Dart Functions

Write serverless functions in Dart — the same language as your Flutter app. Deploy and invoke from the dashboard or directly from the SDK.

Available runtimes

deno

TypeScript / JavaScript

Default runtime. Full Deno 2 API, npm compatible.

dart

Dart

Flutter-native runtime. Write functions in the same language as your app.

Writing a Dart function

A Dart function must export an async handler function that accepts a context map and returns a map.

Future<Map<String, dynamic>> handler(Map<String, dynamic> ctx) async {
  // Access request body
  final body = ctx['request']['body'] as Map<String, dynamic>? ?? {};
  final name = body['name'] as String? ?? 'World';

  // Access database
  final db = ctx['db'] as Map<String, dynamic>;
  final records = await (db['find'] as Function)('users', {'active': true});

  return {
    'message': 'Hello, $name!',
    'user_count': (records['records'] as List?)?.length ?? 0,
  };
}

Function signature

The handler must be a top-level function named handler with the signature Future<Map<String, dynamic>> handler(Map<String, dynamic> ctx).

Using pub.dev packages

Dart functions can declare third-party dependencies via a pubspec.yaml file. Koolbase resolves them server-side at deploy time, caches the result, and makes packages available to your function's import 'package:...' statements.

Example: a function that imports package:crypto to compute a SHA-256 hash.

hash.dart

dart

import 'package:crypto/crypto.dart';
import 'dart:convert';

export const metadata = {
  title: 'Dart Runtime — Functions',
  description: 'Write serverless functions in Dart — the same language as your Flutter app. Deploy and invoke from the dashboard or directly from the SDK.',
}

Future<Map<String, dynamic>> handler(Map<String, dynamic> ctx) async {
  final input = ctx['request']?['body']?['text'] as String? ?? 'hello';
  final digest = sha256.convert(utf8.encode(input));
  return {'sha256': digest.toString()};
}

pubspec.yaml

yaml

name: hash_function
environment:
  sdk: ^3.0.0
dependencies:
  crypto: ^3.0.5

How resolution works

When you deploy a Dart function with a pubspec:

The pubspec content is hashed (SHA-256).
If that hash has been resolved before — across any project — the cached resolution is reused. Near-instant.
If new, dart pub get runs server-side with a 3-minute timeout. The resolved pubspec.lock is stored on the function record.
Two simultaneous deploys with the same pubspec serialize through a per-hash mutex — only one resolution runs.

CLI deploy with auto-detection

When deploying via the CLI, if a pubspec.yaml sits next to your source file, it's uploaded automatically:

terminal

bash

$ ls
hash.dart  pubspec.yaml

$ koolbase deploy hash-fn --file hash.dart --project proj_abc
Found pubspec.yaml — packages will be resolved server-side.
Deploying hash-fn (dart runtime)...

 Deployed hash-fn v1
   Runtime:  dart
   Timeout:  10000ms
   Project:  proj_abc
   Pubspec:  uploaded

Dashboard deploy

The deploy modal in the dashboard includes a runtime selector. Choosing Dart reveals an optional pubspec.yaml editor below the code editor. After deploy, the function detail view's Code tab includes a file switcher between index.dart and pubspec.yaml.

Requirements & limits

Must include name and environment.sdk fields.
Maximum pubspec size: 64 KB.
Resolved dependencies on disk must not exceed 500 MB.
Resolution timeout: 3 minutes for first-time resolution; cache hits are instant.
Pubspec is opt-in — Dart functions without one continue to run with dart:* built-ins only.

Not yet supported (v2)

Multi-line imports in your source file (rare in practice; use single-line form).
Private or custom pub registries.
Vulnerability scanning of declared dependencies.

For deeper coverage — failure modes, AES-GCM encryption, HMAC webhook signature verification, function version locking, and deploying via the SDK API — see the Dart Dependencies guide.

Context object

The ctx map contains everything your function needs:

Future<Map<String, dynamic>> handler(Map<String, dynamic> ctx) async {
  // Request data
  final request = ctx['request'] as Map<String, dynamic>;
  final body = request['body'] as Map<String, dynamic>? ?? {};
  final headers = request['headers'] as Map<String, dynamic>? ?? {};

  // Database helpers
  final db = ctx['db'] as Map<String, dynamic>;

  // Insert a record
  final record = await (db['insert'] as Function)('posts', {
    'title': 'Hello from Dart',
    'published': true,
  });

  // Query records
  final posts = await (db['find'] as Function)('posts', {'published': true}, 10);

  // Update a record
  await (db['update'] as Function)(record['id'], {'title': 'Updated'});

  // Delete a record
  await (db['delete'] as Function)(record['id']);

  return {'ok': true};
}

Deploy from dashboard

Go to your project in app.koolbase.com → Functions → New Function. Select Dart as the runtime, paste your code, and click Deploy.

Deploy from Flutter SDK

Deploy functions programmatically using the Flutter SDK. Requires an authenticated user session.

lib/deploy_function.dart

Dart

await Koolbase.functions.deploy(
  projectId: 'your-project-id',
  name: 'send-welcome-email',
  runtime: FunctionRuntime.dart,
  timeoutMs: 15000,
  code: r'''
    Future<Map<String, dynamic>> handler(Map<String, dynamic> ctx) async {
      final body = ctx['request']['body'] as Map<String, dynamic>? ?? {};
      final email = body['email'] as String?;

      // Send email logic here

      return {'sent': true, 'to': email};
    }
  ''',
);

Invoke from Flutter

Invoke any function regardless of runtime — the invoke() API is the same for both Deno and Dart functions.

lib/home_screen.dart

Dart

final result = await Koolbase.functions.invoke(
  'send-welcome-email',
  body: {
    'email': '[email protected]',
    'name': 'Kennedy',
  },
);

if (result.success) {
  print(result.data); // {'sent': true, 'to': '[email protected]'}
}

Invoke via REST API

curl -X POST https://api.koolbase.com/v1/sdk/functions/send-welcome-email \
  -H "Content-Type: application/json" \
  -H "x-api-key: pk_live_your_key" \
  -d '{"body": {"email": "[email protected]"}}'

Limits

Max execution time30 seconds

Max code size1 MB

Dart SDK version3.11.4

Network accessAllowed (HTTP/HTTPS)

File system accessNot allowed

DB triggersSupported — same as Deno functions