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- <div class="SECT1">
- <h1 class="SECT1"><a name="FILTER-FILE" id="FILTER-FILE">9. Filter Files</a></h1>
- <p>On-the-fly text substitutions need to be defined in a <span class="QUOTE">"filter file"</span>. Once defined,
- they can then be invoked as an <span class="QUOTE">"action"</span>.</p>
- <p><span class="APPLICATION">Privoxy</span> supports three different pcrs-based filter actions: <tt class=
- "LITERAL"><a href="actions-file.html#FILTER">filter</a></tt> to rewrite the content that is send to the client,
- <tt class="LITERAL"><a href="actions-file.html#CLIENT-HEADER-FILTER">client-header-filter</a></tt> to rewrite
- headers that are send by the client, and <tt class="LITERAL"><a href=
- "actions-file.html#SERVER-HEADER-FILTER">server-header-filter</a></tt> to rewrite headers that are send by the
- server.</p>
- <p><span class="APPLICATION">Privoxy</span> also supports two tagger actions: <tt class="LITERAL"><a href=
- "actions-file.html#CLIENT-HEADER-TAGGER">client-header-tagger</a></tt> and <tt class="LITERAL"><a href=
- "actions-file.html#SERVER-HEADER-TAGGER">server-header-tagger</a></tt>. Taggers and filters use the same syntax in
- the filter files, the difference is that taggers don't modify the text they are filtering, but use a rewritten
- version of the filtered text as tag. The tags can then be used to change the applying actions through sections with
- <a href="actions-file.html#TAG-PATTERN">tag-patterns</a>.</p>
- <p>Finally <span class="APPLICATION">Privoxy</span> supports the <tt class="LITERAL"><a href=
- "actions-file.html#EXTERNAL-FILTER">external-filter</a></tt> action to enable <tt class="LITERAL"><a href=
- "filter-file.html#EXTERNAL-FILTER-SYNTAX">external filters</a></tt> written in proper programming languages.</p>
- <p>Multiple filter files can be defined through the <tt class="LITERAL"><a href=
- "config.html#FILTERFILE">filterfile</a></tt> config directive. The filters as supplied by the developers are
- located in <tt class="FILENAME">default.filter</tt>. It is recommended that any locally defined or modified filters
- go in a separately defined file such as <tt class="FILENAME">user.filter</tt>.</p>
- <p>Common tasks for content filters 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.</p>
- <p>Enabled content filters are applied to any content whose <span class="QUOTE">"Content Type"</span> header is
- recognised as a sign of text-based content, with the exception of <tt class="LITERAL">text/plain</tt>. Use the
- <a href="actions-file.html#FORCE-TEXT-MODE">force-text-mode</a> action to also filter other content.</p>
- <p>Substitutions are made at the source level, so if you want to <span class="QUOTE">"roll your own"</span>
- filters, you should first be familiar with HTML syntax, and, of course, regular expressions.</p>
- <p>Just like the <a href="actions-file.html">actions files</a>, the filter file is organized in sections, which are
- called <span class="emphasis"><i class="EMPHASIS">filters</i></span> here. Each filter consists of a heading line,
- that starts with one of the <span class="emphasis"><i class="EMPHASIS">keywords</i></span> <tt class=
- "LITERAL">FILTER:</tt>, <tt class="LITERAL">CLIENT-HEADER-FILTER:</tt> or <tt class=
- "LITERAL">SERVER-HEADER-FILTER:</tt> followed by the filter's <span class="emphasis"><i class=
- "EMPHASIS">name</i></span>, and a short (one line) <span class="emphasis"><i class=
- "EMPHASIS">description</i></span> of what it does. Below that line come the <span class="emphasis"><i class=
- "EMPHASIS">jobs</i></span>, i.e. lines that define the actual text substitutions. By convention, the name of a
- filter should describe what the filter <span class="emphasis"><i class="EMPHASIS">eliminates</i></span>. The
- comment is used in the <a href="http://config.privoxy.org/" target="_top">web-based user interface</a>.</p>
- <p>Once a filter called <tt class="REPLACEABLE"><i>name</i></tt> has been defined in the filter file, it can be
- invoked by using an action of the form +<tt class="LITERAL"><a href=
- "actions-file.html#FILTER">filter</a>{<tt class="REPLACEABLE"><i>name</i></tt>}</tt> in any <a href=
- "actions-file.html">actions file</a>.</p>
- <p>Filter definitions start with a header line that contains the filter type, the filter name and the filter
- description. A content filter header line for a filter called <span class="QUOTE">"foo"</span> could look like
- this:</p>
