1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895
// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//! Utilities for safe zero-copy parsing and serialization.
//!
//! This crate provides utilities which make it easy to perform zero-copy
//! parsing and serialization by allowing zero-copy conversion to/from byte
//! slices.
//!
//! This is enabled by three core marker traits:
//! - [`FromBytes`] indicates that a type may safely be converted from an
//! arbitrary byte sequence
//! - [`AsBytes`] indicates that a type may safely be converted *to* a byte
//! sequence
//! - [`Unaligned`] indicates that a type's alignment requirement is 1
//!
//! Types which implement a subset of these traits can then be converted to/from
//! byte sequences with little to no runtime overhead.
#![feature(refcell_map_split)]
#![cfg_attr(not(test), no_std)]
#[cfg(test)]
extern crate core;
use core::cell::{Ref, RefMut};
use core::fmt::{self, Debug, Display, Formatter};
use core::marker::PhantomData;
use core::mem;
use core::ops::{Deref, DerefMut};
// implement an unsafe trait for all signed and unsigned primitive types
macro_rules! impl_for_primitives {
($trait:ident) => (
impl_for_primitives!(@inner $trait, u8, i8, u16, i16, u32, i32, u64, i64, u128, i128, usize, isize);
);
(@inner $trait:ident, $type:ty) => (
unsafe impl $trait for $type {}
);
(@inner $trait:ident, $type:ty, $($types:ty),*) => (
unsafe impl $trait for $type {}
impl_for_primitives!(@inner $trait, $($types),*);
);
}
// implement an unsafe trait for all array lengths up to 32 with an element type
// which implements the trait
macro_rules! impl_for_array_sizes {
($trait:ident) => (
impl_for_array_sizes!(@inner $trait, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32);
);
(@inner $trait:ident, $n:expr) => (
unsafe impl<T: $trait> $trait for [T; $n] {}
);
(@inner $trait:ident, $n:expr, $($ns:expr),*) => (
unsafe impl<T: $trait> $trait for [T; $n] {}
impl_for_array_sizes!(@inner $trait, $($ns),*);
);
}
/// Types for which any byte pattern is valid.
///
/// `FromBytes` types can safely be deserialized from an untrusted sequence of
/// bytes because any byte sequence corresponds to a valid instance of the type.
///
/// # Safety
///
/// If `T: FromBytes`, then unsafe code may assume that it is sound to treat any
/// initialized sequence of bytes of length `size_of::<T>()` as a `T`. If a type
/// is marked as `FromBytes` which violates this contract, it may cause
/// undefined behavior.
///
/// If a type has the following properties, then it is safe to implement
/// `FromBytes` for that type:
/// - If the type is a struct:
/// - It must be `repr(C)` or `repr(transparent)`
/// - All of its fields must implement `FromBytes`
/// - If the type is an enum:
/// - It must be a C-like enum (meaning that all variants have no fields)
/// - It must be `repr(u8)`, `repr(u16)`, `repr(u32)`, or `repr(u64)`
/// - The maximum number of discriminants must be used (so that every possible
/// bit pattern is a valid one)
pub unsafe trait FromBytes {}
/// Types which are safe to treat as an immutable byte slice.
///
/// `AsBytes` types can be safely viewed as a slice of bytes. In particular,
/// this means that, in any valid instance of the type, none of the bytes of the
/// instance are uninitialized. This precludes the following types:
/// - Structs with internal padding
/// - Unions in which not all variants have the same length
///
/// # Safety
///
/// If `T: AsBytes`, then unsafe code may assume that it is sound to treat any
/// instance of the type as an immutable `[u8]` of the appropriate length. If a
/// type is marked as `AsBytes` which violates this contract, it may cause
/// undefined behavior.
///
/// If a type has the following properties, then it is safe to implement
/// `AsBytes` for that type:
/// - If the type is a struct:
/// - It must be `repr(C)` or `repr(transparent)`
/// - If it is `repr(C)`, its layout must have no inter-field padding (this
/// can be accomplished either by using `repr(packed)` or by manually adding
/// padding fields)
/// - All of its fields must implement `AsBytes`
/// - If the type is an enum:
/// - It must be a C-like enum (meaning that all variants have no fields)
/// - It must be `repr(u8)`, `repr(u16)`, `repr(u32)`, or `repr(u64)`
pub unsafe trait AsBytes {}
impl_for_primitives!(FromBytes);
impl_for_primitives!(AsBytes);
impl_for_array_sizes!(FromBytes);
impl_for_array_sizes!(AsBytes);
/// Types with no alignment requirement.
