Opera Developer News

Custom Protocol and Content Handlers in Opera 11.60 beta

The Opera 11.60 alpha snapshot introduces support for HTML5 custom scheme and content handlers.

Not yet supported are the isProtocolHandlerRegistered, isContentHandlerRegistered, unregisterContentHandler, unregisterProtocolHandler methods which were added to the spec recently.

The idea is pretty simple. Your site can offer to handle certain MIME types or schemes (aka “protocols”) and the user has the option of opting in. One obvious use-case is webmail. For example, a service like Fastmail.fm or Gmail could tell your browser to open its "Compose" page if you click on a "mailto:" link rather than open a native mail application.

Of course, there are reasons why you wouldn’t want to pass off every type of content to a web-app—we want JavaScript and CSS to be handled by the browser, for example—so a blacklist exists. For security reasons, there's also a whitelist for schemes (but with the option to create a custom “web+” scheme).

Protocol Registration

navigator.registerProtocolHandler takes three arguments: the protocol, a URL which points to the custom handler application with a placeholder “%s”, and a title.

navigator.registerProtocolHandler(
  "tel",                           //protocol
  "/protocolhandler.html?%s",      //handler
  "Telephony"                      //title
);

In a user-agent that supports this, the user will be prompted to allow this registration to happen. Here is how this currently looks in Opera 11.60 alpha:

Once that’s taken care of, all “tel:” links will have the opportunity to be handled by this “Telephony” app. For example: clicking on tel: 555-1234 brings up a dialog asking if you would like to open the link with the just-registered application, or the default.

The browser then navigates to http://miketaylr.com/pres/capjs/demo/?tel%3A5551234. A script can then parse the URL and operate on the “tel%3A5551234” content (in this case, just put the phone number in the phone’s LED).

You can try it out here.

Content Registration

navigator.registerContentHanlder takes three arguments as well: the content-type, a URL which points to the custom content handler with a placeholder “%s”, and a title.

navigator.registerContentHandler(
  "text/x-cheeseburger",                     //content-type
  "http://miketaylr.com/code/cb.html?cb=%s", //handler
  "Cheeseburger Parser"                      //title
);

Just like registerProtocolHandler, the user will be prompted to allow the content-type registration to happen.

In this example, we have a custom text/x-cheeseburger content-type parser (see the syntax diagram) to operate on our .cheeseburger files. When we download a resource with the text/x-cheeseburger content-type, our browser will ask us to allow it to open it with our custom handler.

Again, just like registerProtocolHandler, the application is opened with the “%s” placeholder replaced by the URL of resource to be handled. In this case, http://miketaylr.com/code/cb.html?cb=http%3A%2F%2Fmiketaylr.com%2Fpres%2Fcapjs%2Fdemo%2Fsingle.cheeseburger. Now our script can fetch the contents and present it in a colorful way.