centrifuge

Centrifuge client for NodeJS and browser

This client can connect to Centrifuge server (and Centrifugo in particular) using Websocket or SockJS transports from web browser or NodeJS environments.

• Install and quick start
• Connection Token
• Configuration parameters
• Client API
• Private channels subscription
• Connection expiration
• Protobuf support
• Browser support

Javascript client can connect to the server in two ways: using pure Websockets or using SockJS library to be able to use various available fallback transports if client browser does not support Websockets.

Install and quick start

The simplest way to use javascript client is download it from dist folder and include into your web page using script tag:

<script src="centrifuge.js"></script>

Or using cdn (replace X to concrete version number):

<script src="//cdn.rawgit.com/centrifugal/centrifuge-js/2.X.X/dist/centrifuge.min.js"></script>

Client is also available via npm:

npm install centrifuge

And then:

var Centrifuge = require("centrifuge");

Default library works with JSON only, see Protobuf support section to see how to import client with Protobuf support.

As soon as you included all libraries you can create new Centrifuge object instance, subscribe on channel and call .connect() method to make actual connection to server:

var centrifuge = new Centrifuge('ws://centrifuge.example.com/connection/websocket');

centrifuge.subscribe("news", function(message) {
    console.log(message);
});

centrifuge.connect();

In example above we initialize Centrifuge object instance, subscribe on channel news, print all new messages received from channel news into console and actually make connection to Centrifugo. And that's all code which required for simple real-time messaging handling on client side!

If you want to use SockJS you must also import SockJS client before centrifuge.js

<script src="//cdn.jsdelivr.net/sockjs/1.1/sockjs.min.js" type="text/javascript"></script>
<script src="centrifuge.js" type="text/javascript"></script>

Or provide it explicitly:

var Centrifuge = require("centrifuge");
var SockJS = require('sockjs-client');

var centrifuge = new Centrifuge("http://localhost:8000/connection/sockjs", {
  sockjs: SockJS
})

Centrifuge object is an instance of EventEmitter.

Connection Token

If you are connecting to Centrifugo you must also provide connection token:

var centrifuge = new Centrifuge('ws://centrifuge.example.com/connection/websocket');

centrifuge.setToken(YOUR_TOKEN);

centrifuge.subscribe("news", function(message) {
    console.log(message);
});

centrifuge.connect();

This token contains information about user of your application that tries to connect. See documentation for connection JWT token in Centrifugo docs.

Connection token comes to Javascript code from application backend - i.e. generated on backend.

Configuration parameters

Let's also look at optional configuration parameters available when initializing Centrifuge object instance.

sockjsTransports

In case of using SockJS additional configuration parameter can be used - sockjsTransports.

It defines allowed SockJS transports and by default equals

var centrifuge = new Centrifuge(
  'http://centrifuge.example.com/connection/sockjs', 
  {
    sockjsTransports: [
        'websocket', 
        'xdr-streaming',
        'xhr-streaming',
        'eventsource',
        'iframe-eventsource',
        'iframe-htmlfile',
        'xdr-polling',
        'xhr-polling',
        'iframe-xhr-polling',
        'jsonp-polling'
    ]
});

i.e. all possible SockJS transports.

So to say centrifuge-js to use only websocket and xhr-streaming transports when using SockJS endpoint:

var centrifuge = new Centrifuge('http://centrifuge.example.com/connection/sockjs', {
    sockjsTransports: ["websocket", "xhr-streaming"]
});

sockjs

sockjs option allows to explicitly provide SockJS client object to Centrifuge client.

For example this can be useful if you develop in ES6 with imports:

import Centrifuge from 'centrifuge'
import SockJS from 'sockjs-client'

var centrifuge = new Centrifuge('https://centrifuge.example.com/connection/sockjs', {
  sockjs: SockJS
});

sockjsServer

sockjsServer is SockJS specific option to set server name into connection urls instead of random chars. See SockJS docs for more info.

debug

debug is a boolean option which is false by default. When enabled lots of various debug messages will be logged into javascript console. Mostly useful for development or troubleshooting.

insecure

insecure is a boolean option which is false by default. When enabled client will connect to server in insecure mode - read about this mode in special docs chapter.

