raw_parts/lib.rs
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#![warn(clippy::all)]
#![warn(clippy::pedantic)]
#![warn(clippy::cargo)]
#![allow(clippy::option_if_let_else)]
#![allow(unknown_lints)]
#![warn(missing_docs)]
#![warn(missing_debug_implementations)]
#![warn(missing_copy_implementations)]
#![warn(rust_2018_idioms)]
#![warn(rust_2021_compatibility)]
#![warn(trivial_casts, trivial_numeric_casts)]
#![warn(unsafe_op_in_unsafe_fn)]
#![warn(unused_qualifications)]
#![warn(variant_size_differences)]
// Enable feature callouts in generated documentation:
// https://doc.rust-lang.org/beta/unstable-book/language-features/doc-cfg.html
//
// This approach is borrowed from tokio.
#![cfg_attr(docsrs, feature(doc_cfg))]
#![cfg_attr(docsrs, feature(doc_alias))]
//! A wrapper around the decomposed parts of a `Vec<T>`.
//!
//! This crate defines a struct that contains the `Vec`'s internal pointer,
//! length, and allocated capacity.
//!
//! [`RawParts`] makes [`Vec::from_raw_parts`] and [`Vec::into_raw_parts`] easier
//! to use by giving names to the returned values. This prevents errors from
//! mixing up the two `usize` values of length and capacity.
//!
//! # Examples
//!
//! ```
//! use raw_parts::RawParts;
//!
//! let v: Vec<i32> = vec![-1, 0, 1];
//!
//! let RawParts { ptr, length, capacity } = RawParts::from_vec(v);
//!
//! let rebuilt = unsafe {
//! // We can now make changes to the components, such as
//! // transmuting the raw pointer to a compatible type.
//! let ptr = ptr as *mut u32;
//! let raw_parts = RawParts { ptr, length, capacity };
//!
//! raw_parts.into_vec()
//! };
//! assert_eq!(rebuilt, [4294967295, 0, 1]);
//! ```
//!
//! # `no_std`
//!
//! raw-parts is `no_std` compatible with a required dependency on [`alloc`].
#![no_std]
#![doc(html_root_url = "https://docs.rs/raw-parts/2.1.0")]
extern crate alloc;
use alloc::vec::Vec;
use core::fmt;
use core::hash::{Hash, Hasher};
use core::mem::ManuallyDrop;
/// A wrapper around the decomposed parts of a `Vec<T>`.
///
/// This struct contains the `Vec`'s internal pointer, length, and allocated
/// capacity.
///
/// `RawParts` makes [`Vec::from_raw_parts`] and [`Vec::into_raw_parts`] easier
/// to use by giving names to the returned values. This prevents errors from
/// mixing up the two `usize` values of length and capacity.
///
/// # Examples
///
/// ```
/// use raw_parts::RawParts;
///
/// let v: Vec<i32> = vec![-1, 0, 1];
///
/// let RawParts { ptr, length, capacity } = RawParts::from_vec(v);
///
/// let rebuilt = unsafe {
/// // We can now make changes to the components, such as
/// // transmuting the raw pointer to a compatible type.
/// let ptr = ptr as *mut u32;
/// let raw_parts = RawParts { ptr, length, capacity };
///
/// raw_parts.into_vec()
/// };
/// assert_eq!(rebuilt, [4294967295, 0, 1]);
/// ```
pub struct RawParts<T> {
/// A non-null pointer to a buffer of `T`.
///
/// This pointer is the same as the value returned by [`Vec::as_mut_ptr`] in
/// the source vector.
pub ptr: *mut T,
/// The number of elements in the source vector, also referred to as its
/// "length".
///
/// This value is the same as the value returned by [`Vec::len`] in the
/// source vector.
pub length: usize,
/// The number of elements the source vector can hold without reallocating.
///
/// This value is the same as the value returned by [`Vec::capacity`] in the
/// source vector.
pub capacity: usize,
}
impl<T> From<Vec<T>> for RawParts<T> {
/// Decompose a `Vec<T>` into its raw components.
fn from(vec: Vec<T>) -> Self {
Self::from_vec(vec)
}
}
impl<T> fmt::Debug for RawParts<T> {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt.debug_struct("RawParts")
.field("ptr", &self.ptr)
.field("length", &self.length)
.field("capacity", &self.capacity)
.finish()
}
}
impl<T> PartialEq for RawParts<T> {
fn eq(&self, other: &Self) -> bool {
self.ptr == other.ptr && self.length == other.length && self.capacity == other.capacity
}
}
impl<T> Eq for RawParts<T> {}
impl<T> Hash for RawParts<T> {
fn hash<H: Hasher>(&self, state: &mut H) {
self.ptr.hash(state);
self.length.hash(state);
self.capacity.hash(state);
}
}
// Do not implement the `From` trait in the other direction since `crate::from`
// is an unsafe function.
