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Change Log
=======
All notable changes to this project will be documented in this file.
The format is based on [Keep a Changelog](http://keepachangelog.com/)
and this project adheres to [Semantic Versioning](http://semver.org/).
# [unreleased]

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[package]
name = "raw-slice"
version = "0.1.0"
edition = "2024"
authors = ["Robin Mueller <muellerr@irs.uni-stuttgart.de>"]
description = "Generic low-level raw slice types"
homepage = "https://egit.irs.uni-stuttgart.de/rust/raw-slice"
repository = "https://egit.irs.uni-stuttgart.de/rust/raw-slice"
license = "Apache-2.0 OR MIT"
keywords = ["no-std", "slice", "embedded", "dma", "pointer", "unsafe", "memory"]
categories = ["no-std", "hardware-support", "embedded", "embedded::no-std", "data-structures"]
[dependencies]
embedded-dma = "0.2"

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`raw-slice`: Generic raw slice types
======
This crate provides generic raw slice type, which allows erasing the lifetime of a borrowed slice.
The documentation provides more details on the motivation of this crate and how it can be used.

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//! # Raw Slice Types
//!
//! This crate provides two generic raw slice type, [RawSlice] and [RawSliceMut], which allow
//! erasing the lifetime of a borrowed slice.
//!
//! ## Motivation
//!
//! In Rust, lifetimes are a powerful tool for ensuring memory safety at compile time.
//! However, there are cases where lifetimes become too restrictive, such as when working
//! with borrowed data across asynchronous or interrupt-driven contexts.
//!
//! This data structure is particularly useful in embedded systems, where data may be
//! passed to asynchronous peripherals such as serial TX drivers using interrupts or DMA.
//! The data may be static, but it could also reside on the stack. By using a shared [RawBufSlice],
//! you can pass borrowed data to a driver **without** needing to explicitly manage lifetimes.
//!
//! ## Safety Considerations
//!
//! - **No Lifetime Tracking:** Since [RawSlice] erases lifetimes, **the caller must ensure**
//! that the referenced data remains valid while the [RawSlice] is in use.
//! - **Concurrency Risks:** Accessing the same underlying data from multiple contexts
//! (e.g., an ISR and a task) requires proper synchronization.
//! - **Immutability:** [RawSlice] provides a **read-only view** of the data. If you need
//! mutability, [RawSliceMut] can be used.
//!
//! ## Usage Example
//!
//! ```rust
//! use raw_slice::RawBufSlice;
//!
//! static DATA: &[u8] = &[1, 2, 3, 4];
//!
//! let raw_buf = unsafe { RawBufSlice::new(DATA) };
//!
//! // Later, in an ISR or different context
//! unsafe {
//! if let Some(slice) = raw_buf.get() {
//! // Process the data, e.g. send it via serial interface
//! // self.rx.write(slice);
//! }
//! }
//! ```
//!
//! ## API Design
//!
//! While this crate provides methods to interact with the stored data, most of these operations
//! remain `unsafe` due to the compiler's inability to enforce lifetimes after erasure. Users should
//! carefully ensure the referenced data remains valid for the required duration. In addition
//! to the concept of a slice being empty, a raw slice can also be NULL.
//!
//! ## Embedded DMA Support
//!
//! - The [RawBufSlice] structure implements the [embedded_dma::ReadBuffer] trait
//! - The [RawBufSliceMut] structure implements the [embedded_dma::WriteBuffer] trait
#![no_std]
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
pub struct RawSlice<T> {
data: *const T,
len: usize,
}
/// Safety: This type MUST be used with mutex to ensure concurrent access is valid.
unsafe impl<T: Send> Send for RawSlice<T> {}
impl<T> RawSlice<T> {
/// Creates a new `RawSlice<T>` from a slice reference.
///
/// # Safety
///
/// - The caller **must** ensure that the slice outlives this `RawSlice<T>`.
/// - The original slice **must not** be mutated while this `RawSlice<T>` is used.
#[allow(dead_code)]
pub const unsafe fn new(data: &[T]) -> Self {
Self {
data: data.as_ptr(),
len: data.len(),
}
}
/// Creates an empty `RawSlice<T>`, equivalent to a null pointer with zero length.
pub const fn new_nulled() -> Self {
Self {
data: core::ptr::null(),
len: 0,
}
}
/// Updates the raw pointer and length to point to a new slice.
///
/// # Safety
///
/// - The caller **must** ensure that the slice outlives this `RawSlice<T>`.
