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Publish/Subscribe API for Dart SDK

PubNub delivers messages worldwide in less than 30 ms. Send a message to one recipient or broadcast to thousands of subscribers.

For higher-level conceptual details on publishing and subscribing, refer to Connection Management and to Publish Messages.

Publish

publish() sends a message to all channel subscribers. PubNub replicates the message across its points of presence and delivers it to all subscribed clients on that channel.

You must initialize PubNub with the publishKey.
You don't have to be subscribed to a channel to publish to it.
You cannot publish to multiple channels simultaneously.

Secure messages with Transport Layer Security (TLS) or Secure Sockets Layer (SSL) by setting ssl to true during initialization. You can also encrypt messages.

The message can contain any JavaScript Object Notation (JSON)-serializable data (objects, arrays, integers, strings). Avoid special classes or functions. Strings can include any UTF‑8 characters.

Don't JSON serialize

You should not JSON serialize the message and meta parameters when sending signals, messages, or files as the serialization is automatic. Pass the full object as the message/meta payload and let PubNub handle everything.

The maximum message size is 32 KiB. This includes the escaped character count and the channel name. Aim for under 1,800 bytes for optimal performance.

If your message exceeds the limit, you'll receive a Message Too Large error. To learn more or calculate payload size, see Message size limits.

You can optionally provide the customMessageType parameter to add your business-specific label or category to the message, for example text, action, or poll.

Publish to a channel serially (not concurrently).
Verify a success return code (for example, [1,"Sent","136074940..."]).
Publish the next message only after a success return code.
On failure ([0,"blah","<timetoken>"]), retry.
Keep the in-memory queue under 100 messages to avoid drops.
Throttle bursts to meet latency needs (for example, no more than 5 messages per second).

Method(s)

To Publish a message you can use the following method(s) in the Dart SDK:

1pubnub.publish(
String channel,
dynamic message,
{Keyset? keyset,
String? using,
dynamic meta,
bool? storeMessage,
int? ttl,
String? customMessageType}
10) 

* required

Parameter	Description
`channel` * Type: `String` Default: n/a	Destination of the `message` (channel ID).
`message` * Type: `Any` Default: n/a	The payload.
`keyset` Type: `Keyset` Default: n/a	Override for the PubNub default keyset configuration.
`using` Type: `String` Default: n/a	Keyset name from the `keysetStore` to be used for this method call.
`meta` Type: `dynamic` Default: Not set	Metadata object which can be used with the filtering ability.
`storeMessage` Type: `bool` Default: Account default	Store message in history. If not specified, the decision depends on whether Message Persistence has been enabled for the key or not.
`ttl` Type: `int` Default: n/a	Set a per message time to live in Message Persistence. 1. If `storeMessage = true`, and `ttl = 0`, the message is stored with no expiry time. 2. If `storeMessage = true` and `ttl = X` (`X` is an Integer value), the message is stored with an expiry time of `X` hours unless you have message retention set to `Unlimited` on your keyset configuration in the Admin Portal. 3. If `storeMessage = false`, the `ttl` parameter is ignored. 4. If `ttl` isn't specified, then expiration of the message defaults back to the expiry value for the key.
`customMessageType` Type: `String` Default: n/a	A case-sensitive, alphanumeric string from 3 to 50 characters describing the business-specific label or category of the message. Dashes `-` and underscores `_` are allowed. The value cannot start with special characters or the string `pn_` or `pn-`. Examples: `text`, `action`, `poll`.

Sample code

Reference code

This example is a self-contained code snippet ready to be run. It includes necessary imports and executes methods with console logging. Use it as a reference when working with other examples in this document.

Publish a message to a channel:

1import 'package:pubnub/pubnub.dart';
2

3void main() async {
// Create PubNub instance with default keyset.
var pubnub = PubNub(
  defaultKeyset: Keyset(
    subscribeKey: 'demo',
    publishKey: 'demo',
    userId: UserId('myUniqueUserId'),
  ),
);
12

// Channel to publish the message to
String channel = 'myChannel';
15

// Message to publish
String message = 'hello world!';
18

try {
  // Publish the message
  var result = await pubnub.publish(
    channel,
    message,
    customMessageType: 'text-message',
  );
26

  // Print the publish result
  print('Message "${result.description}" with timetoken: ${result.timetoken}');
} catch (e) {
  print('Error publishing message: $e');
}
32}
show all 32 lines

Returns

The publish() operation returns a PublishResult which contains the following operations:

Method	Description
`description` Type: `String`	The description, for example `Sent`.
`timetoken` Type: `int`	Returns an `int` representation of the timetoken when the message was published.

