<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Appendix</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REL="HOME" TITLE="Privoxy 3.0.12 User Manual" HREF="index.html"><LINK REL="PREVIOUS" TITLE="See Also" HREF="seealso.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="../p_doc.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"> <LINK REL="STYLESHEET" TYPE="text/css" HREF="p_doc.css"> </head ><BODY CLASS="SECT1" BGCOLOR="#EEEEEE" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >Privoxy 3.0.12 User Manual</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="seealso.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" > </TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="APPENDIX" >14. Appendix</A ></H1 ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="REGEX" >14.1. Regular Expressions</A ></H2 ><P > <SPAN CLASS="APPLICATION" >Privoxy</SPAN > uses Perl-style <SPAN CLASS="QUOTE" >"regular expressions"</SPAN > in its <A HREF="actions-file.html" >actions files</A > and <A HREF="filter-file.html" >filter file</A >, through the <A HREF="http://www.pcre.org/" TARGET="_top" >PCRE</A > and <SPAN CLASS="APPLICATION" >PCRS</SPAN > libraries.</P ><P > If you are reading this, you probably don't understand what <SPAN CLASS="QUOTE" >"regular expressions"</SPAN > are, or what they can do. So this will be a very brief introduction only. A full explanation would require a <A HREF="http://www.oreilly.com/catalog/regex/" TARGET="_top" >book</A > ;-)</P ><P > 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 <SPAN CLASS="QUOTE" >"meta-characters"</SPAN > have special meanings and are used to build complex patterns to be matched against. Perl Compatible Regular Expressions are an especially convenient <SPAN CLASS="QUOTE" >"dialect"</SPAN > of the regular expression language.</P ><P > To make a simple analogy, we do something similar when we use wild-card characters when listing files with the <B CLASS="COMMAND" >dir</B > command in DOS. <TT CLASS="LITERAL" >*.*</TT > matches all filenames. The <SPAN CLASS="QUOTE" >"special"</SPAN > character here is the asterisk which matches any and all characters. We can be more specific and use <TT CLASS="LITERAL" >?</TT > to match just individual characters. So <SPAN CLASS="QUOTE" >"dir file?.text"</SPAN > would match <SPAN CLASS="QUOTE" >"file1.txt"</SPAN >, <SPAN CLASS="QUOTE" >"file2.txt"</SPAN >, etc. We are pattern matching, using a similar technique to <SPAN CLASS="QUOTE" >"regular expressions"</SPAN >!</P ><P > Regular expressions do essentially the same thing, but are much, much more powerful. There are many more <SPAN CLASS="QUOTE" >"special characters"</SPAN > and ways of building complex patterns however. Let's look at a few of the common ones, and then some examples:</P ><P ><P ></P ><TABLE BORDER="0" ><TBODY ><TR ><TD > <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >.</I ></SPAN > - Matches any single character, e.g. <SPAN CLASS="QUOTE" >"a"</SPAN >, <SPAN CLASS="QUOTE" >"A"</SPAN >, <SPAN CLASS="QUOTE" >"4"</SPAN >, <SPAN CLASS="QUOTE" >":"</SPAN >, or <SPAN CLASS="QUOTE" >"@"</SPAN >. </TD ></TR ></TBODY ></TABLE ><P ></P ></P ><P ><P ></P ><TABLE BORDER="0" ><TBODY ><TR ><TD > <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >?</I ></SPAN > - The preceding character or expression is matched ZERO or ONE times. Either/or. </TD ></TR ></TBODY ></TABLE ><P ></P ></P ><P ><P ></P ><TABLE BORDER="0" ><TBODY ><TR ><TD > <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >+</I ></SPAN > - The preceding character or expression is matched ONE or MORE times. </TD ></TR ></TBODY ></TABLE ><P ></P ></P ><P ><P ></P ><TABLE BORDER="0" ><TBODY ><TR ><TD > <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >*</I ></SPAN > - The preceding character or expression is matched ZERO or MORE times. </TD ></TR ></TBODY ></TABLE ><P ></P ></P ><P ><P ></P ><TABLE BORDER="0" ><TBODY ><TR ><TD > <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >\</I ></SPAN > - The <SPAN CLASS="QUOTE" >"escape"</SPAN > character denotes that the following character should be taken literally. This is used where one of the special characters (e.g. <SPAN CLASS="QUOTE" >"."