/// - The original slice **must not** be mutated while this `RawSlice<T>` is used.
pub const unsafe fn set(&mut self, data: &[T]) {
self.data = data.as_ptr();
self.len = data.len();
}
/// Set the internal data pointer to NULL and also clears the data length.
pub const fn set_null(&mut self) {
self.data = core::ptr::null();
self.len = 0;
}
/// Check whether the internal data pointer is NULL.
pub const fn is_null(&self) -> bool {
self.data.is_null()
}
/// Converts the raw pointer into a slice.
///
/// Returns [None] if the pointer is null.
///
/// # Safety
///
/// - The caller **must** ensure that the underlying memory is still valid.
/// - Using this function after the original slice is dropped results in UB.
pub const unsafe fn get(&self) -> Option<&[T]> {
if self.data.is_null() {
return None;
}
Some(unsafe { core::slice::from_raw_parts(self.data, self.len) })
}
/// Returns [None] if the pointer is null and whether [Self::len] is 0 otherwise.
pub const fn is_empty(&self) -> Option<bool> {
if self.is_null() {
return None;
}
Some(self.len == 0)
}
/// Returns [None] if the pointer is null and the length of the raw slice otherwise.
pub const fn len(&self) -> Option<usize> {
if self.is_null() {
return None;
}
Some(self.len)
}
}
impl<T> Default for RawSlice<T> {
fn default() -> Self {
Self::new_nulled()
}
}
pub type RawBufSlice = RawU8Slice;
pub type RawU8Slice = RawSlice<u8>;
pub type RawU16Slice = RawSlice<u16>;
pub type RawU32Slice = RawSlice<u32>;
macro_rules! impl_dma_read_buf {
($slice_type:ident, $ty:ident) => {
/// This allows using [Self] in DMA APIs which expect a [embedded_dma::ReadBuffer].
///
/// However, the user still must ensure that any alignment rules for DMA buffers required by
/// the hardware are met and than any MPU/MMU configuration necessary is also performed for this
/// to work properly.
unsafe impl embedded_dma::ReadBuffer for $slice_type {
type Word = $ty;
unsafe fn read_buffer(&self) -> (*const Self::Word, usize) {
(self.data, self.len)
}
}
};
}
impl_dma_read_buf!(RawBufSlice, u8);
impl_dma_read_buf!(RawU16Slice, u16);
impl_dma_read_buf!(RawU32Slice, u32);
#[derive(Debug, Copy, Clone)]
pub struct RawSliceMut<T> {
data: *mut T,
len: usize,
}
/// Safety: This type MUST be used with mutex to ensure concurrent access is valid.
unsafe impl<T: Send> Send for RawSliceMut<T> {}
impl<T> RawSliceMut<T> {
/// Creates a new `RawSlice<T>` from a slice reference.
///
/// # Safety
///
/// - The caller **must** ensure that the slice outlives this `RawSlice<T>`.
/// - The original slice **must not** be mutated while this `RawSlice<T>` is used.
#[allow(dead_code)]
pub const unsafe fn new(data: &mut [T]) -> Self {
Self {
data: data.as_mut_ptr(),
len: data.len(),
}
}
/// Creates an empty `RawSlice<T>`, equivalent to a null pointer with zero length.
pub const fn new_nulled() -> Self {
Self {
data: core::ptr::null_mut(),
len: 0,
}
}
/// Updates the raw pointer and length to point to a new slice.
///
/// # Safety
///
/// - The caller **must** ensure that the slice outlives this `RawSlice<T>`.
/// - The original slice **must not** be mutated while this `RawSlice<T>` is used.
pub const unsafe fn set(&mut self, data: &mut [T]) {
self.data = data.as_mut_ptr();
self.len = data.len();
}
/// Converts the raw pointer into a slice.
///
/// Returns [None] if the pointer is null.
///
/// # Safety
///
/// - The caller **must** ensure that the underlying memory is still valid.
/// - Using this function after the original slice is dropped results in UB.
pub const unsafe fn get<'slice>(&self) -> Option<&'slice [T]> {
if self.data.is_null() {
return None;
}
Some(unsafe { core::slice::from_raw_parts(self.data, self.len) })
}
/// Converts the raw pointer into a mutable slice.
///
/// Returns [None] if the pointer is null.
///
/// # Safety
///
/// - The caller **must** ensure that the underlying memory is still valid.
