4. Quickstart to Using Privoxy

4.1. Quickstart to Ad Blocking

Ad blocking is but one of Privoxy's array of features. Many of these features are for the technically minded advanced user. But, ad and banner blocking is surely common ground for everybody.

This section will provide a quick summary of ad blocking so you can get up to speed quickly without having to read the more extensive information provided below, though this is highly recommended.

First a bit of a warning ... blocking ads is much like blocking SPAM: the more aggressive you are about it, the more likely you are to block things that were not intended. So there is a trade off here. If you want extreme ad free browsing, be prepared to deal with more "problem" sites, and to spend more time adjusting the configuration to solve these unintended consequences. In short, there is not an easy way to eliminate all ads. Either take the easy way and settle for most ads blocked with the default configuration, or jump in and tweak it for your personal surfing habits and preferences.

Secondly, a brief explanation of Privoxy's "actions". "Actions" in this context, are the directives we use to tell Privoxy to perform some task relating to HTTP transactions (i.e. web browsing). We tell Privoxy to take some "action". Each action has a unique name and function. While there are many potential actions in Privoxy's arsenal, only a few are used for ad blocking. Actions, and action configuration files, are explained in depth below.

Actions are specified in Privoxy's configuration, followed by one or more URLs to which the action should apply. URLs can actually be URL type patterns that use wildcards so they can apply potentially to a range of similar URLs. The actions, together with the URL patterns are called a section.

When you connect to a website, the full URL will either match one or more of the sections as defined in Privoxy's configuration, or not. If so, then Privoxy will perform the respective actions. If not, then nothing special happens. Furthermore, web pages may contain embedded, secondary URLs that your web browser will use to load additional components of the page, as it parses the original page's HTML content. An ad image for instance, is just an URL embedded in the page somewhere. The image itself may be on the same server, or a server somewhere else on the Internet. Complex web pages will have many such embedded URLs.

The actions we need to know about for ad blocking are: block, handle-as-image, and set-image-blocker:

• block - this action stops any contact between your browser and any URL patterns that match this action's configuration. It can be used for blocking ads, but also anything that is determined to be unwanted. By itself, it simply stops any communication with the remote server and sends Privoxy's own built-in BLOCKED page instead to let you now what has happened.

• handle-as-image - tells Privoxy to treat this URL as an image. Privoxy's default configuration already does this for all common image types (e.g. GIF), but there are many situations where this is not so easy to determine. So we'll force it in these cases. This is particularly important for ad blocking, since only if we know that it's an image of some kind, can we replace it with an image of our choosing, instead of the Privoxy BLOCKED page (which would only result in a "broken image" icon). There are some limitations to this though. For instance, you can't just brute-force an image substitution for an entire HTML page in most situations.

• set-image-blocker - tells Privoxy what to display in place of an ad image that has hit a block rule. For this to come into play, the URL must match a block action somewhere in the configuration, and, it must also match an handle-as-image action.

  The configuration options on what to display instead of the ad are:

  pattern - a checkerboard pattern, so that an ad replacement is obvious. This is the default.

  blank - A very small empty GIF image is displayed. This is the so-called "invisible" configuration option.

  http://<URL> - A redirect to any image anywhere of the user's choosing (advanced usage).

The quickest way to adjust any of these settings is with your browser through the special Privoxy editor at http://config.privoxy.org/show-status (shortcut: http://p.p/show-status). This is an internal page, and does not require Internet access. Select the appropriate "actions" file, and click "Edit". It is best to put personal or local preferences in user.action since this is not meant to be overwritten during upgrades, and will over-ride the settings in other files. Here you can insert new "actions", and URLs for ad blocking or other purposes, and make other adjustments to the configuration. Privoxy will detect these changes automatically.

A quick and simple step by step example:

• Right click on the ad image to be blocked, then select "Copy Link Location" from the pop-up menu.

• Set your browser to http://config.privoxy.org/show-status

• Find user.action in the top section, and click on "Edit":

  Figure 1. Actions Files in Use

  

• You should have a section with only block listed under "Actions:". If not, click a "Insert new section below" button, and in the new section that just appeared, click the Edit button right under the word "Actions:". This will bring up a list of all actions. Find block near the top, and click in the "Enabled" column, then "Submit" just below the list.

• Now, in the block actions section, click the "Add" button, and paste the URL the browser got from "Copy Link Location". Remove the http:// at the beginning of the URL. Then, click "Submit" (or "OK" if in a pop-up window).

• Now go back to the original page, and press SHIFT-Reload (or flush all browser caches). The image should be gone now.

This is a very crude and simple example. There might be good reasons to use a wildcard pattern match to include potentially similar images from the same site. For a more extensive explanation of "patterns", and the entire actions concept, see the Actions section.

For advanced users who want to hand edit their config files, you might want to now go to the Actions Files Tutorial. The ideas explained therein also apply to the web-based editor.