///
/// If `T: Unaligned`, then `align_of::<T>() == 1`.
///
/// # Safety
///
/// If `T: Unaligned`, then unsafe code may assume that it is sound to produce a
/// reference to `T` at any memory location regardless of alignment. If a type
/// is marked as `Unaligned` which violates this contract, it may cause
/// undefined behavior.
pub unsafe trait Unaligned {}
unsafe impl Unaligned for u8 {}
unsafe impl Unaligned for i8 {}
impl_for_array_sizes!(Unaligned);
/// A length- and alignment-checked reference to a byte slice which can safely
/// be reinterpreted as another type.
///
/// `LayoutVerified` is a byte slice reference (`&[u8]`, `&mut [u8]`,
/// `Ref<[u8]>`, `RefMut<[u8]>`, etc) with the invaraint that the slice's length
/// and alignment are each greater than or equal to the length and alignment of
/// `T`. Using this invariant, it implements `Deref` for `T` so long as `T:
/// FromBytes` and `DerefMut` so long as `T: FromBytes + AsBytes`.
///
/// # Examples
///
/// `LayoutVerified` can be used to treat a sequence of bytes as a structured
/// type, and to read and write the fields of that type as if the byte slice
/// reference were simply a reference to that type.
///
/// ```rust
/// use zerocopy::{AsBytes, ByteSlice, ByteSliceMut, FromBytes, LayoutVerified, Unaligned};
///
/// #[repr(C)]
/// struct UdpHeader {
/// src_port: [u8; 2],
/// dst_port: [u8; 2],
/// length: [u8; 2],
/// checksum: [u8; 2],
/// }
///
/// unsafe impl FromBytes for UdpHeader {}
/// unsafe impl AsBytes for UdpHeader {}
/// unsafe impl Unaligned for UdpHeader {}
///
/// struct UdpPacket<B> {
/// header: LayoutVerified<B, UdpHeader>,
/// body: B,
/// }
///
/// impl<B: ByteSlice> UdpPacket<B> {
/// pub fn parse(bytes: B) -> Option<UdpPacket<B>> {
/// let (header, body) = LayoutVerified::new_unaligned_from_prefix(bytes)?;
/// Some(UdpPacket { header, body })
/// }
///
/// pub fn get_src_port(&self) -> [u8; 2] {
/// self.header.src_port
/// }
/// }
///
/// impl<B: ByteSliceMut> UdpPacket<B> {
/// pub fn set_src_port(&mut self, src_port: [u8; 2]) {
/// self.header.src_port = src_port;
/// }
/// }
/// ```
pub struct LayoutVerified<B, T>(B, PhantomData<T>);
impl<B, T> LayoutVerified<B, T>
where
B: ByteSlice,
{
/// Construct a new `LayoutVerified`.
///
/// `new` verifies that `bytes.len() == size_of::<T>()` and that `bytes` is
/// aligned to `align_of::<T>()`, and constructs a new `LayoutVerified`. If
/// either of these checks fail, it returns `None`.
#[inline]
pub fn new(bytes: B) -> Option<LayoutVerified<B, T>> {
if bytes.len() != mem::size_of::<T>() || !aligned_to(bytes.deref(), mem::align_of::<T>()) {
return None;
}
Some(LayoutVerified(bytes, PhantomData))
}
/// Construct a new `LayoutVerified` from the prefix of a byte slice.
///
/// `new_from_prefix` verifies that `bytes.len() >= size_of::<T>()` and that
/// `bytes` is aligned to `align_of::<T>()`. It consumes the first
/// `size_of::<T>()` bytes from `bytes` to construct a `LayoutVerified`, and
/// returns the remaining bytes to the caller. If either the length or
/// alignment checks fail, it returns `None`.
#[inline]
pub fn new_from_prefix(bytes: B) -> Option<(LayoutVerified<B, T>, B)> {
if bytes.len() < mem::size_of::<T>() || !aligned_to(bytes.deref(), mem::align_of::<T>()) {
return None;
}
let (bytes, suffix) = bytes.split_at(mem::size_of::<T>());
Some((LayoutVerified(bytes, PhantomData), suffix))
}
/// Construct a new `LayoutVerified` from the suffix of a byte slice.
///
/// `new_from_suffix` verifies that `bytes.len() >= size_of::<T>()` and that
/// the last `size_of::<T>()` bytes of `bytes` are aligned to
/// `align_of::<T>()`. It consumes the last `size_of::<T>()` bytes from
/// `bytes` to construct a `LayoutVerified`, and returns the preceding bytes
/// to the caller. If either the length or alignment checks fail, it returns
/// `None`.
