Privoxy 3.1.1 User Manual
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# 8. Actions Files

The actions files are used to define what actions Privoxy takes for which URLs, and thus determine how ad images, cookies and various other aspects of HTTP content and transactions are handled, and on which sites (or even parts thereof). There are three such files included with Privoxy (as of version 2.9.15), with differing purposes:

- `default.action` - is the primary action file that sets the initial values for all actions. It is intended to provide a base level of functionality for Privoxy's array of features. So it is a set of broad rules that should work reasonably well for users everywhere. This is the file that the developers are keeping updated, and making available to users.

- `user.action` - is intended to be for local site preferences and exceptions. As an example, if your ISP or your bank has specific requirements, and need special handling, this kind of thing should go here. This file will not be upgraded.

- `standard.action` - is used by the web based editor, to set various pre-defined sets of rules for the default actions section in `default.action`. These have increasing levels of aggressiveness and have no influence on your browsing unless you select them explicitly in the editor. It is not recommend to edit this file.

The list of actions files to be used are defined in the main configuration file, and are processed in the order they are defined. The content of these can all be viewed and edited from http://config.privoxy.org/show-status.

An actions file typically has multiple sections. If you want to use "aliases" in an actions file, you have to place the (optional) alias section at the top of that file. Then comes the default set of rules which will apply universally to all sites and pages (be very careful with using such a universal set in `user.action` or any other actions file after `default.action`, because it will override the result from consulting any previous file). And then below that, exceptions to the defined universal policies. You can regard `user.action` as an appendix to `default.action`, with the advantage that is a separate file, which makes preserving your personal settings across Privoxy upgrades easier.

Actions can be used to block anything you want, including ads, banners, or just some obnoxious URL that you would rather not see. Cookies can be accepted or rejected, or accepted only during the current browser session (i.e. not written to disk), content can be modified, JavaScripts tamed, user-tracking fooled, and much more. See below for a complete list of actions.

## 8.1. Finding the Right Mix

Note that some actions, like cookie suppression or script disabling, may render some sites unusable that rely on these techniques to work properly. Finding the right mix of actions is not always easy and certainly a matter of personal taste. In general, it can be said that the more "aggressive" your default settings (in the top section of the actions file) are, the more exceptions for "trusted" sites you will have to make later. If, for example, you want to kill popup windows per default, you'll have to make exceptions from that rule for sites that you regularly use and that require popups for actually useful content, like maybe your bank, favorite shop, or newspaper.

We have tried to provide you with reasonable rules to start from in the distribution actions files. But there is no general rule of thumb on these things. There just are too many variables, and sites are constantly changing. Sooner or later you will want to change the rules (and read this chapter again :).

## 8.2. How to Edit

The easiest way to edit the actions files is with a browser by using our browser-based editor, which can be reached from http://config.privoxy.org/show-status. The editor allows both fine-grained control over every single feature on a per-URL basis, and easy choosing from wholesale sets of defaults like "Cautious", "Medium" or "Advanced".

If you prefer plain text editing to GUIs, you can of course also directly edit the the actions files. Look at `default.action` which is richly commented.

## 8.3. How Actions are Applied to URLs

Actions files are divided into sections. There are special sections, like the "alias" sections which will be discussed later. For now let's concentrate on regular sections: They have a heading line (often split up to multiple lines for readability) which consist of a list of actions, separated by whitespace and enclosed in curly braces. Below that, there is a list of URL patterns, each on a separate line.

To determine which actions apply to a request, the URL of the request is compared to all patterns in each action file file. Every time it matches, the list of applicable actions for the URL is incrementally updated, using the heading of the section in which the pattern is located. If multiple matches for the same URL set the same action differently, the last match wins. If not, the effects are aggregated. E.g. a URL might match a regular section with a heading line of `{ +handle-as-image }`, then later another one with just `{ +block }`, resulting in both actions to apply.

You can trace this process for any given URL by visiting http://config.privoxy.org/show-url-info.

More detail on this is provided in the Appendix, Anatomy of an Action.

## 8.4. Patterns

Generally, a pattern has the form `<domain>/<path>`, where both the `<domain>` and `<path>` are optional. (This is why the pattern `/` matches all URLs).

`www.example.com/`

  is a domain-only pattern and will match any request to `www.example.com`, regardless of which document on that server is requested.

`www.example.com`

  means exactly the same. For domain-only patterns, the trailing `/` may be omitted.

`www.example.com/index.html`

  matches only the single document `/index.html` on `www.example.com`.

`/index.html`

  matches the document `/index.html`, regardless of the domain, i.e. on any web server.

`index.html`

  matches nothing, since it would be interpreted as a domain name and there is no top-level domain called `.html`.

### 8.4.1. The Domain Pattern

The matching of the domain part offers some flexible options: if the domain starts or ends with a dot, it becomes unanchored at that end. For example:

`.example.com`

  matches any domain that ENDS in `.example.com`

`www.`

  matches any domain that STARTS with `www.`

`.example.`

  matches any domain that CONTAINS `.example.` (Correctly speaking: It matches any FQDN that contains `example` as a domain.)

Additionally, there are wild-cards that you can use in the domain names themselves. They work pretty similar to shell wild-cards: "*" stands for zero or more arbitrary characters, "?" stands for any single character, you can define character classes in square brackets and all of that can be freely mixed:

`ad*.example.com`

  matches "adserver.example.com", "ads.example.com", etc but not "sfads.example.com"

`*ad*.example.com`

  matches all of the above, and then some.

`.?pix.com`

  matches `www.ipix.com`, `pictures.epix.com`, `a.b.c.d.e.upix.com` etc.