Other examples

Publish with metadata

1var result = await pubnub.publish('my_channel', 'hello', meta: '<json data>', customMessageType: 'text-message');

Publishing JsonObject (Google GSON)

1var message = {'hello': 'world'};
2var result = await pubnub.publish('my_channel', message, customMessageType: 'text-message');

Publishing JsonArray (Google GSON)

1var message = ['hello', 'world'];
2var result = await pubnub.publish('my_channel', message, customMessageType: 'text-message');

Publishing JSONObject (org.json)

1var jsonString = '{"score": 40}';
2var result = await pubnub.publish('my_channel', jsonDecode(jsonString), customMessageType: 'text-message');

Publishing JSONArray (org.json)

1var jsonString = '''
2[
3  {"score": 40},
4  {"score": 80}
5]
6''';
7var result = await pubnub.publish('my_channel', jsonDecode(jsonString), customMessageType: 'text-message');

Store the published message for 10 hours

1var result =
2    await pubnub.publish('my_channel', 'hello', storeMessage: true, ttl: 10, customMessageType: 'text-message');

Signal

The signal() function sends a signal to all subscribers of a channel.

By default, signals are limited to a message payload size of 64 bytes. This limit applies only to the payload, and not to the URI or headers. If you require a larger payload size, please contact support.

Method(s)

To Signal a message you can use the following method(s) in the Dart SDK:

1pubnub.signal(
String channel,
dynamic message,
{Keyset? keyset,
String? using,
String? customMessageType}
7) 

* required

Parameter	Description
`channel` * Type: `String`	Destination of the `message` (channel ID).
`message` * Type: `Any`	The payload.
`keyset` Type: `Keyset`	Override for the PubNub default keyset configuration.
`using` Type: `String`	Keyset name from the `keysetStore` to be used for this method call.
`customMessageType` Type: `String`	A case-sensitive, alphanumeric string from 3 to 50 characters describing the business-specific label or category of the message. Dashes `-` and underscores `_` are allowed. The value cannot start with special characters or the string `pn_` or `pn-`. Examples: `text`, `action`, `poll`.

Sample code

Signal a message to a channel:

1var result = await pubnub.signal('myChannel', 'signal!', customMessageType: 'text-message');

Response

The signal() operation returns a SignalResult which contains the following operations:

Method	Description
`description` Type: `String`	The description, for example `Sent`.
`timetoken` Type: `int`	Returns an `int` representation of the timetoken when the signal was published.

Receive messages

Your app receives messages and events via event listeners. The event listener is a single point through which your app receives all the messages, signals, and events that are sent in any channel you are subscribed to.

For more information about adding a listener, refer to the Subscription section.

Description

This function causes the client to create an open TCP socket to the PubNub Real-Time Network and begin listening for messages on a specified channel ID. To subscribe to a channel ID the client must send the appropriate subscribeKey at initialization.

By default a newly subscribed client will only receive messages published to the channel after the subscribe() call completes.

If a client gets disconnected from a channel, it can automatically attempt to reconnect to that channel ID and retrieve any available messages that were missed during that period. This can be achieved by setting retryPolicy to RetryPolicy.linear, when initializing the client.

Unsubscribing from all channels

Unsubscribing from all channels, and then subscribing to a new channel Y is not the same as subscribing to channel Y and then unsubscribing from the previously subscribed channel(s). Unsubscribing from all channels resets the last-received timetoken and thus, there could be some gaps in the subscription that may lead to message loss.

Method(s)

To Subscribe to a channel you can use the following method(s) in the Dart SDK:

1pubnub.subscribe(
{Set<String>? channels,
Set<String>? channelGroups,
bool withPresence = false,
Timetoken? timetoken,
Keyset? keyset,
String? using}
8) 

* required

Parameter	Description
`channels` * Type: `Set<String>`	`channels` to subscribe to. Either `channel` ID or `channelGroup` is required.
`channelGroups` * Type: `Set<String>`	`channelGroups` to subscribe to. Either `channel` ID or `channelGroup` is required.
`withPresence` Type: `bool`	Also subscribe to related presence information. For information on how to receive presence events and what those events are, refer to Presence Events.
`timetoken` Type: `Timetoken`	Timetoken to start the subscription from.
`keyset` Type: `Keyset`	Override for the PubNub default keyset configuration.
`using` Type: `String`	Keyset name from the `keysetStore` to be used for this method call.

