Publish/Subscribe API for PubNub Kotlin SDK

The foundation of the PubNub service is the ability to send a message and have it delivered anywhere in less than 100ms. Send a message to just one other person, or broadcast to thousands of subscribers at once.

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

Calling Kotlin methods

Most PubNub Kotlin SDK method invocations return an Endpoint object, which allows you to decide whether to perform the operation synchronously or asynchronously. You must choose one of these or the operation will not be performed at all.

For example, the following code is valid and will compile, but the publish won't be performed:

pubnub.publish(
message = "this sdk rules!",
channel = "my_channel"
)

To successfully publish a message, you must follow the actual method invocation with whether to perform it synchronously or asynchronously, for example:

pubnub.publish(
message = "this sdk rules!",
channel = "my_channel"
).async { result, status ->
if (status.error) {
// handle error
} else {
// handle successful method result
}
}

Publish

Description

The publish() function is used to send a message to all subscribers of a channel. To publish a message you must first specify a valid publishKey at initialization. A successfully published message is replicated across the PubNub Real-Time Network and sent simultaneously to all subscribed clients on a channel.

Messages in transit can be secured from potential eavesdroppers with SSL/TLS by setting ssl to true during initialization.

Publish Anytime

It's not required to be subscribed to a channel in order to publish to that channel.

Message Data

The message argument can contain any JSON serializable data, including: Objects, Arrays, Ints and Strings. data should not contain special classes or functions as these will not serialize. String content can include any single-byte or multi-byte UTF-8 character.

Don't JSON serialize

It is important to note that you should not JSON serialize when sending signals/messages via PUBNUB. Why? Because the serialization is done for you automatically. Instead, just pass the full object as the message payload. PubNub takes care of everything for you.

Message Size

The maximum number of characters per message is 32 KiB by default. The maximum message size is based on the final escaped character count, including the channel name. An ideal message size is under 1800 bytes which allows a message to be compressed and sent using single IP datagram (1.5 KiB) providing optimal network performance.

If the message you publish exceeds the configured size, you will receive the following message:

Message Too Large Error
["PUBLISHED",[0,"Message Too Large","13524237335750949"]]

For further details, check the support article.

Message Publish Rate

Messages can be published as fast as bandwidth conditions will allow. There is a soft limit based on max throughput since messages will be discarded if the subscriber can't keep pace with the publisher.

For example, if 200 messages are published simultaneously before a subscriber has had a chance to receive any messages, the subscriber may not receive the first 100 messages because the message queue has a limit of only 100 messages stored in memory.

Publishing to Multiple Channels

It is not possible to publish a message to multiple channels simultaneously. The message must be published to one channel at a time.

Publishing Messages Reliably

There are some best practices to ensure messages are delivered when publishing to a channel:

  • Publish to any given channel in a serial manner (not concurrently).
  • Check that the return code is success (for example, [1,"Sent","136074940..."])
  • Publish the next message only after receiving a success return code.
  • If a failure code is returned ([0,"blah","<timetoken>"]), retry the publish.
  • Avoid exceeding the in-memory queue's capacity of 100 messages. An overflow situation (aka missed messages) can occur if slow subscribers fail to keep up with the publish pace in a given period of time.
  • Throttle publish bursts in accordance with your app's latency needs, for example, Publish no faster than 5 msgs per second to any one channel.

Method(s)

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

pubnub.publish(
message: Any,
channel: String,
shouldStore: Boolean,
meta: Any,
queryParam: Map<String, String>,
usePost: Boolean,
ttl: Integer
).async { result, status -> }
ParameterTypeRequiredDefaultDescription
messageAnyYesThe payload
channelStringYesDestination of the message
shouldStoreBooleanOptionalaccount defaultStore message in history.
If not specified, the decision depends on whether storage has been enabled for the key or not.
metaAnyOptionalNot setMetadata object which can be used with the filtering ability.
queryParamMap<String, String>OptionalNot setOne or more query parameters to be passed to the server, for analytics purposes.
Overridden in case of conflicts with reserved PubNub parameters, such as UUID or instance_id. Accessible from the Admin Portal, and never returned in server responses.
usePostBooleanOptionalfalseUse HTTP POST to publish.
ttlIntegerOptionalSet a per message time to live in storage.
1. If shouldStore = true, and ttl = 0, the message is stored with no expiry time.
2. If shouldStore = true and ttl = X (X is an Integer value), the message is stored with an expiry time of X hours.
3. If shouldStore = 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.