</SPAN >) needs to be taken literally and not as a special meta-character. Example: <SPAN CLASS="QUOTE" >"example\.com"</SPAN >, makes sure the period is recognized only as a period (and not expanded to its meta-character meaning of any single character). </TD ></TR ></TBODY ></TABLE ><P ></P ></P ><P ><P ></P ><TABLE BORDER="0" ><TBODY ><TR ><TD > <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >[ ]</I ></SPAN > - Characters enclosed in brackets will be matched if any of the enclosed characters are encountered. For instance, <SPAN CLASS="QUOTE" >"[0-9]"</SPAN > matches any numeric digit (zero through nine). As an example, we can combine this with <SPAN CLASS="QUOTE" >"+"</SPAN > to match any digit one of more times: <SPAN CLASS="QUOTE" >"[0-9]+"</SPAN >. </TD ></TR ></TBODY ></TABLE ><P ></P ></P ><P ><P ></P ><TABLE BORDER="0" ><TBODY ><TR ><TD > <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >( )</I ></SPAN > - parentheses are used to group a sub-expression, or multiple sub-expressions. </TD ></TR ></TBODY ></TABLE ><P ></P ></P ><P ><P ></P ><TABLE BORDER="0" ><TBODY ><TR ><TD > <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >|</I ></SPAN > - The <SPAN CLASS="QUOTE" >"bar"</SPAN > character works like an <SPAN CLASS="QUOTE" >"or"</SPAN > conditional statement. A match is successful if the sub-expression on either side of <SPAN CLASS="QUOTE" >"|"</SPAN > matches. As an example: <SPAN CLASS="QUOTE" >"/(this|that) example/"</SPAN > uses grouping and the bar character and would match either <SPAN CLASS="QUOTE" >"this example"</SPAN > or <SPAN CLASS="QUOTE" >"that example"</SPAN >, and nothing else. </TD ></TR ></TBODY ></TABLE ><P ></P ></P ><P > These are just some of the ones you are likely to use when matching URLs with <SPAN CLASS="APPLICATION" >Privoxy</SPAN >, and is a long way from a definitive list. This is enough to get us started with a few simple examples which may be more illuminating:</P ><P > <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" ><TT CLASS="LITERAL" >/.*/banners/.*</TT ></I ></SPAN > - A simple example that uses the common combination of <SPAN CLASS="QUOTE" >"."</SPAN > and <SPAN CLASS="QUOTE" >"*"</SPAN > to denote any character, zero or more times. In other words, any string at all. So we start with a literal forward slash, then our regular expression pattern (<SPAN CLASS="QUOTE" >".*"</SPAN >) another literal forward slash, the string <SPAN CLASS="QUOTE" >"banners"</SPAN >, another forward slash, and lastly another <SPAN CLASS="QUOTE" >".*"</SPAN >. We are building a directory path here. This will match any file with the path that has a directory named <SPAN CLASS="QUOTE" >"banners"</SPAN > in it. The <SPAN CLASS="QUOTE" >".*"</SPAN > matches any characters, and this could conceivably be more forward slashes, so it might expand into a much longer looking path. For example, this could match: <SPAN CLASS="QUOTE" >"/eye/hate/spammers/banners/annoy_me_please.gif"</SPAN >, or just <SPAN CLASS="QUOTE" >"/banners/annoying.html"</SPAN >, or almost an infinite number of other possible combinations, just so it has <SPAN CLASS="QUOTE" >"banners"</SPAN > in the path somewhere.</P ><P > And now something a little more complex:</P ><P > <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" ><TT CLASS="LITERAL" >/.*/adv((er)?ts?|ertis(ing|ements?))?/</TT ></I ></SPAN > - We have several literal forward slashes again (<SPAN CLASS="QUOTE" >"/"</SPAN >), so we are building another expression that is a file path statement. We have another <SPAN CLASS="QUOTE" >".*"</SPAN >, so we are matching against any conceivable sub-path, just so it matches our expression. The only true literal that <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >must match</I ></SPAN > our pattern is <SPAN CLASS="APPLICATION" >adv</SPAN >, together with the forward slashes. What comes after the <SPAN CLASS="QUOTE" >"adv"</SPAN > string is the interesting part. </P ><P > Remember the <SPAN CLASS="QUOTE" >"?"</SPAN > means the preceding expression (either a literal character or anything grouped with <SPAN CLASS="QUOTE" >"(...)"</SPAN > in this case) can exist or not, since this means either zero or one match. So <SPAN CLASS="QUOTE" >"((er)?ts?|ertis(ing|ements?))"</SPAN > is optional, as are the individual sub-expressions: <SPAN CLASS="QUOTE" >"(er)"</SPAN >, <SPAN CLASS="QUOTE" >"(ing|ements?)"</SPAN >, and the <SPAN CLASS="QUOTE" >"s"</SPAN >. The <SPAN CLASS="QUOTE" >"|"</SPAN > means <SPAN CLASS="QUOTE" >"or"</SPAN >. We have two of those. For instance, <SPAN CLASS="QUOTE" >"(ing|ements?)"</SPAN >, can expand to match either <SPAN CLASS="QUOTE" >"ing"</SPAN > <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >OR</I ></SPAN > <SPAN CLASS="QUOTE" >"ements?"</SPAN >. What is being done here, is an attempt at matching as many variations of <SPAN CLASS="QUOTE" >"advertisement"</SPAN >, and similar, as possible. So this would expand to match just <SPAN CLASS="QUOTE" >"adv"</SPAN >, or <SPAN CLASS="QUOTE" >"advert"</SPAN >, or <SPAN CLASS="QUOTE" >"adverts"</SPAN >, or <SPAN CLASS="QUOTE" >"advertising"</SPAN >, or <SPAN CLASS="QUOTE" >"advertisement"</SPAN >, or <SPAN CLASS="QUOTE" >"advertisements"</SPAN >. You get the idea. But it would not match <SPAN CLASS="QUOTE" >"advertizements"</SPAN > (with a <SPAN CLASS="QUOTE" >"z"</SPAN >). We could fix that by changing our regular expression to: <SPAN CLASS="QUOTE" >"/.