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#![allow(clippy::missing_safety_doc)] use crate::ffi::{c_char, libc::strlen, CStr}; use alloc::borrow::{Borrow, Cow}; use core::{ fmt, mem, ops, ptr, slice::{self, memchr}, str::Utf8Error, }; /// A type representing an owned, C-compatible, nul-terminated string with no /// nul bytes in the middle. /// /// This type serves the purpose of being able to safely generate a C-compatible /// string from a Rust byte slice or vector. An instance of this type is a /// static guarantee that the underlying bytes contain no interior 0 bytes ("nul /// characters") and that the final byte is 0 ("nul terminator"). /// /// `CString` is to `&`[`CStr`] as [`String`] is to `&`[`str`]: the former in /// each pair are owned strings; the latter are borrowed references. /// /// # Creating a `CString` /// /// A `CString` is created from either a byte slice or a byte vector, or /// anything that implements [`Into`]`<`[`Vec`]`<`[`u8`]`>>` (for example, you /// can build a `CString` straight out of a [`String`] or a `&`[`str`], since /// both implement that trait). /// /// The [`CString::new`] method will actually check that the provided `&[u8]` /// does not have 0 bytes in the middle, and return an error if it finds one. /// /// # Extracting a raw pointer to the whole C string /// /// `CString` implements a `as_ptr` method through the [`core::ops::Deref`] /// trait. This method will give you a `*const c_char` which you can feed /// directly to extern functions that expect a nul-terminated string, like C's /// `strdup()`. Notice that `as_ptr` returns a read-only pointer; if the C code /// writes to it, that causes undefined behavior. /// /// # Extracting a slice of the whole C string /// /// Alternatively, you can obtain a `&[`[`u8`]`]` slice from a `CString` with /// the [`CString::as_bytes`] method. Slices produced in this way do *not* /// contain the trailing nul terminator. This is useful when you will be calling /// an extern function that takes a `*const u8` argument which is not /// necessarily nul-terminated, plus another argument with the length of the /// string — like C's `strndup()`. You can of course get the slice's length with /// its `len` method. /// /// If you need a `&[`[`u8`]`]` slice *with* the nul terminator, you can use /// [`CString::as_bytes_with_nul`] instead. /// /// Once you have the kind of slice you need (with or without a nul terminator), /// you can call the slice's own `as_ptr` method to get a read-only raw pointer /// to pass to extern functions. See the documentation for that function for a /// discussion on ensuring the lifetime of the raw pointer. /// /// # Examples /// /// ``` /// use drone_core::ffi::{c_char, CString}; /// /// extern "C" fn my_printer(s: *const c_char) {} /// /// // We are certain that our string doesn't have 0 bytes in the middle, /// // so we can .expect() /// let c_to_print = CString::new("Hello, world!").expect("CString::new failed"); /// unsafe { /// my_printer(c_to_print.as_ptr()); /// } /// ``` /// /// # Safety /// /// `CString` is intended for working with traditional C-style strings (a /// sequence of non-nul bytes terminated by a single nul byte); the primary use /// case for these kinds of strings is interoperating with C-like code. Often /// you will need to transfer ownership to/from that external code. It is /// strongly recommended that you thoroughly read through the documentation of /// `CString` before use, as improper ownership management of `CString` /// instances can lead to invalid memory accesses, memory leaks, and other /// memory errors. #[derive(PartialEq, PartialOrd, Eq, Ord, Hash, Clone)] pub struct CString { // Invariant 1: the slice ends with a zero byte and has a length of at least one. // Invariant 2: the slice contains only one zero byte. // Improper usage of unsafe function can break Invariant 2, but not Invariant 1. pub(super) inner: Box<[u8]>, } /// An error indicating that an interior nul byte was found. /// /// While Rust strings may contain nul bytes in the middle, C strings can't, as /// that byte would effectively truncate the string. /// /// This