- <table border="0" bgcolor="#E0E0E0" width="100%">
- <tr>
- <td>
- <pre class="SCREEN">FILTER: foo Replace all "foo" with "bar"</pre>
- </td>
- </tr>
- </table>
- <p>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 <a href="http://www.perl.org/" target="_top">Perl</a>'s
- <tt class="LITERAL">s///</tt> operator. If you are familiar with Perl, you will find this to be quite intuitive,
- and may want to look at the PCRS documentation for the subtle differences to Perl behaviour.</p>
- <p>Most notably, the non-standard option letter <tt class="LITERAL">U</tt> is supported, which turns the default to
- ungreedy matching (add <tt class="LITERAL">?</tt> to quantifiers to turn them greedy again).</p>
- <p>The non-standard option letter <tt class="LITERAL">D</tt> (dynamic) allows to use the variables $host, $origin
- (the IP address the request came from), $path, $url and $listen-address (the address on which Privoxy accepted the
- client request. Example: 127.0.0.1:8118). They will be replaced with the value they refer to before the filter is
- executed.</p>
- <p>Note that '$' is a bad choice for a delimiter in a dynamic filter as you might end up with unintended variables
- if you use a variable name directly after the delimiter. Variables will be resolved without escaping anything,
- therefore you also have to be careful not to chose delimiters that appear in the replacement text. For example
- '<' should be save, while '?' will sooner or later cause conflicts with $url.</p>
- <p>The non-standard option letter <tt class="LITERAL">T</tt> (trivial) prevents parsing for backreferences in the
- substitute. Use it if you want to include text like '$&' in your substitute without quoting.</p>
- <p>If you are new to <a href="http://en.wikipedia.org/wiki/Regular_expressions" target="_top"><span class=
- "QUOTE">"Regular Expressions"</span></a>, you might want to take a look at the <a href=
- "appendix.html#REGEX">Appendix on regular expressions</a>, and see the <a href=
- "http://perldoc.perl.org/perlre.html" target="_top">Perl manual</a> for <a href=
- "http://perldoc.perl.org/perlop.html" target="_top">the <tt class="LITERAL">s///</tt> operator's syntax</a> and
- <a href="http://perldoc.perl.org/perlre.html" target="_top">Perl-style regular expressions</a> in general. The
- below examples might also help to get you started.</p>
- <div class="SECT2">
- <h2 class="SECT2"><a name="FILTER-FILE-TUT" id="FILTER-FILE-TUT">9.1. Filter File Tutorial</a></h2>
- <p>Now, let's complete our <span class="QUOTE">"foo"</span> content filter. We have already defined the heading,
- but the jobs are still missing. Since all it does is to replace <span class="QUOTE">"foo"</span> with
- <span class="QUOTE">"bar"</span>, there is only one (trivial) job needed:</p>
- <table border="0" bgcolor="#E0E0E0" width="100%">
- <tr>
- <td>
- <pre class="SCREEN">s/foo/bar/</pre>
- </td>
- </tr>
- </table>
- <p>But wait! Didn't the comment say that <span class="emphasis"><i class="EMPHASIS">all</i></span> occurrences of
- <span class="QUOTE">"foo"</span> should be replaced? Our current job will only take care of the first
- <span class="QUOTE">"foo"</span> on each page. For global substitution, we'll need to add the <tt class=
- "LITERAL">g</tt> option:</p>
- <table border="0" bgcolor="#E0E0E0" width="100%">
- <tr>
- <td>
- <pre class="SCREEN">s/foo/bar/g</pre>
- </td>
- </tr>
- </table>
- <p>Our complete filter now looks like this:</p>
- <table border="0" bgcolor="#E0E0E0" width="100%">
- <tr>
- <td>
- <pre class="SCREEN">FILTER: foo Replace all "foo" with "bar"
-s/foo/bar/g</pre>
- </td>
- </tr>
- </table>
- <p>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:</p>
- <table border="0" bgcolor="#E0E0E0" width="100%">
- <tr>
- <td>
- <pre class="SCREEN">FILTER: js-annoyances Get rid of particularly annoying JavaScript abuse
+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd">
+<HTML
+><HEAD
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+COLSPAN="3"
+ALIGN="center"
+>Privoxy 3.0.27 User Manual</TH
+></TR
+><TR
+><TD
+WIDTH="10%"
+ALIGN="left"
+VALIGN="bottom"
+><A
+HREF="actions-file.html"
+ACCESSKEY="P"
+>Prev</A
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+WIDTH="80%"
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+>Next</A
+></TD
+></TR
+></TABLE
+><HR
+ALIGN="LEFT"
+WIDTH="100%"></DIV
+><DIV
+CLASS="SECT1"
+><H1
+CLASS="SECT1"
+><A
+NAME="FILTER-FILE"
+>9. Filter Files</A
+></H1
+><P
+> On-the-fly text substitutions need
