doc/webserver/user-manual/actions-file.html

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  24         <th colspan="3" align="center">Privoxy 3.0.22 User Manual</th>
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  41     <h1 class="SECT1"><a name="ACTIONS-FILE" id="ACTIONS-FILE">8. Actions
  42     Files</a></h1>
  43
  44     <p>The actions files are used to define what <span class=
  45     "emphasis"><i class="EMPHASIS">actions</i></span> <span class=
  46     "APPLICATION">Privoxy</span> takes for which URLs, and thus determines
  47     how ad images, cookies and various other aspects of HTTP content and
  48     transactions are handled, and on which sites (or even parts thereof).
  49     There are a number of such actions, with a wide range of functionality.
  50     Each action does something a little different. These actions give us a
  51     veritable arsenal of tools with which to exert our control, preferences
  52     and independence. Actions can be combined so that their effects are
  53     aggregated when applied against a given set of URLs.</p>
  54
  55     <p>There are three action files included with <span class=
  56     "APPLICATION">Privoxy</span> with differing purposes:</p>
  57
  58     <ul>
  59       <li>
  60         <p><tt class="FILENAME">match-all.action</tt> - is used to define
  61         which <span class="QUOTE">"actions"</span> relating to
  62         banner-blocking, images, pop-ups, content modification, cookie
  63         handling etc should be applied by default. It should be the first
  64         actions file loaded</p>
  65       </li>
  66
  67       <li>
  68         <p><tt class="FILENAME">default.action</tt> - defines many exceptions
  69         (both positive and negative) from the default set of actions that's
  70         configured in <tt class="FILENAME">match-all.action</tt>. It is a set
  71         of rules that should work reasonably well as-is for most users. This
  72         file is only supposed to be edited by the developers. It should be
  73         the second actions file loaded.</p>
  74       </li>
  75
  76       <li>
  77         <p><tt class="FILENAME">user.action</tt> - is intended to be for
  78         local site preferences and exceptions. As an example, if your ISP or
  79         your bank has specific requirements, and need special handling, this
  80         kind of thing should go here. This file will not be upgraded.</p>
  81       </li>
  82
  83       <li>
  84         <p><span class="GUIBUTTON">Edit</span> <span class="GUIBUTTON">Set to
  85         Cautious</span> <span class="GUIBUTTON">Set to Medium</span>
  86         <span class="GUIBUTTON">Set to Advanced</span></p>
  87
  88         <p>These have increasing levels of aggressiveness <span class=
  89         "emphasis"><i class="EMPHASIS">and have no influence on your browsing
  90         unless you select them explicitly in the editor</i></span>. A default
  91         installation should be pre-set to <tt class="LITERAL">Cautious</tt>.
  92         New users should try this for a while before adjusting the settings
  93         to more aggressive levels. The more aggressive the settings, then the
  94         more likelihood there is of problems such as sites not working as
  95         they should.</p>
  96
  97         <p>The <span class="GUIBUTTON">Edit</span> button allows you to turn
  98         each action on/off individually for fine-tuning. The <span class=
  99         "GUIBUTTON">Cautious</span> button changes the actions list to
 100         low/safe settings which will activate ad blocking and a minimal set
 101         of <span class="APPLICATION">Privoxy</span>'s features, and
 102         subsequently there will be less of a chance for accidental problems.
 103         The <span class="GUIBUTTON">Medium</span> button sets the list to a
 104         medium level of other features and a low level set of privacy
 105         features. The <span class="GUIBUTTON">Advanced</span> button sets the
 106         list to a high level of ad blocking and medium level of privacy. See
 107         the chart below. The latter three buttons over-ride any changes via
 108         with the <span class="GUIBUTTON">Edit</span> button. More fine-tuning
 109         can be done in the lower sections of this internal page.</p>
 110
 111         <p>While the actions file editor allows to enable these settings in
 112         all actions files, they are only supposed to be enabled in the first
 113         one to make sure you don't unintentionally overrule earlier
 114         rules.</p>
 115
 116         <p>The default profiles, and their associated actions, as pre-defined
 117         in <tt class="FILENAME">default.action</tt> are:</p>
 118
 119         <div class="TABLE">
 120           <a name="AEN2863" id="AEN2863"></a>
 121
 122           <p><b>Table 1. Default Configurations</b></p>
 123
 124           <table border="1" frame="border" rules="all" class="CALSTABLE">
 125             <col width="1*" title="C1">
 126             <col width="1*" title="C2">
 127             <col width="1*" title="C3">
 128             <col width="1*" title="C4">
 129
 130             <thead>
 131               <tr>
 132                 <th>Feature</th>
 133
 134                 <th>Cautious</th>
 135
 136                 <th>Medium</th>
 137
 138                 <th>Advanced</th>
 139               </tr>
 140             </thead>
 141
 142             <tbody>
 143               <tr>
 144                 <td>Ad-blocking Aggressiveness</td>
 145
 146                 <td>medium</td>
 147
 148                 <td>high</td>
 149
 150                 <td>high</td>
 151               </tr>
 152
 153               <tr>
 154                 <td>Ad-filtering by size</td>
 155
 156                 <td>no</td>
 157
 158                 <td>yes</td>
 159
 160                 <td>yes</td>
 161               </tr>
 162
 163               <tr>
 164                 <td>Ad-filtering by link</td>
 165
 166                 <td>no</td>
 167
 168                 <td>no</td>
 169
 170                 <td>yes</td>
 171               </tr>
 172
 173               <tr>
 174                 <td>Pop-up killing</td>
 175
 176                 <td>blocks only</td>
 177
 178                 <td>blocks only</td>
 179
 180                 <td>blocks only</td>
 181               </tr>
 182
 183               <tr>
 184                 <td>Privacy Features</td>
 185
 186                 <td>low</td>
 187
 188                 <td>medium</td>
 189
 190                 <td>medium/high</td>
 191               </tr>
 192
 193               <tr>
 194                 <td>Cookie handling</td>
 195
 196                 <td>none</td>
 197
 198                 <td>session-only</td>
 199
 200                 <td>kill</td>
 201               </tr>
 202
 203               <tr>
 204                 <td>Referer forging</td>
 205
 206                 <td>no</td>
 207
 208                 <td>yes</td>
 209
 210                 <td>yes</td>
 211               </tr>
 212
 213               <tr>
 214                 <td>GIF de-animation</td>
 215
 216                 <td>no</td>
 217
 218                 <td>yes</td>
 219
 220                 <td>yes</td>
 221               </tr>
 222
 223               <tr>
 224                 <td>Fast redirects</td>
 225
 226                 <td>no</td>
 227
 228                 <td>no</td>
 229
 230                 <td>yes</td>
 231               </tr>
 232
 233               <tr>
 234                 <td>HTML taming</td>
 235
 236                 <td>no</td>
 237
 238                 <td>no</td>
 239
 240                 <td>yes</td>
 241               </tr>
 242
 243               <tr>
 244                 <td>JavaScript taming</td>
 245
 246                 <td>no</td>
 247
 248                 <td>no</td>
 249
 250                 <td>yes</td>
 251               </tr>
 252
 253               <tr>
 254                 <td>Web-bug killing</td>
 255
 256                 <td>no</td>
 257
 258                 <td>yes</td>
 259
 260                 <td>yes</td>
 261               </tr>
 262
 263               <tr>
 264                 <td>Image tag reordering</td>
 265
 266                 <td>no</td>
 267
 268                 <td>yes</td>
 269
 270                 <td>yes</td>
 271               </tr>
 272             </tbody>
 273           </table>
 274         </div>
 275       </li>
 276     </ul>
 277
 278     <p>The list of actions files to be used are defined in the main
 279     configuration file, and are processed in the order they are defined (e.g.
 280     <tt class="FILENAME">default.action</tt> is typically processed before
 281     <tt class="FILENAME">user.action</tt>). The content of these can all be
 282     viewed and edited from <a href="http://config.privoxy.org/show-status"
 283     target="_top">http://config.privoxy.org/show-status</a>. The over-riding
 284     principle when applying actions, is that the last action that matches a
 285     given URL wins. The broadest, most general rules go first (defined in
 286     <tt class="FILENAME">default.action</tt>), followed by any exceptions
 287     (typically also in <tt class="FILENAME">default.action</tt>), which are
 288     then followed lastly by any local preferences (typically in <span class=
 289     "emphasis"><i class="EMPHASIS">user</i></span><tt class=
 290     "FILENAME">.action</tt>). Generally, <tt class=
 291     "FILENAME">user.action</tt> has the last word.</p>
 292
 293     <p>An actions file typically has multiple sections. If you want to use
 294     <span class="QUOTE">"aliases"</span> in an actions file, you have to
 295     place the (optional) <a href="actions-file.html#ALIASES">alias
 296     section</a> at the top of that file. Then comes the default set of rules
 297     which will apply universally to all sites and pages (be <span class=
 298     "emphasis"><i class="EMPHASIS">very careful</i></span> with using such a
 299     universal set in <tt class="FILENAME">user.action</tt> or any other
 300     actions file after <tt class="FILENAME">default.action</tt>, because it
 301     will override the result from consulting any previous file). And then
 302     below that, exceptions to the defined universal policies. You can regard
 303     <tt class="FILENAME">user.action</tt> as an appendix to <tt class=
 304     "FILENAME">default.action</tt>, with the advantage that it is a separate
 305     file, which makes preserving your personal settings across <span class=
 306     "APPLICATION">Privoxy</span> upgrades easier.</p>
 307
 308     <p>Actions can be used to block anything you want, including ads,
 309     banners, or just some obnoxious URL whose content you would rather not
 310     see. Cookies can be accepted or rejected, or accepted only during the
 311     current browser session (i.e. not written to disk), content can be
 312     modified, some JavaScripts tamed, user-tracking fooled, and much more.
 313     See below for a <a href="actions-file.html#ACTIONS">complete list of
 314     actions</a>.</p>
 315
 316     <div class="SECT2">
 317       <h2 class="SECT2"><a name="AEN2962" id="AEN2962">8.1. Finding the Right
 318       Mix</a></h2>
 319
 320       <p>Note that some <a href="actions-file.html#ACTIONS">actions</a>, like
 321       cookie suppression or script disabling, may render some sites unusable
 322       that rely on these techniques to work properly. Finding the right mix
 323       of actions is not always easy and certainly a matter of personal taste.
 324       And, things can always change, requiring refinements in the
 325       configuration. In general, it can be said that the more <span class=
 326       "QUOTE">"aggressive"</span> your default settings (in the top section
 327       of the actions file) are, the more exceptions for <span class=
 328       "QUOTE">"trusted"</span> sites you will have to make later. If, for
 329       example, you want to crunch all cookies per default, you'll have to
 330       make exceptions from that rule for sites that you regularly use and
 331       that require cookies for actually useful purposes, like maybe your
 332       bank, favorite shop, or newspaper.</p>
 333
 334       <p>We have tried to provide you with reasonable rules to start from in
 335       the distribution actions files. But there is no general rule of thumb
 336       on these things. There just are too many variables, and sites are
 337       constantly changing. Sooner or later you will want to change the rules
 338       (and read this chapter again :).</p>
 339     </div>
 340
 341     <div class="SECT2">
 342       <h2 class="SECT2"><a name="AEN2969" id="AEN2969">8.2. How to
 343       Edit</a></h2>
 344
 345       <p>The easiest way to edit the actions files is with a browser by using
 346       our browser-based editor, which can be reached from <a href=
 347       "http://config.privoxy.org/show-status" target=
 348       "_top">http://config.privoxy.org/show-status</a>. Note: the config file
 349       option <a href=
 350       "config.html#ENABLE-EDIT-ACTIONS">enable-edit-actions</a> must be
 351       enabled for this to work. The editor allows both fine-grained control
 352       over every single feature on a per-URL basis, and easy choosing from
 353       wholesale sets of defaults like <span class="QUOTE">"Cautious"</span>,
 354       <span class="QUOTE">"Medium"</span> or <span class=
 355       "QUOTE">"Advanced"</span>. Warning: the <span class=
 356       "QUOTE">"Advanced"</span> setting is more aggressive, and will be more
 357       likely to cause problems for some sites. Experienced users only!</p>
 358
 359       <p>If you prefer plain text editing to GUIs, you can of course also
 360       directly edit the the actions files with your favorite text editor.
 361       Look at <tt class="FILENAME">default.action</tt> which is richly
 362       commented with many good examples.</p>
 363     </div>
 364
 365     <div class="SECT2">
 366       <h2 class="SECT2"><a name="ACTIONS-APPLY" id="ACTIONS-APPLY">8.3. How
 367       Actions are Applied to Requests</a></h2>
 368
 369       <p>Actions files are divided into sections. There are special sections,
 370       like the <span class="QUOTE">"<a href=
 371       "actions-file.html#ALIASES">alias</a>"</span> sections which will be
 372       discussed later. For now let's concentrate on regular sections: They
 373       have a heading line (often split up to multiple lines for readability)
 374       which consist of a list of actions, separated by whitespace and
 375       enclosed in curly braces. Below that, there is a list of URL and tag
 376       patterns, each on a separate line.</p>
 377
 378       <p>To determine which actions apply to a request, the URL of the
 379       request is compared to all URL patterns in each <span class=
 380       "QUOTE">"action file"</span>. Every time it matches, the list of
 381       applicable actions for the request is incrementally updated, using the
 382       heading of the section in which the pattern is located. The same is
 383       done again for tags and tag patterns later on.</p>
 384
 385       <p>If multiple applying sections set the same action differently, the
 386       last match wins. If not, the effects are aggregated. E.g. a URL might
 387       match a regular section with a heading line of <tt class="LITERAL">{
 388       +<a href="actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a>
 389       }</tt>, then later another one with just <tt class="LITERAL">{
 390       +<a href="actions-file.html#BLOCK">block</a> }</tt>, resulting in
 391       <span class="emphasis"><i class="EMPHASIS">both</i></span> actions to
 392       apply. And there may well be cases where you will want to combine
 393       actions together. Such a section then might look like:</p>
 394
 395       <table border="0" bgcolor="#E0E0E0" width="100%">
 396         <tr>
 397           <td>
 398             <pre class="SCREEN">
 399   { +<tt class="LITERAL">handle-as-image</tt>  +<tt class=
 400 "LITERAL">block{Banner ads.}</tt> }
 401   # Block these as if they were images. Send no block page.
 402    banners.example.com
 403    media.example.com/.*banners
 404    .example.com/images/ads/
 405 </pre>
 406           </td>
 407         </tr>
 408       </table>
 409
 410       <p>You can trace this process for URL patterns and any given URL by
 411       visiting <a href="http://config.privoxy.org/show-url-info" target=
 412       "_top">http://config.privoxy.org/show-url-info</a>.</p>
 413
 414       <p>Examples and more detail on this is provided in the Appendix,
 415       <a href="appendix.html#ACTIONSANAT">Troubleshooting: Anatomy of an
 416       Action</a> section.</p>
 417     </div>
 418
 419     <div class="SECT2">
 420       <h2 class="SECT2"><a name="AF-PATTERNS" id="AF-PATTERNS">8.4.
