WebAssembly is a way to safely run code compiled in other languages. Runtimes
execute WebAssembly Modules (Wasm), which are most often binaries with a .wasm
extension.
wazero is a [WebAssembly 1.0][1] spec compliant runtime written in Go. It has zero dependencies, and doesn't rely on CGO. This means you can run applications in other languages and still keep cross compilation.
Import wazero and extend your Go application with code written in any language!
The best way to learn this and other features you get with wazero is by trying one of our examples.
For the impatient, here's how invoking a factorial function looks in wazero:
func main() {
// Choose the context to use for function calls.
ctx := context.Background()
// Read a WebAssembly binary containing an exported "fac" function.
// * Ex. (func (export "fac") (param i64) (result i64) ...
source, _ := os.ReadFile("./path/to/fac.wasm")
// Instantiate the module and return its exported functions
module, _ := wazero.NewRuntime().InstantiateModuleFromCode(ctx, source)
defer module.Close(ctx)
// Discover 7! is 5040
fmt.Println(module.ExportedFunction("fac").Call(ctx, 7))
}Note: fac.wasm was compiled from [fac.wat][3], in the [WebAssembly 1.0][1]
Text Format, it could have been written in another language that compiles to
(targets) WebAssembly, such as AssemblyScript, C, C++, Rust, TinyGo or Zig.
The former example is a pure function. While a good start, you probably are wondering how to do something more realistic, like read a file. WebAssembly Modules (Wasm) are sandboxed similar to containers. They can't read anything on your machine unless you explicitly allow it.
The WebAssembly Core Specification is a standard, governed by W3C process, but it has no scope to specify how system resources like files are accessed. Instead, WebAssembly defines "host functions" and the signatures they can use. In wazero, "host functions" are written in Go, and let you do anything including access files. The main constraint is that WebAssembly only allows numeric types.
For example, you can grant WebAssembly code access to your console by exporting a function written in Go. The below function can be imported into standard WebAssembly as the module "env" and the function name "log_i32".
env, err := r.NewModuleBuilder("env").
ExportFunction("log_i32", func(v uint32) {
fmt.Println("log_i32 >>", v)
}).
Instantiate(ctx)
if err != nil {
log.Fatal(err)
}
defer env.Close(ctx)The WebAssembly community has [subgroups][4] which maintain work that may not result in a Web Standard. One such group is the WebAssembly System Interface ([WASI][5]), which defines functions similar to Go's [x/sys/unix][6].
The [wasi_snapshot_preview1][13] tag of WASI is widely implemented, so wazero bundles an implementation. That way, you don't have to write these functions.
For example, here's how you can allow WebAssembly modules to read "/work/home/a.txt" as "/a.txt" or "./a.txt":
wm, err := wasi.InstantiateSnapshotPreview1(ctx, r)
defer wm.Close(ctx)
config := wazero.ModuleConfig().WithFS(os.DirFS("/work/home"))
module, err := r.InstantiateModule(ctx, binary, config)
defer module.Close(ctx)
...While we hope this deeper dive was useful, we also provide examples to elaborate each point. Please try these before raising usage questions as they may answer them for you!
There is one runtime configuration - interpreter:
r := wazero.NewRuntimeWithConfig(wazero.NewRuntimeConfigInterpreter())Interpreter is a naive interpreter-based implementation of Wasm virtual
machine. Its implementation doesn't have any platform (GOARCH, GOOS) specific
code, therefore interpreter can be used for any compilation target available
for Go (such as riscv64).
Both runtimes pass [WebAssembly 1.0 spectests][7] on supported platforms:
| Runtime | Usage | amd64 | arm64 | others |
|---|---|---|---|---|
| Interpreter | wazero.NewRuntimeConfigInterpreter() |
✅ | ✅ | ✅ |
The below support policy focuses on compatability concerns of those embedding wazero into their Go applications.
wazero is an early project, so APIs are subject to change until version 1.0.
We expect [wazero 1.0][9] to be at or before Q3 2022, so please practice the current APIs to ensure they work for you!
wazero has no dependencies except Go, so the only source of conflict in your project's use of wazero is the Go version.
To simplify our support policy, we adopt Go's [Release Policy][10] (two versions).
This means wazero will remain compilable and tested on the version prior to the latest release of Go.
For example, once Go 1.29 is released, wazero may use a Go 1.28 feature.
wazero has one runtime mode: Interpreter. The only Linux operating system is one we test, but that doesn't necessarily mean other operating system versions won't work.
wazero has no dependencies and doesn't require CGO. This means it can also be embedded in an application that doesn't use an operating system. This is a main differentiator between wazero and alternatives.
We verify zero dependencies by running tests in Docker's [scratch image][12]. This approach ensures compatibility with any parent image.
wazero understands that while no-one desired to create confusion, confusion exists both in what is a standard and what in practice is in fact a standard feature. To help with this, we created some guidance both on the status quo of WebAssembly portability and what we support.
The WebAssembly Core Specification is the only specification relevant to wazero, governed by a standards body. Release [1.0][1] is a Web Standard (REC). Release [2.0][2] is a Working Draft (WD), so not yet a Web Standard.
Many compilers implement system calls using the WebAssembly System Interface, [WASI][5]. WASI is a WebAssembly community [subgroup][4], but has not published any working drafts as a result of their work. WASI's last stable point was [wasi_snapshot_preview1][13], tagged at the end of 2020.
While this seems scary, the confusion caused by pre-standard features is not as bad as it sounds. The WebAssembly ecosystem is generally responsive regardless of where things are written down and wazero provides tools, such as built-in support for WASI, to reduce pain.
