNulErrorKind::NotNulTerminated => "data provided is not nul terminated", + } + } +} + +/// An error indicating that no nul byte was present. +/// +/// A slice used to create a [`CStr`] must contain a nul byte somewhere +/// within the slice. +/// +/// This error is created by the [`CStr::from_bytes_until_nul`] method. +/// +#[derive(Clone, PartialEq, Eq, Debug)] +#[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")] +pub struct FromBytesUntilNulError(()); + +#[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")] +impl fmt::Display for FromBytesUntilNulError { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + write!(f, "data provided does not contain a nul") + } +} + +#[stable(feature = "cstr_debug", since = "1.3.0")] +impl fmt::Debug for CStr { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + write!(f, "\"")?; + for byte in self.to_bytes().iter().flat_map(|&b| ascii::escape_default(b)) { + f.write_char(byte as char)?; + } + write!(f, "\"") + } +} + +#[stable(feature = "cstr_default", since = "1.10.0")] +impl Default for &CStr { + fn default() -> Self { + const SLICE: &[c_char] = &[0]; + // SAFETY: `SLICE` is indeed pointing to a valid nul-terminated string. + unsafe { CStr::from_ptr(SLICE.as_ptr()) } + } +} + +#[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")] +impl fmt::Display for FromBytesWithNulError { + #[allow(deprecated, deprecated_in_future)] + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.write_str(self.__description())?; + if let FromBytesWithNulErrorKind::InteriorNul(pos) = self.kind { + write!(f, " at byte pos {pos}")?; + } + Ok(()) + } +} + +impl CStr { + /// Wraps a raw C string with a safe C string wrapper. + /// + /// This function will wrap the provided `ptr` with a `CStr` wrapper, which + /// allows inspection and interoperation of non-owned C strings. The total + /// size of the raw C string must be smaller than `isize::MAX` **bytes** + /// in memory due to calling the `slice::from_raw_parts` function. + /// + /// # Safety + /// + /// * The memory pointed to by `ptr` must contain a valid nul terminator at the + /// end of the string. + /// + /// * `ptr` must be [valid] for reads of bytes up to and including the null terminator. + /// This means in particular: + /// + /// * The entire memory range of this `CStr` must be contained within a single allocated object! + /// * `ptr` must be non-null even for a zero-length cstr. + /// + /// * The memory referenced by the returned `CStr` must not be mutated for + /// the duration of lifetime `'a`. + /// + /// > **Note**: This operation is intended to be a 0-cost cast but it is + /// > currently implemented with an up-front calculation of the length of + /// > the string. This is not guaranteed to always be the case. + /// + /// # Caveat + /// + /// The lifetime for the returned slice is inferred from its usage. To prevent accidental misuse, + /// it's suggested to tie the lifetime to whichever source lifetime is safe in the context, + /// such as by providing a helper function taking the lifetime of a host value for the slice, + /// or by explicit annotation. + /// + /// # Examples + /// + /// ```ignore (extern-declaration) + /// # fn main() { + /// use std::ffi::CStr; + /// use std::os::raw::c_char; + /// + /// extern "C" { + /// fn my_string() -> *const c_char; + /// } + /// + /// unsafe { + /// let slice = CStr::from_ptr(my_string()); + /// println!