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Rust ABI safe code generator
https://github.com/h33p/cglue

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Rust ABI safe code generator

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README 

        

# CGlue



[![Crates.io]][crates] [![API Docs]][docs] [![Build and test]][workflows] [![MIT licensed]][license] [![Rustc 1.45]][rust]



[Crates.io]: https://img.shields.io/crates/v/cglue.svg

[crates]: https://crates.io/crates/cglue

[API Docs]: https://docs.rs/cglue/badge.svg

[docs]: https://docs.rs/cglue

[Build and test]: https://github.com/h33p/cglue/actions/workflows/build.yml/badge.svg

[workflows]: https://github.com/h33p/cglue/actions/workflows/build.yml

[MIT licensed]: https://img.shields.io/badge/license-MIT-blue.svg

[license]: https://github.com/h33p/cglue/blob/main/LICENSE

[Rustc 1.45]: https://img.shields.io/badge/rustc-1.45+-lightgray.svg

[rust]: https://blog.rust-lang.org/2020/07/16/Rust-1.45.0.html



If all code is glued together, our glue is the safest on the market.



## The most complete dynamic trait object implementation, period.



- [Overview](#overview)

- [In-depth look](#in-depth-look)

  - [Safety assumptions](#safety-assumptions)

  - [Name generation](#name-generation)

  - [Generics in groups](#generics-in-groups)

    - [Manully implementing groups](#manually-implementing-groups)

  - [External traits](#external-traits)

  - [Type wrapping](#type-wrapping)

  - [Associated type wrapping](#associated-type-wrapping)

  - [Generic associated types](#generic-associated-types)

  - [Plugin system](#plugin-system)

  - [Working with cbindgen](#working-with-cbindgen)

    - [Setup](#setup)

    - [cglue-bindgen](#cglue-bindgen)

- [Limitations](#limitations)

  - [Unstable feature](#unstable-feature)

- [Projects using CGlue](#projects-using-cglue)

- [Changelog](#changelog)



## Overview



CGlue exposes `dyn Trait` in FFI-safe manner. It bridges Rust traits between C and other

languages. It aims to be seamless to integrate - just add a few annotations around your traits,

and they should be good to go!



```rust

use cglue::*;



// One annotation for the trait.

#[cglue_trait]

pub trait InfoPrinter {

    type Mark;

    fn print_info(&self, mark: Self::Mark);

}



struct Info {

    value: usize

}



impl InfoPrinter for Info {

    type Mark = u8;



    fn print_info(&self, mark: Self::Mark) {

        println!("{} - info struct: {}", mark, self.value);

    }

}



fn use_info_printer(printer: &T, mark: T::Mark) {

    println!("Printing info:");

    printer.print_info(mark);

}



fn main() -> () {

    let mut info = Info {

        value: 5

    };



    // Here, the object is fully opaque, and is FFI and ABI safe.

    let obj = trait_obj!(&mut info as InfoPrinter);



    use_info_printer(&obj, 42);

}

```



Rust does not guarantee your code will work with

neither [2 different compiler versions clashing](https://pastebin.com/raw/un1TbJCe), nor [any other minor changes](https://github.com/rust-lang/compiler-team/issues/457),

CGlue glues it all together in a way that works.



This is done by generating wrapper vtables (virtual function tables) for the specified trait, and creating an opaque object with matching table.



`cglue_trait` annotation generates a `InfoPrinterVtbl` structure, and all the code needed to construct it for a type implementing the `InfoPrinter` trait. Then, a `CGlueTraitObj` is constructed that wraps the input object and implements the `InfoPrinter` trait.