+ to be defined in a <SPAN
+CLASS="QUOTE"
+>"filter file"</SPAN
+>. Once defined, they
+ can then be invoked as an <SPAN
+CLASS="QUOTE"
+>"action"</SPAN
+>.</P
+><P
+> <SPAN
+CLASS="APPLICATION"
+>Privoxy</SPAN
+> supports three different pcrs-based filter actions:
+ <TT
+CLASS="LITERAL"
+><A
+HREF="actions-file.html#FILTER"
+>filter</A
+></TT
+> to
+ rewrite the content that is send to the client,
+ <TT
+CLASS="LITERAL"
+><A
+HREF="actions-file.html#CLIENT-HEADER-FILTER"
+>client-header-filter</A
+></TT
+>
+ to rewrite headers that are send by the client, and
+ <TT
+CLASS="LITERAL"
+><A
+HREF="actions-file.html#SERVER-HEADER-FILTER"
+>server-header-filter</A
+></TT
+>
+ to rewrite headers that are send by the server.</P
+><P
+> <SPAN
+CLASS="APPLICATION"
+>Privoxy</SPAN
+> also supports two tagger actions:
+ <TT
+CLASS="LITERAL"
+><A
+HREF="actions-file.html#CLIENT-HEADER-TAGGER"
+>client-header-tagger</A
+></TT
+>
+ and
+ <TT
+CLASS="LITERAL"
+><A
+HREF="actions-file.html#SERVER-HEADER-TAGGER"
+>server-header-tagger</A
+></TT
+>.
+ Taggers and filters use the same syntax in the filter files, the difference
+ is that taggers don't modify the text they are filtering, but use a rewritten
+ version of the filtered text as tag. The tags can then be used to change the
+ applying actions through sections with <A
+HREF="actions-file.html#TAG-PATTERN"
+>tag-patterns</A
+>.</P
+><P
+> Finally <SPAN
+CLASS="APPLICATION"
+>Privoxy</SPAN
+> supports the
+ <TT
+CLASS="LITERAL"
+><A
+HREF="actions-file.html#EXTERNAL-FILTER"
+>external-filter</A
+></TT
+> action
+ to enable <TT
+CLASS="LITERAL"
+><A
+HREF="filter-file.html#EXTERNAL-FILTER-SYNTAX"
+>external filters</A
+></TT
+>
+ written in proper programming languages.</P
+><P
+> Multiple filter files can be defined through the <TT
+CLASS="LITERAL"
+> <A
+HREF="config.html#FILTERFILE"
+>filterfile</A
+></TT
+> config directive. The filters
+ as supplied by the developers are located in
+ <TT
+CLASS="FILENAME"
+>default.filter</TT
+>. It is recommended that any locally
+ defined or modified filters go in a separately defined file such as
+ <TT
+CLASS="FILENAME"
+>user.filter</TT
+>.
+ </P
+><P
+> Common tasks for content filters 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.</P
+><P
+> Enabled content filters are applied to any content whose
+ <SPAN
+CLASS="QUOTE"
+>"Content Type"</SPAN
+> header is recognised as a sign
+ of text-based content, with the exception of <TT
+CLASS="LITERAL"
+>text/plain</TT
+>.
+ Use the <A
+HREF="actions-file.html#FORCE-TEXT-MODE"
+>force-text-mode</A
+> action
+ to also filter other content.</P
+><P
+> Substitutions are made at the source level, so if you want to <SPAN
+CLASS="QUOTE"
+>"roll
+ your own"</SPAN
+> filters, you should first be familiar with HTML syntax,
+ and, of course, regular expressions.</P
+><P
+> Just like the <A
+HREF="actions-file.html"
+>actions files</A
+>, the
+ filter file is organized in sections, which are called <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>filters</I
+></SPAN
+>
+ here. Each filter consists of a heading line, that starts with one of the
+ <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>keywords</I
+></SPAN
+> <TT
+CLASS="LITERAL"
+>FILTER:</TT
+>,
+ <TT
+CLASS="LITERAL"
+>CLIENT-HEADER-FILTER:</TT
+> or <TT
+CLASS="LITERAL"
+>SERVER-HEADER-FILTER:</TT
+>
+ followed by the filter's <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>name</I
+></SPAN
+>, and a short (one line)
+ <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>description</I
+></SPAN
+> of what it does. Below that line
+ come the <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>jobs</I
+></SPAN
+>, i.e. lines that define the actual
+ text substitutions. By convention, the name of a filter
+ should describe what the filter <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>eliminates</I
+></SPAN
+>. The
+ comment is used in the <A
+HREF="http://config.privoxy.org/"
+TARGET="_top"
+>web-based
+ user interface</A
+>.</P
+><P
+> Once a filter called <TT
+CLASS="REPLACEABLE"
+><I
+>name</I
+></TT
+> has been defined
+ in the filter file, it can be invoked by using an action of the form
+ +<TT
+CLASS="LITERAL"
+><A
+HREF="actions-file.html#FILTER"
+>filter</A
+>{<TT
+CLASS="REPLACEABLE"
+><I
+>name</I
+></TT
+>}</TT
+>
+ in any <A
+HREF="actions-file.html"
+>actions file</A
+>.</P
+><P
+> Filter definitions start with a header line that contains the filter
+ type, the filter name and the filter description.
