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40 <h1 class="SECT1"><a name="FILTER-FILE" id="FILTER-FILE">9. Filter
43 <p>On-the-fly text substitutions need to be defined in a <span class=
44 "QUOTE">"filter file"</span>. Once defined, they can then be invoked as
45 an <span class="QUOTE">"action"</span>.</p>
47 <p><span class="APPLICATION">Privoxy</span> supports three different
48 filter actions: <tt class="LITERAL"><a href=
49 "actions-file.html#FILTER">filter</a></tt> to rewrite the content that is
50 send to the client, <tt class="LITERAL"><a href=
51 "actions-file.html#CLIENT-HEADER-FILTER">client-header-filter</a></tt> to
52 rewrite headers that are send by the client, and <tt class=
54 "actions-file.html#SERVER-HEADER-FILTER">server-header-filter</a></tt> to
55 rewrite headers that are send by the server.</p>
57 <p><span class="APPLICATION">Privoxy</span> also supports two tagger
58 actions: <tt class="LITERAL"><a href=
59 "actions-file.html#CLIENT-HEADER-TAGGER">client-header-tagger</a></tt>
60 and <tt class="LITERAL"><a href=
61 "actions-file.html#SERVER-HEADER-TAGGER">server-header-tagger</a></tt>.
62 Taggers and filters use the same syntax in the filter files, the
63 difference is that taggers don't modify the text they are filtering, but
64 use a rewritten version of the filtered text as tag. The tags can then be
65 used to change the applying actions through sections with <a href=
66 "actions-file.html#TAG-PATTERN">tag-patterns</a>.</p>
68 <p>Multiple filter files can be defined through the <tt class=
69 "LITERAL"><a href="config.html#FILTERFILE">filterfile</a></tt> config
70 directive. The filters as supplied by the developers are located in
71 <tt class="FILENAME">default.filter</tt>. It is recommended that any
72 locally defined or modified filters go in a separately defined file such
73 as <tt class="FILENAME">user.filter</tt>.</p>
75 <p>Common tasks for content filters are to eliminate common annoyances in
76 HTML and JavaScript, such as pop-up windows, exit consoles, crippled
77 windows without navigation tools, the infamous <BLINK> tag etc, to
78 suppress images with certain width and height attributes (standard banner
79 sizes or web-bugs), or just to have fun.</p>
81 <p>Enabled content filters are applied to any content whose <span class=
82 "QUOTE">"Content Type"</span> header is recognised as a sign of
83 text-based content, with the exception of <tt class=
84 "LITERAL">text/plain</tt>. Use the <a href=
85 "actions-file.html#FORCE-TEXT-MODE">force-text-mode</a> action to also
86 filter other content.</p>
88 <p>Substitutions are made at the source level, so if you want to
89 <span class="QUOTE">"roll your own"</span> filters, you should first be
90 familiar with HTML syntax, and, of course, regular expressions.</p>
92 <p>Just like the <a href="actions-file.html">actions files</a>, the
93 filter file is organized in sections, which are called <span class=
94 "emphasis"><i class="EMPHASIS">filters</i></span> here. Each filter
95 consists of a heading line, that starts with one of the <span class=
96 "emphasis"><i class="EMPHASIS">keywords</i></span> <tt class=
97 "LITERAL">FILTER:</tt>, <tt class="LITERAL">CLIENT-HEADER-FILTER:</tt> or
98 <tt class="LITERAL">SERVER-HEADER-FILTER:</tt> followed by the filter's
99 <span class="emphasis"><i class="EMPHASIS">name</i></span>, and a short
100 (one line) <span class="emphasis"><i class=
101 "EMPHASIS">description</i></span> of what it does. Below that line come
102 the <span class="emphasis"><i class="EMPHASIS">jobs</i></span>, i.e.
