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Version: 1.x

Building components with Rust

The Rust ecosystem has excellent support for building WebAssembly components.

Starting with the wasm32-unknown-unknown target used in the past for bare WebAssembly modules, extending to the wasm32-wasip2 (which reached Tier 2 support in 2024) which has the latest and greatest of the component model, Rust has done much to keep up with and help grow the WebAssembly ecosystem.

The main wasmCloud/wasmCloud repository contains Rust exmaples directly in-tree, with examples of components and providers listed there.

Rust's standard toolchain is WebAssembly-ready​

Standard Rust tooling can be used with Rust's WebAssembly support. Often the only thing needed to be able to build a Rust webassembly project is an added target (e.g. wasm32-wasip1, wasm32-wasip2), or a properly formatted rust-toolchain.toml file in the project folder.

To install the wasm32-wasip1 or wasm32-wasip2 targets, you can use rustup:

console
rustup target add wasm32-wasip2

Once tools are installed, components can be built with cargo:

cargo build --target=wasm32-wasip2
tip

The wasmCloud Shell (wash) is the easiest way to build wasmCloud projects

Get started​

In this walkthrough, we will create an compoennt that responds to HTTP requests using Rust.

This walkthrough requires:

Step 1: Build a project with wash​

The wasmCloud Shell (wash) CLI helps developers build component-based applications that can be deployed with wasmCloud, bundling and re-using language-specific tooling to build wasmCLoud projects.

We can use wash new to scaffold out a new Rust project:

console
wash new component http-test --template-name hello-world-rust

This will create a http-test folder which we can cd into:

console
cd http-test

We can then immediately run wash build to build our project as a WebAssembly component:

console
wash build
tip

Similar to other Rust projects, WebAssembly binaries are placed in target after being built.

The wash inspect subcommand enables us to examine the new component's imports and exports:

console
wash inspect --wit build/http_hello_world_s.wasm

You should see output that looks like the following:

wit
package root:component;

world root {
  import wasi:io/poll@0.2.2;
  import wasi:clocks/wall-clock@0.2.2;
  import wasi:random/random@0.2.2;
  import wasi:io/error@0.2.2;
  import wasi:io/streams@0.2.2;
  import wasi:cli/stdout@0.2.2;
  import wasi:cli/stderr@0.2.2;
  import wasi:cli/stdin@0.2.2;
  import wasi:http/types@0.2.2;
  import wasi:cli/environment@0.2.2;
  import wasi:cli/exit@0.2.2;
  import wasi:filesystem/types@0.2.2;
  import wasi:filesystem/preopens@0.2.2;

  export wasi:http/incoming-handler@0.2.2;
}

Once our component is built, we can start a local developer loop to use our app locally:

console
wash dev

While wash dev won't return, it will have started a HTTP server that you can query for you.

tip

wash dev is able to start up a HTTP server automatically because it discovers your application's dependencies via WIT.

After a second or two, in another console/tab, we can curl the application that was deployed locally:

$ curl localhost:8000
Hello from Rust!

Next steps​