This option nice if you want to use Centrifugo for quick real-time ideas prototyping, demos as it allows to connect to Centrifugo without sign, exp and user. And moreover without application backend! Please, read separate chapter about insecure modes.

retry

When client disconnected from server it will automatically try to reconnect using exponential backoff algorithm to get interval between reconnect attempts which value grows exponentially. retry option sets minimal interval value in milliseconds. Default is 1000 milliseconds.

maxRetry

maxRetry sets upper interval value limit when reconnecting. Or your clients will never reconnect as exponent grows very fast:) Default is 20000 milliseconds.

subscribeEndpoint

subscribeEndpoint is url to use when sending auth request for authorizing subscription on private channel. By default /centrifuge/subscribe. See also useful related options:

• subscribeHeaders - map of headers to send with subscribe request (default `{}``)
• subscribeParams - map of params to include in subscribe endpoint url (default {})

refreshEndpoint

refreshEndpoint is url to use when refreshing client connection parameters when connection check mechanism enabled in Centrifugo configuration. See also related options:

• refreshHeaders - map of headers to send with refresh request (default `{}``)
• refreshParams - map of params to include in refresh url (default {})
• refreshData - send extra data in body (as JSON payload) when sending AJAX POST refresh request.
• refreshAttempts - limit amount of refresh requests before giving up (by default null - unlimited)
• onRefreshFailed - callback function called when refreshAttempts came to the end. By default null - i.e. nothing called.

Client API

When Centrifuge object properly initialized then it is ready to start communicating with server.

connect method

As we showed before, we must call connect() method to make an actual connection request to Centrifugo server:

var centrifuge = new Centrifuge('ws://centrifuge.example.com/connection/websocket');

centrifuge.connect();

connect() triggers an actual connection request to server.

connect event

After connection will be established and client credentials you provided authorized then connect event on Centrifuge object instance will be called.

You can listen to this setting event listener function on connect event:

centrifuge.on('connect', function(context) {
    // now client connected to Centrifugo and authorized
});

What's in context:

{
    client: "79ec54fa-8348-4671-650b-d299c193a8a3",
    transport: "raw-websocket",
    latency: 21
}

• client – client ID Centrifugo gave to this connection (string)
• transport – name of transport used to establish connection with server (string)
• latency – latency in milliseconds (int). This measures time passed between sending connect client protocol command and receiving connect response.

disconnect event

disconnect event fired on centrifuge object every time client disconnects for some reason. This can be network disconnect or disconnect initiated by Centrifugo server.

centrifuge.on('disconnect', function(context) {
    // do whatever you need in case of disconnect from server
});

What's in context?

{
    reason: "connection closed",
    reconnect: true
}

• reason – the reason of client's disconnect (string)
• reconnect – flag indicating if client will reconnect or not (boolean)

disconnect method

In some cases you may need to disconnect your client from server, use disconnect method to do this:

centrifuge.disconnect();

After calling this client will not try to reestablish connection periodically. You must call connect method manually again.

Subscriptions

Of course being just connected is useless. What we usually want from Centrifugo is to receive new messages published into channels. So our next step is subscribe on channel from which we want to receive real-time messages.

subscribe method

To subscribe on channel we must use subscribe method of Centrifuge object instance.

The simplest usage that allow to subscribe on channel and listen to new messages is:

var subscription = centrifuge.subscribe("news", function(message) {
    // handle new message coming from channel "news"
    console.log(message);
});

And that's all! For lots of cases it's enough! But let's look at possible events that can happen with subscription:

• publish – called when new publication message received (callback function in our previous example is publish event callback btw)
• join – called when someone joined channel
• leave – called when someone left channel
• subscribe – called when subscription on channel successful and acknowledged by Centrifugo server. It can be called several times during lifetime as browser client automatically resubscribes on channels after successful reconnect (caused by temporary network disconnect for example or Centrifugo server restart)
• error – called when subscription on channel failed with error. It can be called several times during lifetime as browser client automatically resubscribes on channels after successful reconnect (caused by temporary network disconnect for example or Centrifugo server restart)
• unsubscribe – called every time subscription that was successfully subscribed unsubscribes from channel (can be caused by network disconnect or by calling unsubscribe method of subscription object)

Don't be frightened by amount of events available. In most cases you only need some of them until you need full control to what happens with your subscriptions. We will look at format of messages for this event callbacks later below.

