X-Git-Url: http://www.privoxy.org/gitweb/?p=privoxy.git;a=blobdiff_plain;f=doc%2Fwebserver%2Fuser-manual%2Ffilter-file.html;h=8b625a8c0189fba96a78e065bdf813d18e7fe689;hp=fa278a0a210744ed5202649ff82494ce56229bc6;hb=HEAD;hpb=107c84d0c43b24ad437933c75774276f67165959 diff --git a/doc/webserver/user-manual/filter-file.html b/doc/webserver/user-manual/filter-file.html index fa278a0a..8b625a8c 100644 --- a/doc/webserver/user-manual/filter-file.html +++ b/doc/webserver/user-manual/filter-file.html @@ -1,1124 +1,591 @@ - + -
-
+ 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 (add ? to quantifiers to turn them greedy again).
+The non-standard option letter D (dynamic) allows to use the variables $host, $origin + (the IP address the request came from), $path, $url and $listen-address (the address on which Privoxy accepted the + client request. Example: 127.0.0.1:8118). They will be replaced with the value they refer to before the filter is + executed.
+Note that '$' is a bad choice for a delimiter in a dynamic filter as you might end up with unintended variables + if you use a variable name directly after the delimiter. Variables will be resolved without escaping anything, + therefore you also have to be careful not to chose delimiters that appear in the replacement text. For example + '<' should be save, while '?' will sooner or later cause conflicts with $url.
+The non-standard option letter T (trivial) prevents parsing for backreferences in the + substitute. Use it if you want to include text like '$&' in your substitute without quoting.
+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:
+- Privoxy 3.0.25 User Manual - | +
+ 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:
+- Prev + |
+ s/foo/bar/g |
- + |
Our complete filter now looks like this:
+
+ FILTER: foo Replace all "foo" with "bar" + s/foo/bar/g |
- - Next + |
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 |
- 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 - pcrs-based 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. -
-- Finally Privoxy supports the external-filter action - to enable external filters - written in proper programming languages. -
-- 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: -
--
+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:
--FILTER: foo Replace all "foo" with "bar" -+ # 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/(<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 - |
+
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 \ + | customer[ -]focused \ + | market[ -]driven \ + | award[ -]winning # Comments are OK, too! \ + | high[ -]performance \ + | solutions[ -]based \ + | 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?
+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 filter 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 -
- 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. - -- -
+
-
- 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: - -
-
-
-
+ - 9.3. External filter syntax --- 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 filters are experimental and the syntax may change in the - future. - External filters are experimental and the syntax may change in the future. - - + + + - |