dart_meteor — a Meteor DDP client for Dart/Flutter

Connect your Flutter app to a Meteor backend over DDP. Designed to work seamlessly with StreamBuilder and FutureBuilder.

• Platforms: Dart VM, Flutter iOS/Android/Web
• Dart: 3.6 or newer
• Meteor: compatible with Meteor 2.x and 3.x servers (tested against Meteor 3.5.1)

Features

• Method calls with Future-based results
• Subscriptions and reactive collections as Streams
• Accounts: login with password/token, logout, password management
• Automatic reconnection with backoff, re-login and re-subscription
• App lifecycle aware: detects a connection that died while the device slept
• DateTime values are converted to/from EJSON $date automatically

Installation

Add the package to your pubspec.yaml:

dependencies:
  dart_meteor: ^4.1.0

Quick start

Create a single MeteorClient instance in your app's global scope so you can use it anywhere in your project. The client connects immediately and keeps the connection alive:

import 'package:flutter/material.dart';
import 'package:dart_meteor/dart_meteor.dart';

final meteor = MeteorClient.connect(url: 'https://yourdomain.com');

void main() => runApp(MyApp());

The url may be https://… or wss://…; the client appends the /websocket DDP endpoint for you.

Then build widgets from the client's streams:

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: const Text('dart_meteor example')),
        body: Column(
          children: [
            // Show the live connection status.
            StreamBuilder<DdpConnectionStatus>(
              stream: meteor.status(),
              builder: (context, snapshot) {
                if (!snapshot.hasData) return const Text('Status: ---');
                return Text('Status: ${snapshot.data}');
              },
            ),
            // Show a login/logout button depending on the current user.
            StreamBuilder<String?>(
              stream: meteor.userId(),
              builder: (context, snapshot) {
                if (snapshot.data != null) {
                  return ElevatedButton(
                    onPressed: () => meteor.logout(),
                    child: const Text('Logout'),
                  );
                }
                return ElevatedButton(
                  onPressed: () =>
                      meteor.loginWithPassword('username', 'password'),
                  child: const Text('Login'),
                );
              },
            ),
          ],
        ),
      ),
    );
  }
}

A complete runnable app is in /example: a Flutter chat client (iOS, Android and Web) that connects to the live demo server at https://simple-meteor-chat.tanutapi.dev and exercises login, subscriptions, collections and method calls. There is also a longer walk-through covering connection status, authentication, and subscriptions in this Medium post.

Method calls

meteor.call() returns a Future. Always handle errors — an unhandled MeteorError will otherwise crash your app:

try {
  final result = await meteor.call('sumMethod', args: [5, 10]);
  print('Answer is $result'); // 15
} on MeteorError catch (err) {
  print('${err.error}: ${err.reason}');
}

Arguments are optional — meteor.call('helloMethod') works too. A DateTime anywhere in the arguments or the result is converted to/from Meteor's EJSON date format automatically.

Method calls also fit naturally into a FutureBuilder:

FutureBuilder<dynamic>(
  future: meteor.call('sumMethod', args: [5, 10]),
  builder: (context, snapshot) {
    if (snapshot.hasError) return Text('Error: ${snapshot.error}');
    if (!snapshot.hasData) return const CircularProgressIndicator();
    return Text('Answer is: ${snapshot.data}');
  },
),

Subscriptions and collections

Subscribe to a publication on the server, and read the documents it publishes through meteor.collection():

class YourWidget extends StatefulWidget {
  const YourWidget({super.key});

  @override
  State<YourWidget> createState() => _YourWidgetState();
}

class _YourWidgetState extends State<YourWidget> {
  late SubscriptionHandler _subscription;

  @override
  void initState() {
    super.initState();
    _subscription = meteor.subscribe('your_pub', args: ['param_1', 'param_2']);
  }

  @override
  void dispose() {
    _subscription.stop();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return StreamBuilder<Map<String, dynamic>>(
      stream: meteor.collection('your_collection'),
      builder: (context, snapshot) {
        final docCount = snapshot.data?.length ?? 0;
        return Text('Total document count: $docCount');
      },
    );
  }
}

Details worth knowing:

• meteor.subscribe() returns a SubscriptionHandler with stop() and a ready() stream that emits true once the server has sent the initial batch of documents. Optional onReady and onStop callbacks are also supported. Subscriptions are re-established automatically after a reconnect.
• meteor.collection() returns a stream backed by an rxdart BehaviorSubject: every new listener immediately receives the latest value, so a StreamBuilder starts with snapshot.hasData == true and an empty map before any documents arrive.
• The emitted value is a Map<String, dynamic> keyed by document _id, with the whole document as the value:

{
  "DGbsysgxzSf7Cr8Jg": {
    "_id": "DGbsysgxzSf7Cr8Jg",
    "field1": 0,
    "field2": "a",
    "field3": true,
    "field4": "2020-08-30T16:15:57.000Z" // delivered as a Dart DateTime
  }
}

There is no minimongo on the client. Use plain Dart collection operations (where, map, reduce, …) to query the map — they cover the same ground as minimongo queries in the Meteor web client.