But that's not all, you can also group traits together!



```rust

use cglue::*;



// Extra trait definitions



#[cglue_trait]

pub trait InfoChanger {

    fn change_info(&mut self, new_val: usize);

}



impl InfoChanger for Info {

    fn change_info(&mut self, new_val: usize) {

        self.value = new_val;

    }

}



#[cglue_trait]

pub trait InfoDeleter {

    fn delete_info(&mut self);

}



// Define a trait group.

//

// Here, `InfoPrinter` is mandatory - always required to be implemented,

// whereas `InfoChanger` with `InfoDeleter` are optional traits - a checked

// cast must be performed to access them.

cglue_trait_group!(InfoGroup, InfoPrinter, { InfoChanger, InfoDeleter });



// Implement the group for `Info` structure, defining

// only that `InfoChanger` is optionally implemented.

// This is not required if `unstable` feature is being used!

cglue_impl_group!(Info, InfoGroup, InfoChanger);



let mut info = Info { value: 5 };



let mut obj = group_obj!(info as InfoGroup);



// Object does not implement `InfoDeleter`

assert!(as_ref!(&obj impl InfoDeleter).is_none());



change_info(&mut cast!(obj impl InfoChanger).unwrap(), 20);



fn change_info(change: &mut (impl InfoPrinter + InfoChanger), new_val: usize) {

    println!("Old info:");

    change.print_info();

    change.change_info(new_val);

    println!("New info:");

    change.print_info();

}

```



And there is much more! Here are some highlights:



1. Ability to use self-consuming trait functions.



2. Some standard library traits are exposed (`Clone`).



3. Ability to wrap associated trait types into new CGlue trait objects and groups.



4. The above ability also works with mutable, and const reference associated type returns[*](#associated-type-wrapping).



5. Generic traits and their groups.



6. [Library reference counting](#plugin-system).



7. Optional runtime ABI/API validation with [abi\_stable](https://crates.io/crates/abi_stable) (enable `layout_checks` feature).



## In-depth look



### Safety assumptions



This crate relies on the assumption that opaque objects will not be tampered with, that is

vtable functions will not be modified. It is being ensured through encapsulation of fields

from anywhere by using hidden submodules. However, unverifiable users (C libraries) may still

be able to modify the tables. This library assumes they are not malicious and does not

perform any runtime verification. API version mismatch checking with

[abi\_stable](https://crates.io/crates/abi_stable) is an opt-in feature (requires rustc 1.46+).



Other than 2 bits in [associated type wrapping](#associated-type-wrapping), this crate should

be safe.



The crate employs a number of `unsafe` traits that get auto-implemented, or traits with unsafe

functions. Their usage inside the code generator should be safe, they are marked in such a way

so that manual implementations can not introduce undefined behaviour.



### Name generation



`#[cglue_trait]` macro for `MyTrait` will generate the following important types:



| Name | Purpose | Instance type | [Context](#plugin-system) |

--- | --- | --- | ----

| `MyTraitBox` | Regular owned CGlue object. | [`CBox`](crate::boxed::CBox) | [`NoContext`](crate::trait_group::NoContext) |

| `MyTraitCtxBox` | Owned CGlue object with a [context](#plugin-system). | [`CBox`](crate::boxed::CBox) | `Ctx` |

| `MyTraitArcBox` | Owned CGlue object with a reference counted context. | [`CBox`](crate::boxed::CBox) | [`CArc`](crate::arc::CArc) |

| `MyTraitMut` | By-mut-ref CGlue object. | `&mut c_void`. | [`NoContext`](crate::trait_group::NoContext) |

| `MyTraitCtxMut` | By-mut-ref CGlue object with a context. | `&mut c_void`. | `Ctx` |

| `MyTraitArcMut` | By-mut-ref CGlue object with a reference counted context. | `&mut c_void`. | [`CArc`](crate::arc::CArc) |

| `MyTraitRef` | By-ref (const) CGlue object. | `&c_void`. | [`NoContext`](crate::trait_group::NoContext) |

| `MyTraitCtxRef` | By-ref (const) CGlue object with a context. | `&c_void`. | `Ctx` |

| `MyTraitArcRef` | By-ref (const) CGlue object with a reference counted context. | `&c_void`. | [`CArc`](crate::arc::CArc) |



Only opaque types provide functionality. Non-opaque types can be used as `Into` trait bounds

and are required to type check trait bounds.