//
// ```
// impl<T> From<RawParts<T>> for Vec<T> {
// fn from(raw_parts: RawParts<T>) -> Self {
// // ERROR: this requires `unsafe`, which we don't want to hide in a
// // `From` impl.
// from(raw_parts)
// }
// }
impl<T> RawParts<T> {
/// Construct the raw components of a `Vec<T>` by decomposing it.
///
/// Returns a struct containing the raw pointer to the underlying data, the
/// length of the vector (in elements), and the allocated capacity of the
/// data (in elements).
///
/// After calling this function, the caller is responsible for the memory
/// previously managed by the `Vec`. The only way to do this is to convert
/// the raw pointer, length, and capacity back into a `Vec` with the
/// [`Vec::from_raw_parts`] function or the [`into_vec`] function, allowing
/// the destructor to perform the cleanup.
///
/// [`into_vec`]: Self::into_vec
///
/// # Examples
///
/// ```
/// use raw_parts::RawParts;
///
/// let v: Vec<i32> = vec![-1, 0, 1];
///
/// let RawParts { ptr, length, capacity } = RawParts::from_vec(v);
///
/// let rebuilt = unsafe {
/// // We can now make changes to the components, such as
/// // transmuting the raw pointer to a compatible type.
/// let ptr = ptr as *mut u32;
/// let raw_parts = RawParts { ptr, length, capacity };
///
/// raw_parts.into_vec()
/// };
/// assert_eq!(rebuilt, [4294967295, 0, 1]);
/// ```
#[must_use]
pub fn from_vec(vec: Vec<T>) -> Self {
// FIXME Update this when vec_into_raw_parts is stabilized
// See: https://doc.rust-lang.org/1.69.0/src/alloc/vec/mod.rs.html#823-826
// See: https://doc.rust-lang.org/beta/unstable-book/library-features/vec-into-raw-parts.html
//
// https://github.com/rust-lang/rust/issues/65816
let mut me = ManuallyDrop::new(vec);
let (ptr, length, capacity) = (me.as_mut_ptr(), me.len(), me.capacity());
Self {
ptr,
length,
capacity,
}
}
/// Creates a `Vec<T>` directly from the raw components of another vector.
///
/// # Safety
///
/// This function has the same safety invariants as [`Vec::from_raw_parts`],
/// which are repeated in the following paragraphs.
///
/// This is highly unsafe, due to the number of invariants that aren't
/// checked:
///
/// * `ptr` must have been allocated using the global allocator, such as via
/// the [`alloc::alloc`] function.
/// * `T` needs to have the same alignment as what `ptr` was allocated with.
/// (`T` having a less strict alignment is not sufficient, the alignment really
/// needs to be equal to satisfy the [`dealloc`] requirement that memory must be
/// allocated and deallocated with the same layout.)
/// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
/// to be the same size as the pointer was allocated with. (Because similar to
/// alignment, [`dealloc`] must be called with the same layout `size`.)
/// * `length` needs to be less than or equal to `capacity`.
/// * The first `length` values must be properly initialized values of type `T`.
/// * `capacity` needs to be the capacity that the pointer was allocated with.
/// * The allocated size in bytes must be no larger than `isize::MAX`.
/// See the safety documentation of [`pointer::offset`].
///
/// These requirements are always upheld by any `ptr` that has been allocated
/// via `Vec<T>`. Other allocation sources are allowed if the invariants are
/// upheld.
///
/// Violating these may cause problems like corrupting the allocator's
/// internal data structures. For example it is normally **not** safe
/// to build a `Vec<u8>` from a pointer to a C `char` array with length
/// `size_t`, doing so is only safe if the array was initially allocated by
/// a `Vec` or `String`.
/// It's also not safe to build one from a `Vec<u16>` and its length, because
/// the allocator cares about the alignment, and these two types have different
/// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
/// turning it into a `Vec<u8>` it'll be deallocated with alignment 1. To avoid
/// these issues, it is often preferable to do casting/transmuting using
/// [`slice::from_raw_parts`] instead.
///
/// The ownership of `ptr` is effectively transferred to the
/// `Vec<T>` which may then deallocate, reallocate or change the
/// contents of memory pointed to by the pointer at will. Ensure
/// that nothing else uses the pointer after calling this
/// function.