103 lines that define the actual text substitutions. By convention, the name
104 of a filter should describe what the filter <span class=
105 "emphasis"><i class="EMPHASIS">eliminates</i></span>. The comment is used
106 in the <a href="http://config.privoxy.org/" target="_top">web-based user
109 <p>Once a filter called <tt class="REPLACEABLE"><i>name</i></tt> has been
110 defined in the filter file, it can be invoked by using an action of the
111 form +<tt class="LITERAL"><a href=
112 "actions-file.html#FILTER">filter</a>{<tt class=
113 "REPLACEABLE"><i>name</i></tt>}</tt> in any <a href=
114 "actions-file.html">actions file</a>.</p>
116 <p>Filter definitions start with a header line that contains the filter
117 type, the filter name and the filter description. A content filter header
118 line for a filter called <span class="QUOTE">"foo"</span> could look like
121 <table border="0" bgcolor="#E0E0E0" width="100%">
125 FILTER: foo Replace all "foo" with "bar"
131 <p>Below that line, and up to the next header line, come the jobs that
132 define what text replacements the filter executes. They are specified in
133 a syntax that imitates <a href="http://www.perl.org/" target=
134 "_top">Perl</a>'s <tt class="LITERAL">s///</tt> operator. If you are
135 familiar with Perl, you will find this to be quite intuitive, and may
136 want to look at the PCRS documentation for the subtle differences to Perl
137 behaviour. Most notably, the non-standard option letter <tt class=
138 "LITERAL">U</tt> is supported, which turns the default to ungreedy
141 <p>If you are new to <a href=
142 "http://en.wikipedia.org/wiki/Regular_expressions" target=
143 "_top"><span class="QUOTE">"Regular Expressions"</span></a>, you might
144 want to take a look at the <a href="appendix.html#REGEX">Appendix on
145 regular expressions</a>, and see the <a href=
146 "http://perldoc.perl.org/perlre.html" target="_top">Perl manual</a> for
147 <a href="http://perldoc.perl.org/perlop.html" target="_top">the
148 <tt class="LITERAL">s///</tt> operator's syntax</a> and <a href=
149 "http://perldoc.perl.org/perlre.html" target="_top">Perl-style regular
150 expressions</a> in general. The below examples might also help to get you
154 <h2 class="SECT2"><a name="AEN5143" id="AEN5143">9.1. Filter File
157 <p>Now, let's complete our <span class="QUOTE">"foo"</span> content
158 filter. We have already defined the heading, but the jobs are still
159 missing. Since all it does is to replace <span class=
160 "QUOTE">"foo"</span> with <span class="QUOTE">"bar"</span>, there is
161 only one (trivial) job needed:</p>
163 <table border="0" bgcolor="#E0E0E0" width="100%">
173 <p>But wait! Didn't the comment say that <span class=
174 "emphasis"><i class="EMPHASIS">all</i></span> occurrences of
175 <span class="QUOTE">"foo"</span> should be replaced? Our current job
176 will only take care of the first <span class="QUOTE">"foo"</span> on
177 each page. For global substitution, we'll need to add the <tt class=
178 "LITERAL">g</tt> option:</p>
180 <table border="0" bgcolor="#E0E0E0" width="100%">
190 <p>Our complete filter now looks like this:</p>
192 <table border="0" bgcolor="#E0E0E0" width="100%">
196 FILTER: foo Replace all "foo" with "bar"
203 <p>Let's look at some real filters for more interesting examples. Here
204 you see a filter that protects against some common annoyances that
205 arise from JavaScript abuse. Let's look at its jobs one after the
208 <table border="0" bgcolor="#E0E0E0" width="100%">
212 FILTER: js-annoyances Get rid of particularly annoying JavaScript abuse
214 # Get rid of JavaScript referrer tracking. Test page: http://www.randomoddness.com/untitled.htm
216 s|(<script.*)document\.referrer(.*</script>)|$1"Not Your Business!"$2|Usg
222 <p>Following the header line and a comment, you see the job. Note that
223 it uses <tt class="LITERAL">|</tt> as the delimiter instead of
224 <tt class="LITERAL">/</tt>, because the pattern contains a forward
225 slash, which would otherwise have to be escaped by a backslash
226 (<tt class="LITERAL">\</tt>).</p>
228 <p>Now, let's examine the pattern: it starts with the text <tt class=
229 "LITERAL"><script.*</tt> enclosed in parentheses. Since the dot
230 matches any character, and <tt class="LITERAL">*</tt> means:
231 <span class="QUOTE">"Match an arbitrary number of the element left of
232 myself"</span>, this matches <span class="QUOTE">"<script"</span>,
233 followed by <span class="emphasis"><i class="EMPHASIS">any</i></span>
234 text, i.e. it matches the whole page, from the start of the first
235 <script> tag.</p>
237 <p>That's more than we want, but the pattern continues: <tt class=
238 "LITERAL">document\.referrer</tt> matches only the exact string
239 <span class="QUOTE">"document.referrer"</span>. The dot needed to be
240 <span class="emphasis"><i class="EMPHASIS">escaped</i></span>, i.e.
