Composable Factory

Build Wasm Components with Wasm Components

The API

A Factory generates a Wasm Component. An implementor provides a ComponentBuilder:

impl ComponentBuilder for Builder {
    fn build_world(&self, world: &mut World) -> Result<()>;
    fn build_function(&self, function: &ExportedFunction, imports: &Imports) -> Result<()>;
}

• build_world declares the generated component's surface.
• build_function is then called once per exported function to emit its body.

Passing a ComponentBuilder to build invokes both callbacks and returns the encoded component:

composable_factory::build(&Builder)  // -> Result<Vec<u8>>

The Factory as a Component

A Factory can itself be built as a Wasm Component. The WIT interface to export is composable:factory/factory, and its build function returns the bytes of the component it generates:

build: async func() -> result<list<u8>, string>

Since that function takes no arguments, a Factory Component relies on its own imports for configuration, for fetching dynamic information needed to declare its target World, and for any functionality it calls at build time.

Examples

• helloworld: generates a greeter component, joining a literal greeting with a received "name" value.
• calculator: generates a 4-function calculator component, emitting Wasm instructions directly.
• logging-interceptor: generates a component that mirrors a target component's exports, forwards to them as imports, and logs each call and return.

Each has a run.sh that builds the factory, generates a component with the factory, and then invokes the generated component.

License

Copyright (c) 2026 Modulewise Inc and the Composable Factory contributors.

Apache License v2.0: see LICENSE for details.