Skip to main content

HTML5 WebSockets in ColdFusion 10 - Workflow diagram

The HTML5 Web Sockets represent the next evolution of web communications. A WebSocket is a full duplex, bidirectional communication channel that operates over a single TCP socket. It has become a standard for building real time web applications. In ColdFusion 10, a messaging layer has been provided that implements the Web Socket protocol. It enables you to build applications that are based on publisher/subscriber model and applications that are based on subscriber model wherein a push from a server is possible.

Publisher/Subscriber model

In this broadcast based method, publisher posts a message and a subscriber consumes it. A subscriber subscribes to a channel to which a publisher posts the message. A subscriber can subscribe to multiple channels and consume the data sent through the channel:


To implement the broadcast based approach in ColdFusion, you can specify the channel details in Application.cfc file, use the new tag - cfwebsocket to create a websocket and then send, receive and manage the connection through various JavaScript functions.


component {
.name = "WebSocketAPP";
.wschannels = [{name="channel1"},{name="channel2"},{name="channel3"}]; }

The websocket channels through which the communication takes place between the publisher and subscriber is specified in the wschannels variable. As observed in the above code snippet, the channel names are specified in a struct. Optionally, you can also specify the cfclistener key which contains channel listener functions for each channel (I plan to cover this workflow in my next post).

Creating a WebSocket:

To create a websocket, the cfwebsocket tag is used:

<cfwebsocket name="socket" onMessage="messageHandler" onOpen="openHandler" onClose="closeHandler" onError="errorHandler" subscribeTo="channel1,channel2">

The cfwebsocket tag will establish a connection with the WebSocket Server and the server will respond with a ‘Welcome’ message; acknowledging the publisher or subscriber that the connection has been established. As observed in the above code snippet various handlers are specified. These are JavaScript functions that the user has to implement. The onMessage handler (messageHandler in code) is called when the server responds with a message or when a data is received through the subscribed channel. The complete workflow is as shown below:

JavaScript Functions:

Once a connection is established with the server, the websocket object is then used to manage the connection. Here is list of JavaScript functions (please note this is not a complete list, only those relevant to the example are mentioned):


By default, a connection is established with the server when the cfwebsocket tag is specified in the page. If the user chooses to close the connection (see closeConnection function below) and then establish again, then this function should be called on the socket object. Example:



This function is used to check whether the connection is established with the server. It returns a boolean value true if the connection is established or false if the connection is closed. Example:



Instead of specifying the channels to subscribe in the subscribeTo attribute of the cfwebsocket tag, you can use the JavaScript function ‘subscribe’ to subscribe to a channel. This function optionally takes two arguments – subscriberInfo and messageHandler. Subscriber information can include subscriber related data such as id,name,age in a struct. If a messageHandler function is specified then whenever a message is received through the channel, the messageHandler would be invoked. Example:

socket.subscribe(“channel1”,{name: ‘Sagar’, id: ‘888’}, channelHandler);


The ‘unsubscribe’ function is used to unsubscribe from a channel. Once a user unsubscribes from the channel, the messages from the channel are no longer delivered to the client. Example:

socket.unsubscribe(“channel1”,{name: ‘Sagar’, id: ‘888’});


The publisher can send data through a channel using the ‘publish’ method. The Server acknowledges this action by sending an acknowledgement to the publisher. The third argument of the publish method is a struct containing the publisher information. Again this is an optional argument. Example:

socket.publish(“channel1”,”message_here”,{name: ‘Publisher’, id: ‘222’});


The user can close the connection by calling the ‘closeConnection’ function on the socket object. This function will close the connection with the server and the user will not receive any messages. If a user wants to open the connection then the ‘openConnection’ function should be called. Example:


Working Example

I have created a sample application, you can download it here. Open two browser instances and run the cfm file. You’ll be able to see the communication taking place between the two instances when some message is sent through the channel.


