Function Example_hello

example_test.go:668–716

An example of instantiating a small wasm module which imports functionality from the host, then calling into wasm which calls back into the host.

()

// An example of instantiating a small wasm module which imports functionality
// from the host, then calling into wasm which calls back into the host.
func Example_hello() {
	// Almost all operations in wasmtime require a contextual `store`
	// argument to share, so create that first
	store := wasmtime.NewStore(wasmtime.NewEngine())

	// Compiling modules requires WebAssembly binary input, but the wasmtime
	// package also supports converting the WebAssembly text format to the
	// binary format.
	wasm, err := wasmtime.Wat2Wasm(`
	(module
	  (import "" "hello" (func $hello))
	  (func (export "run")
	    (call $hello)
	  )
	)
	`)
	if err != nil {
		log.Fatal(err)
	}

	// Once we have our binary `wasm` we can compile that into a `*Module`
	// which represents compiled JIT code.
	module, err := wasmtime.NewModule(store.Engine, wasm)
	if err != nil {
		log.Fatal(err)
	}

	// Our `hello.wat` file imports one item, so we create that function
	// here.
	item := wasmtime.WrapFunc(store, func() {
		fmt.Println("Hello from Go!")
	})

	// Next up we instantiate a module which is where we link in all our
	// imports. We've got one import so we pass that in here.
	instance, err := wasmtime.NewInstance(store, module, []wasmtime.AsExtern{item})
	if err != nil {
		log.Fatal(err)
	}

	// After we've instantiated we can lookup our `run` function and call
	// it.
	run := instance.GetFunc(store, "run")
	_, err = run.Call(store)
	if err != nil {
		log.Fatal(err)
	}
	// Output: Hello from Go!
}

// An example of a wasm module which calculates the GCD of two numbers
func Example_gcd() {