*/adv((er)?ts?|erti(s|z)(ing|ements?))?/"</SPAN >, which would then match either spelling.</P ><P > <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" ><TT CLASS="LITERAL" >/.*/advert[0-9]+\.(gif|jpe?g)</TT ></I ></SPAN > - Again another path statement with forward slashes. Anything in the square brackets <SPAN CLASS="QUOTE" >"[ ]"</SPAN > can be matched. This is using <SPAN CLASS="QUOTE" >"0-9"</SPAN > as a shorthand expression to mean any digit one through nine. It is the same as saying <SPAN CLASS="QUOTE" >"0123456789"</SPAN >. So any digit matches. The <SPAN CLASS="QUOTE" >"+"</SPAN > means one or more of the preceding expression must be included. The preceding expression here is what is in the square brackets -- in this case, any digit one through nine. Then, at the end, we have a grouping: <SPAN CLASS="QUOTE" >"(gif|jpe?g)"</SPAN >. This includes a <SPAN CLASS="QUOTE" >"|"</SPAN >, so this needs to match the expression on either side of that bar character also. A simple <SPAN CLASS="QUOTE" >"gif"</SPAN > on one side, and the other side will in turn match either <SPAN CLASS="QUOTE" >"jpeg"</SPAN > or <SPAN CLASS="QUOTE" >"jpg"</SPAN >, since the <SPAN CLASS="QUOTE" >"?"</SPAN > means the letter <SPAN CLASS="QUOTE" >"e"</SPAN > is optional and can be matched once or not at all. So we are building an expression here to match image GIF or JPEG type image file. It must include the literal string <SPAN CLASS="QUOTE" >"advert"</SPAN >, then one or more digits, and a <SPAN CLASS="QUOTE" >"."</SPAN > (which is now a literal, and not a special character, since it is escaped with <SPAN CLASS="QUOTE" >"\"</SPAN >), and lastly either <SPAN CLASS="QUOTE" >"gif"</SPAN >, or <SPAN CLASS="QUOTE" >"jpeg"</SPAN >, or <SPAN CLASS="QUOTE" >"jpg"</SPAN >. Some possible matches would include: <SPAN CLASS="QUOTE" >"//advert1.jpg"</SPAN >, <SPAN CLASS="QUOTE" >"/nasty/ads/advert1234.gif"</SPAN >, <SPAN CLASS="QUOTE" >"/banners/from/hell/advert99.jpg"</SPAN >. It would not match <SPAN CLASS="QUOTE" >"advert1.gif"</SPAN > (no leading slash), or <SPAN CLASS="QUOTE" >"/adverts232.jpg"</SPAN > (the expression does not include an <SPAN CLASS="QUOTE" >"s"</SPAN >), or <SPAN CLASS="QUOTE" >"/advert1.jsp"</SPAN > (<SPAN CLASS="QUOTE" >"jsp"</SPAN > is not in the expression anywhere).</P ><P > We are barely scratching the surface of regular expressions here so that you can understand the default <SPAN CLASS="APPLICATION" >Privoxy</SPAN > configuration files, and maybe use this knowledge to customize your own installation. There is much, much more that can be done with regular expressions. Now that you know enough to get started, you can learn more on your own :/</P ><P > More reading on Perl Compatible Regular expressions: <A HREF="http://perldoc.perl.org/perlre.html" TARGET="_top" >http://perldoc.perl.org/perlre.html</A ></P ><P > For information on regular expression based substitutions and their applications in filters, please see the <A HREF="filter-file.html" >filter file tutorial</A > in this manual.</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="AEN5174" >14.2. Privoxy's Internal Pages</A ></H2 ><P > Since <SPAN CLASS="APPLICATION" >Privoxy</SPAN > proxies each requested web page, it is easy for <SPAN CLASS="APPLICATION" >Privoxy</SPAN > to trap certain special URLs. In this way, we can talk directly to <SPAN CLASS="APPLICATION" >Privoxy</SPAN >, and see how it is configured, see how our rules are being applied, change these rules and other configuration options, and even turn <SPAN CLASS="APPLICATION" >Privoxy's</SPAN > filtering off, all with a web browser. </P ><P > The URLs listed below are the special ones that allow direct access to <SPAN CLASS="APPLICATION" >Privoxy</SPAN >. Of course, <SPAN CLASS="APPLICATION" >Privoxy</SPAN > must be running to access these. If not, you will get a friendly error message. Internet access is not necessary either.</P ><P > <P ></P ><UL ><LI ><P > Privoxy main page: </P ><A NAME="AEN5188" ></A ><BLOCKQUOTE CLASS="BLOCKQUOTE" ><P > <A HREF="http://config.privoxy.org/" TARGET="_top" >http://config.privoxy.org/</A > </P ></BLOCKQUOTE ><P > There is a shortcut: <A HREF="http://p.p/" TARGET="_top" >http://p.p/</A > (But it doesn't provide a fall-back to a real page, in case the request is not sent through <SPAN CLASS="APPLICATION" >Privoxy</SPAN >) </P ></LI ><LI ><P > Show information about the current configuration, including viewing and editing of actions files: </P ><A NAME="AEN5196" ></A ><BLOCKQUOTE CLASS="BLOCKQUOTE" ><P > <A HREF="http://config.privoxy.org/show-status" TARGET="_top" >http://config.privoxy.org/show-status</A > </P ></BLOCKQUOTE ></LI ><LI ><P > Show the source code version numbers: </P ><A NAME="AEN5201" ></A ><BLOCKQUOTE CLASS="BLOCKQUOTE" ><P > <A HREF="http://config.privoxy.org/show-version" TARGET="_top" >http://config.privoxy.org/show-version</A > </P ></BLOCKQUOTE ></LI ><LI ><P > Show the browser's request headers: </P ><A NAME="AEN5206" ></A ><BLOCKQUOTE CLASS="BLOCKQUOTE" ><P > <A HREF="http://config.privoxy.org/show-request" TARGET="_top" >http://config.privoxy.org/show-request</A > </P ></BLOCKQUOTE ></LI ><LI ><P > Show which actions apply to a URL and why: </P ><A NAME="AEN5211" ></A ><BLOCKQUOTE CLASS="BLOCKQUOTE" ><P > <A HREF="http://config.privoxy.org/show-url-info" TARGET="_top" >http://config.privoxy.org/show-url-info</A > </P ></BLOCKQUOTE ></LI ><LI ><P > Toggle Privoxy on or off. This feature can be turned off/on in the main <TT CLASS="FILENAME" >config</TT > file. When toggled <SPAN CLASS="QUOTE" >"off"</SPAN >, <SPAN CLASS="QUOTE" >"Privoxy"</SPAN > continues to run, but only as a pass-through proxy, with no actions taking place: </P ><A NAME="AEN5219" ></A ><BLOCKQUOTE CLASS="BLOCKQUOTE" ><P > <A HREF="http://config.privoxy.org/toggle" TARGET="_top" >http://config.privoxy.org/toggle</A > </P ></BLOCKQUOTE ><P > Short cuts. Turn off, then on: </P ><A NAME="AEN5223" ></A ><BLOCKQUOTE CLASS="BLOCKQUOTE" ><P > <A HREF="http://config.privoxy.org/toggle?set=disable" TARGET="_top" >http://config.privoxy.org/toggle?set=disable</A > </P ></BLOCKQUOTE ><A NAME="AEN5226" ></A ><BLOCKQUOTE CLASS="BLOCKQUOTE" ><P > <A HREF="http://config.privoxy.org/toggle?set=enable" TARGET="_top" >http://config.privoxy.org/toggle?set=enable</A > </P ></BLOCKQUOTE ></LI ></UL ></P ><P > These may be bookmarked for quick reference. See next. </P ><DIV CLASS="SECT3" ><H3 CLASS="SECT3" ><A NAME="BOOKMARKLETS" >14.2.1. Bookmarklets</A ></H3 ><P > Below are some <SPAN CLASS="QUOTE" >"bookmarklets"</SPAN > to allow you to easily access a <SPAN CLASS="QUOTE" >"mini"</SPAN > version of some of <SPAN CLASS="APPLICATION" >Privoxy's</SPAN > 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).</P ><P > To save them, right-click the link and choose <SPAN CLASS="QUOTE" >"Add to Favorites"</SPAN > (IE) or <SPAN CLASS="QUOTE" >"Add Bookmark"</SPAN > (Netscape). You will get a warning that the bookmark <SPAN CLASS="QUOTE" >"may not be safe"</SPAN > - just click OK. Then you can run the Bookmarklet directly from your favorites/bookmarks. For even faster access, you can put them on the <SPAN CLASS="QUOTE" >"Links"</SPAN > bar (IE) or the <SPAN CLASS="QUOTE" >"Personal Toolbar"</SPAN > (Netscape), and run them with a single click. </P ><P > <P ></P ><UL ><LI ><P > <A HREF="javascript:void(window.open('http://config.privoxy.org/toggle?mini=y&set=enabled','ijbstatus','width=250,height=100,resizable=yes,scrollbars=no,toolbar=no,location=no,directories=no,status=no,menubar=no,copyhistory=no').focus());" TARGET="_top" >Privoxy - Enable</A > </P ></LI ><LI ><P > <A HREF="javascript:void(window.open('http://config.privoxy.org/toggle?mini=y&set=disabled','ijbstatus','width=250,height=100,resizable=yes,scrollbars=no,toolbar=no,location=no,directories=no,status=no,menubar=no,copyhistory=no').focus());" TARGET="_top" >Privoxy - Disable</A > </P ></LI ><LI ><P > <A HREF="javascript:void(window.open('http://config.privoxy.org/toggle?mini=y&set=toggle','ijbstatus','width=250,height=100,resizable=yes,scrollbars=no,toolbar=no,location=no,directories=no,status=no,menubar=no,copyhistory=no').focus());" TARGET="_top" >Privoxy - Toggle Privoxy</A > (Toggles between enabled and disabled) </P ></LI ><LI ><P > <A HREF="javascript:void(window.open('http://config.privoxy.org/toggle?mini=y','ijbstatus','width=250,height=2,resizable=yes,scrollbars=no,toolbar=no,location=no,directories=no,status=no,menubar=no,copyhistory=no').focus());" TARGET="_top" >Privoxy- View Status</A > </P ></LI ><LI ><P > <A HREF="javascript:void(window.open('http://config.privoxy.org/show-url-info?url='+escape(location.href),'Why').focus());" TARGET="_top" >Privoxy - Why?</A > </P ></LI ></UL ></P ><P > Credit: The site which gave us the general idea for these bookmarklets is <A HREF="http://www.bookmarklets.com/" TARGET="_top" >www.bookmarklets.com</A >. They have more information about bookmarklets. </P ></DIV ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="CHAIN" >14.3. Chain of Events</A ></H2 ><P > Let's take a quick look at how some of <SPAN CLASS="APPLICATION" >Privoxy's</SPAN > core features are triggered, and the ensuing sequence of events when a web page is requested by your browser:</P ><P > <P ></P ><UL ><LI ><P > First, your web browser requests a web page. The browser knows to send the request to <SPAN CLASS="APPLICATION" >Privoxy</SPAN >, which will in turn, relay the request to the remote web server after passing the