Privoxy 3.1.1 User Manual

Copyright © 2001, 2002 by Privoxy Developers

$Id: user-manual.txt,v 1.1 2003/06/19 16:12:42 lionel Exp $

The User Manual gives users information on how to install, configure and use 
Privoxy.

Privoxy is a web proxy with advanced filtering capabilities for protecting
privacy, filtering web page content, managing cookies, controlling access, and
removing ads, banners, pop-ups and other obnoxious Internet junk. Privoxy has a
very flexible configuration and can be customized to suit individual needs and
tastes. Privoxy has application for both stand-alone systems and multi-user
networks.

Privoxy is based on Internet Junkbuster (tm).

You can find the latest version of the User Manual at http://www.privoxy.org/
user-manual/. Please see the Contact section on how to contact the developers.

-------------------------------------------------------------------------------

Table of Contents
1. Introduction
   
    1.1. Features
   
2. Installation
   
    2.1. Binary Packages
       
        2.1.1. Red Hat, SuSE and Conectiva RPMs
        2.1.2. Debian
        2.1.3. Windows
        2.1.4. Solaris, NetBSD, FreeBSD, HP-UX
        2.1.5. OS/2
        2.1.6. Mac OSX
        2.1.7. AmigaOS
        2.1.8. Gentoo
       
    2.2. Building from Source
    2.3. Keeping your Installation Up-to-Date
   
3. Note to Upgraders
4. Quickstart to Using Privoxy
   
    4.1. Quickstart to Ad Blocking
   
5. Starting Privoxy
   
    5.1. Red Hat and Conectiva
    5.2. Debian
    5.3. SuSE
    5.4. Windows
    5.5. Solaris, NetBSD, FreeBSD, HP-UX and others
    5.6. OS/2
    5.7. Mac OSX
    5.8. AmigaOS
    5.9. Gentoo
    5.10. Command Line Options
   
6. Privoxy Configuration
   
    6.1. Controlling Privoxy with Your Web Browser
    6.2. Configuration Files Overview
   
7. The Main Configuration File
   
    7.1. Configuration and Log File Locations
       
        7.1.1. confdir
        7.1.2. logdir
        7.1.3. actionsfile
        7.1.4. filterfile
        7.1.5. logfile
        7.1.6. jarfile
        7.1.7. trustfile
       
    7.2. Local Set-up Documentation
       
        7.2.1. user-manual
        7.2.2. trust-info-url
        7.2.3. admin-address
        7.2.4. proxy-info-url
       
    7.3. Debugging
       
        7.3.1. debug
        7.3.2. single-threaded
       
    7.4. Access Control and Security
       
        7.4.1. listen-address
        7.4.2. toggle
        7.4.3. enable-remote-toggle
        7.4.4. enable-edit-actions
        7.4.5. ACLs: permit-access and deny-access
        7.4.6. buffer-limit
       
    7.5. Forwarding
       
        7.5.1. forward
        7.5.2. forward-socks4 and forward-socks4a
        7.5.3. Advanced Forwarding Examples
       
    7.6. Windows GUI Options
   
8. Actions Files
   
    8.1. Finding the Right Mix
    8.2. How to Edit
    8.3. How Actions are Applied to URLs
    8.4. Patterns
       
        8.4.1. The Domain Pattern
        8.4.2. The Path Pattern
       
    8.5. Actions
       
        8.5.1. add-header
        8.5.2. block
        8.5.3. crunch-incoming-cookies
        8.5.4. crunch-outgoing-cookies
        8.5.5. deanimate-gifs
        8.5.6. downgrade-http-version
        8.5.7. fast-redirects
        8.5.8. filter
        8.5.9. handle-as-image
        8.5.10. hide-forwarded-for-headers
        8.5.11. hide-from-header
        8.5.12. hide-referrer
        8.5.13. hide-user-agent
        8.5.14. kill-popups
        8.5.15. limit-connect
        8.5.16. prevent-compression
        8.5.17. send-vanilla-wafer
        8.5.18. send-wafer
        8.5.19. session-cookies-only
        8.5.20. set-image-blocker
        8.5.21. Summary
       
    8.6. Aliases
    8.7. Actions Files Tutorial
       
        8.7.1. default.action
        8.7.2. user.action
       
9. The Filter File
   
    9.1. Filter File Tutorial
   
10. Templates
11. Contacting the Developers, Bug Reporting and Feature Requests
   
    11.1. Get Support
    11.2. Report Bugs
    11.3. Request New Features
    11.4. Report Ads or Other Actions-Related Problems
    11.5. Other
   
12. Privoxy Copyright, License and History
   
    12.1. License
    12.2. History
    12.3. Authors
   
13. See Also
14. Appendix
   
    14.1. Regular Expressions
    14.2. Privoxy's Internal Pages
       
        14.2.1. Bookmarklets
       
    14.3. Chain of Events
    14.4. Anatomy of an Action
   
1. Introduction

This documentation is included with the current alpha version of Privoxy,
v.3.1.1, and is mostly complete at this point. The most up to date reference
for the time being is still the comments in the source files and in the
individual configuration files. Development of version 3.0 is currently nearing
completion, and includes many significant changes and enhancements over earlier
versions. The target release date for stable v3.0 is "soon" ;-).

Since this is a alpha version, not all new features are well tested. This
documentation may be slightly out of sync as a result (especially with CVS
sources). And there may be bugs, though hopefully not many!

-------------------------------------------------------------------------------

1.1. Features

In addition to Internet Junkbuster's traditional features of ad and banner
blocking and cookie management, Privoxy provides new features, some of them
currently under development:

  * Integrated browser based configuration and control utility at http://
    config.privoxy.org/ (shortcut: http://p.p/). Browser-based tracing of rule
    and filter effects. Remote toggling.
   
  * Web page content filtering (removes banners based on size, invisible
    "web-bugs", JavaScript and HTML annoyances, pop-up windows, etc.)
   
  * Modularized configuration that allows for standard settings and user
    settings to reside in separate files, so that installing updated actions
    files won't overwrite individual user settings.
   
  * HTTP/1.1 compliant (but not all optional 1.1 features are supported).
   
  * Support for Perl Compatible Regular Expressions in the configuration files,
    and generally a more sophisticated and flexible configuration syntax over
    previous versions.
   
  * Improved cookie management features (e.g. session based cookies).
   
  * GIF de-animation.
   
  * Bypass many click-tracking scripts (avoids script redirection).
   
  * Multi-threaded (POSIX and native threads).
   
  * User-customizable HTML templates for all proxy-generated pages (e.g.
    "blocked" page).
   
  * Auto-detection and re-reading of config file changes.
   
  * Improved signal handling, and a true daemon mode (Unix).
   
  * Every feature now controllable on a per-site or per-location basis,
    configuration more powerful and versatile over-all.
   
  * Many smaller new features added, limitations and bugs removed, and security
    holes fixed.
   
-------------------------------------------------------------------------------

2. Installation

Privoxy is available both in convenient pre-compiled packages for a wide range
of operating systems, and as raw source code. For most users, we recommend
using the packages, which can be downloaded from our Privoxy Project Page.

Note: If you have a previous Junkbuster or Privoxy installation on your system,
you will need to remove it. On some platforms, this may be done for you as part
of their installation procedure. (See below for your platform). In any case be
sure to backup your old configuration if it is valuable to you. See the note to
upgraders section below.

-------------------------------------------------------------------------------

2.1. Binary Packages

How to install the binary packages depends on your operating system:

-------------------------------------------------------------------------------

2.1.1. Red Hat, SuSE and Conectiva RPMs

RPMs can be installed with rpm -Uvh privoxy-3.1.1-1.rpm, and will use /etc/
privoxy for the location of configuration files.

Note that on Red Hat, Privoxy will not be automatically started on system boot.
You will need to enable that using chkconfig, ntsysv, or similar methods. Note
that SuSE will automatically start Privoxy in the boot process.

If you have problems with failed dependencies, try rebuilding the SRC RPM: rpm
--rebuild privoxy-3.1.1-1.src.rpm. This will use your locally installed
libraries and RPM version.

Also note that if you have a Junkbuster RPM installed on your system, you need
to remove it first, because the packages conflict. Otherwise, RPM will try to
remove Junkbuster automatically, before installing Privoxy.

-------------------------------------------------------------------------------

2.1.2. Debian

DEBs can be installed with dpkg -i privoxy_3.1.1-1.deb, and will use /etc/
privoxy for the location of configuration files.

-------------------------------------------------------------------------------

2.1.3. Windows

Just double-click the installer, which will guide you through the installation
process. You will find the configuration files in the same directory as you
installed Privoxy in. We do not use the registry of Windows.

-------------------------------------------------------------------------------

2.1.4. Solaris, NetBSD, FreeBSD, HP-UX

Create a new directory, cd to it, then unzip and untar the archive. For the
most part, you'll have to figure out where things go.

-------------------------------------------------------------------------------

2.1.5. OS/2

First, make sure that no previous installations of Junkbuster and / or Privoxy
are left on your system. Check that no Junkbuster or Privoxy objects are in
your startup folder. 

Then, just double-click the WarpIN self-installing archive, which will guide
you through the installation process. A shadow of the Privoxy executable will
be placed in your startup folder so it will start automatically whenever OS/2
starts.

The directory you choose to install Privoxy into will contain all of the
configuration files.

-------------------------------------------------------------------------------

2.1.6. Mac OSX

Unzip the downloaded file (you can either double-click on the file from the
finder, or from the desktop if you downloaded it there). Then, double-click on
the package installer icon named Privoxy.pkg and follow the installation
process. Privoxy will be installed in the folder /Library/Privoxy. It will
start automatically whenever you start up. To prevent it from starting
automatically, remove or rename the folder /Library/StartupItems/Privoxy.

To start Privoxy by hand, double-click on StartPrivoxy.command in the /Library/
Privoxy folder. Or, type this command in the Terminal:

  /Library/Privoxy/StartPrivoxy.command                                        
                                                                               

You will be prompted for the administrator password.

-------------------------------------------------------------------------------

2.1.7. AmigaOS

Copy and then unpack the lha archive to a suitable location. All necessary
files will be installed into Privoxy directory, including all configuration and
log files. To uninstall, just remove this directory.

-------------------------------------------------------------------------------

2.1.8. Gentoo

Gentoo source packages (Ebuilds) for Privoxy are contained in the Gentoo
Portage Tree (they are not on the download page, but there is a Gentoo section,
where you can see when a new Privoxy Version is added to the Portage Tree).

Before installing Privoxy under Gentoo just do first emerge rsync to get the
latest changes from the Portage tree. With emerge privoxy you install the
latest version.

Configuration files are in /etc/privoxy, the documentation is in /usr/share/doc
/privoxy-3.1.1 and the Log directory is in /var/log/privoxy.

-------------------------------------------------------------------------------

2.2. Building from Source

The most convenient way to obtain the Privoxy sources is to download the source
tarball from our project page.

If you like to live on the bleeding edge and are not afraid of using possibly
unstable development versions, you can check out the up-to-the-minute version
directly from the CVS repository or simply download the nightly CVS tarball.

