====== Messaging / MQTT ======

===== API =====

==== void MQTTsetGroup(String group) ====
Sets the MQTT group where all messages are sent and all subscriptions are done.

Can be used to easily separate different applications/users/groups

e.g. specify one group per game or one group per boards playing in the same game.


==== void MQTTonMessage(void (cb)(String &topic, String &message)) ====
Sets the callback function that is called one a MQTT message is received for one of the subscribed topics.

needs a callback function with signature:

''topic - String topic on which the message was received\\
message - String content of the received message.''


==== boolean MQTTpublish(const char topic[], String message) ====
Publishes/sents a message to the specified MQTT topic.

if an MQTT group is set, the topic is automatically preceded with this group string.

''topic - topic to which the message will be sent\\
message - content of the message.''

     
==== boolean MQTTpublish(String topic, String message) ====
Publishes/sents a message to the specified MQTT topic.

if an MQTT group is set, the topic is automatically preceded with this group string.

''topic - topic to which the message will be sent\\
message - content of the message.''


==== boolean MQTTsubscribe(const char topic[]) ====
Subscribes to the specified MQTT topic. Once a message is received for a subscribed topic, the MQTTonMessage callback is called.

If an MQTT group is set, the topic is automatically preceded with this group string.
see https://www.hivemq.com/blog/mqtt-essentials-part-5-mqtt-topics-best-practices for more information on topic subscriptions.

''topic - topic to subscribe to''

==== boolean MQTTsubscribe( String s_topic) ====
Subscribes to the specified MQTT topic. Once a message is received for a subscribed topic, the MQTTonMessage callback is called.

if an MQTT group is set, the topic is automatically preceded with this group string.
see https://www.hivemq.com/blog/mqtt-essentials-part-5-mqtt-topics-best-practices for more information on topic subscriptions.

''topic - topic to subscribe to''

==== boolean MQTTunsubscribe(const char topic[]) ====
Unsubscribes from the specified MQTT topic.

if an MQTT group is set, the topic is automatically preceded with this group string.

''topic - topic to unsubscribe from''

==== void MQTTconnectRGB() ====
Subscribes the Kniwwelinos RGB LED to specific MQTT topics. If a message is received, the LED color will be changed.

if an MQTT group is set, the topic is automatically preceded with this group string.

The board will listen on //group/RGB/COLOR// for messages.

**Message format:** 

''"FF00FF", first 2 digits specify the RED, second the GREEN, third the BLUE component.''



==== void MQTTconnectMATRIX() ====
Subscribes the Kniwwelinos MATRIX to specific MQTT topics. 

if an MQTT group is set, the topic is automatically preceded with this group string. 

The board will listen on //group/MATRIX/ICON// for icons. If a message is received, the ICON will be displayed.

**Message format:**

''"B1111100000111110000011111" 25 pixels binary one after the other, prefix B or\\
"0x7008E828A0" one byte for each 5px row, prefix 0x''

The board will listen on //group/MATRIX/TEXT// for icons. If a message is received, the Text will be displayed.

**Message format:** 

''"Hello World!"''

	

===== Wiring =====

===== Examples =====