##emqttd_publish_client_activity

This is a work in progress relating to publishing messages on mqtt or Kafka topics relating to mqtt client's realtime activity using emqttd broker.

This plugin in genral enhances the ability of a pub-sub system as it keeps on publishing messages to mqtt or kafka topics on various events whenever a client connects/disconnects/publishes/acknowledges a message/subscribes to a topic/unsubscribe to a topic, so that you can easily perform action on these events in any programming language just by having MQTT or kafka clients in your project subscribed to below mentioned SYSTEM/# channels. (example async tasks like storing these events in a database).

Use cases:

publish messages on to

1> "SYSTEM/presence/connected" when a client connects broker,

2> "SYSTEM/presence/disconnected" when a client connects broker,

3> "SYSTEM/subscription/subscribed" when a client subscribes to a channel,

4> "SYSTEM/subscription/unsubscribed" when a client unsubscribes to a channel,

5> "SYSTEM/message" when a client publishes a message to a channel,

6> "SYSTEM/msgack" when a client acknowledges a messages (Very useful)

with a configurable QoS value (in progres)

The data published on above events can be used to track message and client's activity in realtime.

Details about message published on each channel:

A> "SYSTEM/msgack"

A new message is published to "SYSTEM/msgack" whenever a client acknowledges a new message the published payload is a following json string :

{
	"pub_client_id":"client id of who published this message",
	"ack_client_id":"client id of who acknowleded this message",
	"product_id":"your product id",
	"message_id":"your custom message id",
	"topic":"topic this message was published on"
}

All the above parameters can then be utilized to figure out which clientId acknowledged which uniquely published message.

NOTE: you will get acknowledgement on "SYSTEM/msgack" only if you publish your payload as serialized json with following mandatory keys:

{
	"product_id":"your custom product id",
	"message_id":"your custom message id",
	"payload":"data"
} 

why? If you are interesting in getting the acknowledgement then while publishing the message you should specify the
A = product_id and
B = message_id and make sure that A^B(A intersection B) is always unique.

Q.why product_id (isn't just message_id sufficient)
Ans> this is because if you are using this in a company then there might exist a possibility that there are many products having same message_id, therefore to uniquely identify a message you should send the message as a json with both product_id and message_id.

B> "SYSTEM/presence/connected"

Whenever a client connects it publishes a message to this channel with payload (serialized json):

{
	"client_id":"which client id connected"
}

C> "SYSTEM/presence/disconnected"

Whenever a client disconnects it publishes a message to this channel with payload (serialized json):

{
	"client_id":"which client id disconnected",
	"reason":"reason why it got disconnected"
}

D> "SYSTEM/subscription/subscribed"

Whenever a client subscribes to a chennel, it publishes a message to this channel with payload (serialized json):

{
	"client_id":"which client id subscribed",
	"topic":"topic to which it subscribed"
}

E> "SYSTEM/subscription/unsubscribed"

Whenever a client unsubscribes a channel, it publishes a message to this channel with payload (serialized json):

{
	"client_id":"which client id unsubscribed",
	"topic":"topic to which it unsubscribed"
}

F> "SYSTEM/message"

Whenever a client publishes a new message on a channel with payload serialized json):

{
	"pub_client_id":"client id of publisher",
	"topic":"topic on which message is published",
	"payload":"message payload",
	"qos":"qos with which message was sent"
} 

##Goals:
Integration with kafka, configurable option to publish these messages to kafka/mqtt SYSTEM/# topics

##Important:
make sure you dont have any client_id with "broker" since it is reserved for emqtt broker in this plugin.