These are the generic types needed for bounds checking:



| Name | Purpose | Instance type | Context |

--- | --- | --- | ---

| `MyTraitBaseBox` | Base owned CGlue object. | [`CBox`](crate::boxed::CBox) | [`NoContext`](crate::trait_group::NoContext) |

| `MyTraitBaseCtxBox` | Base owned CGlue object with [some context](#plugin-system). | [`CBox`](crate::boxed::CBox) | `Ctx` |

| `MyTraitBaseArcBox` | Base owned CGlue object with reference counted context. | [`CBox`](crate::boxed::CBox) | [`CArc`](crate::arc::CArc) |

| `MyTraitBaseMut` | Base by-mut-ref CGlue object. | `&mut T`. | [`NoContext`](crate::trait_group::NoContext) |

| `MyTraitBaseRef` | Typedef for generic by-ref (const) CGlue object. | `&T`. | [`NoContext`](crate::trait_group::NoContext) |

| `MyTraitBase` | Base (non-opaque) CGlue object. It can have any compatible instance and context | `Inst` | `Ctx` |



Finally, the following underlying types exist, but do not need to be interacted with in Rust:



| Name | Purpose |

--- | ---

| `MyTraitVtbl` | Table of all functions of the trait. Should be opaque to the user. |

| `MyTraitRetTmp` | Structure for temporary return values. It should be opaque to the user. |



Instead, every opaque CGlue object implements `MyTraitOpaqueObj` trait, which contains the type

of the vtable.



`cglue_trait_group!` macro for `MyGroup` will generate the following main types:



| Name | Purpose | Instance type | Context |

--- | --- | --- | ---

| `MyGroupBox` | Owned CGlue trait group. | [`CBox`](crate::boxed::CBox) | [`NoContext`](crate::trait_group::NoContext) |

| `MyGroupCtxBox` | Owned CGlue trait group with [some context](#plugin-system). | [`CBox`](crate::boxed::CBox) | `Ctx` |

| `MyGroupArcBox` | Typedef for opaque owned CGlue trait group with reference counted context. | [`CBox`](crate::boxed::CBox) | [`CArc`](crate::arc::CArc) |

| `MyGroupMut` | Typedef for opaque by-mut-ref CGlue trait group. | `&mut c_void`. | [`NoContext`](crate::trait_group::NoContext) |

| `MyGroupCtxMut` | Typedef for opaque by-mut-ref CGlue trait group with a custom context. | `&mut c_void`. | `Ctx` |

| `MyGroupArcMut` | Typedef for opaque by-mut-ref CGlue trait group with a reference counted context. | `&mut c_void`. | [`CArc`](crate::arc::CArc) |

| `MyGroupRef` | Typedef for opaque by-ref (const) CGlue trait group. | `&c_void`. | [`NoContext`](crate::trait_group::NoContext) |

| `MyGroupCtxRef` | Typedef for opaque by-ref (const) CGlue trait group with a custom context. | `&c_void`. | `Ctx` |

| `MyGroupArcRef` | Typedef for opaque by-ref (const) CGlue trait group with a reference counted context. | `&c_void`. | [`CArc`](crate::arc::CArc) |



Base types are as follows:



| Name | Purpose | Instance type | Context |

--- | --- | --- | ---

| `MyGroupBaseBox` | Base owned CGlue trait group. Its container is a [`CBox`](crate::boxed::CBox) |

| `MyGroupBaseCtxBox` | Base owned CGlue trait group with [some context](#plugin-system). | [`CBox`](crate::boxed::CBox) | `Ctx` |

| `MyGroupBaseArcBox` | Base owned CGlue trait group with reference counted context. | [`CBox`](crate::boxed::CBox) | [`CArc`](crate::arc::CArc) |

| `MyGroupBaseMut` | Base by-mut-ref CGlue trait group. | `&mut T`. | [`NoContext`](crate::trait_group::NoContext) |

| `MyGroupBaseCtxMut` | Base by-mut-ref CGlue trait group with a context. | `&mut T`. | `Ctx` |

| `MyGroupBaseArcMut` | Base by-mut-ref CGlue trait group with a reference counted context. | `&mut T`. | [`CArc`](crate::arc::CArc) |