Basic Usage

Publish a message to a channel:

pubnub.publish(
message = JsonObject().apply {
addProperty("lat", 32L)
addProperty("lng", 32L)
},
channel = "my_channel"
).async { result, status ->
if (!status.error) {
println("Publish timetoken ${result!!.timetoken}")
}
println("Status code ${status.statusCode}")
}
Subscribe to the channel

Before running the above publish example, either using the Debug Console or in a separate script running in a separate terminal window, subscribe to the same channel that is being published to.

Returns

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

MethodTypeDescription
timetokenLongReturns a Long representation of the timetoken when the message was published.

Other Examples

Publish with metadata

pubnub.publish(
message = mapOf("hello" to "there"),
channel = "my_channel",
shouldStore = true,
meta = mapOf("lang" to "en"),
usePost = true
).async { result, status ->
// handle publish result or error
}

Publishing JsonObject (Google GSON)

pubnub.publish(
message = JsonObject().apply {
addProperty("lat", 32L)
addProperty("lng", 32L)
},
channel = "my_channel"
).async { _, _ -> }

Publishing JsonArray (Google GSON)

pubnub.publish(
message = JsonArray().apply {
add(32L)
add(35L)
},
channel = "my_channel"
).async { _, _ -> }

Publishing JSONObject (org.json)

pubnub.publish(
message = JSONObject().apply {
put("lat", 32L)
put("lng", 32L)
},
channel = "my_channel"
).async { _, _ -> }

Publishing JSONArray (org.json)

pubnub.publish(
message = JSONArray().apply {
put(32L)
put(33L)
},
channel = "my_channel"
).async { _, _ -> }

Store the published message for 10 hours

pubnub.publish(
message = "test",
channel = "my_channel",
shouldStore = true,
ttl = 10
).async { _, _ -> }

Fire

Description

The fire endpoint allows the client to send a message to PubNub Functions Event Handlers. These messages will go directly to any Event Handlers registered on the channel that you fire to and will trigger their execution. The content of the fired request will be available for processing within the Event Handler. The message sent via fire() isn't replicated, and so won't be received by any subscribers to the channel. The message is also not stored in history.

Method(s)

To Fire a message you can use the following method(s) in the Kotlin SDK:

pubnub.fire(
message: Any,
channel: String,
meta: Any,
usePost: Boolean
).async { result, status -> }
ParameterTypeRequiredDefaultDescription
messageAnyYesThe payload
channelStringYesDestination of the message
metaAnyOptionalNot setMetadata object which can be used with the filtering ability
usePostBooleanOptionalfalseUse POST to publish

Basic Usage

Fire a message to a channel:

pubnub.fire(
message = listOf("hello", "there"),
channel = "my_channel"
).async { result, status ->
if (status.error) {
// something bad happened
status.exception?.printStackTrace()
} else {
println("Fire worked! Timetoken ${result?.timetoken}")
}
}

Signal

Description

The signal() function is used to send 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 Kotlin SDK:

pubnub.signal(
message: Any,
channel: String
).async { result, status -> }
ParameterTypeRequiredDefaultDescription
messageAnyYesThe payload
channelStringYesDestination of the message

Basic Usage

Signal a message to a channel:

pubnub.signal(
message = "hello",
channel = "my_channel"
).async { result, status ->
if (!status.error) {
println("Timetoken: ${result?.timetoken}")
} else {
// handle error
status.exception?.printStackTrace()
}
}

Response

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

MethodTypeDescription
timetokenLongReturns a Long representation of the timetoken when the signal was published.