#[inline]
pub fn new_from_suffix(bytes: B) -> Option<(B, LayoutVerified<B, T>)> {
let bytes_len = bytes.len();
if bytes_len < mem::size_of::<T>() {
return None;
}
let (prefix, bytes) = bytes.split_at(bytes_len - mem::size_of::<T>());
if !aligned_to(bytes.deref(), mem::align_of::<T>()) {
return None;
}
Some((prefix, LayoutVerified(bytes, PhantomData)))
}
#[inline]
pub fn bytes(&self) -> &[u8] {
&self.0
}
}
fn map_zeroed<B: ByteSliceMut, T>(
opt: Option<LayoutVerified<B, T>>,
) -> Option<LayoutVerified<B, T>> {
match opt {
Some(mut lv) => {
for b in lv.0.iter_mut() {
*b = 0;
}
Some(lv)
}
None => None,
}
}
fn map_prefix_tuple_zeroed<B: ByteSliceMut, T>(
opt: Option<(LayoutVerified<B, T>, B)>,
) -> Option<(LayoutVerified<B, T>, B)> {
match opt {
Some((mut lv, rest)) => {
for b in lv.0.iter_mut() {
*b = 0;
}
Some((lv, rest))
}
None => None,
}
}
fn map_suffix_tuple_zeroed<B: ByteSliceMut, T>(
opt: Option<(B, LayoutVerified<B, T>)>,
) -> Option<(B, LayoutVerified<B, T>)> {
map_prefix_tuple_zeroed(opt.map(|(a, b)| (b, a))).map(|(a, b)| (b, a))
}
impl<B, T> LayoutVerified<B, T>
where
B: ByteSliceMut,
{
/// Construct a new `LayoutVerified` after zeroing the bytes.
///
/// `new_zeroed` verifies that `bytes.len() == size_of::<T>()` and that
/// `bytes` is aligned to `align_of::<T>()`, and constructs a new
/// `LayoutVerified`. If either of these checks fail, it returns `None`.
///
/// If the checks succeed, then `bytes` will be initialized to zero. This
/// can be useful when re-using buffers to ensure that sensitive data
/// previously stored in the buffer is not leaked.
#[inline]
pub fn new_zeroed(bytes: B) -> Option<LayoutVerified<B, T>> {
map_zeroed(Self::new(bytes))
}
/// Construct a new `LayoutVerified` from the prefix of a byte slice,
/// zeroing the prefix.
///
/// `new_from_prefix_zeroed` verifies that `bytes.len() >= size_of::<T>()`
/// and that `bytes` is aligned to `align_of::<T>()`. It consumes the first
/// `size_of::<T>()` bytes from `bytes` to construct a `LayoutVerified`, and
/// returns the remaining bytes to the caller. If either the length or
/// alignment checks fail, it returns `None`.
///
/// If the checks succeed, then the prefix which is consumed will be
/// initialized to zero. This can be useful when re-using buffers to ensure
/// that sensitive data previously stored in the buffer is not leaked.
#[inline]
pub fn new_from_prefix_zeroed(bytes: B) -> Option<(LayoutVerified<B, T>, B)> {
map_prefix_tuple_zeroed(Self::new_from_prefix(bytes))
}
/// Construct a new `LayoutVerified` from the suffix of a byte slice,
/// zeroing the suffix.
///
/// `new_from_suffix_zeroed` verifies that `bytes.len() >= size_of::<T>()` and that
/// the last `size_of::<T>()` bytes of `bytes` are aligned to
/// `align_of::<T>()`. It consumes the last `size_of::<T>()` bytes from
/// `bytes` to construct a `LayoutVerified`, and returns the preceding bytes
/// to the caller. If either the length or alignment checks fail, it returns
/// `None`.
///
/// If the checks succeed, then the suffix which is consumed will be
/// initialized to zero. This can be useful when re-using buffers to ensure
/// that sensitive data previously stored in the buffer is not leaked.
#[inline]
pub fn new_from_suffix_zeroed(bytes: B) -> Option<(B, LayoutVerified<B, T>)> {
map_suffix_tuple_zeroed(Self::new_from_suffix(bytes))
}
}
impl<B, T> LayoutVerified<B, T>
where
B: ByteSlice,
T: Unaligned,
{
/// Construct a new `LayoutVerified` for a type with no alignment
/// requirement.