 421       Patterns</a></h2>
 422
 423       <p>As mentioned, <span class="APPLICATION">Privoxy</span> uses
 424       <span class="QUOTE">"patterns"</span> to determine what <span class=
 425       "emphasis"><i class="EMPHASIS">actions</i></span> might apply to which
 426       sites and pages your browser attempts to access. These <span class=
 427       "QUOTE">"patterns"</span> use wild card type <span class=
 428       "emphasis"><i class="EMPHASIS">pattern</i></span> matching to achieve a
 429       high degree of flexibility. This allows one expression to be expanded
 430       and potentially match against many similar patterns.</p>
 431
 432       <p>Generally, an URL pattern has the form <tt class=
 433       "LITERAL">&lt;host&gt;&lt;port&gt;/&lt;path&gt;</tt>, where the
 434       <tt class="LITERAL">&lt;host&gt;</tt>, the <tt class=
 435       "LITERAL">&lt;port&gt;</tt> and the <tt class=
 436       "LITERAL">&lt;path&gt;</tt> are optional. (This is why the special
 437       <tt class="LITERAL">/</tt> pattern matches all URLs). Note that the
 438       protocol portion of the URL pattern (e.g. <tt class=
 439       "LITERAL">http://</tt>) should <span class="emphasis"><i class=
 440       "EMPHASIS">not</i></span> be included in the pattern. This is assumed
 441       already!</p>
 442
 443       <p>The pattern matching syntax is different for the host and path parts
 444       of the URL. The host part uses a simple globbing type matching
 445       technique, while the path part uses more flexible <a href=
 446       "http://en.wikipedia.org/wiki/Regular_expressions" target=
 447       "_top"><span class="QUOTE">"Regular Expressions"</span></a> (POSIX
 448       1003.2).</p>
 449
 450       <p>The port part of a pattern is a decimal port number preceded by a
 451       colon (<tt class="LITERAL">:</tt>). If the host part contains a
 452       numerical IPv6 address, it has to be put into angle brackets
 453       (<tt class="LITERAL">&lt;</tt>, <tt class="LITERAL">&gt;</tt>).</p>
 454
 455       <div class="VARIABLELIST">
 456         <dl>
 457           <dt><tt class="LITERAL">www.example.com/</tt></dt>
 458
 459           <dd>
 460             <p>is a host-only pattern and will match any request to
 461             <tt class="LITERAL">www.example.com</tt>, regardless of which
 462             document on that server is requested. So ALL pages in this domain
 463             would be covered by the scope of this action. Note that a simple
 464             <tt class="LITERAL">example.com</tt> is different and would NOT
 465             match.</p>
 466           </dd>
 467
 468           <dt><tt class="LITERAL">www.example.com</tt></dt>
 469
 470           <dd>
 471             <p>means exactly the same. For host-only patterns, the trailing
 472             <tt class="LITERAL">/</tt> may be omitted.</p>
 473           </dd>
 474
 475           <dt><tt class="LITERAL">www.example.com/index.html</tt></dt>
 476
 477           <dd>
 478             <p>matches all the documents on <tt class=
 479             "LITERAL">www.example.com</tt> whose name starts with <tt class=
 480             "LITERAL">/index.html</tt>.</p>
 481           </dd>
 482
 483           <dt><tt class="LITERAL">www.example.com/index.html$</tt></dt>
 484
 485           <dd>
 486             <p>matches only the single document <tt class=
 487             "LITERAL">/index.html</tt> on <tt class=
 488             "LITERAL">www.example.com</tt>.</p>
 489           </dd>
 490
 491           <dt><tt class="LITERAL">/index.html$</tt></dt>
 492
 493           <dd>
 494             <p>matches the document <tt class="LITERAL">/index.html</tt>,
 495             regardless of the domain, i.e. on <span class=
 496             "emphasis"><i class="EMPHASIS">any</i></span> web server
 497             anywhere.</p>
 498           </dd>
 499
 500           <dt><tt class="LITERAL">/</tt></dt>
 501
 502           <dd>
 503             <p>Matches any URL because there's no requirement for either the
 504             domain or the path to match anything.</p>
 505           </dd>
 506
 507           <dt><tt class="LITERAL">:8000/</tt></dt>
 508
 509           <dd>
 510             <p>Matches any URL pointing to TCP port 8000.</p>
 511           </dd>
 512
 513           <dt><tt class="LITERAL">10.0.0.1/</tt></dt>
 514
 515           <dd>
 516             <p>Matches any URL with the host address <tt class=
 517             "LITERAL">10.0.0.1</tt>. (Note that the real URL uses plain
 518             brackets, not angle brackets.)</p>
 519           </dd>
 520
 521           <dt><tt class="LITERAL">&lt;2001:db8::1&gt;/</tt></dt>
 522
 523           <dd>
 524             <p>Matches any URL with the host address <tt class=
 525             "LITERAL">2001:db8::1</tt>. (Note that the real URL uses plain
 526             brackets, not angle brackets.)</p>
 527           </dd>
 528
 529           <dt><tt class="LITERAL">index.html</tt></dt>
 530
 531           <dd>
 532             <p>matches nothing, since it would be interpreted as a domain
 533             name and there is no top-level domain called <tt class=
 534             "LITERAL">.html</tt>. So its a mistake.</p>
 535           </dd>
 536         </dl>
 537       </div>
 538
 539       <div class="SECT3">
 540         <h3 class="SECT3"><a name="HOST-PATTERN" id="HOST-PATTERN">8.4.1. The
 541         Host Pattern</a></h3>
 542
 543         <p>The matching of the host part offers some flexible options: if the
 544         host pattern starts or ends with a dot, it becomes unanchored at that
 545         end. The host pattern is often referred to as domain pattern as it is
 546         usually used to match domain names and not IP addresses. For
 547         example:</p>
 548
 549         <div class="VARIABLELIST">
 550           <dl>
 551             <dt><tt class="LITERAL">.example.com</tt></dt>
 552
 553             <dd>
 554               <p>matches any domain with first-level domain <tt class=
 555               "LITERAL">com</tt> and second-level domain <tt class=
 556               "LITERAL">example</tt>. For example <tt class=
 557               "LITERAL">www.example.com</tt>, <tt class=
 558               "LITERAL">example.com</tt> and <tt class=
 559               "LITERAL">foo.bar.baz.example.com</tt>. Note that it wouldn't
 560               match if the second-level domain was <tt class=
 561               "LITERAL">another-example</tt>.</p>
 562             </dd>
 563
 564             <dt><tt class="LITERAL">www.</tt></dt>
 565
 566             <dd>
 567               <p>matches any domain that <span class="emphasis"><i class=
 568               "EMPHASIS">STARTS</i></span> with <tt class="LITERAL">www.</tt>
 569               (It also matches the domain <tt class="LITERAL">www</tt> but
 570               most of the time that doesn't matter.)</p>
 571             </dd>
 572
 573             <dt><tt class="LITERAL">.example.</tt></dt>
 574
 575             <dd>
 576               <p>matches any domain that <span class="emphasis"><i class=
 577               "EMPHASIS">CONTAINS</i></span> <tt class=
 578               "LITERAL">.example.</tt>. And, by the way, also included would
 579               be any files or documents that exist within that domain since
 580               no path limitations are specified. (Correctly speaking: It
 581               matches any FQDN that contains <tt class="LITERAL">example</tt>
 582               as a domain.) This might be <tt class=
 583               "LITERAL">www.example.com</tt>, <tt class=
 584               "LITERAL">news.example.de</tt>, or <tt class=
 585               "LITERAL">www.example.net/cgi/testing.pl</tt> for instance. All
 586               these cases are matched.</p>
 587             </dd>
 588           </dl>
 589         </div>
 590
 591         <p>Additionally, there are wild-cards that you can use in the domain
 592         names themselves. These work similarly to shell globbing type
 593         wild-cards: <span class="QUOTE">"*"</span> represents zero or more
 594         arbitrary characters (this is equivalent to the <a href=
 595         "http://en.wikipedia.org/wiki/Regular_expressions" target=
 596         "_top"><span class="QUOTE">"Regular Expression"</span></a> based
 597         syntax of <span class="QUOTE">".*"</span>), <span class=
 598         "QUOTE">"?"</span> represents any single character (this is
 599         equivalent to the regular expression syntax of a simple <span class=
 600         "QUOTE">"."</span>), and you can define <span class=
 601         "QUOTE">"character classes"</span> in square brackets which is
 602         similar to the same regular expression technique. All of this can be
 603         freely mixed:</p>
 604
 605         <div class="VARIABLELIST">
 606           <dl>
 607             <dt><tt class="LITERAL">ad*.example.com</tt></dt>
 608
 609             <dd>
 610               <p>matches <span class="QUOTE">"adserver.example.com"</span>,
 611               <span class="QUOTE">"ads.example.com"</span>, etc but not
 612               <span class="QUOTE">"sfads.example.com"</span></p>
 613             </dd>
 614
 615             <dt><tt class="LITERAL">*ad*.example.com</tt></dt>
 616
 617             <dd>
 618               <p>matches all of the above, and then some.</p>
 619             </dd>
 620
 621             <dt><tt class="LITERAL">.?pix.com</tt></dt>
 622
 623             <dd>
 624               <p>matches <tt class="LITERAL">www.ipix.com</tt>, <tt class=
 625               "LITERAL">pictures.epix.com</tt>, <tt class=
 626               "LITERAL">a.b.c.d.e.upix.com</tt> etc.</p>
 627             </dd>
 628
 629             <dt><tt class="LITERAL">www[1-9a-ez].example.c*</tt></dt>
 630
 631             <dd>
 632               <p>matches <tt class="LITERAL">www1.example.com</tt>,
 633               <tt class="LITERAL">www4.example.cc</tt>, <tt class=
 634               "LITERAL">wwwd.example.cy</tt>, <tt class=
 635               "LITERAL">wwwz.example.com</tt> etc., but <span class=
 636               "emphasis"><i class="EMPHASIS">not</i></span> <tt class=
 637               "LITERAL">wwww.example.com</tt>.</p>
 638             </dd>
 639           </dl>
 640         </div>
 641
 642         <p>While flexible, this is not the sophistication of full regular
 643         expression based syntax.</p>
 644       </div>
 645
 646       <div class="SECT3">
 647         <h3 class="SECT3"><a name="AEN3163" id="AEN3163">8.4.2. The Path
 648         Pattern</a></h3>
 649
 650         <p><span class="APPLICATION">Privoxy</span> uses <span class=
 651         "QUOTE">"modern"</span> POSIX 1003.2 <a href=
 652         "http://en.wikipedia.org/wiki/Regular_expressions" target=
 653         "_top"><span class="QUOTE">"Regular Expressions"</span></a> for
 654         matching the path portion (after the slash), and is thus more
 655         flexible.</p>
 656
 657         <p>There is an <a href="appendix.html#REGEX">Appendix</a> with a
 658         brief quick-start into regular expressions, you also might want to
 659         have a look at your operating system's documentation on regular
 660         expressions (try <tt class="LITERAL">man re_format</tt>).</p>
 661
 662         <p>Note that the path pattern is automatically left-anchored at the
 663         <span class="QUOTE">"/"</span>, i.e. it matches as if it would start
 664         with a <span class="QUOTE">"^"</span> (regular expression speak for
 665         the beginning of a line).</p>
 666
 667         <p>Please also note that matching in the path is <span class=
 668         "emphasis"><i class="EMPHASIS">CASE INSENSITIVE</i></span> by
 669         default, but you can switch to case sensitive at any point in the
 670         pattern by using the <span class="QUOTE">"(?-i)"</span> switch:
 671         <tt class="LITERAL">www.example.com/(?-i)PaTtErN.*</tt> will match
 672         only documents whose path starts with <tt class=
 673         "LITERAL">PaTtErN</tt> in <span class="emphasis"><i class=
 674         "EMPHASIS">exactly</i></span> this capitalization.</p>
 675
 676         <div class="VARIABLELIST">
 677           <dl>
 678             <dt><tt class="LITERAL">.example.com/.*</tt></dt>
 679
 680             <dd>
 681               <p>Is equivalent to just <span class=
 682               "QUOTE">".example.com"</span>, since any documents within that
 683               domain are matched with or without the <span class=
 684               "QUOTE">".*"</span> regular expression. This is redundant</p>
 685             </dd>
 686
 687             <dt><tt class="LITERAL">.example.com/.*/index.html$</tt></dt>
 688
 689             <dd>
 690               <p>Will match any page in the domain of <span class=
 691               "QUOTE">"example.com"</span> that is named <span class=
 692               "QUOTE">"index.html"</span>, and that is part of some path. For
 693               example, it matches <span class=
 694               "QUOTE">"www.example.com/testing/index.html"</span> but NOT
 695               <span class="QUOTE">"www.example.com/index.html"</span> because
 696               the regular expression called for at least two <span class=
 697               "QUOTE">"/'s"</span>, thus the path requirement. It also would
 698               match <span class=
 699               "QUOTE">"www.example.com/testing/index_html"</span>, because of
 700               the special meta-character <span class="QUOTE">"."</span>.</p>
 701             </dd>
 702
 703             <dt><tt class="LITERAL">.example.com/(.*/)?index\.html$</tt></dt>
 704
 705             <dd>
 706               <p>This regular expression is conditional so it will match any
 707               page named <span class="QUOTE">"index.html"</span> regardless
 708               of path which in this case can have one or more <span class=
 709               "QUOTE">"/'s"</span>. And this one must contain exactly
 710               <span class="QUOTE">".html"</span> (but does not have to end
 711               with that!).</p>
 712             </dd>
 713
 714             <dt><tt class=
 715             "LITERAL">.example.com/(.*/)(ads|banners?|junk)</tt></dt>
 716
 717             <dd>
 718               <p>This regular expression will match any path of <span class=
 719               "QUOTE">"example.com"</span> that contains any of the words
 720               <span class="QUOTE">"ads"</span>, <span class=
 721               "QUOTE">"banner"</span>, <span class="QUOTE">"banners"</span>
 722               (because of the <span class="QUOTE">"?"</span>) or <span class=
 723               "QUOTE">"junk"</span>. The path does not have to end in these
 724               words, just contain them.</p>
 725             </dd>
 726
 727             <dt><tt class=
 728             "LITERAL">.example.com/(.*/)(ads|banners?|junk)/.*\.(jpe?g|gif|png)$</tt></dt>
 729
 730             <dd>
 731               <p>This is very much the same as above, except now it must end
 732               in either <span class="QUOTE">".jpg"</span>, <span class=
 733               "QUOTE">".jpeg"</span>, <span class="QUOTE">".gif"</span> or
 734               <span class="QUOTE">".png"</span>. So this one is limited to
 735               common image formats.</p>
 736             </dd>
 737           </dl>
 738         </div>
 739
 740         <p>There are many, many good examples to be found in <tt class=
 741         "FILENAME">default.action</tt>, and more tutorials below in <a href=
 742         "appendix.html#REGEX">Appendix on regular expressions</a>.</p>
 743       </div>
 744
 745       <div class="SECT3">
 746         <h3 class="SECT3"><a name="TAG-PATTERN" id="TAG-PATTERN">8.4.3. The
 747         Tag Pattern</a></h3>
 748
 749         <p>Tag patterns are used to change the applying actions based on the
 750         request's tags. Tags can be created with either the <a href=
 751         "actions-file.html#CLIENT-HEADER-TAGGER">client-header-tagger</a> or
 752         the <a href=
 753         "actions-file.html#SERVER-HEADER-TAGGER">server-header-tagger</a>
 754         action.</p>
 755
 756         <p>Tag patterns have to start with <span class="QUOTE">"TAG:"</span>,
 757         so <span class="APPLICATION">Privoxy</span> can tell them apart from
 758         URL patterns. Everything after the colon including white space, is
 759         interpreted as a regular expression with path pattern syntax, except
 760         that tag patterns aren't left-anchored automatically (<span class=
 761         "APPLICATION">Privoxy</span> doesn't silently add a <span class=
 762         "QUOTE">"^"</span>, you have to do it yourself if you need it).</p>
 763
 764         <p>To match all requests that are tagged with <span class=
 765         "QUOTE">"foo"</span> your pattern line should be <span class=
 766         "QUOTE">"TAG:^foo$"</span>, <span class="QUOTE">"TAG:foo"</span>
 767         would work as well, but it would also match requests whose tags
 768         contain <span class="QUOTE">"foo"</span> somewhere. <span class=
 769         "QUOTE">"TAG: foo"</span> wouldn't work as it requires white
 770         space.</p>
 771
 772         <p>Sections can contain URL and tag patterns at the same time, but
 773         tag patterns are checked after the URL patterns and thus always
 774         overrule them, even if they are located before the URL patterns.</p>
 775
 776         <p>Once a new tag is added, Privoxy checks right away if it's matched
 777         by one of the tag patterns and updates the action settings
 778         accordingly. As a result tags can be used to activate other tagger
 779         actions, as long as these other taggers look for headers that haven't
 780         already be parsed.</p>
 781
 782         <p>For example you could tag client requests which use the <tt class=
 783         "LITERAL">POST</tt> method, then use this tag to activate another
 784         tagger that adds a tag if cookies are sent, and then use a block
 785         action based on the cookie tag. This allows the outcome of one
 786         action, to be input into a subsequent action. However if you'd
 787         reverse the position of the described taggers, and activated the
 788         method tagger based on the cookie tagger, no method tags would be
 789         created. The method tagger would look for the request line, but at
 790         the time the cookie tag is created, the request line has already been
 791         parsed.</p>
 792
 793         <p>While this is a limitation you should be aware of, this kind of
 794         indirection is seldom needed anyway and even the example doesn't make
 795         too much sense.</p>
 796       </div>
 797
 798       <div class="SECT3">
 799         <h3 class="SECT3"><a name="NEGATIVE-TAG-PATTERNS" id=
 800         "NEGATIVE-TAG-PATTERNS">8.4.4. The Negative Tag Patterns</a></h3>
 801
 802         <p>To match requests that do not have a certain tag, specify a
 803         negative tag pattern by prefixing the tag pattern line with either
 804         <span class="QUOTE">"NO-REQUEST-TAG:"</span> or <span class=
 805         "QUOTE">"NO-RESPONSE-TAG:"</span> instead of <span class=
 806         "QUOTE">"TAG:"</span>.</p>
 807
 808         <p>Negative tag patterns created with <span class=
 809         "QUOTE">"NO-REQUEST-TAG:"</span> are checked after all client headers
 810         are scanned, the ones created with <span class=
 811         "QUOTE">"NO-RESPONSE-TAG:"</span> are checked after all server
 812         headers are scanned. In both cases all the created tags are
 813         considered.</p>
 814       </div>
 815     </div>
 816
 817     <div class="SECT2">
 818       <h2 class="SECT2"><a name="ACTIONS" id="ACTIONS">8.5. Actions</a></h2>
 819
 820       <p>All actions are disabled by default, until they are explicitly
 821       enabled somewhere in an actions file. Actions are turned on if preceded
 822       with a <span class="QUOTE">"+"</span>, and turned off if preceded with
 823       a <span class="QUOTE">"-"</span>. So a <tt class="LITERAL">+action</tt>
 824       means <span class="QUOTE">"do that action"</span>, e.g. <tt class=
 825       "LITERAL">+block</tt> means <span class="QUOTE">"please block URLs that
 826       match the following patterns"</span>, and <tt class=
 827       "LITERAL">-block</tt> means <span class="QUOTE">"don't block URLs that
 828       match the following patterns, even if <tt class="LITERAL">+block</tt>
 829       previously applied."</span></p>
 830
 831       <p>Again, actions are invoked by placing them on a line, enclosed in
 832       curly braces and separated by whitespace, like in <tt class=
 833       "LITERAL">{+some-action -some-other-action{some-parameter}}</tt>,
 834       followed by a list of URL patterns, one per line, to which they apply.