There are 2 ways setting callback functions for events above.

First is providing object containing event callbacks as second argument to subscribe method.

var callbacks = {
    "publish": function(message) {
        // See below description of message format
        console.log(message);
    },
    "join": function(message) {
        // See below description of join message format
        console.log(message);
    },
    "leave": function(message) {
        // See below description of leave message format
        console.log(message);
    },
    "subscribe": function(context) {
        // See below description of subscribe callback context format
        console.log(context);
    },
    "error": function(errContext) {
        // See below description of subscribe error callback context format
        console.log(err);
    },
    "unsubscribe": function(context) {
        // See below description of unsubscribe event callback context format
        console.log(context);
    }
}

var subscription = centrifuge.subscribe("news", callbacks);

Another way is setting callbacks using on method of subscription. Subscription object is event emitter so you can simply do the following:

var subscription = centrifuge.subscribe("news");

subscription.on("publish", publishHandlerFunction);
subscription.on("subscribe", subscribeHandlerFunction);
subscription.on("error", subscribeErrorHandlerFunction);

Subscription objects are instances of EventEmitter.

join and leave events of subscription

As you know you can enable join_leave option for channel in Centrifugo configuration. This gives you an opportunity to listen to join and leave events in those channels. Just set event handlers on join and leave events of subscription.

var subscription = centrifuge.subscribe("news", function(message) {
    // handle message
}).on("join", function(message) {
    console.log("Client joined channel", message);
}).on("leave", function(message) {
    console.log("Client left channel", message);
});

Note, that in order join/leave events to work corresponding options must be enabled in server channel configuration (on top level or for channel namespace)

subscription event context formats

We already know how to listen for events on subscription. Let's look at format of messages event callback functions receive as arguments.

format of message event context

Let's look at message format of new message received from channel:

{
    "uid":"6778c79fccb2",
    "data":{"input":"hello"},
}

I.e. data field contains actual data that was published.

Message can optionally contain client field (client ID that published message) - if it was provided when publishing new message:

{
    "uid":"6778c79fccb2",
    "data":{"input":"hello"},
    "client":"7080fd2a-bd69-4f1f-6648-5f3ceba4b643"
}

And it can optionally contain additional client info in case when this message was published by javascript client directly using publish method (see details below):

{
    "uid":"6778c79f-ccb2-4a1b-5768-2e7381bc5410",
    "info":{
        "user":"2694",
        "client":"7080fd2a-bd69-4f1f-6648-5f3ceba4b643",
        "default_info":{"name":"Alexandr"},
        "channel_info":{"extra":"extra JSON data when authorizing private channel"}
    },
    "data":{"input":"hello"},
    "client":"7080fd2a-bd69-4f1f-6648-5f3ceba4b643"
}

format of join/leave event message

I.e. on("join", function(message) {...}) or on("leave", function(message) {...})

{
    "info":{
        "user":"2694",
        "client":"2724adea-6e9b-460b-4430-a9f999e94c36",
        "conn_info":{"first_name":"Alexandr"},
        "chan_info":{"extra":"extra JSON data when authorizing"}
    }
}

conn_info and chan_info exist in message only if not empty.

format of subscribe event context

I.e. on("subscribe", function(context) {...})

{
    "channel": "$public:chat",
    "isResubscribe": true,
    "recovered": false
}

isResubscribe – boolean flag showing if this was initial subscribe (false) or resubscribe (true) recovered – boolean flag that indicated whether missed messages were recovered on reconnect or not (recovery works according to Centrifugo channel configuration)

format of subscription error event context

I.e. on("error", function(err) {...})

{
    "error": "permission denied",
    "channel": "$public:chat",
    "isResubscribe": true
}

error - error description isResubscribe – flag showing if this was initial subscribe (false) or resubscribe (true)

format of unsubscribe event context

I.e on("unsubscribe", function(context) {...})

{
    "channel": "$public:chat"
}

presence method of subscription

presence allows to get information about clients which are subscribed on channel at this moment. Note that this information is only available if presence option enabled in Centrifugo configuration for all channels or for channel namespace.

var subscription = centrifuge.subscribe("news", function(message) {
    // handle message
});

subscription.presence().then(function(message) {
    // presence data received
}, function(err) {
    // presence call failed with error
});

presence is internally a promise that will be resolved with data or error only when subscription actually subscribed.

