Dart Wasm Run

A Web Assembly executor for the Dart programming language.

Currently it uses the wasmtime 14.0 or wasmi 0.31 Rust crates for parsing and executing WASM modules. Bindings are created using package:flutter_rust_bridge.

Pub	Source	Description
	wasm_run	Wasm executor and utilities
	wasm_run_flutter	Native libraries to use package:wasm_run in Flutter projects
	wasm_wit_component	Wit bindings and code generator for Wasm components
	compression_rs	Compression, decompression, zip and tar achieves (brotli, lz4, zstd, gzip, zlib, ...)
	image_ops	Enconding, deconding, transformations and operations over multiple image formats (png, jpeg, ico, gif, bmp, tiff, webp, avif, tga, farbfeld, ...)
	rust_crypto	Hashes, Hmacs, Argon2 Passwords and AES-GCM-SIV encryption. Digests for sha1, sha2, md5, blake3, crc32
	wasm_parser	Wasm, Wat and Wit parser, validator, printer and Wasm component tools
	y_crdt	y.js (https://github.com/yjs/yjs) Dart port, a CRDT implementation. CRDTs allow for local, offline editing and synchronization of shared data.
	typesql_parser	SQL parser, AST and visitors
	typesql	SQL type utilities and helpers for Dart model code generator and query execution
	typesql_generator	SQL types code generator from .sql files to Dart queries and models

• Dart Wasm Run
• Features
  • Supported Wasm Features
  • Execute WASM on any platform
    • Flutter
      • Runtime for Platform
    • Pure Dart (CLI/Backend/Web)
    • WASM Web bindings
  • Parse Web Assembly Text Format (WAT)
  • Parse and Introspect WASM Modules
    • Imports and Exports
  • Execute WASM Function in Worker Threads
    • Threads Example
    • Web Workers configuration
  • Web Assembly System Interface (WASI)
    • WASI Examples
      • Dart Wit Component Generator
      • WASI Web
    • Stdio (stdin, stdout, stderr)
    • Directories
    • Environment and Arguments
    • Clocks and Randomness
  • Wasm Components and Wasm Interface Type (WIT)
    • Generate Dart code from Wit files
      • wasm_wit_component:generate CLI
      • Generate from the Dart API
    • Multiple Types Example
• Documentation
  • Getting started
  • Usage
  • Integers, BigInt and Web Browsers
  • Load Wasm Modules with WasmFileUris
  • Configure Dynamic Libraries with WasmRunLibrary
  • WasmInstanceBuilder
  • WasmInstanceFuel
  • Wit Tutorial
    • Dart Package
    • Rust Package
    • Rust Implementation and Wit Package API
    • Build WASM
    • Generate WIT Host Dart Bindings
    • Loading and Testing the Dart Library

Features

Supported Wasm Features

Feature\Runtime	Wasmtime 14.0	Wasmi 0.31	Chrome[1]
multi_value	✅	✅	✅
bulk_memory	✅	✅	✅
reference_types	✅	✅	✅
mutable_global	✅	✅	✅
saturating_float_to_int	✅	✅	✅
sign_extension	✅	✅	✅
extended_const	✅	✅	✅
floats	✅	✅	✅
simd	✅	❌	✅
relaxed_simd	🏳	❌	🏳
threads_shared_memory_atomics	🏳	❌	✅
multi_memory	🏳	❌	❌
memory64	🏳	❌	🏳
component_model	❌[2]	❌	❌
tail_call	❌	🏳	✅
exceptions	❌	❌	✅
garbage_collection	❌	❌	🏳
memory_control	❌	❌	❌
type_reflection	✅	✅	🏳
wasi_snapshot_preview_1	✅	✅	✅
wasi_nn	❌[2]	❌	❌
wasi_crypto	❌[2]	❌	❌
wasi_threads	❌[2]	❌	❌

• 🏳: Not enabled by default, may require additional configuration or a custom browser flag.
• [1]: For up-to-date values in browsers please visit https://webassembly.org/roadmap/.
• [2]: Supported, but not implemented.

Execute WASM on any platform

Flutter

We provide package:wasm_run_flutter to bundle the right binaries for your platform compilation targets.

Runtime for Platform

Platform	Architecture	Runtime[1]
Linux	aarch64 x86_64	Wasmtime 14.0
MacOS	aarch64 x86_64	Wasmtime 14.0
Windows	aarch64 x86_64	Wasmtime 14.0
iOS	aarch64 x86_64 aarch64-sim	Wasmi 0.31
Android	armeabi-v7a x86 x86_64	Wasmi 0.31
Android	arm64-v8a	Wasmtime 14.0
Web	N/A	Browser/Wasmi 0.31

• [1]: Wasmi 0.31 supports any platform that Rust could be compiled to.