 835       Together, the actions line and the following pattern lines make up a
 836       section of the actions file.</p>
 837
 838       <p>Actions fall into three categories:</p>
 839
 840       <ul>
 841         <li>
 842           <p>Boolean, i.e the action can only be <span class=
 843           "QUOTE">"enabled"</span> or <span class="QUOTE">"disabled"</span>.
 844           Syntax:</p>
 845
 846           <table border="0" bgcolor="#E0E0E0" width="90%">
 847             <tr>
 848               <td>
 849                 <pre class="SCREEN">
 850   +<tt class="REPLACEABLE"><i>name</i></tt>        # enable action <tt class=
 851 "REPLACEABLE"><i>name</i></tt>
 852   -<tt class=
 853 "REPLACEABLE"><i>name</i></tt>        # disable action <tt class="REPLACEABLE"><i>name</i></tt>
 854 </pre>
 855               </td>
 856             </tr>
 857           </table>
 858
 859           <p>Example: <tt class="LITERAL">+handle-as-image</tt></p>
 860         </li>
 861
 862         <li>
 863           <p>Parameterized, where some value is required in order to enable
 864           this type of action. Syntax:</p>
 865
 866           <table border="0" bgcolor="#E0E0E0" width="90%">
 867             <tr>
 868               <td>
 869                 <pre class="SCREEN">
 870   +<tt class="REPLACEABLE"><i>name</i></tt>{<tt class=
 871 "REPLACEABLE"><i>param</i></tt>}  # enable action and set parameter to <tt class="REPLACEABLE"><i>param</i></tt>,
 872                # overwriting parameter from previous match if necessary
 873   -<tt class=
 874 "REPLACEABLE"><i>name</i></tt>         # disable action. The parameter can be omitted
 875 </pre>
 876               </td>
 877             </tr>
 878           </table>
 879
 880           <p>Note that if the URL matches multiple positive forms of a
 881           parameterized action, the last match wins, i.e. the params from
 882           earlier matches are simply ignored.</p>
 883
 884           <p>Example: <tt class="LITERAL">+hide-user-agent{Mozilla/5.0 (X11;
 885           U; FreeBSD i386; en-US; rv:1.8.1.4) Gecko/20070602
 886           Firefox/2.0.0.4}</tt></p>
 887         </li>
 888
 889         <li>
 890           <p>Multi-value. These look exactly like parameterized actions, but
 891           they behave differently: If the action applies multiple times to
 892           the same URL, but with different parameters, <span class=
 893           "emphasis"><i class="EMPHASIS">all</i></span> the parameters from
 894           <span class="emphasis"><i class="EMPHASIS">all</i></span> matches
 895           are remembered. This is used for actions that can be executed for
 896           the same request repeatedly, like adding multiple headers, or
 897           filtering through multiple filters. Syntax:</p>
 898
 899           <table border="0" bgcolor="#E0E0E0" width="90%">
 900             <tr>
 901               <td>
 902                 <pre class="SCREEN">
 903   +<tt class="REPLACEABLE"><i>name</i></tt>{<tt class=
 904 "REPLACEABLE"><i>param</i></tt>}   # enable action and add <tt class=
 905 "REPLACEABLE"><i>param</i></tt> to the list of parameters
 906   -<tt class="REPLACEABLE"><i>name</i></tt>{<tt class=
 907 "REPLACEABLE"><i>param</i></tt>}   # remove the parameter <tt class=
 908 "REPLACEABLE"><i>param</i></tt> from the list of parameters
 909                 # If it was the last one left, disable the action.
 910   <tt class=
 911 "REPLACEABLE"><i>-name</i></tt>          # disable this action completely and remove all parameters from the list
 912 </pre>
 913               </td>
 914             </tr>
 915           </table>
 916
 917           <p>Examples: <tt class="LITERAL">+add-header{X-Fun-Header: Some
 918           text}</tt> and <tt class=
 919           "LITERAL">+filter{html-annoyances}</tt></p>
 920         </li>
 921       </ul>
 922
 923       <p>If nothing is specified in any actions file, no <span class=
 924       "QUOTE">"actions"</span> are taken. So in this case <span class=
 925       "APPLICATION">Privoxy</span> would just be a normal, non-blocking,
 926       non-filtering proxy. You must specifically enable the privacy and
 927       blocking features you need (although the provided default actions files
 928       will give a good starting point).</p>
 929
 930       <p>Later defined action sections always over-ride earlier ones of the
 931       same type. So exceptions to any rules you make, should come in the
 932       latter part of the file (or in a file that is processed later when
 933       using multiple actions files such as <tt class=
 934       "FILENAME">user.action</tt>). For multi-valued actions, the actions are
 935       applied in the order they are specified. Actions files are processed in
 936       the order they are defined in <tt class="FILENAME">config</tt> (the
 937       default installation has three actions files). It also quite possible
 938       for any given URL to match more than one <span class=
 939       "QUOTE">"pattern"</span> (because of wildcards and regular
 940       expressions), and thus to trigger more than one set of actions! Last
 941       match wins.</p>
 942
 943       <p>The list of valid <span class="APPLICATION">Privoxy</span> actions
 944       are:</p>
 945
 946       <div class="SECT3">
 947         <h4 class="SECT3"><a name="ADD-HEADER" id="ADD-HEADER">8.5.1.
 948         add-header</a></h4>
 949
 950         <div class="VARIABLELIST">
 951           <dl>
 952             <dt>Typical use:</dt>
 953
 954             <dd>
 955               <p>Confuse log analysis, custom applications</p>
 956             </dd>
 957
 958             <dt>Effect:</dt>
 959
 960             <dd>
 961               <p>Sends a user defined HTTP header to the web server.</p>
 962             </dd>
 963
 964             <dt>Type:</dt>
 965
 966             <dd>
 967               <p>Multi-value.</p>
 968             </dd>
 969
 970             <dt>Parameter:</dt>
 971
 972             <dd>
 973               <p>Any string value is possible. Validity of the defined HTTP
 974               headers is not checked. It is recommended that you use the
 975               <span class="QUOTE">"<tt class="LITERAL">X-</tt>"</span> prefix
 976               for custom headers.</p>
 977             </dd>
 978
 979             <dt>Notes:</dt>
 980
 981             <dd>
 982               <p>This action may be specified multiple times, in order to
 983               define multiple headers. This is rarely needed for the typical
 984               user. If you don't know what <span class="QUOTE">"HTTP
 985               headers"</span> are, you definitely don't need to worry about
 986               this one.</p>
 987
 988               <p>Headers added by this action are not modified by other
 989               actions.</p>
 990             </dd>
 991
 992             <dt>Example usage:</dt>
 993
 994             <dd>
 995               <table border="0" bgcolor="#E0E0E0" width="90%">
 996                 <tr>
 997                   <td>
 998                     <pre class="SCREEN">
 999 +add-header{X-User-Tracking: sucks}
1000 </pre>
1001                   </td>
1002                 </tr>
1003               </table>
1004             </dd>
1005           </dl>
1006         </div>
1007       </div>
1008
1009       <div class="SECT3">
1010         <h4 class="SECT3"><a name="BLOCK" id="BLOCK">8.5.2. block</a></h4>
1011
1012         <div class="VARIABLELIST">
1013           <dl>
1014             <dt>Typical use:</dt>
1015
1016             <dd>
1017               <p>Block ads or other unwanted content</p>
1018             </dd>
1019
1020             <dt>Effect:</dt>
1021
1022             <dd>
1023               <p>Requests for URLs to which this action applies are blocked,
1024               i.e. the requests are trapped by <span class=
1025               "APPLICATION">Privoxy</span> and the requested URL is never
1026               retrieved, but is answered locally with a substitute page or
1027               image, as determined by the <tt class="LITERAL"><a href=
1028               "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a></tt>,
1029               <tt class="LITERAL"><a href=
1030               "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a></tt>,
1031               and <tt class="LITERAL"><a href=
1032               "actions-file.html#HANDLE-AS-EMPTY-DOCUMENT">handle-as-empty-document</a></tt>
1033               actions.</p>
1034             </dd>
1035
1036             <dt>Type:</dt>
1037
1038             <dd>
1039               <p>Parameterized.</p>
1040             </dd>
1041
1042             <dt>Parameter:</dt>
1043
1044             <dd>
1045               <p>A block reason that should be given to the user.</p>
1046             </dd>
1047
1048             <dt>Notes:</dt>
1049
1050             <dd>
1051               <p><span class="APPLICATION">Privoxy</span> sends a special
1052               <span class="QUOTE">"BLOCKED"</span> page for requests to
1053               blocked pages. This page contains the block reason given as
1054               parameter, a link to find out why the block action applies, and
1055               a click-through to the blocked content (the latter only if the
1056               force feature is available and enabled).</p>
1057
1058               <p>A very important exception occurs if <span class=
1059               "emphasis"><i class="EMPHASIS">both</i></span> <tt class=
1060               "LITERAL">block</tt> and <tt class="LITERAL"><a href=
1061               "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a></tt>,
1062               apply to the same request: it will then be replaced by an
1063               image. If <tt class="LITERAL"><a href=
1064               "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a></tt>
1065               (see below) also applies, the type of image will be determined
1066               by its parameter, if not, the standard checkerboard pattern is
1067               sent.</p>
1068
1069               <p>It is important to understand this process, in order to
1070               understand how <span class="APPLICATION">Privoxy</span> deals
1071               with ads and other unwanted content. Blocking is a core
1072               feature, and one upon which various other features depend.</p>
1073
1074               <p>The <tt class="LITERAL"><a href=
1075               "actions-file.html#FILTER">filter</a></tt> action can perform a
1076               very similar task, by <span class="QUOTE">"blocking"</span>
1077               banner images and other content through rewriting the relevant
1078               URLs in the document's HTML source, so they don't get requested
1079               in the first place. Note that this is a totally different
1080               technique, and it's easy to confuse the two.</p>
1081             </dd>
1082
1083             <dt>Example usage (section):</dt>
1084
1085             <dd>
1086               <table border="0" bgcolor="#E0E0E0" width="90%">
1087                 <tr>
1088                   <td>
1089                     <pre class="SCREEN">
1090 {+block{No nasty stuff for you.}}
1091 # Block and replace with "blocked" page
1092  .nasty-stuff.example.com
1093
1094 {+block{Doubleclick banners.} +handle-as-image}
1095 # Block and replace with image
1096  .ad.doubleclick.net
1097  .ads.r.us/banners/
1098
1099 {+block{Layered ads.} +handle-as-empty-document}
1100 # Block and then ignore
1101  adserver.example.net/.*\.js$
1102 </pre>
1103                   </td>
1104                 </tr>
1105               </table>
1106             </dd>
1107           </dl>
1108         </div>
1109       </div>
1110
1111       <div class="SECT3">
1112         <h4 class="SECT3"><a name="CHANGE-X-FORWARDED-FOR" id=
1113         "CHANGE-X-FORWARDED-FOR">8.5.3. change-x-forwarded-for</a></h4>
1114
1115         <div class="VARIABLELIST">
1116           <dl>
1117             <dt>Typical use:</dt>
1118
1119             <dd>
1120               <p>Improve privacy by not forwarding the source of the request
1121               in the HTTP headers.</p>
1122             </dd>
1123
1124             <dt>Effect:</dt>
1125
1126             <dd>
1127               <p>Deletes the <span class="QUOTE">"X-Forwarded-For:"</span>
1128               HTTP header from the client request, or adds a new one.</p>
1129             </dd>
1130
1131             <dt>Type:</dt>
1132
1133             <dd>
1134               <p>Parameterized.</p>
1135             </dd>
1136
1137             <dt>Parameter:</dt>
1138
1139             <dd>
1140               <ul>
1141                 <li>
1142                   <p><span class="QUOTE">"block"</span> to delete the
1143                   header.</p>
1144                 </li>
1145
1146                 <li>
1147                   <p><span class="QUOTE">"add"</span> to create the header
1148                   (or append the client's IP address to an already existing
1149                   one).</p>
1150                 </li>
1151               </ul>
1152             </dd>
1153
1154             <dt>Notes:</dt>
1155
1156             <dd>
1157               <p>It is safe and recommended to use <tt class=
1158               "LITERAL">block</tt>.</p>
1159
1160               <p>Forwarding the source address of the request may make sense
1161               in some multi-user setups but is also a privacy risk.</p>
1162             </dd>
1163
1164             <dt>Example usage:</dt>
1165
1166             <dd>
1167               <table border="0" bgcolor="#E0E0E0" width="90%">
1168                 <tr>
1169                   <td>
1170                     <pre class="SCREEN">
1171 +change-x-forwarded-for{block}
1172 </pre>
1173                   </td>
1174                 </tr>
1175               </table>
1176             </dd>
1177           </dl>
1178         </div>
1179       </div>
1180
1181       <div class="SECT3">
1182         <h4 class="SECT3"><a name="CLIENT-HEADER-FILTER" id=
1183         "CLIENT-HEADER-FILTER">8.5.4. client-header-filter</a></h4>
1184
1185         <div class="VARIABLELIST">
1186           <dl>
1187             <dt>Typical use:</dt>
1188
1189             <dd>
1190               <p>Rewrite or remove single client headers.</p>
1191             </dd>
1192
1193             <dt>Effect:</dt>
1194
1195             <dd>
1196               <p>All client headers to which this action applies are filtered
1197               on-the-fly through the specified regular expression based
1198               substitutions.</p>
1199             </dd>
1200
1201             <dt>Type:</dt>
1202
1203             <dd>
1204               <p>Parameterized.</p>
1205             </dd>
1206
1207             <dt>Parameter:</dt>
1208
1209             <dd>
1210               <p>The name of a client-header filter, as defined in one of the
1211               <a href="filter-file.html">filter files</a>.</p>
1212             </dd>
1213
1214             <dt>Notes:</dt>
1215
1216             <dd>
1217               <p>Client-header filters are applied to each header on its own,
1218               not to all at once. This makes it easier to diagnose problems,
1219               but on the downside you can't write filters that only change
1220               header x if header y's value is z. You can do that by using
1221               tags though.</p>
1222
1223               <p>Client-header filters are executed after the other header
1224               actions have finished and use their output as input.</p>
1225
1226               <p>If the request URI gets changed, <span class=
1227               "APPLICATION">Privoxy</span> will detect that and use the new
1228               one. This can be used to rewrite the request destination behind
1229               the client's back, for example to specify a Tor exit relay for
1230               certain requests.</p>
1231
1232               <p>Please refer to the <a href="filter-file.html">filter file
1233               chapter</a> to learn which client-header filters are available
1234               by default, and how to create your own.</p>
1235             </dd>
1236
1237             <dt>Example usage (section):</dt>
1238
1239             <dd>
1240               <table border="0" bgcolor="#E0E0E0" width="90%">
1241                 <tr>
1242                   <td>
1243                     <pre class="SCREEN">
1244 # Hide Tor exit notation in Host and Referer Headers
1245 {+client-header-filter{hide-tor-exit-notation}}
1246 /
1247
1248 </pre>
1249                   </td>
1250                 </tr>
1251               </table>
1252             </dd>
1253           </dl>
1254         </div>
1255       </div>
1256
1257       <div class="SECT3">
1258         <h4 class="SECT3"><a name="CLIENT-HEADER-TAGGER" id=
1259         "CLIENT-HEADER-TAGGER">8.5.5. client-header-tagger</a></h4>
1260
1261         <div class="VARIABLELIST">
1262           <dl>
1263             <dt>Typical use:</dt>
1264
1265             <dd>
1266               <p>Block requests based on their headers.</p>
1267             </dd>
1268
1269             <dt>Effect:</dt>
1270
1271             <dd>
1272               <p>Client headers to which this action applies are filtered
1273               on-the-fly through the specified regular expression based
1274               substitutions, the result is used as tag.</p>
1275             </dd>
1276
1277             <dt>Type:</dt>
1278
1279             <dd>
1280               <p>Parameterized.</p>
1281             </dd>
1282
1283             <dt>Parameter:</dt>
1284
1285             <dd>
1286               <p>The name of a client-header tagger, as defined in one of the
1287               <a href="filter-file.html">filter files</a>.</p>
1288             </dd>
1289
1290             <dt>Notes:</dt>
1291
1292             <dd>
1293               <p>Client-header taggers are applied to each header on its own,
1294               and as the header isn't modified, each tagger <span class=
1295               "QUOTE">"sees"</span> the original.</p>
1296
1297               <p>Client-header taggers are the first actions that are
1298               executed and their tags can be used to control every other
1299               action.</p>
1300             </dd>
1301
1302             <dt>Example usage (section):</dt>
1303
1304             <dd>
1305               <table border="0" bgcolor="#E0E0E0" width="90%">
1306                 <tr>
1307                   <td>
1308                     <pre class="SCREEN">
1309 # Tag every request with the User-Agent header
1310 {+client-header-tagger{user-agent}}
1311 /
1312
1313 # Tagging itself doesn't change the action
1314 # settings, sections with TAG patterns do:
1315 #
1316 # If it's a download agent, use a different forwarding proxy,
1317 # show the real User-Agent and make sure resume works.