| `MyGroupBaseRef` | Base by-ref (const) CGlue trait group. | `&T`. | [`NoContext`](crate::trait_group::NoContext) |

| `MyGroupBaseCtxRef` | Base by-ref (const) CGlue trait group with a context. | `&T`. | `Ctx` |

| `MyGroupBaseArcRef` | Base by-ref (const) CGlue trait group with a reference counted context. | `&T`. | [`CArc`](crate::arc::CArc) |

| `MyGroup` | Base definiton of the group. It needs to be manually made opaque. | `Inst` | `Ctx` |



Container type (opaque to Rust users) that is placed within the group:



| Name | Purpose |

--- | ---

| `MyGroupContainer` | Stores temporary return storage. Vtables are built for this type.



And finally, the filler trait that is required for an object to be grouppable:



| Name | Purpose |

--- | ---

| `MyGroupVtableFiller` | Trait that allows an object to specify which optional traits are available, through the use of `enable_trait` functions. |



The macro generation will also generate structures for all combinations of optional traits

being used. For more convenient by-macro usage, the names of optional traits inside are sorted

in alphabetical order. If not using macros, check `MyGroup` documentation for underlying

conversion function definitions.



### Generics in groups



Groups are fairly flexible - they are not limited to basic types. They can also contain generic

parameters, associated types, and self returns (this also applies to single-trait objects).



Use of generics in trait groups is rather straightforward, with a couple of tiny nuances.



Define a group with the standard template syntax:



```rust

cglue_trait_group!(GenGroup, Getter, { TA });

```



It is also possible to specify trait bounds:



```rust

cglue_trait_group!(GenGroup, Getter, { TA });

```



Or:



```rust

cglue_trait_group!(GenGroup where T: Eq {}, Getter, { TA });

```



Implement the group on a generic type:



```rust

cglue_impl_group!(GA, GenGroup, { TA });

```



Note that in the above case, `GA` will be grouppable, if, and only if it implements both,

`Getter` and `TA` for `T: Eq`. If `GA` implements different sets of optional traits with

different type parameters, then provide multiple implementations, with specified types. On each

implementation, still add a generic type `T`, but specify its type with an equality somewhere

on the line:



```rust

cglue_impl_group!(GA, GenGroup, {});

cglue_impl_group!(GA, GenGroup, { TA });

```



Here, `GA` implements only `Getter`, while `GA` implements both

`Getter` and `TA`.



Finally, you can also mix the 2, assuming the most general implementation has the most

optional traits defined:



```rust

cglue_impl_group!(GA, GenGroup, { TA });

cglue_impl_group!(GA, GenGroup, {});

```



#### Manually implementing groups



NOTE: This is not supported if [`unstable`](#unstable-feature) feature is enabled. Instead, you

have to do nothing!



It is also possible to manually implement the groups by implementing `MyGroupVtableFiller`. Here is what

the above 2 macro invocations expand to:



```rust

impl<

        'cglue_a,

        CGlueInst: ::core::ops::Deref>,

        CGlueCtx: cglue::trait_group::ContextBounds,

        T: Eq,

    > GenGroupVtableFiller<'cglue_a, CGlueInst, CGlueCtx, T> for GA

where

    Self: TA,

    &'cglue_a TAVtbl<'cglue_a, GenGroupContainer,

    >:

        'cglue_a + Default,

    T: cglue::trait_group::GenericTypeBounds,

{

    fn fill_table(

        table: GenGroupVtables<'cglue_a, CGlueInst, CGlueCtx, T>,

    ) -> GenGroupVtables<'cglue_a, CGlueInst, CGlueCtx, T> {

        table.enable_ta()

    }

}

impl<

        'cglue_a,

        CGlueInst: ::core::ops::Deref>,

        CGlueCtx: cglue::trait_group::ContextBounds,

    > GenGroupVtableFiller<'cglue_a, CGlueInst, CGlueCtx, u64> for GA

{

    fn fill_table(

        table: GenGroupVtables<'cglue_a, CGlueInst, CGlueCtx, u64>,

    ) -> GenGroupVtables<'cglue_a, CGlueInst, CGlueCtx, u64> {

        table

    }

}