Sample code

Subscribe to a channel:

1var channel = "my_channel";
2var subscription = pubnub.subscribe(channels: {channel});

Returns

The subscribe() method returns a Subscription. For more information, refer to Subscription.

Subscription

A Subscription contains a Dart stream of messages from the channel(s) to which you are subscribed. You can transform that stream in the usual ways, or add a listener using listen.

Listeners

For a list of available listeners, refer to the Listeners section.

Cancel

The cancel() method cancels the subscription. This disposes of internal streams, so the subscription becomes unusable.

Method(s)

1subscription.cancel();

Sample code

1// var subscription = pubnub.subscribe(channels: {'my_channel'});
2// active subscription available
3await subscription.cancel();

Returns

The cancel() operation on Subscription doesn't return any object. It disposes of internal streams, so the subscription becomes unusable.

Dispose

The dispose() method is an alias for the cancel() method.

The subscribe() method is an alias for the resume() method with additional reconnection logic. If the subscription is not intentionally paused, it reconnects the subscription. Otherwise, it resumes the subscription.

Method(s)

1subscription.subscribe()

Sample code

1var subscription = pubnub.subscription(channels: {'my_channel'});
2// Later, activate the subscription
3subscription.subscribe();

Unsubscribe

The unsubscribe() method is an alias for the pause() method.

Pause

Pausing a subscription prevents the message and presence streams from emitting messages. Keep in mind that you may miss messages while subscription is paused. If subscription is currently paused, this method is a no-op.

Method(s)

1subscription.pause() 

Sample code

1var subscription = pubnub.subscribe(channels: {'my_channel'});
2// active subscription available
3subscription.pause();

Returns

The pause() operation on Subscription doesn't return any object. Pausing subscription prevents the messages and presence streams from emitting messages.

Resume

Resumes a paused subscription. If a subscription isn't paused, then this method is a no-op.

Method(s)

1subscription.resume() 

Sample code

1// If subscription is paused
2subscription.resume();

Returns

The resume() operation on Subscription object doesn't return any object. If subscription isn't paused, then this method does nothing.

Restore

Restores the subscription. This method is useful when a subscription encounters an error and you want to recover without creating a new subscription.

Method(s)

1subscription.restore()

Sample code

1var subscription = pubnub.subscribe(channels: {'my_channel'});
2

3subscription.messages.listen(
4  (message) {
5    print('Received: ${message.content}');
6  },
7  onError: (error) async {
8    print('Error occurred: $error');
9    // Restore the subscription after an error
10    await subscription.restore();
11  }
12);

Returns

The restore() operation returns a Future<void> that completes when the subscription has been restored.

Other examples

1// Create a root logger
2var logger = StreamLogger.root('root', logLevel: Level.all);
3

4// Subscribe to messages with a default printer
5var sub = logger.stream.listen(
6    LogRecord.createPrinter(r'[$time] (${level.name}) $scope: $message'));
7

8// Provide logging only for the parts that you are interested in.
9var _ = await provideLogger(logger, () async {
10  var subscription = pubnub.subscribe(channels: {'test'});
11

12  var message = subscription.messages.first;
13

14  await pubnub.publish('test', {'message': 'My message'});
15

16  print(await message);
17

18  await subscription.dispose();
19});
show all 19 lines

Unsubscribe from all channels

Cancels all existing subscriptions across all keysets.

1// Create subscriptions
2var subscription1 = pubnub.subscribe(channels: {'channel1'});
3var subscription2 = pubnub.subscribe(channels: {'channel2', 'channel3'});
4

5// Later, unsubscribe from all channels
6await pubnub.unsubscribeAll();

Unsubscribing from all channels

Unsubscribing from all channels resets the last-received timetoken.

Subscribing to multiple channels

It's possible to subscribe to more than one channel using the Multiplexing feature. The example shows how to do that using an array to specify the channel names.

