go-wasm

This repo contains examples of how to work with WebAssembly and WASI in the Go ecosystem.

Regular WASM is meant to be executed inside a browser (like Chrome or Firefox) or JavaScript runtime (like Node, Deno or Bun). As such it only has access to web APIs or runtime-specific APIs.

WASI on the other hand, as the name "WebAssembly System Interface" suggests, provides more direct access to the host system, like to the filesystem or network sockets. Similar to how the browser executes JavaScript and WebAssembly in a sandbox, WASI runtimes also execute WASI programs in a sandbox, requiring explicit permissions for things like file access.

Table of Contents

• WASM
  • Execute WASM directly
    • Browser
    • Node
    • Deno
    • Bun
  • Embed WASM in Go
• WASI
  • Execute WASI directly
  • Embed WASI in Go
    • wazero
    • wasmtime
    • Wasmer

WASM

This works with Go versions prior to 1.21, as it's "regular" WASM, not WASI.

Compile the Go program to WebAssembly: GOOS=js GOARCH=wasm go build -o go-wasm.wasm

Execute WASM directly

Go WASM execution requires a Go-specific wrapper, wasm_exec.js. This can then be executed by any JavaScript runtime, in or outside the browser. The Go project provides this in $(go env GOROOT)/misc/wasm/wasm_exec.js.

The non-browser runtimes differ in how files are read from the host's filesystem, so for reading the wasm_exec.js file, in addition to this file itself, we need to have another runtime-specific wrapper.

Browser

For running the WASM program in the browser, you can serve the files with any web server that supports the application/wasm MIME type. You can use a regular Go server (http.ListenAndServe(...)), Caddy, or others.

cp go-wasm.wasm browser
cp $(go env GOROOT)/misc/wasm/wasm_exec.js browser/wasm_exec.js
cd browser
caddy file-server --listen :2015

Then in your browser visit http://localhost:2015.

Tested with Firefox 116.0.3

Node

cp go-wasm.wasm node
cp $(go env GOROOT)/misc/wasm/wasm_exec.js deno/wasm_exec.js
cd node
node node.js

The Go authors also provide a convenience script for this, so instead of copying the wasm_exec.js and writing our own node.js wrapper script, we can simply run:

$(go env GOROOT)/misc/wasm/go_js_wasm_exec go-wasm.wasm

Tested with Node v18.17.1

Deno

cp go-wasm.wasm deno
cp $(go env GOROOT)/misc/wasm/wasm_exec.js deno/wasm_exec.js
cd deno
deno run --allow-read=./go-wasm.wasm deno.js

ℹ️: Deno runs programs in a sandbox by default, so for reading the WASM file we need to grant the permission accordingly.

Tested with Deno 1.36.1

Bun

cp go-wasm.wasm bun
cp $(go env GOROOT)/misc/wasm/wasm_exec.js deno/wasm_exec.js
cd bun
bun bun.js

Tested with Bun 0.7.3

Embed WASM in Go

🚧 TODO

WASI

Go 1.21 has official WASI preview1 support, so we can compile Go programs to WASM that execute outside of a browser / JavaScript runtime.

Compile Go program to WASI: GOOS=wasip1 GOARCH=wasm go build -o go-wasi.wasm

Execute WASI directly

Any WASM runtime with WASI support, on any OS, can then execute this file:

• wasmtime: wasmtime go-wasi.wasm (tested with wasmtime CLI 11.0.0)
• Wasmer: wasmer run go-wasi.wasm (tested with Wasmer 4.1.1)
• wazero: wazero run go-wasi.wasm (tested with wazero 1.4.0)

Embed WASI in Go

Or we run the WASI program with an embeddable WASM runtime from within another Go program. Most of the ⬆️ listed runtimes also have Go libraries for embedding.

wazero

cp go-wasi.wasm embed-wasi/wazero
cd embed-wasi/wazero
go run .

wasmtime

🚧 TODO: https://github.com/bytecodealliance/wasmtime-go

Wasmer

🚧 TODO: https://github.com/wasmerio/wasmer-go