Privoxy 3.0.10 User Manual
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9. Filter Files

On-the-fly text substitutions need - to be defined in a "filter file". Once defined, they - can then be invoked as an "action".

Privoxy supports three different filter actions: - filter to - rewrite the content that is send to the client, - client-header-filter - to rewrite headers that are send by the client, and - server-header-filter - to rewrite headers that are send by the server.

Privoxy also supports two tagger actions: - client-header-tagger - and - server-header-tagger. - 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 tag-patterns.

Multiple filter files can be defined through the filterfile config directive. The filters - as supplied by the developers are located in - default.filter. It is recommended that any locally - defined or modified filters go in a separately defined file such as - user.filter. -

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.

Enabled content filters are applied to any content whose - "Content Type" header is recognised as a sign - of text-based content, with the exception of text/plain. - Use the force-text-mode action - to also filter other content.

Substitutions are made at the source level, so if you want to "roll - your own" filters, you should first be familiar with HTML syntax, - and, of course, regular expressions.

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

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

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 "foo" could look - like this:

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

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

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

9.1. Filter File Tutorial

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

s/foo/bar/

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

s/foo/bar/g

Our complete filter now looks like this:

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

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

+ +
FILTER: js-annoyances Get rid of particularly annoying JavaScript abuse + + + + + Filter Files + + + + + + + + + + +
+ + + + + + + + + + + + +
Privoxy 3.0.21 User Manual
Prev Next
+
+
+ +
+
9. Filter + Files
+ +
On-the-fly text substitutions need to be defined in a "filter file". Once defined, they can then be invoked as + an "action".
+ +
Privoxy supports three different + filter actions: filter to rewrite the content that is + send to the client, client-header-filter to + rewrite headers that are send by the client, and server-header-filter to + rewrite headers that are send by the server.
+ +
Privoxy also supports two tagger + actions: client-header-tagger + and server-header-tagger. + 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 tag-patterns.
+ +
Multiple filter files can be defined through the filterfile config + directive. The filters as supplied by the developers are located in + default.filter. It is recommended that any + locally defined or modified filters go in a separately defined file such + as user.filter.
+ +
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.
+ +
Enabled content filters are applied to any content whose "Content Type" header is recognised as a sign of + text-based content, with the exception of text/plain. Use the force-text-mode action to also + filter other content.
+ +
Substitutions are made at the source level, so if you want to + "roll your own" filters, you should first be + familiar with HTML syntax, and, of course, regular expressions.
+ +
Just like the actions files, the + filter file is organized in sections, which are called filters here. Each filter + consists of a heading line, that starts with one of the keywords FILTER:, CLIENT-HEADER-FILTER: or + SERVER-HEADER-FILTER: followed by the filter's + name, and a short + (one line) description of what it does. Below that line come + the jobs, i.e. + lines that define the actual text substitutions. By convention, the name + of a filter should describe what the filter eliminates. The comment is used + in the web-based user + interface.
+ +
Once a filter called name has been + defined in the filter file, it can be invoked by using an action of the + form +filter{name} in any actions file.
+ +
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 "foo" could look like + this:
+ + + + + +
+
+FILTER: foo Replace all "foo" with "bar" +
+
+ +
Below that line, and up to the next header line, come the jobs that + define what text replacements the filter executes. They are specified in + a syntax that imitates Perl's s/// operator. If you are + familiar with Perl, you will find this to be quite intuitive, and may + want to look at the PCRS documentation for the subtle differences to Perl + behaviour. Most notably, the non-standard option letter U is supported, which turns the default to ungreedy + matching.
+ +
If you are new to "Regular Expressions", you might + want to take a look at the Appendix on + regular expressions, and see the Perl manual for + the + s/// operator's syntax and Perl-style regular + expressions in general. The below examples might also help to get you + started.
+ +
+
9.1. Filter File + Tutorial
+ +