To build Privoxy from source, autoconf, GNU make (gmake), and, of course, a C
compiler like gcc are required.

When building from a source tarball (either release version or nightly CVS
tarball), first unpack the source:

 tar xzvf privoxy-3.1.1-beta-src* [.tgz or .tar.gz]                            
 cd privoxy-3.1.1-beta                                                         

For retrieving the current CVS sources, you'll need CVS installed. Note that
sources from CVS are development quality, and may not be stable, or well
tested. To download CVS source:

  cvs -d:pserver:anonymous@cvs.ijbswa.sourceforge.net:/cvsroot/ijbswa login          
  cvs -z3 -d:pserver:anonymous@cvs.ijbswa.sourceforge.net:/cvsroot/ijbswa co current 
  cd current                                                                         

This will create a directory named current/, which will contain the source
tree.

Then, in either case, to build from unpacked tarball or CVS source:

 autoheader                                                                    
 autoconf                                                                      
 ./configure      # (--help to see options)                                    
 make             # (the make from gnu, gmake for *BSD)                        
 su                                                                            
 make -n install  # (to see where all the files will go)                       
 make install     # (to really install)                                        

+-----------------------------------------------------------------------------+
|                                   Warning                                   |
|-----------------------------------------------------------------------------|
|The "make install" target is temporary quite broken! It is recommended to use|
|a binary package, or do a source build, and manually install the components. |
|Sorry.                                                                       |
+-----------------------------------------------------------------------------+

If you have gnu make, you can have the first four steps automatically done for
you by just typing:

  make                                                                         

in the freshly downloaded or unpacked source directory.

For more detailed instructions on how to build Redhat and SuSE RPMs, Windows
self-extracting installers, building on platforms with special requirements
etc, please consult the developer manual.

-------------------------------------------------------------------------------

2.3. Keeping your Installation Up-to-Date

As user feedback comes in and development continues, we will make updated
versions of both the main actions file (as a separate package) and the software
itself (including the actions file) available for download.

If you wish to receive an email notification whenever we release updates of
Privoxy or the actions file, subscribe to our announce mailing list,
ijbswa-announce@lists.sourceforge.net.

In order not to loose your personal changes and adjustments when updating to
the latest default.action file we strongly recommend that you use user.action
for your customization of Privoxy. See the Chapter on actions files for
details.

-------------------------------------------------------------------------------

3. Note to Upgraders

There are very significant changes from earlier Junkbuster versions to the
current Privoxy. The number, names, syntax, and purposes of configuration files
have substantially changed. Junkbuster 2.0.x configuration files will not
migrate, Junkbuster 2.9.x and Privoxy configurations will need to be ported.
The functionalities of the old blockfile, cookiefile and imagelist are now
combined into the "actions files". default.action, is the main actions file.
Local exceptions should best be put into user.action.

A "filter file" (typically default.filter) is new as of Privoxy 2.9.x, and
provides some of the new sophistication (explained below). config is much the
same as before.

If upgrading from a 2.0.x version, you will have to use the new config files,
and possibly adapt any personal rules from your older files. When porting
personal rules over from the old blockfile to the new actions files, please
note that even the pattern syntax has changed. If upgrading from 2.9.x
development versions, it is still recommended to use the new configuration
files.

A quick list of things to be aware of before upgrading:

  * The default listening port is now 8118 due to a conflict with another
    service (NAS).
   
  * Some installers may remove earlier versions completely. Save any important
    configuration files!
   
  * Privoxy is controllable with a web browser at the special URL: http://
    config.privoxy.org/ (Shortcut: http://p.p/). Many aspects of configuration
    can be done here, including temporarily disabling Privoxy.
   
  * The primary configuration files for cookie management, ad and banner
    blocking, and many other aspects of Privoxy configuration are the actions
    files. It is strongly recommended to become familiar with the new actions
    concept below, before modifying these files. Locally defined rules should
    go into user.action.
   
  * Some installers may not automatically start Privoxy after installation.
   
-------------------------------------------------------------------------------

4. Quickstart to Using Privoxy

  * If upgrading, from versions before 2.9.16, please back up any configuration
    files. See the Note to Upgraders Section.
   
  * Install Privoxy. See the Installation Section below for platform specific
    information.
   
  * Advanced users and those who want to offer Privoxy service to more than
    just their local machine should check the main config file, especially the 
    security-relevant options. These are off by default.
   
  * Start Privoxy, if the installation program has not done this already (may
    vary according to platform). See the section Starting Privoxy.
   
  * Set your browser to use Privoxy as HTTP and HTTPS proxy by setting the
    proxy configuration for address of 127.0.0.1 and port 8118. (Junkbuster and
    earlier versions of Privoxy used port 8000.) See the section Starting
    Privoxy below for more details on this.
   
  * Flush your browser's disk and memory caches, to remove any cached ad
    images.
   
  * A default installation should provide a reasonable starting point for most.
    There will undoubtedly be occasions where you will want to adjust the
    configuration, but that can be dealt with as the need arises. Little to no
    initial configuration is required in most cases.
   
    See the Configuration section for more configuration options, and how to
    customize your installation.
   
  * If you experience ads that slipped through, innocent images that are
    blocked, or otherwise feel the need to fine-tune Privoxy's behaviour, take
    a look at the actions files. As a quick start, you might find the richly
    commented examples helpful. You can also view and edit the actions files
    through the web-based user interface. The Appendix "Anatomy of an Action"
    has hints how to debug actions that "misbehave".
   
  * Please see the section Contacting the Developers on how to report bugs or
    problems with websites or to get help.
   
  * Now enjoy surfing with enhanced comfort and privacy!
   
-------------------------------------------------------------------------------

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
   
    [files-in-u]
   
  * 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.

-------------------------------------------------------------------------------

5. Starting Privoxy

Before launching Privoxy for the first time, you will want to configure your
browser(s) to use Privoxy as a HTTP and HTTPS proxy. The default is 127.0.0.1
(or localhost) for the proxy address, and port 8118 (earlier versions used port
8000). This is the one configuration step that must be done!

Please note that Privoxy can only proxy HTTP and HTTPS traffic. It will not
work with FTP or other protocols.

Figure 2. Proxy Configuration (Mozilla)

[proxy_setu]

With Netscape (and Mozilla), this can be set under:

 Edit
   |_   
         Preferences
                |_       
                        Advanced
                              |_     
                                    Proxies
                                         |_       
                                                HTTP Proxy

For Internet Explorer:

 Tools
     |_   
         Internet Properties
                            |_       
                                      Connections
                                               |_     
                                                            LAN Settings

Then, check "Use Proxy" and fill in the appropriate info (Address: 127.0.0.1,
Port: 8118). Include HTTPS (SSL), if you want HTTPS proxy support too.

After doing this, flush your browser's disk and memory caches to force a
re-reading of all pages and to get rid of any ads that may be cached. You are
now ready to start enjoying the benefits of using Privoxy!

Privoxy is typically started by specifying the main configuration file to be
used on the command line. If no configuration file is specified on the command
line, Privoxy will look for a file named config in the current directory.
Except on Win32 where it will try config.txt.

-------------------------------------------------------------------------------

5.1. Red Hat and Conectiva

We use a script. Note that Red Hat does not start Privoxy upon booting per
default. It will use the file /etc/privoxy/config as its main configuration
file.

 # /etc/rc.d/init.d/privoxy start                                              

-------------------------------------------------------------------------------

5.2. Debian

We use a script. Note that Debian starts Privoxy upon booting per default. It
will use the file /etc/privoxy/config as its main configuration file.

 # /etc/init.d/privoxy start                                                   

-------------------------------------------------------------------------------

5.3. SuSE

We use a script. It will use the file /etc/privoxy/config as its main
configuration file. Note that SuSE starts Privoxy upon booting your PC.

 # rcprivoxy start                                                             

-------------------------------------------------------------------------------

5.4. Windows

Click on the Privoxy Icon to start Privoxy. If no configuration file is
specified on the command line, Privoxy will look for a file named config.txt.
Note that Windows will automatically start Privoxy upon booting you PC.

-------------------------------------------------------------------------------

5.5. Solaris, NetBSD, FreeBSD, HP-UX and others

Example Unix startup command:

 # /usr/sbin/privoxy /etc/privoxy/config                                       

-------------------------------------------------------------------------------

5.6. OS/2

During installation, Privoxy is configured to start automatically when the
system restarts. You can start it manually by double-clicking on the Privoxy
icon in the Privoxy folder.

-------------------------------------------------------------------------------

5.7. Mac OSX

During installation, Privoxy is configured to start automatically when the
system restarts. To start Privoxy by hand, double-click on the
StartPrivoxy.command icon in the /Library/Privoxy folder. Or, type this command
in the Terminal:

  /Library/Privoxy/StartPrivoxy.command                                        
                                                                               

You will be prompted for the administrator password.

-------------------------------------------------------------------------------

5.8. AmigaOS

Start Privoxy (with RUN <>NIL:) in your startnet script (AmiTCP), in s:
user-startup (RoadShow), as startup program in your startup script (Genesis),
or as startup action (Miami and MiamiDx). Privoxy will automatically quit when
you quit your TCP/IP stack (just ignore the harmless warning your TCP/IP stack
may display that Privoxy is still running).

-------------------------------------------------------------------------------

5.9. Gentoo

A script is again used. It will use the file /etc/privoxy/config as its main
configuration file.

 /etc/init.d/privoxy start                                                     
                                                                               

Note that Privoxy is not automatically started at boot time by default. You can
change this with the rc-update command.

 rc-update add privoxy default                                                 
                                                                               

-------------------------------------------------------------------------------

5.10. Command Line Options

Privoxy may be invoked with the following command-line options:

  * --version
   
    Print version info and exit. Unix only.
   
  * --help
   
    Print short usage info and exit. Unix only.
   
  * --no-daemon
   
    Don't become a daemon, i.e. don't fork and become process group leader, and
    don't detach from controlling tty. Unix only.
   
  * --pidfile FILE
   
    On startup, write the process ID to FILE. Delete the FILE on exit. Failure
    to create or delete the FILE is non-fatal. If no FILE option is given, no
    PID file will be used. Unix only.
   
  * --user USER[.GROUP]
   
    After (optionally) writing the PID file, assume the user ID of USER, and if
    included the GID of GROUP. Exit if the privileges are not sufficient to do
    so. Unix only.
   
  * configfile
   
    If no configfile is included on the command line, Privoxy will look for a
    file named "config" in the current directory (except on Win32 where it will
    look for "config.txt" instead). Specify full path to avoid confusion. If no
    config file is found, Privoxy will fail to start.
   
-------------------------------------------------------------------------------

6. Privoxy Configuration

All Privoxy configuration is stored in text files. These files can be edited
with a text editor. Many important aspects of Privoxy can also be controlled
easily with a web browser.

