Nucom

Nucom provides a cross-platform implementation of the Component Object Model (COM) architecture found on the Windows platform, for C, C++, and Rust.

The project contains C/C++ code, but the Rust crates do not need a C compiler to work. Compiling the C/C++ library however does need a Rust compiler, since the IDL compiler, nuidl, is written in Rust.

Example code: Here's test code to ensure calling methods on COM classes written in C/C++/Rust from those three languages works.

How to use

From C/C++: Use the Nix package manager to get the library. The Nix flake URL for this repository is "git+https://git.dblsaiko.net/nucom". Best support is with the CMake build system, which also provides support to build IDL files, but a pkg-config file is also provided by the Nix package.

From Rust: Add the nucomcore and nuidl crates to your project. To enable auto-detection for IDL include paths, add a build.rs file with this content:

fn main() {
  nuidl::cargo::use_cargo_deps();
}

Why?

Initially this started as part of an effort to port a Windows application heavily using COM interfaces to Linux. It has since outgrown that project.

A full COM implementation is a one-stop shop for these:

• object model for C, which maps 1:1 onto C++ classes and can be adapted to work for various other languages like Rust
• stable C ABI
• IPC and network transparency

Specifically for Rust, this means that in the absence of a stable Rust ABI, it can be used as that, for example as part of a plugin interface. This also doesn't limit plugin implementers to any particular language, rather, anything that can use C types could in theory be used. It's also yet another way to achieve C++ to Rust interop.

(Personally I also just think it's really neat.)

Goals

• Documentation -- :))))
• Support for creating COM classes in C/C++ -- done
• Support for creating COM classes in Rust -- works but not nice to use yet
• Support for Win32's standard COM base interfaces -- partially done
• IDL compiler for Rust, C++ and C -- usable for basic IDL files
• Binary compatibility with libraries written for Win32 COM -- not done, not currently testing anything on Windows
• RPC -- not done, this is a huge protocol
• Marshalling and DCOM -- not done, needs RPC

Undecided

• Windows concepts of COM servers and automatic activation -- this is kinda cursed and also requires a system-wide registry of some kind

Non-Goals

• 1:1 source compatibility for C/C++ or IDL (rather, this tries to improve upon Win32's API)

Related Projects

• The Wine project, which implements the entirety of COM as it exists on Windows
• intercom, a Rust crate for cross-platform COM
• windows-rs, Rust bindings to the Windows API
• DCE/RPC, the RPC protocol used in DCOM, implementation written in C