`www[1-9a-ez].example.c*`

  matches `www1.example.com`, `www4.example.cc`, `wwwd.example.cy`, `wwwz.example.com` etc., but not `wwww.example.com`.

### 8.4.2. The Path Pattern

Privoxy uses Perl compatible regular expressions (through the PCRE library) for matching the path.

There is an Appendix with a brief quick-start into regular expressions, and full (very technical) documentation on PCRE regex syntax is available on-line at http://www.pcre.org/man.txt. You might also find the Perl man page on regular expressions (`man perlre`) useful, which is available on-line at http://www.perldoc.com/perl5.6/pod/perlre.html.

Note that the path pattern is automatically left-anchored at the "/", i.e. it matches as if it would start with a "^" (regular expression speak for the beginning of a line).

Please also note that matching in the path is CASE INSENSITIVE by default, but you can switch to case sensitive at any point in the pattern by using the "(?-i)" switch: `www.example.com/(?-i)PaTtErN.*` will match only documents whose path starts with `PaTtErN` in exactly this capitalization.

## 8.5. Actions

All actions are disabled by default, until they are explicitly enabled somewhere in an actions file. Actions are turned on if preceded with a "+", and turned off if preceded with a "-". So a `+action` means "do that action", e.g. `+block` means "please block URLs that match the following patterns", and `-block` means "don't block URLs that match the following patterns, even if `+block` previously applied."

Again, actions are invoked by placing them on a line, enclosed in curly braces and separated by whitespace, like in `{+some-action -some-other-action{some-parameter}}`, followed by a list of URL patterns, one per line, to which they apply. Together, the actions line and the following pattern lines make up a section of the actions file.

There are three classes of actions:

- Boolean, i.e the action can only be "enabled" or "disabled". Syntax:

        +name        # enable action name
        -name        # disable action name

  Example: `+block`

- Parameterized, where some value is required in order to enable this type of action. Syntax:

        +name{param}  # enable action and set parameter to param,
                     # overwriting parameter from previous match if necessary
        -name         # disable action. The parameter can be omitted

  Note that if the URL matches multiple positive forms of a parameterized action, the last match wins, i.e. the params from earlier matches are simply ignored.

  Example: `+hide-user-agent{ Mozilla 1.0 }`

- Multi-value. These look exactly like parameterized actions, but they behave differently: If the action applies multiple times to the same URL, but with different parameters, all the parameters from all matches are remembered. This is used for actions that can be executed for the same request repeatedly, like adding multiple headers, or filtering through multiple filters. Syntax:

        +name{param}   # enable action and add param to the list of parameters
        -name{param}   # remove the parameter param from the list of parameters
                      # If it was the last one left, disable the action.
        -name          # disable this action completely and remove all parameters from the list

  Examples: `+add-header{X-Fun-Header: Some text}` and `+filter{html-annoyances}`

If nothing is specified in any actions file, no "actions" are taken. So in this case Privoxy would just be a normal, non-blocking, non-anonymizing proxy. You must specifically enable the privacy and blocking features you need (although the provided default actions files will give a good starting point).

Later defined actions always over-ride earlier ones. So exceptions to any rules you make, should come in the latter part of the file (or in a file that is processed later when using multiple actions files). For multi-valued actions, the actions are applied in the order they are specified. Actions files are processed in the order they are defined in `config` (the default installation has three actions files). It also quite possible for any given URL pattern to match more than one pattern and thus more than one set of actions!

The list of valid Privoxy actions are:

#### 8.5.1. add-header

Typical use:

  Confuse log analysis, custom applications

Effect:

  Sends a user defined HTTP header to the web server.

Type:

  Multi-value.

Parameter:

  Any string value is possible. Validity of the defined HTTP headers is not checked. It is recommended that you use the "`X-`" prefix for custom headers.

Notes:

  This action may be specified multiple times, in order to define multiple headers. This is rarely needed for the typical user. If you don't know what "HTTP headers" are, you definitely don't need to worry about this one.

Example usage:

      +add-header{X-User-Tracking: sucks}

#### 8.5.2. block

Typical use:

  Block ads or other obnoxious content

Effect:

  Requests for URLs to which this action applies are blocked, i.e. the requests are not forwarded to the remote server, but answered locally with a substitute page or image, as determined by the `handle-as-image` and `set-image-blocker` actions.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  Privoxy sends a special "BLOCKED" page for requests to blocked pages. This page contains links to find out why the request was blocked, and a click-through to the blocked content (the latter only if compiled with the force feature enabled). The "BLOCKED" page adapts to the available screen space -- it displays full-blown if space allows, or miniaturized and text-only if loaded into a small frame or window. If you are using Privoxy right now, you can take a look at the "BLOCKED" page.

  A very important exception occurs if both `block` and `handle-as-image`, apply to the same request: it will then be replaced by an image. If `set-image-blocker` (see below) also applies, the type of image will be determined by its parameter, if not, the standard checkerboard pattern is sent.

  It is important to understand this process, in order to understand how Privoxy deals with ads and other unwanted content.

  The `filter` action can perform a very similar task, by "blocking" banner images and other content through rewriting the relevant URLs in the document's HTML source, so they don't get requested in the first place. Note that this is a totally different technique, and it's easy to confuse the two.

Example usage (section):

      {+block}      # Block and replace with "blocked" page
      .nasty-stuff.example.com

      {+block +handle-as-image} # Block and replace with image
      .ad.doubleclick.net
      .ads.r.us

#### 8.5.3. crunch-incoming-cookies

Typical use:

  Prevent the web server from setting any cookies on your system

Effect:

  Deletes any "Set-Cookie:" HTTP headers from server replies.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  This action is only concerned with incoming cookies. For outgoing cookies, use `crunch-outgoing-cookies`. Use both to disable cookies completely.