Subscribe

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 Event Listeners 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. To subscribe to a channel 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 and retrieve any available messages that were missed during that period. This can be achieved by setting setReconnectionPolicy to PNReconnectionPolicy.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 Kotlin SDK:

pubnub.subscribe(
channels: List<String>,
channelGroups: List<String>,
withTimetoken: Long,
withPresence: Boolean
)
ParameterTypeRequiredDescription
channelsList<String>OptionalSubscribe to channels. Either channel or channelGroup is required.
channelGroupsList<String>OptionalSubscribe to channelGroups. Either channel or channelGroup is required.
withTimetokenLongOptionalPass a timetoken.
withPresenceBooleanOptionalAlso subscribe to related presence information.

Basic Usage

Subscribe to a channel:

pubnub.subscribe(
channels = listOf("my_channel")
)
Event listeners

The response of the call is handled by adding a Listener. Please see the Listeners section for more details. Listeners should be added before calling the method.

Returns

PNMessageResult

PNMessageResult is returned in the Listeners.

The subscribe() operation returns a PNStatus which contains the following operations:

MethodTypeDescriptions
categoryPNStatusCategoryDetails of PNStatusCategory are here.
errorBooleanIs true in case of an error

The subscribe() operation returns a PNMessageResult for messages which contains the following operations:

MethodTypeDescriptions
messageJsonElementThe message sent on the channel
subscriptionString?The channel group or wildcard subscription match (if exists).
channelStringThe channel for which the message belongs
timetokenLong?Timetoken for the message
userMetadataJsonElement?User metadata

The subscribe() operation returns a PNPresenceEventResult for presence which contains the following operations:

MethodTypeDescriptions
eventStringEvents like join, leave, timeout, state-change, interval.
uuidStringUUID for the event
timestampLongTimestamp for the event
occupancyIntCurrent occupancy
stateJsonElement?State of the UUID
subscriptionStringThe channel group or wildcard subscription match (if exists)
channelStringThe channel of which the message belongs
timetokenLongTimetoken of the message
userMetadataAnyUser metadata

The subscribe() operation returns a PNSignalResult for signals which contains the following operations:

MethodTypeDescriptions
messageJsonElementThe signal sent on the channel
subscriptionStringThe channel group or wildcard subscription match (if exists)
channelStringThe channel of which the message belongs
timetokenLongTimetoken of the message
userMetadataAnyUser metadata

Other Examples

Basic subscribe with logging

val pnConfiguration = PNConfiguration().apply {
subscribeKey = "my_subkey"
publishKey = "my_pubkey"
logVerbosity = PNLogVerbosity.BODY
}

val pubnub = PubNub(pnConfiguration)

pubnub.subscribe(
channels = listOf("my_channel")
)

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.

pubnub.subscribe(
channels = listOf("ch1", "ch2") // subscribe to channels information
)

Subscribing to a Presence channel

Requires Presence add-on

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

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#presence(PubNub, PNPresenceResult) callback.

pubnub.subscribe(
channels = listOf("my_channel"), // subscribe to channels
withPresence = true // also subscribe to related presence information
)

Sample Responses

Join Event

if (presence.event == "join") {
presence.uuid // 175c2c67-b2a9-470d-8f4b-1db94f90e39e
presence.timestamp // 1345546797
presence.occupancy // # users in channel
}

Leave Event

if (presence.event == "leave") {
presence.uuid // 175c2c67-b2a9-470d-8f4b-1db94f90e39e
presence.timestamp // 1345546797
presence.occupancy // # users in channel
}

Timeout Event

if (presence.event == "timeout") {
presence.uuid // 175c2c67-b2a9-470d-8f4b-1db94f90e39e
presence.timestamp // 1345546797
presence.occupancy // # users in channel
}

Custom Presence Event (State Change)

if (presence.event == "state-change") {
presence.uuid // 175c2c67-b2a9-470d-8f4b-1db94f90e39e
presence.timestamp // 1345546797
presence.occupancy // # users in channel
presence.state?.asJsonObject // {"data":{"isTyping":true}}
}

Interval Event

if (presence.event == "interval") {
presence.uuid // 175c2c67-b2a9-470d-8f4b-1db94f90e39e
presence.timestamp // 1345546797
presence.occupancy // # users in channel
}

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
  • timedout

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

if (presence.event == "interval") {
presence.timestamp // 1345546797
presence.occupancy // # users in channel
presence.join // ["uuid1", "uuid2"]
presence.timeout // ["uuid3"]
}

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.

if (presence.event == "interval") {
presence.timestamp // 1345546797
presence.occupancy // # users in channel
presence.hereNowRefresh // true
}

Wildcard subscribe to channels

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 (.).

pubnub.subscribe(
channels = listOf("foo.*") // subscribe to channels information
)
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.*.