///
/// `new_unaligned` verifies that `bytes.len() == size_of::<T>()` and
/// constructs a new `LayoutVerified`. If the check fails, it returns
/// `None`.
#[inline]
pub fn new_unaligned(bytes: B) -> Option<LayoutVerified<B, T>> {
if bytes.len() != mem::size_of::<T>() {
return None;
}
Some(LayoutVerified(bytes, PhantomData))
}
/// Construct a new `LayoutVerified` from the prefix of a byte slice for a
/// type with no alignment requirement.
///
/// `new_unaligned_from_prefix` verifies that `bytes.len() >=
/// size_of::<T>()`. It consumes the first `size_of::<T>()` bytes from
/// `bytes` to construct a `LayoutVerified`, and returns the remaining bytes
/// to the caller. If the length check fails, it returns `None`.
#[inline]
pub fn new_unaligned_from_prefix(bytes: B) -> Option<(LayoutVerified<B, T>, B)> {
if bytes.len() < mem::size_of::<T>() {
return None;
}
let (bytes, suffix) = bytes.split_at(mem::size_of::<T>());
Some((LayoutVerified(bytes, PhantomData), suffix))
}
/// Construct a new `LayoutVerified` from the suffix of a byte slice for a
/// type with no alignment requirement.
///
/// `new_unaligned_from_suffix` verifies that `bytes.len() >=
/// size_of::<T>()`. It consumes the last `size_of::<T>()` bytes from
/// `bytes` to construct a `LayoutVerified`, and returns the preceding bytes
/// to the caller. If the length check fails, it returns `None`.
#[inline]
pub fn new_unaligned_from_suffix(bytes: B) -> Option<(B, LayoutVerified<B, T>)> {
let bytes_len = bytes.len();
if bytes_len < mem::size_of::<T>() {
return None;
}
let (prefix, bytes) = bytes.split_at(bytes_len - mem::size_of::<T>());
Some((prefix, LayoutVerified(bytes, PhantomData)))
}
}
impl<B, T> LayoutVerified<B, T>
where
B: ByteSliceMut,
T: Unaligned,
{
/// Construct a new `LayoutVerified` for a type with no alignment
/// requirement, zeroing the bytes.
///
/// `new_unaligned_zeroed` verifies that `bytes.len() == size_of::<T>()` and
/// constructs a new `LayoutVerified`. If the check fails, it returns
/// `None`.
///
/// If the check succeeds, then `bytes` will be initialized to zero. This
/// can be useful when re-using buffers to ensure that sensitive data
/// previously stored in the buffer is not leaked.
#[inline]
pub fn new_unaligned_zeroed(bytes: B) -> Option<LayoutVerified<B, T>> {
map_zeroed(Self::new_unaligned(bytes))
}
/// Construct a new `LayoutVerified` from the prefix of a byte slice for a
/// type with no alignment requirement, zeroing the prefix.
///
/// `new_unaligned_from_prefix_zeroed` verifies that `bytes.len() >=
/// size_of::<T>()`. It consumes the first `size_of::<T>()` bytes from
/// `bytes` to construct a `LayoutVerified`, and returns the remaining bytes
/// to the caller. If the length check fails, it returns `None`.
///
/// If the check succeeds, then the prefix which is consumed will be
/// initialized to zero. This can be useful when re-using buffers to ensure
/// that sensitive data previously stored in the buffer is not leaked.
#[inline]
pub fn new_unaligned_from_prefix_zeroed(bytes: B) -> Option<(LayoutVerified<B, T>, B)> {
map_prefix_tuple_zeroed(Self::new_unaligned_from_prefix(bytes))
}
/// Construct a new `LayoutVerified` from the suffix of a byte slice for a
/// type with no alignment requirement, zeroing the suffix.
///
/// `new_unaligned_from_suffix_zeroed` verifies that `bytes.len() >=
/// size_of::<T>()`. It consumes the last `size_of::<T>()` bytes from
/// `bytes` to construct a `LayoutVerified`, and returns the preceding bytes
/// to the caller. If the length check fails, it returns `None`.
///
/// If the check succeeds, then the suffix which is consumed will be
/// initialized to zero. This can be useful when re-using buffers to ensure
/// that sensitive data previously stored in the buffer is not leaked.