+ A content filter header line for a filter called <SPAN
+CLASS="QUOTE"
+>"foo"</SPAN
+> could look
+ like this:</P
+><TABLE
+BORDER="0"
+BGCOLOR="#E0E0E0"
+WIDTH="100%"
+><TR
+><TD
+><PRE
+CLASS="SCREEN"
+>FILTER: foo Replace all "foo" with "bar"</PRE
+></TD
+></TR
+></TABLE
+><P
+> 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 <A
+HREF="http://www.perl.org/"
+TARGET="_top"
+>Perl</A
+>'s
+ <TT
+CLASS="LITERAL"
+>s///</TT
+> operator. If you are familiar with Perl, you
+ will find this to be quite intuitive, and may want to look at the
+ PCRS documentation for the subtle differences to Perl behaviour.</P
+><P
+> Most notably, the non-standard option letter <TT
+CLASS="LITERAL"
+>U</TT
+> is supported,
+ which turns the default to ungreedy matching (add <TT
+CLASS="LITERAL"
+>?</TT
+> to
+ quantifiers to turn them greedy again).</P
+><P
+> The non-standard option letter <TT
+CLASS="LITERAL"
+>D</TT
+> (dynamic) allows
+ to use the variables $host, $origin (the IP address the request came from),
+ $path, $url and $listen-address (the address on which Privoxy accepted the
+ client request. Example: 127.0.0.1:8118).
+ They will be replaced with the value they refer to before the filter
+ is executed.</P
+><P
+> Note that '$' is a bad choice for a delimiter in a dynamic filter as you
+ might end up with unintended variables if you use a variable name
+ directly after the delimiter. Variables will be resolved without
+ escaping anything, therefore you also have to be careful not to chose
+ delimiters that appear in the replacement text. For example '<' should
+ be save, while '?' will sooner or later cause conflicts with $url.</P
+><P
+> The non-standard option letter <TT
+CLASS="LITERAL"
+>T</TT
+> (trivial) prevents
+ parsing for backreferences in the substitute. Use it if you want to include
+ text like '$&' in your substitute without quoting.</P
+><P
+> If you are new to
+ <A
+HREF="http://en.wikipedia.org/wiki/Regular_expressions"
+TARGET="_top"
+><SPAN
+CLASS="QUOTE"
+>"Regular
+ Expressions"</SPAN
+></A
+>, you might want to take a look at
+ the <A
+HREF="appendix.html#REGEX"
+>Appendix on regular expressions</A
+>, and
+ see the <A
+HREF="http://perldoc.perl.org/perlre.html"
+TARGET="_top"
+>Perl
+ manual</A
+> for
+ <A
+HREF="http://perldoc.perl.org/perlop.html"
+TARGET="_top"
+>the
+ <TT
+CLASS="LITERAL"
+>s///</TT
+> operator's syntax</A
+> and <A
+HREF="http://perldoc.perl.org/perlre.html"
+TARGET="_top"
+>Perl-style regular
+ expressions</A
+> in general.