error is created by the [`new`](CString::new) method on [`CString`]. /// See its documentation for more. /// /// # Examples /// /// ``` /// use drone_core::ffi::{CString, NulError}; /// /// let _: NulError = CString::new(b"f\0oo".to_vec()).unwrap_err(); /// ``` #[derive(Clone, PartialEq, Eq, Debug)] pub struct NulError(usize, Vec<u8>); /// An error indicating invalid UTF-8 when converting a [`CString`] into a /// [`String`]. /// /// `CString` is just a wrapper over a buffer of bytes with a nul terminator; /// [`CString::into_string`] performs UTF-8 validation on those bytes and may /// return this error. /// /// This `struct` is created by the [`CString::into_string`] method on /// [`CString`]. See its documentation for more. #[derive(Clone, PartialEq, Eq, Debug)] pub struct IntoStringError { inner: CString, error: Utf8Error, } impl CString { /// Creates a new C-compatible string from a container of bytes. /// /// This function will consume the provided data and use the underlying /// bytes to construct a new string, ensuring that there is a trailing 0 /// byte. This trailing 0 byte will be appended by this function; the /// provided data should *not* contain any 0 bytes in it. /// /// # Examples /// /// ``` /// use drone_core::ffi::{c_char, CString}; /// /// extern "C" fn puts(_s: *const c_char) {} /// /// let to_print = CString::new("Hello!").expect("CString::new failed"); /// unsafe { /// puts(to_print.as_ptr()); /// } /// ``` /// /// # Errors /// /// This function will return an error if the supplied bytes contain an /// internal 0 byte. The [`NulError`] returned will contain the bytes as /// well as the position of the nul byte. pub fn new<T: Into<Vec<u8>>>(t: T) -> Result<Self, NulError> { Self::_new(t.into()) } fn _new(bytes: Vec<u8>) -> Result<Self, NulError> { match memchr::memchr(0, &bytes) { Some(i) => Err(NulError(i, bytes)), None => Ok(unsafe { Self::from_vec_unchecked(bytes) }), } } /// Creates a C-compatible string by consuming a byte vector, without /// checking for interior 0 bytes. /// /// This method is equivalent to [`CString::new`] except that no runtime /// assertion is made that `v` contains no 0 bytes, and it requires an /// actual byte vector, not anything that can be converted to one with /// [`Into`]. /// /// # Examples /// /// ``` /// use drone_core::ffi::CString; /// /// let raw = b"foo".to_vec(); /// unsafe { /// let c_string = CString::from_vec_unchecked(raw); /// } /// ``` pub unsafe fn from_vec_unchecked(mut v: Vec<u8>) -> Self { v.reserve_exact(1); v.push(0); Self { inner: v.into_boxed_slice() } } /// Retakes ownership of a `CString` that was transferred to C via /// [`CString::into_raw`]. /// /// Additionally, the length of the string will be recalculated from the /// pointer. /// /// # Safety /// /// This should only ever be called with a pointer that was earlier obtained /// by calling [`CString::into_raw`] on a `CString`. Other usage (e.g., /// trying to take ownership of a string that was allocated by foreign /// code) is likely to lead to undefined behavior or allocator /// corruption. /// /// > **Note:** If you need to borrow a string that was allocated by /// > foreign code, use [`CStr`]. If you need to take ownership of /// > a string that was allocated by foreign code, you will need to /// > make your own provisions for freeing it appropriately, likely /// > with the foreign code's API to do that. /// /// # Examples /// /// Creates a `CString`, pass ownership to an `extern` function (via raw /// pointer), then retake ownership with `from_raw`: /// /// ``` /// use drone_core::ffi::{c_char, CString}; /// /// extern "C" fn some_extern_function(_s: *mut c_char) {} /// /// let c_string = CString::new("Hello!").expect("CString::new failed"); /// let raw = c_string.into_raw(); /// unsafe { /// some_extern_function(raw); /// let c_string = CString::from_raw(raw); /// } /// ``` pub unsafe fn from_raw(ptr: *mut c_char) -> Self { unsafe { let len = strlen(ptr) + 1; // Including the NUL byte let slice = slice::from_raw_parts_mut(ptr, len as usize); Self { inner: Box::from_raw(slice as *mut [c_char] as *mut [u8]) } } } /// Consumes the `CString` and transfers ownership of the string to a C /// caller. /// /// The pointer which this function returns must be returned to Rust and /// reconstituted using [`CString::from_raw`] to be properly deallocated. /// Specifically, one should *not* use the standard C `free()` function /// to deallocate this string. /// /// Failure to call [`CString::from_raw`] will lead to a memory leak. /// /// # Examples /// /// ``` /// use drone_core::ffi::CString; /// /// let c_string = CString::new("foo").expect("CString::new failed"); /// /// let ptr = c_string.into_raw(); /// /// unsafe { /// assert_eq!