dart_monty 0.3.4

Dart and Flutter bindings for Monty, a Rust-built embeddable sandbox that runs a restricted subset of Python. Native FFI and browser WASM.

dart_monty

Live Demo — try it in your browser

Flutter plugin that exposes the Monty sandboxed Python interpreter to Dart and Flutter apps.

Run Python code from Dart — on desktop, mobile, and web — with resource limits, iterative execution, and snapshot/restore support.

Platform Support

Platform	Status
macOS	Supported
Linux	Supported
Web (browser)	Supported
Windows	Planned
iOS	Planned
Android	Planned

Installation

flutter pub add dart_monty

Usage

import 'package:dart_monty/dart_monty.dart';

// Simple execution
final monty = MontyPlatform.instance;
final result = await monty.run('2 + 2');
print(result.value); // 4

// With resource limits
final limited = await monty.run(
  'fib(30)',
  limits: MontyLimits(timeoutMs: 5000, memoryBytes: 10 * 1024 * 1024),
);

// Iterative execution (external functions)
var progress = await monty.start(
  'fetch("https://example.com")',
  externalFunctions: ['fetch'],
);

if (progress is MontyPending) {
  print('Python called: ${progress.functionName}');
  progress = await monty.resume(myResult);
}

final complete = progress as MontyComplete;
print(complete.result.value);

// Error injection
progress = await monty.resumeWithError('network timeout');

// Cleanup
await monty.dispose();

Architecture

Federated plugin with six packages:

Package	Type	Description
dart_monty	Flutter plugin	App-facing API
dart_monty_platform_interface	Pure Dart	Abstract contract — no Flutter dependency
dart_monty_ffi	Pure Dart	Native FFI bindings (dart:ffi -> Rust)
dart_monty_wasm	Pure Dart	WASM bindings (dart:js_interop -> Web Worker)
dart_monty_desktop	Flutter plugin	Desktop platform (macOS/Linux, Isolate)
dart_monty_web	Flutter plugin	Web platform (browser, script injection)

The three pure-Dart packages can be used without Flutter (e.g. in CLI tools or server-side Dart).

Native Path (desktop)

Dart app -> MontyDesktop (Isolate)
  -> MontyFfi (dart:ffi)
    -> libdart_monty_native.{dylib,so}
      -> Monty Rust interpreter

Web Path (browser)

Dart app (compiled to JS) -> DartMontyWeb
  -> MontyWasm (dart:js_interop)
    -> Web Worker -> @pydantic/monty WASM

The Web Worker architecture bypasses Chrome's 8 MB synchronous WASM compilation limit.

Web Setup

The web backend requires COOP/COEP HTTP headers for SharedArrayBuffer support:

Cross-Origin-Opener-Policy: same-origin
Cross-Origin-Embedder-Policy: require-corp

Contributing

See CONTRIBUTING.md for development setup, gate scripts, and CI details.

See PLAN.md for engineering milestones and quality gates.

License

MIT License. See LICENSE.