("string returned: {}", slice.to_str().unwrap()); + /// } + /// # } + /// ``` + /// + /// [valid]: core::ptr#safety + #[inline] + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + pub unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr { + // SAFETY: The caller has provided a pointer that points to a valid C + // string with a NUL terminator of size less than `isize::MAX`, whose + // content remain valid and doesn't change for the lifetime of the + // returned `CStr`. + // + // Thus computing the length is fine (a NUL byte exists), the call to + // from_raw_parts is safe because we know the length is at most `isize::MAX`, meaning + // the call to `from_bytes_with_nul_unchecked` is correct. + // + // The cast from c_char to u8 is ok because a c_char is always one byte. + unsafe { + extern "C" { + /// Provided by libc or compiler_builtins. + fn strlen(s: *const c_char) -> usize; + } + let len = strlen(ptr); + let ptr = ptr as *const u8; + CStr::from_bytes_with_nul_unchecked(slice::from_raw_parts(ptr, len as usize + 1)) + } + } + + /// Creates a C string wrapper from a byte slice. + /// + /// This method will create a `CStr` from any byte slice that contains at + /// least one nul byte. The caller does not need to know or specify where + /// the nul byte is located. + /// + /// If the first byte is a nul character, this method will return an + /// empty `CStr`. If multiple nul characters are present, the `CStr` will + /// end at the first one. + /// + /// If the slice only has a single nul byte at the end, this method is + /// equivalent to [`CStr::from_bytes_with_nul`]. + /// + /// # Examples + /// ``` + /// #![feature(cstr_from_bytes_until_nul)] + /// + /// use std::ffi::CStr; + /// + /// let mut buffer = [0u8; 16]; + /// unsafe { + /// // Here we might call an unsafe C function that writes a string + /// // into the buffer. + /// let buf_ptr = buffer.as_mut_ptr(); + /// buf_ptr.write_bytes(b'A', 8); + /// } + /// // Attempt to extract a C nul-terminated string from the buffer. + /// let c_str = CStr::from_bytes_until_nul(&buffer[..]).unwrap(); + /// assert_eq!(c_str.to_str().unwrap(), "AAAAAAAA"); + /// ``` + /// + #[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")] + pub fn from_bytes_until_nul(bytes: &[u8]) -> Result<&CStr, FromBytesUntilNulError> { + let nul_pos = memchr::memchr(0, bytes); + match nul_pos { + Some(nul_pos) => { + let subslice = &bytes[..nul_pos + 1]; + // SAFETY: We know there is a nul byte at nul_pos, so this slice + // (ending at the nul byte) is a well-formed C string. + Ok(unsafe { CStr::from_bytes_with_nul_unchecked(subslice) }) + } + None => Err(FromBytesUntilNulError(())), + } + } + + /// Creates a C string wrapper from a byte slice. + /// + /// This function will cast the provided `bytes` to a `CStr` + /// wrapper after ensuring that the byte slice is nul-terminated + /// and does not contain any interior nul bytes. + /// + /// If the nul byte may not be at the end, + /// [`CStr::from_bytes_until_nul`] can be used instead. + /// + /// # Examples + /// + /// ``` + /// use std::ffi::CStr; + /// + /// let cstr = CStr::from_bytes_with_nul(b"hello\0"); + /// assert!(cstr.is_ok()); + /// ``` + /// + /// Creating a `CStr` without a trailing nul terminator is an error: + /// + /// ``` + /// use std::ffi::CStr; + /// + /// let cstr = CStr::from_bytes_with_nul(b"hello"); + /// assert!(cstr.is_err()); + /// ``` + /// + /// Creating a `CStr` with an interior nul byte is an error: + /// + /// ``` + /// use std::ffi::CStr; + /// + /// let cstr = CStr::from_bytes_with_nul(b"he\0llo\0"); + /// assert!(cstr.is_err()); + /// ``` + #[stable(feature = "cstr_from_bytes", since = "1.10.0")] + pub fn from_bytes_with_nul(bytes: &[u8]) -> Result<&Self, FromBytesWithNulError> { + let nul_pos = memchr::memchr(0, bytes); + match nul_pos { + Some(nul_pos) if nul_pos + 1 == bytes.len() => { + // SAFETY: We know there is only one nul byte, at the end + // of the byte slice. + Ok(unsafe { Self::from_bytes_with_nul_unchecked(bytes) }) + } + Some(nul_pos) => Err(FromBytesWithNulError::interior_nul(nul_pos)), + None => Err(FromBytesWithNulError::not_nul_terminated()), + } + } + + /// Unsafely creates a C string wrapper from a byte slice. + /// + /// This function will cast the provided `bytes` to a `CStr` wrapper without + /// performing any sanity checks. + /// + /// # Safety + /// The provided slice **must** be nul-terminated and not contain any interior + /// nul bytes. + /// + /// # Examples + /// + /// ``` + /// use std::ffi::{CStr, CString}; + /// + /// unsafe { + /// let cstring = CString::new("hello").expect("CString::new failed"); + /// let cstr = CStr::from_bytes_with_nul_unchecked(cstring.to_bytes_with_nul()); + /// assert_eq!