(b'f', *ptr as u8); /// assert_eq!(b'o', *ptr.offset(1) as u8); /// assert_eq!(b'o', *ptr.offset(2) as u8); /// assert_eq!(b'\0', *ptr.offset(3) as u8); /// /// // retake pointer to free memory /// let _ = CString::from_raw(ptr); /// } /// ``` #[inline] pub fn into_raw(self) -> *mut c_char { Box::into_raw(self.into_inner()).cast::<c_char>() } /// Converts the `CString` into a [`String`] if it contains valid UTF-8 /// data. /// /// On failure, ownership of the original `CString` is returned. /// /// # Examples /// /// ``` /// use drone_core::ffi::CString; /// /// let valid_utf8 = vec![b'f', b'o', b'o']; /// let cstring = CString::new(valid_utf8).expect("CString::new failed"); /// assert_eq!(cstring.into_string().expect("into_string() call failed"), "foo"); /// /// let invalid_utf8 = vec![b'f', 0xff, b'o', b'o']; /// let cstring = CString::new(invalid_utf8).expect("CString::new failed"); /// let err = cstring.into_string().err().expect("into_string().err() failed"); /// assert_eq!(err.utf8_error().valid_up_to(), 1); /// ``` pub fn into_string(self) -> Result<String, IntoStringError> { String::from_utf8(self.into_bytes()).map_err(|e| IntoStringError { error: e.utf8_error(), inner: unsafe { Self::from_vec_unchecked(e.into_bytes()) }, }) } /// Consumes the `CString` and returns the underlying byte buffer. /// /// The returned buffer does **not** contain the trailing nul terminator, /// and it is guaranteed to not have any interior nul bytes. /// /// # Examples /// /// ``` /// use drone_core::ffi::CString; /// /// let c_string = CString::new("foo").expect("CString::new failed"); /// let bytes = c_string.into_bytes(); /// assert_eq!(bytes, vec![b'f', b'o', b'o']); /// ``` pub fn into_bytes(self) -> Vec<u8> { let mut vec = self.into_inner().into_vec(); let nul = vec.pop(); debug_assert_eq!(nul, Some(0_u8)); vec } /// Equivalent to the [`CString::into_bytes`] function except that the /// returned vector includes the trailing nul terminator. /// /// # Examples /// /// ``` /// use drone_core::ffi::CString; /// /// let c_string = CString::new("foo").expect("CString::new failed"); /// let bytes = c_string.into_bytes_with_nul(); /// assert_eq!(bytes, vec![b'f', b'o', b'o', b'\0']); /// ``` pub fn into_bytes_with_nul(self) -> Vec<u8> { self.into_inner().into_vec() } /// Returns the contents of this `CString` as a slice of bytes. /// /// The returned slice does **not** contain the trailing nul terminator, and /// it is guaranteed to not have any interior nul bytes. If you need the nul /// terminator, use [`CString::as_bytes_with_nul`] instead. /// /// # Examples /// /// ``` /// use drone_core::ffi::CString; /// /// let c_string = CString::new("foo").expect("CString::new failed"); /// let bytes = c_string.as_bytes(); /// assert_eq!(bytes, &[b'f', b'o', b'o']); /// ``` #[inline] pub fn as_bytes(&self) -> &[u8] { &self.inner[..self.inner.len() - 1] } /// Equivalent to the [`CString::as_bytes`] function except that the /// returned slice includes the trailing nul terminator. /// /// # Examples /// /// ``` /// use drone_core::ffi::CString; /// /// let c_string = CString::new("foo").expect("CString::new failed"); /// let bytes = c_string.as_bytes_with_nul(); /// assert_eq!(bytes, &[b'f', b'o', b'o', b'\0']); /// ``` #[inline] pub fn as_bytes_with_nul(&self) -> &[u8] { &self.inner } /// Extracts a [`CStr`] slice containing the entire string. /// /// # Examples /// /// ``` /// use drone_core::ffi::{CStr, CString}; /// /// let c_string = CString::new(b"foo".to_vec()).expect("CString::new failed"); /// let c_str = c_string.as_c_str(); /// assert_eq!