241 preceded by a backslash, to take away its special meaning as a joker,
242 and make it just a regular dot. So far, the meaning is: Match from the
243 start of the first <script> tag in a the page, up to, and
244 including, the text <span class="QUOTE">"document.referrer"</span>, if
245 <span class="emphasis"><i class="EMPHASIS">both</i></span> are present
246 in the page (and appear in that order).</p>
248 <p>But there's still more pattern to go. The next element, again
249 enclosed in parentheses, is <tt class="LITERAL">.*</script></tt>.
250 You already know what <tt class="LITERAL">.*</tt> means, so the whole
251 pattern translates to: Match from the start of the first <script>
252 tag in a page to the end of the last <script> tag, provided that
253 the text <span class="QUOTE">"document.referrer"</span> appears
254 somewhere in between.</p>
256 <p>This is still not the whole story, since we have ignored the options
257 and the parentheses: The portions of the page matched by sub-patterns
258 that are enclosed in parentheses, will be remembered and be available
259 through the variables <tt class="LITERAL">$1, $2, ...</tt> in the
260 substitute. The <tt class="LITERAL">U</tt> option switches to ungreedy
261 matching, which means that the first <tt class="LITERAL">.*</tt> in the
262 pattern will only <span class="QUOTE">"eat up"</span> all text in
263 between <span class="QUOTE">"<script"</span> and the <span class=
264 "emphasis"><i class="EMPHASIS">first</i></span> occurrence of
265 <span class="QUOTE">"document.referrer"</span>, and that the second
266 <tt class="LITERAL">.*</tt> will only span the text up to the
267 <span class="emphasis"><i class="EMPHASIS">first</i></span>
268 <span class="QUOTE">"</script>"</span> tag. Furthermore, the
269 <tt class="LITERAL">s</tt> option says that the match may span multiple
270 lines in the page, and the <tt class="LITERAL">g</tt> option again
271 means that the substitution is global.</p>
273 <p>So, to summarize, the pattern means: Match all scripts that contain
274 the text <span class="QUOTE">"document.referrer"</span>. Remember the
275 parts of the script from (and including) the start tag up to (and
276 excluding) the string <span class="QUOTE">"document.referrer"</span> as
277 <tt class="LITERAL">$1</tt>, and the part following that string, up to
278 and including the closing tag, as <tt class="LITERAL">$2</tt>.</p>
280 <p>Now the pattern is deciphered, but wasn't this about substituting
281 things? So lets look at the substitute: <tt class="LITERAL">$1"Not Your
282 Business!"$2</tt> is easy to read: The text remembered as <tt class=
283 "LITERAL">$1</tt>, followed by <tt class="LITERAL">"Not Your
284 Business!"</tt> (<span class="emphasis"><i class=
285 "EMPHASIS">including</i></span> the quotation marks!), followed by the
286 text remembered as <tt class="LITERAL">$2</tt>. This produces an exact
287 copy of the original string, with the middle part (the <span class=
288 "QUOTE">"document.referrer"</span>) replaced by <tt class=
289 "LITERAL">"Not Your Business!"</tt>.</p>
291 <p>The whole job now reads: Replace <span class=
292 "QUOTE">"document.referrer"</span> by <tt class="LITERAL">"Not Your
293 Business!"</tt> wherever it appears inside a <script> tag. Note
294 that this job won't break JavaScript syntax, since both the original
295 and the replacement are syntactically valid string objects. The script
296 just won't have access to the referrer information anymore.</p>
298 <p>We'll show you two other jobs from the JavaScript taming department,
299 but this time only point out the constructs of special interest:</p>
301 <table border="0" bgcolor="#E0E0E0" width="100%">
305 # The status bar is for displaying link targets, not pointless blahblah
307 s/window\.status\s*=\s*(['"]).*?\1/dUmMy=1/ig
313 <p><tt class="LITERAL">\s</tt> stands for whitespace characters (space,
314 tab, newline, carriage return, form feed), so that <tt class=
315 "LITERAL">\s*</tt> means: <span class="QUOTE">"zero or more
316 whitespace"</span>. The <tt class="LITERAL">?</tt> in <tt class=
317 "LITERAL">.*?</tt> makes this matching of arbitrary text ungreedy.
