X-Git-Url: http://www.privoxy.org/gitweb/?a=blobdiff_plain;f=doc%2Fwebserver%2Fuser-manual%2Ffilter-file.html;h=0d0b65daafbe491a197a3c68321d4d121b7108f7;hb=ba8c8fd40fb5e150e24819471977f46172acbae6;hp=c1c08a43da8eae25987786e8ad526a0fbdfc9ce7;hpb=3db7a58b2bbed7b6356b2a0600e93ec4f2846499;p=privoxy.git diff --git a/doc/webserver/user-manual/filter-file.html b/doc/webserver/user-manual/filter-file.html index c1c08a43..0d0b65da 100644 --- a/doc/webserver/user-manual/filter-file.html +++ b/doc/webserver/user-manual/filter-file.html @@ -1,867 +1,260 @@ - -
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.
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 + + + ++ |
+
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, PRIVOXY_LISTEN_ADDRESS 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.
+