Alternative subscription methods

You can also use Wildcard Subscribe and Channel Groups to subscribe to multiple channels at a time. To use these features, the Stream Controller add-on must be enabled on your keyset in the Admin Portal.

1var subscription = pubnub.subscribe(channels: {'my_channel', 'channel1'});

Subscribing to a presence channel

Requires Presence

This method requires that the Presence add-on is enabled for your key in the Admin Portal.

For information on how to receive presence events and what those events are, refer to Presence Events.

For any given channel there is an associated Presence channel. You can subscribe directly to the channel by appending -pnpres to the channel name. For example the channel named my_channel would have the presence channel named my_channel-pnpres. Presence data can be observed inside the SubscribeCallback#message(PubNub, PNMessageResult) callback.

1var subscription =
2    pubnub.subscribe(channels: {'my_channel'}, withPresence: true);

Sample Responses

Join event

1{
  "Event": "join",
  "Uuid": "175c2c67-uuid-uuid-8f4b-1db94f90e39e",
  "Timestamp": 1345546797,
  "Occupancy": 2,
  "State": null,
  "Channel":" my_channel",
  "Subscription": "",
  "Timetoken": 15034141109823424,
  "UserMetadata": null,
  "Join": null,
  "Timeout": null,
  "Leave": null,
  "HereNowRefresh": false
15}

Leave event

1{
  "Event": "leave",
  "Uuid": "175c2c67-uuid-uuid-8f4b-1db94f90e39e",
  "Timestamp": 1345546797,
  "Occupancy": 1,
  "State": null,
  "Channel": "my_channel",
  "Subscription": "",
  "Timetoken": 15034141109823424,
  "UserMetadata": null,
  "Join": null,
  "Timeout": null,
  "Leave": null,
  "HereNowRefresh": false
15}

Timeout event

1{
"Event": "timeout",
"Uuid": "175c2c67-uuid-uuid-8f4b-1db94f90e39e",
"Timestamp": 1345546797,
"Occupancy": 0,
"State": null,
"Channel": "my_channel",
"Subscription": "",
"Timetoken": 15034141109823424,
"UserMetadata": null,
"Join": null,
"Timeout": null,
"Leave": null,
"HereNowRefresh": false
15} 

State change event

1{
"Event":  "state-change",
"Uuid":  "175c2c67-uuid-uuid-8f4b-1db94f90e39e",
"Timestamp": 1345546797,
"Occupancy": 1,
"State": {
    "isTyping": true
},
"Channel":  "my_channel",
"Subscription":  "",
"Timetoken": 15034141109823424,
"UserMetadata": null,
"Join": null,
"Timeout": null,
"Leave": null,
"HereNowRefresh": false
17}
show all 17 lines

Interval event

1{
  "Event": "interval",
  "Uuid": "175c2c67-uuid-uuid-8f4b-1db94f90e39e",
  "Timestamp": 1345546797,
  "Occupancy": 2,
  "State": null,
  "Channel": "my_channel",
  "Subscription": "",
  "Timetoken": 15034141109823424,
  "UserMetadata": null,
  "Join": null,
  "Timeout": null,
  "Leave": null,
  "HereNowRefresh": false
15}

When a channel is in interval mode with presence_deltas pnconfig flag enabled, the interval message may also include the following fields which contain an array of changed UUIDs since the last interval message. This settings can be altered in the Admin Portal.

joined
left
timed out

For example, this interval message indicates there were 2 new UUIDs that joined and 1 timed out UUID since the last interval:

1{
  "Event": "interval",
  "Uuid": "175c2c67-uuid-uuid-8f4b-1db94f90e39e",
  "Timestamp": <unix timestamp>,
  "Occupancy": <# users in channel>,
  "State": null,
  "Channel": "my_channel",
  "Subscription": "",
  "Timetoken": 15034141109823424,
  "UserMetadata": null,
  "Join": ["uuid2", "uuid3"],
  "Timeout": ["uuid1"],
  "Leave": null,
  "HereNowRefresh": false
15}

If the full interval message is greater than 30KiB (since the max publish payload is ∼32KiB), none of the extra fields will be present. Instead, there will be a here_now_refresh Boolean field set to true. This indicates to the user that they should do a hereNow request to get the complete list of users present in the channel.