Pure Dart (CLI/Backend/Web)

For pure Dart application (backend or cli, for example), you may download the compiled dynamic libraries for each platform and specify the ffi.DynamicLibrary in the WasmRunLibrary.set function or execute the script dart run wasm_run:setup (or the function WasmRunLibrary.setUp) to download the right library for your current platform and configure it so that you don't need to call WasmRunLibrary.set manually. The compiled libraries can be found in the releases assets of this repository.

For the web platform we provide the same interface but it uses the WASM runtime provided by the browser instead of the native library (you may also use the Wasmi WASM module // TODO: not implemented yet).

WASM Web bindings

We use package:wasm_interop to implement the browser web API. We don't need to provide a custom runtime since the browser already has one.

However, in web browsers there is no support for the WAT format and other queries that you may perform over the WASM modules on native platforms. For example, WASM function type definitions of arguments and results are not provided in most browsers. If you need these features, you may use the compiled WASM module (TODO: Not implemented yet).

We use the wasm-feature-detect JavaScript library for feature detection in the browser. To use this functionality in Dart web applications you will need to add the following script to your HTML:

<script src="./packages/wasm_run/assets/wasm-feature-detect.js"></script>
<script type="module" src="./packages/wasm_run/assets/browser_wasi_shim.js"></script>

This is also required in Flutter, in web/index.html, if your code calls any function, or needs any object implemented in browser_wasi_shim:

<head>
<script src="/assets/packages/wasm_run/lib/assets/wasm-feature-detect.js" defer></script>
<script type="module" src="/assets/packages/wasm_run/lib/assets/browser_wasi_shim.js" defer></script>
<head>

Parse Web Assembly Text Format (WAT)

Support for compiling modules in WAT format. At the moment this is only supported in native platforms.

Parse and Introspect WASM Modules

Parsing WASM and WAT modules to explore the exposed interface.

Imports and Exports

You may retrieve the names and types of each import and export defined in a WASM module.

Execute WASM Function in Worker Threads

At the moment this is experimental and will not work in the Wasmi runtime.

The native implementation uses Rust's rayon crate to execute tasks with a work-stealing scheduler.

To use it you must call WasmInstance.runParallel with the WasmFunction to execute and the group of arguments to pass to the different threads.

The web implementation uses web workers for running the functions and a simple task queue for scheduling.

Only shared memories can be accessed when running Wasm functions in workers. Regular memories, tables and globals will be instantiated separately for each worker and can not be easily accessed from the Dart API (imports will not be the same reference in Dart). Function imports will be correctly executed in the main Dart process (requires SharedBuffer support for web browsers). Wasm reference values will not work in the web browser and are not properly tested in native platforms.

Threads Example

The repository's packages/rust_threads_example directory contains an implementation example for a WASM module with shared memories, atomics, thread locals and simd. You may compile it with Rust's Cargo nightly toolchain:

RUSTFLAGS='-C target-feature=+atomics,+bulk-memory,+mutable-globals' \
  cargo +nightly build --target wasm32-unknown-unknown --release -Z build-std=std,panic_abort

The threads_test.dart contains a benchmark and multiple usage and configuration examples.

Web Workers configuration

The assets/wasm.worker.js is used as the script for implementing the worker, you may override it with the workerScriptUrl configuration in WorkersConfig.

You may also configure the WASM imports are by using the mapWorkerWasmImports parameter. An example of the script can be found in worker_map_imports.js, it exposes a mapWorkerWasmImports that receives the imports, the WASM module and other information, and returns the mapped WASM imports object.

Web Assembly System Interface (WASI)

We support WASI wasi_snapshot_preview1 through the wasmtime_wasi or wasmi_wasi Rust crates, chosen depending on the target platform.

In the web platform we support WASI modules by using bjorn3/browser_wasi_shim. The file system directories exported by the host are in-memory Maps where the files are represented as Uint8List buffers. Other APIs, such as time and random are implemented using the JavaScript browser APIs.

WASI Examples

Usage within Dart can be found in the wasi_test.dart.

The WASI module used to execute the test is compiled from the rust_wasi_example Rust project within this repo.

You may compile it with the following commands inside the project's directory:

cargo build --target wasm32-wasi

or, if you have cargo-wasi installed:

cargo wasi build

Dart Wit Component Generator

Another example of a Wasm module using Wasi is the Dart Wit Component Generator.

WASI Web

We use the bjorn3/browser_wasi_shim JavaScript library that provides a shim around the browser API and an in-memory file system with webBrowserFileSystem.

Stdio (stdin, stdout, stderr)

You may choose to inherit stdin, stdout and stderr from the current process. Or capture stdout and stderr to execute some custom logic for the stdio exposed by the execution of the specific WASI module.

