Minimal example of a CloudFlare Worker that calls into a WASM module. The Worker is a JavaScript module bundled with wrangler and the WASM module is written in Rust using wasm-bindgen to generate the JS shims that handle passing arguments from JavaScript and returning values from Rust.
src/worker.js is the Worker module. It passes the
last element of the request URL to the greet function exported by
the WASM module and returns the resulting string as the HTTP response.
npm start runs the Worker locally using Miniflare and demonstrates
using esbuild to bundle worker.js and the WASM shims into a single
dist/worker.js module. The esbuild config in serve.js
declares "*.wasm" as external to preserve imports of WASM bytecode
which are resolved to WebAssembly.Module instances by the Workers
runtime.
rust/src/lib.rs contains the Rust code which called
from the Worker, a function named greet which takes a single
argument name and returns a String greeting in the form "hello, $name".
Compiling this Rust crate to WASM requires the Rust
toolchain and the wasm-bindgen-cli crate which
generates JavaScript shims necessary for passing arguments from
JavaScript and handling return values from Rust.
Build steps:
cargo install wasm-bindgen-cli
cargo build --release --target wasm32-unknown-unknown
wasm-bindgen --target web --no-typescript \
--out-dir ../src/wasm \
target/wasm32-unknown-unknown/release/greet.wasm