1318 {+forward-override{forward-socks5 10.0.0.2:2222 .} \
1319  -hide-if-modified-since      \
1320  -overwrite-last-modified     \
1321  -hide-user-agent             \
1322  -filter                      \
1323  -deanimate-gifs              \
1324 }
1325 TAG:^User-Agent: NetBSD-ftp/
1326 TAG:^User-Agent: Novell ZYPP Installer
1327 TAG:^User-Agent: RPM APT-HTTP/
1328 TAG:^User-Agent: fetch libfetch/
1329 TAG:^User-Agent: Ubuntu APT-HTTP/
1330 TAG:^User-Agent: MPlayer/
1331
1332 </pre>
1333                   </td>
1334                 </tr>
1335               </table>
1336
1337               <table border="0" bgcolor="#E0E0E0" width="90%">
1338                 <tr>
1339                   <td>
1340                     <pre class="SCREEN">
1341 # Tag all requests with the Range header set
1342 {+client-header-tagger{range-requests}}
1343 /
1344
1345 # Disable filtering for the tagged requests.
1346 #
1347 # With filtering enabled Privoxy would remove the Range headers
1348 # to be able to filter the whole response. The downside is that
1349 # it prevents clients from resuming downloads or skipping over
1350 # parts of multimedia files.
1351 {-filter -deanimate-gifs}
1352 TAG:^RANGE-REQUEST$
1353
1354 </pre>
1355                   </td>
1356                 </tr>
1357               </table>
1358             </dd>
1359           </dl>
1360         </div>
1361       </div>
1362
1363       <div class="SECT3">
1364         <h4 class="SECT3"><a name="CONTENT-TYPE-OVERWRITE" id=
1365         "CONTENT-TYPE-OVERWRITE">8.5.6. content-type-overwrite</a></h4>
1366
1367         <div class="VARIABLELIST">
1368           <dl>
1369             <dt>Typical use:</dt>
1370
1371             <dd>
1372               <p>Stop useless download menus from popping up, or change the
1373               browser's rendering mode</p>
1374             </dd>
1375
1376             <dt>Effect:</dt>
1377
1378             <dd>
1379               <p>Replaces the <span class="QUOTE">"Content-Type:"</span> HTTP
1380               server header.</p>
1381             </dd>
1382
1383             <dt>Type:</dt>
1384
1385             <dd>
1386               <p>Parameterized.</p>
1387             </dd>
1388
1389             <dt>Parameter:</dt>
1390
1391             <dd>
1392               <p>Any string.</p>
1393             </dd>
1394
1395             <dt>Notes:</dt>
1396
1397             <dd>
1398               <p>The <span class="QUOTE">"Content-Type:"</span> HTTP server
1399               header is used by the browser to decide what to do with the
1400               document. The value of this header can cause the browser to
1401               open a download menu instead of displaying the document by
1402               itself, even if the document's format is supported by the
1403               browser.</p>
1404
1405               <p>The declared content type can also affect which rendering
1406               mode the browser chooses. If XHTML is delivered as <span class=
1407               "QUOTE">"text/html"</span>, many browsers treat it as yet
1408               another broken HTML document. If it is send as <span class=
1409               "QUOTE">"application/xml"</span>, browsers with XHTML support
1410               will only display it, if the syntax is correct.</p>
1411
1412               <p>If you see a web site that proudly uses XHTML buttons, but
1413               sets <span class="QUOTE">"Content-Type: text/html"</span>, you
1414               can use <span class="APPLICATION">Privoxy</span> to overwrite
1415               it with <span class="QUOTE">"application/xml"</span> and
1416               validate the web master's claim inside your XHTML-supporting
1417               browser. If the syntax is incorrect, the browser will complain
1418               loudly.</p>
1419
1420               <p>You can also go the opposite direction: if your browser
1421               prints error messages instead of rendering a document falsely
1422               declared as XHTML, you can overwrite the content type with
1423               <span class="QUOTE">"text/html"</span> and have it rendered as
1424               broken HTML document.</p>
1425
1426               <p>By default <tt class="LITERAL">content-type-overwrite</tt>
1427               only replaces <span class="QUOTE">"Content-Type:"</span>
1428               headers that look like some kind of text. If you want to
1429               overwrite it unconditionally, you have to combine it with
1430               <tt class="LITERAL"><a href=
1431               "actions-file.html#FORCE-TEXT-MODE">force-text-mode</a></tt>.
1432               This limitation exists for a reason, think twice before
1433               circumventing it.</p>
1434
1435               <p>Most of the time it's easier to replace this action with a
1436               custom <tt class="LITERAL"><a href=
1437               "actions-file.html#SERVER-HEADER-FILTER">server-header
1438               filter</a></tt>. It allows you to activate it for every
1439               document of a certain site and it will still only replace the
1440               content types you aimed at.</p>
1441
1442               <p>Of course you can apply <tt class=
1443               "LITERAL">content-type-overwrite</tt> to a whole site and then
1444               make URL based exceptions, but it's a lot more work to get the
1445               same precision.</p>
1446             </dd>
1447
1448             <dt>Example usage (sections):</dt>
1449
1450             <dd>
1451               <table border="0" bgcolor="#E0E0E0" width="90%">
1452                 <tr>
1453                   <td>
1454                     <pre class="SCREEN">
1455 # Check if www.example.net/ really uses valid XHTML
1456 { +content-type-overwrite{application/xml} }
1457 www.example.net/
1458
1459 # but leave the content type unmodified if the URL looks like a style sheet
1460 {-content-type-overwrite}
1461 www.example.net/.*\.css$
1462 www.example.net/.*style
1463 </pre>
1464                   </td>
1465                 </tr>
1466               </table>
1467             </dd>
1468           </dl>
1469         </div>
1470       </div>
1471
1472       <div class="SECT3">
1473         <h4 class="SECT3"><a name="CRUNCH-CLIENT-HEADER" id=
1474         "CRUNCH-CLIENT-HEADER">8.5.7. crunch-client-header</a></h4>
1475
1476         <div class="VARIABLELIST">
1477           <dl>
1478             <dt>Typical use:</dt>
1479
1480             <dd>
1481               <p>Remove a client header <span class=
1482               "APPLICATION">Privoxy</span> has no dedicated action for.</p>
1483             </dd>
1484
1485             <dt>Effect:</dt>
1486
1487             <dd>
1488               <p>Deletes every header sent by the client that contains the
1489               string the user supplied as parameter.</p>
1490             </dd>
1491
1492             <dt>Type:</dt>
1493
1494             <dd>
1495               <p>Parameterized.</p>
1496             </dd>
1497
1498             <dt>Parameter:</dt>
1499
1500             <dd>
1501               <p>Any string.</p>
1502             </dd>
1503
1504             <dt>Notes:</dt>
1505
1506             <dd>
1507               <p>This action allows you to block client headers for which no
1508               dedicated <span class="APPLICATION">Privoxy</span> action
1509               exists. <span class="APPLICATION">Privoxy</span> will remove
1510               every client header that contains the string you supplied as
1511               parameter.</p>
1512
1513               <p>Regular expressions are <span class="emphasis"><i class=
1514               "EMPHASIS">not supported</i></span> and you can't use this
1515               action to block different headers in the same request, unless
1516               they contain the same string.</p>
1517
1518               <p><tt class="LITERAL">crunch-client-header</tt> is only meant
1519               for quick tests. If you have to block several different
1520               headers, or only want to modify parts of them, you should use a
1521               <tt class="LITERAL"><a href=
1522               "actions-file.html#CLIENT-HEADER-FILTER">client-header
1523               filter</a></tt>.</p>
1524
1525               <div class="WARNING">
1526                 <table class="WARNING" border="1" width="90%">
1527                   <tr>
1528                     <td align="center"><b>Warning</b></td>
1529                   </tr>
1530
1531                   <tr>
1532                     <td align="left">
1533                       <p>Don't block any header without understanding the
1534                       consequences.</p>
1535                     </td>
1536                   </tr>
1537                 </table>
1538               </div>
1539             </dd>
1540
1541             <dt>Example usage (section):</dt>
1542
1543             <dd>
1544               <table border="0" bgcolor="#E0E0E0" width="90%">
1545                 <tr>
1546                   <td>
1547                     <pre class="SCREEN">
1548 # Block the non-existent "Privacy-Violation:" client header
1549 { +crunch-client-header{Privacy-Violation:} }
1550 /
1551
1552 </pre>
1553                   </td>
1554                 </tr>
1555               </table>
1556             </dd>
1557           </dl>
1558         </div>
1559       </div>
1560
1561       <div class="SECT3">
1562         <h4 class="SECT3"><a name="CRUNCH-IF-NONE-MATCH" id=
1563         "CRUNCH-IF-NONE-MATCH">8.5.8. crunch-if-none-match</a></h4>
1564
1565         <div class="VARIABLELIST">
1566           <dl>
1567             <dt>Typical use:</dt>
1568
1569             <dd>
1570               <p>Prevent yet another way to track the user's steps between
1571               sessions.</p>
1572             </dd>
1573
1574             <dt>Effect:</dt>
1575
1576             <dd>
1577               <p>Deletes the <span class="QUOTE">"If-None-Match:"</span> HTTP
1578               client header.</p>
1579             </dd>
1580
1581             <dt>Type:</dt>
1582
1583             <dd>
1584               <p>Boolean.</p>
1585             </dd>
1586
1587             <dt>Parameter:</dt>
1588
1589             <dd>
1590               <p>N/A</p>
1591             </dd>
1592
1593             <dt>Notes:</dt>
1594
1595             <dd>
1596               <p>Removing the <span class="QUOTE">"If-None-Match:"</span>
1597               HTTP client header is useful for filter testing, where you want
1598               to force a real reload instead of getting status code
1599               <span class="QUOTE">"304"</span> which would cause the browser
1600               to use a cached copy of the page.</p>
1601
1602               <p>It is also useful to make sure the header isn't used as a
1603               cookie replacement (unlikely but possible).</p>
1604
1605               <p>Blocking the <span class="QUOTE">"If-None-Match:"</span>
1606               header shouldn't cause any caching problems, as long as the
1607               <span class="QUOTE">"If-Modified-Since:"</span> header isn't
1608               blocked or missing as well.</p>
1609
1610               <p>It is recommended to use this action together with
1611               <tt class="LITERAL"><a href=
1612               "actions-file.html#HIDE-IF-MODIFIED-SINCE">hide-if-modified-since</a></tt>
1613               and <tt class="LITERAL"><a href=
1614               "actions-file.html#OVERWRITE-LAST-MODIFIED">overwrite-last-modified</a></tt>.</p>
1615             </dd>
1616
1617             <dt>Example usage (section):</dt>
1618
1619             <dd>
1620               <table border="0" bgcolor="#E0E0E0" width="90%">
1621                 <tr>
1622                   <td>
1623                     <pre class="SCREEN">
1624 # Let the browser revalidate cached documents but don't
1625 # allow the server to use the revalidation headers for user tracking.
