cranelift/docs/lang-go.md

Using WebAssembly from Go

Wasmtime is available as a Go Module. This guide will go over adding Wasmtime to your project, and some provided examples of what can be done with WebAssembly modules.

Make sure you're using Go 1.12 or later with modules support.

Getting started and simple example

First up you'll want to start a new module:

$ mkdir hello-wasm
$ cd hello-wasm
$ go mod init hello-wasm
$ go get github.com/bytecodealliance/wasmtime-go

Next, copy this example WebAssembly text module into your project. It exports a function for calculating the greatest common denominator of two numbers.

{{#include ../examples/gcd.wat}}

Next, we can write our code in main.go which reads this file and runs it:

package main

import (
    "fmt"
    "github.com/bytecodealliance/wasmtime-go"
)

func main() {
    engine := wasmtime.NewEngine()
    store := wasmtime.NewStore(engine)
    module, err := wasmtime.NewModuleFromFile(engine, "gcd.wat")
    check(err)
    instance, err := wasmtime.NewInstance(store, module, []wasmtime.AsExtern{})
    check(err)

    gcd := instance.GetExport(store, "gcd").Func()
    val, err := gcd.Call(store, 6, 27)
    check(err)
    fmt.Printf("gcd(6, 27) = %d\n", val.(int32))
}

func check(err error) {
    if err != nil {
        panic(err)
    }
}

And finally we can build and run it:

$ go run main.go
gcd(6, 27) = 3

If this is the output you see, congrats! You've successfully ran your first WebAssembly code in Go!

More examples and contributing

The wasmtime Go package lives in its own repository and has a number of other more advanced examples as well. Feel free to browse those, but if you find anything missing don't hesitate to open an issue and let us know if you have any questions!