#[inline]
pub fn new_unaligned_from_suffix_zeroed(bytes: B) -> Option<(B, LayoutVerified<B, T>)> {
map_suffix_tuple_zeroed(Self::new_unaligned_from_suffix(bytes))
}
}
fn aligned_to(bytes: &[u8], align: usize) -> bool {
(bytes as *const _ as *const () as usize) % align == 0
}
impl<B, T> LayoutVerified<B, T>
where
B: ByteSliceMut,
{
#[inline]
pub fn bytes_mut(&mut self) -> &mut [u8] {
&mut self.0
}
}
impl<B, T> Deref for LayoutVerified<B, T>
where
B: ByteSlice,
T: FromBytes,
{
type Target = T;
#[inline]
fn deref(&self) -> &T {
unsafe { &mut *(self.0.as_ptr() as *mut T) }
}
}
impl<B, T> DerefMut for LayoutVerified<B, T>
where
B: ByteSliceMut,
T: FromBytes + AsBytes,
{
#[inline]
fn deref_mut(&mut self) -> &mut T {
unsafe { &mut *(self.0.as_mut_ptr() as *mut T) }
}
}
impl<T, B> Display for LayoutVerified<B, T>
where
B: ByteSlice,
T: FromBytes + Display,
{
#[inline]
fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
let inner: &T = self;
inner.fmt(fmt)
}
}
impl<T, B> Debug for LayoutVerified<B, T>
where
B: ByteSlice,
T: FromBytes + Debug,
{
#[inline]
fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
let inner: &T = self;
fmt.debug_tuple("LayoutVerified").field(&inner).finish()
}
}
mod sealed {
use core::cell::{Ref, RefMut};
pub trait Sealed {}
impl<'a> Sealed for &'a [u8] {}
impl<'a> Sealed for &'a mut [u8] {}
impl<'a> Sealed for Ref<'a, [u8]> {}
impl<'a> Sealed for RefMut<'a, [u8]> {}
}
// ByteSlice and ByteSliceMut abstract over [u8] references (&[u8], &mut [u8],
// Ref<[u8]>, RefMut<[u8]>, etc). We rely on various behaviors of these
// references such as that a given reference will never changes its length
// between calls to deref() or deref_mut(), and that split_at() works as
// expected. If ByteSlice or ByteSliceMut were not sealed, consumers could
// implement them in a way that violated these behaviors, and would break our
// unsafe code. Thus, we seal them and implement it only for known-good
// reference types. For the same reason, they're unsafe traits.
/// A mutable or immutable reference to a byte slice.
///
/// `ByteSlice` abstracts over the mutability of a byte slice reference, and is
/// implemented for various special reference types such as `Ref<[u8]>` and
/// `RefMut<[u8]>`.
pub unsafe trait ByteSlice: Deref<Target = [u8]> + Sized + self::sealed::Sealed {
fn as_ptr(&self) -> *const u8;
fn split_at(self, mid: usize) -> (Self, Self);
}
/// A mutable reference to a byte slice.
///
/// `ByteSliceMut` abstracts over various ways of storing a mutable reference to
/// a byte slice, and is implemented for various special reference types such as
/// `RefMut<[u8]>`.
pub unsafe trait ByteSliceMut: ByteSlice + DerefMut {
fn as_mut_ptr(&mut self) -> *mut u8;
}
unsafe impl<'a> ByteSlice for &'a [u8] {
fn as_ptr(&self) -> *const u8 {
<[u8]>::as_ptr(self)
}
fn split_at(self, mid: usize) -> (Self, Self) {
<[u8]>::split_at(self, mid)
}
}
unsafe impl<'a> ByteSlice for &'a mut [u8] {
fn as_ptr(&self) -> *const u8 {
<[u8]>::as_ptr(self)
}
fn split_at(self, mid: usize) -> (Self, Self) {
<[u8]>::split_at_mut(self, mid)
}
}
unsafe impl<'a> ByteSlice for Ref<'a, [u8]> {
fn as_ptr(&self) -> *const u8 {
<[u8]>::as_ptr(self)
}
fn split_at(self, mid: usize) -> (Self, Self) {
Ref::map_split(self, |slice| <[u8]>::split_at(slice, mid))
}
}
unsafe impl<'a> ByteSlice for RefMut<'a, [u8]> {
fn as_ptr(&self) -> *const u8 {
<[u8]>::as_ptr(self)
}
fn split_at(self, mid: usize) -> (Self, Self) {
RefMut::map_split(self, |slice| <[u8]>::split_at_mut(slice, mid))
}
}
unsafe impl<'a> ByteSliceMut for &'a mut [u8] {
fn as_mut_ptr(&mut self) -> *mut u8 {
<[u8]>::as_mut_ptr(self)
}
}
unsafe impl<'a> ByteSliceMut for RefMut<'a, [u8]> {
fn as_mut_ptr(&mut self) -> *mut u8 {
<[u8]>::as_mut_ptr(self)
}
}
#[cfg(test)]
mod tests {
use core::ops::Deref;
use core::ptr;
use super::LayoutVerified;
// B should be [u8; N]. T will require that the entire structure is aligned
// to the alignment of T.
