Message Persistence API for PubNub Kotlin SDK

The message persistence service provides real-time access to the history of all messages published to PubNub. Each published message is timestamped to the nearest 10 nanoseconds and is stored across multiple availability zones in several geographical locations. Stored messages can be encrypted with AES-256 message encryption, ensuring that they are not readable while stored on PubNub's network. For more information, refer to Message Persistence.

Messages can be stored for a configurable duration or forever, as controlled by the retention policy that is configured on your account. The following options are available: 1, 3, 5, 7, 15, or 30 days, and Forever.

You can retrieve the following:

  • Messages
  • Message actions
  • Files (using Files API)
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
}
}

History

Requires Message Persistence add-on

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

Description

This function fetches historical messages of a channel.

It is possible to control how messages are returned and in what order, for example you can:

  • Search for messages starting on the newest end of the timeline (default behavior - reverse = false)
  • Search for messages from the oldest end of the timeline by setting reverse to true.
  • Page through results by providing a start OR end timetoken.
  • Retrieve a slice of the time line by providing both a start AND end timetoken.
  • Limit the number of messages to a specific quantity using the count parameter.
Start & End parameter usage clarity

If only the start parameter is specified (without end), you will receive messages that are older than and up to that start timetoken value. If only the end parameter is specified (without start) you will receive messages that match that end timetoken value and newer. Specifying values for both start and end parameters will return messages between those timetoken values (inclusive on the end value). Keep in mind that you will still receive a maximum of 100 messages even if there are more messages that meet the timetoken values. Iterative calls to history adjusting the start timetoken is necessary to page through the full set of results if more than 100 messages meet the timetoken values.

Method(s)

To run history(), you can use the following method(s) in the Kotlin SDK:

pubnub.history(
channel: String,
reverse: Boolean,
includeTimetoken: Boolean,
includeMeta: Boolean,
start: Long,
end: Long,
count: Int
).async { result, status -> }
ParameterTypeRequiredDefaultDescription
channelStringYesSpecifies channel to return history messages from.
reverseBooleanOptionalfalseSetting to true will traverse the time line in reverse starting with the oldest message first.
includeTimetokenBooleanOptionalfalseWhether event dates timetokens should be included in response or not.
includeMetaBooleanOptionalfalseWhether to include message metadata within response or not.
startLongOptionalTimetoken delimiting the start of time slice (exclusive) to pull messages from.
endLongOptionalTimetoken delimiting the end of time slice (inclusive) to pull messages from.
countIntOptional100Specifies the number of historical messages to return.
Default/Maximum is 100.
Using the reverse parameter:

Messages are always returned sorted in ascending time direction from history regardless of reverse. The reverse direction matters when you have more than 100 (or count, if it's set) messages in the time interval, in which case reverse determines the end of the time interval from which it should start retrieving the messages.

Basic Usage

Retrieve the last 100 messages on a channel:

pubnub.history(
channel = "history_channel", // where to fetch history from
count = 100 // how many items to fetch
).async { result, status -> }

Returns

The history() operation returns a PNHistoryResult which contains the following operations:

MethodTypeDescription
messagesList<PNHistoryItemResult>List of messages of type PNHistoryItemResult. See PNHistoryItemResult for more details.
startTimetokenLongStart timetoken.
endTimetokenLongEnd timetoken.

PNHistoryItemResult

MethodTypeDescription
timetokenLong?Timetoken of the message. Is null if not requested.
entryJsonElementMessage
metaJsonElement?Metadata of the message. Is null if not requested, otherwise an empty string if requested but no associated metadata.

Other Examples

Use history() to retrieve the three oldest messages by retrieving from the time line in reverse

pubnub.history(
channel = "my_channel", // where to fetch history from
count = 3, // how many items to fetch
reverse = true // should go in reverse?
).async { result, status -> }

Response:

if (!status.error) {
result!!.messages.forEach {
it.entry // custom JSON structure for message
}
}

Use history() to retrieve messages newer than a given timetoken by paging from oldest message to newest message starting at a single point in time (exclusive)

pubnub.history(
channel = "my_channel", // where to fetch history from
start = 13847168620721752L, // first timestamp
reverse = true // should go in reverse?
).async { result, status -> }

Response:

if (!status.error) {
result!!.messages.forEach {
it.entry // custom JSON structure for message
}
} else {
// handle error
status.exception?.printStackTrace()
}

Use history() to retrieve messages until a given timetoken by paging from newest message to oldest message until a specific end point in time (inclusive)

pubnub.history(
channel = "my_channel", // where to fetch history from
count = 100, // how many items to fetch
start = -1, // first timestamp
end = 13847168819178600L, // last timestamp
reverse = true // should go in reverse?
).async { result, status -> }