Now, let's complete our "foo" content + filter. We have already defined the heading, but the jobs are still + missing. Since all it does is to replace "foo" with "bar", there is + only one (trivial) job needed:
+ + + + + +
+
+s/foo/bar/ +
+
+ +
But wait! Didn't the comment say that all occurrences of + "foo" should be replaced? Our current job + will only take care of the first "foo" on + each page. For global substitution, we'll need to add the g option:
+ + + + + +
+
+s/foo/bar/g +
+
+ +
Our complete filter now looks like this:
+ + + + + +
+
+FILTER: foo Replace all "foo" with "bar" +s/foo/bar/g +
+
+ +
Let's look at some real filters for more interesting examples. Here + you see a filter that protects against some common annoyances that + arise from JavaScript abuse. Let's look at its jobs one after the + other:
+ + + +
+
+FILTER: js-annoyances Get rid of particularly annoying JavaScript abuse # Get rid of JavaScript referrer tracking. Test page: http://www.randomoddness.com/untitled.htm # -s|(<script.*)document\.referrer(.*</script>)|$1"Not Your Business!"$2|Usg
Following the header line and a comment, you see the job. Note that it uses - | as the delimiter instead of /, because - the pattern contains a forward slash, which would otherwise have to be escaped - by a backslash (\).
Now, let's examine the pattern: it starts with the text <script.* - enclosed in parentheses. Since the dot matches any character, and * - means: "Match an arbitrary number of the element left of myself", this - matches "<script", followed by any text, i.e. - it matches the whole page, from the start of the first <script> tag.
That's more than we want, but the pattern continues: document\.referrer - matches only the exact string "document.referrer". The dot needed to - be escaped, i.e. preceded by a backslash, to take away its - special meaning as a joker, and make it just a regular dot. So far, the meaning is: - Match from the start of the first <script> tag in a the page, up to, and including, - the text "document.referrer", if both are present - in the page (and appear in that order).
But there's still more pattern to go. The next element, again enclosed in parentheses, - is .*</script>. You already know what .* - means, so the whole pattern translates to: Match from the start of the first <script> - tag in a page to the end of the last <script> tag, provided that the text - "document.referrer" appears somewhere in between.
This is still not the whole story, since we have ignored the options and the parentheses: - The portions of the page matched by sub-patterns that are enclosed in parentheses, will be - remembered and be available through the variables $1, $2, ... in - the substitute. The U option switches to ungreedy matching, which means - that the first .* in the pattern will only "eat up" all - text in between "<script" and the first occurrence - of "document.referrer", and that the second .* will - only span the text up to the first "</script>" - tag. Furthermore, the s option says that the match may span - multiple lines in the page, and the g option again means that the - substitution is global.
So, to summarize, the pattern means: Match all scripts that contain the text - "document.referrer". Remember the parts of the script from - (and including) the start tag up to (and excluding) the string - "document.referrer" as $1, and the part following - that string, up to and including the closing tag, as $2.
Now the pattern is deciphered, but wasn't this about substituting things? So - lets look at the substitute: $1"Not Your Business!"$2 is - easy to read: The text remembered as $1, followed by - "Not Your Business!" (including - the quotation marks!), followed by the text remembered as $2. - This produces an exact copy of the original string, with the middle part - (the "document.referrer") replaced by "Not Your - Business!".
The whole job now reads: Replace "document.referrer" by - "Not Your Business!" wherever it appears inside a - <script> tag. Note that this job won't break JavaScript syntax, - since both the original and the replacement are syntactically valid - string objects. The script just won't have access to the referrer - information anymore.
We'll show you two other jobs from the JavaScript taming department, but - this time only point out the constructs of special interest:
+ +
# The status bar is for displaying link targets, not pointless blahblah +s|(<script.*)document\.referrer(.*</script>)|$1"Not Your Business!"$2|Usg +
+
+ +
Following the header line and a comment, you see the job. Note that + it uses | as the delimiter instead of + /, because the pattern contains a forward + slash, which would otherwise have to be escaped by a backslash + (\).
+ +
Now, let's examine the pattern: it starts with the text <script.* enclosed in parentheses. Since the dot + matches any character, and * means: + "Match an arbitrary number of the element left of + myself", this matches "<script", + followed by any + text, i.e. it matches the whole page, from the start of the first + <script> tag.
+ +
That's more than we want, but the pattern continues: document\.referrer matches only the exact string + "document.referrer". The dot needed to be + escaped, i.e. + preceded by a backslash, to take away its special meaning as a joker, + and make it just a regular dot. So far, the meaning is: Match from the + start of the first <script> tag in a the page, up to, and + including, the text "document.referrer", if + both are present + in the page (and appear in that order).
