Publish/Subscribe API for PubNub Arduino SDK


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'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 Arduino 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 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 Calculating Message Payload Size Before Publish.

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 (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.


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


If you want to include the publisher information in your message payload, you need to set the client UUID manually and explicitly include it in your message payload. Refer to Sending publisher UUID for more information.

Pubnub_BASE_CLIENT *publish(const char *channel, const char *message, int timeout = 30);
channelconst char*YesThe channel to publish to.
messageconst char*YesThe JSON message to publish.
timeoutintOptionalTimeout of the publish, in seconds.
Defaults to 30.

Basic Usage

Publish a message to a channel:

PubNub_BASE_CLIENT *client = PubNub.publish("my_channel", "\"message\"");
if (client != 0) {

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.

Rest Response from Server

Pubnub_BASE_CLIENTPointer to the object to be used to check the outcome and get the response from PubNub.
On failure to start publishing it's 0.


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 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.


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

PubnubSubClient *subscribe(const char *channel, int timeout = 30);
channelconst char*YesThe channel to subscribe to.
timeoutintOptionalTimeout of the subscribe, in seconds.

Defaults to 30.

Basic Usage

Subscribe to a channel:

PubSubClient *sclient = Pubnub.subscribe("my_channel");
if (sclient != 0) {
while (sclient->wait_for_data()) {


The following objects will be returned in the Subscribe Message Response

PubSubClientPointer to the object to be used to check the outcome and get the messages int the response from Pubnub. On failure to start publishing it's 0.
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