-------------------------------------------------------------------------------

6.1. Controlling Privoxy with Your Web Browser

Privoxy's user interface can be reached through the special URL http://
config.privoxy.org/ (shortcut: http://p.p/), which is a built-in page and works
without Internet access. You will see the following section: 

     Privoxy Menu                                                              
        ?  View & change the current configuration                             
        ?  View the source code version numbers                                
        ?  View the request headers.                                           
        ?  Look up which actions apply to a URL and why                        
        ?  Toggle Privoxy on or off                                            
        ?  Documentation                                                       
                                                                               

This should be self-explanatory. Note the first item leads to an editor for the
actions files, which is where the ad, banner, cookie, and URL blocking magic is
configured as well as other advanced features of Privoxy. This is an easy way
to adjust various aspects of Privoxy configuration. The actions file, and other
configuration files, are explained in detail below.

"Toggle Privoxy On or Off" is handy for sites that might have problems with
your current actions and filters. You can in fact use it as a test to see
whether it is Privoxy causing the problem or not. Privoxy continues to run as a
proxy in this case, but all manipulation is disabled, i.e. Privoxy acts like a
normal forwarding proxy. There is even a toggle Bookmarklet offered, so that
you can toggle Privoxy with one click from your browser.

-------------------------------------------------------------------------------

6.2. Configuration Files Overview

For Unix, *BSD and Linux, all configuration files are located in /etc/privoxy/
by default. For MS Windows, OS/2, and AmigaOS these are all in the same
directory as the Privoxy executable. The name and number of configuration files
has changed from previous versions, and is subject to change as development
progresses.

The installed defaults provide a reasonable starting point, though some
settings may be aggressive by some standards. For the time being, the principle
configuration files are:

  * The main configuration file is named config on Linux, Unix, BSD, OS/2, and
    AmigaOS and config.txt on Windows. This is a required file.
   
  * default.action (the main actions file) is used to define which "actions"
    relating to banner-blocking, images, pop-ups, content modification, cookie
    handling etc should be applied by default. It also defines many exceptions
    (both positive and negative) from this default set of actions that enable
    Privoxy to selectively eliminate the junk, and only the junk, on as many
    websites as possible.
   
    Multiple actions files may be defined in config. These are processed in the
    order they are defined. Local customizations and locally preferred
    exceptions to the default policies as defined in default.action (which you
    will most probably want to define sooner or later) are probably best
    applied in user.action, where you can preserve them across upgrades.
    standard.action is for Privoxy's internal use.
   
    There is also a web based editor that can be accessed from http://
    config.privoxy.org/show-status (Shortcut: http://p.p/show-status) for the
    various actions files.
   
  * default.filter (the filter file) can be used to re-write the raw page
    content, including viewable text as well as embedded HTML and JavaScript,
    and whatever else lurks on any given web page. The filtering jobs are only
    pre-defined here; whether to apply them or not is up to the actions files.
   
All files use the "#" character to denote a comment (the rest of the line will
be ignored) and understand line continuation through placing a backslash ("\")
as the very last character in a line. If the # is preceded by a backslash, it
looses its special function. Placing a # in front of an otherwise valid
configuration line to prevent it from being interpreted is called "commenting
out" that line.

The actions files and default.filter can use Perl style regular expressions for
maximum flexibility.

After making any changes, there is no need to restart Privoxy in order for the
changes to take effect. Privoxy detects such changes automatically. Note,
however, that it may take one or two additional requests for the change to take
effect. When changing the listening address of Privoxy, these "wake up"
requests must obviously be sent to the old listening address.

While under development, the configuration content is subject to change. The
below documentation may not be accurate by the time you read this. Also, what
constitutes a "default" setting, may change, so please check all your
configuration files on important issues.

-------------------------------------------------------------------------------

7. The Main Configuration File

Again, the main configuration file is named config on Linux/Unix/BSD and OS/2,
and config.txt on Windows. Configuration lines consist of an initial keyword
followed by a list of values, all separated by whitespace (any number of spaces
or tabs). For example:

  confdir /etc/privoxy

Assigns the value /etc/privoxy to the option confdir and thus indicates that
the configuration directory is named "/etc/privoxy/".

All options in the config file except for confdir and logdir are optional.
Watch out in the below description for what happens if you leave them unset.

The main config file controls all aspects of Privoxy's operation that are not
location dependent (i.e. they apply universally, no matter where you may be
surfing).

-------------------------------------------------------------------------------

7.1. Configuration and Log File Locations

Privoxy can (and normally does) use a number of other files for additional
configuration, help and logging. This section of the configuration file tells
Privoxy where to find those other files.

The user running Privoxy, must have read permission for all configuration
files, and write permission to any files that would be modified, such as log
files and actions files.

-------------------------------------------------------------------------------

7.1.1. confdir

Specifies:
   
    The directory where the other configuration files are located
   
Type of value:
   
    Path name
   
Default value:
   
    /etc/privoxy (Unix) or Privoxy installation dir (Windows)
   
Effect if unset:
   
    Mandatory
   
Notes:
   
    No trailing "/", please
   
    When development goes modular and multi-user, the blocker, filter, and
    per-user config will be stored in subdirectories of "confdir". For now, the
    configuration directory structure is flat, except for confdir/templates,
    where the HTML templates for CGI output reside (e.g. Privoxy's 404 error
    page).
   
-------------------------------------------------------------------------------

7.1.2. logdir

Specifies:
   
    The directory where all logging takes place (i.e. where logfile and jarfile
    are located)
   
Type of value:
   
    Path name
   
Default value:
   
    /var/log/privoxy (Unix) or Privoxy installation dir (Windows)
   
Effect if unset:
   
    Mandatory
   
Notes:
   
    No trailing "/", please
   
-------------------------------------------------------------------------------

7.1.3. actionsfile

Specifies:
   
    The actions file(s) to use
   
Type of value:
   
    File name, relative to confdir, without the .action suffix
   
Default values:
   
      standard     # Internal purposes, no editing recommended
                                                              
      default      # Main actions file                        
                                                              
      user         # User customizations                      
   
Effect if unset:
   
    No actions are taken at all. Simple neutral proxying.
   
Notes:
   
    Multiple actionsfile lines are permitted, and are in fact recommended!
   
    The default values include standard.action, which is used for internal
    purposes and should be loaded, default.action, which is the "main" actions
    file maintained by the developers, and user.action, where you can make your
    personal additions.
   
    Actions files are where all the per site and per URL configuration is done
    for ad blocking, cookie management, privacy considerations, etc. There is
    no point in using Privoxy without at least one actions file.
   
-------------------------------------------------------------------------------

7.1.4. filterfile

Specifies:
   
    The filter file to use
   
Type of value:
   
    File name, relative to confdir
   
Default value:
   
    default.filter (Unix) or default.filter.txt (Windows)
   
Effect if unset:
   
    No textual content filtering takes place, i.e. all +filter{name} actions in
    the actions files are turned neutral.
   
Notes:
   
    The filter file contains content modification rules that use regular
    expressions. These rules permit powerful changes on the content of Web
    pages, e.g., you could disable your favorite JavaScript annoyances,
    re-write the actual displayed text, or just have some fun replacing
    "Microsoft" with "MicroSuck" wherever it appears on a Web page.
   
    The +filter{name} actions rely on the relevant filter (name) to be defined
    in the filter file!
   
    A pre-defined filter file called default.filter that contains a bunch of
    handy filters for common problems is included in the distribution. See the
    section on the filter action for a list.
   
-------------------------------------------------------------------------------

7.1.5. logfile

Specifies:
   
    The log file to use
   
Type of value:
   
    File name, relative to logdir
   
Default value:
   
    logfile (Unix) or privoxy.log (Windows)
   
Effect if unset:
   
    No log file is used, all log messages go to the console (STDERR).
   
Notes:
   
    The windows version will additionally log to the console.
   
    The logfile is where all logging and error messages are written. The level
    of detail and number of messages are set with the debug option (see below).
    The logfile can be useful for tracking down a problem with Privoxy (e.g.,
    it's not blocking an ad you think it should block) but in most cases you
    probably will never look at it.
   
    Your logfile will grow indefinitely, and you will probably want to
    periodically remove it. On Unix systems, you can do this with a cron job
    (see "man cron"). For Red Hat, a logrotate script has been included.
   
    On SuSE Linux systems, you can place a line like "/var/log/privoxy.* +1024k
    644 nobody.nogroup" in /etc/logfiles, with the effect that cron.daily will
    automatically archive, gzip, and empty the log, when it exceeds 1M size.
   
    Any log files must be writable by whatever user Privoxy is being run as
    (default on UNIX, user id is "privoxy").
   
-------------------------------------------------------------------------------

7.1.6. jarfile

Specifies:
   
    The file to store intercepted cookies in
   
Type of value:
   
    File name, relative to logdir
   
Default value:
   
    jarfile (Unix) or privoxy.jar (Windows)
   
Effect if unset:
   
    Intercepted cookies are not stored at all.
   
Notes:
   
    The jarfile may grow to ridiculous sizes over time.
   
-------------------------------------------------------------------------------

7.1.7. trustfile

Specifies:
   
    The trust file to use
   
Type of value:
   
    File name, relative to confdir
   
Default value:
   
    Unset (commented out). When activated: trust (Unix) or trust.txt (Windows)
   
Effect if unset:
   
    The whole trust mechanism is turned off.
   
Notes:
   
    The trust mechanism is an experimental feature for building white-lists and
    should be used with care. It is NOT recommended for the casual user.
   
    If you specify a trust file, Privoxy will only allow access to sites that
    are named in the trustfile. You can also mark sites as trusted referrers
    (with +), with the effect that access to untrusted sites will be granted,
    if a link from a trusted referrer was used. The link target will then be
    added to the "trustfile". Possible applications include limiting Internet
    access for children.
   
    If you use + operator in the trust file, it may grow considerably over
    time.
   
-------------------------------------------------------------------------------

7.2. Local Set-up Documentation

If you intend to operate Privoxy for more users than just yourself, it might be
a good idea to let them know how to reach you, what you block and why you do
that, your policies, etc.

-------------------------------------------------------------------------------

7.2.1. user-manual

Specifies:
   
    Location of the Privoxy User Manual.
   
Type of value:
   
    A fully qualified URI
   
Default value:
   
    Unset
   
Effect if unset:
   
    http://www.privoxy.org/version/user-manual/ will be used, where version is
    the Privoxy version.
   
Notes:
   
    The User Manual URI is used for help links from some of the internal CGI
    pages. The manual itself is normally packaged with the binary
    distributions, so you probably want to set this to a locally installed
    copy. For multi-user setups, you could provide a copy on a local webserver
    for all your users and use the corresponding URL here.
   
    Examples:
   
    Unix, in local filesystem:
   
    user-manual  file:///usr/share/doc/privoxy-3.1.1/user-manual/      
   
    Any platform, on local webserver (called "local-webserver"):
   
    user-manual  http://local-webserver/privoxy-user-manual/           
   
    +-----------------------------------------------------------------+
    |                             Warning                             |
    |-----------------------------------------------------------------|
    |If set, this option should be the first option in the config     |
    |file, because it is used while the config file is being read.    |
    +-----------------------------------------------------------------+

-------------------------------------------------------------------------------

7.2.2. trust-info-url

Specifies:
   
    A URL to be displayed in the error page that users will see if access to an
    untrusted page is denied.
   