#[derive(Default)]
struct AlignedBuffer<T, B> {
buf: B,
_t: T,
}
impl<T, B: Default> AlignedBuffer<T, B> {
fn clear_buf(&mut self) {
self.buf = B::default();
}
}
// convert a u64 to bytes using this platform's endianness
fn u64_to_bytes(u: u64) -> [u8; 8] {
unsafe { ptr::read(&u as *const u64 as *const [u8; 8]) }
}
#[test]
fn test_address() {
// test that the Deref and DerefMut implementations return a reference which
// points to the right region of memory
let buf = [0];
let lv = LayoutVerified::<_, u8>::new(&buf[..]).unwrap();
let buf_ptr = buf.as_ptr();
let deref_ptr = lv.deref() as *const u8;
assert_eq!(buf_ptr, deref_ptr);
}
// verify that values written to a LayoutVerified are properly shared
// between the typed and untyped representations
fn test_new_helper<'a>(mut lv: LayoutVerified<&'a mut [u8], u64>) {
// assert that the value starts at 0
assert_eq!(*lv, 0);
// assert that values written to the typed value are reflected in the
// byte slice
const VAL1: u64 = 0xFF00FF00FF00FF00;
*lv = VAL1;
assert_eq!(lv.bytes(), &u64_to_bytes(VAL1));
// assert that values written to the byte slice are reflected in the
// typed value
const VAL2: u64 = !VAL1; // different from VAL1
lv.bytes_mut().copy_from_slice(&u64_to_bytes(VAL2)[..]);
assert_eq!(*lv, VAL2);
}
// verify that values written to a LayoutVerified are properly shared
// between the typed and untyped representations
fn test_new_helper_unaligned<'a>(mut lv: LayoutVerified<&'a mut [u8], [u8; 8]>) {
// assert that the value starts at 0
assert_eq!(*lv, [0; 8]);
// assert that values written to the typed value are reflected in the
// byte slice
const VAL1: [u8; 8] = [0xFF, 0x00, 0xFF, 0x00, 0xFF, 0x00, 0xFF, 0x00];
*lv = VAL1;
assert_eq!(lv.bytes(), &VAL1);
// assert that values written to the byte slice are reflected in the
// typed value
const VAL2: [u8; 8] = [0x00, 0xFF, 0x00, 0xFF, 0x00, 0xFF, 0x00, 0xFF]; // different from VAL1
lv.bytes_mut().copy_from_slice(&VAL2[..]);
assert_eq!(*lv, VAL2);
}
#[test]
fn test_new_aligned_sized() {
// Test that a properly-aligned, properly-sized buffer works for new,
// new_from_preifx, and new_from_suffix, and that new_from_prefix and
// new_from_suffix return empty slices. Test that xxx_zeroed behaves
// the same, and zeroes the memory.
// a buffer with an alignment of 8
let mut buf = AlignedBuffer::<u64, [u8; 8]>::default();
// buf.buf should be aligned to 8, so this should always succeed
test_new_helper(LayoutVerified::<_, u64>::new(&mut buf.buf[..]).unwrap());
buf.buf = [0xFFu8; 8];
test_new_helper(LayoutVerified::<_, u64>::new_zeroed(&mut buf.buf[..]).unwrap());
{
// in a block so that lv and suffix don't live too long
buf.clear_buf();
let (lv, suffix) = LayoutVerified::<_, u64>::new_from_prefix(&mut buf.buf[..]).unwrap();
assert!(suffix.is_empty());
test_new_helper(lv);
}
{
buf.buf = [0xFFu8; 8];
let (lv, suffix) =
LayoutVerified::<_, u64>::new_from_prefix_zeroed(&mut buf.buf[..]).unwrap();
assert!(suffix.is_empty());
test_new_helper(lv);
}
{
buf.clear_buf();
let (prefix, lv) = LayoutVerified::<_, u64>::new_from_suffix(&mut buf.buf[..]).unwrap();
assert!(prefix.is_empty());
test_new_helper(lv);
}
{
buf.buf = [0xFFu8; 8];
let (prefix, lv) =
LayoutVerified::<_, u64>::new_from_suffix_zeroed(&mut buf.buf[..]).unwrap();
assert!(prefix.is_empty());
test_new_helper(lv);
}
}
#[test]
fn test_new_unaligned_sized() {
// Test that an unaligned, properly-sized buffer works for
// new_unaligned, new_unaligned_from_prefix, and
// new_unaligned_from_suffix, and that new_unaligned_from_prefix
// new_unaligned_from_suffix return empty slices. Test that xxx_zeroed
// behaves the same, and zeroes the memory.
