zerocopy
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Fast, safe, compile error. Pick two.
Zerocopy makes zero-cost memory manipulation effortless. We write unsafe
so you don't have to.
Overview
Zerocopy provides four core marker traits, each of which can be derived
(e.g., #[derive(FromZeros)]):
-
FromZerosindicates that a sequence of zero bytes represents a valid instance of a type -
FromBytesindicates that a type may safely be converted from an arbitrary byte sequence -
IntoBytesindicates that a type may safely be converted to a byte sequence -
Unalignedindicates 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.
Zerocopy also provides byte-order aware integer types that support these
conversions; see the byteorder module. These types are especially useful
for network parsing.
Cargo Features
-
allocBy default,zerocopyisno_std. When theallocfeature is enabled, thealloccrate is added as a dependency, and some allocation-related functionality is added. -
deriveProvides derives for the core marker traits via thezerocopy-derivecrate. These derives are re-exported fromzerocopy, so it is not necessary to depend onzerocopy-derivedirectly.However, you may experience better compile times if you instead directly depend on both
zerocopyandzerocopy-derivein yourCargo.toml, since doing so will allow Rust to compile these crates in parallel. To do so, do not enable thederivefeature, and list both dependencies in yourCargo.tomlwith the same leading non-zero version number; e.g:[dependencies] zerocopy = "0.X" zerocopy-derive = "0.X"
-
simdWhen thesimdfeature is enabled,FromZeros,FromBytes, andIntoBytesimpls are emitted for all stable SIMD types which exist on the target platform. Note that the layout of SIMD types is not yet stabilized, so these impls may be removed in the future if layout changes make them invalid. For more information, see the Unsafe Code Guidelines Reference page on the layout of packed SIMD vectors. -
simd-nightlyEnables thesimdfeature and adds support for SIMD types which are only available on nightly. Since these types are unstable, support for any type may be removed at any point in the future.
Security Ethos
Zerocopy is expressly designed for use in security-critical contexts. We strive to ensure that that zerocopy code is sound under Rust's current memory model, and any future memory model. We ensure this by:
-
...not 'guessing' about Rust's semantics.
We annotate
unsafecode with a precise rationale for its soundness that cites a relevant section of Rust's official documentation. When Rust's documented semantics are unclear, we work with the Rust Operational Semantics Team to clarify Rust's documentation. - ...rigorously testing our implementation. We run tests using Miri, ensuring that zerocopy is sound across a wide array of supported target platforms of varying endianness and pointer width, and across both current and experimental memory models of Rust.
- ...formally proving the correctness of our implementation. We apply formal verification tools like Kani to prove zerocopy's correctness.
For more information, see our full soundness policy.
Relationship to Project Safe Transmute
Project Safe Transmute is an official initiative of the Rust Project to develop language-level support for safer transmutation. The Project consults with crates like zerocopy to identify aspects of safer transmutation that would benefit from compiler support, and has developed an experimental, compiler-supported analysis which determines whether, for a given type, any value of that type may be soundly transmuted into another type. Once this functionality is sufficiently mature, zerocopy intends to replace its internal transmutability analysis (implemented by our custom derives) with the compiler-supported one. This change will likely be an implementation detail that is invisible to zerocopy's users.
Project Safe Transmute will not replace the need for most of zerocopy's
higher-level abstractions. The experimental compiler analysis is a tool for
checking the soundness of unsafe code, not a tool to avoid writing
unsafe code altogether. For the foreseeable future, crates like zerocopy
will still be required in order to provide higher-level abstractions on top
of the building block provided by Project Safe Transmute.
MSRV
See our MSRV policy.
Changelog
Zerocopy uses GitHub Releases.
Disclaimer
Disclaimer: Zerocopy is not an officially supported Google product.