Presence

Presence in Redis

One of the most important and resource intensive operation in chat systems is handling user presence. Because in order to start the chat one should provide the presence information. And keeping this data up-to-date is another challenge.

There are 3 main parts for handling user presence,

Notification
Persistency
Data source

Starting with number one:

If we calculate the message count with a standart architecture for sending notifications to the online users: count = (online user count) * (channel participant count) * (events), since every part is a multiplication even increasing by one will cause huge effects.

Number two:

Transient presence data should be commited and updated regularly, after an inactive duration presence data should be set to offline either by the application or by the persistency layer

Number three:

Online clients should notify the presence system with their unique identifier repeatedly. We can call it as heartbeat.

"This package aims to handle the persistency layer for presence"

For usage see examples below or go to godoc page.

Install and Usage

Install the package with:

go get github.com/cihangir/presence

Import it with:

import "github.com/cihangir/presence"

Examples

Initialization of a new Redisence

// create a presence system
backend, err := NewRedis(serverAddr, dbNumber, timeoutDuration)
if err != nil {
    return err
}

s, err := New(backend)
if err != nil {
    return err
}

Basic Operations

// send online presence data to system - user log in
err = s.Online("id")
err = s.Online("id2")


// send offline presence data to system - user log out
err = s.Offline("id")
err = s.Offline("id2")

// get status of some ids
status, err := s.Status([]string{"id20", "id21"}...)
if err != nil {
    return err
}

for _, st := range status {
    if st.Status != Offline {
        //....
    }
}

Listening for events

go func() {
    s.Online("id")
    time.Sleep(time.Second * 1)
    s.Online("id")
    s.Online("id2")
}()

// start listening to them
for event := range s.ListenStatusChanges() {
    switch event.Status {
    case Online:
        // ....
    case Offline:
        // ....
    }
}

Redis configuration

To get the events from the redis database we should uptade the redis config with the following data

redis-cli config set notify-keyspace-events Ex$

Or set in redis.conf notify-keyspace-events "Ex$"

for more info http://redis.io/topics/notifications

License

The MIT License (MIT) - see LICENSE for more details

zulal/presence