Crate rkyv

rkyv

rkyv (archive) is a zero-copy deserialization framework for Rust.

It’s similar to other zero-copy deserialization frameworks such as Cap’n Proto and FlatBuffers. However, while the former have external schemas and heavily restricted data types, rkyv allows all serialized types to be defined in code and can serialize a wide variety of types that the others cannot. Additionally, rkyv is designed to have little to no overhead, and in most cases will perform exactly the same as native types.

Design

Like serde, rkyv uses Rust’s powerful trait system to serialize data without the need for reflection. Despite having a wide array of features, you also only pay for what you use. If your data checks out, the serialization process can be as simple as a memcpy! Like serde, this allows rkyv to perform at speeds similar to handwritten serializers.

Unlike serde, rkyv produces data that is guaranteed deserialization free. If you wrote your data to disk, you can just mmap your file into memory, cast a pointer, and your data is ready to use. This makes it ideal for high-performance and IO-bound applications.

Limited data mutation is supported through Pin APIs, and archived values can be truly deserialized with Deserialize if full mutation capabilities are needed.

Type support

rkyv has a hashmap implementation that is built for zero-copy deserialization, so you can serialize your hashmaps with abandon. The implementation performs perfect hashing with the compress, hash and displace algorithm to use as little memory as possible while still performing fast lookups.

rkyv also has support for contextual serialization, deserialization, and validation. It can properly serialize and deserialize shared pointers like Rc and Arc, and can be extended to support custom contextual types.

One of the most impactful features made possible by rkyv is the ability to serialize trait objects and use them as trait objects without deserialization. See the archive_dyn crate for more details.

Tradeoffs

rkyv is designed primarily for loading bulk game data as efficiently as possible. While rkyv is a great format for final data, it lacks a full schema system and isn’t well equipped for data migration. Using a serialization library like serde can help fill these gaps, and you can use serde with the same types as rkyv conflict-free.

Features

• const_generics: Improves the trait implementations for arrays with support for all lengths (enabled by default)
• size_64: Archives *size as *64 instead of *32. This is for large archive support
• specialization: Enables support for the unstable specialization feature for increased performance for a few specific cases
• std: Enables standard library support (enabled by default)
• strict: Guarantees that types will have the same representations across platforms and compilations. This is already the case in practice, but this feature provides a guarantee. It additionally provides C type compatibility.
• validation: Enables validation support through bytecheck

Examples

See Archive for examples of how to use rkyv.

Re-exports

pub use util::*;
pub use validation::check_archived_root;
pub use validation::check_archived_value;

Modules

core_impl	Archive implementations for core types.
de	Deserialization traits, deserializers, and adapters.
ser	Serialization traits, serializers, and adapters.
std_impl	Archive implementations for std types.
util	Utilities for common archive operations.
validation	Validation implementations and helper types.

Macros

offset_of	Calculates the offset of the specified field from the start of the named struct.
offset_of_tuple	Calculates the offset of the specified field from the start of the tuple.
project_struct	Maps a mutable MaybeUninit struct reference to a mutable MaybeUninit field reference.
project_tuple	Maps a mutable MaybeUninit tuple reference to a mutable MaybeUninit index reference.

Structs

Infallible	A fallible type that cannot produce errors
RawRelPtr	An untyped pointer which resolves relative to its position in memory.
RelPtr	A pointer which resolves to relative to its position in memory.

Enums

Unreachable

An error that can never be produced

Traits

Archive	A type that can be used without deserializing.
ArchiveCopy	An Archive type that is a bitwise copy of itself and without additional processing.
ArchivePointee	An archived type with associated metadata for its relative pointer.
ArchiveUnsized	A counterpart of Archive that’s suitable for unsized types.
Deserialize	Converts a type back from its archived form.
DeserializeUnsized	A counterpart of Deserialize that’s suitable for unsized types.
Fallible	Contains the error type for traits with methods that can fail
Serialize	Converts a type to its archived form.
SerializeUnsized	A counterpart of Serialize that’s suitable for unsized types.

Type Definitions

Archived	Alias for the archived version of some Archive type.
ArchivedIsize	The type used for offsets in relative pointers.
ArchivedMetadata	Alias for the archived metadata for some ArchiveUnsized type.
ArchivedUsize	The type used for sizes in archived types.
MetadataResolver	Alias for the metadata resolver for some ArchiveUnsized type.
Resolver	Alias for the resolver for some Archive type.

Derive Macros

Archive	Derives Archive for the labeled type.
Deserialize	Derives Deserialize for the labeled type.
Serialize	Derives Serialize for the labeled type.