Plaid Cap

On a recent project, I was tasked with getting a Firefox extension to communicate with an Adobe AIR application that resides on the clients computer. It took a while to find help online, so I thought I would post about the solution I found, and possibly some of you out there have a better solution to this problem.

First of all, I guess you could ask why you would want this communication. Well, a Firefox extension can have a lot more functionality if it is able to communicate with a local application. Firefox can capture events from the browser, and then the AIR application can receive these events and do some kind of action accordingly. The Adobe AIR application can also make calls to the Firefox extension. These are the steps to create this communication…

The basic idea is to embed a flash file into the Firefox extension, then communicate with the AIR application via the swf file. Before creating the Firefox extension, you’ll want to get successful communication between the AIR app and the swf file.

1. Use the LocalConnection class to open a connection with a swf file. This should be done in the Adobe AIR application. You can find more information on the LocalConnection class at http://livedocs.adobe.com/labs/flex3/langref/flash/net/LocalConnection.html.

   var _conn:LocalConnection;
   
   public function init():void{
   _conn = new LocalConnection();
   _conn.allowDomain('*');
   _conn.connect('_connectionname');
   _conn.client = this;
   
   Alert.show("initialized");
   }
   
   public function methodToBeCalled(value:String):void{
   // the swf file will be calling this method
   }

2. Now you can create your swf file and finish the connection to the AIR application

   Security.allowDomain('*');
   var conn:LocalConnection;
   conn = new LocalConnection();
   conn.allowDomain('*');
   conn.send('_connectionname', 'methodToBeCalled',                                           value);

   It is important to note the Security.allowDomain and the conn.allowDomain. You will want to allow all, every place this is available. Also, notice the underscore before the connection name. This is not convention, but it is required for communication on local files.

3. Still in the swf file, you’ll want to enable a communication path to the Firefox javascript that will reside in the extension. It is essential to have a good understanding of XUL and other Firefox technologies.To enable communication to the swf file from javascript, we’ll want to make good use of the ExternalInterface class. You can read up on this class at http://livedocs.adobe.com/flash/9.0/main/wwhelp/wwhimpl/common/html/wwhelp.htm?context=LiveDocs_Parts&file=00000340.html.
   You’ll want to add this bit of code to allow the javascript to make calls to the swf file…

   ExternalInterface.addCallback("methodToAllow", methodToAllow);

   Now, the javascript can call the method methodToAllow() and pass values to it if necessary.

4. The last step is to embed the swf file into Firefox. I placed the swf in the top toolbox of firefox.

   <toolbox id="navigator-toolbox">
   
   <html:embed xsrc="chrome://path/to/your/file.swf" mce_src="chrome://path/to/your/file.swf"  id="file" width="0" height="0" align="middle" type="application/x-shockwave-flash" pluginspage="http://www.adobe.com/go/getflashplayer" allowscriptaccess="always" name="file" bgcolor="#869ca7" quality="high" hidden="true"></html:embed>
   
   </toolbox>

   Your javascript can now get this object by ‘getElementById’ and can call the method ‘methodToAllow()’.

Now, put the pieces together. You have full communication between Firefox and your local computer.

Anyone have any better ideas to communicate between a browser and the desktop?