1626 {+hide-if-modified-since{-60} \
1627  +overwrite-last-modified{randomize} \
1628  +crunch-if-none-match}
1629 /
1630 </pre>
1631                   </td>
1632                 </tr>
1633               </table>
1634             </dd>
1635           </dl>
1636         </div>
1637       </div>
1638
1639       <div class="SECT3">
1640         <h4 class="SECT3"><a name="CRUNCH-INCOMING-COOKIES" id=
1641         "CRUNCH-INCOMING-COOKIES">8.5.9. crunch-incoming-cookies</a></h4>
1642
1643         <div class="VARIABLELIST">
1644           <dl>
1645             <dt>Typical use:</dt>
1646
1647             <dd>
1648               <p>Prevent the web server from setting HTTP cookies on your
1649               system</p>
1650             </dd>
1651
1652             <dt>Effect:</dt>
1653
1654             <dd>
1655               <p>Deletes any <span class="QUOTE">"Set-Cookie:"</span> HTTP
1656               headers from server replies.</p>
1657             </dd>
1658
1659             <dt>Type:</dt>
1660
1661             <dd>
1662               <p>Boolean.</p>
1663             </dd>
1664
1665             <dt>Parameter:</dt>
1666
1667             <dd>
1668               <p>N/A</p>
1669             </dd>
1670
1671             <dt>Notes:</dt>
1672
1673             <dd>
1674               <p>This action is only concerned with <span class=
1675               "emphasis"><i class="EMPHASIS">incoming</i></span> HTTP
1676               cookies. For <span class="emphasis"><i class=
1677               "EMPHASIS">outgoing</i></span> HTTP cookies, use <tt class=
1678               "LITERAL"><a href=
1679               "actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a></tt>.
1680               Use <span class="emphasis"><i class="EMPHASIS">both</i></span>
1681               to disable HTTP cookies completely.</p>
1682
1683               <p>It makes <span class="emphasis"><i class="EMPHASIS">no sense
1684               at all</i></span> to use this action in conjunction with the
1685               <tt class="LITERAL"><a href=
1686               "actions-file.html#SESSION-COOKIES-ONLY">session-cookies-only</a></tt>
1687               action, since it would prevent the session cookies from being
1688               set. See also <tt class="LITERAL"><a href=
1689               "actions-file.html#FILTER-CONTENT-COOKIES">filter-content-cookies</a></tt>.</p>
1690             </dd>
1691
1692             <dt>Example usage:</dt>
1693
1694             <dd>
1695               <table border="0" bgcolor="#E0E0E0" width="90%">
1696                 <tr>
1697                   <td>
1698                     <pre class="SCREEN">
1699 +crunch-incoming-cookies
1700 </pre>
1701                   </td>
1702                 </tr>
1703               </table>
1704             </dd>
1705           </dl>
1706         </div>
1707       </div>
1708
1709       <div class="SECT3">
1710         <h4 class="SECT3"><a name="CRUNCH-SERVER-HEADER" id=
1711         "CRUNCH-SERVER-HEADER">8.5.10. crunch-server-header</a></h4>
1712
1713         <div class="VARIABLELIST">
1714           <dl>
1715             <dt>Typical use:</dt>
1716
1717             <dd>
1718               <p>Remove a server header <span class=
1719               "APPLICATION">Privoxy</span> has no dedicated action for.</p>
1720             </dd>
1721
1722             <dt>Effect:</dt>
1723
1724             <dd>
1725               <p>Deletes every header sent by the server that contains the
1726               string the user supplied as parameter.</p>
1727             </dd>
1728
1729             <dt>Type:</dt>
1730
1731             <dd>
1732               <p>Parameterized.</p>
1733             </dd>
1734
1735             <dt>Parameter:</dt>
1736
1737             <dd>
1738               <p>Any string.</p>
1739             </dd>
1740
1741             <dt>Notes:</dt>
1742
1743             <dd>
1744               <p>This action allows you to block server headers for which no
1745               dedicated <span class="APPLICATION">Privoxy</span> action
1746               exists. <span class="APPLICATION">Privoxy</span> will remove
1747               every server header that contains the string you supplied as
1748               parameter.</p>
1749
1750               <p>Regular expressions are <span class="emphasis"><i class=
1751               "EMPHASIS">not supported</i></span> and you can't use this
1752               action to block different headers in the same request, unless
1753               they contain the same string.</p>
1754
1755               <p><tt class="LITERAL">crunch-server-header</tt> is only meant
1756               for quick tests. If you have to block several different
1757               headers, or only want to modify parts of them, you should use a
1758               custom <tt class="LITERAL"><a href=
1759               "actions-file.html#SERVER-HEADER-FILTER">server-header
1760               filter</a></tt>.</p>
1761
1762               <div class="WARNING">
1763                 <table class="WARNING" border="1" width="90%">
1764                   <tr>
1765                     <td align="center"><b>Warning</b></td>
1766                   </tr>
1767
1768                   <tr>
1769                     <td align="left">
1770                       <p>Don't block any header without understanding the
1771                       consequences.</p>
1772                     </td>
1773                   </tr>
1774                 </table>
1775               </div>
1776             </dd>
1777
1778             <dt>Example usage (section):</dt>
1779
1780             <dd>
1781               <table border="0" bgcolor="#E0E0E0" width="90%">
1782                 <tr>
1783                   <td>
1784                     <pre class="SCREEN">
1785 # Crunch server headers that try to prevent caching
1786 { +crunch-server-header{no-cache} }
1787 /
1788 </pre>
1789                   </td>
1790                 </tr>
1791               </table>
1792             </dd>
1793           </dl>
1794         </div>
1795       </div>
1796
1797       <div class="SECT3">
1798         <h4 class="SECT3"><a name="CRUNCH-OUTGOING-COOKIES" id=
1799         "CRUNCH-OUTGOING-COOKIES">8.5.11. crunch-outgoing-cookies</a></h4>
1800
1801         <div class="VARIABLELIST">
1802           <dl>
1803             <dt>Typical use:</dt>
1804
1805             <dd>
1806               <p>Prevent the web server from reading any HTTP cookies from
1807               your system</p>
1808             </dd>
1809
1810             <dt>Effect:</dt>
1811
1812             <dd>
1813               <p>Deletes any <span class="QUOTE">"Cookie:"</span> HTTP
1814               headers from client requests.</p>
1815             </dd>
1816
1817             <dt>Type:</dt>
1818
1819             <dd>
1820               <p>Boolean.</p>
1821             </dd>
1822
1823             <dt>Parameter:</dt>
1824
1825             <dd>
1826               <p>N/A</p>
1827             </dd>
1828
1829             <dt>Notes:</dt>
1830
1831             <dd>
1832               <p>This action is only concerned with <span class=
1833               "emphasis"><i class="EMPHASIS">outgoing</i></span> HTTP
1834               cookies. For <span class="emphasis"><i class=
1835               "EMPHASIS">incoming</i></span> HTTP cookies, use <tt class=
1836               "LITERAL"><a href=
1837               "actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a></tt>.
1838               Use <span class="emphasis"><i class="EMPHASIS">both</i></span>
1839               to disable HTTP cookies completely.</p>
1840
1841               <p>It makes <span class="emphasis"><i class="EMPHASIS">no sense
1842               at all</i></span> to use this action in conjunction with the
1843               <tt class="LITERAL"><a href=
1844               "actions-file.html#SESSION-COOKIES-ONLY">session-cookies-only</a></tt>
1845               action, since it would prevent the session cookies from being
1846               read.</p>
1847             </dd>
1848
1849             <dt>Example usage:</dt>
1850
1851             <dd>
1852               <table border="0" bgcolor="#E0E0E0" width="90%">
1853                 <tr>
1854                   <td>
1855                     <pre class="SCREEN">
1856 +crunch-outgoing-cookies
1857 </pre>
1858                   </td>
1859                 </tr>
1860               </table>
1861             </dd>
1862           </dl>
1863         </div>
1864       </div>
1865
1866       <div class="SECT3">
1867         <h4 class="SECT3"><a name="DEANIMATE-GIFS" id=
1868         "DEANIMATE-GIFS">8.5.12. deanimate-gifs</a></h4>
1869
1870         <div class="VARIABLELIST">
1871           <dl>
1872             <dt>Typical use:</dt>
1873
1874             <dd>
1875               <p>Stop those annoying, distracting animated GIF images.</p>
1876             </dd>
1877
1878             <dt>Effect:</dt>
1879
1880             <dd>
1881               <p>De-animate GIF animations, i.e. reduce them to their first
1882               or last image.</p>
1883             </dd>
1884
1885             <dt>Type:</dt>
1886
1887             <dd>
1888               <p>Parameterized.</p>
1889             </dd>
1890
1891             <dt>Parameter:</dt>
1892
1893             <dd>
1894               <p><span class="QUOTE">"last"</span> or <span class=
1895               "QUOTE">"first"</span></p>
1896             </dd>
1897
1898             <dt>Notes:</dt>
1899
1900             <dd>
1901               <p>This will also shrink the images considerably (in bytes, not
1902               pixels!). If the option <span class="QUOTE">"first"</span> is
1903               given, the first frame of the animation is used as the
1904               replacement. If <span class="QUOTE">"last"</span> is given, the
1905               last frame of the animation is used instead, which probably
1906               makes more sense for most banner animations, but also has the
1907               risk of not showing the entire last frame (if it is only a
1908               delta to an earlier frame).</p>
1909
1910               <p>You can safely use this action with patterns that will also
1911               match non-GIF objects, because no attempt will be made at
1912               anything that doesn't look like a GIF.</p>
1913             </dd>
1914
1915             <dt>Example usage:</dt>
1916
1917             <dd>
1918               <table border="0" bgcolor="#E0E0E0" width="90%">
1919                 <tr>
1920                   <td>
1921                     <pre class="SCREEN">
1922 +deanimate-gifs{last}
1923 </pre>
1924                   </td>
1925                 </tr>
1926               </table>
1927             </dd>
1928           </dl>
1929         </div>
1930       </div>
1931
1932       <div class="SECT3">
1933         <h4 class="SECT3"><a name="DOWNGRADE-HTTP-VERSION" id=
1934         "DOWNGRADE-HTTP-VERSION">8.5.13. downgrade-http-version</a></h4>
1935
1936         <div class="VARIABLELIST">
1937           <dl>
1938             <dt>Typical use:</dt>
1939
1940             <dd>
1941               <p>Work around (very rare) problems with HTTP/1.1</p>
1942             </dd>
1943
1944             <dt>Effect:</dt>
1945
1946             <dd>
1947               <p>Downgrades HTTP/1.1 client requests and server replies to
1948               HTTP/1.0.</p>
1949             </dd>
1950
1951             <dt>Type:</dt>
1952
1953             <dd>
1954               <p>Boolean.</p>
1955             </dd>
1956
1957             <dt>Parameter:</dt>
1958
1959             <dd>
1960               <p>N/A</p>
1961             </dd>
1962
1963             <dt>Notes:</dt>
1964
1965             <dd>
1966               <p>This is a left-over from the time when <span class=
1967               "APPLICATION">Privoxy</span> didn't support important HTTP/1.1
1968               features well. It is left here for the unlikely case that you
1969               experience HTTP/1.1-related problems with some server out
1970               there.</p>
1971
1972               <p>Note that enabling this action is only a workaround. It
1973               should not be enabled for sites that work without it. While it
1974               shouldn't break any pages, it has an (usually negative)
1975               performance impact.</p>
1976
1977               <p>If you come across a site where enabling this action helps,
1978               please report it, so the cause of the problem can be analyzed.
1979               If the problem turns out to be caused by a bug in <span class=
1980               "APPLICATION">Privoxy</span> it should be fixed so the
1981               following release works without the work around.</p>
1982             </dd>
1983
1984             <dt>Example usage (section):</dt>
1985
1986             <dd>
1987               <table border="0" bgcolor="#E0E0E0" width="90%">
1988                 <tr>
1989                   <td>
1990                     <pre class="SCREEN">
1991 {+downgrade-http-version}
1992 problem-host.example.com
1993 </pre>
1994                   </td>
1995                 </tr>
1996               </table>
1997             </dd>
1998           </dl>
1999         </div>
2000       </div>
2001
2002       <div class="SECT3">
2003         <h4 class="SECT3"><a name="FAST-REDIRECTS" id=
2004         "FAST-REDIRECTS">8.5.14. fast-redirects</a></h4>
2005
2006         <div class="VARIABLELIST">
2007           <dl>
2008             <dt>Typical use:</dt>
2009
2010             <dd>
2011               <p>Fool some click-tracking scripts and speed up indirect
2012               links.</p>
2013             </dd>
2014
2015             <dt>Effect:</dt>
2016
2017             <dd>
2018               <p>Detects redirection URLs and redirects the browser without
2019               contacting the redirection server first.</p>
2020             </dd>
2021
2022             <dt>Type:</dt>
2023
2024             <dd>
2025               <p>Parameterized.</p>
2026             </dd>
2027
2028             <dt>Parameter:</dt>
2029
2030             <dd>
2031               <ul>
2032                 <li>
2033                   <p><span class="QUOTE">"simple-check"</span> to just search
2034                   for the string <span class="QUOTE">"http://"</span> to
2035                   detect redirection URLs.</p>
2036                 </li>
2037
2038                 <li>
2039                   <p><span class="QUOTE">"check-decoded-url"</span> to decode
2040                   URLs (if necessary) before searching for redirection
2041                   URLs.</p>
2042                 </li>
2043               </ul>
2044             </dd>
2045
2046             <dt>Notes:</dt>
2047
2048             <dd>
2049               <p>Many sites, like yahoo.com, don't just link to other sites.
2050               Instead, they will link to some script on their own servers,
2051               giving the destination as a parameter, which will then redirect
2052               you to the final target. URLs resulting from this scheme
2053               typically look like: <span class=
2054               "QUOTE">"http://www.example.org/click-tracker.cgi?target=http%3a//www.example.net/"</span>.</p>
2055
2056               <p>Sometimes, there are even multiple consecutive redirects
2057               encoded in the URL. These redirections via scripts make your
2058               web browsing more traceable, since the server from which you
2059               follow such a link can see where you go to. Apart from that,
2060               valuable bandwidth and time is wasted, while your browser asks
2061               the server for one redirect after the other. Plus, it feeds the
2062               advertisers.</p>
2063
2064               <p>This feature is currently not very smart and is scheduled
2065               for improvement. If it is enabled by default, you will have to
2066               create some exceptions to this action. It can lead to failures
2067               in several ways:</p>
2068
2069               <p>Not every URLs with other URLs as parameters is evil. Some
2070               sites offer a real service that requires this information to
2071               work. For example a validation service needs to know, which
2072               document to validate. <tt class="LITERAL">fast-redirects</tt>
2073               assumes that every URL parameter that looks like another URL is
2074               a redirection target, and will always redirect to the last one.
2075               Most of the time the assumption is correct, but if it isn't,
2076               the user gets redirected anyway.</p>
2077
2078               <p>Another failure occurs if the URL contains other parameters
2079               after the URL parameter. The URL: <span class=
2080               "QUOTE">"http://www.example.org/?redirect=http%3a//www.example.net/&amp;foo=bar"</span>.
2081               contains the redirection URL <span class=
2082               "QUOTE">"http://www.example.net/"</span>, followed by another
2083               parameter. <tt class="LITERAL">fast-redirects</tt> doesn't know
2084               that and will cause a redirect to <span class=
2085               "QUOTE">"http://www.example.net/&amp;foo=bar"</span>. Depending
2086               on the target server configuration, the parameter will be
2087               silently ignored or lead to a <span class="QUOTE">"page not
2088               found"</span> error. You can prevent this problem by first
2089               using the <tt class="LITERAL"><a href=
2090               "actions-file.html#REDIRECT">redirect</a></tt> action to remove
2091               the last part of the URL, but it requires a little effort.</p>
2092
2093               <p>To detect a redirection URL, <tt class=
2094               "LITERAL">fast-redirects</tt> only looks for the string
2095               <span class="QUOTE">"http://"</span>, either in plain text
2096               (invalid but often used) or encoded as <span class=
2097               "QUOTE">"http%3a//"</span>. Some sites use their own URL
2098               encoding scheme, encrypt the address of the target server or
2099               replace it with a database id. In theses cases <tt class=
2100               "LITERAL">fast-redirects</tt> is fooled and the request reaches
2101               the redirection server where it probably gets logged.</p>
2102             </dd>
2103
2104             <dt>Example usage:</dt>
2105
2106             <dd>
2107               <table border="0" bgcolor="#E0E0E0" width="90%">
2108                 <tr>
2109                   <td>
2110                     <pre class="SCREEN">
2111  { +fast-redirects{simple-check} }
2112    one.example.com
2113
2114  { +fast-redirects{check-decoded-url} }
2115    another.example.com/testing
2116 </pre>
2117                   </td>
2118                 </tr>
2119               </table>
2120             </dd>
2121           </dl>
2122         </div>
2123       </div>
2124
2125       <div class="SECT3">
2126         <h4 class="SECT3"><a name="FILTER" id="FILTER">8.5.15.