Type of value:
   
    URL
   
Default value:
   
    Two example URL are provided
   
Effect if unset:
   
    No links are displayed on the "untrusted" error page.
   
Notes:
   
    The value of this option only matters if the experimental trust mechanism
    has been activated. (See trustfile above.)
   
    If you use the trust mechanism, it is a good idea to write up some on-line
    documentation about your trust policy and to specify the URL(s) here. Use
    multiple times for multiple URLs.
   
    The URL(s) should be added to the trustfile as well, so users don't end up
    locked out from the information on why they were locked out in the first
    place!
   
-------------------------------------------------------------------------------

7.2.3. admin-address

Specifies:
   
    An email address to reach the proxy administrator.
   
Type of value:
   
    Email address
   
Default value:
   
    Unset
   
Effect if unset:
   
    No email address is displayed on error pages and the CGI user interface.
   
Notes:
   
    If both admin-address and proxy-info-url are unset, the whole "Local
    Privoxy Support" box on all generated pages will not be shown.
   
-------------------------------------------------------------------------------

7.2.4. proxy-info-url

Specifies:
   
    A URL to documentation about the local Privoxy setup, configuration or
    policies.
   
Type of value:
   
    URL
   
Default value:
   
    Unset
   
Effect if unset:
   
    No link to local documentation is displayed on error pages and the CGI user
    interface.
   
Notes:
   
    If both admin-address and proxy-info-url are unset, the whole "Local
    Privoxy Support" box on all generated pages will not be shown.
   
    This URL shouldn't be blocked ;-)
   
-------------------------------------------------------------------------------

7.3. Debugging

These options are mainly useful when tracing a problem. Note that you might
also want to invoke Privoxy with the --no-daemon command line option when
debugging.

-------------------------------------------------------------------------------

7.3.1. debug

Specifies:
   
    Key values that determine what information gets logged to the logfile.
   
Type of value:
   
    Integer values
   
Default value:
   
    12289 (i.e.: URLs plus informational and warning messages)
   
Effect if unset:
   
    Nothing gets logged.
   
Notes:
   
    The available debug levels are:
   
      debug         1 # show each GET/POST/CONNECT request             
      debug         2 # show each connection status                    
      debug         4 # show I/O status                                
      debug         8 # show header parsing                            
      debug        16 # log all data into the logfile                  
      debug        32 # debug force feature                            
      debug        64 # debug regular expression filter                
      debug       128 # debug fast redirects                           
      debug       256 # debug GIF de-animation                         
      debug       512 # Common Log Format                              
      debug      1024 # debug kill pop-ups                             
      debug      2048 # CGI user interface                             
      debug      4096 # Startup banner and warnings.                   
      debug      8192 # Non-fatal errors                               
   
    To select multiple debug levels, you can either add them or use multiple
    debug lines.
   
    A debug level of 1 is informative because it will show you each request as
    it happens. 1, 4096 and 8192 are highly recommended so that you will notice
    when things go wrong. The other levels are probably only of interest if you
    are hunting down a specific problem. They can produce a hell of an output
    (especially 16).
   
    The reporting of fatal errors (i.e. ones which crash Privoxy) is always on
    and cannot be disabled.
   
    If you want to use CLF (Common Log Format), you should set "debug 512" ONLY
    and not enable anything else.
   
-------------------------------------------------------------------------------

7.3.2. single-threaded

Specifies:
   
    Whether to run only one server thread
   
Type of value:
   
    None
   
Default value:
   
    Unset
   
Effect if unset:
   
    Multi-threaded (or, where unavailable: forked) operation, i.e. the ability
    to serve multiple requests simultaneously.
   
Notes:
   
    This option is only there for debug purposes and you should never need to
    use it. It will drastically reduce performance.
   
-------------------------------------------------------------------------------

7.4. Access Control and Security

This section of the config file controls the security-relevant aspects of
Privoxy's configuration.

-------------------------------------------------------------------------------

7.4.1. listen-address

Specifies:
   
    The IP address and TCP port on which Privoxy will listen for client
    requests.
   
Type of value:
   
    [IP-Address]:Port
   
Default value:
   
    127.0.0.1:8118
   
Effect if unset:
   
    Bind to 127.0.0.1 (localhost), port 8118. This is suitable and recommended
    for home users who run Privoxy on the same machine as their browser.
   
Notes:
   
    You will need to configure your browser(s) to this proxy address and port.
   
    If you already have another service running on port 8118, or if you want to
    serve requests from other machines (e.g. on your local network) as well,
    you will need to override the default.
   
    If you leave out the IP address, Privoxy will bind to all interfaces
    (addresses) on your machine and may become reachable from the Internet. In
    that case, consider using access control lists (ACL's, see below), and/or a
    firewall.
   
    If you open Privoxy to untrusted users, you will also want to turn off the 
    enable-edit-actions and enable-remote-toggle options!
   
Example:
   
    Suppose you are running Privoxy on a machine which has the address
    192.168.0.1 on your local private network (192.168.0.0) and has another
    outside connection with a different address. You want it to serve requests
    from inside only:
   
      listen-address  192.168.0.1:8118                                 
   
-------------------------------------------------------------------------------

7.4.2. toggle

Specifies:
   
    Initial state of "toggle" status
   
Type of value:
   
    1 or 0
   
Default value:
   
    1
   
Effect if unset:
   
    Act as if toggled on
   
Notes:
   
    If set to 0, Privoxy will start in "toggled off" mode, i.e. behave like a
    normal, content-neutral proxy where all ad blocking, filtering, etc are
    disabled. See enable-remote-toggle below. This is not really useful
    anymore, since toggling is much easier via the web interface than via
    editing the conf file.
   
    The windows version will only display the toggle icon in the system tray if
    this option is present.
   
-------------------------------------------------------------------------------

7.4.3. enable-remote-toggle

Specifies:
   
    Whether or not the web-based toggle feature may be used
   
Type of value:
   
    0 or 1
   
Default value:
   
    1
   
Effect if unset:
   
    The web-based toggle feature is disabled.
   
Notes:
   
    When toggled off, Privoxy acts like a normal, content-neutral proxy, i.e.
    it acts as if none of the actions applied to any URL.
   
    For the time being, access to the toggle feature can not be controlled
    separately by "ACLs" or HTTP authentication, so that everybody who can
    access Privoxy (see "ACLs" and listen-address above) can toggle it for all
    users. So this option is not recommended for multi-user environments with
    untrusted users.
   
    Note that you must have compiled Privoxy with support for this feature,
    otherwise this option has no effect.
   
-------------------------------------------------------------------------------

7.4.4. enable-edit-actions

Specifies:
   
    Whether or not the web-based actions file editor may be used
   
Type of value:
   
    0 or 1
   
Default value:
   
    1
   
Effect if unset:
   
    The web-based actions file editor is disabled.
   
Notes:
   
    For the time being, access to the editor can not be controlled separately
    by "ACLs" or HTTP authentication, so that everybody who can access Privoxy
    (see "ACLs" and listen-address above) can modify its configuration for all
    users. So this option is not recommended for multi-user environments with
    untrusted users.
   
    Note that you must have compiled Privoxy with support for this feature,
    otherwise this option has no effect.
   
-------------------------------------------------------------------------------

7.4.5. ACLs: permit-access and deny-access

Specifies:
   
    Who can access what.
   
Type of value:
   
    src_addr[/src_masklen] [dst_addr[/dst_masklen]]
   
    Where src_addr and dst_addr are IP addresses in dotted decimal notation or
    valid DNS names, and src_masklen and dst_masklen are subnet masks in CIDR
    notation, i.e. integer values from 2 to 30 representing the length (in
    bits) of the network address. The masks and the whole destination part are
    optional.
   
Default value:
   
    Unset
   
Effect if unset:
   
    Don't restrict access further than implied by listen-address
   
Notes:
   
    Access controls are included at the request of ISPs and systems
    administrators, and are not usually needed by individual users. For a
    typical home user, it will normally suffice to ensure that Privoxy only
    listens on the localhost (127.0.0.1) or internal (home) network address by
    means of the listen-address option.
   
    Please see the warnings in the FAQ that this proxy is not intended to be a
    substitute for a firewall or to encourage anyone to defer addressing basic
    security weaknesses.
   
    Multiple ACL lines are OK. If any ACLs are specified, then the Privoxy
    talks only to IP addresses that match at least one permit-access line and
    don't match any subsequent deny-access line. In other words, the last match
    wins, with the default being deny-access.
   
    If Privoxy is using a forwarder (see forward below) for a particular
    destination URL, the dst_addr that is examined is the address of the
    forwarder and NOT the address of the ultimate target. This is necessary
    because it may be impossible for the local Privoxy to determine the IP
    address of the ultimate target (that's often what gateways are used for).
   
    You should prefer using IP addresses over DNS names, because the address
    lookups take time. All DNS names must resolve! You can not use domain
    patterns like "*.org" or partial domain names. If a DNS name resolves to
    multiple IP addresses, only the first one is used.
   
    Denying access to particular sites by ACL may have undesired side effects
    if the site in question is hosted on a machine which also hosts other
    sites.
   
Examples:
   
    Explicitly define the default behavior if no ACL and listen-address are
    set: "localhost" is OK. The absence of a dst_addr implies that all
    destination addresses are OK:
   
      permit-access  localhost                                         
   
    Allow any host on the same class C subnet as www.privoxy.org access to
    nothing but www.example.com:
   
      permit-access  www.privoxy.org/24 www.example.com/32             
   
    Allow access from any host on the 26-bit subnet 192.168.45.64 to anywhere,
    with the exception that 192.168.45.73 may not access
    www.dirty-stuff.example.com:
   
      permit-access  192.168.45.64/26                                  
      deny-access    192.168.45.73    www.dirty-stuff.example.com      
   
-------------------------------------------------------------------------------

7.4.6. buffer-limit

Specifies:
   
    Maximum size of the buffer for content filtering.
   
Type of value:
   
    Size in Kbytes
   
Default value:
   
    4096
   
Effect if unset:
   
    Use a 4MB (4096 KB) limit.
   
Notes:
   
    For content filtering, i.e. the +filter and +deanimate-gif actions, it is
    necessary that Privoxy buffers the entire document body. This can be
    potentially dangerous, since a server could just keep sending data
    indefinitely and wait for your RAM to exhaust -- with nasty consequences.
    Hence this option.
   
    When a document buffer size reaches the buffer-limit, it is flushed to the
    client unfiltered and no further attempt to filter the rest of the document
    is made. Remember that there may be multiple threads running, which might
    require up to buffer-limit Kbytes each, unless you have enabled
    "single-threaded" above.
   
-------------------------------------------------------------------------------

7.5. Forwarding

This feature allows routing of HTTP requests through a chain of multiple
proxies. It can be used to better protect privacy and confidentiality when
accessing specific domains by routing requests to those domains through an
anonymous public proxy (see e.g. http://www.multiproxy.org/anon_list.htm) Or to
use a caching proxy to speed up browsing. Or chaining to a parent proxy may be
necessary because the machine that Privoxy runs on has no direct Internet
access.