Subscribing with State

Requires Presence add-on

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

Required UUID

Always set the UUID to uniquely identify the user or device that connects to PubNub. This UUID should be persisted, and should remain unchanged for the lifetime of the user or the device. If you don't set the UUID, you won't be able to connect to PubNub.

val pnConfiguration = PNConfiguration().apply {
subscribeKey = "demo"
publishKey = "demo"
}

class ComplexData(
val fieldA: String,
val fieldB: Int
)

val pubnub = PubNub(pnConfiguration)

pubnub.addListener(object : SubscribeCallback() {
override fun status(pubnub: PubNub, status: PNStatus) {
if (status.category == PNStatusCategory.PNConnectedCategory) {
show all 29 lines

Subscribe to a channel group

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.

pubnub.subscribe(
channels = listOf("ch1", "ch2"), // subscribe to channels
channelGroups = listOf("cg1", "cg2"), // subscribe to channel groups
withTimetoken = 1337L, // optional, pass a timetoken
withPresence = true // also subscribe to related presence information
)

Subscribe to the presence channel of a channel group

Requires Stream Controller and Presence add-ons

This method requires both the Stream Controller and Presence add-ons are enabled for your key in the Admin Portal. Read the support page on enabling add-on features on your keys.

pubnub.subscribe(
channelGroups = listOf("cg1", "cg2"), // subscribe to channel groups
withTimetoken = 1337L, // optional, pass a timetoken
withPresence = true // also subscribe to related presence information
)

Unsubscribe

Description

When subscribed to a single channel, this function causes the client to issue a leave from the channel and close any open socket to the PubNub Network. For multiplexed channels, the specified channel(s) will be removed and the socket remains open until there are no more channels remaining in the list.

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 Unsubscribe from a channel you can use the following method(s) in the Kotlin SDK:

pubnub.unsubscribe(
channels: List<String>,
channelGroups: List<String>
)
ParameterTypeRequiredDescription
channelsList<String>OptionalUnsubscribe from channels. Either channel or channelGroup is required.
channelGroupsList<String>OptionalUnsubscribe from channelGroups. Either channel or channelGroup is required`.

Basic Usage

Unsubscribe from a channel:

pubnub.unsubscribe(
channels = listOf("my_channel") // subscribe to channel groups
)
Event listeners

The response of the call is handled by adding a Listener. Please see the Listeners section for more details. Listeners should be added before calling the method.

Response

The output below demonstrates the response to a successful call:

override fun presence(pubnub: PubNub, presence: PNPresenceEventResult) {
if (presence.event == "leave") {
presence.timestamp // 1345546797
presence.occupancy // 2
presence.uuid // left_uuid
}
}

Other Examples

Unsubscribing from multiple channels

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.

pubnub.unsubscribe(
channels = listOf("ch1", "ch2", "ch3"),
channelGroups = listOf("cg1", "cg2", "cg3")
)

Example response:

override fun presence(pubnub: PubNub, presence: PNPresenceEventResult) {
if (presence.event == "leave") {
presence.timestamp // 1345546797
presence.occupancy // 2
presence.uuid // left_uuid
}
}

Unsubscribing from a channel group

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.

pubnub.unsubscribe(
channelGroups = listOf("cg1", "cg2", "cg3")
)

Example response:

override fun presence(pubnub: PubNub, presence: PNPresenceEventResult) {
if (presence.event == "leave") {
presence.timestamp // 1345546797
presence.occupancy // 2
presence.uuid // left_uuid
}
}

Unsubscribe All

Description

Unsubscribe from all channels and all channel groups.

Method(s)

pubnub.unsubscribeAll()

Basic Usage

pubnub.unsubscribeAll()

Returns

None

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