  It makes no sense at all to use this action in conjunction with the `session-cookies-only` action, since it would prevent the session cookies from being set.

Example usage:

      +crunch-incoming-cookies

#### 8.5.4. crunch-outgoing-cookies

Typical use:

  Prevent the web server from reading any cookies from your system

Effect:

  Deletes any "Cookie:" HTTP headers from client requests.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  This action is only concerned with outgoing cookies. For incoming cookies, use `crunch-incoming-cookies`. Use both to disable cookies completely.

  It makes no sense at all to use this action in conjunction with the `session-cookies-only` action, since it would prevent the session cookies from being read.

Example usage:

      +crunch-outgoing-cookies

#### 8.5.5. deanimate-gifs

Typical use:

  Stop those annoying, distracting animated GIF images.

Effect:

  De-animate GIF animations, i.e. reduce them to their first or last image.

Type:

  Parameterized.

Parameter:

  "last" or "first"

Notes:

  This will also shrink the images considerably (in bytes, not pixels!). If the option "first" is given, the first frame of the animation is used as the replacement. If "last" is given, the last frame of the animation is used instead, which probably makes more sense for most banner animations, but also has the risk of not showing the entire last frame (if it is only a delta to an earlier frame).

  You can safely use this action with patterns that will also match non-GIF objects, because no attempt will be made at anything that doesn't look like a GIF.

Example usage:

      +deanimate-gifs{last}

#### 8.5.6. downgrade-http-version

Typical use:

  Work around (very rare) problems with HTTP/1.1

Effect:

  Downgrades HTTP/1.1 client requests and server replies to HTTP/1.0.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  This is a left-over from the time when Privoxy didn't support important HTTP/1.1 features well. It is left here for the unlikely case that you experience HTTP/1.1 related problems with some server out there. Not all (optional) HTTP/1.1 features are supported yet, so there is a chance you might need this action.

Example usage (section):

      {+downgrade-http-version}
      problem-host.example.com

#### 8.5.7. fast-redirects

Typical use:

  Fool some click-tracking scripts and speed up indirect links

Effect:

  Cut off all but the last valid URL from requests.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  Many sites, like yahoo.com, don't just link to other sites. Instead, they will link to some script on their own servers, giving the destination as a parameter, which will then redirect you to the final target. URLs resulting from this scheme typically look like: http://some.place/click-tracker.cgi?target=http://some.where.else.

  Sometimes, there are even multiple consecutive redirects encoded in the URL. These redirections via scripts make your web browsing more traceable, since the server from which you follow such a link can see where you go to. Apart from that, valuable bandwidth and time is wasted, while your browser ask the server for one redirect after the other. Plus, it feeds the advertisers.

  This feature is currently not very smart and is scheduled for improvement. It is likely to break some sites. You should expect to need possibly many exceptions to this action, if it is enabled by default in `default.action`. Some sites just don't work without it.

Example usage:

      {+fast-redirects}

#### 8.5.8. filter

Typical use:

  Get rid of HTML and JavaScript annoyances, banner advertisements (by size), do fun text replacements, etc.

Effect:

  Text documents, including HTML and JavaScript, to which this action applies, are filtered on-the-fly through the specified regular expression based substitutions.

Type:

  Parameterized.

Parameter:

  The name of a filter, as defined in the filter file (typically `default.filter`, set by the `filterfile` option in the config file). Filtering can be completely disabled without the use of parameters.

Notes:

  For your convenience, there are a number of pre-defined filters available in the distribution filter file that you can use. See the examples below for a list.

  This is potentially a very powerful feature! But "rolling your own" filters requires a knowledge of regular expressions and HTML.

  Filtering requires buffering the page content, which may appear to slow down page rendering since nothing is displayed until all content has passed the filters. (It does not really take longer, but seems that way since the page is not incrementally displayed.) This effect will be more noticeable on slower connections.

  The amount of data that can be filtered is limited to the `buffer-limit` option in the main config file. The default is 4096 KB (4 Megs). Once this limit is exceeded, the buffered data, and all pending data, is passed through unfiltered. Inappropriate MIME types are not filtered.

  At this time, Privoxy cannot (yet!) uncompress compressed documents. If you want filtering to work on all documents, even those that would normally be sent compressed, use the `prevent-compression` action in conjunction with `filter`.

  Filtering can achieve some of the same effects as the `block` action, i.e. it can be used to block ads and banners. But the mechanism works quite differently. One effective use, is to block ad banners based on their size (see below), since many of these seem to be somewhat standardized.

  Feedback with suggestions for new or improved filters is particularly welcome!

Example usage (with filters from the distribution `default.filter` file):

      +filter{html-annoyances}     # Get rid of particularly annoying HTML abuse.

      +filter{js-annoyances}       # Get rid of particularly annoying JavaScript abuse

      +filter{banners-by-size}     # Kill banners based on their size for this page (very efficient!)

      +filter{banners-by-link}     # Kill banners based on the link they are contained in (experimental)

      +filter{img-reorder}         # Reorder attributes in <img> tags to make the banners-by-* filters more effective

      +filter{content-cookies}     # Kill cookies that come sneaking in the HTML or JS content

      +filter{popups}              # Kill all popups in JS and HTML

      +filter{webbugs}             # Squish WebBugs (1x1 invisible GIFs used for user tracking)

      +filter{fun}                 # Text replacements for subversive browsing fun!

      +filter{frameset-borders}    # Give frames a border and make them resizeable

      +filter{refresh-tags}        # Kill automatic refresh tags (for dial-on-demand setups)

      +filter{nimda}               # Remove Nimda (virus) code.