following tests: </P ></LI ><LI ><P > <SPAN CLASS="APPLICATION" >Privoxy</SPAN > traps any request for its own internal CGI pages (e.g <A HREF="http://p.p/" TARGET="_top" >http://p.p/</A >) and sends the CGI page back to the browser. </P ></LI ><LI ><P > Next, <SPAN CLASS="APPLICATION" >Privoxy</SPAN > checks to see if the URL matches any <A HREF="actions-file.html#BLOCK" ><SPAN CLASS="QUOTE" >"+block"</SPAN ></A > patterns. If so, the URL is then blocked, and the remote web server will not be contacted. <A HREF="actions-file.html#HANDLE-AS-IMAGE" ><SPAN CLASS="QUOTE" >"+handle-as-image"</SPAN ></A > and <A HREF="actions-file.html#HANDLE-AS-EMPTY-DOCUMENT" ><SPAN CLASS="QUOTE" >"+handle-as-empty-document"</SPAN ></A > are then checked, and if there is no match, an HTML <SPAN CLASS="QUOTE" >"BLOCKED"</SPAN > page is sent back to the browser. Otherwise, if it does match, an image is returned for the former, and an empty text document for the latter. The type of image would depend on the setting of <A HREF="actions-file.html#SET-IMAGE-BLOCKER" ><SPAN CLASS="QUOTE" >"+set-image-blocker"</SPAN ></A > (blank, checkerboard pattern, or an HTTP redirect to an image elsewhere). </P ></LI ><LI ><P > Untrusted URLs are blocked. If URLs are being added to the <TT CLASS="FILENAME" >trust</TT > file, then that is done. </P ></LI ><LI ><P > If the URL pattern matches the <A HREF="actions-file.html#FAST-REDIRECTS" ><SPAN CLASS="QUOTE" >"+fast-redirects"</SPAN ></A > action, it is then processed. Unwanted parts of the requested URL are stripped. </P ></LI ><LI ><P > Now the rest of the client browser's request headers are processed. If any of these match any of the relevant actions (e.g. <A HREF="actions-file.html#HIDE-USER-AGENT" ><SPAN CLASS="QUOTE" >"+hide-user-agent"</SPAN ></A >, etc.), headers are suppressed or forged as determined by these actions and their parameters. </P ></LI ><LI ><P > Now the web server starts sending its response back (i.e. typically a web page). </P ></LI ><LI ><P > 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 <A HREF="actions-file.html#CRUNCH-INCOMING-COOKIES" ><SPAN CLASS="QUOTE" >"+crunch-incoming-cookies"</SPAN ></A >, <A HREF="actions-file.html#SESSION-COOKIES-ONLY" ><SPAN CLASS="QUOTE" >"+session-cookies-only"</SPAN ></A >, and <A HREF="actions-file.html#DOWNGRADE-HTTP-VERSION" ><SPAN CLASS="QUOTE" >"+downgrade-http-version"</SPAN ></A > actions. </P ></LI ><LI ><P > If any <A HREF="actions-file.html#FILTER" ><SPAN CLASS="QUOTE" >"+filter"</SPAN ></A > action or <A HREF="actions-file.html#DEANIMATE-GIFS" ><SPAN CLASS="QUOTE" >"+deanimate-gifs"</SPAN ></A > 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 <TT CLASS="FILENAME" >default.filter</TT > 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 <SPAN CLASS="APPLICATION" >Privoxy</SPAN > back to your browser. </P ><P > If neither a <A HREF="actions-file.html#FILTER" ><SPAN CLASS="QUOTE" >"+filter"</SPAN ></A > action or <A HREF="actions-file.html#DEANIMATE-GIFS" ><SPAN CLASS="QUOTE" >"+deanimate-gifs"</SPAN ></A > matches, then <SPAN CLASS="APPLICATION" >Privoxy</SPAN > passes the raw data through to the client browser as it becomes available. </P ></LI ><LI ><P > 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 separate request (this is easily viewable in <SPAN CLASS="APPLICATION" >Privoxy's</SPAN > logs). And each such request is in turn processed just as above. Note that a complex web page will have many, many such embedded URLs. If these secondary requests are to a different server, then quite possibly a very differing set of actions is triggered. </P ></LI ></UL ></P ><P > NOTE: This is somewhat of a simplistic overview of what happens with each URL request. For the sake of brevity and simplicity, we have focused on <SPAN CLASS="APPLICATION" >Privoxy's</SPAN > core features only.</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="ACTIONSANAT" >14.4. Troubleshooting: Anatomy of an Action</A ></H2 ><P > The way <SPAN CLASS="APPLICATION" >Privoxy</SPAN > applies <A HREF="actions-file.html#ACTIONS" >actions</A > and <A HREF="actions-file.html#FILTER" >filters</A > 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 <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >see</I ></SPAN > just what <SPAN CLASS="APPLICATION" >Privoxy</SPAN > is doing. Especially, if something <SPAN CLASS="APPLICATION" >Privoxy</SPAN > is doing 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 <A HREF="appendix.html#REGEX" >regular expressions</A > whose consequences are not always so obvious. </P ><P > One quick test to see if <SPAN CLASS="APPLICATION" >Privoxy</SPAN > is causing a problem or not, is to disable it temporarily. This should be the first troubleshooting step. See <A HREF="appendix.html#BOOKMARKLETS" >the Bookmarklets</A > 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. (Note that both the toggle feature and logging are enabled via <TT CLASS="FILENAME" >config</TT > file settings, and may need to be turned <SPAN CLASS="QUOTE" >"on"</SPAN >.)