```



### External traits



Certain traits may not be available for `#[cglue_trait]` annotation. Thus, there are mechanisms

in place to allow constructing CGlue objects of external traits. The core primitive is

`#[cglue_trait_ext]`. Essentially the user needs to provide a sufficient definition for the

actual trait, like so:



```rust

#[cglue_trait_ext]

pub trait Clone {

    fn clone(&self) -> Self;

}

```



Notice how this trait does not have the `clone_from` function. Having a separate `&Self`

parameter is not supported, but the trait can still be implemented, because `clone_from` is

merely an optional optimization and there already is a blanket implementation for it.



Usage of external traits is the same when constructing single-trait objects. It gets more

complicated when groups are involved. This is how a `MaybeClone` group would be implemented:



```rust

cglue_trait_group!(MaybeClone, { }, { ext::Clone }, {

    pub trait Clone {

        fn clone(&self) -> Self;

    }

});

```



The first change is to use `ext::Clone`. This marks cglue to create external trait glue code.

The second bit is the trait definition. Yes, unfortunately the group needs another definition

of the trait. CGlue does not have the context of the crate, and it needs to know the function

signatures.



This is far from ideal, thus there is an additional mechanism in place - built-in external

traits. It is a store of trait definitions that can be used without providing multiple trait

definitions. With `Clone` being both inside the store, and marked as prelude export, the above

code gets simplified to just this:



```rust

cglue_trait_group!(MaybeClone, { }, { Clone });

```



For traits not in the prelude, they can be accessed through their fully qualified `::ext` path:



```rust

cglue_trait_group!(MaybeAsRef, { }, { ::ext::core::convert::AsRef });

```



Note that `use` imports do not work - a fully qualified path is required.



The trait store is the least complete part of this system. If you encounter missing traits and

wish to use them, please file a pull request with their definitions, and I will be glad to

include them.



### Type wrapping



As for details, commonly used Rust structures are automatically wrapped in a way that works

effectively.



For instance, slices and `str` types get converted to C-compatible slices.



```rust

fn with_slice(&self, slice: &[usize]) {}



// Generated vtable entry:



with_slice: extern "C" fn(&CGlueC, slice: CSlice),

```



`Option` types that can not have [nullable pointer optimization](https://doc.rust-lang.org/nomicon/ffi.html#the-nullable-pointer-optimization) are wrapped into [COption](crate::option::COption):



```rust

fn non_npo_option(&self, opt: Option) {}



// Generated vtable entry:



non_npo_option: extern "C" fn(&CGlueC, opt: Option),

```



`Result` is automatically wrapped into [CResult](crate::result::CResult):



```rust

fn with_cresult(&self) -> Result {}



// Generated vtable entry:



with_cresult: extern "C" fn(&CGlueC) -> CResult,

```



`Result` with [IntError](crate::result::IntError) type can return an integer code with `Ok` value written to a variable:



```rust

#[int_result]

fn with_int_result(&self) -> Result {}



// Generated vtable entry:



with_int_result: extern "C" fn(&CGlueC, ok_out: &mut MaybeUninit) -> i32,

```



All wrapping and conversion is handled transparently behind the scenes, with user's control.



### Associated type wrapping



Associated types can be wrapped into custom CGlue objects. Below is a minimal example of

this in action:



```rust

use cglue::*;

#[cglue_trait]

pub trait ObjReturn {

    #[wrap_with_obj(InfoPrinter)]

    type ReturnType: InfoPrinter + 'static;



    fn or_1(&self) -> Self::ReturnType;

}



struct InfoBuilder {}



impl ObjReturn for InfoBuilder {

    type ReturnType = Info;



    fn or_1(&self) -> Self::ReturnType {

        Info {

            value: 80

        }

    }

}



let builder = InfoBuilder {};



let obj = trait_obj!(builder as ObjReturn);



let info_printer = obj.or_1();



info_printer.print_info();

```



This also works if the trait were to return a `&Self::ReturnType`, or `&mut Self::ReturnType`.