(cstr, &*cstring); + /// } + /// ``` + #[inline] + #[must_use] + #[stable(feature = "cstr_from_bytes", since = "1.10.0")] + #[rustc_const_stable(feature = "const_cstr_unchecked", since = "1.59.0")] + #[rustc_allow_const_fn_unstable(const_eval_select)] + pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr { + fn rt_impl(bytes: &[u8]) -> &CStr { + // Chance at catching some UB at runtime with debug builds. + debug_assert!(!bytes.is_empty() && bytes[bytes.len() - 1] == 0); + + // SAFETY: Casting to CStr is safe because its internal representation + // is a [u8] too (safe only inside std). + // Dereferencing the obtained pointer is safe because it comes from a + // reference. Making a reference is then safe because its lifetime + // is bound by the lifetime of the given `bytes`. + unsafe { &*(bytes as *const [u8] as *const CStr) } + } + + const fn const_impl(bytes: &[u8]) -> &CStr { + // Saturating so that an empty slice panics in the assert with a good + // message, not here due to underflow. + let mut i = bytes.len().saturating_sub(1); + assert!(!bytes.is_empty() && bytes[i] == 0, "input was not nul-terminated"); + + // Ending null byte exists, skip to the rest. + while i != 0 { + i -= 1; + let byte = bytes[i]; + assert!(byte != 0, "input contained interior nul"); + } + + // SAFETY: See `rt_impl` cast. + unsafe { &*(bytes as *const [u8] as *const CStr) } + } + + // SAFETY: The const and runtime versions have identical behavior + // unless the safety contract of `from_bytes_with_nul_unchecked` is + // violated, which is UB. + unsafe { intrinsics::const_eval_select((bytes,), const_impl, rt_impl) } + } + + /// Returns the inner pointer to this C string. + /// + /// The returned pointer will be valid for as long as `self` is, and points + /// to a contiguous region of memory terminated with a 0 byte to represent + /// the end of the string. + /// + /// **WARNING** + /// + /// The returned pointer is read-only; writing to it (including passing it + /// to C code that writes to it) causes undefined behavior. + /// + /// It is your responsibility to make sure that the underlying memory is not + /// freed too early. For example, the following code will cause undefined + /// behavior when `ptr` is used inside the `unsafe` block: + /// + /// ```no_run + /// # #![allow(unused_must_use)] #![allow(temporary_cstring_as_ptr)] + /// use std::ffi::CString; + /// + /// let ptr = CString::new("Hello").expect("CString::new failed").as_ptr(); + /// unsafe { + /// // `ptr` is dangling + /// *ptr; + /// } + /// ``` + /// + /// This happens because the pointer returned by `as_ptr` does not carry any + /// lifetime information and the `CString` is deallocated immediately after + /// the `CString::new("Hello").expect("CString::new failed").as_ptr()` + /// expression is evaluated. + /// To fix the problem, bind the `CString` to a local variable: + /// + /// ```no_run + /// # #![allow(unused_must_use)] + /// use std::ffi::CString; + /// + /// let hello = CString::new("Hello").expect("CString::new failed"); + /// let ptr = hello.as_ptr(); + /// unsafe { + /// // `ptr` is valid because `hello` is in scope + /// *ptr; + /// } + /// ``` + /// + /// This way, the lifetime of the `CString` in `hello` encompasses + /// the lifetime of `ptr` and the `unsafe` block. + #[inline] + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + #[rustc_const_stable(feature = "const_str_as_ptr", since = "1.32.0")] + pub const fn as_ptr(&self) -> *const c_char { + self.inner.as_ptr() + } + + /// Converts this C string to a byte slice. + /// + /// The returned slice will **not** contain the trailing nul terminator that this C + /// string has. + /// + /// > **Note**: This method is currently implemented as a constant-time + /// > cast, but it is planned to alter its definition in the future to + /// > perform the length calculation whenever this method is called. + /// + /// # Examples + /// + /// ``` + /// use std::ffi::CStr; + /// + /// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"); + /// assert_eq!