///
/// [`String`]: alloc::string::String
/// [`alloc::alloc`]: alloc::alloc::alloc
/// [`dealloc`]: alloc::alloc::GlobalAlloc::dealloc
/// [`slice::from_raw_parts`]: core::slice::from_raw_parts
/// [`pointer::offset`]: https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.offset
///
/// # Examples
///
/// ```
/// use core::ptr;
/// use core::mem;
///
/// use raw_parts::RawParts;
///
/// let v = vec![1, 2, 3];
///
/// // Pull out the various important pieces of information about `v`
/// let RawParts { ptr, length, capacity } = RawParts::from_vec(v);
///
/// unsafe {
/// // Overwrite memory with 4, 5, 6
/// for i in 0..length as isize {
/// ptr::write(ptr.offset(i), 4 + i);
/// }
///
/// // Put everything back together into a Vec
/// let raw_parts = RawParts { ptr, length, capacity };
/// let rebuilt = raw_parts.into_vec();
/// assert_eq!(rebuilt, [4, 5, 6]);
/// }
/// ```
#[must_use]
pub unsafe fn into_vec(self) -> Vec<T> {
let Self {
ptr,
length,
capacity,
} = self;
// Safety:
//
// The safety invariants that callers must uphold when calling `from` match
// the safety invariants of `Vec::from_raw_parts`.
unsafe { Vec::from_raw_parts(ptr, length, capacity) }
}
}
#[cfg(test)]
mod tests {
use alloc::format;
use alloc::vec::Vec;
use core::hash::{Hash, Hasher};
use fnv::FnvHasher;
use crate::RawParts;
#[test]
fn roundtrip() {
let mut vec = Vec::with_capacity(100); // capacity is 100
vec.extend_from_slice(b"123456789"); // length is 9
let raw_parts = RawParts::from_vec(vec);
let raw_ptr = raw_parts.ptr;
let mut roundtripped_vec = unsafe { raw_parts.into_vec() };
assert_eq!(roundtripped_vec.capacity(), 100);
assert_eq!(roundtripped_vec.len(), 9);
assert_eq!(roundtripped_vec.as_mut_ptr(), raw_ptr);
}
#[test]
fn from_vec_sets_ptr() {
let mut vec = Vec::with_capacity(100); // capacity is 100
vec.extend_from_slice(b"123456789"); // length is 9
let ptr = vec.as_mut_ptr();
let raw_parts = RawParts::from_vec(vec);
assert_eq!(raw_parts.ptr, ptr);
}
#[test]
fn from_vec_sets_length() {
let mut vec = Vec::with_capacity(100); // capacity is 100
vec.extend_from_slice(b"123456789"); // length is 9
let raw_parts = RawParts::from_vec(vec);
assert_eq!(raw_parts.length, 9);
}
#[test]
fn from_vec_sets_capacity() {
let mut vec = Vec::with_capacity(100); // capacity is 100
vec.extend_from_slice(b"123456789"); // length is 9
let raw_parts = RawParts::from_vec(vec);
assert_eq!(raw_parts.capacity, 100);
}
#[test]
fn from_sets_ptr() {
let mut vec = Vec::with_capacity(100); // capacity is 100
vec.extend_from_slice(b"123456789"); // length is 9
let ptr = vec.as_mut_ptr();
let raw_parts = RawParts::from(vec);
assert_eq!(raw_parts.ptr, ptr);
}
#[test]
fn from_sets_length() {
let mut vec = Vec::with_capacity(100); // capacity is 100
vec.extend_from_slice(b"123456789"); // length is 9
let raw_parts = RawParts::from(vec);
assert_eq!(raw_parts.length, 9);
}
#[test]
fn from_sets_capacity() {
let mut vec = Vec::with_capacity(100); // capacity is 100
vec.extend_from_slice(b"123456789"); // length is 9
let raw_parts = RawParts::from(vec);
assert_eq!(raw_parts.capacity, 100);
}
#[test]
fn debug_test() {
let mut vec = Vec::with_capacity(100); // capacity is 100
vec.extend_from_slice(b"123456789"); // length is 9
let raw_parts = RawParts::from_vec(vec);
assert_eq!(
format!(
"RawParts {{ ptr: {:?}, length: 9, capacity: 100 }}",
raw_parts.ptr
),
format!("{:?}", raw_parts)
);
}
#[test]
fn partial_eq_fail_pointer() {
let mut vec_1 = Vec::with_capacity(100); // capacity is 100
vec_1.extend_from_slice(b"123456789"); // length is 9
let mut vec_2 = Vec::with_capacity(100); // capacity is 100
vec_2.extend_from_slice(b"123456789"); // length is 9