+ The below examples might also help to get you started.</P
+><DIV
+CLASS="SECT2"
+><H2
+CLASS="SECT2"
+><A
+NAME="FILTER-FILE-TUT"
+>9.1. Filter File Tutorial</A
+></H2
+><P
+> Now, let's complete our <SPAN
+CLASS="QUOTE"
+>"foo"</SPAN
+> content filter. We have already defined
+ the heading, but the jobs are still missing. Since all it does is to replace
+ <SPAN
+CLASS="QUOTE"
+>"foo"</SPAN
+> with <SPAN
+CLASS="QUOTE"
+>"bar"</SPAN
+>, there is only one (trivial) job
+ needed:</P
+><TABLE
+BORDER="0"
+BGCOLOR="#E0E0E0"
+WIDTH="100%"
+><TR
+><TD
+><PRE
+CLASS="SCREEN"
+>s/foo/bar/</PRE
+></TD
+></TR
+></TABLE
+><P
+> But wait! Didn't the comment say that <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>all</I
+></SPAN
+> occurrences
+ of <SPAN
+CLASS="QUOTE"
+>"foo"</SPAN
+> should be replaced? Our current job will only take
+ care of the first <SPAN
+CLASS="QUOTE"
+>"foo"</SPAN
+> on each page. For global substitution,
+ we'll need to add the <TT
+CLASS="LITERAL"
+>g</TT
+> option:</P
+><TABLE
+BORDER="0"
+BGCOLOR="#E0E0E0"
+WIDTH="100%"
+><TR
+><TD
+><PRE
+CLASS="SCREEN"
+>s/foo/bar/g</PRE
+></TD
+></TR
+></TABLE
+><P
+> Our complete filter now looks like this:</P
+><TABLE
+BORDER="0"
+BGCOLOR="#E0E0E0"
+WIDTH="100%"
+><TR
+><TD
+><PRE
+CLASS="SCREEN"
+>FILTER: foo Replace all "foo" with "bar"
+s/foo/bar/g</PRE
+></TD
+></TR
+></TABLE
+><P
+> 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:</P
+><TABLE
+BORDER="0"
+BGCOLOR="#E0E0E0"
+WIDTH="100%"
+><TR
+><TD
+><PRE
+CLASS="SCREEN"
+>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</pre>
- </td>
- </tr>
- </table>
- <p>Following the header line and a comment, you see the job. Note that it uses <tt class="LITERAL">|</tt> as the
- delimiter instead of <tt class="LITERAL">/</tt>, because the pattern contains a forward slash, which would
- otherwise have to be escaped by a backslash (<tt class="LITERAL">\</tt>).</p>
- <p>Now, let's examine the pattern: it starts with the text <tt class="LITERAL"><script.*</tt> enclosed in
- parentheses. Since the dot matches any character, and <tt class="LITERAL">*</tt> means: <span class=
- "QUOTE">"Match an arbitrary number of the element left of myself"</span>, this matches <span class=
- "QUOTE">"<script"</span>, followed by <span class="emphasis"><i class="EMPHASIS">any</i></span> text, i.e. it
- matches the whole page, from the start of the first <script> tag.</p>
- <p>That's more than we want, but the pattern continues: <tt class="LITERAL">document\.referrer</tt> matches only
- the exact string <span class="QUOTE">"document.referrer"</span>. The dot needed to be <span class=
- "emphasis"><i class="EMPHASIS">escaped</i></span>, 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 <span class="QUOTE">"document.referrer"</span>,
- if <span class="emphasis"><i class="EMPHASIS">both</i></span> are present in the page (and appear in that
- order).</p>
- <p>But there's still more pattern to go. The next element, again enclosed in parentheses, is <tt class=
- "LITERAL">.*</script></tt>. You already know what <tt class="LITERAL">.*</tt> 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 <span class="QUOTE">"document.referrer"</span> appears somewhere in
- between.</p>
- <p>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 <tt class="LITERAL">$1, $2, ...</tt> in the substitute. The <tt class="LITERAL">U</tt> option switches
- to ungreedy matching, which means that the first <tt class="LITERAL">.*</tt> in the pattern will only
- <span class="QUOTE">"eat up"</span> all text in between <span class="QUOTE">"<script"</span> and the
- <span class="emphasis"><i class="EMPHASIS">first</i></span> occurrence of <span class=
- "QUOTE">"document.referrer"</span>, and that the second <tt class="LITERAL">.*</tt> will only span the text up to
- the <span class="emphasis"><i class="EMPHASIS">first</i></span> <span class="QUOTE">"</script>"</span> tag.
- Furthermore, the <tt class="LITERAL">s</tt> option says that the match may span multiple lines in the page, and
- the <tt class="LITERAL">g</tt> option again means that the substitution is global.</p>
- <p>So, to summarize, the pattern means: Match all scripts that contain the text <span class=
- "QUOTE">"document.referrer"</span>. Remember the parts of the script from (and including) the start tag up to
- (and excluding) the string <span class="QUOTE">"document.referrer"</span> as <tt class="LITERAL">$1</tt>, and the
- part following that string, up to and including the closing tag, as <tt class="LITERAL">$2</tt>.</p>
- <p>Now the pattern is deciphered, but wasn't this about substituting things? So lets look at the substitute:
- <tt class="LITERAL">$1"Not Your Business!"$2</tt> is easy to read: The text remembered as <tt class=
- "LITERAL">$1</tt>, followed by <tt class="LITERAL">"Not Your Business!"</tt> (<span class="emphasis"><i class=
- "EMPHASIS">including</i></span> the quotation marks!), followed by the text remembered as <tt class=
- "LITERAL">$2</tt>. This produces an exact copy of the original string, with the middle part (the <span class=
- "QUOTE">"document.referrer"</span>) replaced by <tt class="LITERAL">"Not Your Business!"</tt>.</p>
- <p>The whole job now reads: Replace <span class="QUOTE">"document.referrer"</span> by <tt class="LITERAL">"Not
- Your Business!"</tt> 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.</p>
- <p>We'll show you two other jobs from the JavaScript taming department, but this time only point out the
- constructs of special interest:</p>
- <table border="0" bgcolor="#E0E0E0" width="100%">
- <tr>
- <td>
- <pre class="SCREEN"># The status bar is for displaying link targets, not pointless blahblah
+s|(<script.*)document\.referrer(.*</script>)|$1"Not Your Business!"$2|Usg</PRE
+></TD
+></TR
+></TABLE
+><P
+> Following the header line and a comment, you see the job. Note that it uses
+ <TT
+CLASS="LITERAL"
+>|</TT
+> as the delimiter instead of <TT
+CLASS="LITERAL"
+>/</TT
+>, because
+ the pattern contains a forward slash, which would otherwise have to be escaped
+ by a backslash (<TT
+CLASS="LITERAL"
+>\</TT
+>).</P
+><P
+> Now, let's examine the pattern: it starts with the text <TT
+CLASS="LITERAL"
+><script.*</TT
+>
+ enclosed in parentheses. Since the dot matches any character, and <TT
+CLASS="LITERAL"
+>*</TT
+>
+ means: <SPAN
+CLASS="QUOTE"
+>"Match an arbitrary number of the element left of myself"</SPAN
+>, this
+ matches <SPAN
+CLASS="QUOTE"
+>"<script"</SPAN
+>, followed by <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>any</I
+></SPAN
+> text, i.e.