(cstr.to_bytes(), b"foo"); + /// ``` + #[inline] + #[must_use = "this returns the result of the operation, \ + without modifying the original"] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn to_bytes(&self) -> &[u8] { + let bytes = self.to_bytes_with_nul(); + // SAFETY: to_bytes_with_nul returns slice with length at least 1 + unsafe { bytes.get_unchecked(..bytes.len() - 1) } + } + + /// Converts this C string to a byte slice containing the trailing 0 byte. + /// + /// This function is the equivalent of [`CStr::to_bytes`] except that it + /// will retain the trailing nul terminator instead of chopping it off. + /// + /// > **Note**: This method is currently implemented as a 0-cost cast, but + /// > it is planned to alter its definition in the future to perform the + /// > length calculation whenever this method is called. + /// + /// # Examples + /// + /// ``` + /// use std::ffi::CStr; + /// + /// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"); + /// assert_eq!(cstr.to_bytes_with_nul(), b"foo\0"); + /// ``` + #[inline] + #[must_use = "this returns the result of the operation, \ + without modifying the original"] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn to_bytes_with_nul(&self) -> &[u8] { + // SAFETY: Transmuting a slice of `c_char`s to a slice of `u8`s + // is safe on all supported targets. + unsafe { &*(&self.inner as *const [c_char] as *const [u8]) } + } + + /// Yields a <code>&[str]</code> slice if the `CStr` contains valid UTF-8. + /// + /// If the contents of the `CStr` are valid UTF-8 data, this + /// function will return the corresponding <code>&[str]</code> slice. Otherwise, + /// it will return an error with details of where UTF-8 validation failed. + /// + /// [str]: prim@str "str" + /// + /// # Examples + /// + /// ``` + /// use std::ffi::CStr; + /// + /// let cstr = CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"); + /// assert_eq!(cstr.to_str(), Ok("foo")); + /// ``` + #[stable(feature = "cstr_to_str", since = "1.4.0")] + pub fn to_str(&self) -> Result<&str, str::Utf8Error> { + // N.B., when `CStr` is changed to perform the length check in `.to_bytes()` + // instead of in `from_ptr()`, it may be worth considering if this should + // be rewritten to do the UTF-8 check inline with the length calculation + // instead of doing it afterwards. + str::from_utf8(self.to_bytes()) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl PartialEq for CStr { + fn eq(&self, other: &CStr) -> bool { + self.to_bytes().eq(other.to_bytes()) + } +} +#[stable(feature = "rust1", since = "1.0.0")] +impl Eq for CStr {} +#[stable(feature = "rust1", since = "1.0.0")] +impl PartialOrd for CStr { + fn partial_cmp(&self, other: &CStr) -> Option<Ordering> { + self.to_bytes().partial_cmp(&other.to_bytes()) + } +} +#[stable(feature = "rust1", since = "1.0.0")] +impl Ord for CStr { + fn cmp(&self, other: &CStr) -> Ordering { + self.to_bytes().cmp(&other.to_bytes()) + } +} + +#[stable(feature = "cstr_range_from", since = "1.47.0")] +impl ops::Index<ops::RangeFrom<usize>> for CStr { + type Output = CStr; + + fn index(&self, index: ops::RangeFrom<usize>) -> &CStr { + let bytes = self.to_bytes_with_nul(); + // we need to manually check the starting index to account for the null + // byte, since otherwise we could get an empty string that doesn't end + // in a null. + if index.start < bytes.len() { + // SAFETY: Non-empty tail of a valid `CStr` is still a valid `CStr`. + unsafe { CStr::from_bytes_with_nul_unchecked(&bytes[index.start..]) } + } else { + panic!( + "index out of bounds: the len is {} but the index is {}", + bytes.len(), + index.start + ); + } + } +} + +#[stable(feature = "cstring_asref", since = "1.7.0")] +impl AsRef<CStr> for CStr { + #[inline] + fn as_ref(&self) -> &CStr { + self + } +} |