9.1. Regular Expressions

14.1. Regular Expressions

Privoxy can use "regular expressions" - in various config files. Assuming support for uses Perl-style "pcre" (Perl - Compatible Regular Expressions) is compiled in, which is the default. Such - configuration directives do not require regular expressions, but they can be - used to increase flexibility by matching a pattern with wild-cards against - URLs.

"regular + expressions" in its actions + files and filter file, + through the PCRE and + PCRS libraries.

If you are reading this, you probably don't understand what "regular expressions" are, or what they can do. So this will be a very brief - introduction only. A full explanation would require a book ;-)

book ;-)

Regular expressions provide a language to describe patterns that can be + run against strings of characters (letter, numbers, etc), to see if they + match the string or not. The patterns are themselves (sometimes complex) + strings of literal characters, combined with wild-cards, and other special + characters, called meta-characters. The "Regular expressions" is a way of matching one character - expression against another to see if it matches or not. One of the +>"meta-characters" have + special meanings and are used to build complex patterns to be matched against. + Perl Compatible Regular Expressions are an especially convenient "expressions" is a literal string of readable characters - (letter, numbers, etc), and the other is a complex string of literal - characters combined with wild-cards, and other special characters, called - meta-characters. The "meta-characters" have special meanings and - are used to build the complex pattern to be matched against. Perl Compatible - Regular Expressions is an enhanced form of the regular expression language - with backward compatibility.

"dialect" of the regular expression language.

To make a simple analogy, we do something similar when we use wild-card characters when listing files with the

. - Matches any single character, e.g. "a"

? - The preceding character or expression is matched ZERO or ONE times. Either/or.

+ - The preceding character or expression is matched ONE or MORE times.

* - The preceding character or expression is matched ZERO or MORE times.

\ - The "escape"".") needs to be taken literally and - not as a special meta-character. + not as a special meta-character. Example: "example\.com", makes + sure the period is recognized only as a period (and not expanded to its + meta-character meaning of any single character).

[][ ] - Characters enclosed in brackets will be matched if - any of the enclosed characters are encountered. + any of the enclosed characters are encountered. For instance, "[0-9]" + matches any numeric digit (zero through nine). As an example, we can combine + this with "+" to match any digit one of more times: "[0-9]+".

()( ) - parentheses are used to group a sub-expression, or multiple sub-expressions.

| - The "bar""|" matches. -

s/string1/string2/g - This is used to rewrite strings of text. +> matches. As an example: "string1" is replaced by "/(this|that) example/" uses grouping and the bar character + and would match either "string2" in this - example. +>"this example" or "that + example", and nothing else.

These are just some of the ones you are likely to use when matching URLs with

/.*/banners/.* - A simple example that uses the common combination of in the path somewhere.

A now something a little more complex:

And now something a little more complex:
/.*/adv((er)?ts?|ertis(ing|ements?))?/ - We have several literal forward slashes again (".*", so we are matching against any conceivable sub-path, just so - it matches our expression. The only true literal that must match our pattern is adv"ing" - OR "ements?", which would then match either spelling.
/.*/advert[0-9]+\.(gif|jpe?g) - Again another path statement with forward slashes. Anything in the square brackets "[]""[ ]" can be matched. This is using "0-9" is not in the expression anywhere).
s/microsoft(?!.com)/MicroSuck/i - This is - a substitution. "MicroSuck" will replace any occurrence of - "microsoft". The "i" at the end of the expression - means ignore case. The "(?!.com)" means - the match should fail if "microsoft" is followed by - ".com". In other words, this acts like a "NOT" - modifier. In case this is a hyperlink, we don't want to break it ;-).
We are barely scratching the surface of regular expressions here so that you can understand the default
More reading on Perl Compatible Regular expressions: http://www.perldoc.com/perl5.6/pod/perlre.htmlhttp://perldoc.perl.org/perlre.html
For information on regular expression based substitutions and their applications + in filters, please see the filter file tutorial + in this manual.