+ it matches the whole page, from the start of the first <script> tag.</P
+><P
+> That's more than we want, but the pattern continues: <TT
+CLASS="LITERAL"
+>document\.referrer</TT
+>
+ matches only the exact string <SPAN
+CLASS="QUOTE"
+>"document.referrer"</SPAN
+>. The dot needed to
+ be <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>escaped</I
+></SPAN
+>, 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 <SPAN
+CLASS="QUOTE"
+>"document.referrer"</SPAN
+>, if <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>both</I
+></SPAN
+> are present
+ in the page (and appear in that order).</P
+><P
+> But there's still more pattern to go. The next element, again enclosed in parentheses,
+ is <TT
+CLASS="LITERAL"
+>.*</script></TT
+>. You already know what <TT
+CLASS="LITERAL"
+>.*</TT
+>
+ 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
+ <SPAN
+CLASS="QUOTE"
+>"document.referrer"</SPAN
+> appears somewhere in between.</P
+><P
+> 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 <TT
+CLASS="LITERAL"
+>$1, $2, ...</TT
+> in
+ the substitute. The <TT
+CLASS="LITERAL"
+>U</TT
+> option switches to ungreedy matching, which means
+ that the first <TT
+CLASS="LITERAL"
+>.*</TT
+> in the pattern will only <SPAN
+CLASS="QUOTE"
+>"eat up"</SPAN
+> all
+ text in between <SPAN
+CLASS="QUOTE"
+>"<script"</SPAN
+> and the <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>first</I
+></SPAN
+> occurrence
+ of <SPAN
+CLASS="QUOTE"
+>"document.referrer"</SPAN
+>, and that the second <TT
+CLASS="LITERAL"
+>.*</TT
+> will
+ only span the text up to the <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>first</I
+></SPAN
+> <SPAN
+CLASS="QUOTE"
+>"</script>"</SPAN
+>
+ tag. Furthermore, the <TT
+CLASS="LITERAL"
+>s</TT
+> option says that the match may span
+ multiple lines in the page, and the <TT
+CLASS="LITERAL"
+>g</TT
+> option again means that the
+ substitution is global.</P
+><P
+> So, to summarize, the pattern means: Match all scripts that contain the text
+ <SPAN
+CLASS="QUOTE"
+>"document.referrer"</SPAN
+>. Remember the parts of the script from
+ (and including) the start tag up to (and excluding) the string
+ <SPAN
+CLASS="QUOTE"
+>"document.referrer"</SPAN
+> as <TT
+CLASS="LITERAL"
+>$1</TT
+>, and the part following
+ that string, up to and including the closing tag, as <TT
+CLASS="LITERAL"
+>$2</TT
+>.</P
+><P
+> Now the pattern is deciphered, but wasn't this about substituting things? So
+ lets look at the substitute: <TT
+CLASS="LITERAL"
+>$1"Not Your Business!"$2</TT
+> is
+ easy to read: The text remembered as <TT
+CLASS="LITERAL"
+>$1</TT
+>, followed by
+ <TT
+CLASS="LITERAL"
+>"Not Your Business!"</TT
+> (<SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>including</I
+></SPAN
+>
+ the quotation marks!), followed by the text remembered as <TT
+CLASS="LITERAL"
+>$2</TT
+>.