let mut buf = [0u8; 8];
test_new_helper_unaligned(
LayoutVerified::<_, [u8; 8]>::new_unaligned(&mut buf[..]).unwrap(),
);
buf = [0xFFu8; 8];
test_new_helper_unaligned(
LayoutVerified::<_, [u8; 8]>::new_unaligned_zeroed(&mut buf[..]).unwrap(),
);
{
// in a block so that lv and suffix don't live too long
buf = [0u8; 8];
let (lv, suffix) =
LayoutVerified::<_, [u8; 8]>::new_unaligned_from_prefix(&mut buf[..]).unwrap();
assert!(suffix.is_empty());
test_new_helper_unaligned(lv);
}
{
buf = [0xFFu8; 8];
let (lv, suffix) = LayoutVerified::<_, [u8; 8]>::new_unaligned_from_prefix_zeroed(
&mut buf[..],
).unwrap();
assert!(suffix.is_empty());
test_new_helper_unaligned(lv);
}
{
buf = [0u8; 8];
let (prefix, lv) =
LayoutVerified::<_, [u8; 8]>::new_unaligned_from_suffix(&mut buf[..]).unwrap();
assert!(prefix.is_empty());
test_new_helper_unaligned(lv);
}
{
buf = [0xFFu8; 8];
let (prefix, lv) = LayoutVerified::<_, [u8; 8]>::new_unaligned_from_suffix_zeroed(
&mut buf[..],
).unwrap();
assert!(prefix.is_empty());
test_new_helper_unaligned(lv);
}
}
#[test]
fn test_new_oversized() {
// Test that a properly-aligned, overly-sized buffer works for
// new_from_prefix and new_from_suffix, and that they return the
// remainder and prefix of the slice respectively. Test that xxx_zeroed
// behaves the same, and zeroes the memory.
let mut buf = AlignedBuffer::<u64, [u8; 16]>::default();
{
// in a block so that lv and suffix don't live too long
// buf.buf should be aligned to 8, so this should always succeed
let (lv, suffix) = LayoutVerified::<_, u64>::new_from_prefix(&mut buf.buf[..]).unwrap();
assert_eq!(suffix.len(), 8);
test_new_helper(lv);
}
{
buf.buf = [0xFFu8; 16];
// buf.buf should be aligned to 8, so this should always succeed
let (lv, suffix) =
LayoutVerified::<_, u64>::new_from_prefix_zeroed(&mut buf.buf[..]).unwrap();
// assert that the suffix wasn't zeroed
assert_eq!(suffix, &[0xFFu8; 8]);
test_new_helper(lv);
}
{
buf.clear_buf();
// buf.buf should be aligned to 8, so this should always succeed
let (prefix, lv) = LayoutVerified::<_, u64>::new_from_suffix(&mut buf.buf[..]).unwrap();
assert_eq!(prefix.len(), 8);
test_new_helper(lv);
}
{
buf.buf = [0xFFu8; 16];
// buf.buf should be aligned to 8, so this should always succeed
let (prefix, lv) =
LayoutVerified::<_, u64>::new_from_suffix_zeroed(&mut buf.buf[..]).unwrap();
// assert that the prefix wasn't zeroed
assert_eq!(prefix, &[0xFFu8; 8]);
test_new_helper(lv);
}
}
#[test]
fn test_new_unaligned_oversized() {
// Test than an unaligned, overly-sized buffer works for
// new_unaligned_from_prefix and new_unaligned_from_suffix, and that
// they return the remainder and prefix of the slice respectively. Test
// that xxx_zeroed behaves the same, and zeroes the memory.