318 (Note that the <tt class="LITERAL">U</tt> option is not set). The
319 <tt class="LITERAL">['"]</tt> construct means: <span class="QUOTE">"a
320 single <span class="emphasis"><i class="EMPHASIS">or</i></span> a
321 double quote"</span>. Finally, <tt class="LITERAL">\1</tt> is a
322 back-reference to the first parenthesis just like <tt class=
323 "LITERAL">$1</tt> above, with the difference that in the <span class=
324 "emphasis"><i class="EMPHASIS">pattern</i></span>, a backslash
325 indicates a back-reference, whereas in the <span class=
326 "emphasis"><i class="EMPHASIS">substitute</i></span>, it's the
329 <p>So what does this job do? It replaces assignments of single- or
330 double-quoted strings to the <span class="QUOTE">"window.status"</span>
331 object with a dummy assignment (using a variable name that is hopefully
332 odd enough not to conflict with real variables in scripts). Thus, it
333 catches many cases where e.g. pointless descriptions are displayed in
334 the status bar instead of the link target when you move your mouse over
337 <table border="0" bgcolor="#E0E0E0" width="100%">
341 # Kill OnUnload popups. Yummy. Test: http://www.zdnet.com/zdsubs/yahoo/tree/yfs.html
343 s/(<body [^>]*)onunload(.*>)/$1never$2/iU
349 <p>Including the <a href=
350 "http://www.w3.org/TR/2000/REC-DOM-Level-2-Events-20001113/events.html#Events-eventgroupings-htmlevents"
351 target="_top">OnUnload event binding</a> in the HTML DOM was a
352 <span class="emphasis"><i class="EMPHASIS">CRIME</i></span>. When I
353 close a browser window, I want it to close and die. Basta. This job
354 replaces the <span class="QUOTE">"onunload"</span> attribute in
355 <span class="QUOTE">"<body>"</span> tags with the dummy word
356 <tt class="LITERAL">never</tt>. Note that the <tt class=
357 "LITERAL">i</tt> option makes the pattern matching case-insensitive.
358 Also note that ungreedy matching alone doesn't always guarantee a
359 minimal match: In the first parenthesis, we had to use <tt class=
360 "LITERAL">[^>]*</tt> instead of <tt class="LITERAL">.*</tt> to
361 prevent the match from exceeding the <body> tag if it doesn't
362 contain <span class="QUOTE">"OnUnload"</span>, but the page's content
365 <p>The last example is from the fun department:</p>
367 <table border="0" bgcolor="#E0E0E0" width="100%">
371 FILTER: fun Fun text replacements
373 # Spice the daily news:
375 s/microsoft(?!\.com)/MicroSuck/ig
381 <p>Note the <tt class="LITERAL">(?!\.com)</tt> part (a so-called
382 negative lookahead) in the job's pattern, which means: Don't match, if
383 the string <span class="QUOTE">".com"</span> appears directly following
384 <span class="QUOTE">"microsoft"</span> in the page. This prevents links
385 to microsoft.com from being trashed, while still replacing the word
388 <table border="0" bgcolor="#E0E0E0" width="100%">
392 # Buzzword Bingo (example for extended regex syntax)
394 s* industry[ -]leading \
396 | customer[ -]focused \
398 | award[ -]winning # Comments are OK, too! \
399 | high[ -]performance \
400 | solutions[ -]based \
404 *<font color="red"><b>BINGO!</b></font> \
411 <p>The <tt class="LITERAL">x</tt> option in this job turns on extended
412 syntax, and allows for e.g. the liberal use of (non-interpreted!)