</P ><P > Another easy troubleshooting step to try is if you have done any customization of your installation, revert back to the installed defaults and see if that helps. There are times the developers get complaints about one thing or another, and the problem is more related to a customized configuration issue.</P ><P > <SPAN CLASS="APPLICATION" >Privoxy</SPAN > also provides the <A HREF="http://config.privoxy.org/show-url-info" TARGET="_top" >http://config.privoxy.org/show-url-info</A > page that can show us very specifically how <SPAN CLASS="APPLICATION" >actions</SPAN > are being applied to any given URL. This is a big help for troubleshooting.</P ><P > First, enter one URL (or partial URL) at the prompt, and then <SPAN CLASS="APPLICATION" >Privoxy</SPAN > will tell us how the current configuration will handle it. This will not help with filtering effects (i.e. the <A HREF="actions-file.html#FILTER" ><SPAN CLASS="QUOTE" >"+filter"</SPAN ></A > 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 <SPAN CLASS="QUOTE" >"View Page Source"</SPAN > option for this. Or right click on the ad, and grab the URL.</P ><P > Let's try an example, <A HREF="http://google.com" TARGET="_top" >google.com</A >, and look at it one section at a time in a sample configuration (your real configuration may vary):</P ><P > <TABLE BORDER="0" BGCOLOR="#E0E0E0" WIDTH="100%" ><TR ><TD ><PRE CLASS="SCREEN" > Matches for http://www.google.com: In file: default.action <SPAN CLASS="GUIBUTTON" >[ View ]</SPAN > <SPAN CLASS="GUIBUTTON" >[ Edit ]</SPAN > {+change-x-forwarded-for{block} +deanimate-gifs {last} +fast-redirects {check-decoded-url} +filter {refresh-tags} +filter {img-reorder} +filter {banners-by-size} +filter {webbugs} +filter {jumping-windows} +filter {ie-exploits} +hide-from-header {block} +hide-referrer {forge} +session-cookies-only +set-image-blocker {pattern} / { -session-cookies-only } .google.com { -fast-redirects } .google.com In file: user.action <SPAN CLASS="GUIBUTTON" >[ View ]</SPAN > <SPAN CLASS="GUIBUTTON" >[ Edit ]</SPAN > (no matches in this file) </PRE ></TD ></TR ></TABLE ></P ><P > This is telling us how we have defined our <A HREF="actions-file.html#ACTIONS" ><SPAN CLASS="QUOTE" >"actions"</SPAN ></A >, and which ones match for our test case, <SPAN CLASS="QUOTE" >"google.com"</SPAN >. Displayed is all the actions that are available to us. Remember, the <TT CLASS="LITERAL" >+</TT > sign denotes <SPAN CLASS="QUOTE" >"on"</SPAN >. <TT CLASS="LITERAL" >-</TT > denotes <SPAN CLASS="QUOTE" >"off"</SPAN >. So some are <SPAN CLASS="QUOTE" >"on"</SPAN > here, but many are <SPAN CLASS="QUOTE" >"off"</SPAN >. Each example we try may provide a slightly different end result, depending on our configuration directives.</P ><P > The first listing is for our <TT CLASS="FILENAME" >default.action</TT > 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 <SPAN CLASS="QUOTE" >"actions"</SPAN > file, this would be the section just below the <SPAN CLASS="QUOTE" >"aliases"</SPAN > section near the top. This will apply to all URLs as signified by the single forward slash at the end of the listing -- <SPAN CLASS="QUOTE" >" / "</SPAN >.</P ><P > But we have defined additional actions that would be exceptions to these general rules, and then we list specific URLs (or patterns) that these exceptions would apply to. Last match wins. Just below this then are two explicit matches for <SPAN CLASS="QUOTE" >".google.com"</SPAN >. The first is negating our previous cookie setting, which was for <A HREF="actions-file.html#SESSION-COOKIES-ONLY" ><SPAN CLASS="QUOTE" >"+session-cookies-only"</SPAN ></A > (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 <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >off</I ></SPAN > any <A HREF="actions-file.html#FAST-REDIRECTS" ><SPAN CLASS="QUOTE" >"+fast-redirects"</SPAN ></A > action, allowing this to take place unmolested. Note that there is a leading dot here -- <SPAN CLASS="QUOTE" >".google.com"</SPAN >. This will match any hosts and sub-domains, in the google.com domain also, such as <SPAN CLASS="QUOTE" >"www.google.com"</SPAN > or <SPAN CLASS="QUOTE" >"mail.google.com"</SPAN >. But it would not match <SPAN CLASS="QUOTE" >"www.google.de"</SPAN >! So, apparently, we have these two actions defined as exceptions to the general rules at the top somewhere in the lower part of our <TT CLASS="FILENAME" >default.action</TT > file, and <SPAN CLASS="QUOTE" >"google.com"</SPAN > is referenced somewhere in these latter sections.