let mut buf = [0u8; 16];
{
// in a block so that lv and suffix don't live too long
let (lv, suffix) =
LayoutVerified::<_, [u8; 8]>::new_unaligned_from_prefix(&mut buf[..]).unwrap();
assert_eq!(suffix.len(), 8);
test_new_helper_unaligned(lv);
}
{
buf = [0xFFu8; 16];
let (lv, suffix) = LayoutVerified::<_, [u8; 8]>::new_unaligned_from_prefix_zeroed(
&mut buf[..],
).unwrap();
// assert that the suffix wasn't zeroed
assert_eq!(suffix, &[0xFF; 8]);
test_new_helper_unaligned(lv);
}
{
buf = [0u8; 16];
let (prefix, lv) =
LayoutVerified::<_, [u8; 8]>::new_unaligned_from_suffix(&mut buf[..]).unwrap();
assert_eq!(prefix.len(), 8);
test_new_helper_unaligned(lv);
}
{
buf = [0xFFu8; 16];
let (prefix, lv) = LayoutVerified::<_, [u8; 8]>::new_unaligned_from_suffix_zeroed(
&mut buf[..],
).unwrap();
// assert that the prefix wasn't zeroed
assert_eq!(prefix, &[0xFF; 8]);
test_new_helper_unaligned(lv);
}
}
#[test]
fn test_new_fail() {
// fail because the buffer is too large
// a buffer with an alignment of 8
let mut buf = AlignedBuffer::<u64, [u8; 16]>::default();
// buf.buf should be aligned to 8, so only the length check should fail
assert!(LayoutVerified::<_, u64>::new(&buf.buf[..]).is_none());
assert!(LayoutVerified::<_, u64>::new_zeroed(&mut buf.buf[..]).is_none());
assert!(LayoutVerified::<_, [u8; 8]>::new_unaligned(&buf.buf[..]).is_none());
assert!(LayoutVerified::<_, [u8; 8]>::new_unaligned_zeroed(&mut buf.buf[..]).is_none());
// fail because the buffer is too small
// a buffer with an alignment of 8
let mut buf = AlignedBuffer::<u64, [u8; 4]>::default();
// buf.buf should be aligned to 8, so only the length check should fail
assert!(LayoutVerified::<_, u64>::new(&buf.buf[..]).is_none());
assert!(LayoutVerified::<_, u64>::new_zeroed(&mut buf.buf[..]).is_none());
assert!(LayoutVerified::<_, [u8; 8]>::new_unaligned(&buf.buf[..]).is_none());
assert!(LayoutVerified::<_, [u8; 8]>::new_unaligned_zeroed(&mut buf.buf[..]).is_none());
assert!(LayoutVerified::<_, u64>::new_from_prefix(&buf.buf[..]).is_none());
assert!(LayoutVerified::<_, u64>::new_from_prefix_zeroed(&mut buf.buf[..]).is_none());
assert!(LayoutVerified::<_, u64>::new_from_suffix(&buf.buf[..]).is_none());
assert!(LayoutVerified::<_, u64>::new_from_suffix_zeroed(&mut buf.buf[..]).is_none());
assert!(LayoutVerified::<_, [u8; 8]>::new_unaligned_from_prefix(&buf.buf[..]).is_none());
assert!(
LayoutVerified::<_, [u8; 8]>::new_unaligned_from_prefix_zeroed(&mut buf.buf[..])
.is_none()
);
assert!(LayoutVerified::<_, [u8; 8]>::new_unaligned_from_suffix(&buf.buf[..]).is_none());
assert!(
LayoutVerified::<_, [u8; 8]>::new_unaligned_from_suffix_zeroed(&mut buf.buf[..])
.is_none()
);
// fail because the alignment is insufficient
// a buffer with an alignment of 8
let mut buf = AlignedBuffer::<u64, [u8; 12]>::default();
// slicing from 4, we get a buffer with size 8 (so the length check
// should succeed) but an alignment of only 4, which is insufficient
assert!(LayoutVerified::<_, u64>::new(&buf.buf[4..]).is_none());
assert!(LayoutVerified::<_, u64>::new_zeroed(&mut buf.buf[4..]).is_none());
assert!(LayoutVerified::<_, u64>::new_from_prefix(&buf.buf[4..]).is_none());
assert!(LayoutVerified::<_, u64>::new_from_prefix_zeroed(&mut buf.buf[4..]).is_none());
// slicing from 4 should be unnecessary because new_from_suffix[_zeroed]
// use the suffix of the slice
assert!(LayoutVerified::<_, u64>::new_from_suffix(&buf.buf[..]).is_none());
assert!(LayoutVerified::<_, u64>::new_from_suffix_zeroed(&mut buf.buf[..]).is_none());
}
#[test]
fn test_display_debug() {
let buf = AlignedBuffer::<u64, [u8; 8]>::default();
let lv = LayoutVerified::<_, u64>::new(&buf.buf[..]).unwrap();
assert_eq!(format!("{}", lv), "0");
assert_eq!(format!("{:?}", lv), "LayoutVerified(0)");
}
}