2127         filter</a></h4>
2128
2129         <div class="VARIABLELIST">
2130           <dl>
2131             <dt>Typical use:</dt>
2132
2133             <dd>
2134               <p>Get rid of HTML and JavaScript annoyances, banner
2135               advertisements (by size), do fun text replacements, add
2136               personalized effects, etc.</p>
2137             </dd>
2138
2139             <dt>Effect:</dt>
2140
2141             <dd>
2142               <p>All instances of text-based type, most notably HTML and
2143               JavaScript, to which this action applies, can be filtered
2144               on-the-fly through the specified regular expression based
2145               substitutions. (Note: as of version 3.0.3 plain text documents
2146               are exempted from filtering, because web servers often use the
2147               <tt class="LITERAL">text/plain</tt> MIME type for all files
2148               whose type they don't know.)</p>
2149             </dd>
2150
2151             <dt>Type:</dt>
2152
2153             <dd>
2154               <p>Parameterized.</p>
2155             </dd>
2156
2157             <dt>Parameter:</dt>
2158
2159             <dd>
2160               <p>The name of a content filter, as defined in the <a href=
2161               "filter-file.html">filter file</a>. Filters can be defined in
2162               one or more files as defined by the <tt class=
2163               "LITERAL"><a href="config.html#FILTERFILE">filterfile</a></tt>
2164               option in the <a href="config.html">config file</a>. <tt class=
2165               "FILENAME">default.filter</tt> is the collection of filters
2166               supplied by the developers. Locally defined filters should go
2167               in their own file, such as <tt class=
2168               "FILENAME">user.filter</tt>.</p>
2169
2170               <p>When used in its negative form, and without parameters,
2171               <span class="emphasis"><i class="EMPHASIS">all</i></span>
2172               filtering is completely disabled.</p>
2173             </dd>
2174
2175             <dt>Notes:</dt>
2176
2177             <dd>
2178               <p>For your convenience, there are a number of pre-defined
2179               filters available in the distribution filter file that you can
2180               use. See the examples below for a list.</p>
2181
2182               <p>Filtering requires buffering the page content, which may
2183               appear to slow down page rendering since nothing is displayed
2184               until all content has passed the filters. (The total time until
2185               the page is completely rendered doesn't change much, but it may
2186               be perceived as slower since the page is not incrementally
2187               displayed.) This effect will be more noticeable on slower
2188               connections.</p>
2189
2190               <p><span class="QUOTE">"Rolling your own"</span> filters
2191               requires a knowledge of <a href=
2192               "http://en.wikipedia.org/wiki/Regular_expressions" target=
2193               "_top"><span class="QUOTE">"Regular Expressions"</span></a> and
2194               <a href="http://en.wikipedia.org/wiki/Html" target=
2195               "_top"><span class="QUOTE">"HTML"</span></a>. This is very
2196               powerful feature, and potentially very intrusive. Filters
2197               should be used with caution, and where an equivalent
2198               <span class="QUOTE">"action"</span> is not available.</p>
2199
2200               <p>The amount of data that can be filtered is limited to the
2201               <tt class="LITERAL"><a href=
2202               "config.html#BUFFER-LIMIT">buffer-limit</a></tt> option in the
2203               main <a href="config.html">config file</a>. The default is 4096
2204               KB (4 Megs). Once this limit is exceeded, the buffered data,
2205               and all pending data, is passed through unfiltered.</p>
2206
2207               <p>Inappropriate MIME types, such as zipped files, are not
2208               filtered at all. (Again, only text-based types except plain
2209               text). Encrypted SSL data (from HTTPS servers) cannot be
2210               filtered either, since this would violate the integrity of the
2211               secure transaction. In some situations it might be necessary to
2212               protect certain text, like source code, from filtering by
2213               defining appropriate <tt class="LITERAL">-filter</tt>
2214               exceptions.</p>
2215
2216               <p>Compressed content can't be filtered either, but if
2217               <span class="APPLICATION">Privoxy</span> is compiled with zlib
2218               support and a supported compression algorithm is used (gzip or
2219               deflate), <span class="APPLICATION">Privoxy</span> can first
2220               decompress the content and then filter it.</p>
2221
2222               <p>If you use a <span class="APPLICATION">Privoxy</span>
2223               version without zlib support, but want filtering to work on as
2224               much documents as possible, even those that would normally be
2225               sent compressed, you must use the <tt class="LITERAL"><a href=
2226               "actions-file.html#PREVENT-COMPRESSION">prevent-compression</a></tt>
2227               action in conjunction with <tt class="LITERAL">filter</tt>.</p>
2228
2229               <p>Content filtering can achieve some of the same effects as
2230               the <tt class="LITERAL"><a href=
2231               "actions-file.html#BLOCK">block</a></tt> action, i.e. it can be
2232               used to block ads and banners. But the mechanism works quite
2233               differently. One effective use, is to block ad banners based on
2234               their size (see below), since many of these seem to be somewhat
2235               standardized.</p>
2236
2237               <p><a href="contact.html">Feedback</a> with suggestions for new
2238               or improved filters is particularly welcome!</p>
2239
2240               <p>The below list has only the names and a one-line description
2241               of each predefined filter. There are <a href=
2242               "filter-file.html#PREDEFINED-FILTERS">more verbose
2243               explanations</a> of what these filters do in the <a href=
2244               "filter-file.html">filter file chapter</a>.</p>
2245             </dd>
2246
2247             <dt>Example usage (with filters from the distribution <tt class=
2248             "FILENAME">default.filter</tt> file). See <a href=
2249             "filter-file.html#PREDEFINED-FILTERS">the Predefined Filters
2250             section</a> for more explanation on each:</dt>
2251
2252             <dd>
2253               <p><a name="FILTER-JS-ANNOYANCES" id=
2254               "FILTER-JS-ANNOYANCES"></a></p>
2255
2256               <table border="0" bgcolor="#E0E0E0" width="90%">
2257                 <tr>
2258                   <td>
2259                     <pre class="SCREEN">
2260 +filter{js-annoyances}       # Get rid of particularly annoying JavaScript abuse.
2261 </pre>
2262                   </td>
2263                 </tr>
2264               </table>
2265
2266               <p><a name="FILTER-JS-EVENTS" id="FILTER-JS-EVENTS"></a></p>
2267
2268               <table border="0" bgcolor="#E0E0E0" width="90%">
2269                 <tr>
2270                   <td>
2271                     <pre class="SCREEN">
2272 +filter{js-events}           # Kill JavaScript event bindings and timers (Radically destructive! Only for extra nasty sites).
2273 </pre>
2274                   </td>
2275                 </tr>
2276               </table>
2277
2278               <p><a name="FILTER-HTML-ANNOYANCES" id=
2279               "FILTER-HTML-ANNOYANCES"></a></p>
2280
2281               <table border="0" bgcolor="#E0E0E0" width="90%">
2282                 <tr>
2283                   <td>
2284                     <pre class="SCREEN">
2285 +filter{html-annoyances}     # Get rid of particularly annoying HTML abuse.
2286 </pre>
2287                   </td>
2288                 </tr>
2289               </table>
2290
2291               <p><a name="FILTER-CONTENT-COOKIES" id=
2292               "FILTER-CONTENT-COOKIES"></a></p>
2293
2294               <table border="0" bgcolor="#E0E0E0" width="90%">
2295                 <tr>
2296                   <td>
2297                     <pre class="SCREEN">
2298 +filter{content-cookies}     # Kill cookies that come in the HTML or JS content.
2299 </pre>
2300                   </td>
2301                 </tr>
2302               </table>
2303
2304               <p><a name="FILTER-REFRESH-TAGS" id=
2305               "FILTER-REFRESH-TAGS"></a></p>
2306
2307               <table border="0" bgcolor="#E0E0E0" width="90%">
2308                 <tr>
2309                   <td>
2310                     <pre class="SCREEN">
2311 +filter{refresh-tags}        # Kill automatic refresh tags if refresh time is larger than 9 seconds.
2312 </pre>
2313                   </td>
2314                 </tr>
2315               </table>
2316
2317               <p><a name="FILTER-UNSOLICITED-POPUPS" id=
2318               "FILTER-UNSOLICITED-POPUPS"></a></p>
2319
2320               <table border="0" bgcolor="#E0E0E0" width="90%">
2321                 <tr>
2322                   <td>
2323                     <pre class="SCREEN">
2324 +filter{unsolicited-popups}  # Disable only unsolicited pop-up windows.
2325 </pre>
2326                   </td>
2327                 </tr>
2328               </table>
2329
2330               <p><a name="FILTER-ALL-POPUPS" id="FILTER-ALL-POPUPS"></a></p>
2331
2332               <table border="0" bgcolor="#E0E0E0" width="90%">
2333                 <tr>
2334                   <td>
2335                     <pre class="SCREEN">
2336 +filter{all-popups}          # Kill all popups in JavaScript and HTML.
2337 </pre>
2338                   </td>
2339                 </tr>
2340               </table>
2341
2342               <p><a name="FILTER-IMG-REORDER" id=
2343               "FILTER-IMG-REORDER"></a></p>
2344
2345               <table border="0" bgcolor="#E0E0E0" width="90%">
2346                 <tr>
2347                   <td>
2348                     <pre class="SCREEN">
2349 +filter{img-reorder}         # Reorder attributes in &lt;img&gt; tags to make the banners-by-* filters more effective.
2350 </pre>
2351                   </td>
2352                 </tr>
2353               </table>
2354
2355               <p><a name="FILTER-BANNERS-BY-SIZE" id=
2356               "FILTER-BANNERS-BY-SIZE"></a></p>
2357
2358               <table border="0" bgcolor="#E0E0E0" width="90%">
2359                 <tr>
2360                   <td>
2361                     <pre class="SCREEN">
2362 +filter{banners-by-size}     # Kill banners by size.
2363 </pre>
2364                   </td>
2365                 </tr>
2366               </table>
2367
2368               <p><a name="FILTER-BANNERS-BY-LINK" id=
2369               "FILTER-BANNERS-BY-LINK"></a></p>
2370
2371               <table border="0" bgcolor="#E0E0E0" width="90%">
2372                 <tr>
2373                   <td>
2374                     <pre class="SCREEN">
2375 +filter{banners-by-link}     # Kill banners by their links to known clicktrackers.
2376 </pre>
2377                   </td>
2378                 </tr>
2379               </table>
2380
2381               <p><a name="FILTER-WEBBUGS" id="FILTER-WEBBUGS"></a></p>
2382
2383               <table border="0" bgcolor="#E0E0E0" width="90%">
2384                 <tr>
2385                   <td>
2386                     <pre class="SCREEN">
2387 +filter{webbugs}             # Squish WebBugs (1x1 invisible GIFs used for user tracking).
2388 </pre>
2389                   </td>
2390                 </tr>
2391               </table>
2392
2393               <p><a name="FILTER-TINY-TEXTFORMS" id=
2394               "FILTER-TINY-TEXTFORMS"></a></p>
2395
2396               <table border="0" bgcolor="#E0E0E0" width="90%">
2397                 <tr>
2398                   <td>
2399                     <pre class="SCREEN">
2400 +filter{tiny-textforms}      # Extend those tiny textareas up to 40x80 and kill the hard wrap.
2401 </pre>
2402                   </td>
2403                 </tr>
2404               </table>
2405
2406               <p><a name="FILTER-JUMPING-WINDOWS" id=
2407               "FILTER-JUMPING-WINDOWS"></a></p>
2408
2409               <table border="0" bgcolor="#E0E0E0" width="90%">
2410                 <tr>
2411                   <td>
2412                     <pre class="SCREEN">
2413 +filter{jumping-windows}     # Prevent windows from resizing and moving themselves.
2414 </pre>
2415                   </td>
2416                 </tr>
2417               </table>
2418
2419               <p><a name="FILTER-FRAMESET-BORDERS" id=
2420               "FILTER-FRAMESET-BORDERS"></a></p>
2421
2422               <table border="0" bgcolor="#E0E0E0" width="90%">
2423                 <tr>
2424                   <td>
2425                     <pre class="SCREEN">
2426 +filter{frameset-borders}    # Give frames a border and make them resizable.
2427 </pre>
2428                   </td>
2429                 </tr>
2430               </table>
2431
2432               <p><a name="FILTER-IFRAMES" id="FILTER-IFRAMES"></a></p>
2433
2434               <table border="0" bgcolor="#E0E0E0" width="90%">
2435                 <tr>
2436                   <td>
2437                     <pre class="SCREEN">
2438 +filter{iframes}             # Removes all detected iframes. Should only be enabled for individual sites.
2439 </pre>
2440                   </td>
2441                 </tr>
2442               </table>
2443
2444               <p><a name="FILTER-DEMORONIZER" id=
2445               "FILTER-DEMORONIZER"></a></p>
2446
2447               <table border="0" bgcolor="#E0E0E0" width="90%">
2448                 <tr>
2449                   <td>
2450                     <pre class="SCREEN">
2451 +filter{demoronizer}         # Fix MS's non-standard use of standard charsets.
2452 </pre>
2453                   </td>
2454                 </tr>
2455               </table>
2456
2457               <p><a name="FILTER-SHOCKWAVE-FLASH" id=
2458               "FILTER-SHOCKWAVE-FLASH"></a></p>
2459
2460               <table border="0" bgcolor="#E0E0E0" width="90%">
2461                 <tr>
2462                   <td>
2463                     <pre class="SCREEN">
2464 +filter{shockwave-flash}     # Kill embedded Shockwave Flash objects.
2465 </pre>
2466                   </td>
2467                 </tr>
2468               </table>
2469
2470               <p><a name="FILTER-QUICKTIME-KIOSKMODE" id=
2471               "FILTER-QUICKTIME-KIOSKMODE"></a></p>
2472
2473               <table border="0" bgcolor="#E0E0E0" width="90%">
2474                 <tr>
2475                   <td>
2476                     <pre class="SCREEN">
2477 +filter{quicktime-kioskmode} # Make Quicktime movies saveable.
2478 </pre>
2479                   </td>
2480                 </tr>
2481               </table>
2482
2483               <p><a name="FILTER-FUN" id="FILTER-FUN"></a></p>
2484
2485               <table border="0" bgcolor="#E0E0E0" width="90%">
2486                 <tr>
2487                   <td>
2488                     <pre class="SCREEN">
2489 +filter{fun}                 # Text replacements for subversive browsing fun!
2490 </pre>
2491                   </td>
2492                 </tr>
2493               </table>
2494
2495               <p><a name="FILTER-CRUDE-PARENTAL" id=
2496               "FILTER-CRUDE-PARENTAL"></a></p>
2497
2498               <table border="0" bgcolor="#E0E0E0" width="90%">
2499                 <tr>
2500                   <td>
2501                     <pre class="SCREEN">
2502 +filter{crude-parental}      # Crude parental filtering. Note that this filter doesn't work reliably.