      +filter{shockwave-flash}     # Kill embedded Shockwave Flash objects

      +filter{crude-parental}      # Kill all web pages that contain the words "sex" or "warez"

      +filter{js-events}           # Kill all JS event bindings (Radically destructive! Only for extra nasty sites)

#### 8.5.9. handle-as-image

Typical use:

  Mark URLs as belonging to images (so they'll be replaced by images if they get blocked)

Effect:

  This action alone doesn't do anything noticeable. It just marks URLs as images. If the `block` action also applies, the presence or absence of this mark decides whether an HTML "blocked" page, or a replacement image (as determined by the `set-image-blocker` action) will be sent to the client as a substitute for the blocked content.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  The below generic example section is actually part of `default.action`. It marks all URLs with well-known image file name extensions as images and should be left intact.

  Users will probably only want to use the handle-as-image action in conjunction with `block`, to block sources of banners, whose URLs don't reflect the file type, like in the second example section.

  Note that you cannot treat HTML pages as images in most cases. For instance, (in-line) ad frames require an HTML page to be sent, or they won't display properly. Forcing `handle-as-image` in this situation will not replace the ad frame with an image, but lead to error messages.

Example usage (sections):

      # Generic image extensions:
      #
      {+handle-as-image}
      /.*\.(gif|jpg|jpeg|png|bmp|ico)$

      # These don't look like images, but they're banners and should be
      # blocked as images:
      #
      {+block +handle-as-image}
      some.nasty-banner-server.com/junk.cgi?output=trash

      # Banner source! Who cares if they also have non-image content?
      ad.doubleclick.net

#### 8.5.10. hide-forwarded-for-headers

Typical use:

  Improve privacy by hiding the true source of the request

Effect:

  Deletes any existing "X-Forwarded-for:" HTTP header from client requests, and prevents adding a new one.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  It is fairly safe to leave this on.

  This action is scheduled for improvement: It should be able to generate forged "X-Forwarded-for:" headers using random IP addresses from a specified network, to make successive requests from the same client look like requests from a pool of different users sharing the same proxy.

Example usage:

      +hide-forwarded-for-headers

#### 8.5.11. hide-from-header

Typical use:

  Keep your (old and ill) browser from telling web servers your email address

Effect:

  Deletes any existing "From:" HTTP header, or replaces it with the specified string.

Type:

  Parameterized.

Parameter:

  Keyword: "block", or any user defined value.

Notes:

  The keyword "block" will completely remove the header (not to be confused with the `block` action).

  Alternately, you can specify any value you prefer to be sent to the web server. If you do, it is a matter of fairness not to use any address that is actually used by a real person.

  This action is rarely needed, as modern web browsers don't send "From:" headers anymore.

Example usage:

      +hide-from-header{block}

  or

      +hide-from-header{spam-me-senseless@sittingduck.example.com}

#### 8.5.12. hide-referrer

Typical use:

  Conceal which link you followed to get to a particular site

Effect:

  Deletes the "Referer:" (sic) HTTP header from the client request, or replaces it with a forged one.

Type:

  Parameterized.

Parameter:

  - "block" to delete the header completely.

  - "forge" to pretend to be coming from the homepage of the server we are talking to.

  - Any other string to set a user defined referrer.

Notes:

  "forge" is the preferred option here, since some servers will not send images back otherwise, in an attempt to prevent their valuable content from being embedded elsewhere (and hence, without being surrounded by their banners).

  `hide-referer` is an alternate spelling of `hide-referrer` and the two can be can be freely substituted with each other. ("referrer" is the correct English spelling, however the HTTP specification has a bug - it requires it to be spelled as "referer".)

Example usage:

      +hide-referrer{forge}

  or

      +hide-referrer{http://www.yahoo.com/}

#### 8.5.13. hide-user-agent

Typical use:

  Conceal your type of browser and client operating system

Effect:

  Replaces the value of the "User-Agent:" HTTP header in client requests with the specified value.

Type:

  Parameterized.

Parameter:

  Any user-defined string.

Notes:

  Warning
  This breaks many web sites that depend on looking at this header in order to customize their content for different browsers (which, by the way, is NOT a smart way to do that!).

  Using this action in multi-user setups or wherever different types of browsers will access the same Privoxy is not recommended. In single-user, single-browser setups, you might use it to delete your OS version information from the headers, because it is an invitation to exploit known bugs for your OS. It is also occasionally useful to forge this in order to access sites that won't let you in otherwise (though there may be a good reason in some cases). Example of this: some MSN sites will not let Mozilla enter, yet forging to a Netscape 6.1 user-agent works just fine. (Must be just a silly MS goof, I'm sure :-).

  This action is scheduled for improvement.

Example usage:

      +hide-user-agent{Netscape 6.1 (X11; I; Linux 2.4.18 i686)}

#### 8.5.14. kill-popups

Typical use:

  Eliminate those annoying pop-up windows

Effect:

  While loading the document, replace JavaScript code that opens pop-up windows with (syntactically neutral) dummy code on the fly.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  This action is easily confused with the built-in, hardwired `filter` action, but there are important differences: For `kill-popups`, the document need not be buffered, so it can be incrementally rendered while downloading. But `kill-popups` doesn't catch as many pop-ups as `filter{`popups`}` does.

  Think of it as a fast and efficient replacement for a filter that you can use if you don't want any filtering at all. Note that it doesn't make sense to combine it with any `filter` action, since as soon as one `filter` applies, the whole document needs to be buffered anyway, which destroys the advantage of the `kill-popups` action over its filter equivalent.

  Killing all pop-ups is a dangerous business. Many shops and banks rely on pop-ups to display forms, shopping carts etc, and killing only the unwanted pop-ups would require artificial intelligence in Privoxy. If the only kind of pop-ups that you want to kill are exit consoles (those really nasty windows that appear when you close an other one), you might want to use `filter{`js-annoyances`}` instead.