1{
  "Event": "interval",
  "Uuid": "175c2c67-uuid-uuid-8f4b-1db94f90e39e",
  "Timestamp": <unix timestamp>,
  "Occupancy": <# users in channel>,
  "State": null,
  "Channel": "my_channel",
  "Subscription": "",
  "Timetoken": 15034141109823424,
  "UserMetadata": null,
  "Join": null,
  "Timeout": null,
  "Leave": null,
  "HereNowRefresh": true
15}

Requires Stream Controller add-on

This method requires that the Stream Controller add-on is enabled for your key in the Admin Portal (with Enable Wildcard Subscribe checked). Read the support page on enabling add-on features on your keys.

Wildcard subscribes allow the client to subscribe to multiple channels using wildcard. For example, if you subscribe to a.* you will get all messages for a.b, a.c, a.x. The wildcarded * portion refers to any portion of the channel string name after the dot (.).

1var subscription = pubnub.subscribe(channels: {'foo.*'});

Wildcard grants and revokes

Only one level (a.*) of wildcarding is supported. If you grant on * or a.b.*, the grant will treat * or a.b.* as a single channel named either * or a.b.*. The same rule applies to revokes - you can revoke permissions with wildcards from one level deep, like a.*. However, you can do that only if you initially used wildcards to grant permissions to a.*.

Requires Stream Controller add-on

This method requires that the Stream Controller add-on is enabled for your key in the Admin Portal. Read the support page on enabling add-on features on your keys.

1var subscription = pubnub.subscribe(channelGroups: {'cg1'});

Requires Stream Controller add-on

This method requires that the Stream Controller add-on is enabled for your key in the Admin Portal. Read the support page on enabling add-on features on your keys.

1var subscription =
2    pubnub.subscribe(channelGroups: {'cg1', 'cg2'}, withPresence: true);

Publish​

Don't JSON serialize

Method(s)​

Sample code​

Reference code

Returns​

Other examples​

Publish with metadata​

Publishing JsonObject (Google GSON)​

Publishing JsonArray (Google GSON)​

Publishing JSONObject (org.json)​

Publishing JSONArray (org.json)​

Store the published message for 10 hours​

Signal​

Method(s)​

Sample code​

Response​

Subscribe​

Receive messages​

Description​

Unsubscribing from all channels

Method(s)​

Sample code​

Returns​

Subscription​

Listeners​

Cancel​

Method(s)​

Sample code​

Returns​

Dispose​

Subscribe​

Method(s)​

Sample code​

Unsubscribe​

Pause​

Method(s)​

Sample code​

Returns​

Resume​

Method(s)​

Sample code​

Returns​

Restore​

Method(s)​

Sample code​

Returns​

Other examples​

Basic subscribe with logging​

Unsubscribe from all channels​

Unsubscribing from all channels

Subscribing to multiple channels​

Alternative subscription methods

Subscribing to a presence channel​

Requires Presence

Sample Responses​

Join event​

Leave event​

Timeout event​

State change event​

Interval event​

Wildcard subscribe to channels​

Requires Stream Controller add-on

Wildcard grants and revokes

Subscribe to a channel group​

Requires Stream Controller add-on

Subscribe to the presence channel of a channel group​

Requires Stream Controller add-on

Publish

Method(s)

Sample code

Returns

Other examples

Publish with metadata

Publishing JsonObject (Google GSON)

Publishing JsonArray (Google GSON)

Publishing JSONObject (org.json)

Publishing JSONArray (org.json)

Store the published message for 10 hours

Signal

Method(s)

Sample code

Response

Subscribe

Receive messages

Description

Method(s)

Sample code

Returns

Subscription

Listeners

Cancel

Method(s)

Sample code

Returns

Dispose

Subscribe

Method(s)

Sample code

Unsubscribe

Pause

Method(s)

Sample code

Returns

Resume

Method(s)

Sample code

Returns

Restore

Method(s)

Sample code

Returns

Other examples

Basic subscribe with logging

Unsubscribe from all channels

Subscribing to multiple channels

Subscribing to a presence channel

Sample Responses

Join event

Leave event

Timeout event

State change event

Interval event

Wildcard subscribe to channels

Subscribe to a channel group

Subscribe to the presence channel of a channel group