[−][src]Crate abi_stable

For Rust-to-Rust ffi, with a focus on creating libraries loaded at program startup, and with load-time type-checking.

This library allows defining Rust libraries that can be loaded at runtime, even if they were built with a different Rust version than the crate that depends on it.

These are some usecases for this library:

Converting a Rust dependency tree from compiling statically into a single binary, into one binary (and potentially) many dynamic libraries, allowing separate re-compilation on changes.
Creating a plugin system (without support for unloading).

Features

Currently this library has these features:

Features the #[sabi_trait] attribute,for creating ffi-safe trait objects.
ffi-safe equivalent of some trait objects for any combination of them.
Provides ffi-safe alternatives/wrappers for many standard library types, in the std_types module.
Provides ffi-safe wrappers for some crates, in the external_types module.
Provides the StableAbi trait for asserting that types are ffi-safe.
Features for building extensible modules and vtables, without breaking ABI compatibility.
Supports ffi-safe nonexhaustive enums, wrapped in NonExhaustive<>.
Checking at load-time that the types in the dynamic library have the expected layout, allowing for semver compatible changes while checking the layout of types.
Provides the StableAbi derive macro to both assert that the type is ffi compatible, and to get the layout of the type at load-time to check that it is still compatible.

Examples

For examples of using abi_stable you can look at the readme, or for the crates in the examples directory in the repository for this crate. This crate also has examples for most features on their own.

To run the examples generally you'll have to build the *_impl crate, then run the *_user crate (all *_user crates should have a help message and a readme.md).

Glossary

interface crate:the crate that declares the public functions and types that are necessary to load the library at runtime.

ìmplementation crate:A crate that implements all the functions in the interface crate.

user crate:A crate that depends on an interface crate and loads 1 or more ìmplementation crates for it.

module:refers to a struct of function pointers and other static values. The root module implement the RootModule trait. These are declared in the interface crate,exported in the implementation crate, and loaded in the user crate.

Rust-to-Rust FFI types.

Types must implement StableAbi to be safely passed through the FFI boundary, which can be done using the StableAbi derive macro.

For how to evolve dynamically loaded libraries look here.

These are the kinds of types passed through FFI:

Value kind:
The layout of types passed by value must not change in a minor version. This is the default kind when deriving StableAbi.
Nonexhaustive enums:
Enums wrapped inside NonExhaustive<>, which can add variants in minor versions of the library.
Opaque kind:
Types wrapped in DynTrait<SomePointer<()>,Interface>, whose layout can change in any version of the library, and can only be unwrapped back to the original type in the dynamic library/binary that created it.
Trait objects:
Trait object-like types generated using #[sabi_trait], which erase the type of the value they wrap,implements the methods of the trait, and can be unwrapped back to the original type in the dynamic library/binary that created it (if it was constructed to be unerasable and implements Any).
Prefix kind:
Types only accessible through shared references, most commonly vtables and modules, which can be extended in minor versions while staying ABI compatible. by adding fields at the end.

Extra documentation

Unsafe code guidelines:
Describes how to write unsafe code ,relating to this library.
Troubleshooting:
Some problems and their solutions.

Macros (derive and attribute)

sabi_trait attribute macro:
For generating ffi-safe trait objects.
StableAbi derive macro:
For asserting abi-stability of a type, and obtaining the layout of the type at runtime.
Nonexhaustive enums:
Details for how to declare nonexhaustive enums.
Prefix-types (using the StableAbi derive macro) :
The method by which vtables and modules are implemented, allowing extending them in minor versions of a library.

Modules

abi_stability	types and traits related to abi stability.
const_utils	Utilities for const contexts.
docs	Documentation for macros,and guides.
erased_types	Types and traits related to type erasure.
external_types	Ffi wrapper for types defined outside the standard library.
inline_storage	Contains the `InlineStorage` trait,and related items.
library	Traits and types related to loading an abi_stable dynamic library, as well as functions/modules within.
marker_type	Zero-sized types .
nonexhaustive_enum	Contains types and traits for nonexhaustive enums.
pointer_trait	Traits for pointers.
prefix_type	Types,traits,and functions used by prefix-types.
reexports	Miscelaneous items re-exported from core_extensions.
reflection	Types and submodules for doing runtime reflection.
sabi_trait	Contains items related to the `#[sabi_trait]` attribute.
sabi_types	ffi-safe types that aren't wrappers for other types.
std_types	Contains many ffi-safe equivalents of standard library types. The vast majority of them can be converted to and from std equivalents.
traits	Where miscellaneous traits reside.
type_layout	Types for modeling the layout of a datatype
type_level	Types used to represent values at compile-time,eg:True/False.
utils	Utility functions.

Macros

RTuple	Use this macro to get the type of a `Tuple*` with the types passed to the macro.
declare_root_module_statics	Implements the `RootModule::root_module_statics` associated function.
extern_fn_panic_handling	Use this to make sure that you handle panics inside `extern fn` correctly.
impl_get_type_info	Constructs the abi_stable::erased_types::TypeInfo for some type.
make_item_info	Constructs a abi_stable::type_layout::ItemInfo, with information about the place where it's called.
nul_str	Constructs a NulStr from a string literal.
package_version_strings	Instantiates a `abi_stable::version::VersionStrings` with the major.minor.patch version of the library where it is invoked.
rslice	A macro to construct `RSlice<'_,T>` constants.
rstr	A macro to construct `RStr<'static>` constants.
rtry	Equivalent to `?` for `RResult<_,_>`.
rtry_opt	Equivalent to `?` for `ROption<_>`.
rtuple	Use this macro to construct a `Tuple*` with the values passed to the macro.
rvec	Constructs an `RVec<_>` using the same syntax that the `std::vec` macro uses.
tag	Constructs a abi_stable::abi_stability::Tag, a dynamically typed value for users to check extra properties about their types when doing runtime type checking.
tl_genparams	Use this when constructing a `abi_stable::type_layout::MonoTypeLayout` when manually implementing StableAbi.
type_identity	Allows converting between `Copy` generic types that are the same concrete type (using AssertEq to prove that they are).

ImplType	An `implementation type`, with an associated `interface type` which describes the traits that must be implemented when constructing a `DynTrait` from Self, using the `from_value` and `from_ptr` constructors, so as to pass an opaque type across ffi.
InterfaceType	Defines the usable/required traits when creating a `DynTrait<Pointer<()>,ThisInterfaceType>` from a type that implements `ImplType<Interface= ThisInterfaceType >` .
StableAbi	Represents a type whose layout is stable.

Attribute Macros

export_root_module	This attribute is used for functions which export a module in an `implementation crate`.
sabi_extern_fn	This macro is documented in abi_stable::docs::sabi_extern_fn
sabi_trait	This macro is documented in `abi_stable::docs::sabi_trait_attribute` .

Derive Macros

GetStaticEquivalent	This macro is documented in `abi_stable::docs::get_static_equivalent`
StableAbi	This macro is documented in abi_stable::docs::stable_abi_derive