  1. Great post - it's starting to make sense. When you pass optional data with the Subscribe(), do you *also* have to pass that data along to the Unsubscribe() for the channel to be unsubscribed?

  2. Ben, the subscriber info provided in subscribe and unsubscribe methods come handy when dealing with user defined Channel listeners. A channel listener is a CFC containing methods which are called when a WebSocket object's JavaScript functions are called. The methods in CFC can take the decision (to allow subscribing) based on the info included in the subscribe function.

    For the ones without user defined channel listeners it is not required to provide subscriber info.

  3.  Ok cool - I'm gonna be working on some WS stuff today, see if I can wrap my head around it.

  4. Anuragjain DelhiJune 14, 2012 at 5:09 PM

    Is there websockets support in CF 9

  5. No. It was added in ColdFusion 10.

  6. What is the limitations to the number of channels we can have. Also can we have dynamic channels like ch.id1, ch.id2
    the number of channels being dependent on the number of user groups that are logged in from id1 to idn. What is the limitation to the number of channels. Each group ch.id1 etc. could have any number of subscribers 1 to 10 say.

  7. Refer to this link

    and w.r.t the number of channels I'm not sure, but you can post the question on Adobe forum. Someone from the team should answer that.

  8. Does anyone know how CF10 standard handles the 100 connection limitation? I'm working on a project that is running on a Standard installation and while I'm trying to get them to move to Enterprise, I'd really like to know what happens when the 100 connection limit is approached. I'm going to run some tests to see if I can artificially create that much traffic, but if anyone has been able to find that info already, it'd be nice to hear from you...

  9. You can ask this question on the Adobe forums, the engineers\pm's would answer that.

  10. Just wondering how you handle socket disconnects. Using the example provided after X minutes it seems like the socket disconnects when trying to push data back to the socket. Even though each function is wrapped in an socket.isConnectionOpen() qualifier to trip a socket.openConnection(); however it still doesn't seem to pick the connection back up.


Post a Comment

Popular posts from this blog

Custom validation messages for HTML5 Input elements using the constraint validation API

HTML5 has introduced several input types such as EMAIL, URL, RANGE, SEARCH, DATE, TIME, etc,. Most of the modern browsers have implemented them and are ready to be used in a HTML document. Another exciting feature introduced in HTML5 is the form validation. Instead of writing JavaScript to validate users input, browsers can now validate it and show an appropriate message if the validation fails. The validation message is shown in line with the field for which the validation has failed. The default error message is shown when the validation fails. In this post I'll explain how these error messages can be changed.

Adding beforeRender and afterRender functions to a Backbone View

I was working on a Backbone application that updated the DOM when a response was received from the server. In a Backbone View, the initialize method would perform some operations and then call the render method to update the view. This worked fine, however there was scenario where in I wanted to perform some tasks before and after rendering the view. This can be considered as firing an event before and after the function had completed its execution. I found a very simple way to do this with Underscore's wrap method.

A cheat sheet of keyboard shortcuts in ColdFusion Builder

In my last post I have explained about keyboard shortcuts in ColdFusion Builder 2.0. This blog post contains a list of all shortcut keys and I have listed these keyboard shortcuts based on the categories that it falls into. Well, this post was not planned since users can easily get to know the keyboard shortcuts by navigating to the preferences (ColdFusion -> Profiles -> Keys). However, I met Joshua at Scotch on the rocks in Edinburgh and he suggested that it would be nice to have the list of keyboard shortcuts handy. So this post is for those who would like to have the list with them and refer it whenever required.

Keyboard shortcuts for inserting text:

These are the keyboard shortcuts which are used to insert some text into the editor:

CommandKeyboard shortcuts on WindowsKeyboard shortcuts on MacInsert anchor tagCTRL + T, LCMD + T, LInsert bold tagCTRL + T, BCMD + T, BInsert br tagCTRL + T, RCMD + T, RInsert cfabortCTRL + T, ACMD + T, AInsert cfdumpCTRL + T, DCMD + T, DInsert cfs…