Response:

if (!status.error) {
result!!.messages // ["Pub3","Pub4","Pub5"]
result.startTimetoken // 13406746780720711
result.endTimetoken // 13406746845892666
}

History Paging Example

fun main() {
getAllMessages("my_channel", start = 0L, count = 10) { result ->
result.messages.forEach {
println(it.entry)
}
}
}

/**
* Fetches channel history in a recursive manner, in chunks of specified size, starting from the most recent,
* with every subset (with predefined size) sorted by the timestamp the messages were published.
*
* @param channel The channel where to fetch history from
* @param start The timetoken which the fetching starts from
* @param count Chunk size
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Include timetoken in history response

pubnub.history(
channel = "history_channel", // where to fetch history from
count = 10, // how many items to fetch]
includeTimetoken = true // include timetoken with each entry
).async { result, status ->
if (!status.error) {
result!!.messages.forEach {
it.entry // custom JSON structure for message
it.timetoken // requested message timetoken
}
}
}

Batch History

Requires Message Persistence add-on

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

Description

This function fetches historical messages from multiple channels. The includeMessageActions or includeActions flag also allows you to fetch message actions along with the messages.

It's possible to control how messages are returned and in what order. For example, you can:

  • Search for messages starting on the newest end of the timeline.
  • Search for messages from the oldest end of the timeline.
  • Page through results by providing a start OR end timetoken.
  • Retrieve a slice of the time line by providing both a start AND end timetoken.
  • Retrieve a specific (maximum) number of messages using the count parameter.

Batch history returns up to 100 messages on a single channel, or 25 per channel on a maximum of 500 channels. Use the start and end timestamps to page through the next batch of messages.

Start & End parameter usage clarity

If you specify only the start parameter (without end), you will receive messages that are older than the start timetoken.

If you specify only the end parameter (without start), you will receive messages from that end timetoken and newer.

Specify values for both start and end parameters to retrieve messages between those timetokens (inclusive of the end value).

Keep in mind that you will still receive a maximum of 100 messages (or 25, for multiple channels) even if there are more messages that meet the timetoken values. Iterative calls to history adjusting the start timetoken are necessary to page through the full set of results if more messages meet the timetoken values.

Method(s)

To run fetchMessages(), you can use the following method(s) in the Kotlin SDK:

pubnub.fetchMessages(
channels: List<String>,
page: PNBoundedPage,
includeMeta: Boolean,
includeMessageAction: Boolean
).async { result, status -> }
ParameterTypeRequiredDefaultDescription
channelsList<String>YesSpecifies channels to return history messages from.
pagePNBoundedPageOptionalThe paging object used for pagination. Set limit to specify the number of historical messages to return per channel.
If includeMessageActions is false, then 1 is the default (and maximum) value. Otherwise it's 25.
Set start to delimit the start of time slice (exclusive) to pull messages from.
Set end to delimit the end of time slice (inclusive) to pull messages from.
includeMetaBooleanOptionalfalseWhether to include message metadata within response or not.
includeMessageActionsBooleanOptionalfalseThe flag denoting to retrieve history messages with message actions. If true, the method is limited to one channel only.

Basic Usage

Retrieve the last 25 messages on a channel:

pubnub.fetchMessages(
channels = listOf("ch1"),
page = PNBoundedPage(limit = 25),
includeMessageActions = true,
includeMeta = true
).async { result, status ->
if (!status.error) {
result!!.channels.forEach { (channel, messages) ->
println("Channel: $channel")
messages.forEach { messageItem: PNFetchMessageItem ->
println(messageItem.message) // actual message payload
println(messageItem.timetoken) // included by default
messageItem.actions?.forEach { actionType, map ->
println("Action type: $actionType")
map.forEach { (actionValue, publishers) ->
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Returns

The fetchMessages() operation returns a map of channels and List<PNFetchMessagesResult> and PNBoundedPage object.

MethodTypeDescription
channelsHashMap<String, List<PNFetchMessageItem>>Map of channels and their respective lists of PNFetchMessageItem. See PNFetchMessageItem for more details.
pagePNBoundedPageIf exists indicates that more data is available. It can be passed directly to another call of fetchMessages to retrieve this remaining data.

PNFetchMessageItem

MethodTypeDescription
messageJsonElementMessage
timetokenLongTimetoken of the message. Always returned by default.
metaJsonElement?Metadata of the message. Is null if not requested, otherwise an empty string if requested but no associated metadata.
actionsMap<String, HashMap<String, List<Action>>>?The message actions associated with the message. Is null if not requested. The key of the map is the action type. The value is another map, which key is the actual value of the message action, and the key being a list of actions, ie. a list of UUIDs which have posted such a message action. See Action for more details.

