+ </td>
+ </tr>
+ </table>
+
+ <p>
+ The <tt class="LITERAL">x</tt> option in this job turns on extended
+ syntax, and allows for e.g. the liberal use of (non-interpreted!)
+ whitespace for nicer formatting.
+ </p>
+ <p>
+ You get the idea?
+ </p>
+ </div>
+ <div class="SECT2">
+ <h2 class="SECT2">
+ <a name="PREDEFINED-FILTERS">9.2. The Pre-defined Filters</a>
+ </h2>
+ <p>
+ The distribution <tt class="FILENAME">default.filter</tt> file
+ contains a selection of pre-defined filters for your convenience:
+ </p>
+ <div class="VARIABLELIST">
+ <dl>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">js-annoyances</i></span>
+ </dt>
+ <dd>
+ <p>
+ The purpose of this filter is to get rid of particularly
+ annoying JavaScript abuse. To that end, it
+ </p>
+ <ul>
+ <li>
+ <p>
+ replaces JavaScript references to the browser's referrer
+ information with the string "Not Your Business!". This
+ compliments the <tt class="LITERAL"><a href=
+ "actions-file.html#HIDE-REFERRER">hide-referrer</a></tt>
+ action on the content level.
+ </p>
+ </li>
+ <li>
+ <p>
+ removes the bindings to the DOM's <a href=
+ "http://www.w3.org/TR/2000/REC-DOM-Level-2-Events-20001113/events.html#Events-eventgroupings-htmlevents"
+ target="_top">unload event</a> which we feel has no
+ right to exist and is responsible for most <span class=
+ "QUOTE">"exit consoles"</span>, i.e. nasty windows that
+ pop up when you close another one.
+ </p>
+ </li>
+ <li>
+ <p>
+ removes code that causes new windows to be opened with
+ undesired properties, such as being full-screen,
+ non-resizeable, without location, status or menu bar etc.
+ </p>
+ </li>
+ </ul>
+
+ <p>
+ Use with caution. This is an aggressive filter, and can break
+ sites that rely heavily on JavaScript.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class="EMPHASIS">js-events</i></span>
+ </dt>
+ <dd>
+ <p>
+ This is a very radical measure. It removes virtually all
+ JavaScript event bindings, which means that scripts can not
+ react to user actions such as mouse movements or clicks,
+ window resizing etc, anymore. Use with caution!
+ </p>
+ <p>
+ We <span class="emphasis"><i class="EMPHASIS">strongly
+ discourage</i></span> using this filter as a default since it
+ breaks many legitimate scripts. It is meant for use only on
+ extra-nasty sites (should you really need to go there).
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">html-annoyances</i></span>
+ </dt>
+ <dd>
+ <p>
+ This filter will undo many common instances of HTML based
+ abuse.
+ </p>
+ <p>
+ The <tt class="LITERAL">BLINK</tt> and <tt class=
+ "LITERAL">MARQUEE</tt> tags are neutralized (yeah baby!), and
+ browser windows will be created as resizeable (as of course
+ they should be!), and will have location, scroll and menu
+ bars -- even if specified otherwise.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">content-cookies</i></span>
+ </dt>
+ <dd>
+ <p>
+ Most cookies are set in the HTTP dialog, where they can be
+ intercepted by the <tt class="LITERAL"><a href=
+ "actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a></tt>
+ and <tt class="LITERAL"><a href=
+ "actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a></tt>
+ actions. But web sites increasingly make use of HTML meta
+ tags and JavaScript to sneak cookies to the browser on the
+ content level.
+ </p>
+ <p>
+ This filter disables most HTML and JavaScript code that reads
+ or sets cookies. It cannot detect all clever uses of these
+ types of code, so it should not be relied on as an absolute
+ fix. Use it wherever you would also use the cookie crunch
+ actions.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">refresh-tags</i></span>
+ </dt>
+ <dd>
+ <p>
+ Disable any refresh tags if the interval is greater than nine
+ seconds (so that redirections done via refresh tags are not
+ destroyed). This is useful for dial-on-demand setups, or for
+ those who find this HTML feature annoying.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">unsolicited-popups</i></span>
+ </dt>
+ <dd>
+ <p>
+ This filter attempts to prevent only <span class=
+ "QUOTE">"unsolicited"</span> pop-up windows from opening, yet
+ still allow pop-up windows that the user has explicitly
+ chosen to open. It was added in version 3.0.1, as an
+ improvement over earlier such filters.
+ </p>
+ <p>
+ Technical note: The filter works by redefining the
+ window.open JavaScript function to a dummy function, <tt
+ class="LITERAL">PrivoxyWindowOpen()</tt>, during the loading
+ and rendering phase of each HTML page access, and restoring
+ the function afterward.