413 whitespace for nicer formatting.</p>
415 <p>You get the idea?</p>
419 <h2 class="SECT2"><a name="PREDEFINED-FILTERS" id=
420 "PREDEFINED-FILTERS">9.2. The Pre-defined Filters</a></h2>
422 <p>The distribution <tt class="FILENAME">default.filter</tt> file
423 contains a selection of pre-defined filters for your convenience:</p>
425 <div class="VARIABLELIST">
427 <dt><span class="emphasis"><i class=
428 "EMPHASIS">js-annoyances</i></span></dt>
431 <p>The purpose of this filter is to get rid of particularly
432 annoying JavaScript abuse. To that end, it</p>
436 <p>replaces JavaScript references to the browser's referrer
437 information with the string "Not Your Business!". This
438 compliments the <tt class="LITERAL"><a href=
439 "actions-file.html#HIDE-REFERRER">hide-referrer</a></tt>
440 action on the content level.</p>
444 <p>removes the bindings to the DOM's <a href=
445 "http://www.w3.org/TR/2000/REC-DOM-Level-2-Events-20001113/events.html#Events-eventgroupings-htmlevents"
446 target="_top">unload event</a> which we feel has no right to
447 exist and is responsible for most <span class="QUOTE">"exit
448 consoles"</span>, i.e. nasty windows that pop up when you
449 close another one.</p>
453 <p>removes code that causes new windows to be opened with
454 undesired properties, such as being full-screen,
455 non-resizeable, without location, status or menu bar etc.</p>
459 <p>Use with caution. This is an aggressive filter, and can break
460 sites that rely heavily on JavaScript.</p>
463 <dt><span class="emphasis"><i class=
464 "EMPHASIS">js-events</i></span></dt>
467 <p>This is a very radical measure. It removes virtually all
468 JavaScript event bindings, which means that scripts can not react
469 to user actions such as mouse movements or clicks, window
470 resizing etc, anymore. Use with caution!</p>
472 <p>We <span class="emphasis"><i class="EMPHASIS">strongly
473 discourage</i></span> using this filter as a default since it
474 breaks many legitimate scripts. It is meant for use only on
475 extra-nasty sites (should you really need to go there).</p>
478 <dt><span class="emphasis"><i class=
479 "EMPHASIS">html-annoyances</i></span></dt>
482 <p>This filter will undo many common instances of HTML based
485 <p>The <tt class="LITERAL">BLINK</tt> and <tt class=
486 "LITERAL">MARQUEE</tt> tags are neutralized (yeah baby!), and
487 browser windows will be created as resizeable (as of course they
488 should be!), and will have location, scroll and menu bars -- even
489 if specified otherwise.</p>
492 <dt><span class="emphasis"><i class=
493 "EMPHASIS">content-cookies</i></span></dt>
496 <p>Most cookies are set in the HTTP dialog, where they can be
497 intercepted by the <tt class="LITERAL"><a href=
498 "actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a></tt>
499 and <tt class="LITERAL"><a href=
500 "actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a></tt>
501 actions. But web sites increasingly make use of HTML meta tags
502 and JavaScript to sneak cookies to the browser on the content
505 <p>This filter disables most HTML and JavaScript code that reads
506 or sets cookies. It cannot detect all clever uses of these types
507 of code, so it should not be relied on as an absolute fix. Use it
508 wherever you would also use the cookie crunch actions.</p>
511 <dt><span class="emphasis"><i class=
512 "EMPHASIS">refresh-tags</i></span></dt>
515 <p>Disable any refresh tags if the interval is greater than nine
516 seconds (so that redirections done via refresh tags are not
517 destroyed). This is useful for dial-on-demand setups, or for
518 those who find this HTML feature annoying.</p>
521 <dt><span class="emphasis"><i class=
522 "EMPHASIS">unsolicited-popups</i></span></dt>
525 <p>This filter attempts to prevent only <span class=
526 "QUOTE">"unsolicited"</span> pop-up windows from opening, yet
527 still allow pop-up windows that the user has explicitly chosen to
528 open. It was added in version 3.0.1, as an improvement over
529 earlier such filters.</p>
531 <p>Technical note: The filter works by redefining the window.open
532 JavaScript function to a dummy function, <tt class=
533 "LITERAL">PrivoxyWindowOpen()</tt>, during the loading and
534 rendering phase of each HTML page access, and restoring the
535 function afterward.</p>
537 <p>This is recommended only for browsers that cannot perform this
538 function reliably themselves. And be aware that some sites
539 require such windows in order to function normally. Use with
543 <dt><span class="emphasis"><i class=
544 "EMPHASIS">all-popups</i></span></dt>
547 <p>Attempt to prevent <span class="emphasis"><i class=
548 "EMPHASIS">all</i></span> pop-up windows from opening. Note this
549 should be used with even more discretion than the above, since it
550 is more likely to break some sites that require pop-ups for
551 normal usage. Use with caution.</p>
554 <dt><span class="emphasis"><i class=
555 "EMPHASIS">img-reorder</i></span></dt>
558 <p>This is a helper filter that has no value if used alone. It
559 makes the <tt class="LITERAL">banners-by-size</tt> and <tt class=
560 "LITERAL">banners-by-link</tt> (see below) filters more effective
561 and should be enabled together with them.</p>
564 <dt><span class="emphasis"><i class=
565 "EMPHASIS">banners-by-size</i></span></dt>
568 <p>This filter removes image tags purely based on what size they
569 are. Fortunately for us, many ads and banner images tend to
570 conform to certain standardized sizes, which makes this filter
571 quite effective for ad stripping purposes.</p>
573 <p>Occasionally this filter will cause false positives on images
574 that are not ads, but just happen to be of one of the standard
577 <p>Recommended only for those who require extreme ad blocking.