Action

MethodTypeDescription
uuidStringThe UUID of the publisher.
actionTimetokenStringThe publish timetoken of the action.

Other Examples

Paging History Responses

fun main() {
getAllMessages(listOf("ch1", "ch2"), start = 0L) { result ->
result.channels.forEach { (channel, messages) ->
println("Channel $channel")
messages.forEach { item ->
println(item)
}
}
}
}

private fun getAllMessages(
channels: List<String>,
start: Long,
callback: (result: PNFetchMessagesResult) -> Unit
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Delete Messages from History

Requires Message Persistence add-on

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

Description

Removes the messages from the history of a specific channel.

Required setting

There is a setting to accept delete from history requests for a key, which you must enable by checking the Enable Delete-From-History checkbox in the key settings for your key in the Admin Portal.

Requires Initialization with secret key.

Method(s)

To deleteMessages() you can use the following method(s) in the Kotlin SDK.

pubnub.deleteMessages(
channels:P List<String>,
start: Long,
end: Long
).async { result, status -> }
ParameterTypeRequiredDefaultDescription
channelsList<String>YesSpecifies channels to delete messages from.
startLongOptionalTimetoken delimiting the start of time slice (inclusive) to delete messages from.
endLongOptionalTimetoken delimiting the end of time slice (exclusive) to delete messages from.

Basic Usage

pubnub.deleteMessages(
channels = listOf("channel_1", "channel_2"),
start = 1460693607379L,
end = 1460893617271L
).async { _, status ->
// The deleteMessages() method does not return actionable data.
// Be sure to check the status on the outcome of the operation
// by checking the status.error
if (status.error) {
// handle error
status.exception?.printStackTrace()
}
}

Other Examples

Delete specific message from history

To delete a specific message, pass the publish timetoken (received from a successful publish) in the End parameter and timetoken +/- 1 in the Start parameter. For example, if 15526611838554310 is the publish timetoken, pass 15526611838554309 in Start and 15526611838554310 in End parameters respectively as shown in the following code snippet.

pubnub.deleteMessages(
channels = listOf("channel_1"),
start = 15526611838554309L,
end = 15526611838554310L
).async { _, status ->
// The deleteMessages() method does not return actionable data.
// Be sure to check the status on the outcome of the operation
// by checking the status.error
if (status.error) {
// handle error
status.exception?.printStackTrace()
}
}

Message Counts

Requires Message Persistence add-on

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

Description

Returns the number of messages published on one or more channels since a given time. The count returned is the number of messages in history with a timetoken value greater than or equal to than the passed value in the channelsTimetokenparameter.

Unlimited message retention

For keys with unlimited message retention enabled, this method considers only messages published in the last 30 days.

Method(s)

To run messageCounts(), you can use the following method(s) in the Kotlin SDK:

pubnub.messageCounts(
channels: List<String>,
channelsTimetoken: List<Long>
).async { result, status -> }
ParameterTypeRequiredDefaultDescription
channelsList<String>YesThe channels to fetch the message count.
channelsTimetokenList<Long>YesList of timetokens, in order of the channels list. Specify a single timetoken to apply it to all channels. Otherwise, the list of timetokens must be the same length as the list of channels, or the function returns a PNStatus with an error flag.

Basic Usage

val lastHourTimetoken = System.currentTimeMillis() - TimeUnit.HOURS.toMillis(1)

pubnub.messageCounts(
channels = listOf("news"),
channelsTimetoken = listOf(lastHourTimetoken * 10_000L)
).async { result, status ->
if (!status.error) {
result!!.channels.forEach { (channel, count) ->
println("$count new messages on $channel")
}
} else {
// handle error
status.exception?.printStackTrace()
}
}

Returns

MethodTypeDescription
channelsMap<String, Long>A map with values of Long for each channel. Channels without messages have a count of 0. Channels with 10,000 messages or more have a count of 10000.

Other Examples

val lastHourTimetoken = System.currentTimeMillis() - TimeUnit.HOURS.toMillis(1)
val lastDayTimetoken = System.currentTimeMillis() - TimeUnit.DAYS.toMillis(1)

pubnub.messageCounts(
channels = listOf("news", "info"),
channelsTimetoken = listOf(lastHourTimetoken, lastDayTimetoken).map { it * 10_000L }
).async { result, status ->
if (!status.error) {
result!!.channels.forEach { (channel, count) ->
println("$count new messages on $channel")
}
} else {
// handle error
status.exception?.printStackTrace()
}
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