+ </p>
+ <p>
+ This is recommended only for browsers that cannot perform
+ this function reliably themselves. And be aware that some
+ sites require such windows in order to function normally. Use
+ with caution.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">all-popups</i></span>
+ </dt>
+ <dd>
+ <p>
+ Attempt to prevent <span class="emphasis"><i class=
+ "EMPHASIS">all</i></span> pop-up windows from opening. Note
+ this should be used with even more discretion than the above,
+ since it is more likely to break some sites that require
+ pop-ups for normal usage. Use with caution.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">img-reorder</i></span>
+ </dt>
+ <dd>
+ <p>
+ This is a helper filter that has no value if used alone. It
+ makes the <tt class="LITERAL">banners-by-size</tt> and <tt
+ class="LITERAL">banners-by-link</tt> (see below) filters more
+ effective and should be enabled together with them.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">banners-by-size</i></span>
+ </dt>
+ <dd>
+ <p>
+ This filter removes image tags purely based on what size they
+ are. Fortunately for us, many ads and banner images tend to
+ conform to certain standardized sizes, which makes this
+ filter quite effective for ad stripping purposes.
+ </p>
+ <p>
+ Occasionally this filter will cause false positives on images
+ that are not ads, but just happen to be of one of the
+ standard banner sizes.
+ </p>
+ <p>
+ Recommended only for those who require extreme ad blocking.
+ The default block rules should catch 95+% of all ads <span
+ class="emphasis"><i class="EMPHASIS">without</i></span> this
+ filter enabled.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">banners-by-link</i></span>
+ </dt>
+ <dd>
+ <p>
+ This is an experimental filter that attempts to kill any
+ banners if their URLs seem to point to known or suspected
+ click trackers. It is currently not of much value and is not
+ recommended for use by default.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class="EMPHASIS">webbugs</i></span>
+ </dt>
+ <dd>
+ <p>
+ Webbugs are small, invisible images (technically 1X1 GIF
+ images), that are used to track users across websites, and
+ collect information on them. As an HTML page is loaded by the
+ browser, an embedded image tag causes the browser to contact
+ a third-party site, disclosing the tracking information
+ through the requested URL and/or cookies for that third-party
+ domain, without the user ever becoming aware of the
+ interaction with the third-party site. HTML-ized spam also
+ uses a similar technique to verify email addresses.
+ </p>
+ <p>
+ This filter removes the HTML code that loads such <span
+ class="QUOTE">"webbugs"</span>.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">tiny-textforms</i></span>
+ </dt>
+ <dd>
+ <p>
+ A rather special-purpose filter that can be used to enlarge
+ textareas (those multi-line text boxes in web forms) and turn
+ off hard word wrap in them. It was written for the
+ sourceforge.net tracker system where such boxes are a
+ nuisance, but it can be handy on other sites, too.
+ </p>
+ <p>
+ It is not recommended to use this filter as a default.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">jumping-windows</i></span>
+ </dt>
+ <dd>
+ <p>
+ Many consider windows that move, or resize themselves to be
+ abusive. This filter neutralizes the related JavaScript code.
+ Note that some sites might not display or behave as intended
+ when using this filter. Use with caution.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">frameset-borders</i></span>
+ </dt>
+ <dd>
+ <p>
+ Some web designers seem to assume that everyone in the world
+ will view their web sites using the same browser brand and
+ version, screen resolution etc, because only that assumption
+ could explain why they'd use static frame sizes, yet prevent
+ their frames from being resized by the user, should they be
+ too small to show their whole content.
+ </p>
+ <p>
+ This filter removes the related HTML code. It should only be
+ applied to sites which need it.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">demoronizer</i></span>
+ </dt>
+ <dd>
+ <p>
+ Many Microsoft products that generate HTML use non-standard
+ extensions (read: violations) of the ISO 8859-1 aka Latin-1
+ character set. This can cause those HTML documents to display
+ with errors on standard-compliant platforms.
+ </p>
+ <p>
+ This filter translates the MS-only characters into Latin-1
+ equivalents. It is not necessary when using MS products, and
+ will cause corruption of all documents that use 8-bit
+ character sets other than Latin-1. It's mostly worthwhile for
+ Europeans on non-MS platforms, if weird garbage characters
+ sometimes appear on some pages, or user agents that don't
+ correct for this on the fly.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">shockwave-flash</i></span>
+ </dt>
+ <dd>
+ <p>
+ A filter for shockwave haters. As the name suggests, this
+ filter strips code out of web pages that is used to embed
+ shockwave flash objects.