+ +
But there's still more pattern to go. The next element, again + enclosed in parentheses, is .*</script>. + You already know what .* means, so the whole + pattern translates to: Match from the start of the first <script> + tag in a page to the end of the last <script> tag, provided that + the text "document.referrer" appears + somewhere in between.
+ +
This is still not the whole story, since we have ignored the options + and the parentheses: The portions of the page matched by sub-patterns + that are enclosed in parentheses, will be remembered and be available + through the variables $1, $2, ... in the + substitute. The U option switches to ungreedy + matching, which means that the first .* in the + pattern will only "eat up" all text in + between "<script" and the first occurrence of + "document.referrer", and that the second + .* will only span the text up to the + first + "</script>" tag. Furthermore, the + s option says that the match may span multiple + lines in the page, and the g option again + means that the substitution is global.
+ +
So, to summarize, the pattern means: Match all scripts that contain + the text "document.referrer". Remember the + parts of the script from (and including) the start tag up to (and + excluding) the string "document.referrer" as + $1, and the part following that string, up to + and including the closing tag, as $2.
+ +
Now the pattern is deciphered, but wasn't this about substituting + things? So lets look at the substitute: $1"Not Your + Business!"$2 is easy to read: The text remembered as $1, followed by "Not Your + Business!" (including the quotation marks!), followed by the + text remembered as $2. This produces an exact + copy of the original string, with the middle part (the "document.referrer") replaced by "Not Your Business!".
+ +
The whole job now reads: Replace "document.referrer" by "Not Your + Business!" wherever it appears inside a <script> tag. Note + that this job won't break JavaScript syntax, since both the original + and the replacement are syntactically valid string objects. The script + just won't have access to the referrer information anymore.
+ +
We'll show you two other jobs from the JavaScript taming department, + but this time only point out the constructs of special interest:
+ + + +
+
+# The status bar is for displaying link targets, not pointless blahblah # -s/window\.status\s*=\s*(['"]).*?\1/dUmMy=1/ig
\s stands for whitespace characters (space, tab, newline, - carriage return, form feed), so that \s* means: "zero - or more whitespace". The ? in .*? - makes this matching of arbitrary text ungreedy. (Note that the U - option is not set). The ['"] construct means: "a single - or a double quote". Finally, \1 is - a back-reference to the first parenthesis just like $1 above, - with the difference that in the pattern, a backslash indicates - a back-reference, whereas in the substitute, it's the dollar.
So what does this job do? It replaces assignments of single- or double-quoted - strings to the "window.status" object with a dummy assignment - (using a variable name that is hopefully odd enough not to conflict with - real variables in scripts). Thus, it catches many cases where e.g. pointless - descriptions are displayed in the status bar instead of the link target when - you move your mouse over links.
+ +
# Kill OnUnload popups. Yummy. Test: http://www.zdnet.com/zdsubs/yahoo/tree/yfs.html +s/window\.status\s*=\s*(['"]).*?\1/dUmMy=1/ig +
+
+ +
\s stands for whitespace characters (space, + tab, newline, carriage return, form feed), so that \s* means: "zero or more + whitespace". The ? in .*? makes this matching of arbitrary text ungreedy. + (Note that the U option is not set). The + ['"] construct means: "a + single or a + double quote". Finally, \1 is a + back-reference to the first parenthesis just like $1 above, with the difference that in the pattern, a backslash + indicates a back-reference, whereas in the substitute, it's the + dollar.
+ +
So what does this job do? It replaces assignments of single- or + double-quoted strings to the "window.status" + object with a dummy assignment (using a variable name that is hopefully + odd enough not to conflict with real variables in scripts). Thus, it + catches many cases where e.g. pointless descriptions are displayed in + the status bar instead of the link target when you move your mouse over + links.
+ + + +
+
+# Kill OnUnload popups. Yummy. Test: http://www.zdnet.com/zdsubs/yahoo/tree/yfs.html # -s/(<body [^>]*)onunload(.*>)/$1never$2/iU
Including the - OnUnload - event binding in the HTML DOM was a CRIME. - When I close a browser window, I want it to close and die. Basta. - This job replaces the "onunload" attribute in - "<body>" tags with the dummy word never. - Note that the i option makes the pattern matching - case-insensitive. Also note that ungreedy matching alone doesn't always guarantee - a minimal match: In the first parenthesis, we had to use [^>]* - instead of .* to prevent the match from exceeding the - <body> tag if it doesn't contain "OnUnload", but the page's - content does.