/// - Using this function after the original slice is dropped results in UB.
pub const unsafe fn get_mut<'slice>(&mut self) -> Option<&'slice mut [T]> {
if self.data.is_null() {
return None;
}
Some(unsafe { core::slice::from_raw_parts_mut(self.data, self.len) })
}
pub const fn set_null(&mut self) {
self.data = core::ptr::null_mut();
self.len = 0;
}
pub const fn is_null(&self) -> bool {
self.data.is_null()
}
/// Returns [None] if the pointer is null and whether [Self::len] is 0 otherwise.
pub const fn is_empty(&self) -> Option<bool> {
if self.is_null() {
return None;
}
Some(self.len == 0)
}
/// Returns [None] if the pointer is null and the length of the raw slice otherwise.
pub const fn len(&self) -> Option<usize> {
if self.is_null() {
return None;
}
Some(self.len)
}
}
impl<T> Default for RawSliceMut<T> {
fn default() -> Self {
Self::new_nulled()
}
}
pub type RawBufSliceMut = RawU8SliceMut;
pub type RawU8SliceMut = RawSliceMut<u8>;
pub type RawU16SliceMut = RawSliceMut<u16>;
pub type RawU32SliceMut = RawSliceMut<u32>;
macro_rules! impl_dma_write_buf {
($slice_type:ident, $ty:ident) => {
/// This allows using [Self] in DMA APIs which expect a [embedded_dma::WriteBuffer].
///
/// However, the user still must ensure that any alignment rules for DMA buffers required by
/// the hardware are met and than any MPU/MMU configuration necessary was also performed.
unsafe impl embedded_dma::WriteBuffer for $slice_type {
type Word = $ty;
unsafe fn write_buffer(&mut self) -> (*mut Self::Word, usize) {
(self.data, self.len)
}
}
};
}
impl_dma_write_buf!(RawBufSliceMut, u8);
impl_dma_write_buf!(RawU16SliceMut, u16);
impl_dma_write_buf!(RawU32SliceMut, u32);
#[cfg(test)]
mod tests {
use super::*;
#[test]
pub fn test_basic() {
let slice = [1, 2, 3, 4];
let mut slice_raw = unsafe { RawBufSlice::new(&slice) };
assert_eq!(slice_raw.len().unwrap(), 4);
assert!(!slice_raw.is_null());
assert!(!slice_raw.is_empty().unwrap());
assert_eq!(slice_raw.len().unwrap(), 4);
let slice_read_back = unsafe { slice_raw.get().unwrap() };
assert_eq!(slice_read_back, slice);
slice_raw.set_null();
generic_empty_test(&slice_raw);
}
#[test]
pub fn test_empty() {
let empty = RawBufSlice::new_nulled();
generic_empty_test(&empty);
}
#[test]
pub fn test_empty_mut() {
let mut empty = RawBufSliceMut::new_nulled();
generic_empty_test_mut(&mut empty);
}
#[test]
pub fn test_clonable() {
let slice = [1, 2, 3, 4];
let slice_raw = unsafe { RawBufSlice::new(&slice) };
let slice_copied = slice_raw;
assert_eq!(slice_copied, slice_raw);
}
#[test]
pub fn test_basic_mut() {
let mut slice = [1, 2, 3, 4];
let mut slice_raw = unsafe { RawBufSliceMut::new(&mut slice) };
assert_eq!(slice_raw.len().unwrap(), 4);
assert!(!slice_raw.is_null());
assert!(!slice_raw.is_empty().unwrap());
assert_eq!(slice_raw.len().unwrap(), 4);
let slice_read_back = unsafe { slice_raw.get().unwrap() };
assert_eq!(slice_read_back, slice);
let mut_slice_read_back = unsafe { slice_raw.get_mut().unwrap() };
assert_eq!(slice_read_back, mut_slice_read_back);
mut_slice_read_back[0] = 5;
assert_eq!(slice[0], 5);
slice_raw.set_null();
generic_empty_test_mut(&mut slice_raw);
}
fn generic_empty_test(slice: &RawBufSlice) {
assert!(slice.is_null());
assert!(slice.is_empty().is_none());
assert!(slice.len().is_none());
assert!(unsafe { slice.get() }.is_none());
}
fn generic_empty_test_mut(slice: &mut RawBufSliceMut) {
assert!(slice.is_null());
assert!(slice.is_empty().is_none());
assert!(slice.len().is_none());
assert!(unsafe { slice.get() }.is_none());
assert!(unsafe { slice.get_mut() }.is_none());
}
}