Also specified here are SOCKS proxies. Privoxy supports the SOCKS 4 and SOCKS
4A protocols.

-------------------------------------------------------------------------------

7.5.1. forward

Specifies:
   
    To which parent HTTP proxy specific requests should be routed.
   
Type of value:
   
    target_pattern http_parent[:port]
   
    where target_pattern is a URL pattern that specifies to which requests
    (i.e. URLs) this forward rule shall apply. Use / to denote "all URLs".
    http_parent[:port] is the DNS name or IP address of the parent HTTP proxy
    through which the requests should be forwarded, optionally followed by its
    listening port (default: 8080). Use a single dot (.) to denote "no
    forwarding".
   
Default value:
   
    Unset
   
Effect if unset:
   
    Don't use parent HTTP proxies.
   
Notes:
   
    If http_parent is ".", then requests are not forwarded to another HTTP
    proxy but are made directly to the web servers.
   
    Multiple lines are OK, they are checked in sequence, and the last match
    wins.
   
Examples:
   
    Everything goes to an example anonymizing proxy, except SSL on port 443
    (which it doesn't handle):
   
      forward   /      anon-proxy.example.org:8080                     
      forward   :443   .                                               
   
    Everything goes to our example ISP's caching proxy, except for requests to
    that ISP's sites:
   
      forward   /                  caching-proxy.example-isp.net:8000  
      forward   .example-isp.net   .                                   
   
-------------------------------------------------------------------------------

7.5.2. forward-socks4 and forward-socks4a

Specifies:
   
    Through which SOCKS proxy (and to which parent HTTP proxy) specific
    requests should be routed.
   
Type of value:
   
    target_pattern socks_proxy[:port] http_parent[:port]
   
    where target_pattern is a URL pattern that specifies to which requests
    (i.e. URLs) this forward rule shall apply. Use / to denote "all URLs".
    http_parent and socks_proxy are IP addresses in dotted decimal notation or
    valid DNS names (http_parent may be "." to denote "no HTTP forwarding"),
    and the optional port parameters are TCP ports, i.e. integer values from 1
    to 64535
   
Default value:
   
    Unset
   
Effect if unset:
   
    Don't use SOCKS proxies.
   
Notes:
   
    Multiple lines are OK, they are checked in sequence, and the last match
    wins.
   
    The difference between forward-socks4 and forward-socks4a is that in the
    SOCKS 4A protocol, the DNS resolution of the target hostname happens on the
    SOCKS server, while in SOCKS 4 it happens locally.
   
    If http_parent is ".", then requests are not forwarded to another HTTP
    proxy but are made (HTTP-wise) directly to the web servers, albeit through
    a SOCKS proxy.
   
Examples:
   
    From the company example.com, direct connections are made to all "internal"
    domains, but everything outbound goes through their ISP's proxy by way of
    example.com's corporate SOCKS 4A gateway to the Internet.
   
      forward-socks4a   /              socks-gw.example.com:1080  www-cache.example-isp.net:8080 
      forward           .example.com   .                                                         
   
    A rule that uses a SOCKS 4 gateway for all destinations but no HTTP parent
    looks like this:
   
      forward-socks4   /               socks-gw.example.com:1080  .    
   
-------------------------------------------------------------------------------

7.5.3. Advanced Forwarding Examples

If you have links to multiple ISPs that provide various special content only to
their subscribers, you can configure multiple Privoxies which have connections
to the respective ISPs to act as forwarders to each other, so that your users
can see the internal content of all ISPs.

Assume that host-a has a PPP connection to isp-a.net. And host-b has a PPP
connection to isp-b.net. Both run Privoxy. Their forwarding configuration can
look like this:

host-a:

  forward    /           .                                                     
  forward    .isp-b.net  host-b:8118                                           

host-b:

  forward    /           .                                                     
  forward    .isp-a.net  host-a:8118                                           

Now, your users can set their browser's proxy to use either host-a or host-b
and be able to browse the internal content of both isp-a and isp-b.

If you intend to chain Privoxy and squid locally, then chain as browser ->
squid -> privoxy is the recommended way.

Assuming that Privoxy and squid run on the same box, your squid configuration
could then look like this:

  # Define Privoxy as parent proxy (without ICP)                               
  cache_peer 127.0.0.1 parent 8118 7 no-query                                  
                                                                               
  # Define ACL for protocol FTP                                                
  acl ftp proto FTP                                                            
                                                                               
  # Do not forward FTP requests to Privoxy                                     
  always_direct allow ftp                                                      
                                                                               
  # Forward all the rest to Privoxy                                            
  never_direct allow all                                                       

You would then need to change your browser's proxy settings to squid's address
and port. Squid normally uses port 3128. If unsure consult http_port in
squid.conf.

You could just as well decide to only forward requests for Windows executables
through a virus-scanning parent proxy, say, on antivir.example.com, port 8010:

  forward   /                          .                                       
  forward   /.*\.(exe|com|dll|zip)$    antivir.example.com:8010                

-------------------------------------------------------------------------------

7.6. Windows GUI Options

Privoxy has a number of options specific to the Windows GUI interface:

If "activity-animation" is set to 1, the Privoxy icon will animate when
"Privoxy" is active. To turn off, set to 0.

  activity-animation 1
   

If "log-messages" is set to 1, Privoxy will log messages to the console window:

  log-messages 1
   

If "log-buffer-size" is set to 1, the size of the log buffer, i.e. the amount
of memory used for the log messages displayed in the console window, will be
limited to "log-max-lines" (see below).

Warning: Setting this to 0 will result in the buffer to grow infinitely and eat
up all your memory!

  log-buffer-size 1
   

log-max-lines is the maximum number of lines held in the log buffer. See above.

  log-max-lines 200
   

If "log-highlight-messages" is set to 1, Privoxy will highlight portions of the
log messages with a bold-faced font:

  log-highlight-messages 1
   

The font used in the console window:

  log-font-name Comic Sans MS
   

Font size used in the console window:

  log-font-size 8
   

"show-on-task-bar" controls whether or not Privoxy will appear as a button on
the Task bar when minimized:

  show-on-task-bar 0
   

If "close-button-minimizes" is set to 1, the Windows close button will minimize
Privoxy instead of closing the program (close with the exit option on the File
menu).

  close-button-minimizes 1
   

The "hide-console" option is specific to the MS-Win console version of Privoxy.
If this option is used, Privoxy will disconnect from and hide the command
console.

  #hide-console
   

-------------------------------------------------------------------------------

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 filters
   
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.

-------------------------------------------------------------------------------

9. The Filter File

All text substitutions that can be invoked through the filter action must first
be defined in the filter file, which is typically called default.filter and
which can be selected through the filterfile config option.

Typical reasons for doing such substitutions are to eliminate common annoyances
in HTML and JavaScript, such as pop-up windows, exit consoles, crippled windows
without navigation tools, the infamous <BLINK> tag etc, to suppress images with
certain width and height attributes (standard banner sizes or web-bugs), or
just to have fun. The possibilities are endless.

Filtering works on any text-based document type, including plain text, HTML,
JavaScript, CSS etc. (all text/* MIME types). Substitutions are made at the
source level, so if you want to "roll your own" filters, you should be familiar
with HTML syntax.

Just like the actions files, the filter file is organized in sections, which
are called filters here. Each filter consists of a heading line, that starts
with the keyword FILTER:, followed by the filter's name, and a short (one line)
description of what it does. Below that line come the jobs, i.e. lines that
define the actual text substitutions. By convention, the name of a filter
should describe what the filter eliminates. The comment is used in the 
web-based user interface.

Once a filter called name has been defined in the filter file, it can be
invoked by using an action of the form +filter{name} in any actions file.

A filter header line for a filter called "foo" could look like this:

FILTER: foo Replace all "foo" with "bar"                                       

Below that line, and up to the next header line, come the jobs that define what
text replacements the filter executes. They are specified in a syntax that
imitates Perl's s/// operator. If you are familiar with Perl, you will find
this to be quite intuitive, and may want to look at the PCRS man page for the
subtle differences to Perl behaviour. Most notably, the non-standard option
letter U is supported, which turns the default to ungreedy matching.

If you are new to regular expressions, you might want to take a look at the 
Appendix on regular expressions, and see the Perl manual for the s///
operator's syntax and Perl-style regular expressions in general. The below
examples might also help to get you started.

-------------------------------------------------------------------------------

9.1. Filter File Tutorial

Now, let's complete our "foo" filter. We have already defined the heading, but
the jobs are still missing. Since all it does is to replace "foo" with "bar",
there is only one (trivial) job needed:

s/foo/bar/                                                                     

But wait! Didn't the comment say that all occurrences of "foo" should be
replaced? Our current job will only take care of the first "foo" on each page.
For global substitution, we'll need to add the g option:

s/foo/bar/g                                                                    

Our complete filter now looks like this:

FILTER: foo Replace all "foo" with "bar"                                       
s/foo/bar/g                                                                    

Let's look at some real filters for more interesting examples. Here you see a
filter that protects against some common annoyances that arise from JavaScript
abuse. Let's look at its jobs one after the other:

FILTER: js-annoyances Get rid of particularly annoying JavaScript abuse                         
                                                                                                
# Get rid of JavaScript referrer tracking. Test page: http://www.randomoddness.com/untitled.htm 
#                                                                                               
s|(<script.*)document\.referrer(.*</script>)|$1"Not Your Business!"$2|Usg                       

Following the header line and a comment, you see the job. Note that it uses |
as the delimiter instead of /, because the pattern contains a forward slash,
which would otherwise have to be escaped by a backslash (\).

Now, let's examine the pattern: it starts with the text <script.* enclosed in
parentheses. Since the dot matches any character, and * means: "Match an
arbitrary number of the element left of myself", this matches "<script",
followed by any text, i.e. it matches the whole page, from the start of the
first <script> tag.

That's more than we want, but the pattern continues: document\.referrer matches
only the exact string "document.referrer". The dot needed to be escaped, i.e.
preceded by a backslash, to take away its special meaning as a joker, and make
it just a regular dot. So far, the meaning is: Match from the start of the
first <script> tag in a the page, up to, and including, the text
"document.referrer", if both are present in the page (and appear in that
order).

But there's still more pattern to go. The next element, again enclosed in
parentheses, is .*</script>. You already know what .* means, so the whole
pattern translates to: Match from the start of the first <script> tag in a page
to the end of the last <script> tag, provided that the text "document.referrer"
appears somewhere in between.

This is still not the whole story, since we have ignored the options and the
parentheses: The portions of the page matched by sub-patterns that are enclosed
in parentheses, will be remembered and be available through the variables $1,
$2, ... in the substitute. The U option switches to ungreedy matching, which
means that the first .* in the pattern will only "eat up" all text in between "
<script" and the first occurrence of "document.referrer", and that the second .
* will only span the text up to the first "</script>" tag. Furthermore, the s
option says that the match may span multiple lines in the page, and the g
option again means that the substitution is global.