The last example is from the fun department:
+ +
FILTER: fun Fun text replacements +s/(<body [^>]*)onunload(.*>)/$1never$2/iU +
+
+ +
Including the OnUnload event binding in the HTML DOM was a + CRIME. When I + close a browser window, I want it to close and die. Basta. This job + replaces the "onunload" attribute in + "<body>" tags with the dummy word + never. Note that the i option makes the pattern matching case-insensitive. + Also note that ungreedy matching alone doesn't always guarantee a + minimal match: In the first parenthesis, we had to use [^>]* instead of .* to + prevent the match from exceeding the <body> tag if it doesn't + contain "OnUnload", but the page's content + does.
+ +
The last example is from the fun department:
+ + + +
+
+FILTER: fun Fun text replacements # Spice the daily news: # -s/microsoft(?!\.com)/MicroSuck/ig
Note the (?!\.com) part (a so-called negative lookahead) - in the job's pattern, which means: Don't match, if the string - ".com" appears directly following "microsoft" - in the page. This prevents links to microsoft.com from being trashed, while - still replacing the word everywhere else.
+ +
# Buzzword Bingo (example for extended regex syntax) +s/microsoft(?!\.com)/MicroSuck/ig +
+
+ +
Note the (?!\.com) part (a so-called + negative lookahead) in the job's pattern, which means: Don't match, if + the string ".com" appears directly following + "microsoft" in the page. This prevents links + to microsoft.com from being trashed, while still replacing the word + everywhere else.
+ + + +
+
+# Buzzword Bingo (example for extended regex syntax) # s* industry[ -]leading \ | cutting[ -]edge \ @@ -873,780 +401,457 @@ s* industry[ -]leading \ | unmatched \ | unparalleled \ | unrivalled \ -*<font color="red"><b>BINGO!</b></font> \ -*igx
The x option in this job turns on extended syntax, and allows for - e.g. the liberal use of (non-interpreted!) whitespace for nicer formatting.
You get the idea?
9.2. The Pre-defined Filters
The distribution default.filter file contains a selection of -pre-defined filters for your convenience:
js-annoyances
The purpose of this filter is to get rid of particularly annoying JavaScript abuse. - To that end, it -
replaces JavaScript references to the browser's referrer information - with the string "Not Your Business!". This compliments the hide-referrer action on the content level. -
removes the bindings to the DOM's - unload - event which we feel has no right to exist and is responsible for most "exit consoles", i.e. - nasty windows that pop up when you close another one. -
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. -
-
Use with caution. This is an aggressive filter, and can break sites that - rely heavily on JavaScript. -
js-events
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! -
We strongly discourage 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). -
html-annoyances
This filter will undo many common instances of HTML based abuse. -
The BLINK and MARQUEE 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. -
content-cookies
Most cookies are set in the HTTP dialog, where they can be intercepted - by the - crunch-incoming-cookies - and crunch-outgoing-cookies - actions. But web sites increasingly make use of HTML meta tags and JavaScript - to sneak cookies to the browser on the content level. -
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. -
refresh tags
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. -
unsolicited-popups
This filter attempts to prevent only "unsolicited" 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. -
Technical note: The filter works by redefining the window.open JavaScript - function to a dummy function, PrivoxyWindowOpen(), - during the loading and rendering phase of each HTML page access, and - restoring the function afterward. -
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. -
all-popups
Attempt to prevent all 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. -
img-reorder
This is a helper filter that has no value if used alone. It makes the - banners-by-size and banners-by-link - (see below) filters more effective and should be enabled together with them. -
banners-by-size
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. -
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. -
Recommended only for those who require extreme ad blocking. The default - block rules should catch 95+% of all ads without this filter enabled. -
banners-by-link
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. -
webbugs
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. -
This filter removes the HTML code that loads such "webbugs". -
tiny-textforms
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. -
It is not recommended to use this filter as a default. -
jumping-windows
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. -
frameset-borders
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. -
This filter removes the related HTML code. It should only be applied to sites - which need it. -
demoronizer
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. -
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. - -
shockwave-flash
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. -