It is done by storing wrapped return value in an intermediate storage, and then returning

references to there.



However, there is a `SAFETY WARNING`:



Wrapping `&Self::ReturnType` in a function that takes a non-mutable `&self` technically breaks

Rust's safety rules by potentially overwriting data that is already being borrowed as const.

However, in real world a function that takes `&self` and returns `&T` will usually return the

same reference, and it should be alright, but YOU HAVE BEEN WARNED. `TODO: Disallow this?`



The above warning does not apply to `&mut self` functions, because the returned reference is

bound to the same lifetime and can not be re-created while being borrowed.



In addition, there is quite a bit of type safety being broken when when wrapping associated

types in anonymous lifetime references. It should be okay, but the situation is as follows:



1. Due to no GAT, `CGlueObjRef/Mut<'_>` is being promoted to `CGlueObjRef/Mut<'static>`. This

   should be okay, given it is not possible to clone non-CBox objects, and these objects are

   returned by-reference, not value (see GATs section for how to avoid this).



2. Trait bounds are only checked for one lifetime (lifetime of the vtable), and the C function

   is being cast into a HRTB one unsafely. This is because it is not possible to specify the

   HRTB upper bound (`for<'b: 'a>`). It should be okay, since the vtable can be created for the

   vtable's lifetime, the returned reference will not outlive the vtable, and the C function is

   fully type checked otherwise.



However, if there is a glaring issue I am missing, and there is a solution to this unsafety,

please file an issue report.



Generally speaking, you will want to use `wrap_with_obj/wrap_with_group` in `Self::ReturnType`

functions, `wrap_with_obj_mut/wrap_with_group_mut` in `&mut Self::ReturnType` functions, and

`wrap_with_obj_ref/wrap_with_group_ref` in `&Self::ReturnType` functions. It is important to

note that if there is a trait that returns a combination of these types, it is not possible to

use wrapping, because the underlying object types differ. If possible, split up the type to

multiple associated types.



### Generic associated types



CGlue has limited support for GATs! More specifically, single lifetime GATs are supported,

which allows one to implement a form of `LendingIterator`:



```rust

use cglue::*;

#[cglue_trait]

pub trait LendingPrinter {

    #[wrap_with_obj(InfoPrinter)]

    type Printer<'a>: InfoPrinter + 'a where Self: 'a;



    fn borrow_printer<'a>(&'a mut self) -> Self::Printer<'a>;

}



impl<'a> InfoPrinter for &'a mut Info {

    fn print_info(&self) {

        (**self).print_info();

    }

}



struct InfoStore {

    info: Info,

}



impl LendingPrinter for InfoStore {

    type Printer<'a> = &'a mut Info;



    fn borrow_printer(&mut self) -> Self::Printer<'_> {

        &mut self.info

    }

}



let builder = InfoStore { info: Info { value: 50 } };



let mut obj = trait_obj!(builder as LendingPrinter);



let info_printer = obj.borrow_printer();



info_printer.print_info();

```



### Plugin system



A full example is available in the repo's `examples` subdirectory.



CGlue currently does not provide an out-of-the box plugin system, but there are primitives in

place for relatively safe trait usage using dynamically loaded libraries. The core primitive is

a cloneable context, such as a libloading::Library` Arc, which will keep the library opened

until all of the CGlue objects are dropped.



```rust

use cglue::prelude::v1::*;



#[cglue_trait]

pub trait PluginRoot {

    // ...

}



impl PluginRoot for () {}



let root = ();

// This could be a `libloading::Library` arc.

let ref_to_count = CArc::from(());

// Merely passing a tuple is enough.

let obj = trait_obj!((root, ref_to_count) as PluginRoot);

// ...

```



Reference counting the Arc allows to safeguard the dynamically loaded library from being

unloaded prematurely.