</P ><P > Then, for our <TT CLASS="FILENAME" >user.action</TT > file, we again have no hits. So there is nothing google-specific that we might have added to our own, local configuration. If there was, those actions would over-rule any actions from previously processed files, such as <TT CLASS="FILENAME" >default.action</TT >. <TT CLASS="FILENAME" >user.action</TT > typically has the last word. This is the best place to put hard and fast exceptions,</P ><P > And finally we pull it all together in the bottom section and summarize how <SPAN CLASS="APPLICATION" >Privoxy</SPAN > is applying all its <SPAN CLASS="QUOTE" >"actions"</SPAN > to <SPAN CLASS="QUOTE" >"google.com"</SPAN >: </P ><P > <TABLE BORDER="0" BGCOLOR="#E0E0E0" WIDTH="100%" ><TR ><TD ><PRE CLASS="SCREEN" > Final results: -add-header -block +change-x-forwarded-for{block} -client-header-filter{hide-tor-exit-notation} -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 -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 {google} -filter {yahoo} -filter {msn} -filter {blogspot} -filter {no-ping} -force-text-mode -handle-as-empty-document -handle-as-image -hide-accept-language -hide-content-disposition +hide-from-header {block} -hide-if-modified-since +hide-referrer {forge} -hide-user-agent -limit-connect -overwrite-last-modified -prevent-compression -redirect -server-header-filter{xml-to-html} -server-header-filter{html-to-xml} -session-cookies-only +set-image-blocker {pattern} </PRE ></TD ></TR ></TABLE ></P ><P > Notice the only difference here to the previous listing, is to <SPAN CLASS="QUOTE" >"fast-redirects"</SPAN > and <SPAN CLASS="QUOTE" >"session-cookies-only"</SPAN >, which are activated specifically for this site in our configuration, and thus show in the <SPAN CLASS="QUOTE" >"Final Results"</SPAN >.</P ><P > Now another example, <SPAN CLASS="QUOTE" >"ad.doubleclick.net"</SPAN >:</P ><P > <TABLE BORDER="0" BGCOLOR="#E0E0E0" WIDTH="100%" ><TR ><TD ><PRE CLASS="SCREEN" > { +block{Domains starts with "ad"} } ad*. { +block{Domain contains "ad"} } .ad. { +block{Doubleclick banner server} +handle-as-image } .[a-vx-z]*.doubleclick.net</PRE ></TD ></TR ></TABLE ></P ><P > We'll just show the interesting part here - the explicit matches. It is matched three different times. Two <SPAN CLASS="QUOTE" >"+block{}"</SPAN > sections, and a <SPAN CLASS="QUOTE" >"+block{} +handle-as-image"</SPAN >, which is the expanded form of one of our aliases that had been defined as: <SPAN CLASS="QUOTE" >"+block-as-image"</SPAN >. (<A HREF="actions-file.html#ALIASES" ><SPAN CLASS="QUOTE" >"Aliases"</SPAN ></A > are defined in the first section of the actions file and typically used to combine more than one action.)</P ><P > Any one of these would have done the trick and blocked this as an unwanted image. This is unnecessarily redundant since the last case effectively would also cover the first. No point in taking chances with these guys though ;-) Note that if you want an ad or obnoxious URL to be invisible, it should be defined as <SPAN CLASS="QUOTE" >"ad.doubleclick.net"</SPAN > is done here -- as both a <A HREF="actions-file.html#BLOCK" ><SPAN CLASS="QUOTE" >"+block{}"</SPAN ></A > <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >and</I ></SPAN > an <A HREF="actions-file.html#HANDLE-AS-IMAGE" ><SPAN CLASS="QUOTE" >"+handle-as-image"</SPAN ></A >. The custom alias <SPAN CLASS="QUOTE" >"<TT CLASS="LITERAL" >+block-as-image</TT >"</SPAN > just simplifies the process and make it more readable.</P ><P > One last example. Let's try <SPAN CLASS="QUOTE" >"http://www.example.net/adsl/HOWTO/"</SPAN >. This one is giving us problems. We are getting a blank page. Hmmm ...</P ><P > <TABLE BORDER="0" BGCOLOR="#E0E0E0" WIDTH="100%" ><TR ><TD ><PRE CLASS="SCREEN" > Matches for http://www.example.net/adsl/HOWTO/: In file: default.action <SPAN CLASS="GUIBUTTON" >[ View ]</SPAN > <SPAN CLASS="GUIBUTTON" >[ Edit ]</SPAN > {-add-header -block +change-x-forwarded-for{block} -client-header-filter{hide-tor-exit-notation} -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 {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 {google} -filter {yahoo} -filter {msn} -filter {blogspot} -filter {no-ping} -force-text-mode -handle-as-empty-document -handle-as-image -hide-accept-language -hide-content-disposition +hide-from-header{block} +hide-referer{forge} -hide-user-agent -overwrite-last-modified +prevent-compression -redirect -server-header-filter{xml-to-html} -server-header-filter{html-to-xml} +session-cookies-only +set-image-blocker{blank} } / { +block{Path contains "ads".