quicktime-kioskmode
Change HTML code that embeds Quicktime objects so that kioskmode, which - prevents saving, is disabled. -
fun
Text replacements for subversive browsing fun. Make fun of your favorite - Monopolist or play buzzword bingo. -
crude-parental
A demonstration-only filter that shows how Privoxy - can be used to delete web content on a keyword basis. -
ie-exploits
An experimental collection of text replacements to disable malicious HTML and JavaScript - code that exploits known security holes in Internet Explorer. -
Presently, it only protects against Nimda and a cross-site scripting bug, and - would need active maintenance to provide more substantial protection. -
site-specifics
Some web sites have very specific problems, the cure for which doesn't apply - anywhere else, or could even cause damage on other sites. -
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 - default.action file does. Users shouldn't need to change - anything regarding this filter. -
google
A CSS based block for Google text ads. Also removes a width limitation - and the toolbar advertisement. -
yahoo
Another CSS based block, this time for Yahoo text ads. And removes - a width limitation as well. -
msn
Another CSS based block, this time for MSN text ads. And removes - tracking URLs, as well as a width limitation. -
blogspot
Cleans up some Blogspot blogs. Read the fine print before using this one! -
This filter also intentionally removes some navigation stuff and sets the - page width to 100%. As a result, some rounded "corners" 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. -
xml-to-html
Server-header filter to change the Content-Type from xml to html. -
html-to-xml
Server-header filter to change the Content-Type from html to xml. -
no-ping
Removes the non-standard ping attribute from - anchor and area HTML tags. -
hide-tor-exit-notation
Client-header filter to remove the Tor exit node notation - found in Host and Referer headers. -
If Privoxy and Tor are chained and Privoxy - is configured to use socks4a, one can use "http://www.example.org.foobar.exit/" - to access the host "www.example.org" through the - Tor exit node "foobar". -
As the HTTP client isn't aware of this notation, it treats the - whole string "www.example.org.foobar.exit" as host and uses it - for the "Host" and "Referer" headers. From the - server's point of view the resulting headers are invalid and can cause problems. -
An invalid "Referer" header can trigger "hot-linking" - protections, an invalid "Host" header will make it impossible for - the server to find the right vhost (several domains hosted on the same IP address). -
This client-header filter removes the "foo.exit" 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 Tor exit node based on the IP address - the request is coming from. -
Prev Home Next
Actions Files Privoxy's Template Files
\ No newline at end of file +*<font color="red"><b>BINGO!</b></font> \ +*igx +
+
+ +