The goal of this section isn't to promote a W3C recommendation exclusive approach, rather to help you understand common language around portable features and which of those wazero supports at the moment. While we consider features formalized through W3C recommendation status mandatory, we actively pursue pre-standard features as well interop with commonly used infrastructure such as AssemblyScript.
In summary, we hope this section can guide you in terms of what wazero supports as well as how to classify a request for a feature we don't yet support.
wazero conforms with spectests [7] defined alongside WebAssembly Core Specification [1.0][1]. There is also [work in progress][14] towards release [2.0][2], despite it not being a Web Standard, yet.
One current limitation of wazero is that it doesn't fully implement the Text
Format, yet, e.g. compiling .wat files. The intent is to [finish this][15],
and meanwhile users can work around this using tools such as wat2wasm to
compile the text format into the binary format. In practice, the text format is
too low level for most users, so delays here have limited impact.
Features regardless of W3C release are inventoried in the [Proposals][16]. repository. wazero implements [Finished Proposals][17] based on user demand, using [wazero.RuntimeConfig][18] feature flags.
Features not yet assigned to a W3C release are not reliable. Encourage the [WebAssembly community][19] to formalize features you rely on, so that they become assigned to a release, and reach the W3C recommendation (REC) phase.
Many compilers implement system calls using the WebAssembly System Interface, [WASI][5]. WASI is a WebAssembly community [subgroup][4], but has not published any working drafts as a result of their work. WASI's last stable point was [wasi_snapshot_preview1][13], tagged at the end of 2020.
Some functions in this tag are used in practice while some others are not known to be used at all. Further confusion exists because some compilers, like GrainLang, import functions not used. Finally, [wasi_snapshot_preview1][13] includes features such as "rights" that [will be removed][20].
For all of these reasons, wazero will not implement all WASI features, just to complete the below chart. If you desire something not yet implemented, please raise an issue and include your use case (ex which language you are using to compile, a.k.a. target Wasm).
Click to see the full list of supported WASI functions
| Function | Status | Known Usage |
|---|---|---|
| args_get | ✅ | TinyGo |
| args_sizes_get | ✅ | TinyGo |
| environ_get | ✅ | TinyGo |
| environ_sizes_get | ✅ | TinyGo |
| clock_res_get | ❌ | |
| clock_time_get | ✅ | TinyGo |
| fd_advise | ❌ | |
| fd_allocate | ❌ | |
| fd_close | ✅ | TinyGo |
| fd_datasync | ❌ | |
| fd_fdstat_get | ✅ | TinyGo |
| fd_fdstat_set_flags | ❌ | |
| fd_fdstat_set_rights | ❌ | |
| fd_filestat_get | ❌ | |
| fd_filestat_set_size | ❌ | |
| fd_filestat_set_times | ❌ | |
| fd_pread | ❌ | |
| fd_prestat_get | ✅ | TinyGo,fs.FS |
| fd_prestat_dir_name | ✅ | TinyGo |
| fd_pwrite | ❌ | |
| fd_read | ✅ | TinyGo,fs.FS |
| fd_readdir | ❌ | |
| fd_renumber | ❌ | |
| fd_seek | ✅ | TinyGo |
| fd_sync | ❌ | |
| fd_tell | ❌ | |
| fd_write | ✅ | fs.FS |
| path_create_directory | ❌ | |
| path_filestat_get | ❌ | |
| path_filestat_set_times | ❌ | |
| path_link | ❌ | |
| path_open | ✅ | TinyGo,fs.FS |
| path_readlink | ❌ | |
| path_remove_directory | ❌ | |
| path_rename | ❌ | |
| path_symlink | ❌ | |
| path_unlink_file | ❌ | |
| poll_oneoff | ✅ | TinyGo |
| proc_exit | ✅ | AssemblyScript |
| proc_raise | ❌ | |
| sched_yield | ❌ | |
| random_get | ✅ | |
| sock_recv | ❌ | |
| sock_send | ❌ | |
| sock_shutdown | ❌ |
wazero was originally developed by [Takeshi Yoneda][21] as a hobby project in mid 2020. In late 2021, it was sponsored by Tetrate as a top-level project. That said, Takeshi's original motivation is as relevant today as when he started the project, and worthwhile reading:
If you want to provide Wasm host environments in your Go programs, currently there's no other choice than using CGO leveraging the state-of-the-art runtimes written in C++/Rust (e.g. V8, Wasmtime, Wasmer, WAVM, etc.), and there's no pure Go Wasm runtime out there. (There's only one exception named [wagon][22], but it was archived with the mention to this project.)
First, why do you want to write host environments in Go? You might want to have plugin systems in your Go project and want these plugin systems to be safe/fast/flexible, and enable users to write plugins in their favorite languages. That's where Wasm comes into play. You write your own Wasm host environments and embed Wasm runtime in your projects, and now users are able to write plugins in their own favorite languages (AssemblyScript, C, C++, Rust, Zig, etc.). As a specific example, you maybe write proxy severs in Go and want to allow users to extend the proxy via [Proxy-Wasm ABI][23]. Maybe you are writing server-side rendering applications via Wasm, or [OpenPolicyAgent][24] is using Wasm for plugin system.
However, experienced Golang developers often avoid using CGO because it introduces complexity. For example, CGO projects are larger and complicated to consume due to their libc + shared library dependency. Debugging is more difficult for Go developers when most of a library is written in Rustlang. [CGO is not Go][25] [ -- Rob Pike][26] dives in deeper. In short, the primary motivation to start wazero was to avoid CGO.