host-command-component

Rust command component

This example imports the adder interface, calls it from main(), and prints the result. It uses wit_bindgen::generate! to generate bindings during compilation and builds directly with Cargo for wasm32-wasip2. The macro loads the adder's WIT package before this component's host world, replacing the dependency resolution previously handled by cargo-component metadata. There is no separate wit-bindgen-rt dependency or cargo-component build step.

Rust's wasm32-wasip2 binary build supplies the wasi:cli/run entrypoint for main(). The component tutorial describes another approach: a cdylib that explicitly exports and implements wasi:cli/run. The Rust runnable-components guide documents both approaches. Both can be executed with wasmtime run after their application imports are satisfied through composition.

Build and run

Run these commands from host-command-component/ with the wac and wasmtime CLIs installed.

1. Install the Rust target and build the command component:

   rustup target add wasm32-wasip2
   cargo build --target wasm32-wasip2

2. Build the adder component:

   cargo build -p guest-interfaced-adder-rs --release --target wasm32-wasip2

3. Compose the command and adder components:

   wac plug ../target/wasm32-wasip2/debug/host-command-component.wasm \
     --plug ../target/wasm32-wasip2/release/guest_interfaced_adder_rs.wasm \
     -o ../target/composed-component.wasm

   Alternatively, upload the two input components to wasmbuilder.app and compose them as shown below.

   

4. Run the composed component:

   wasmtime run ../target/composed-component.wasm

   Expected output: result: 3.