2503 </pre>
2504                   </td>
2505                 </tr>
2506               </table>
2507
2508               <p><a name="FILTER-IE-EXPLOITS" id=
2509               "FILTER-IE-EXPLOITS"></a></p>
2510
2511               <table border="0" bgcolor="#E0E0E0" width="90%">
2512                 <tr>
2513                   <td>
2514                     <pre class="SCREEN">
2515 +filter{ie-exploits}         # Disable some known Internet Explorer bug exploits.
2516 </pre>
2517                   </td>
2518                 </tr>
2519               </table>
2520
2521               <p><a name="FILTER-SITE-SPECIFICS" id=
2522               "FILTER-SITE-SPECIFICS"></a></p>
2523
2524               <table border="0" bgcolor="#E0E0E0" width="90%">
2525                 <tr>
2526                   <td>
2527                     <pre class="SCREEN">
2528 +filter{site-specifics}      # Cure for site-specific problems. Don't apply generally!
2529 </pre>
2530                   </td>
2531                 </tr>
2532               </table>
2533
2534               <p><a name="FILTER-NO-PING" id="FILTER-NO-PING"></a></p>
2535
2536               <table border="0" bgcolor="#E0E0E0" width="90%">
2537                 <tr>
2538                   <td>
2539                     <pre class="SCREEN">
2540 +filter{no-ping}             # Removes non-standard ping attributes in &lt;a&gt; and &lt;area&gt; tags.
2541 </pre>
2542                   </td>
2543                 </tr>
2544               </table>
2545
2546               <p><a name="FILTER-GOOGLE" id="FILTER-GOOGLE"></a></p>
2547
2548               <table border="0" bgcolor="#E0E0E0" width="90%">
2549                 <tr>
2550                   <td>
2551                     <pre class="SCREEN">
2552 +filter{google}              # CSS-based block for Google text ads. Also removes a width limitation and the toolbar advertisement.
2553 </pre>
2554                   </td>
2555                 </tr>
2556               </table>
2557
2558               <p><a name="FILTER-YAHOO" id="FILTER-YAHOO"></a></p>
2559
2560               <table border="0" bgcolor="#E0E0E0" width="90%">
2561                 <tr>
2562                   <td>
2563                     <pre class="SCREEN">
2564 +filter{yahoo}               # CSS-based block for Yahoo text ads. Also removes a width limitation.
2565 </pre>
2566                   </td>
2567                 </tr>
2568               </table>
2569
2570               <p><a name="FILTER-MSN" id="FILTER-MSN"></a></p>
2571
2572               <table border="0" bgcolor="#E0E0E0" width="90%">
2573                 <tr>
2574                   <td>
2575                     <pre class="SCREEN">
2576 +filter{msn}                 # CSS-based block for MSN text ads. Also removes tracking URLs and a width limitation.
2577 </pre>
2578                   </td>
2579                 </tr>
2580               </table>
2581
2582               <p><a name="FILTER-BLOGSPOT" id="FILTER-BLOGSPOT"></a></p>
2583
2584               <table border="0" bgcolor="#E0E0E0" width="90%">
2585                 <tr>
2586                   <td>
2587                     <pre class="SCREEN">
2588 +filter{blogspot}            # Cleans up some Blogspot blogs. Read the fine print before using this.
2589 </pre>
2590                   </td>
2591                 </tr>
2592               </table>
2593             </dd>
2594           </dl>
2595         </div>
2596       </div>
2597
2598       <div class="SECT3">
2599         <h4 class="SECT3"><a name="FORCE-TEXT-MODE" id=
2600         "FORCE-TEXT-MODE">8.5.16. force-text-mode</a></h4>
2601
2602         <div class="VARIABLELIST">
2603           <dl>
2604             <dt>Typical use:</dt>
2605
2606             <dd>
2607               <p>Force <span class="APPLICATION">Privoxy</span> to treat a
2608               document as if it was in some kind of <span class=
2609               "emphasis"><i class="EMPHASIS">text</i></span> format.</p>
2610             </dd>
2611
2612             <dt>Effect:</dt>
2613
2614             <dd>
2615               <p>Declares a document as text, even if the <span class=
2616               "QUOTE">"Content-Type:"</span> isn't detected as such.</p>
2617             </dd>
2618
2619             <dt>Type:</dt>
2620
2621             <dd>
2622               <p>Boolean.</p>
2623             </dd>
2624
2625             <dt>Parameter:</dt>
2626
2627             <dd>
2628               <p>N/A</p>
2629             </dd>
2630
2631             <dt>Notes:</dt>
2632
2633             <dd>
2634               <p>As explained <tt class="LITERAL"><a href=
2635               "actions-file.html#FILTER">above</a></tt>, <span class=
2636               "APPLICATION">Privoxy</span> tries to only filter files that
2637               are in some kind of text format. The same restrictions apply to
2638               <tt class="LITERAL"><a href=
2639               "actions-file.html#CONTENT-TYPE-OVERWRITE">content-type-overwrite</a></tt>.
2640               <tt class="LITERAL">force-text-mode</tt> declares a document as
2641               text, without looking at the <span class=
2642               "QUOTE">"Content-Type:"</span> first.</p>
2643
2644               <div class="WARNING">
2645                 <table class="WARNING" border="1" width="90%">
2646                   <tr>
2647                     <td align="center"><b>Warning</b></td>
2648                   </tr>
2649
2650                   <tr>
2651                     <td align="left">
2652                       <p>Think twice before activating this action. Filtering
2653                       binary data with regular expressions can cause file
2654                       damage.</p>
2655                     </td>
2656                   </tr>
2657                 </table>
2658               </div>
2659             </dd>
2660
2661             <dt>Example usage:</dt>
2662
2663             <dd>
2664               <table border="0" bgcolor="#E0E0E0" width="90%">
2665                 <tr>
2666                   <td>
2667                     <pre class="SCREEN">
2668 +force-text-mode
2669
2670 </pre>
2671                   </td>
2672                 </tr>
2673               </table>
2674             </dd>
2675           </dl>
2676         </div>
2677       </div>
2678
2679       <div class="SECT3">
2680         <h4 class="SECT3"><a name="FORWARD-OVERRIDE" id=
2681         "FORWARD-OVERRIDE">8.5.17. forward-override</a></h4>
2682
2683         <div class="VARIABLELIST">
2684           <dl>
2685             <dt>Typical use:</dt>
2686
2687             <dd>
2688               <p>Change the forwarding settings based on User-Agent or
2689               request origin</p>
2690             </dd>
2691
2692             <dt>Effect:</dt>
2693
2694             <dd>
2695               <p>Overrules the forward directives in the configuration
2696               file.</p>
2697             </dd>
2698
2699             <dt>Type:</dt>
2700
2701             <dd>
2702               <p>Multi-value.</p>
2703             </dd>
2704
2705             <dt>Parameter:</dt>
2706
2707             <dd>
2708               <ul>
2709                 <li>
2710                   <p><span class="QUOTE">"forward ."</span> to use a direct
2711                   connection without any additional proxies.</p>
2712                 </li>
2713
2714                 <li>
2715                   <p><span class="QUOTE">"forward 127.0.0.1:8123"</span> to
2716                   use the HTTP proxy listening at 127.0.0.1 port 8123.</p>
2717                 </li>
2718
2719                 <li>
2720                   <p><span class="QUOTE">"forward-socks4a 127.0.0.1:9050
2721                   ."</span> to use the socks4a proxy listening at 127.0.0.1
2722                   port 9050. Replace <span class=
2723                   "QUOTE">"forward-socks4a"</span> with <span class=
2724                   "QUOTE">"forward-socks4"</span> to use a socks4 connection
2725                   (with local DNS resolution) instead, use <span class=
2726                   "QUOTE">"forward-socks5"</span> for socks5 connections
2727                   (with remote DNS resolution).</p>
2728                 </li>
2729
2730                 <li>
2731                   <p><span class="QUOTE">"forward-socks4a 127.0.0.1:9050
2732                   proxy.example.org:8000"</span> to use the socks4a proxy
2733                   listening at 127.0.0.1 port 9050 to reach the HTTP proxy
2734                   listening at proxy.example.org port 8000. Replace
2735                   <span class="QUOTE">"forward-socks4a"</span> with
2736                   <span class="QUOTE">"forward-socks4"</span> to use a socks4
2737                   connection (with local DNS resolution) instead, use
2738                   <span class="QUOTE">"forward-socks5"</span> for socks5
2739                   connections (with remote DNS resolution).</p>
2740                 </li>
2741               </ul>
2742             </dd>
2743
2744             <dt>Notes:</dt>
2745
2746             <dd>
2747               <p>This action takes parameters similar to the <a href=
2748               "config.html#FORWARDING">forward</a> directives in the
2749               configuration file, but without the URL pattern. It can be used
2750               as replacement, but normally it's only used in cases where
2751               matching based on the request URL isn't sufficient.</p>
2752
2753               <div class="WARNING">
2754                 <table class="WARNING" border="1" width="90%">
2755                   <tr>
2756                     <td align="center"><b>Warning</b></td>
2757                   </tr>
2758
2759                   <tr>
2760                     <td align="left">
2761                       <p>Please read the description for the <a href=
2762                       "config.html#FORWARDING">forward</a> directives before
2763                       using this action. Forwarding to the wrong people will
2764                       reduce your privacy and increase the chances of
2765                       man-in-the-middle attacks.</p>
2766
2767                       <p>If the ports are missing or invalid, default values
2768                       will be used. This might change in the future and you
2769                       shouldn't rely on it. Otherwise incorrect syntax causes
2770                       Privoxy to exit.</p>
2771
2772                       <p>Use the <a href=
2773                       "http://config.privoxy.org/show-url-info" target=
2774                       "_top">show-url-info CGI page</a> to verify that your
2775                       forward settings do what you thought the do.</p>
2776                     </td>
2777                   </tr>
2778                 </table>
2779               </div>
2780             </dd>
2781
2782             <dt>Example usage:</dt>
2783
2784             <dd>
2785               <table border="0" bgcolor="#E0E0E0" width="90%">
2786                 <tr>
2787                   <td>
2788                     <pre class="SCREEN">
2789 # Always use direct connections for requests previously tagged as
2790 # <span class="QUOTE">"User-Agent: fetch libfetch/2.0"</span> and make sure
2791 # resuming downloads continues to work.
2792 # This way you can continue to use Tor for your normal browsing,
2793 # without overloading the Tor network with your FreeBSD ports updates
2794 # or downloads of bigger files like ISOs.
2795 # Note that HTTP headers are easy to fake and therefore their
2796 # values are as (un)trustworthy as your clients and users.
2797 {+forward-override{forward .} \
2798  -hide-if-modified-since      \
2799  -overwrite-last-modified     \
2800 }
2801 TAG:^User-Agent: fetch libfetch/2\.0$
2802
2803 </pre>
2804                   </td>
2805                 </tr>
2806               </table>
2807             </dd>
2808           </dl>
2809         </div>
2810       </div>
2811
2812       <div class="SECT3">
2813         <h4 class="SECT3"><a name="HANDLE-AS-EMPTY-DOCUMENT" id=
2814         "HANDLE-AS-EMPTY-DOCUMENT">8.5.18. handle-as-empty-document</a></h4>
2815
2816         <div class="VARIABLELIST">
2817           <dl>
2818             <dt>Typical use:</dt>
2819
2820             <dd>
2821               <p>Mark URLs that should be replaced by empty documents
2822               <span class="emphasis"><i class="EMPHASIS">if they get
2823               blocked</i></span></p>
2824             </dd>
2825
2826             <dt>Effect:</dt>
2827
2828             <dd>
2829               <p>This action alone doesn't do anything noticeable. It just
2830               marks URLs. If the <tt class="LITERAL"><a href=
2831               "actions-file.html#BLOCK">block</a></tt> action <span class=
2832               "emphasis"><i class="EMPHASIS">also applies</i></span>, the
2833               presence or absence of this mark decides whether an HTML
2834               <span class="QUOTE">"BLOCKED"</span> page, or an empty document
2835               will be sent to the client as a substitute for the blocked
2836               content. The <span class="emphasis"><i class=
2837               "EMPHASIS">empty</i></span> document isn't literally empty, but
2838               actually contains a single space.</p>
2839             </dd>
2840
2841             <dt>Type:</dt>
2842
2843             <dd>
2844               <p>Boolean.</p>
2845             </dd>
2846
2847             <dt>Parameter:</dt>
2848
2849             <dd>
2850               <p>N/A</p>
2851             </dd>
2852
2853             <dt>Notes:</dt>
2854
2855             <dd>
2856               <p>Some browsers complain about syntax errors if JavaScript
2857               documents are blocked with <span class=
2858               "APPLICATION">Privoxy's</span> default HTML page; this option
2859               can be used to silence them. And of course this action can also
2860               be used to eliminate the <span class=
2861               "APPLICATION">Privoxy</span> BLOCKED message in frames.</p>
2862
2863               <p>The content type for the empty document can be specified
2864               with <tt class="LITERAL"><a href=
2865               "actions-file.html#CONTENT-TYPE-OVERWRITE">content-type-overwrite{}</a></tt>,
2866               but usually this isn't necessary.</p>
2867             </dd>
2868
2869             <dt>Example usage:</dt>
2870
2871             <dd>
2872               <table border="0" bgcolor="#E0E0E0" width="90%">
2873                 <tr>
2874                   <td>
2875                     <pre class="SCREEN">
2876 # Block all documents on example.org that end with ".js",
2877 # but send an empty document instead of the usual HTML message.