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

+ +

You get the idea?

+ +

9.2. The Pre-defined Filters

+ +

The distribution default.filter file + contains a selection of pre-defined filters for your convenience:

+ +

js-annoyances

The purpose of this filter is to get rid of particularly + annoying JavaScript abuse. To that end, it

+ +

+
replaces JavaScript references to the browser's referrer + information with the string "Not Your Business!". This + compliments the hide-referrer + action on the content level.
+
+
removes the bindings to the DOM's unload event which we feel has no right to + exist and is responsible for most "exit + consoles", i.e. nasty windows that pop up when you + close another one.
+
+
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.
+

+ +

Use with caution. This is an aggressive filter, and can break + sites that rely heavily on JavaScript.

js-events

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!

+ +

We strongly + discourage 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).

html-annoyances

This filter will undo many common instances of HTML based + abuse.

+ +

The BLINK and MARQUEE 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.

content-cookies

Most cookies are set in the HTTP dialog, where they can be + intercepted by the crunch-incoming-cookies + and crunch-outgoing-cookies + actions. But web sites increasingly make use of HTML meta tags + and JavaScript to sneak cookies to the browser on the content + level.

+ +

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.

refresh-tags

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.

unsolicited-popups

This filter attempts to prevent only "unsolicited" 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.

+ +

Technical note: The filter works by redefining the window.open + JavaScript function to a dummy function, PrivoxyWindowOpen(), during the loading and + rendering phase of each HTML page access, and restoring the + function afterward.

+ +

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.

all-popups

Attempt to prevent all 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.

img-reorder

This is a helper filter that has no value if used alone. It + makes the banners-by-size and banners-by-link (see below) filters more effective + and should be enabled together with them.

banners-by-size

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.

+ +

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.

+ +

Recommended only for those who require extreme ad blocking. + The default block rules should catch 95+% of all ads without this filter + enabled.

banners-by-link

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.

webbugs

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.

+ +

This filter removes the HTML code that loads such "webbugs".

tiny-textforms

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.

+ +

It is not recommended to use this filter as a default.

jumping-windows

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.

frameset-borders

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.

+ +

This filter removes the related HTML code. It should only be + applied to sites which need it.

demoronizer

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.

+ +

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.

shockwave-flash

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.

quicktime-kioskmode

Change HTML code that embeds Quicktime objects so that + kioskmode, which prevents saving, is disabled.

fun

Text replacements for subversive browsing fun. Make fun of + your favorite Monopolist or play buzzword bingo.

crude-parental

A demonstration-only filter that shows how Privoxy can be used to delete web content on + a keyword basis.

ie-exploits

An experimental collection of text replacements to disable + malicious HTML and JavaScript code that exploits known security + holes in Internet Explorer.

+ +

Presently, it only protects against Nimda and a cross-site + scripting bug, and would need active maintenance to provide more + substantial protection.

site-specifics

Some web sites have very specific problems, the cure for which + doesn't apply anywhere else, or could even cause damage on other + sites.

+ +

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 default.action file + does. Users shouldn't need to change anything regarding this + filter.

google

A CSS based block for Google text ads. Also removes a width + limitation and the toolbar advertisement.

yahoo

Another CSS based block, this time for Yahoo text ads. And + removes a width limitation as well.

msn

Another CSS based block, this time for MSN text ads. And + removes tracking URLs, as well as a width limitation.

blogspot

Cleans up some Blogspot blogs. Read the fine print before + using this one!

+ +

This filter also intentionally removes some navigation stuff + and sets the page width to 100%. As a result, some rounded + "corners" 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.

xml-to-html

Server-header filter to change the Content-Type from xml to + html.

html-to-xml

Server-header filter to change the Content-Type from html to + xml.

no-ping

Removes the non-standard ping + attribute from anchor and area HTML tags.

hide-tor-exit-notation

Client-header filter to remove the Tor + exit node notation found in Host and Referer headers.

+ +

If Privoxy and Tor are chained and Privoxy is configured to use socks4a, one + can use "http://www.example.org.foobar.exit/" to access + the host "www.example.org" through the + Tor exit node "foobar".

+ +

As the HTTP client isn't aware of this notation, it treats the + whole string "www.example.org.foobar.exit" as host and uses it + for the "Host" and "Referer" headers. From the server's point of view + the resulting headers are invalid and can cause problems.

+ +

An invalid "Referer" header can + trigger "hot-linking" protections, an + invalid "Host" header will make it + impossible for the server to find the right vhost (several + domains hosted on the same IP address).

+ +

This client-header filter removes the "foo.exit" 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 + Tor exit node based on the IP address the + request is coming from.