If `PluginRoot` were to branch out and build new objects that can be dropped after the instance

of `PluginRoot`, for instance an `InfoPrinter` object, the Arc gets moved/cloned into the new

object.



```rust

#[cglue_trait]

pub trait PluginRoot {

    #[wrap_with_obj(InfoPrinter)]

    type PrinterType: InfoPrinter;



    fn get_printer(&self) -> Self::PrinterType;

}



impl PluginRoot for () {

    type PrinterType = Info;



    fn get_printer(&self) -> Self::PrinterType {

        Info { value: 42 }

    }

}



let root = ();

// This could be a `libloading::Library` arc.

let ref_to_count = CArc::from(());

let obj = trait_obj!((root, ref_to_count) as PluginRoot);

let printer = obj.get_printer();

// It is safe to drop obj now:

std::mem::drop(obj);

printer.print_info();

```



Note that this is not foolproof, and there may be situations where returned data could depend

on the library. The most error prone of which are unhandled `Err(E)` conditions, where `E` is

some static str. `main` function could return an error pointing to the memory of the library,

unload it, and then attempt to print it out, resulting in a segfault. If possible, try to use

`IntError` types, and mark the trait with `#[int_result]`, which would prevent this particular

issue from happening.



### Working with cbindgen



[cbindgen](https://github.com/eqrion/cbindgen) can be used to generate C and C++ bindings.

There is some important setup needed.



In addition, [`cglue-bindgen`](https://crates.io/crates/cglue-bindgen) provides additional

helper method generation, making working with CGlue from C/C++ much more convenient.



#### Setup



Firstly, create a `cbindgen.toml`, and make sure both cglue, and any crates using cglue are

included and have macro expansion enabled:



```toml

[parse]

parse_deps = true

include = ["cglue", "your-crate"]



[parse.expand]

crates = ["cglue", "your-crate"]

```



Macro expansion currently requires nightly Rust. Thus, it is then possible to generate bindings

like so:



```sh

rustup run nightly cbindgen --config cbindgen.toml --crate your_crate --output output_header.h

```



You can set C or C++ language mode by appending `-l c` or `-l c++` flag. Alternatively, set it

in the toml:



```toml

language = "C"

```



Export any shortened typedefs that are not used by any of the extern C functions:



```toml

[export]

include = ["FeaturesGroupArcBox", "PluginInnerRef", "PluginInnerMut"]

```



#### cglue-bindgen



[`cglue-bindgen`](https://crates.io/crates/cglue-bindgen) is a cbindgen wrapper that attempts

to automatically clean up the headers. It also adds an ability to automatically invoke nightly

rust with `+nightly` flag, and also generates vtable wrappers for simpler usage. The change is

simple - just move all cbindgen arguments after `--`:



```sh

cglue-bindgen +nightly -- --config cbindgen.toml --crate your_crate --output output_header.h

```



This wrapper is probably the most fragile part of CGlue - if something does not work, please

open up an issue report. In the future, we will aim to integrate CGlue directly with cbindgen.



## Limitations



1. Associated type function arguments are not possible, because opaque conversion works

   one-way.



2. Functions that accept an additional `Self` types are not possible for the same reason.



3. Custom generic arguments for cglue traits are not yet supported, but this is to be improved

   upon.



4. There probably are some corner cases when it comes to path imports. If you find any, please

   file an issue report :)



### Unstable feature



`cglue_impl_group` may force you into making conservative optional trait choices, because it is

currently not possible to specialize these cases with stable Rust features. But this is not

always desirable. You can solve this, by enabling `unstable` feature.



This feature makes `cglue_impl_group` a no-op, and automatically enables the widest set of

traits for the given object.



To use it you need to either:



- `nightly` Rust compiler.



- Set `RUSTC_BOOTSTRAP=try_default` environment variable when building.



Do note, however, that **Rust's stability guarantees get invalidated** by either of these 2

options.



## Projects using CGlue



* [memflow](https://github.com/memflow/memflow)



If you want your project to be added to the list, please open an issue report :)



## Changelog



It is available in [CHANGELOG.md](https://github.com/h33p/cglue/blob/main/CHANGELOG.md) file.