So, to summarize, the pattern means: Match all scripts that contain the text
"document.referrer". Remember the parts of the script from (and including) the
start tag up to (and excluding) the string "document.referrer" as $1, and the
part following that string, up to and including the closing tag, as $2.

Now the pattern is deciphered, but wasn't this about substituting things? So
lets look at the substitute: $1"Not Your Business!"$2 is easy to read: The text
remembered as $1, followed by "Not Your Business!" (including the quotation
marks!), followed by the text remembered as $2. This produces an exact copy of
the original string, with the middle part (the "document.referrer") replaced by
"Not Your Business!".

The whole job now reads: Replace "document.referrer" by "Not Your Business!"
wherever it appears inside a <script> tag. Note that this job won't break
JavaScript syntax, since both the original and the replacement are
syntactically valid string objects. The script just won't have access to the
referrer information anymore.

We'll show you two other jobs from the JavaScript taming department, but this
time only point out the constructs of special interest:

# The status bar is for displaying link targets, not pointless blahblah        
#                                                                              
s/window\.status\s*=\s*(['"]).*?\1/dUmMy=1/ig                                  

\s stands for whitespace characters (space, tab, newline, carriage return, form
feed), so that \s* means: "zero or more whitespace". The ? in .*? makes this
matching of arbitrary text ungreedy. (Note that the U option is not set). The
['"] construct means: "a single or a double quote". Finally, \1 is a
backreference to the first parenthesis just like $1 above, with the difference
that in the pattern, a backslash indicates a backreference, whereas in the
substitute, it's the dollar.

So what does this job do? It replaces assignments of single- or double-quoted
strings to the "window.status" object with a dummy assignment (using a variable
name that is hopefully odd enough not to conflict with real variables in
scripts). Thus, it catches many cases where e.g. pointless descriptions are
displayed in the status bar instead of the link target when you move your mouse
over links.

# Kill OnUnload popups. Yummy. Test: http://www.zdnet.com/zdsubs/yahoo/tree/yfs.html 
#                                                                                    
s/(<body [^>]*)onunload(.*>)/$1never$2/iU                                            

Including the OnUnload event binding in the HTML DOM was a CRIME. When I close
a browser window, I want it to close and die. Basta. This job replaces the
"onunload" attribute in "<body>" tags with the dummy word never. Note that the
i option makes the pattern matching case-insensitive. Also note that ungreedy
matching alone doesn't always guarantee a minimal match: In the first
parenthesis, we had to use [^>]* instead of .* to prevent the match from
exceeding the <body> tag if it doesn't contain "OnUnload", but the page's
content does.

The last example is from the fun department:

FILTER: fun Fun text replacements                                              
                                                                               
# Spice the daily news:                                                        
#                                                                              
s/microsoft(?!\.com)/MicroSuck/ig                                              

Note the (?!\.com) part (a so-called negative lookahead) in the job's pattern,
which means: Don't match, if the string ".com" appears directly following
"microsoft" in the page. This prevents links to microsoft.com from being
trashed, while still replacing the word everywhere else.

# Buzzword Bingo (example for extended regex syntax)                           
#                                                                              
s* industry[ -]leading \                                                       
|  cutting[ -]edge \                                                           
|  customer[ -]focused \                                                       
|  market[ -]driven \                                                          
|  award[ -]winning # Comments are OK, too! \                                  
|  high[ -]performance \                                                       
|  solutions[ -]based \                                                        
|  unmatched \                                                                 
|  unparalleled \                                                              
|  unrivalled \                                                                
*<font color="red"><b>BINGO!</b></font> \                                      
*igx                                                                           

The x option in this job turns on extended syntax, and allows for e.g. the
liberal use of (non-interpreted!) whitespace for nicer formatting.

You get the idea?

-------------------------------------------------------------------------------

10. Templates

All Privoxy built-in pages, i.e. error pages such as the "404 - No Such Domain"
error page, the "BLOCKED" page and all pages of its web-based user interface,
are generated from templates. (Privoxy must be running for the above links to
work as intended.)

These templates are stored in a subdirectory of the configuration directory
called templates. On Unixish platforms, this is typically /etc/privoxy/
templates/.

The templates are basically normal HTML files, but with place-holders (called
symbols or exports), which Privoxy fills at run time. You can edit the
templates with a normal text editor, should you want to customize them. (Not
recommended for the casual user). Note that just like in configuration files,
lines starting with # are ignored when the templates are filled in.

The place-holders are of the form @name@, and you will find a list of available
symbols, which vary from template to template, in the comments at the start of
each file. Note that these comments are not always accurate, and that it's
probably best to look at the existing HTML code to find out which symbols are
supported and what they are filled in with.

A special application of this substitution mechanism is to make whole blocks of
HTML code disappear when a specific symbol is set. We use this for many
purposes, one of them being to include the beta warning in all our user
interface (CGI) pages when Privoxy in in an alpha or beta development stage:

<!-- @if-unstable-start -->                                                    
                                                                               
  ... beta warning HTML code goes here ...                                     
                                                                               
<!-- if-unstable-end@ -->                                                      

If the "unstable" symbol is set, everything in between and including
@if-unstable-start and if-unstable-end@ will disappear, leaving nothing but an
empty comment:

<!--  -->                                                                      

There's also an if-then-else construct and an #include mechanism, but you'll
sure find out if you are inclined to edit the templates ;-)

All templates refer to a style located at http://config.privoxy.org/
send-stylesheet. This is, of course, locally served by Privoxy and the source
for it can be found and edited in the cgi-style.css template.

-------------------------------------------------------------------------------

11. Contacting the Developers, Bug Reporting and Feature Requests

We value your feedback. In fact, we rely on it to improve Privoxy and its
configuration. However, please note the following hints, so we can provide you
with the best support:

-------------------------------------------------------------------------------

11.1. Get Support

For casual users, our support forum at SourceForge is probably best suited: 
http://sourceforge.net/tracker/?group_id=11118&atid=211118

All users are of course welcome to discuss their issues on the users mailing
list, where the developers also hang around.

-------------------------------------------------------------------------------

11.2. Report Bugs

Please report all bugs only through our bug tracker: http://sourceforge.net/
tracker/?group_id=11118&atid=111118.

Before doing so, please make sure that the bug has not already been submitted
and observe the additional hints at the top of the submit form.

Please try to verify that it is a Privoxy bug, and not a browser or site bug
first. If unsure, try toggling off Privoxy, and see if the problem persists.
The appendix of the user manual also has helpful information on action
debugging. If you are using your own custom configuration, please try the stock
configs to see if the problem is configuration related.

If not using the latest version, chances are that the bug has been found and
fixed in the meantime. We would appreciate if you could take the time to 
upgrade to the latest version (or even the latest CVS snapshot) and verify your
bug, but this is not required for reporting.

-------------------------------------------------------------------------------

11.3. Request New Features

You are welcome to submit ideas on new features or other proposals for
improvement through our feature request tracker at http://sourceforge.net/
tracker/?atid=361118&group_id=11118.

-------------------------------------------------------------------------------

11.4. Report Ads or Other Actions-Related Problems

Please send feedback on ads that slipped through, innocent images that were
blocked, and any other problems relating to the default.action file through our
actions feedback mechanism located at http://www.privoxy.org/actions/. On this
page, you will also find a bookmark which will take you back there from any
troubled site and even pre-fill the form!

New, improved default.action files will occasionally be made available based on
your feedback. These will be announced on the ijbswa-announce list and
available from our the files section of our project page.

-------------------------------------------------------------------------------

11.5. Other

For any other issues, feel free to use the mailing lists. Technically
interested users and people who wish to contribute to the project are also
welcome on the developers list! You can find an overview of all Privoxy-related
mailing lists, including list archives, at: http://sourceforge.net/mail/?
group_id=11118.

-------------------------------------------------------------------------------

12. Privoxy Copyright, License and History

Copyright © 2001, 2002 by Privoxy Developers <developers@privoxy.org>

Some source code is based on code Copyright © 1997 by Anonymous Coders and
Junkbusters, Inc. and licensed under the GNU General Public License.

-------------------------------------------------------------------------------

12.1. License

Privoxy is free software; you can redistribute it and/or modify it under the
terms of the GNU General Public License, version 2, as published by the Free
Software Foundation.

This program is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE. See the GNU General Public License for more details, which
is available from the Free Software Foundation, Inc, 59 Temple Place - Suite
330, Boston, MA 02111-1307, USA.

You should have received a copy of the GNU General Public License along with
this program; if not, write to the

 Free Software
 Foundation, Inc. 59 Temple Place - Suite 330
 Boston, MA 02111-1307
 USA 

-------------------------------------------------------------------------------

12.2. History

In the beginning, there was the Internet Junkbuster, by Anonymous Coders and 
Junkbusters Corporation. It saved many users a lot of pain in the early days of
web advertising and user tracking.

But the web, its protocols and standards, and with it, the techniques for
forcing users to consume ads, give up autonomy over their browsing, and for
spying on them, kept evolving. Unfortunately, the Internet Junkbuster did not.
Version 2.0.2, published in 1998, was (and is) the last official release
available from Junkbusters Corporation. Fortunately, it had been released under
the GNU GPL, which allowed further development by others.

So Stefan Waldherr started maintaining an improved version of the software, to
which eventually a number of people contributed patches. It could already
replace banners with a transparent image, and had a first version of pop-up
killing, but it was still very closely based on the original, with all its
limitations, such as the lack of HTTP/1.1 support, flexible per-site
configuration, or content modification. The last release from this effort was
version 2.0.2-10, published in 2000.

Then, some developers picked up the thread, and started turning the software
inside out, upside down, and then reassembled it, adding many new features
along the way.

The result of this is Privoxy, whose first stable release, 3.0, was released
August, 2002.

-------------------------------------------------------------------------------

12.3. Authors

Current Project Developers:

 Jon Foster
 Andreas Oesterhelt
 Stefan Waldherr
 
 Thomas Steudten
 Rodney Stromlund

Current Project Contributors:

 Rodrigo Barbosa (RPM specfiles)
 Moritz Barsnick
 Hal Burgiss (docs)
 Karsten Hopp (Red Hat)
 Alexander Lazic
 Gábor Lipták
 Guy
 Haroon Rafique
 Roland Rosenfeld (Debian)
 Georg Sauthoff (Gentoo)
 David Schmidt (OS/2, Mac OSX ports)
 Joerg Strohmayer (Amiga)
 Sarantis Paskalis

Based in part on code originally developed by:

 Junkbusters Corp.
 Anonymous Coders

Thanks to the many people who have tested Privoxy, reported bugs, or made
suggestions. These include (in alphabetical order):

 Ken Arromdee
 Devin Bayer
 Reiner Buehl
 Andrew J. Caines
 Clifford Caoile
 Michael T. Davis
 Peter E
 Aaron Hamid
 Magnus Holmgren
 Daniel Leite
 Paul Lieverse
 David Mediavilla 
 Roberto Ragusa
 Maynard Riley
 Bart Schelstraete
 Darren Wiebe
 Jamie Zawinski

-------------------------------------------------------------------------------

13. See Also

Other references and sites of interest to Privoxy users:

http://www.privoxy.org/, the Privoxy Home page.

http://www.privoxy.org/faq/, the Privoxy FAQ.

http://sourceforge.net/projects/ijbswa/, the Project Page for Privoxy on       
SourceForge.                                                                   

http://config.privoxy.org/, the web-based user interface. Privoxy must be      
running for this to work. Shortcut: http://p.p/                                

http://www.privoxy.org/actions/, to submit "misses" to the developers.

http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/ijbswa/contrib/, cool and fun   
ideas from Privoxy users.                                                      

http://www.junkbusters.com/ht/en/cookies.html, an explanation how cookies are  
used to track web users.                                                       

http://www.junkbusters.com/ijb.html, the original Internet Junkbuster.

http://www.waldherr.org/junkbuster/, Stefan Waldherr's version of Junkbuster,  
from which Privoxy was derived.                                                

http://privacy.net/analyze/, a useful site to check what information about you 
is leaked while you browse the web.                                            

http://www.squid-cache.org/, a very popular caching proxy, which is often used 
together with Privoxy.                                                         

http://www.privoxy.org/developer-manual/, the Privoxy developer manual.