+ </p>
+ <p>
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">quicktime-kioskmode</i></span>
+ </dt>
+ <dd>
+ <p>
+ Change HTML code that embeds Quicktime objects so that
+ kioskmode, which prevents saving, is disabled.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class="EMPHASIS">fun</i></span>
+ </dt>
+ <dd>
+ <p>
+ Text replacements for subversive browsing fun. Make fun of
+ your favorite Monopolist or play buzzword bingo.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">crude-parental</i></span>
+ </dt>
+ <dd>
+ <p>
+ A demonstration-only filter that shows how <span class=
+ "APPLICATION">Privoxy</span> can be used to delete web
+ content on a keyword basis.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">ie-exploits</i></span>
+ </dt>
+ <dd>
+ <p>
+ An experimental collection of text replacements to disable
+ malicious HTML and JavaScript code that exploits known
+ security holes in Internet Explorer.
+ </p>
+ <p>
+ Presently, it only protects against Nimda and a cross-site
+ scripting bug, and would need active maintenance to provide
+ more substantial protection.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">site-specifics</i></span>
+ </dt>
+ <dd>
+ <p>
+ Some web sites have very specific problems, the cure for
+ which doesn't apply anywhere else, or could even cause damage
+ on other sites.
+ </p>
+ <p>
+ This is a collection of such site-specific cures which should
+ only be applied to the sites they were intended for, which is
+ what the supplied <tt class="FILENAME">default.action</tt>
+ file does. Users shouldn't need to change anything regarding
+ this filter.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class="EMPHASIS">google</i></span>
+ </dt>
+ <dd>
+ <p>
+ A CSS based block for Google text ads. Also removes a width
+ limitation and the toolbar advertisement.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class="EMPHASIS">yahoo</i></span>
+ </dt>
+ <dd>
+ <p>
+ Another CSS based block, this time for Yahoo text ads. And
+ removes a width limitation as well.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class="EMPHASIS">msn</i></span>
+ </dt>
+ <dd>
+ <p>
+ Another CSS based block, this time for MSN text ads. And
+ removes tracking URLs, as well as a width limitation.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class="EMPHASIS">blogspot</i></span>
+ </dt>
+ <dd>
+ <p>
+ Cleans up some Blogspot blogs. Read the fine print before
+ using this one!
+ </p>
+ <p>
+ This filter also intentionally removes some navigation stuff
+ and sets the page width to 100%. As a result, some rounded
+ <span class="QUOTE">"corners"</span> would appear to early or
+ not at all and as fixing this would require a browser that
+ understands background-size (CSS3), they are removed instead.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">xml-to-html</i></span>
+ </dt>
+ <dd>
+ <p>
+ Server-header filter to change the Content-Type from xml to
+ html.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">html-to-xml</i></span>
+ </dt>
+ <dd>
+ <p>
+ Server-header filter to change the Content-Type from html to
+ xml.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class="EMPHASIS">no-ping</i></span>
+ </dt>
+ <dd>
+ <p>
+ Removes the non-standard <tt class="LITERAL">ping</tt>
+ attribute from anchor and area HTML tags.
+ </p>
+ </dd>
+ <dt>
+ <span class="emphasis"><i class=
+ "EMPHASIS">hide-tor-exit-notation</i></span>
+ </dt>
+ <dd>
+ <p>
+ Client-header filter to remove the <b class="COMMAND">Tor</b>
+ exit node notation found in Host and Referer headers.
+ </p>
+ <p>
+ If <span class="APPLICATION">Privoxy</span> and <b class=
+ "COMMAND">Tor</b> are chained and <span class=
+ "APPLICATION">Privoxy</span> is configured to use socks4a,
+ one can use <span class=
+ "QUOTE">"http://www.example.org.foobar.exit/"</span> to
+ access the host <span class="QUOTE">"www.example.org"</span>
+ through the <b class="COMMAND">Tor</b> exit node <span class=
+ "QUOTE">"foobar"</span>.
+ </p>
+ <p>
+ As the HTTP client isn't aware of this notation, it treats
+ the whole string <span class=
+ "QUOTE">"www.example.org.foobar.exit"</span> as host and uses
+ it for the <span class="QUOTE">"Host"</span> and <span class=
+ "QUOTE">"Referer"</span> headers. From the server's point of
+ view the resulting headers are invalid and can cause
+ problems.
+ </p>
+ <p>
+ An invalid <span class="QUOTE">"Referer"</span> header can
+ trigger <span class="QUOTE">"hot-linking"</span> protections,
+ an invalid <span class="QUOTE">"Host"</span> header will make
+ it impossible for the server to find the right vhost (several
+ domains hosted on the same IP address).