9.2. 14.2. Privoxy's Internal Pages

's Internal Pages
Since
Alternately, this may be reached at There is a shortcut: http://p.p/, but this - variation may not work as reliably as the above in some configurations. +> (But it + doesn't provide a fall-back to a real page, in case the request is not + sent through Privoxy)
- Show information about the current configuration: + Show information about the current configuration, including viewing and + editing of actions files:
- Show the client's request headers: + Show the browser's request headers:
Short cuts. Turn off, then on:
- Edit the actions list file: -
- http://config.privoxy.org/edit-actions -
These may be bookmarked for quick reference.
These may be bookmarked for quick reference. See next.
9.2.1. Bookmarklets
14.2.1. Bookmarklets
Here are some bookmarklets to allow you to easily access a +> Below are some "bookmarklets" to allow you to easily access a "mini" version of this page. They are designed for MS Internet - Explorer, but should work equally well in Netscape, Mozilla, and other - browsers which support JavaScript. They are designed to run directly from - your bookmarks - not by clicking the links below (although that will work for - testing).
version of some of Privoxy's + special pages. They are designed for MS Internet Explorer, but should work + equally well in Netscape, Mozilla, and other browsers which support + JavaScript. They are designed to run directly from your bookmarks - not by + clicking the links below (although that should work for testing).
To save them, right-click the link and choose "may not be safe" - just click OK. Then you can run the - Bookmarklet directly from your favourites/bookmarks. For even faster access, + Bookmarklet directly from your favorites/bookmarks. For even faster access, you can put them on the "Links" Enable PrivoxyPrivoxy - Enable
Disable PrivoxyPrivoxy - Disable
Toggle PrivoxyPrivoxy - Toggle Privoxy (Toggles between enabled and disabled)
View Privoxy StatusPrivoxy- View Status +
Privoxy - Why?
Credit: The site which gave me the general idea for these bookmarklets is +> Credit: The site which gave us the general idea for these bookmarklets is www.bookmarklets.com. They @@ -1028,25 +1072,256 @@ CLASS="SECT2" >
9.3. Anatomy of an Action
14.3. Chain of Events
The way Let's take a quick look at the basic sequence of events when a web page is + requested by your browser and Privoxy applies is on duty:

First, your web browser requests a web page. The browser knows to send + the request to Privoxy, which will in turn, + relay the request to the remote web server after passing the following + tests: +
Privoxy traps any request for its own internal CGI + pages (e.g http://p.p/) and sends the CGI page back to the browser. +
Next, Privoxy checks to see if the URL + matches any "actions""+block" patterns. If + so, the URL is then blocked, and the remote web server will not be contacted. + "+handle-as-image" + is then checked and if it does not match, an + HTML "BLOCKED" page is sent back. Otherwise, if it does match, + an image is returned. The type of image depends on the setting of "+set-image-blocker" - and
Untrusted URLs are blocked. If URLs are being added to the + trust file, then that is done. +
If the URL pattern matches the "filters" to any given URL can be complex, and not always so +>"+fast-redirects" action, + it is then processed. Unwanted parts of the requested URL are stripped. +
Now the rest of the client browser's request headers are processed. If any + of these match any of the relevant actions (e.g. "+hide-user-agent", + etc.), headers are suppressed or forged as determined by these actions and + their parameters. +
Now the web server starts sending its response back (i.e. typically a web page and related + data). +
First, the server headers are read and processed to determine, among other + things, the MIME type (document type) and encoding. The headers are then + filtered as determined by the + "+crunch-incoming-cookies", + "+session-cookies-only", + and "+downgrade-http-version" + actions. +
If the "+kill-popups" + action applies, and it is an HTML or JavaScript document, the popup-code in the + response is filtered on-the-fly as it is received. +
If a "+filter" + or "+deanimate-gifs" + action applies (and the document type fits the action), the rest of the page is + read into memory (up to a configurable limit). Then the filter rules (from + default.filter and any other filter files) are + processed against the buffered content. Filters are applied in the order + they are specified in one of the filter files. Animated GIFs, if present, + are reduced to either the first or last frame, depending on the action + setting.The entire page, which is now filtered, is then sent by + Privoxy back to your browser. +
If neither "+filter" + or "+deanimate-gifs" + matches, then Privoxy passes the raw data through + to the client browser as it becomes available. +
As the browser receives the now (possibly filtered) page content, it + reads and then requests any URLs that may be embedded within the page + source, e.g. ad images, stylesheets, JavaScript, other HTML documents (e.g. + frames), sounds, etc. For each of these objects, the browser issues a new + request. And each such request is in turn processed as above. Note that a + complex web page may have many such embedded URLs. +