-------------------------------------------------------------------------------

14. Appendix

14.1. Regular Expressions

Privoxy uses Perl-style "regular expressions" in its actions files and filter
file, through the PCRE and PCRS libraries.

If you are reading this, you probably don't understand what "regular
expressions" are, or what they can do. So this will be a very brief
introduction only. A full explanation would require a book ;-)

Regular expressions provide a language to describe patterns that can be run
against strings of characters (letter, numbers, etc), to see if they match the
string or not. The patterns are themselves (sometimes complex) strings of
literal characters, combined with wild-cards, and other special characters,
called meta-characters. The "meta-characters" have special meanings and are
used to build complex patterns to be matched against. Perl Compatible Regular
Expressions are an especially convenient "dialect" of the regular expression
language.

To make a simple analogy, we do something similar when we use wild-card
characters when listing files with the dir command in DOS. *.* matches all
filenames. The "special" character here is the asterisk which matches any and
all characters. We can be more specific and use ? to match just individual
characters. So "dir file?.text" would match "file1.txt", "file2.txt", etc. We
are pattern matching, using a similar technique to "regular expressions"!

Regular expressions do essentially the same thing, but are much, much more
powerful. There are many more "special characters" and ways of building complex
patterns however. Let's look at a few of the common ones, and then some
examples:

. - Matches any single character, e.g. "a", "A", "4", ":", or "@".

? - The preceding character or expression is matched ZERO or ONE times. Either/
or.                                                                            

+ - The preceding character or expression is matched ONE or MORE times.

* - The preceding character or expression is matched ZERO or MORE times.

\ - The "escape" character denotes that the following character should be taken
literally. This is used where one of the special characters (e.g. ".") needs to
be taken literally and not as a special meta-character. Example: "example      
\.com", makes sure the period is recognized only as a period (and not expanded 
to its meta-character meaning of any single character).                        

[] - Characters enclosed in brackets will be matched if any of the enclosed    
characters are encountered. For instance, "[0-9]" matches any numeric digit    
(zero through nine). As an example, we can combine this with "+" to match any  
digit one of more times: "[0-9]+".                                             

() - parentheses are used to group a sub-expression, or multiple               
sub-expressions.                                                               

| - The "bar" character works like an "or" conditional statement. A match is   
successful if the sub-expression on either side of "|" matches. As an example: 
"/(this|that) example/" uses grouping and the bar character and would match    
either "this example" or "that example", and nothing else.                     

These are just some of the ones you are likely to use when matching URLs with
Privoxy, and is a long way from a definitive list. This is enough to get us
started with a few simple examples which may be more illuminating:

/.*/banners/.* - A simple example that uses the common combination of "." and "
*" to denote any character, zero or more times. In other words, any string at
all. So we start with a literal forward slash, then our regular expression
pattern (".*") another literal forward slash, the string "banners", another
forward slash, and lastly another ".*". We are building a directory path here.
This will match any file with the path that has a directory named "banners" in
it. The ".*" matches any characters, and this could conceivably be more forward
slashes, so it might expand into a much longer looking path. For example, this
could match: "/eye/hate/spammers/banners/annoy_me_please.gif", or just "/
banners/annoying.html", or almost an infinite number of other possible
combinations, just so it has "banners" in the path somewhere.

A now something a little more complex:

/.*/adv((er)?ts?|ertis(ing|ements?))?/ - We have several literal forward
slashes again ("/"), so we are building another expression that is a file path
statement. We have another ".*", so we are matching against any conceivable
sub-path, just so it matches our expression. The only true literal that must
match our pattern is adv, together with the forward slashes. What comes after
the "adv" string is the interesting part.

Remember the "?" means the preceding expression (either a literal character or
anything grouped with "(...)" in this case) can exist or not, since this means
either zero or one match. So "((er)?ts?|ertis(ing|ements?))" is optional, as
are the individual sub-expressions: "(er)", "(ing|ements?)", and the "s". The "
|" means "or". We have two of those. For instance, "(ing|ements?)", can expand
to match either "ing" OR "ements?". What is being done here, is an attempt at
matching as many variations of "advertisement", and similar, as possible. So
this would expand to match just "adv", or "advert", or "adverts", or
"advertising", or "advertisement", or "advertisements". You get the idea. But
it would not match "advertizements" (with a "z"). We could fix that by changing
our regular expression to: "/.*/adv((er)?ts?|erti(s|z)(ing|ements?))?/", which
would then match either spelling.

/.*/advert[0-9]+\.(gif|jpe?g) - Again another path statement with forward
slashes. Anything in the square brackets "[]" can be matched. This is using
"0-9" as a shorthand expression to mean any digit one through nine. It is the
same as saying "0123456789". So any digit matches. The "+" means one or more of
the preceding expression must be included. The preceding expression here is
what is in the square brackets -- in this case, any digit one through nine.
Then, at the end, we have a grouping: "(gif|jpe?g)". This includes a "|", so
this needs to match the expression on either side of that bar character also. A
simple "gif" on one side, and the other side will in turn match either "jpeg"
or "jpg", since the "?" means the letter "e" is optional and can be matched
once or not at all. So we are building an expression here to match image GIF or
JPEG type image file. It must include the literal string "advert", then one or
more digits, and a "." (which is now a literal, and not a special character,
since it is escaped with "\"), and lastly either "gif", or "jpeg", or "jpg".
Some possible matches would include: "//advert1.jpg", "/nasty/ads/
advert1234.gif", "/banners/from/hell/advert99.jpg". It would not match
"advert1.gif" (no leading slash), or "/adverts232.jpg" (the expression does not
include an "s"), or "/advert1.jsp" ("jsp" is not in the expression anywhere).

We are barely scratching the surface of regular expressions here so that you
can understand the default Privoxy configuration files, and maybe use this
knowledge to customize your own installation. There is much, much more that can
be done with regular expressions. Now that you know enough to get started, you
can learn more on your own :/

More reading on Perl Compatible Regular expressions: http://www.perldoc.com/
perl5.6/pod/perlre.html

For information on regular expression based substitutions and their
applications in filters, please see the filter file tutorial in this manual.

-------------------------------------------------------------------------------

14.2. Privoxy's Internal Pages

Since Privoxy proxies each requested web page, it is easy for Privoxy to trap
certain special URLs. In this way, we can talk directly to Privoxy, and see how
it is configured, see how our rules are being applied, change these rules and
other configuration options, and even turn Privoxy's filtering off, all with a
web browser. 

The URLs listed below are the special ones that allow direct access to Privoxy.
Of course, Privoxy must be running to access these. If not, you will get a
friendly error message. Internet access is not necessary either.

  * Privoxy main page:
   
        http://config.privoxy.org/
       
    There is a shortcut: http://p.p/ (But it doesn't provide a fall-back to a
    real page, in case the request is not sent through Privoxy)
   
  * Show information about the current configuration, including viewing and
    editing of actions files:
   
        http://config.privoxy.org/show-status
       
  * Show the source code version numbers:
   
        http://config.privoxy.org/show-version
       
  * Show the browser's request headers:
   
        http://config.privoxy.org/show-request
       
  * Show which actions apply to a URL and why:
   
        http://config.privoxy.org/show-url-info
       
  * Toggle Privoxy on or off. In this case, "Privoxy" continues to run, but
    only as a pass-through proxy, with no actions taking place:
   
        http://config.privoxy.org/toggle
       
    Short cuts. Turn off, then on:
   
        http://config.privoxy.org/toggle?set=disable
       
        http://config.privoxy.org/toggle?set=enable
       
These may be bookmarked for quick reference. See next. 

-------------------------------------------------------------------------------

14.2.1. Bookmarklets

Below are some "bookmarklets" to allow you to easily access a "mini" version of
some of Privoxy's special pages. They are designed for MS Internet Explorer,
but should work equally well in Netscape, Mozilla, and other browsers which
support JavaScript. They are designed to run directly from your bookmarks - not
by clicking the links below (although that should work for testing).

To save them, right-click the link and choose "Add to Favorites" (IE) or "Add
Bookmark" (Netscape). You will get a warning that the bookmark "may not be
safe" - just click OK. Then you can run the Bookmarklet directly from your
favorites/bookmarks. For even faster access, you can put them on the "Links"
bar (IE) or the "Personal Toolbar" (Netscape), and run them with a single
click.

  * Privoxy - Enable
   
  * Privoxy - Disable
   
  * Privoxy - Toggle Privoxy (Toggles between enabled and disabled)
   
  * Privoxy- View Status
   
  * Privoxy - Submit Actions File Feedback
   
  * Privoxy - Why?
   
Credit: The site which gave us the general idea for these bookmarklets is 
www.bookmarklets.com. They have more information about bookmarklets.

-------------------------------------------------------------------------------

14.3. Chain of Events

Let's take a quick look at the basic sequence of events when a web page is
requested by your browser and Privoxy is on duty:

  * First, your web browser requests a web page. The browser knows to send the
    request to Privoxy, which will in turn, relay the request to the remote web
    server after passing the following tests:
   
  * Privoxy traps any request for its own internal CGI pages (e.g http://p.p/)
    and sends the CGI page back to the browser.
   
  * Next, Privoxy checks to see if the URL matches any "+block" patterns. If
    so, the URL is then blocked, and the remote web server will not be
    contacted. "+handle-as-image" is then checked and if it does not match, an
    HTML "BLOCKED" page is sent back. Otherwise, if it does match, an image is
    returned. The type of image depends on the setting of "+set-image-blocker"
    (blank, checkerboard pattern, or an HTTP redirect to an image elsewhere).
   
  * Untrusted URLs are blocked. If URLs are being added to the trust file, then
    that is done.
   
  * If the URL pattern matches the "+fast-redirects" action, it is then
    processed. Unwanted parts of the requested URL are stripped.
   
  * Now the rest of the client browser's request headers are processed. If any
    of these match any of the relevant actions (e.g. "+hide-user-agent", etc.),
    headers are suppressed or forged as determined by these actions and their
    parameters.
   