+ This produces an exact copy of the original string, with the middle part
+ (the <SPAN
+CLASS="QUOTE"
+>"document.referrer"</SPAN
+>) replaced by <TT
+CLASS="LITERAL"
+>"Not Your
+ Business!"</TT
+>.</P
+><P
+> The whole job now reads: Replace <SPAN
+CLASS="QUOTE"
+>"document.referrer"</SPAN
+> by
+ <TT
+CLASS="LITERAL"
+>"Not Your Business!"</TT
+> 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.</P
+><P
+> We'll show you two other jobs from the JavaScript taming department, but
+ this time only point out the constructs of special interest:</P
+><TABLE
+BORDER="0"
+BGCOLOR="#E0E0E0"
+WIDTH="100%"
+><TR
+><TD
+><PRE
+CLASS="SCREEN"
+># The status bar is for displaying link targets, not pointless blahblah
#
-s/window\.status\s*=\s*(['"]).*?\1/dUmMy=1/ig</pre>
- </td>
- </tr>
- </table>
- <p><tt class="LITERAL">\s</tt> stands for whitespace characters (space, tab, newline, carriage return, form
- feed), so that <tt class="LITERAL">\s*</tt> means: <span class="QUOTE">"zero or more whitespace"</span>. The
- <tt class="LITERAL">?</tt> in <tt class="LITERAL">.*?</tt> makes this matching of arbitrary text ungreedy. (Note
- that the <tt class="LITERAL">U</tt> option is not set). The <tt class="LITERAL">['"]</tt> construct means:
- <span class="QUOTE">"a single <span class="emphasis"><i class="EMPHASIS">or</i></span> a double quote"</span>.
- Finally, <tt class="LITERAL">\1</tt> is a back-reference to the first parenthesis just like <tt class=
- "LITERAL">$1</tt> above, with the difference that in the <span class="emphasis"><i class=
- "EMPHASIS">pattern</i></span>, a backslash indicates a back-reference, whereas in the <span class=
- "emphasis"><i class="EMPHASIS">substitute</i></span>, it's the dollar.</p>
- <p>So what does this job do? It replaces assignments of single- or double-quoted strings to the <span class=
- "QUOTE">"window.status"</span> 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.</p>
- <table border="0" bgcolor="#E0E0E0" width="100%">
- <tr>
- <td>
- <pre class="SCREEN"># Kill OnUnload popups. Yummy. Test: http://www.zdnet.com/zdsubs/yahoo/tree/yfs.html
+s/window\.status\s*=\s*(['"]).*?\1/dUmMy=1/ig</PRE
+></TD
+></TR
+></TABLE
+><P
+> <TT
+CLASS="LITERAL"
+>\s</TT
+> stands for whitespace characters (space, tab, newline,
+ carriage return, form feed), so that <TT
+CLASS="LITERAL"
+>\s*</TT
+> means: <SPAN
+CLASS="QUOTE"
+>"zero
+ or more whitespace"</SPAN
+>. The <TT
+CLASS="LITERAL"
+>?</TT
+> in <TT
+CLASS="LITERAL"
+>.*?</TT
+>
+ makes this matching of arbitrary text ungreedy. (Note that the <TT
+CLASS="LITERAL"
+>U</TT
+>
+ option is not set). The <TT
+CLASS="LITERAL"
+>['"]</TT
+> construct means: <SPAN
+CLASS="QUOTE"
+>"a single
+ <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>or</I
+></SPAN
+> a double quote"</SPAN
+>. Finally, <TT
+CLASS="LITERAL"
+>\1</TT
+> is
+ a back-reference to the first parenthesis just like <TT
+CLASS="LITERAL"
+>$1</TT
+> above,
+ with the difference that in the <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>pattern</I
+></SPAN
+>, a backslash indicates
+ a back-reference, whereas in the <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>substitute</I
+></SPAN
+>, it's the dollar.</P
+><P
+> So what does this job do? It replaces assignments of single- or double-quoted
+ strings to the <SPAN
+CLASS="QUOTE"
+>"window.status"</SPAN
+> 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.</P
+><TABLE
+BORDER="0"
+BGCOLOR="#E0E0E0"
+WIDTH="100%"
+><TR
+><TD
+><PRE
+CLASS="SCREEN"
+># Kill OnUnload popups. Yummy. Test: http://www.zdnet.com/zdsubs/yahoo/tree/yfs.html
#
-s/(<body [^>]*)onunload(.*>)/$1never$2/iU</pre>
- </td>
- </tr>
- </table>
- <p>Including the <a href=
- "http://www.w3.org/TR/2000/REC-DOM-Level-2-Events-20001113/events.html#Events-eventgroupings-htmlevents" target=
- "_top">OnUnload event binding</a> in the HTML DOM was a <span class="emphasis"><i class=
- "EMPHASIS">CRIME</i></span>. When I close a browser window, I want it to close and die. Basta. This job replaces
- the <span class="QUOTE">"onunload"</span> attribute in <span class="QUOTE">"<body>"</span> tags with the
- dummy word <tt class="LITERAL">never</tt>. Note that the <tt class="LITERAL">i</tt> 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 <tt class="LITERAL">[^>]*</tt> instead of <tt class="LITERAL">.*</tt> to
- prevent the match from exceeding the <body> tag if it doesn't contain <span class=
- "QUOTE">"OnUnload"</span>, but the page's content does.</p>
- <p>The last example is from the fun department:</p>
- <table border="0" bgcolor="#E0E0E0" width="100%">
- <tr>
- <td>
- <pre class="SCREEN">FILTER: fun Fun text replacements
+s/(<body [^>]*)onunload(.*>)/$1never$2/iU</PRE
+></TD
+></TR
+></TABLE
+><P
+> Including the
+ <A
+HREF="http://www.w3.org/TR/2000/REC-DOM-Level-2-Events-20001113/events.html#Events-eventgroupings-htmlevents"
+TARGET="_top"
+>OnUnload
+ event binding</A
+> in the HTML DOM was a <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>CRIME</I
+></SPAN
+>.