14.4. Anatomy of an Action

The way Privoxy applies + actions and filters + to any given URL can be complex, and not always so easy to understand what is happening. And sometimes we need to be able to - see just what PrivoxyPrivoxy is doing - is causing us a problem inadvertantly. It can be a little daunting to look at + is causing us a problem inadvertently. It can be a little daunting to look at the actions and filters files themselves, since they tend to be filled with - "regular expressions" whose consequences are not always - so obvious. regular expressions whose consequences are not + always so obvious.

One quick test to see if Privoxy is causing a problem + or not, is to disable it temporarily. This should be the first troubleshooting + step. See the Bookmarklets section on a quick + and easy way to do this (be sure to flush caches afterward!). Looking at the + logs is a good idea too.

Privoxy provides the +> also provides the actions - are being applied to any given URL. This is a big help for troubleshooting. -

First, enter one URL (or partial URL) at the prompt, and then Privoxy will tell us how the current configuration will handle it. This will not - help with filtering effects from the default.filter file! It - also will not tell you about any other URLs that may be embedded within the - URL you are testing. For instance, images such as ads are expressed as URLs - within the raw page source of HTML pages. So you will only get info for the - actual URL that is pasted into the prompt area -- not any sub-URLs. If you - want to know about embedded URLs like ads, you will have to dig those out of - the HTML source. Use your browser's "View Page Source" option - for this. Or right click on the ad, and grab the URL.

Let's look at an example, "+filter" action) from + one of the filter files since this is handled very + differently and not so easy to trap! It also will not tell you about any other + URLs that may be embedded within the URL you are testing. For instance, images + such as ads are expressed as URLs within the raw page source of HTML pages. So + you will only get info for the actual URL that is pasted into the prompt area + -- not any sub-URLs. If you want to know about embedded URLs like ads, you + will have to dig those out of the HTML source. Use your browser's "View + Page Source" option for this. Or right click on the ad, and grab the + URL.

Let's try an example, google.com, - one section at a time:

System default actions: - - { -add-header -block -deanimate-gifs -downgrade -fast-redirects -filter - -hide-forwarded -hide-from -hide-referer -hide-user-agent -image - -image-blocker -limit-connect -no-compression -no-cookies-keep - -no-cookies-read -no-cookies-set -no-popups -vanilla-wafer -wafer } - -

This is the top section, and only tells us of the compiled in defaults. This - is basically what Privoxy would do if there - were not any "actions" defined, i.e. it does nothing. Every action - is disabled. This is not particularly informative for our purposes here. OK, - next section:

Matches for http://google.com: +> Matches for http://google.com: - { -add-header -block +deanimate-gifs -downgrade +fast-redirects - +filter{html-annoyances} +filter{js-annoyances} +filter{no-popups} - +filter{webbugs} +filter{nimda} +filter{banners-by-size} +filter{hal} - +filter{fun} +hide-forwarded +hide-from{block} +hide-referer{forge} - -hide-user-agent -image +image-blocker{blank} +no-compression - +no-cookies-keep -no-cookies-read -no-cookies-set +no-popups - -vanilla-wafer -wafer } - / + In file: default.action [ View ] [ Edit ] - { -no-cookies-keep -no-cookies-read -no-cookies-set } - .google.com + {-add-header + -block + -content-type-overwrite + -crunch-client-header + -crunch-if-none-match + -crunch-incoming-cookies + -crunch-outgoing-cookies + -crunch-server-header + +deanimate-gifs {last} + -downgrade-http-version + +fast-redirects {check-decoded-url} + -filter {js-events} + -filter {content-cookies} + -filter {all-popups} + -filter {banners-by-link} + -filter {tiny-textforms} + -filter {frameset-borders} + -filter {demoronizer} + -filter {shockwave-flash} + -filter {quicktime-kioskmode} + -filter {fun} + -filter {crude-parental} + -filter {site-specifics} + +filter {js-annoyances} + +filter {html-annoyances} + +filter {refresh-tags} + +filter {unsolicited-popups} + +filter {img-reorder} + +filter {banners-by-size} + +filter {webbugs} + +filter {jumping-windows} + +filter {ie-exploits} + -filter-client-headers + -filter-server-headers + -force-text-mode + -handle-as-empty-document + -handle-as-image + -hide-accept-language + -hide-content-disposition + +hide-forwarded-for-headers + +hide-from-header {block} + -hide-if-modified-since + +hide-referrer {forge} + -hide-user-agent + -inspect-jpegs + -kill-popups + -limit-connect + -overwrite-last-modified + +prevent-compression + -redirect + -send-vanilla-wafer + -send-wafer + +session-cookies-only + +set-image-blocker {pattern} + -treat-forbidden-connects-like-blocks } +/ + + { -session-cookies-only } + .google.com { -fast-redirects } - .google.com + .google.com -
[ View ] [ Edit ] +(no matches in this file)