Looking up a document by id

Since the collection is a map keyed by _id, a lookup is just an index operation:

// Non-reactive read of a document by its id.
final doc = meteor.collectionCurrentValue('your_collection_name')?['DGbsysgxzSf7Cr8Jg'];
if (doc != null) {
  // do something
}

// The same works for users.
final user = meteor.collectionCurrentValue('users')?['Sf7Cr8JgDGbsysgxz'];

Reading current values without a stream

When you only need the latest value for a condition check — not a reactive rebuild — every major stream has a non-reactive counterpart:

Reactive stream	Current value
meteor.collection(name)	meteor.collectionCurrentValue(name)
meteor.user()	meteor.userCurrentValue()
meteor.userId()	meteor.userIdCurrentValue()

Accounts

// Log in (works with a username or an email address; the password is sent
// as a SHA-256 digest, never in plain text).
final result = await meteor.loginWithPassword('user_or_email', 'password');

// Resume a session with a saved token, e.g. after an app restart.
await meteor.loginWithToken(token: result.token, tokenExpires: result.tokenExpires);

// Log out.
await meteor.logout();

Related APIs: meteor.user(), meteor.userId(), meteor.loggingIn(), and meteor.logInStatus() are reactive streams of the current account state; logoutOtherClients(), changePassword(), forgotPassword(), and resetPassword() cover the rest of the standard accounts flows. After a reconnect the client re-authenticates automatically using its stored token.

Connection management

meteor.status();     // Stream<DdpConnectionStatus>: connected/connecting/failed/waiting/offline
meteor.reconnect();  // force a reconnection attempt if not connected
meteor.disconnect(); // close the connection and stop reconnecting

While connected, the client exchanges DDP ping/pong with the server and reconnects when the connection is considered dead, backing off between attempts (0s, 5s, 10s, … up to maxRetryInterval) so an unreachable server does not keep the radio busy. disconnect() is final: the client stays offline until you call reconnect().

The timings are configurable if the defaults do not suit your server:

final meteor = MeteorClient.connect(
  url: 'https://yourdomain.com',
  pingInterval: const Duration(seconds: 20),
  pongTimeout: const Duration(seconds: 5),
  maxRetryInterval: const Duration(seconds: 30),
  stalenessThreshold: const Duration(seconds: 25),
);

App lifecycle (mobile)

When a phone sleeps, the OS suspends the process: Dart timers stop firing, and the server can drop the session without the socket ever reporting an error. The app then wakes up believing it is still connected, and stays that way until the next ping happens to time out.

dart_meteor is a pure Dart package, so it does not watch Flutter's lifecycle itself. Forward it from a WidgetsBindingObserver — this is the whole integration:

class _MyAppState extends State<MyApp> with WidgetsBindingObserver {
  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
  }

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    super.dispose();
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    if (state == AppLifecycleState.resumed) {
      meteor.notifyAppResumed();
    } else {
      meteor.notifyAppPaused();
    }
  }
}

On resume the client measures by wall clock how long it was actually away rather than trusting its timers. If the connection has been silent longer than stalenessThreshold it is torn down and replaced immediately, re-resuming the login and re-subscribing. While paused, the client will not tear down a connection just because a timer fired late.

meteor.checkLiveness() runs the same check on demand — useful if your app learns from somewhere else (a connectivity plugin, say) that the network may have changed.

The example app wires this up in lib/main.dart.

Error handling

Server-side Meteor.Errors are thrown as MeteorError, which exposes error, reason, message, details, errorType, and isClientSafe — the same fields you get in a Meteor web client.

A call that was still in flight when the connection dropped — because the device slept, or the network went away — throws MeteorConnectionError instead. The two are worth distinguishing: MeteorError means the server considered the request and said no, while MeteorConnectionError means you never heard back and the method may or may not have run.

try {
  await meteor.call('sendMessage', args: ['hello']);
} on MeteorError catch (err) {
  // The server rejected it.
} on MeteorConnectionError catch (err) {
  // Never got a reply — offer a retry.
}

Calls are not resent automatically after a reconnect: a method like sendMessage is not safe to run twice, so whether to retry is left to you.

Upgrading

See CHANGELOG.md for the full history. The notable breaking changes:

• 4.1.0 — two behaviour changes worth knowing about, both fixes. A method call that is in flight when the connection drops now throws MeteorConnectionError instead of hanging forever, so await meteor.call(…) can now throw where it previously never returned. And reconnect attempts now back off instead of retrying immediately.
• 4.0.0 — requires Dart 3.6+; verified against Meteor 3.x (incl. 3.5.1); web support via web_socket_channel. The DdpClient.PING_SEC_INTERVAL and DdpClient.PONG_WITHIN_SEC fields were renamed to the static constants DdpClient.pingIntervalSeconds and DdpClient.pongTimeoutSeconds.
• 3.0.0 — meteor.collection() streams start with snapshot.hasData == true and an empty map instead of no data.
• 2.0.0 — method/subscription arguments became a named parameter: meteor.call('method', args: [...]), meteor.subscribe('pub', args: [...]) (both optional). prepareCollection() is no longer needed — just call meteor.collection(). DateTime values are supported directly.

Features and bugs

Please file feature requests and bugs at the issue tracker.