578 The default block rules should catch 95+% of all ads <span class=
579 "emphasis"><i class="EMPHASIS">without</i></span> this filter
583 <dt><span class="emphasis"><i class=
584 "EMPHASIS">banners-by-link</i></span></dt>
587 <p>This is an experimental filter that attempts to kill any
588 banners if their URLs seem to point to known or suspected click
589 trackers. It is currently not of much value and is not
590 recommended for use by default.</p>
593 <dt><span class="emphasis"><i class=
594 "EMPHASIS">webbugs</i></span></dt>
597 <p>Webbugs are small, invisible images (technically 1X1 GIF
598 images), that are used to track users across websites, and
599 collect information on them. As an HTML page is loaded by the
600 browser, an embedded image tag causes the browser to contact a
601 third-party site, disclosing the tracking information through the
602 requested URL and/or cookies for that third-party domain, without
603 the user ever becoming aware of the interaction with the
604 third-party site. HTML-ized spam also uses a similar technique to
605 verify email addresses.</p>
607 <p>This filter removes the HTML code that loads such <span class=
608 "QUOTE">"webbugs"</span>.</p>
611 <dt><span class="emphasis"><i class=
612 "EMPHASIS">tiny-textforms</i></span></dt>
615 <p>A rather special-purpose filter that can be used to enlarge
616 textareas (those multi-line text boxes in web forms) and turn off
617 hard word wrap in them. It was written for the sourceforge.net
618 tracker system where such boxes are a nuisance, but it can be
619 handy on other sites, too.</p>
621 <p>It is not recommended to use this filter as a default.</p>
624 <dt><span class="emphasis"><i class=
625 "EMPHASIS">jumping-windows</i></span></dt>
628 <p>Many consider windows that move, or resize themselves to be
629 abusive. This filter neutralizes the related JavaScript code.
630 Note that some sites might not display or behave as intended when
631 using this filter. Use with caution.</p>
634 <dt><span class="emphasis"><i class=
635 "EMPHASIS">frameset-borders</i></span></dt>
638 <p>Some web designers seem to assume that everyone in the world
639 will view their web sites using the same browser brand and
640 version, screen resolution etc, because only that assumption
641 could explain why they'd use static frame sizes, yet prevent
642 their frames from being resized by the user, should they be too
643 small to show their whole content.</p>
645 <p>This filter removes the related HTML code. It should only be
646 applied to sites which need it.</p>
649 <dt><span class="emphasis"><i class=
650 "EMPHASIS">demoronizer</i></span></dt>
653 <p>Many Microsoft products that generate HTML use non-standard
654 extensions (read: violations) of the ISO 8859-1 aka Latin-1
655 character set. This can cause those HTML documents to display
656 with errors on standard-compliant platforms.</p>
658 <p>This filter translates the MS-only characters into Latin-1
659 equivalents. It is not necessary when using MS products, and will
660 cause corruption of all documents that use 8-bit character sets
661 other than Latin-1. It's mostly worthwhile for Europeans on
662 non-MS platforms, if weird garbage characters sometimes appear on
663 some pages, or user agents that don't correct for this on the
667 <dt><span class="emphasis"><i class=
668 "EMPHASIS">shockwave-flash</i></span></dt>
671 <p>A filter for shockwave haters. As the name suggests, this
672 filter strips code out of web pages that is used to embed
673 shockwave flash objects.</p>
676 <dt><span class="emphasis"><i class=
677 "EMPHASIS">quicktime-kioskmode</i></span></dt>
680 <p>Change HTML code that embeds Quicktime objects so that
681 kioskmode, which prevents saving, is disabled.</p>
684 <dt><span class="emphasis"><i class="EMPHASIS">fun</i></span></dt>
687 <p>Text replacements for subversive browsing fun. Make fun of
688 your favorite Monopolist or play buzzword bingo.</p>
691 <dt><span class="emphasis"><i class=
692 "EMPHASIS">crude-parental</i></span></dt>
695 <p>A demonstration-only filter that shows how <span class=
696 "APPLICATION">Privoxy</span> can be used to delete web content on