This is much more informative, and tells us how we have defined our - This is telling us how we have defined our + "actions", and which ones match for our example, - , and + which ones match for our test case, "google.com". The first grouping shows our default - settings, which would apply to all URLs. If you look at your . + Displayed is all the actions that are available to us. Remember, + the + sign denotes "actions""on". - - file, this would be the section just below the "off". So some are "on" here, but many + are "off". Each example we try may provide a slightly different + end result, depending on our configuration directives.

The first listing + is any matches for the standard.action file. No hits at + all here on "standard". Then next is "default", or + our default.action file. The large, multi-line listing, + is how the actions are set to match for all URLs, i.e. our default settings. + If you look at your "actions" file, this would be the section + just below the "aliases" section - near the top. This applies to all URLs as signified by the single forward - slash -- section near the top. This will apply to + all URLs as signified by the single forward slash at the end of the listing + -- "/". -

.
These are the default actions we have enabled. But we can define additional - actions that would be exceptions to these general rules, and then list - specific URLs that these exceptions would apply to. Last match wins. - Just below this then are two explict matches for But we can define additional actions that would be exceptions to these general + rules, and then list specific URLs (or patterns) that these exceptions would + apply to. Last match wins. Just below this then are two explicit matches for + ".google.com". - The first is negating our various cookie blocking actions (i.e. we will allow - cookies here). The second is allowing . The first is negating our previous cookie setting, + which was for "fast-redirects". Note - that there is a leading dot here -- "+session-cookies-only" + (i.e. not persistent). So we will allow persistent cookies for google, at + least that is how it is in this example. The second turns + off any + "+fast-redirects" + action, allowing this to take place unmolested. Note that there is a leading + dot here -- ".google.com". This will - match any hosts and sub-domains, in the google.com domain also, such as +>. This will match any hosts and + sub-domains, in the google.com domain also, such as "www.google.com". So, apparently, we have these actions defined - somewhere in the lower part of our actions file, and - . So, apparently, we have these two actions + defined somewhere in the lower part of our default.action + file, and "google.com" is referenced in these sections.
is referenced somewhere in these latter + sections.
Then, for our user.action file, we again have no hits. + So there is nothing google-specific that we might have added to our own, local + configuration.
And now we pull it altogether in the bottom section and summarize how +> And finally we pull it all together in the bottom section and summarize how Privoxy is appying all its is applying all its "actions" @@ -1242,21 +1639,69 @@ WIDTH="100%" >
Final results: - - -add-header -block -deanimate-gifs -downgrade -fast-redirects - +filter{html-annoyances} +filter{js-annoyances} +filter{no-popups} - +filter{webbugs} +filter{nimda} +filter{banners-by-size} +filter{hal} - +filter{fun} +hide-forwarded +hide-from{block} +hide-referer{forge} - -hide-user-agent -image +image-blocker{blank} -limit-connect +no-compression - -no-cookies-keep -no-cookies-read -no-cookies-set +no-popups -vanilla-wafer - -wafer - -

Notice the only difference here to the previous listing, is to + "fast-redirects" and "session-cookies-only", + which are activated specifically for this site in our configuration, + and thus show in the "Final Results".