Example usage:

      +kill-popups

#### 8.5.15. limit-connect

Typical use:

  Prevent abuse of Privoxy as a TCP proxy relay

Effect:

  Specifies to which ports HTTP CONNECT requests are allowable.

Type:

  Parameterized.

Parameter:

  A comma-separated list of ports or port ranges (the latter using dashes, with the minimum defaulting to 0 and the maximum to 65K).

Notes:

  By default, i.e. if no `limit-connect` action applies, Privoxy only allows HTTP CONNECT requests to port 443 (the standard, secure HTTPS port). Use `limit-connect` if more fine-grained control is desired for some or all destinations.

  The CONNECT methods exists in HTTP to allow access to secure websites ("https://" URLs) through proxies. It works very simply: the proxy connects to the server on the specified port, and then short-circuits its connections to the client and to the remote server. This can be a big security hole, since CONNECT-enabled proxies can be abused as TCP relays very easily.

  If you don't know what any of this means, there probably is no reason to change this one, since the default is already very restrictive.

Example usages:

      +limit-connect{443}                   # This is the default and need not be specified.
      +limit-connect{80,443}                # Ports 80 and 443 are OK.
      +limit-connect{-3, 7, 20-100, 500-}   # Ports less than 3, 7, 20 to 100 and above 500 are OK.
      +limit-connect{-}                     # All ports are OK (gaping security hole!)

#### 8.5.16. prevent-compression

Typical use:

  Ensure that servers send the content uncompressed, so it can be passed through `filter`s

Effect:

  Adds a header to the request that asks for uncompressed transfer.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  More and more websites send their content compressed by default, which is generally a good idea and saves bandwidth. But for the `filter`, `deanimate-gifs` and `kill-popups` actions to work, Privoxy needs access to the uncompressed data. Unfortunately, Privoxy can't yet(!) uncompress, filter, and re-compress the content on the fly. So if you want to ensure that all websites, including those that normally compress, can be filtered, you need to use this action.

  This will slow down transfers from those websites, though. If you use any of the above-mentioned actions, you will typically want to use `prevent-compression` in conjunction with them.

  Note that some (rare) ill-configured sites don't handle requests for uncompressed documents correctly (they send an empty document body). If you use `prevent-compression` per default, you'll have to add exceptions for those sites. See the example for how to do that.

Example usage (sections):

      # Set default:
      #
      {+prevent-compression}
      / # Match all sites

      # Make exceptions for ill sites:
      #
      {-prevent-compression}
      www.debianhelp.org
      www.pclinuxonline.com

#### 8.5.17. send-vanilla-wafer

Typical use:

  Feed log analysis scripts with useless data.

Effect:

  Sends a cookie with each request stating that you do not accept any copyright on cookies sent to you, and asking the site operator not to track you.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  The vanilla wafer is a (relatively) unique header and could conceivably be used to track you.

  This action is rarely used and not enabled in the default configuration.

Example usage:

      +send-vanilla-wafer

#### 8.5.18. send-wafer

Typical use:

  Send custom cookies or feed log analysis scripts with even more useless data.

Effect:

  Sends a custom, user-defined cookie with each request.

Type:

  Multi-value.

Parameter:

  A string of the form "`name`=`value`".

Notes:

  Being multi-valued, multiple instances of this action can apply to the same request, resulting in multiple cookies being sent.

  This action is rarely used and not enabled in the default configuration.

Example usage (section):

      {+send-wafer{UsingPrivoxy=true}}
      my-internal-testing-server.void

#### 8.5.19. session-cookies-only

Typical use:

  Allow only temporary "session" cookies (for the current browser session only).

Effect:

  Deletes the "expires" field from "Set-Cookie:" server headers. Most browsers will not store such cookies permanently and forget them in between sessions.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  This is less strict than `crunch-incoming-cookies` / `crunch-outgoing-cookies` and allows you to browse websites that insist or rely on setting cookies, without compromising your privacy too badly.

  Most browsers will not permanently store cookies that have been processed by `session-cookies-only` and will forget about them between sessions. This makes profiling cookies useless, but won't break sites which require cookies so that you can log in for transactions. This is generally turned on for all sites, and is the recommended setting.

  It makes no sense at all to use `session-cookies-only` together with `crunch-incoming-cookies` or `crunch-outgoing-cookies`. If you do, cookies will be plainly killed.

  Note that it is up to the browser how it handles such cookies without an "expires" field. If you use an exotic browser, you might want to try it out to be sure.

Example usage:

      +session-cookies-only

#### 8.5.20. set-image-blocker

Typical use:

  Choose the replacement for blocked images

Effect:

  This action alone doesn't do anything noticeable. If both `block` and `handle-as-image` also apply, i.e. if the request is to be blocked as an image, then the parameter of this action decides what will be sent as a replacement.

Type:

  Parameterized.

Parameter:

  - "pattern" to send a built-in checkerboard pattern image. The image is visually decent, scales very well, and makes it obvious where banners were busted.

  - "blank" to send a built-in transparent image. This makes banners disappear completely, but makes it hard to detect where Privoxy has blocked images on a given page and complicates troubleshooting if Privoxy has blocked innocent images, like navigation icons.

  - "`target-url`" to send a redirect to `target-url`. You can redirect to any image anywhere, even in your local filesystem (via "file:///" URL).

    A good application of redirects is to use special Privoxy-built-in URLs, which send the built-in images, as `target-url`. This has the same visual effect as specifying "blank" or "pattern" in the first place, but enables your browser to cache the replacement image, instead of requesting it over and over again.