  * Now the web server starts sending its response back (i.e. typically a web
    page and related data).
   
  * First, the server headers are read and processed to determine, among other
    things, the MIME type (document type) and encoding. The headers are then
    filtered as determined by the "+crunch-incoming-cookies", 
    "+session-cookies-only", and "+downgrade-http-version" actions.
   
  * If the "+kill-popups" action applies, and it is an HTML or JavaScript
    document, the popup-code in the response is filtered on-the-fly as it is
    received.
   
  * If a "+filter" or "+deanimate-gifs" action applies (and the document type
    fits the action), the rest of the page is read into memory (up to a
    configurable limit). Then the filter rules (from default.filter) are
    processed against the buffered content. Filters are applied in the order
    they are specified in the default.filter file. Animated GIFs, if present,
    are reduced to either the first or last frame, depending on the action
    setting.The entire page, which is now filtered, is then sent by Privoxy
    back to your browser.
   
    If neither "+filter" or "+deanimate-gifs" matches, then Privoxy passes the
    raw data through to the client browser as it becomes available.
   
  * As the browser receives the now (probably filtered) page content, it reads
    and then requests any URLs that may be embedded within the page source,
    e.g. ad images, stylesheets, JavaScript, other HTML documents (e.g.
    frames), sounds, etc. For each of these objects, the browser issues a new
    request. And each such request is in turn processed as above. Note that a
    complex web page may have many such embedded URLs.
   
-------------------------------------------------------------------------------

14.4. Anatomy of an Action

The way Privoxy applies actions and filters to any given URL can be complex,
and not always so easy to understand what is happening. And sometimes we need
to be able to see just what Privoxy is doing. Especially, if something Privoxy
is doing is causing us a problem inadvertently. It can be a little daunting to
look at the actions and filters files themselves, since they tend to be filled
with regular expressions whose consequences are not always so obvious.

One quick test to see if Privoxy is causing a problem or not, is to disable it
temporarily. This should be the first troubleshooting step. See the
Bookmarklets section on a quick and easy way to do this (be sure to flush
caches afterward!). Looking at the logs is a good idea too.

Privoxy also provides the http://config.privoxy.org/show-url-info page that can
show us very specifically how actions are being applied to any given URL. This
is a big help for troubleshooting.

First, enter one URL (or partial URL) at the prompt, and then Privoxy will tell
us how the current configuration will handle it. This will not help with
filtering effects (i.e. the "+filter" action) from the default.filter file
since this is handled very differently and not so easy to trap! It also will
not tell you about any other URLs that may be embedded within the URL you are
testing. For instance, images such as ads are expressed as URLs within the raw
page source of HTML pages. So you will only get info for the actual URL that is
pasted into the prompt area -- not any sub-URLs. If you want to know about
embedded URLs like ads, you will have to dig those out of the HTML source. Use
your browser's "View Page Source" option for this. Or right click on the ad,
and grab the URL.

Let's try an example, google.com, and look at it one section at a time:

 Matches for http://google.com:                                                
                                                                               
 In file: default.action [ View ] [ Edit ]                                     
                                                                               
{-add-header                                                                   
 -block                                                                        
 -crunch-outgoing-cookies                                                      
 -crunch-incoming-cookies                                                      
 +deanimate-gifs{last}                                                         
 -downgrade-http-version                                                       
 +fast-redirects                                                               
 -filter{popups}                                                               
 -filter{fun}                                                                  
 -filter{shockwave-flash}                                                      
 -filter{crude-parental}                                                       
 +filter{html-annoyances}                                                      
 +filter{js-annoyances}                                                        
 +filter{content-cookies}                                                      
 +filter{webbugs}                                                              
 +filter{refresh-tags}                                                         
 +filter{nimda}                                                                
 +filter{banners-by-size}                                                      
 +hide-forwarded-for-headers                                                   
 +hide-from-header{block}                                                      
 +hide-referer{forge}                                                          
 -hide-user-agent                                                              
 -handle-as-image                                                              
 -kill-popups                                                                  
 -limit-connect                                                                
 +prevent-compression                                                          
 -send-vanilla-wafer                                                           
 -send-wafer                                                                   
 +session-cookies-only                                                         
 +set-image-blocker{pattern} }                                                 
/                                                                              
                                                                               
 { -session-cookies-only }                                                     
 .google.com                                                                   
                                                                               
 { -fast-redirects }                                                           
 .google.com                                                                   
                                                                               
In file: user.action [ View ] [ Edit ]                                         
(no matches in this file)                                                      

This tells us how we have defined our "actions", and which ones match for our
example, "google.com". The first listing is any matches for the standard.action
file. No hits at all here on "standard". Then next is "default", or our
default.action file. The large, multi-line listing, is how the actions are set
to match for all URLs, i.e. our default settings. If you look at your "actions"
file, this would be the section just below the "aliases" section near the top.
This will apply to all URLs as signified by the single forward slash at the end
of the listing -- "/".

But we can define additional actions that would be exceptions to these general
rules, and then list specific URLs (or patterns) that these exceptions would
apply to. Last match wins. Just below this then are two explicit matches for
".google.com". The first is negating our previous cookie setting, which was for
"+session-cookies-only" (i.e. not persistent). So we will allow persistent
cookies for google. The second turns off any "+fast-redirects" action, allowing
this to take place unmolested. Note that there is a leading dot here --
".google.com". This will match any hosts and sub-domains, in the google.com
domain also, such as "www.google.com". So, apparently, we have these two
actions defined somewhere in the lower part of our default.action file, and
"google.com" is referenced somewhere in these latter sections.

Then, for our user.action file, we again have no hits.

And finally we pull it all together in the bottom section and summarize how
Privoxy is applying all its "actions" to "google.com": 

 Final results:                                                                
                                                                               
 -add-header                                                                   
 -block                                                                        
 -crunch-outgoing-cookies                                                      
 -crunch-incoming-cookies                                                      
 +deanimate-gifs{last}                                                         
 -downgrade-http-version                                                       
 -fast-redirects                                                               
 -filter{popups}                                                               
 -filter{fun}                                                                  
 -filter{shockwave-flash}                                                      
 -filter{crude-parental}                                                       
 +filter{html-annoyances}                                                      
 +filter{js-annoyances}                                                        
 +filter{content-cookies}                                                      
 +filter{webbugs}                                                              
 +filter{refresh-tags}                                                         
 +filter{nimda}                                                                
 +filter{banners-by-size}                                                      
 +hide-forwarded-for-headers                                                   
 +hide-from-header{block}                                                      
 +hide-referer{forge}                                                          
 -hide-user-agent                                                              
 -handle-as-image                                                              
 -kill-popups                                                                  
 -limit-connect                                                                
 +prevent-compression                                                          
 -send-vanilla-wafer                                                           
 -send-wafer                                                                   
 -session-cookies-only                                                         
 +set-image-blocker{pattern}                                                   

Notice the only difference here to the previous listing, is to "fast-redirects"
and "session-cookies-only".

Now another example, "ad.doubleclick.net":

 { +block +handle-as-image }                                                   
  .ad.doubleclick.net                                                          
                                                                               
 { +block +handle-as-image }                                                   
  ad*.                                                                         
                                                                               
 { +block +handle-as-image }                                                   
  .doubleclick.net                                                             

We'll just show the interesting part here, the explicit matches. It is matched
three different times. Each as an "+block +handle-as-image", which is the
expanded form of one of our aliases that had been defined as: "+imageblock". (
"Aliases" are defined in the first section of the actions file and typically
used to combine more than one action.)

Any one of these would have done the trick and blocked this as an unwanted
image. This is unnecessarily redundant since the last case effectively would
also cover the first. No point in taking chances with these guys though ;-)
Note that if you want an ad or obnoxious URL to be invisible, it should be
defined as "ad.doubleclick.net" is done here -- as both a "+block" and an 
"+handle-as-image". The custom alias "+imageblock" just simplifies the process
and make it more readable.

One last example. Let's try "http://www.rhapsodyk.net/adsl/HOWTO/". This one is
giving us problems. We are getting a blank page. Hmmm ...

 Matches for http://www.rhapsodyk.net/adsl/HOWTO/:                             
                                                                               
 In file: default.action [ View ] [ Edit ]                                     
                                                                               
 {-add-header                                                                  
  -block                                                                       
  -crunch-incoming-cookies                                                     
  -crunch-outgoing-cookies                                                     
  +deanimate-gifs                                                              
  -downgrade-http-version                                                      
  +fast-redirects                                                              
  +filter{html-annoyances}                                                     
  +filter{js-annoyances}                                                       
  +filter{kill-popups}                                                         
  +filter{webbugs}                                                             
  +filter{nimda}                                                               
  +filter{banners-by-size}                                                     
  +filter{hal}                                                                 
  +filter{fun}                                                                 
  +hide-forwarded-for-headers                                                  
  +hide-from-header{block}                                                     
  +hide-referer{forge}                                                         
  -hide-user-agent                                                             
  -handle-as-image                                                             
  +kill-popups                                                                 
  +prevent-compression                                                         
  -send-vanilla-wafer                                                          
  -send-wafer                                                                  
  +session-cookies-only                                                        
  +set-image-blocker{blank} }                                                  
   /                                                                           
                                                                               
 { +block +handle-as-image }                                                   
  /ads                                                                         

Ooops, the "/adsl/" is matching "/ads"! But we did not want this at all! Now we
see why we get the blank page. We could now add a new action below this that
explicitly does not block ("{-block}") paths with "adsl". There are various
ways to handle such exceptions. Example:

 { -block }                                                                    
  /adsl                                                                        

Now the page displays ;-) Be sure to flush your browser's caches when making
such changes. Or, try using Shift+Reload.

But now what about a situation where we get no explicit matches like we did
with:

 { +block +handle-as-image }                                                   
 /ads                                                                          

That actually was very telling and pointed us quickly to where the problem was.
If you don't get this kind of match, then it means one of the default rules in
the first section is causing the problem. This would require some guesswork,
and maybe a little trial and error to isolate the offending rule. One likely
cause would be one of the "{+filter}" actions. These tend to be harder to
troubleshoot. Try adding the URL for the site to one of aliases that turn off
"+filter":

 {shop}                                                                        
 .quietpc.com                                                                  
 .worldpay.com   # for quietpc.com                                             
 .jungle.com                                                                   
 .scan.co.uk                                                                   
 .forbes.com                                                                   

"{shop}" is an "alias" that expands to "{ -filter -session-cookies-only }". Or
you could do your own exception to negate filtering: 

 {-filter}                                                                     
 .forbes.com                                                                   

This would turn off all filtering for that site. This would probably be most
appropriately put in user.action, for local site exceptions.

Images that are inexplicably being blocked, may well be hitting the "+filter
{banners-by-size}" rule, which assumes that images of certain sizes are ad
banners (works well most of the time since these tend to be standardized).

"{fragile}" is an alias that disables most actions. This can be used as a last
resort for problem sites. Remember to flush caches! If this still does not
work, you will have to go through the remaining actions one by one to find
which one(s) is causing the problem.

