![]() ![]() ![]() The bytecode is executed for each resource in the network subsystem. The engine then executes this bytecode for each resource request, and uses the result to modify the request or inject CSS. Once the rules are passed to WebKit, they are compiled into an efficient bytecode format. If you hack on WebKit, MiniBrowser also lets you load rule sets directly from the Debug menu. In OS X Safari, browser extensions can provide their rules through a new API. In iOS Safari, it is done through the native app extension mechanism. The rules are passed to the engine by the browser. When the rule is activated, cookies are stripped from the request before sending it to the server. The second rule activates for any resource loaded as an image or a style sheet on any domain except “”. When the first rule is activated, the load is blocked. The first rule activates for any URL that contains the string “evil-tracker.js”. For example, here is an extension with two rules: [ In essence, each content blocker extension is a list of rules that tells the engine how to act when loading a resource. Content Blockers in Actionīefore I dive into the details, let’s see what a declarative extension look like in the new format. This model allows for WebKit to compile the ruleset into a format that’s very efficient to apply to loads and page content. One new feature we are developing allows describing content blocking rules in a structured format ahead-of-time, declaratively, rather than running extension-provided code at the moment a decision about blocking needs to be made. We are working on new tools to enable content blocking at a fraction of the cost. Sometimes, they can allocate tremendous amounts of memory, which goes against our efforts to reduce WebKit’s memory footprint. Certain kinds of extensions also reduce the runtime performance of webpages. The current model uses a lot of energy, reducing battery life, and increases page load time by adding latency for each resource. The reason we are unhappy about the JavaScript-based content blocking extensions is they have significant performance drawbacks. Such extensions are the most popular kind they let users decide what should load and not load, who can track them, what should be visible on pages, etc. The JavaScript extensions model has been great for many use cases, but there is one category of extensions where members of the WebKit project felt we should do better: the content blocking extensions. They are essentially little sandboxed applications that are launched on demand to extend some specific piece of functionality, known as an extension point. On OS X and iOS, there is also the concept of App Extensions with a different approach to security and performance. It is the classical way to write extensions for OS X Safari, Web/Epiphany, and other browsers. Most extensions are written in JavaScript and loaded by the browser, following a model introduced by Mozilla over a decade ago. Today, there are several models to extend browsers. With extensions, everyone can change their browser to their preferences. Browser extensions have been a big part of modern browsers for a while now. ![]()
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