Notes:

  The URLs for the built-in images are "http://config.privoxy.org/send-banner?type=`type`", where `type` is either "blank" or "pattern".

  There is a third (advanced) type, called "auto". It is NOT to be used in `set-image-blocker`, but meant for use from filters. Auto will select the type of image that would have applied to the referring page, had it been an image.

Example usage:

  Built-in pattern:

      +set-image-blocker{pattern}

  Redirect to the BSD devil:

      +set-image-blocker{http://www.freebsd.org/gifs/dae_up3.gif}

  Redirect to the built-in pattern for better caching:

      +set-image-blocker{http://config.privoxy.org/send-banner?type=pattern}

### 8.5.21. Summary

Note that many of these actions have the potential to cause a page to misbehave, possibly even not to display at all. There are many ways a site designer may choose to design his site, and what HTTP header content, and other criteria, he may depend on. There is no way to have hard and fast rules for all sites. See the Appendix for a brief example on troubleshooting actions.

## 8.6. Aliases

Custom "actions", known to Privoxy as "aliases", can be defined by combining other actions. These can in turn be invoked just like the built-in actions. Currently, an alias name can contain any character except space, tab, "=", "{" and "}", but we strongly recommend that you only use "a" to "z", "0" to "9", "+", and "-". Alias names are not case sensitive, and are not required to start with a "+" or "-" sign, since they are merely textually expanded.

Aliases can be used throughout the actions file, but they must be defined in a special section at the top of the file! And there can only be one such section per actions file. Each actions file may have its own alias section, and the aliases defined in it are only visible within that file.

There are two main reasons to use aliases: One is to save typing for frequently used combinations of actions, the other one is a gain in flexibility: If you decide once how you want to handle shops by defining an alias called "shop", you can later change your policy on shops in one place, and your changes will take effect everywhere in the actions file where the "shop" alias is used. Calling aliases by their purpose also makes your actions files more readable.

Currently, there is one big drawback to using aliases, though: Privoxy's built-in web-based action file editor honors aliases when reading the actions files, but it expands them before writing. So the effects of your aliases are of course preserved, but the aliases themselves are lost when you edit sections that use aliases with it. This is likely to change in future versions of Privoxy.

Now let's define some aliases...

     # Useful custom aliases we can use later.
     #
     # Note the (required!) section header line and that this section
     # must be at the top of the actions file!
     #
     {{alias}}

     # These aliases just save typing later:
     # (Note that some already use other aliases!)
     #
     +crunch-all-cookies = +crunch-incoming-cookies +crunch-outgoing-cookies
     -crunch-all-cookies = -crunch-incoming-cookies -crunch-outgoing-cookies
     block-as-image      = +block +handle-as-image
     mercy-for-cookies   = -crunch-all-cookies -session-cookies-only

     # These aliases define combinations of actions
     # that are useful for certain types of sites:
     #
     fragile     = -block -crunch-all-cookies -filter -fast-redirects -hide-referer -kill-popups
     shop        = -crunch-all-cookies -filter{popups} -kill-popups

     # Short names for other aliases, for really lazy people ;-)
     #
     c0 = +crunch-all-cookies
     c1 = -crunch-all-cookies

...and put them to use. These sections would appear in the lower part of an actions file and define exceptions to the default actions (as specified further up for the "/" pattern):

     # These sites are either very complex or very keen on
     # user data and require minimal interference to work:
     #
     {fragile}
     .office.microsoft.com
     .windowsupdate.microsoft.com
     .nytimes.com

     # Shopping sites:
     # Allow cookies (for setting and retrieving your customer data)
     #
     {shop}
     .quietpc.com
     .worldpay.com   # for quietpc.com
     .scan.co.uk

     # These shops require pop-ups:
     #
     {shop -kill-popups -filter{popups}}
      .dabs.com
      .overclockers.co.uk

Aliases like "shop" and "fragile" are often used for "problem" sites that require some actions to be disabled in order to function properly.

## 8.7. Actions Files Tutorial

The above chapters have shown which actions files there are and how they are organized, how actions are specified and applied to URLs, how patterns work, and how to define and use aliases. Now, let's look at an example `default.action` and `user.action` file and see how all these pieces come together:

### 8.7.1. default.action

Every config file should start with a short comment stating its purpose:

    # Sample default.action file <developers@privoxy.org>

Then, since this is the `default.action` file, the first section is a special section for internal use that you needn't change or worry about:

    ##########################################################################
    # Settings -- Don't change! For internal Privoxy use ONLY.
    ##########################################################################

    {{settings}}
    for-privoxy-version=3.0

After that comes the (optional) alias section. We'll use the example section from the above chapter on aliases, that also explains why and how aliases are used:

    ##########################################################################
    # Aliases
    ##########################################################################
    {{alias}}

    # These aliases just save typing later:
    # (Note that some already use other aliases!)
    #
    +crunch-all-cookies = +crunch-incoming-cookies +crunch-outgoing-cookies
    -crunch-all-cookies = -crunch-incoming-cookies -crunch-outgoing-cookies
    block-as-image      = +block +handle-as-image
    mercy-for-cookies   = -crunch-all-cookies -session-cookies-only

    # These aliases define combinations of actions
    # that are useful for certain types of sites:
    #
    fragile     = -block -crunch-all-cookies -filter -fast-redirects -hide-referer -kill-popups
    shop        = mercy-for-cookies -filter{popups} -kill-popups

Now come the regular sections, i.e. sets of actions, accompanied by URL patterns to which they apply. Remember all actions are disabled when matching starts, so we have to explicitly enable the ones we want.