+ </p>
+ <p>
+ This client-header filter removes the <span class=
+ "QUOTE">"foo.exit"</span> part in those headers to prevent
+ the mentioned problems. Note that it only modifies the HTTP
+ headers, it doesn't make it impossible for the server to
+ detect your <b class="COMMAND">Tor</b> exit node based on the
+ IP address the request is coming from.
+ </p>
+ </dd>
+ </dl>
+ </div>
+ </div>
+ <div class="SECT2">
+ <h2 class="SECT2">
+ <a name="EXTERNAL-FILTER-SYNTAX">9.3. External filter syntax</a>
+ </h2>
+ <p>
+ External filters are scripts or programs that can modify the
+ content in case common <tt class="LITERAL"><a href=
+ "actions-file.html#FILTER">filters</a></tt> aren't powerful enough.
+ </p>
+ <p>
+ External filters can be written in any language the platform <span
+ class="APPLICATION">Privoxy</span> runs on supports.
+ </p>
+ <p>
+ They are controlled with the <tt class="LITERAL"><a href=
+ "actions-file.html#EXTERNAL-FILTER">external-filter</a></tt> action
+ and have to be defined in the <tt class="LITERAL"><a href=
+ "config.html#FILTERFILE">filterfile</a></tt> first.
+ </p>
+ <p>
+ The header looks like any other filter, but instead of pcrs jobs,
+ external filters contain a single job which can be a program or a
+ shell script (which may call other scripts or programs).
+ </p>
+ <p>
+ External filters read the content from STDIN and write the
+ rewritten content to STDOUT. The environment variables PRIVOXY_URL,
+ PRIVOXY_PATH, PRIVOXY_HOST, PRIVOXY_ORIGIN, PRIVOXY_LISTEN_ADDRESS
+ can be used to get some details about the client request.
+ </p>
+ <p>
+ <span class="APPLICATION">Privoxy</span> will temporary store the
+ content to filter in the <tt class="LITERAL"><a href=
+ "config.html#TEMPORARY-DIRECTORY">temporary-directory</a></tt>.
+ </p>
+ <p>
+ </p>
+ <table border="0" bgcolor="#E0E0E0" width="100%">
+ <tr>
+ <td>
+<pre class="SCREEN">
+EXTERNAL-FILTER: cat Pointless example filter that doesn't actually modify the content
+/bin/cat
+
+# Incorrect reimplementation of the filter above in POSIX shell.
+#
+# Note that it's a single job that spans multiple lines, the line
+# breaks are not passed to the shell, thus the semicolons are required.
+#
+# If the script isn't trivial, it is recommended to put it into an external file.
+#
+# In general, writing external filters entirely in POSIX shell is not
+# considered a good idea.
+EXTERNAL-FILTER: cat2 Pointless example filter that despite its name may actually modify the content
+while read line; \
+do \
+ echo "$line"; \
+done
+
+EXTERNAL-FILTER: rotate-image Rotate an image by 180 degree. Test filter with limited value.
+/usr/local/bin/convert - -rotate 180 -
+
+EXTERNAL-FILTER: citation-needed Adds a "[citation needed]" tag to an image. The coordinates may need adjustment.
+/usr/local/bin/convert - -pointsize 16 -fill white -annotate +17+418 "[citation needed]" -
+</pre>
+ </td>
+ </tr>
+ </table>
+
+ <div class="WARNING">
+ <table class="WARNING" border="1" width="100%">
+ <tr>
+ <td align="CENTER">
+ <b>Warning</b>
+ </td>
+ </tr>
+ <tr>
+ <td align="LEFT">
+ <p>
+ Currently external filters are executed with <span class=
+ "APPLICATION">Privoxy</span>'s privileges! Only use
+ external filters you understand and trust.
+ </p>
+ </td>
+ </tr>
+ </table>
+ </div>
+ <p>
+ External filters are experimental and the syntax may change in the
+ future.
+ </p>
+ </div>
+ </div>
+ <div class="NAVFOOTER">
+ <hr align="LEFT" width="100%">
+ <table summary="Footer navigation table" width="100%" border="0"
+ cellpadding="0" cellspacing="0">
+ <tr>
+ <td width="33%" align="left" valign="top">
+ <a href="actions-file.html" accesskey="P">Prev</a>
+ </td>
+ <td width="34%" align="center" valign="top">
+ <a href="index.html" accesskey="H">Home</a>
+ </td>
+ <td width="33%" align="right" valign="top">
+ <a href="templates.html" accesskey="N">Next</a>
+ </td>
+ </tr>
+ <tr>
+ <td width="33%" align="left" valign="top">
+ Actions Files
+ </td>
+ <td width="34%" align="center" valign="top">
+
+ </td>
+ <td width="33%" align="right" valign="top">
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