let raw_parts_1 = RawParts::from_vec(vec_1);
let raw_parts_2 = RawParts::from_vec(vec_2);
assert_ne!(raw_parts_1, raw_parts_2);
}
#[test]
fn partial_eq_fail_capacity() {
let mut vec_1 = Vec::with_capacity(100); // capacity is 100
vec_1.extend_from_slice(b"123456789"); // length is 9
let mut vec_2 = Vec::with_capacity(101); // capacity is 101
vec_2.extend_from_slice(b"123456789"); // length is 9
let raw_parts_1 = RawParts::from_vec(vec_1);
let raw_parts_2 = RawParts::from_vec(vec_2);
assert_ne!(raw_parts_1, raw_parts_2);
}
#[test]
fn partial_eq_fail_length() {
let mut vec_1 = Vec::with_capacity(100); // capacity is 100
vec_1.extend_from_slice(b"123456789"); // length is 9
let mut vec_2 = Vec::with_capacity(100); // capacity is 100
vec_2.extend_from_slice(b"12345678"); // length is 8
let raw_parts_1 = RawParts::from_vec(vec_1);
let raw_parts_2 = RawParts::from_vec(vec_2);
assert_ne!(raw_parts_1, raw_parts_2);
}
#[test]
fn partial_eq_pass() {
let mut vec = Vec::with_capacity(100); // capacity is 100
vec.extend_from_slice(b"123456789"); // length is 9
let RawParts {
ptr,
length,
capacity,
} = RawParts::from_vec(vec);
let a = RawParts {
ptr,
length,
capacity,
};
let b = RawParts {
ptr,
length,
capacity,
};
assert_eq!(a, b);
}
#[test]
fn hash_fail_pointer() {
let mut vec_1 = Vec::with_capacity(100); // capacity is 100
vec_1.extend_from_slice(b"123456789"); // length is 9
let mut vec_2 = Vec::with_capacity(100); // capacity is 100
vec_2.extend_from_slice(b"123456789"); // length is 9
let raw_parts_1 = RawParts::from_vec(vec_1);
let mut hasher = FnvHasher::default();
raw_parts_1.hash(&mut hasher);
let hash_a = hasher.finish();
let raw_parts_2 = RawParts::from_vec(vec_2);
let mut hasher = FnvHasher::default();
raw_parts_2.hash(&mut hasher);
let hash_b = hasher.finish();
assert_ne!(hash_a, hash_b);
}
#[test]
fn hash_fail_capacity() {
let mut vec_1 = Vec::with_capacity(100); // capacity is 100
vec_1.extend_from_slice(b"123456789"); // length is 9
let mut vec_2 = Vec::with_capacity(101); // capacity is 101
vec_2.extend_from_slice(b"123456789"); // length is 9
let raw_parts_1 = RawParts::from_vec(vec_1);
let mut hasher = FnvHasher::default();
raw_parts_1.hash(&mut hasher);
let hash_a = hasher.finish();
let raw_parts_2 = RawParts::from_vec(vec_2);
let mut hasher = FnvHasher::default();
raw_parts_2.hash(&mut hasher);
let hash_b = hasher.finish();
assert_ne!(hash_a, hash_b);
}
#[test]
fn hash_fail_length() {
let mut vec_1 = Vec::with_capacity(100); // capacity is 100
vec_1.extend_from_slice(b"123456789"); // length is 9
let mut vec_2 = Vec::with_capacity(100); // capacity is 100
vec_2.extend_from_slice(b"12345678"); // length is 8
let raw_parts_1 = RawParts::from_vec(vec_1);
let mut hasher = FnvHasher::default();
raw_parts_1.hash(&mut hasher);
let hash_a = hasher.finish();
let raw_parts_2 = RawParts::from_vec(vec_2);
let mut hasher = FnvHasher::default();
raw_parts_2.hash(&mut hasher);
let hash_b = hasher.finish();
assert_ne!(hash_a, hash_b);
}
#[test]
fn hash_eq_pass() {
let mut vec = Vec::with_capacity(100); // capacity is 100
vec.extend_from_slice(b"123456789"); // length is 9
let raw_parts = RawParts::from_vec(vec);
let mut hasher = FnvHasher::default();
raw_parts.hash(&mut hasher);
let hash_a = hasher.finish();
let mut hasher = FnvHasher::default();
raw_parts.hash(&mut hasher);
let hash_b = hasher.finish();
assert_eq!(hash_a, hash_b);
}
}
// Ensure code blocks in `README.md` compile.
//
// This module declaration should be kept at the end of the file, in order to
// not interfere with code coverage.
#[cfg(doctest)]
#[doc = include_str!("../README.md")]
mod readme {}