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Fast, safe, <span style="color:red;">compile error. Pick two.
Zerocopy makes zero-cost memory manipulation effortless. We write unsafe
so you don't have to.
Thanks for using zerocopy 0.8! For an overview of what changes from 0.7, check out our release notes, which include a step-by-step guide for upgrading from 0.7.
Have questions? Need help? Ask the maintainers on GitHub or on Discord!
Zerocopy provides four derivable traits for zero-cost conversions:
TryFromBytes indicates that a type may safely be converted from
certain byte sequences (conditional on runtime checks)FromZeros indicates that a sequence of zero bytes represents a valid
instance of a typeFromBytes indicates that a type may safely be converted from an
arbitrary byte sequenceIntoBytes indicates that a type may safely be converted to a byte
sequenceThese traits support sized types, slices, and slice DSTs.
Zerocopy provides three derivable marker traits that do not provide any functionality themselves, but are required to call certain methods provided by the conversion traits:
KnownLayout indicates that zerocopy can reason about certain layout
qualities of a typeImmutable indicates that a type is free from interior mutability,
except by ownership or an exclusive (&mut) borrowUnaligned indicates that a type's alignment requirement is 1You should generally derive these marker traits whenever possible.
Zerocopy provides six macros for safe casting between types:
try_[try_transmute])transmute (conditionally) converts a value of
one type to a value of another type of the same sizetry_[try_transmute_mut])transmute_mut (conditionally) converts a
mutable reference of one type to a mutable reference of another type of
the same sizetry_[try_transmute_ref])transmute_ref (conditionally) converts a
mutable or immutable reference of one type to an immutable reference of
another type of the same sizeThese macros perform compile-time size and alignment checks, meaning that unconditional casts have zero cost at runtime. Conditional casts do not need to validate size or alignment runtime, but do need to validate contents.
These macros cannot be used in generic contexts. For generic conversions, use the methods defined by the conversion traits.
Zerocopy provides byte-order aware integer types that support these
conversions; see the byteorder module. These types are especially useful
for network parsing.
alloc
By default, zerocopy is no_std. When the alloc feature is enabled,
the alloc crate is added as a dependency, and some allocation-related
functionality is added.
std
By default, zerocopy is no_std. When the std feature is enabled, the
std crate is added as a dependency (ie, no_std is disabled), and
support for some std types is added. std implies alloc.
derive
Provides derives for the core marker traits via the zerocopy-derive
crate. These derives are re-exported from zerocopy, so it is not
necessary to depend on zerocopy-derive directly.
However, you may experience better compile times if you instead directly
depend on both zerocopy and zerocopy-derive in your Cargo.toml,
since doing so will allow Rust to compile these crates in parallel. To do
so, do not enable the derive feature, and list both dependencies in
your Cargo.toml with the same leading non-zero version number; e.g:
[dependencies]
zerocopy = "0.X"
zerocopy-derive = "0.X"To avoid the risk of duplicate import errors if
one of your dependencies enables zerocopy's derive feature, import
derives as use zerocopy_derive::* rather than by name (e.g., use zerocopy_derive::FromBytes).
simd
When the simd feature is enabled, FromZeros, FromBytes, and
IntoBytes impls 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-nightly
Enables the simd feature 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.
float-nightly
Adds support for the unstable f16 and f128 types. These types are
not yet fully implemented and may not be supported on all platforms.
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:
unsafe code 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.For more information, see our full soundness policy.
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.
See our MSRV policy.
Zerocopy uses GitHub Releases.
Disclaimer: This is not an officially supported Google product.