+ When I close a browser window, I want it to close and die. Basta.
+ This job replaces the <SPAN
+CLASS="QUOTE"
+>"onunload"</SPAN
+> attribute in
+ <SPAN
+CLASS="QUOTE"
+>"<body>"</SPAN
+> tags with the dummy word <TT
+CLASS="LITERAL"
+>never</TT
+>.
+ Note that the <TT
+CLASS="LITERAL"
+>i</TT
+> 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 <TT
+CLASS="LITERAL"
+>[^>]*</TT
+>
+ instead of <TT
+CLASS="LITERAL"
+>.*</TT
+> to prevent the match from exceeding the
+ <body> tag if it doesn't contain <SPAN
+CLASS="QUOTE"
+>"OnUnload"</SPAN
+>, but the page's
+ content does.</P
+><P
+> The last example is from the fun department:</P
+><TABLE
+BORDER="0"
+BGCOLOR="#E0E0E0"
+WIDTH="100%"
+><TR
+><TD
+><PRE
+CLASS="SCREEN"
+>FILTER: fun Fun text replacements
# Spice the daily news:
#
-s/microsoft(?!\.com)/MicroSuck/ig</pre>
- </td>
- </tr>
- </table>
- <p>Note the <tt class="LITERAL">(?!\.com)</tt> part (a so-called negative lookahead) in the job's pattern, which
- means: Don't match, if the string <span class="QUOTE">".com"</span> appears directly following <span class=
- "QUOTE">"microsoft"</span> in the page. This prevents links to microsoft.com from being trashed, while still
- replacing the word everywhere else.</p>
- <table border="0" bgcolor="#E0E0E0" width="100%">
- <tr>
- <td>
- <pre class="SCREEN"># Buzzword Bingo (example for extended regex syntax)
+s/microsoft(?!\.com)/MicroSuck/ig</PRE
+></TD
+></TR
+></TABLE
+><P
+> Note the <TT
+CLASS="LITERAL"
+>(?!\.com)</TT
+> part (a so-called negative lookahead)
+ in the job's pattern, which means: Don't match, if the string
+ <SPAN
+CLASS="QUOTE"
+>".com"</SPAN
+> appears directly following <SPAN
+CLASS="QUOTE"
+>"microsoft"</SPAN
+>
+ in the page. This prevents links to microsoft.com from being trashed, while
+ still replacing the word everywhere else.</P
+><TABLE
+BORDER="0"
+BGCOLOR="#E0E0E0"
+WIDTH="100%"
+><TR
+><TD
+><PRE
+CLASS="SCREEN"
+># Buzzword Bingo (example for extended regex syntax)
#
s* industry[ -]leading \
| cutting[ -]edge \
| unmatched \
| unparalleled \
| unrivalled \
-*<font color="red"><b>BINGO!</b></font> \
-*igx</pre>
- </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" id="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>
- </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" id="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>
- <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
+*<font color="red"><b>BINGO!</b></font> \
+*igx</PRE
+></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
+><P
+></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
+><P
+></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
+><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.
/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">Privoxy's Template Files</td>
- </tr>
- </table>
- </div>
-</body>
-</html>
+/usr/local/bin/convert - -pointsize 16 -fill white -annotate +17+418 "[citation needed]" -</PRE
+></TD
+></TR
+></TABLE
+><DIV
+CLASS="WARNING"
+><P
+></P
+><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"
+>Privoxy's Template Files</TD
+></TR
+></TABLE
+></DIV
+></BODY
+></HTML
+>
\ No newline at end of file
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