3 releases

0.1.2 May 11, 2024
0.1.1 May 9, 2024
0.1.0 May 8, 2024

#911 in WebAssembly

MIT/Apache and GPL-3.0-or-later

1.5K SLoC


Crates.io Docs.rs

Wings is a WASM plugin system for Rust. It integrates directly with the Geese event library, allowing plugins to seamlessly communicate with one another and the host using events and systems. The following features are supported:

  • Sending events to the host: Guests can send and receive strongly-typed events to the host, which will be injected into the host's Geese context.
  • Sending events to other guest systems: Events will propagate between guest systems and from the host's Geese context into WASM modules.
  • Accessing systems of the host: Hosts can expose Geese systems as trait objects, which can be called directly from the guest. Function arguments and return types are serialized across the WASM boundary.
  • Accessing systems of other plugins: Plugins can export their systems as trait objects, which other plugins can call. Just like regular Geese, Wings guarantees that every system is a singleton - if separate plugins are loaded that share a dependency, both plugins will access the same dependency instance.
  • Automatically resolving plugin dependencies/versions: Plugins are built as Rust crates with all transitive dependencies included, so there's no need to worry about creating a dependency resolver. Whenever Wings loads a system, it will choose the newest Semver-compatible version from the set of loaded plugins.


The following is an abridged example of how to use Wings. The complete code may be found in the wings_example folder.

Wings allows for defining traits like the following, which can be shared between the code of hosts and between plugins:

// Define a system that the host will expose.
// This can also be used to expose guest systems to other guest systems.
pub trait ExampleSystem: 'static {
    // Prints a value to the console.
    fn print(&self, value: &str);

Then, the system may be referenced as a trait object from WASM:

// Define a Wings system that will run within WASM
pub struct PluginSystem;

impl WingsSystem for PluginSystem {
    // Declare a dependency on the exported host system
    const DEPENDENCIES: Dependencies = dependencies()
        .with::<dyn ExampleSystem>();

    // Invoked when the plugin is created
    fn new(mut ctx: WingsContextHandle<Self>) -> Self {
        // Get the system from WASM and invoke its function
        ctx.get::<dyn ExampleSystem>().print(&format!("Hello from WASM!"));

Finally, the system may be implemented on the host and exposed to plugins:

// Define a host type
pub struct TestHost;

impl Host for TestHost {
    // Declare the systems that should be exported to WASM,
    // and the traits under which they should be exported
    const SYSTEMS: Systems<Self> = systems()
            .with::<dyn example_host_system::ExampleSystem>());


// Declare an implementation for the WASM-exported system
pub struct ExampleSystemImpl;

impl ExampleSystem for ExampleSystemImpl {
    fn print(&self, value: &str) {
        println!("Plugin says '{value}'");

In general, anything possible with vanilla Geese is also possible with Wings. See the example for demonstration of more functionality.


~92K SLoC