X-Git-Url: http://www.privoxy.org/gitweb/?a=blobdiff_plain;ds=inline;f=doc%2Fwebserver%2Fuser-manual%2Ffilter-file.html;h=2fe7948aee33a85f255df59e0dfb16ba31562438;hb=afdf7f7b2cbdff9a333ac73e0bdb74474015705d;hp=5ea91beeedb43a61861946f07cd6b853981ab90b;hpb=ae6beecce49ef10b169c4b843580985430bc698b;p=privoxy.git diff --git a/doc/webserver/user-manual/filter-file.html b/doc/webserver/user-manual/filter-file.html index 5ea91bee..2fe7948a 100644 --- a/doc/webserver/user-manual/filter-file.html +++ b/doc/webserver/user-manual/filter-file.html @@ -1,815 +1,421 @@ -
On-the-fly text substitutions that can be invoked through the - filter action need - to be defined in a "filter file". Once defined, they - can then be invoked as an "action". Multiple filter files can be - defined through the filterfile config directive. The filters - as supplied by the developers will be found in - default.filter. It is recommended that any locally - defined or modified filters go in a separately defined file such as - user.filter. -
Typical reasons for doing these kinds of substitutions are to eliminate - common annoyances in HTML and JavaScript, such as pop-up windows, - exit consoles, crippled windows without navigation tools, the - infamous <BLINK> tag etc, to suppress images with certain - width and height attributes (standard banner sizes or web-bugs), - or just to have fun. The possibilities are endless.
Filtering works on any text-based document type, including - HTML, JavaScript, CSS etc. (all text/* - MIME types, except text/plain). - 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. By default, filters are only applied - to the raw document content, but can be extended to the HTTP headers with - the supplemental actions: - filter-client-headers and - filter-server-headers.
Just like the actions files, the - filter file is organized in sections, which are called filters - here. Each filter consists of a heading line, that starts with the - keyword FILTER:, followed by - the filter's name, and a short (one line) - description of what it does. Below that line - come the jobs, i.e. lines that define the actual - text substitutions. By convention, the name of a filter - should describe what the filter eliminates. The - comment is used in the web-based - user interface.
Once a filter called name has been defined - in the filter file, it can be invoked by using an action of the form - +filter{name} - in any actions file.
A filter header line for a filter called "foo" could look - like this:
FILTER: foo Replace all "foo" with "bar" |
Below that line, and up to the next header line, come the jobs that - define what text replacements the filter executes. They are specified - in a syntax that imitates Perl's - s/// operator. If you are familiar with Perl, you - will find this to be quite intuitive, and may want to look at the - PCRS 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.
Now, let's complete our "foo" filter. We have already defined - the heading, but the jobs are still missing. Since all it does is to replace - "foo" with "bar", there is only one (trivial) job - needed:
s/foo/bar/ |
But wait! Didn't the comment say that all occurrences - of "foo" should be replaced? Our current job will only take - care of the first "foo" on each page. For global substitution, - we'll need to add the g option:
s/foo/bar/g |
Our complete filter now looks like this:
FILTER: foo Replace all "foo" with "bar" -s/foo/bar/g |
Let's look at some real filters for more interesting examples. Here you see - a filter that protects against some common annoyances that arise from JavaScript - abuse. Let's look at its jobs one after the other:
FILTER: js-annoyances Get rid of particularly annoying JavaScript abuse + + + + ++ |
+
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?
+The distribution default.filter file + contains a selection of pre-defined filters for your convenience:
+ +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.
+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).
+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.
+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.
+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.
+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.
+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.
+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.
+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.
+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 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".
+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.
+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.
+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.
+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.
+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.
+Change HTML code that embeds Quicktime objects so that + kioskmode, which prevents saving, is disabled.
+Text replacements for subversive browsing fun. Make fun of + your favorite Monopolist or play buzzword bingo.
+A demonstration-only filter that shows how Privoxy can be used to delete web content on + a keyword basis.
+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.
+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.
+A CSS based block for Google text ads. Also removes a width + limitation and the toolbar advertisement.
+Another CSS based block, this time for Yahoo text ads. And + removes a width limitation as well.
+Another CSS based block, this time for MSN text ads. And + removes tracking URLs, as well as a width limitation.
+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.
+Server-header filter to change the Content-Type from xml to + html.
+Server-header filter to change the Content-Type from html to + xml.
+Removes the non-standard ping + attribute from anchor and area HTML tags.
+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.
+External filters are scripts or programs that can modify the content + in case common filters aren't powerful enough.
+ +External filters can be written in any language the platform + Privoxy runs on supports.
+ +They are controlled with the external-filter action and + have to be defined in the filterfile first.
+ +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).
+ +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 can be used to get some details about the + client request.
+ +Privoxy will temporary store the + content to filter in the temporary-directory.
+ +
+ +EXTERNAL-FILTER: cat Pointless example filter that doesn't actually modify the content +/bin/cat + +# Incorrect reimplementation of the filter above in POSIX shell. +# +# Note that it's a single job that spans multiple lines, the line +# breaks are not passed to the shell, thus the semicolons are required. +# +# If the script isn't trivial, it is recommended to put it into an external file. +# +# In general, writing external filters entirely in POSIX shell is not +# considered a good idea. +EXTERNAL-FILTER: cat2 Pointless example filter that despite its name may actually modify the content +while read line; \ +do \ + echo "$line"; \ +done + +EXTERNAL-FILTER: rotate-image Rotate an image by 180 degree. Test filter with limited value. +/usr/local/bin/convert - -rotate 180 - + +EXTERNAL-FILTER: citation-needed Adds a "[citation needed]" tag to an image. The coordinates may need adjustment. +/usr/local/bin/convert - -pointsize 16 -fill white -annotate +17+418 "[citation needed]" - ++ |
+
Warning | +
+ Currently external filters are executed with Privoxy's privileges! Only use external + filters you understand and trust. + |
+
External filters are experimental and the syntax may change in the + future.
+