The first regular section is probably the most important. It has only one pattern, "`/`", but this pattern matches all URLs. Therefore, the set of actions used in this "default" section will be applied to all requests as a start. It can be partly or wholly overridden by later matches further down this file, or in user.action, but it will still be largely responsible for your overall browsing experience.

Again, at the start of matching, all actions are disabled, so there is no real need to disable any actions here, but we will do that nonetheless, to have a complete listing for your reference. (Remember: a "+" preceding the action name enables the action, a "-" disables!). Also note how this long line has been made more readable by splitting it into multiple lines with line continuation.

    ##########################################################################
    # "Defaults" section:
    ##########################################################################
     { \
     -add-header \
     -block \
     -crunch-incoming-cookies \
     -crunch-outgoing-cookies \
     +deanimate-gifs \
     -downgrade-http-version \
     +fast-redirects \
     +filter{html-annoyances} \
     +filter{js-annoyances} \
     -filter{content-cookies} \
     +filter{popups} \
     +filter{webbugs} \
     -filter{refresh-tags} \
     -filter{fun} \
     +filter{nimda} \
     +filter{banners-by-size} \
     -filter{banners-by-link} \
     -filter{img-reorder} \
     -filter{shockwave-flash} \
     -filter{crude-parental} \
     -filter{js-events} \
     -handle-as-image \
     +hide-forwarded-for-headers \
     +hide-from-header{block} \
     +hide-referrer{forge} \
     -hide-user-agent \
     -kill-popups \
     -limit-connect \
     +prevent-compression \
     -send-vanilla-wafer \
     -send-wafer \
     +session-cookies-only \
     +set-image-blocker{pattern} \
     }
     / # forward slash will match *all* potential URL patterns.

The default behavior is now set. Note that some actions, like not hiding the user agent, are part of a "general policy" that applies universally and won't get any exceptions defined later. Other choices, like not blocking (which is understandably the default!) need exceptions, i.e. we need to specify explicitly what we want to block in later sections. We will also want to make exceptions from our general pop-up-killing, and use our defined aliases for that.

The first of our specialized sections is concerned with "fragile" sites, i.e. sites that require minimum interference, because they are either very complex or very keen on tracking you (and have mechanisms in place that make them unusable for people who avoid being tracked). We will simply use our pre-defined `fragile` alias instead of stating the list of actions explicitly:

    ##########################################################################
    # Exceptions for sites that'll break under the default action set:
    ##########################################################################

    # "Fragile" Use a minimum set of actions for these sites (see alias above):
    #
    { fragile }
    .office.microsoft.com           # surprise, surprise!
    .windowsupdate.microsoft.com

Shopping sites are not as fragile, but they typically require cookies to log in, and pop-up windows for shopping carts or item details. Again, we'll use a pre-defined alias:

    # Shopping sites:
    #
    { shop }
    .quietpc.com
    .worldpay.com   # for quietpc.com
    .jungle.com
    .scan.co.uk

Then, there are sites which rely on pop-up windows (yuck!) to work. Since we made pop-up-killing our default above, we need to make exceptions now. Mozilla users, who can turn on smart handling of unwanted pop-ups in their browsers, can safely choose -`filter{popups}` (and -`kill-popups`) above and hence don't need this section. Anyway, disabling an already disabled action doesn't hurt, so we'll define our exceptions regardless of what was chosen in the defaults section:

    # These sites require pop-ups too :(
    #
    { -kill-popups -filter{popups} }
    .dabs.com
    .overclockers.co.uk
    .deutsche-bank-24.de

The `fast-redirects` action, which we enabled per default above, breaks some sites. So disable it for popular sites where we know it misbehaves:

    { -fast-redirects }
    login.yahoo.com
    edit.*.yahoo.com
    .google.com
    .altavista.com/.*(like|url|link):http
    .altavista.com/trans.*urltext=http
    .nytimes.com

It is important that Privoxy knows which URLs belong to images, so that if they are to be blocked, a substitute image can be sent, rather than an HTML page. Contacting the remote site to find out is not an option, since it would destroy the loading time advantage of banner blocking, and it would feed the advertisers (in terms of money and information). We can mark any URL as an image with the `handle-as-image` action, and marking all URLs that end in a known image file extension is a good start:

    ##########################################################################
    # Images:
    ##########################################################################

    # Define which file types will be treated as images, in case they get
    # blocked further down this file:
    #
    { +handle-as-image }
    /.*\.(gif|jpe?g|png|bmp|ico)$

And then there are known banner sources. They often use scripts to generate the banners, so it won't be visible from the URL that the request is for an image. Hence we block them and mark them as images in one go, with the help of our `block-as-image` alias defined above. (We could of course just as well use `+block +handle-as-image` here.) Remember that the type of the replacement image is chosen by the `set-image-blocker` action. Since all URLs have matched the default section with its `+set-image-blocker{pattern}` action before, it still applies and needn't be repeated:

    # Known ad generators:
    #
    { block-as-image }
    ar.atwola.com
    .ad.doubleclick.net
    .ad.*.doubleclick.net
    .a.yimg.com/(?:(?!/i/).)*$
    .a[0-9].yimg.com/(?:(?!/i/).)*$
    bs*.gsanet.com
    bs*.einets.com
    .qkimg.net

One of the most important jobs of Privoxy is to block banners. A huge bunch of them are already "blocked" by the `filter{banners-by-size}` action, which we enabled above, and which deletes the references to banner images from the pages while they are loaded, so the browser doesn't request them anymore, and hence they don't need to be blocked here. But this naturally doesn't catch all banners, and some people choose not to use filters, so we need a comprehensive list of patterns for banner URLs here, and apply the `block` action to them.