Format of success callback message:

{
    "channel":"$public:chat",
    "data":{
        "2724adea-6e9b-460b-4430-a9f999e94c36": {
            "user":"2694",
            "client":"2724adea-6e9b-460b-4430-a9f999e94c36"
        },
        "d274505c-ce63-4e24-77cf-971fd8a59f00":{
            "user":"2694",
            "client":"d274505c-ce63-4e24-77cf-971fd8a59f00"
        }
    }
}

As you can see presence data is a map where keys are client IDs and values are objects with client information.

Format of err in error callback:

{
    "error": "timeout",
}

• error – error description (string)

Note, that in order presence to work corresponding options must be enabled in server channel configuration (on top level or for channel namespace)

history method of subscription

history method allows to get last messages published into channel. Note that history for channel must be configured in Centrifugo to be available for history calls from client.

var subscription = centrifuge.subscribe("news", function(message) {
    // handle message
});

subscription.history().then(function(message) {
        // history messages received
    }, function(err) {
        // history call failed with error
    });
});

Success callback message format:

{
    "channel": "$public:chat",
    "data": [
        {
            "uid": "87219102-a31d-44ed-489d-52b1a7fa520c",
            "data": {"input": "hello2"}
        },
        {
            "uid": "71617557-7466-4cbb-760e-639042a5cade",
            "data": {"input": "hello1"}
        }
    ]
}

Where data is an array of messages published into channel.

Note that also additional fields can be included in messages - client, info if those fields were in original messages.

err format – the same as for presence method.

Note, that in order history to work corresponding options must be enabled in server channel configuration (on top level or for channel namespace)

publish method of subscription

publish method of subscription object allows to publish data into channel directly from client. The main idea of Centrifugo is server side only push. Usually your application backend receives new event (for example new comment created, someone clicked like button etc) and then backend posts that event into Centrifugo over API. But in some cases you may need to allow clients to publish data into channels themselves. This can be used for demo projects, when prototyping ideas for example, for personal usage. And this allow to make something with real-time features without any application backend at all. Just javascript code and Centrifugo.

So to emphasize: using client publish is not an idiomatic Centrifugo usage. It's not for production applications but in some cases (demos, personal usage, Centrifugo as backend microservice) can be justified and convenient. In most real-life apps you need to send new data to your application backend first (using the convenient way, for example AJAX request in web app) and then publish data to Centrifugo over Centrifugo API.

To do this you can use publish method. Note that just like presence and history publish must be allowed in Centrifugo configuration for all channels or for channel namespace. When using publish data will go through Centrifugo to all clients in channel. Your application backend won't receive this message.

var subscription = centrifuge.subscribe("news", function(message) {
    // handle message
});

subscription.publish({"input": "hello world"}).then(function() {
        // success ack from Centrifugo received
    }, function(err) {
        // publish call failed with error
    });
});

err format – the same as for presence method.

Note, that in order publish to work corresponding option must be enabled in server channel configuration (on top level or for channel namespace), by default client can not publish into channel

unsubscribe method of subscription

You can call unsubscribe method to unsubscribe from subscription:

subscription.unsubscribe();

subscribe method of subscription

You can restore subscription after unsubscribing calling .subscribe() method:

subscription.subscribe();

ready method of subscription

A small drawback of setting event handlers on subscription using on method is that event handlers can be set after subscribe event of underlying subscription already fired. This is not a problem in general but can be actual if you use one subscription (i.e. subscription to the same channel) from different parts of your javascript application - so be careful.

