Building Oppilo - My Own Ad Blocker

June 20, 2019

Ad-blockers work in two ways.

One, by blocking requests to ad-servers (like google ad services, doubleclick, etc.)

Two, by hiding content that looks like an advertisment, so that you never see it! Consider Facebook or Twitter where most ads you see are actually sponsored or promoted content.

Oppilo is a chrome extension that blocks all network calls that try to seep through to reach an ad server.

It is incredibly easy to code this up, and is just a few lines of javascript, look!

chrome.webRequest.onBeforeRequest.addListener(
    function() {
      return {cancel: true};
    },
    { urls: [
      "*://*.googleadservices.com/*",
      "*://*.googlesyndication.com/*",
      "*://*.doubleclick.net/*"
    ]},
    ["blocking"]
  );

From the documentation -

The onBeforeRequest is fired when a request is about to occur. This event is sent before any TCP connection is made and can be used to cancel or redirect requests.

And that is exactly what we do to block ads! We intercept outgoing network connections that lead to ad-servers, and cancel them.

In the code above, the onBeforeRequest takes three parameters - a callback, a filter that can filter requests based on URLs, image requests, etc, and an optional array that specifies how the callback function is to be handled.
For instance, our optional array in the code above contains blocking, which indicates that the callback function should be handled synchronously. This is crucial for cancelling the request as the request is blocked until the callback returns, which eventually returns cancel: true.

That's it! That is the crux of this simple ad blocker! 🙂

Add a manifest to it, and the chrome extension named Oppilo (because Latin words make for fancy names. 😛) is ready! Be sure to add permissions, and link your javascript file to run in the background. (Code here)

I've added only three URLs for filtering. You can expand your list to block away ads from more providers. Here is an exhaustive list.
Also, AdblockPlus is open source and you can look at all of its code here.

To checkout the code for Oppilo or give it a try - Oppilo