First comes a bunch of generic patterns, which do most of the work, by matching typical domain and path name components of banners. Then comes a list of individual patterns for specific sites, which is omitted here to keep the example short:

    ##########################################################################
    # Block these fine banners:
    ##########################################################################
    { +block }

    # Generic patterns:
    #
    ad*.
    .*ads.
    banner?.
    count*.
    /.*count(er)?\.(pl|cgi|exe|dll|asp|php[34]?)
    /(?:.*/)?(publicite|werbung|rekla(ma|me|am)|annonse|maino(kset|nta|s)?)/

    # Site-specific patterns (abbreviated):
    #
    .hitbox.com

You wouldn't believe how many advertisers actually call their banner servers ads.`company`.com, or call the directory in which the banners are stored simply "banners". So the above generic patterns are surprisingly effective.

But being very generic, they necessarily also catch URLs that we don't want to block. The pattern `.*ads.` e.g. catches "nasty-ads.nasty-corp.com" as intended, but also "downloads.sourcefroge.net" or "adsl.some-provider.net." So here come some well-known exceptions to the `+block` section above.

Note that these are exceptions to exceptions from the default! Consider the URL "downloads.sourcefroge.net": Initially, all actions are deactivated, so it wouldn't get blocked. Then comes the defaults section, which matches the URL, but just deactivates the `block` action once again. Then it matches `.*ads.`, an exception to the general non-blocking policy, and suddenly `+block` applies. And now, it'll match `.*loads.`, where `-block` applies, so (unless it matches again further down) it ends up with no `block` action applying.

    ##########################################################################
    # Save some innocent victims of the above generic block patterns:
    ##########################################################################

    # By domain:
    #
    { -block }
    adv[io]*.  # (for advogato.org and advice.*)
    adsl.      # (has nothing to do with ads)
    ad[ud]*.   # (adult.* and add.*)
    .edu       # (universities don't host banners (yet!))
    .*loads.   # (downloads, uploads etc)

    # By path:
    #
    /.*loads/

    # Site-specific:
    #
    www.globalintersec.com/adv # (adv = advanced)
    www.ugu.com/sui/ugu/adv

Filtering source code can have nasty side effects, so make an exception for our friends at sourceforge.net, and all paths with "cvs" in them. Note that `-filter` disables all filters in one fell swoop!

    # Don't filter code!
    #
    { -filter }
    /.*cvs
    .sourceforge.net

The actual `default.action` is of course more comprehensive, but we hope this example made clear how it works.

### 8.7.2. user.action

So far we are painting with a broad brush by setting general policies, which would be a reasonable starting point for many people. Now, you might want to be more specific and have customized rules that are more suitable to your personal habits and preferences. These would be for narrowly defined situations like your ISP or your bank, and should be placed in `user.action`, which is parsed after all other actions files and hence has the last word, over-riding any previously defined actions. `user.action` is also a safe place for your personal settings, since `default.action` is actively maintained by the Privoxy developers and you'll probably want to install updated versions from time to time.

So let's look at a few examples of things that one might typically do in `user.action`:

    # My user.action file. <fred@foobar.com>

As aliases are local to the actions file that they are defined in, you can't use the ones from `default.action`, unless you repeat them here:

    # (Re-)define aliases for this file:
    #
    {{alias}}
    -crunch-all-cookies = -crunch-incoming-cookies -crunch-outgoing-cookies
    mercy-for-cookies   = -crunch-all-cookies -session-cookies-only
    fragile     = -block -crunch-all-cookies -filter -fast-redirects -hide-referer -kill-popups
    shop        = mercy-for-cookies -filter{popups} -kill-popups
    allow-ads   = -block -filter{banners-by-size} # (see below)

Say you have accounts on some sites that you visit regularly, and you don't want to have to log in manually each time. So you'd like to allow persistent cookies for these sites. The `mercy-for-cookies` alias defined above does exactly that, i.e. it disables crunching of cookies in any direction, and processing of cookies to make them temporary.

    { mercy-for-cookies }
    sunsolve.sun.com
    slashdot.org
    .yahoo.com
    .msdn.microsoft.com
    .redhat.com

Your bank needs popups and is allergic to some filter, but you don't know which, so you disable them all:

    { -filter -kill-popups }
    .your-home-banking-site.com

While browsing the web with Privoxy you noticed some ads that sneaked through, but you were too lazy to report them through our fine and easy feedback system, so you have added them here:

    { +block }
    www.a-popular-site.com/some/unobvious/path
    another.popular.site.net/more/junk/here/

Note that, assuming the banners in the above example have regular image extensions (most do), `+handle-as-image` need not be specified, since all URLs ending in these extensions will already have been tagged as images in the relevant section of `default.action` by now.

Then you noticed that the default configuration breaks Forbes Magazine, but you were too lazy to find out which action is the culprit, and you were again too lazy to give feedback, so you just used the `fragile` alias on the site, and -- whoa! -- it worked:

    { fragile }
    .forbes.com

You like the "fun" text replacements in `default.filter`, but it is disabled in the distributed actions file. (My colleagues on the team just don't have a sense of humour, that's why! ;-). So you'd like to turn it on in your private, update-safe config, once and for all:

    { +filter{fun} }
    / # For ALL sites!

Note that the above is not really a good idea: There are exceptions to the filters in `default.action` for things that really shouldn't be filtered, like code on CVS->Web interfaces. Since `user.action` has the last word, these exceptions won't be valid for the "fun" filtering specified here.

Finally, you might think about how your favourite free websites are funded, and find that they rely on displaying banner advertisements to survive. So you might want to specifically allow banners for those sites that you feel provide value to you:

    { allow-ads }
    .sourceforge.net
    .slashdot.org
    .osdn.net

Note that `allow-ads` has been aliased to `-block` `-filter{banners-by-size}` above.

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