( /// c_str, /// CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed") /// ); /// ``` #[inline] pub fn as_c_str(&self) -> &CStr { &*self } /// Converts this `CString` into a boxed [`CStr`]. /// /// # Examples /// /// ``` /// use drone_core::ffi::{CStr, CString}; /// /// let c_string = CString::new(b"foo".to_vec()).expect("CString::new failed"); /// let boxed = c_string.into_boxed_c_str(); /// assert_eq!( /// &*boxed, /// CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed") /// ); /// ``` pub fn into_boxed_c_str(self) -> Box<CStr> { unsafe { Box::from_raw(Box::into_raw(self.into_inner()) as *mut CStr) } } /// Bypass "move out of struct which implements [`Drop`] trait" restriction. pub(super) fn into_inner(self) -> Box<[u8]> { // Rationale: `mem::forget(self)` invalidates the previous call to // `ptr::read(&self.inner)` so we use `ManuallyDrop` to ensure `self` is // not dropped. Then we can return the box directly without invalidating // it. See https://github.com/rust-lang/rust/issues/62553. let this = mem::ManuallyDrop::new(self); unsafe { ptr::read(&this.inner) } } } impl NulError { /// Returns the position of the nul byte in the slice that caused /// [`CString::new`] to fail. /// /// # Examples /// /// ``` /// use drone_core::ffi::CString; /// /// let nul_error = CString::new("foo\0bar").unwrap_err(); /// assert_eq!(nul_error.nul_position(), 3); /// /// let nul_error = CString::new("foo bar\0").unwrap_err(); /// assert_eq!(nul_error.nul_position(), 7); /// ``` pub fn nul_position(&self) -> usize { self.0 } /// Consumes this error, returning the underlying vector of bytes which /// generated the error in the first place. /// /// # Examples /// /// ``` /// use drone_core::ffi::CString; /// /// let nul_error = CString::new("foo\0bar").unwrap_err(); /// assert_eq!(nul_error.into_vec(), b"foo\0bar"); /// ``` pub fn into_vec(self) -> Vec<u8> { self.1 } } impl IntoStringError { /// Consumes this error, returning original [`CString`] which generated the /// error. pub fn into_cstring(self) -> CString { self.inner } /// Access the underlying UTF-8 error that was the cause of this error. pub fn utf8_error(&self) -> Utf8Error { self.error } } // Turns this `CString` into an empty string to prevent memory unsafe code from // working by accident. Inline to prevent LLVM from optimizing it away in debug // builds. impl Drop for CString { #[inline] fn drop(&mut self) { unsafe { *self.inner.get_unchecked_mut(0) = 0 }; } } impl ops::Deref for CString { type Target = CStr; #[inline] fn deref(&self) -> &CStr { unsafe { CStr::from_bytes_with_nul_unchecked(self.as_bytes_with_nul()) } } } impl fmt::Debug for CString { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { fmt::Debug::fmt(&**self, f) } } impl From<CString> for Vec<u8> { /// Converts a [`CString`] into a [`Vec`]`<u8>`. /// /// The conversion consumes the [`CString`], and removes the terminating NUL /// byte. #[inline] fn from(s: CString) -> Self { s.into_bytes() } } impl Default for CString { /// Creates an empty `CString`. fn default() -> Self { let a: &CStr = Default::default(); a.to_owned() } } impl Borrow<CStr> for CString { #[inline] fn borrow(&self) -> &CStr { self } } impl From<&CStr> for CString { fn from(s: &CStr) -> Self { s.to_owned() } } impl<'a> From<Cow<'a, CStr>> for CString { #[inline] fn from(s: Cow<'a, CStr>) -> Self { s.into_owned() } } impl From<Box<CStr>> for CString { /// Converts a [`Box`]`<CStr>` into a [`CString`] without copying or /// allocating. #[inline] fn from(s: Box<CStr>) -> Self { s.into_c_string() } } impl ops::Index<ops::RangeFull> for CString { type Output = CStr; #[inline] fn index(&self, _index: ops::RangeFull) -> &CStr { self } } impl AsRef<CStr> for CString { #[inline] fn as_ref(&self) -> &CStr { self } } impl fmt::Display for NulError { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { write!(f, "nul byte found in provided data at position: {}", self.0) } } impl fmt::Display for IntoStringError { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { write!(f, "C string contained non-utf8 bytes") } }