For this case one extra helper method .ready(callback, errback) exists. This method calls callback if subscription already subscribed and calls errback if subscription already failed to subscribe with some error (because you subscribed on this channel before). So when you want to call subscribe on channel already subscribed before you may find ready() method useful:

var subscription = centrifuge.subscribe("news", function(message) {
    // handle message;
});

// artificially model subscription to the same channel that happen after
// first subscription successfully subscribed - subscribe on the same
// channel after 5 seconds.
setTimeout(function() {
    var anotherSubscription = centrifuge.subscribe("news", function(message) {
        // another listener of channel "news"
    }).on("subscribe", function() {
        // won't be called on first subscribe because subscription already subscribed!
        // but will be called every time automatic resubscribe after network disconnect
        // happens
    });
    // one of subscribeSuccessHandler (or subscribeErrorHandler) will be called
    // only if subscription already subscribed (or subscribe request already failed).
    anotherSubscription.ready(subscribeSuccessHandler, subscribeErrorHandler);
}, 5000);

When called callback and errback of ready method receive the same arguments as callback functions for subscribe and error events of subscription.

Message batching

There is also message batching support. It allows to send several messages to server in one request - this can be especially useful when connection established via one of SockJS polling transports.

You can start collecting messages to send calling startBatching() method:

centrifuge.startBatching();

Finally if you don't want batching anymore call stopBatching() method:

centrifuge.stopBatching();

This call will flush all collected messages to network.

Private channels subscription

If channel name starts with $ then subscription on this channel will be checked via AJAX POST request from Javascript client to your web application backend.

You can subscribe on private channel as usual:

centrifuge.subscribe('$private', function(message) {
    // process message
});

But in this case Javascript client will first check subscription via your backend sending AJAX POST request to /centrifuge/subscribe endpoint (by default, can be changed via configuration option subscribeEndpoint). As said this is a POST request with JSON body. Request will contain client field on top level of JSON which is your connection client ID and array channels field - one or multiple private channels client wants to subscribe to.

{
  "client": "<CLIENT ID>",
  "channels": ["$chan1", "$chan2"]
}

Your server should validate all these subscriptions and return properly constructed response.

Response is a JSON with array channels field on top level:

{
  "channels": [
    {
      "channel": "$chan1",
      "token": "<SUBSCRIPTION JWT TOKEN>"
    },
    {
      "channel": "$chan2",
      "token": <SUBSCRIPTION JWT TOKEN>
    }
  ]
}

I.e. you need to return individual subscription tokens for each private channel in request. See how to generate private channel tokens in Centrifugo docs.

If you don't want to give client access to channel then just do not include it into response.

There are also two public API methods which can help to subscribe to many private channels sending only one POST request to your web application backend: startSubscribeBatching and stopSubscribeBatching. When you startSubscribeBatching javascript client will collect private subscriptions until stopSubscribeBatching() called – and then send them all at once.

Connection expiration

When connection expiration mechanism is on on server client will automatically ask your backend for updated connection credentials sending AJAX HTTP POST request to /centrifuge/refresh endpoint (by default, can be changed using refreshEndpoint option). Client will send that request when connection ttl is close to the end. In response backend should return response with JSON like this:

{
  "token": "<ACTUAL JWT TOKEN>"
}

Protobuf support

To import client with Protobuf protocol support:

<script src="//cdn.rawgit.com/centrifugal/centrifuge-js/2.X.X/dist/centrifuge.protobuf.min.js"></script>

Or if you are developing with npm:

import Centrifuge from 'centrifuge/dist/centrifuge.protobuf';

This client uses protobuf.js under the hood.

Centrifuge client with Protobuf support also works with JSON. To enable binary websocket add format query param with protobuf value to Websocket endpoint URL:

var centrifuge = new Centrifuge('ws://centrifuge.example.com/connection/websocket?format=protobuf');

Browser support

This client intended to work in all modern browsers with Websocket support: https://caniuse.com/#search=websocket.

To support IE 11 you must additionally polyfill Promise as this library uses Promise.

You can easily polyfill Promise via CDN (example here uses es6-promise library):

<script src="https://cdn.jsdelivr.net/npm/es6-promise@4/dist/es6-promise.auto.min.js"></script>

Or you can explicitly polyfill Promise in your code, see auto-polyfill of es6-promise