} +handle-as-image } /ads</PRE ></TD ></TR ></TABLE ></P ><P > Ooops, the <SPAN CLASS="QUOTE" >"/adsl/"</SPAN > is matching <SPAN CLASS="QUOTE" >"/ads"</SPAN > in our configuration! But we did not want this at all! Now we see why we get the blank page. It is actually triggering two different actions here, and the effects are aggregated so that the URL is blocked, and <SPAN CLASS="APPLICATION" >Privoxy</SPAN > is told to treat the block as if it were an image. But this is, of course, all wrong. We could now add a new action below this (or better in our own <TT CLASS="FILENAME" >user.action</TT > file) that explicitly <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >un</I ></SPAN > blocks ( <A HREF="actions-file.html#BLOCK" ><SPAN CLASS="QUOTE" >"{-block}"</SPAN ></A >) paths with <SPAN CLASS="QUOTE" >"adsl"</SPAN > in them (remember, last match in the configuration wins). There are various ways to handle such exceptions. Example:</P ><P > <TABLE BORDER="0" BGCOLOR="#E0E0E0" WIDTH="100%" ><TR ><TD ><PRE CLASS="SCREEN" > { -block } /adsl</PRE ></TD ></TR ></TABLE ></P ><P > Now the page displays ;-) Remember to flush your browser's caches when making these kinds of changes to your configuration to insure that you get a freshly delivered page! Or, try using <TT CLASS="LITERAL" >Shift+Reload</TT >.</P ><P > But now what about a situation where we get no explicit matches like we did with:</P ><P > <TABLE BORDER="0" BGCOLOR="#E0E0E0" WIDTH="100%" ><TR ><TD ><PRE CLASS="SCREEN" > { +block{Path starts with "ads".} +handle-as-image } /ads</PRE ></TD ></TR ></TABLE ></P ><P > That actually was very helpful and pointed us quickly to where the problem was. If you don't get this kind of match, then it means one of the default rules in the first section of <TT CLASS="FILENAME" >default.action</TT > is causing the problem. This would require some guesswork, and maybe a little trial and error to isolate the offending rule. One likely cause would be one of the <A HREF="actions-file.html#FILTER" ><SPAN CLASS="QUOTE" >"+filter"</SPAN ></A > actions. These tend to be harder to troubleshoot. Try adding the URL for the site to one of aliases that turn off <A HREF="actions-file.html#FILTER" ><SPAN CLASS="QUOTE" >"+filter"</SPAN ></A >:</P ><P > <TABLE BORDER="0" BGCOLOR="#E0E0E0" WIDTH="100%" ><TR ><TD ><PRE CLASS="SCREEN" > { shop } .quietpc.com .worldpay.com # for quietpc.com .jungle.com .scan.co.uk .forbes.com</PRE ></TD ></TR ></TABLE ></P ><P > <SPAN CLASS="QUOTE" >"<TT CLASS="LITERAL" >{ shop }</TT >"</SPAN > is an <SPAN CLASS="QUOTE" >"alias"</SPAN > that expands to <SPAN CLASS="QUOTE" >"<TT CLASS="LITERAL" >{ -filter -session-cookies-only }</TT >"</SPAN >. Or you could do your own exception to negate filtering: </P ><P > <TABLE BORDER="0" BGCOLOR="#E0E0E0" WIDTH="100%" ><TR ><TD ><PRE CLASS="SCREEN" > { -filter } # Disable ALL filter actions for sites in this section .forbes.com developer.ibm.com localhost</PRE ></TD ></TR ></TABLE ></P ><P > This would turn off all filtering for these sites. This is best put in <TT CLASS="FILENAME" >user.action</TT >, for local site exceptions. Note that when a simple domain pattern is used by itself (without the subsequent path portion), all sub-pages within that domain are included automatically in the scope of the action.</P ><P > Images that are inexplicably being blocked, may well be hitting the <A HREF="actions-file.html#FILTER-BANNERS-BY-SIZE" ><SPAN CLASS="QUOTE" >"+filter{banners-by-size}"</SPAN ></A > rule, which assumes that images of certain sizes are ad banners (works well <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >most of the time</I ></SPAN > since these tend to be standardized).</P ><P > <SPAN CLASS="QUOTE" >"<TT CLASS="LITERAL" >{ fragile }</TT >"</SPAN > is an alias that disables most actions that are the most likely to cause trouble. This can be used as a last resort for problem sites. </P ><P > <TABLE BORDER="0" BGCOLOR="#E0E0E0" WIDTH="100%" ><TR ><TD ><PRE CLASS="SCREEN" > { fragile } # Handle with care: easy to break mail.google. mybank.example.com</PRE ></TD ></TR ></TABLE ></P ><P > <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >Remember to flush caches!</I ></SPAN > Note that the <TT CLASS="LITERAL" >mail.google</TT > reference lacks the TLD portion (e.g. <SPAN CLASS="QUOTE" >".com"</SPAN >). This will effectively match any TLD with <TT CLASS="LITERAL" >google</TT > in it, such as <TT CLASS="LITERAL" >mail.google.de.</TT >, just as an example.</P ><P > If this still does not work, you will have to go through the remaining actions one by one to find which one(s) is causing the problem.</P ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="seealso.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" > </TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >See Also</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" > </TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" > </TD ></TR ></TABLE ></DIV ></BODY ></HTML >