700 <dt><span class="emphasis"><i class=
701 "EMPHASIS">ie-exploits</i></span></dt>
704 <p>An experimental collection of text replacements to disable
705 malicious HTML and JavaScript code that exploits known security
706 holes in Internet Explorer.</p>
708 <p>Presently, it only protects against Nimda and a cross-site
709 scripting bug, and would need active maintenance to provide more
710 substantial protection.</p>
713 <dt><span class="emphasis"><i class=
714 "EMPHASIS">site-specifics</i></span></dt>
717 <p>Some web sites have very specific problems, the cure for which
718 doesn't apply anywhere else, or could even cause damage on other
721 <p>This is a collection of such site-specific cures which should
722 only be applied to the sites they were intended for, which is
723 what the supplied <tt class="FILENAME">default.action</tt> file
724 does. Users shouldn't need to change anything regarding this
728 <dt><span class="emphasis"><i class=
729 "EMPHASIS">google</i></span></dt>
732 <p>A CSS based block for Google text ads. Also removes a width
733 limitation and the toolbar advertisement.</p>
736 <dt><span class="emphasis"><i class=
737 "EMPHASIS">yahoo</i></span></dt>
740 <p>Another CSS based block, this time for Yahoo text ads. And
741 removes a width limitation as well.</p>
744 <dt><span class="emphasis"><i class="EMPHASIS">msn</i></span></dt>
747 <p>Another CSS based block, this time for MSN text ads. And
748 removes tracking URLs, as well as a width limitation.</p>
751 <dt><span class="emphasis"><i class=
752 "EMPHASIS">blogspot</i></span></dt>
755 <p>Cleans up some Blogspot blogs. Read the fine print before
758 <p>This filter also intentionally removes some navigation stuff
759 and sets the page width to 100%. As a result, some rounded
760 <span class="QUOTE">"corners"</span> would appear to early or not
761 at all and as fixing this would require a browser that
762 understands background-size (CSS3), they are removed instead.</p>
765 <dt><span class="emphasis"><i class=
766 "EMPHASIS">xml-to-html</i></span></dt>
769 <p>Server-header filter to change the Content-Type from xml to
773 <dt><span class="emphasis"><i class=
774 "EMPHASIS">html-to-xml</i></span></dt>
777 <p>Server-header filter to change the Content-Type from html to
781 <dt><span class="emphasis"><i class=
782 "EMPHASIS">no-ping</i></span></dt>
785 <p>Removes the non-standard <tt class="LITERAL">ping</tt>
786 attribute from anchor and area HTML tags.</p>
789 <dt><span class="emphasis"><i class=
790 "EMPHASIS">hide-tor-exit-notation</i></span></dt>
793 <p>Client-header filter to remove the <b class="COMMAND">Tor</b>
794 exit node notation found in Host and Referer headers.</p>
796 <p>If <span class="APPLICATION">Privoxy</span> and <b class=
797 "COMMAND">Tor</b> are chained and <span class=
798 "APPLICATION">Privoxy</span> is configured to use socks4a, one
800 "QUOTE">"http://www.example.org.foobar.exit/"</span> to access
801 the host <span class="QUOTE">"www.example.org"</span> through the
802 <b class="COMMAND">Tor</b> exit node <span class=
803 "QUOTE">"foobar"</span>.</p>
805 <p>As the HTTP client isn't aware of this notation, it treats the
806 whole string <span class=
807 "QUOTE">"www.example.org.foobar.exit"</span> as host and uses it
808 for the <span class="QUOTE">"Host"</span> and <span class=
809 "QUOTE">"Referer"</span> headers. From the server's point of view
810 the resulting headers are invalid and can cause problems.</p>
812 <p>An invalid <span class="QUOTE">"Referer"</span> header can
813 trigger <span class="QUOTE">"hot-linking"</span> protections, an
814 invalid <span class="QUOTE">"Host"</span> header will make it
815 impossible for the server to find the right vhost (several
816 domains hosted on the same IP address).</p>
818 <p>This client-header filter removes the <span class=
819 "QUOTE">"foo.exit"</span> part in those headers to prevent the
820 mentioned problems. Note that it only modifies the HTTP headers,
821 it doesn't make it impossible for the server to detect your
822 <b class="COMMAND">Tor</b> exit node based on the IP address the
823 request is coming from.</p>
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