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+
+ <div class="SECT1">
+ <h1 class="SECT1"><a name="APPENDIX" id="APPENDIX">14. Appendix</a></h1>
+
+ <div class="SECT2">
+ <h2 class="SECT2"><a name="REGEX" id="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>
+
+ <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>
+
+ <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>
+
+ <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>
+
+ <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>
+
+ <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>
+
+ <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>
+
+ <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>
+
+ <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>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="AEN5902" id="AEN5902">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>
+
+ <ul>
+ <li>
+ <p>Privoxy main page:</p><a name="AEN5916" id="AEN5916"></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="AEN5924" id=
+ "AEN5924"></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="AEN5929" id=
+ "AEN5929"></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="AEN5934" id=
+ "AEN5934"></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="AEN5939"
+ id="AEN5939"></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=
+ "AEN5947" id="AEN5947"></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="AEN5951" id=
+ "AEN5951"></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="AEN5954" id="AEN5954"></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>These may be bookmarked for quick reference. See next.</p>
+
+ <div class="SECT3">
+ <h3 class="SECT3"><a name="BOOKMARKLETS" id="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>
+
+ <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>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" id="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>
+
+ <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>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" id="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>
+
+ <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>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>
+
+ <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>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>
+
+ <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>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>
+
+ <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>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>
+
+ <table border="0" bgcolor="#E0E0E0" width="100%">
+ <tr>
+ <td>
+ <pre class="SCREEN">
+ { -block }
+ /adsl
+</pre>
+ </td>
+ </tr>
+ </table>
+
+ <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>
+
+ <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>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>
+
+ <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><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>
+
+ <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>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>
+
+ <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><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>
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