WasmInstance.stderr and WasmInstance.stdout provide the captured Streams.

Directories

You may provide a list of directories that the WASI module is allowed to access.

Environment and Arguments

You can pass custom environment variables and program arguments to the WASI module or inherit them from the current process.

Clocks and Randomness

The WASI modules can have access to the system clock and randomness.

Wasm Components and Wasm Interface Type (WIT)

An experimental Wasm Interface Type (WIT) code generator for Dart can be found in the dart_wit_component directory.

This is a work in progress and we will provide a separate package or additional tools for using Wasm components.

Generate Dart code from Wit files

The generator is implemented in Rust and the usage within Dart is implemented using package:wasm_run. The wit document for the implementation can be found in wit/dart-wit-generator.wit the Rust implementation can be found in the dart_wit_component folder which uses wit-bindgen. This is a good example of a package (or application) using wit components to implement functionalities in Dart. The usage within Dart is implemented as a cli and as a Dart library in lib/generator.dart. The generated Dart code can be found in lib/src/generator.dart.

wasm_wit_component:generate CLI

Command line interface usage:

dart run wasm_wit_component:generate wit/input-file.wit lib/generated-world.dart --watch --no-copy-with

Argument	Kind	Description	Default
inputWitPath	positional	The path to the wit directory or file	none (Required)
outputDartPath	positional	The path to the dart file that will be generated	next to the wit file
watch	named	Whether to watch for changes in the wit path and regenerate	false
no-default	named	Whether to set to false other generator configurations	false
json-serialization	named	Whether to generate toJson and fromJson	true (false if --no-default)
to-string	named	Whether to generate toString method	true (false if --no-default)
equality	named	Whether to generate equality and hashCode	true (false if --no-default)
copy-with	named	Whether to generate copyWith	true (false if --no-default)

Generate from the Dart API

API usage examples can be found in the wit_generator_test.dart.

Multiple Types Example

Another example with multiple tests can be found in the example directory inside the wasm_wit_component package:

• Wit Component World: rust_wit_component_example/wit/types-example.wit
• Rust Implementation: rust_wit_component_example/src/lib.rs
• Dart Generated Code: lib/types_gen.dart. Generated using:

dart run wasm_wit_component:generate rust_wit_component_example/wit/types-example.wit lib/types_gen.dart

• Tests and Usage: lib/types_gen_test.dart

Documentation

Getting started

When using Flutter:

dependencies:
  flutter:
    sdk: flutter
  wasm_run_flutter: 0.1.0

When using it in a pure Dart application:

dependencies:
  wasm_run: 0.1.0

Fetch the dynamic libraries for your platform by running (or the function WasmRunLibrary.setUp):

dart run wasm_run:setup

Or provide a custom dynamic library from the releases with WasmRunLibrary.set.

Usage

You may explore the testAll function in the main.dart file. It contains multiple test using distinct APIs withing the browser or native.

A simple usage example is the following. It compiles a WASM module with an add export and executes it:

/// WASM WAT source:
///
/// ```wat
/// (module
///     (func (export "add") (param $a i32) (param $b i32) (result i32)
///         local.get $a
///         local.get $b
///         i32.add
///     )
/// )
/// ```
const base64Binary =
    'AGFzbQEAAAABBwFgAn9/AX8DAgEABwcBA2FkZAAACgkBBwAgACABagsAEARuYW1lAgkBAAIAAWEBAWI=';
final Uint8List binary = base64Decode(base64Binary);
final WasmModule module = await compileWasmModule(
  binary,
  config: const ModuleConfig(
    wasmi: ModuleConfigWasmi(),
    wasmtime: ModuleConfigWasmtime(),
  ),
);
final List<WasmModuleExport> exports = module.getExports();

assert(
  exports.first.toString() ==
      const WasmModuleExport('add', WasmExternalKind.function).toString(),
);
final List<WasmModuleImport> imports = module.getImports();
assert(imports.isEmpty);

// configure wasi
WasiConfig? wasiConfig;
final WasmInstanceBuilder builder = module.builder(wasiConfig: wasiConfig);

// create external
// builder.createTable
// builder.createGlobal
// builder.createMemory

// Add imports
// builder.addImport(moduleName, name, value);

final WasmInstance instance = await builder.build();
final WasmFunction add = instance.getFunction('add')!;

final List<ValueTy?> params = add.params;
assert(params.length == 2);

final WasmRuntimeFeatures runtime = await wasmRuntimeFeatures();
if (!runtime.isBrowser) {
  // Types are not supported in browser
  assert(params.every((t) => t == ValueTy.i32));
  assert(add.results!.length == 1);
  assert(add.results!.first == ValueTy.i32);
}

final List<Object?> result = add([1, 4]);
assert(result.length == 1);
assert(result.first == 5);

final resultInner = add.inner(-1, 8) as int;
assert(resultInner == 7);

Integers, BigInt and Web Browsers

At the moment, 64 bit integers are represented differently in the web browser and native platforms. Dart uses JavaScript's number (double) for all numbers when compiled to JavaScript. Since they cannot properly represent the full range of 64 bit integers, WebAssembly uses JavaScript's BigInt (different from Dart's BigInt) for the i64 Wasm type. You may choose to convert i64 values into integers using i64.toInt(I64 value) (a no-op in native platforms) or to Dart's BigInt with i64.toBigInt(I64 value), where value is returned from or received as a parameter in a WasmFunction, or accessed with WasmGlobal.get().