Now another example, "ad.doubleclick.net"

 { +block +image }
+> { +block +handle-as-image }
   .ad.doubleclick.net
 
- { +block +image }
+ { +block +handle-as-image }
   ad*.
 
- { +block +image }
-  .doubleclick.net
-
-

We'll just show the interesting part here, the explicit matches. It is matched three different times. Each as an "+block +image""+block +handle-as-image", which is the expanded form of one of our aliases that had been defined as: "+imageblock". (. ("Aliases" are defined in the - first section of the actions file and typically used to combine more +> are defined in + the first section of the actions file and typically used to combine more than one action.)

Any one of these would have done the trick and blocked this as an unwanted @@ -1309,27 +1755,38 @@ CLASS="QUOTE" CLASS="QUOTE" >"ad.doubleclick.net" - is done here -- as both a "+block" + and an - an + "+image". The custom alias "+handle-as-image". + The custom alias "+imageblock" does this - for us.

just simplifies the process and make + it more readable.
One last example. Let's try "http://www.rhapsodyk.net/adsl/HOWTO/""http://www.example.net/adsl/HOWTO/". - This one is giving us problems. We are getting a blank page. Hmmm...

Matches for http://www.rhapsodyk.net/adsl/HOWTO/: +> Matches for http://www.example.net/adsl/HOWTO/: - { -add-header -block +deanimate-gifs -downgrade +fast-redirects - +filter{html-annoyances} +filter{js-annoyances} +filter{no-popups} - +filter{webbugs} +filter{nimda} +filter{banners-by-size} +filter{hal} - +filter{fun} +hide-forwarded +hide-from{block} +hide-referer{forge} - -hide-user-agent -image +image-blocker{blank} +no-compression - +no-cookies-keep -no-cookies-read -no-cookies-set +no-popups - -vanilla-wafer -wafer } - / + In file: default.action [ View ] [ Edit ] - { +block +image } - /ads + {-add-header + -block + -content-type-overwrite + -crunch-client-header + -crunch-if-none-match + -crunch-incoming-cookies + -crunch-outgoing-cookies + -crunch-server-header + +deanimate-gifs + -downgrade-http-version + +fast-redirects{check-decoded-url} + +filter{html-annoyances} + +filter{js-annoyances} + +filter{kill-popups} + +filter{webbugs} + +filter{nimda} + +filter{banners-by-size} + +filter{hal} + +filter{fun} + -filter-client-headers + -filter-server-headers + -force-text-mode + -handle-as-empty-document + -handle-as-image + -hide-accept-language + -hide-content-disposition + +hide-forwarded-for-headers + +hide-from-header{block} + +hide-referer{forge} + -hide-user-agent + -inspect-jpegs + +kill-popups + -overwrite-last-modified + +prevent-compression + -redirect + -send-vanilla-wafer + -send-wafer + +session-cookies-only + +set-image-blocker{blank} + -treat-forbidden-connects-like-blocks } + / -
is matching "/ads"! But - we did not want this at all! Now we see why we get the blank page. We could - now add a new action below this that explictly does in our + configuration! But we did not want this at all! Now we see why we get the + blank page. We could now add a new action below this that explicitly + not - block (-block) pages with un blocks ("{-block}") paths with + "adsl". There are various ways to - handle such exceptions. Example:
in them (remember, last match in the configuration wins). + There are various ways to handle such exceptions. Example:

{ -block } - /adsl - -
{ -block } - /adsl - -
{ +block +handle-as-image } + /ads"{+filter}" actions. Try - adding the URL for the site to one of aliases that turn off actions. These + tend to be harder to troubleshoot. Try adding the URL for the site to one of + aliases that turn off "+filter":
that expands to "{ -filter -no-cookies -no-cookies-keep }". Or you could do - your own exception to negate filtering:
"{ -filter -session-cookies-only }". + Or you could do your own exception to negate filtering:

{-filter} - .forbes.com - -
This would turn off all filtering for that site. This would probably be most + appropriately put in user.action, for local site + exceptions.
Images that are inexplicably being blocked, may well be hitting the + "+filter{banners-by-size}" rule, which assumes + that images of certain sizes are ad banners (works well most of the time + since these tend to be standardized).
"{fragile}"
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