LuaLua Publish & Subscribe API Reference for Realtime Apps

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 publish_key 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 is 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. Message data should not contain special Lua classes or functions as these will not serialize. String content can include any single-byte or multi-byte UTF-8 character.
Message Size:
The maximum number of characters per message is 32K 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 (1.5KB) 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 please check: https://support.pubnub.com/support/discussions/topics/14000006322

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 cannot 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 (i.e. not concurrently).
  • Check that the return code is success (e.g. [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 e.g. Publish no faster than 5 msgs per second to any one channel.
 

Single string messages are automatically sent to APNS if mobile push is enabled and devices are registered for push on that channel. So if you use encryption (cipher key in the init) and publish the message, then it will be sent to APNS if there is a device(s) registered to that channel.

This is a legacy feature and will be deprecated soon.

To Publish a message you can use the following method(s) in the Lua SDK:
  1. ParameterTypeRequiredDescription
    paramstableYesTable of publish parameters. See Publish Parameters for more details.
    PropertiesTypeRequiredDefaultsDescription
    channelstringYesnoneThe channel to publish to.
    messagestringYesnoneThe message to publish.
    callbackfunction(r)Optionalfunction(r) endThe function to call on success with result.
    errorfunction(r)Optionalfunction(r) endThe function to call on failure, with result.

Publish a message to a channel:

pubnub_obj:publish({
	channel = channel,
	message = text,
	callback = function(r) --textout(r)
	end,
	error = function(r) textout(r)
	end
})
 
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.
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 subscribe_key at initialization.
By default a newly subscribed client will only receive messages published to the channel after the subscribe() call completes.
 Unsubscribing from all the channel(s) 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 the channels resets the timetoken and thus, there could be some gaps in the subscription that may lead to a message loss.
To Subscribe to a channel you can use the following method(s) in the Lua SDK:
  1. ParameterTypeRequiredDescription
    paramstableYesTable of subscribe parameters. See Subscribe Parameters for more details.
    PropertiesTypeRequiredDefaultsDescription
    channelstringYesnoneThe channel to subscribe to - can be a comma-separated list of channels.
    callbackfunction(msg)YesnoThe function to call on each received message.
    errorfunction(r)Optionalfunction(r) endThe function to call on failure, with result.
    connectfunction()Optionalfunction() endThe function to call on connecting to PubNub (before first message).
    reconnectfunction()Optionalfuncition() endCall if connection lost and then re-established.
    presencebooleanOptionalfalseWhether to subscribe to the presence channel(s) for given channel(s).
    timeoutintegerOptionalSUB_TIMEOUT (310)The number of seconds to wait for a response to subscribe.
Subscribe to a channel:
pubnub_obj:subscribe({
	channel = "demo",
	connect = function()
		textout('Connected to channel ')
		textout(channel)
	end,
	callback = function(message)
		textout(message)
	end,
	error = function()
		textout("Oh no!!! Dropped Connection!")
	end
})
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 the channel(s) 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 the channels resets the timetoken and thus, there could be some gaps in the subscription that may lead to a message loss.
To Unsubscribe from a channel you can use the following method(s) in the Lua SDK:
  1. ParameterTypeRequiredDescription
    paramstableYesTable of unsubscribe parameters - channel(s) to unsubscribe from. See Unsubscribe Parameters for more details.
    PropertiesTypeRequiredDefaultsDescription
    channelstringYesnoneThe channel to unsubscribe from - can be a comma-separated list of channels.
Unsubscribe from a channel:
pubnub_obj:unsubscribe({
	channel = "demo",
})