Unfortunately, JavaScript's BigInt is different from dart:core's BigInt and using it directly is not recommended, for example it throws when printed and there is some weird behavior with Dart function (we need to use js_util.callMethod(wasmFunction, 'apply', [null, args]) to call WasmFunction with I64 parameters). If you target web platforms you should always use it with the i64 utility functions for proper multi-platform support. Since native platforms represent i64 using Dart's int class you can always cast the I64 values directly with value as int, and functions such as i64.toInt and i64.fromInt simply return the value passed as argument (they are a no-op).

Other utility functions are provided, for the full API you may look at the source file:

• i64.toInt and i64.fromInt
• i64.toBigInt and i64.fromBigInt
• i64.getInt64, i64.getUint64, i64.setInt64 and i64.setUint64
  • These functions receive a ByteData to get or set the I64 values at the given byte offset inside the buffer.

Load Wasm Modules with WasmFileUris

You can load WasmModules from Uris (using http GET or reading from a file) with the WasmFileUris utility class. You may aldo provide the simdUri and threadsSimdUri fields to conditionally import different WasmModules based on the features supported by the current runtime (retrieved using wasmRuntimeFeatures).

An usage example can be found in the wit component generator function, where the WASM module is loaded from the file system in lib/dart_wit_component.wasm either reading it directly in native platforms or with a GET request for Dart web. As a fallback it will use the releases from the wasm_run repository. And it also received a loadModule custom function if you want to override the behavior. This can be useful if you want to provide a different configuration or implementation, or you are loading it from Flutter assets or from a different HTTP endpoint.

Configure Dynamic Libraries with WasmRunLibrary

The WasmRunLibrary static utility class allows you to configure the external and dynamic libraries used by wasm_run.

• You can use the String version getter to retrieve the package version ("0.1.0").
• Set the dynamic library with the set static method.
• Set up the library using setUp.
  • Flutter: This will do nothing in Flutter since the libraries are already configured for you.
  • Pure Dart: It will download the right binary for your platform from the releases assets in this repository and place it in .dart_tool/wasm_run/<wasm_run_dart_dynamic_library> or in the path provided by the WASM_RUN_DART_DYNAMIC_LIBRARY environment variable. You can also run it with dart run wasm_run:setup in a project that depends on wasm_run.
  • Web Dart: It will configure your html.document.head with script tags (import the libraries) required to use the wasm-feature-detect and bjorn3/browser_wasi_shim JavaScript libraries.

WasmInstanceBuilder

WasmInstanceFuel

Wit Tutorial

In the following sections we will create a Dart package that uses a Wasm Wit component generated from a Rust implementation.

First we will create a Dart package and setup the Rust implementation within it. Then we will create a Wit package API with the connected Rust implementation. This Rust package will be built to Wasm, either to a wasm32-wasi or wasm32-unknown-unknown target depending on whether you require WASI (system) APIs. After that we will generate the wit Dart binding using package:wasm_wit_component's generate CLI command. Finally, we will setup the Wasm module loading and implement some tests for the wasm implementation within Dart.

Dart Package

dart create --template package your_package

cd your_package

Rust Package

cargo new --lib your_package_wasm

cd your_package_wasm

Edit the generated Cargo.toml:

[lib]
crate-type = ['cdylib']

[dependencies]
wit-bindgen = { git = "https://github.com/bytecodealliance/wit-bindgen", version = "0.7.0", rev = "131746313de2f90d2688afbbc40c4a7ca309fe0d" }
image = "0.24.6"

Rust Implementation and Wit Package API

package your-package-namespace:your-package

world your-package {
  hello: func() -> string
}

Within your_package_wasm/src/lib.rs:

Build WASM

cargo add cargo-wasi

cargo wasi build --release

cp target/wasm32-wasi/release/your_package_wasm.wasm ../lib/your_package_wasm.wasm

Generate WIT Host Dart Bindings

cd ..

dart pub add wasm_wit_component wasm_run

dart run wasm_wit_component:generate your_package_wasm/wit/your-package.wit lib/src/your_package_wit.gen.dart

Loading and Testing the Dart Library