2878 {+block{Blocked JavaScript} +handle-as-empty-document}
2879 example.org/.*\.js$
2880
2881 </pre>
2882                   </td>
2883                 </tr>
2884               </table>
2885             </dd>
2886           </dl>
2887         </div>
2888       </div>
2889
2890       <div class="SECT3">
2891         <h4 class="SECT3"><a name="HANDLE-AS-IMAGE" id=
2892         "HANDLE-AS-IMAGE">8.5.19. handle-as-image</a></h4>
2893
2894         <div class="VARIABLELIST">
2895           <dl>
2896             <dt>Typical use:</dt>
2897
2898             <dd>
2899               <p>Mark URLs as belonging to images (so they'll be replaced by
2900               images <span class="emphasis"><i class="EMPHASIS">if they do
2901               get blocked</i></span>, rather than HTML pages)</p>
2902             </dd>
2903
2904             <dt>Effect:</dt>
2905
2906             <dd>
2907               <p>This action alone doesn't do anything noticeable. It just
2908               marks URLs as images. If the <tt class="LITERAL"><a href=
2909               "actions-file.html#BLOCK">block</a></tt> action <span class=
2910               "emphasis"><i class="EMPHASIS">also applies</i></span>, the
2911               presence or absence of this mark decides whether an HTML
2912               <span class="QUOTE">"blocked"</span> page, or a replacement
2913               image (as determined by the <tt class="LITERAL"><a href=
2914               "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a></tt>
2915               action) will be sent to the client as a substitute for the
2916               blocked content.</p>
2917             </dd>
2918
2919             <dt>Type:</dt>
2920
2921             <dd>
2922               <p>Boolean.</p>
2923             </dd>
2924
2925             <dt>Parameter:</dt>
2926
2927             <dd>
2928               <p>N/A</p>
2929             </dd>
2930
2931             <dt>Notes:</dt>
2932
2933             <dd>
2934               <p>The below generic example section is actually part of
2935               <tt class="FILENAME">default.action</tt>. It marks all URLs
2936               with well-known image file name extensions as images and should
2937               be left intact.</p>
2938
2939               <p>Users will probably only want to use the handle-as-image
2940               action in conjunction with <tt class="LITERAL"><a href=
2941               "actions-file.html#BLOCK">block</a></tt>, to block sources of
2942               banners, whose URLs don't reflect the file type, like in the
2943               second example section.</p>
2944
2945               <p>Note that you cannot treat HTML pages as images in most
2946               cases. For instance, (in-line) ad frames require an HTML page
2947               to be sent, or they won't display properly. Forcing <tt class=
2948               "LITERAL">handle-as-image</tt> in this situation will not
2949               replace the ad frame with an image, but lead to error
2950               messages.</p>
2951             </dd>
2952
2953             <dt>Example usage (sections):</dt>
2954
2955             <dd>
2956               <table border="0" bgcolor="#E0E0E0" width="90%">
2957                 <tr>
2958                   <td>
2959                     <pre class="SCREEN">
2960 # Generic image extensions:
2961 #
2962 {+handle-as-image}
2963 /.*\.(gif|jpg|jpeg|png|bmp|ico)$
2964
2965 # These don't look like images, but they're banners and should be
2966 # blocked as images:
2967 #
2968 {+block{Nasty banners.} +handle-as-image}
2969 nasty-banner-server.example.com/junk.cgi\?output=trash
2970 </pre>
2971                   </td>
2972                 </tr>
2973               </table>
2974             </dd>
2975           </dl>
2976         </div>
2977       </div>
2978
2979       <div class="SECT3">
2980         <h4 class="SECT3"><a name="HIDE-ACCEPT-LANGUAGE" id=
2981         "HIDE-ACCEPT-LANGUAGE">8.5.20. hide-accept-language</a></h4>
2982
2983         <div class="VARIABLELIST">
2984           <dl>
2985             <dt>Typical use:</dt>
2986
2987             <dd>
2988               <p>Pretend to use different language settings.</p>
2989             </dd>
2990
2991             <dt>Effect:</dt>
2992
2993             <dd>
2994               <p>Deletes or replaces the <span class=
2995               "QUOTE">"Accept-Language:"</span> HTTP header in client
2996               requests.</p>
2997             </dd>
2998
2999             <dt>Type:</dt>
3000
3001             <dd>
3002               <p>Parameterized.</p>
3003             </dd>
3004
3005             <dt>Parameter:</dt>
3006
3007             <dd>
3008               <p>Keyword: <span class="QUOTE">"block"</span>, or any user
3009               defined value.</p>
3010             </dd>
3011
3012             <dt>Notes:</dt>
3013
3014             <dd>
3015               <p>Faking the browser's language settings can be useful to make
3016               a foreign User-Agent set with <tt class="LITERAL"><a href=
3017               "actions-file.html#HIDE-USER-AGENT">hide-user-agent</a></tt>
3018               more believable.</p>
3019
3020               <p>However some sites with content in different languages check
3021               the <span class="QUOTE">"Accept-Language:"</span> to decide
3022               which one to take by default. Sometimes it isn't possible to
3023               later switch to another language without changing the
3024               <span class="QUOTE">"Accept-Language:"</span> header first.</p>
3025
3026               <p>Therefore it's a good idea to either only change the
3027               <span class="QUOTE">"Accept-Language:"</span> header to
3028               languages you understand, or to languages that aren't wide
3029               spread.</p>
3030
3031               <p>Before setting the <span class=
3032               "QUOTE">"Accept-Language:"</span> header to a rare language,
3033               you should consider that it helps to make your requests unique
3034               and thus easier to trace. If you don't plan to change this
3035               header frequently, you should stick to a common language.</p>
3036             </dd>
3037
3038             <dt>Example usage (section):</dt>
3039
3040             <dd>
3041               <table border="0" bgcolor="#E0E0E0" width="90%">
3042                 <tr>
3043                   <td>
3044                     <pre class="SCREEN">
3045 # Pretend to use Canadian language settings.
3046 {+hide-accept-language{en-ca} \
3047 +hide-user-agent{Mozilla/5.0 (X11; U; OpenBSD i386; en-CA; rv:1.8.0.4) Gecko/20060628 Firefox/1.5.0.4} \
3048 }
3049 /
3050 </pre>
3051                   </td>
3052                 </tr>
3053               </table>
3054             </dd>
3055           </dl>
3056         </div>
3057       </div>
3058
3059       <div class="SECT3">
3060         <h4 class="SECT3"><a name="HIDE-CONTENT-DISPOSITION" id=
3061         "HIDE-CONTENT-DISPOSITION">8.5.21. hide-content-disposition</a></h4>
3062
3063         <div class="VARIABLELIST">
3064           <dl>
3065             <dt>Typical use:</dt>
3066
3067             <dd>
3068               <p>Prevent download menus for content you prefer to view inside
3069               the browser.</p>
3070             </dd>
3071
3072             <dt>Effect:</dt>
3073
3074             <dd>
3075               <p>Deletes or replaces the <span class=
3076               "QUOTE">"Content-Disposition:"</span> HTTP header set by some
3077               servers.</p>
3078             </dd>
3079
3080             <dt>Type:</dt>
3081
3082             <dd>
3083               <p>Parameterized.</p>
3084             </dd>
3085
3086             <dt>Parameter:</dt>
3087
3088             <dd>
3089               <p>Keyword: <span class="QUOTE">"block"</span>, or any user
3090               defined value.</p>
3091             </dd>
3092
3093             <dt>Notes:</dt>
3094
3095             <dd>
3096               <p>Some servers set the <span class=
3097               "QUOTE">"Content-Disposition:"</span> HTTP header for documents
3098               they assume you want to save locally before viewing them. The
3099               <span class="QUOTE">"Content-Disposition:"</span> header
3100               contains the file name the browser is supposed to use by
3101               default.</p>
3102
3103               <p>In most browsers that understand this header, it makes it
3104               impossible to <span class="emphasis"><i class="EMPHASIS">just
3105               view</i></span> the document, without downloading it first,
3106               even if it's just a simple text file or an image.</p>
3107
3108               <p>Removing the <span class=
3109               "QUOTE">"Content-Disposition:"</span> header helps to prevent
3110               this annoyance, but some browsers additionally check the
3111               <span class="QUOTE">"Content-Type:"</span> header, before they
3112               decide if they can display a document without saving it first.
3113               In these cases, you have to change this header as well, before
3114               the browser stops displaying download menus.</p>
3115
3116               <p>It is also possible to change the server's file name
3117               suggestion to another one, but in most cases it isn't worth the
3118               time to set it up.</p>
3119
3120               <p>This action will probably be removed in the future, use
3121               server-header filters instead.</p>
3122             </dd>
3123
3124             <dt>Example usage:</dt>
3125
3126             <dd>
3127               <table border="0" bgcolor="#E0E0E0" width="90%">
3128                 <tr>
3129                   <td>
3130                     <pre class="SCREEN">
3131 # Disarm the download link in Sourceforge's patch tracker
3132 { -filter \
3133  +content-type-overwrite{text/plain}\
3134  +hide-content-disposition{block} }
3135  .sourceforge.net/tracker/download\.php
3136 </pre>
3137                   </td>
3138                 </tr>
3139               </table>
3140             </dd>
3141           </dl>
3142         </div>
3143       </div>
3144
3145       <div class="SECT3">
3146         <h4 class="SECT3"><a name="HIDE-IF-MODIFIED-SINCE" id=
3147         "HIDE-IF-MODIFIED-SINCE">8.5.22. hide-if-modified-since</a></h4>
3148
3149         <div class="VARIABLELIST">
3150           <dl>
3151             <dt>Typical use:</dt>
3152
3153             <dd>
3154               <p>Prevent yet another way to track the user's steps between
3155               sessions.</p>
3156             </dd>
3157
3158             <dt>Effect:</dt>
3159
3160             <dd>
3161               <p>Deletes the <span class="QUOTE">"If-Modified-Since:"</span>
3162               HTTP client header or modifies its value.</p>
3163             </dd>
3164
3165             <dt>Type:</dt>
3166
3167             <dd>
3168               <p>Parameterized.</p>
3169             </dd>
3170
3171             <dt>Parameter:</dt>
3172
3173             <dd>
3174               <p>Keyword: <span class="QUOTE">"block"</span>, or a user
3175               defined value that specifies a range of hours.</p>
3176             </dd>
3177
3178             <dt>Notes:</dt>
3179
3180             <dd>
3181               <p>Removing this header is useful for filter testing, where you
3182               want to force a real reload instead of getting status code
3183               <span class="QUOTE">"304"</span>, which would cause the browser
3184               to use a cached copy of the page.</p>
3185
3186               <p>Instead of removing the header, <tt class=
3187               "LITERAL">hide-if-modified-since</tt> can also add or subtract
3188               a random amount of time to/from the header's value. You specify
3189               a range of minutes where the random factor should be chosen
3190               from and <span class="APPLICATION">Privoxy</span> does the
3191               rest. A negative value means subtracting, a positive value
3192               adding.</p>
3193
3194               <p>Randomizing the value of the <span class=
3195               "QUOTE">"If-Modified-Since:"</span> makes it less likely that
3196               the server can use the time as a cookie replacement, but you
3197               will run into caching problems if the random range is too
3198               high.</p>
3199
3200               <p>It is a good idea to only use a small negative value and let
3201               <tt class="LITERAL"><a href=
3202               "actions-file.html#OVERWRITE-LAST-MODIFIED">overwrite-last-modified</a></tt>
3203               handle the greater changes.</p>
3204
3205               <p>It is also recommended to use this action together with
3206               <tt class="LITERAL"><a href=
3207               "actions-file.html#CRUNCH-IF-NONE-MATCH">crunch-if-none-match</a></tt>,
3208               otherwise it's more or less pointless.</p>
3209             </dd>
3210
3211             <dt>Example usage (section):</dt>
3212
3213             <dd>
3214               <table border="0" bgcolor="#E0E0E0" width="90%">
3215                 <tr>
3216                   <td>
3217                     <pre class="SCREEN">
3218 # Let the browser revalidate but make tracking based on the time less likely.
3219 {+hide-if-modified-since{-60} \
3220  +overwrite-last-modified{randomize} \
3221  +crunch-if-none-match}
3222 /
3223 </pre>
3224                   </td>
3225                 </tr>
3226               </table>
3227             </dd>
3228           </dl>
3229         </div>
3230       </div>
3231
3232       <div class="SECT3">
3233         <h4 class="SECT3"><a name="HIDE-FROM-HEADER" id=
3234         "HIDE-FROM-HEADER">8.5.23. hide-from-header</a></h4>
3235
3236         <div class="VARIABLELIST">
3237           <dl>
3238             <dt>Typical use:</dt>
3239
3240             <dd>
3241               <p>Keep your (old and ill) browser from telling web servers
3242               your email address</p>
3243             </dd>
3244
3245             <dt>Effect:</dt>
3246
3247             <dd>
3248               <p>Deletes any existing <span class="QUOTE">"From:"</span> HTTP
3249               header, or replaces it with the specified string.</p>
3250             </dd>
3251
3252             <dt>Type:</dt>
3253
3254             <dd>
3255               <p>Parameterized.</p>
3256             </dd>
3257
3258             <dt>Parameter:</dt>
3259
3260             <dd>
3261               <p>Keyword: <span class="QUOTE">"block"</span>, or any user
3262               defined value.</p>
3263             </dd>
3264
3265             <dt>Notes:</dt>
3266
3267             <dd>
3268               <p>The keyword <span class="QUOTE">"block"</span> will
3269               completely remove the header (not to be confused with the
3270               <tt class="LITERAL"><a href=
3271               "actions-file.html#BLOCK">block</a></tt> action).</p>
3272
3273               <p>Alternately, you can specify any value you prefer to be sent
3274               to the web server. If you do, it is a matter of fairness not to
3275               use any address that is actually used by a real person.</p>
3276
3277               <p>This action is rarely needed, as modern web browsers don't
3278               send <span class="QUOTE">"From:"</span> headers anymore.</p>
3279             </dd>
3280
3281             <dt>Example usage:</dt>
3282
3283             <dd>
3284               <table border="0" bgcolor="#E0E0E0" width="90%">
3285                 <tr>
3286                   <td>
3287                     <pre class="SCREEN">
3288 +hide-from-header{block}
3289 </pre>
3290                   </td>
3291                 </tr>
3292               </table>or
3293
3294               <table border="0" bgcolor="#E0E0E0" width="90%">
3295                 <tr>
3296                   <td>
3297                     <pre class="SCREEN">
3298 +hide-from-header{spam-me-senseless@sittingduck.example.com}
3299 </pre>
3300                   </td>
3301                 </tr>
3302               </table>
3303             </dd>
3304           </dl>
3305         </div>
3306       </div>
3307
3308       <div class="SECT3">
3309         <h4 class="SECT3"><a name="HIDE-REFERRER" id="HIDE-REFERRER">8.5.24.
3310         hide-referrer</a></h4><a name="HIDE-REFERER" id="HIDE-REFERER"></a>
3311
3312         <div class="VARIABLELIST">
3313           <dl>
3314             <dt>Typical use:</dt>
3315
3316             <dd>
3317               <p>Conceal which link you followed to get to a particular
3318               site</p>
3319             </dd>
3320
3321             <dt>Effect:</dt>
3322
3323             <dd>
3324               <p>Deletes the <span class="QUOTE">"Referer:"</span> (sic) HTTP
3325               header from the client request, or replaces it with a forged
3326               one.</p>
3327             </dd>
3328
3329             <dt>Type:</dt>
3330
3331             <dd>
3332               <p>Parameterized.</p>
3333             </dd>
3334
3335             <dt>Parameter:</dt>
3336
3337             <dd>
3338               <ul>
3339                 <li>
3340                   <p><span class="QUOTE">"conditional-block"</span> to delete
3341                   the header completely if the host has changed.</p>
3342                 </li>
3343
3344                 <li>
3345                   <p><span class="QUOTE">"conditional-forge"</span> to forge
3346                   the header if the host has changed.</p>
3347                 </li>
3348
3349                 <li>
3350                   <p><span class="QUOTE">"block"</span> to delete the header
3351                   unconditionally.</p>
3352                 </li>
3353
3354                 <li>
3355                   <p><span class="QUOTE">"forge"</span> to pretend to be
3356                   coming from the homepage of the server we are talking
3357                   to.</p>
3358                 </li>
3359
3360                 <li>
3361                   <p>Any other string to set a user defined referrer.</p>
3362                 </li>
3363               </ul>
3364             </dd>
3365
3366             <dt>Notes:</dt>
3367
3368             <dd>
3369               <p><tt class="LITERAL">conditional-block</tt> is the only
3370               parameter, that isn't easily detected in the server's log file.
3371               If it blocks the referrer, the request will look like the
3372               visitor used a bookmark or typed in the address directly.</p>
3373
3374               <p>Leaving the referrer unmodified for requests on the same
3375               host allows the server owner to see the visitor's <span class=
3376               "QUOTE">"click path"</span>, but in most cases she could also
3377               get that information by comparing other parts of the log file:
3378               for example the User-Agent if it isn't a very common one, or
3379               the user's IP address if it doesn't change between different
3380               requests.</p>
3381
3382               <p>Always blocking the referrer, or using a custom one, can
3383               lead to failures on servers that check the referrer before they
3384               answer any requests, in an attempt to prevent their content
3385               from being embedded or linked to elsewhere.</p>
3386
3387               <p>Both <tt class="LITERAL">conditional-block</tt> and
3388               <tt class="LITERAL">forge</tt> will work with referrer checks,
3389               as long as content and valid referring page are on the same
3390               host. Most of the time that's the case.</p>
3391
3392               <p><tt class="LITERAL">hide-referer</tt> is an alternate
3393               spelling of <tt class="LITERAL">hide-referrer</tt> and the two
3394               can be can be freely substituted with each other. (<span class=
3395               "QUOTE">"referrer"</span> is the correct English spelling,
3396               however the HTTP specification has a bug - it requires it to be
3397               spelled as <span class="QUOTE">"referer"</span>.)</p>
3398             </dd>
3399
3400             <dt>Example usage:</dt>
3401
3402             <dd>
3403               <table border="0" bgcolor="#E0E0E0" width="90%">
3404                 <tr>
3405                   <td>
3406                     <pre class="SCREEN">
3407 +hide-referrer{forge}
3408 </pre>
3409                   </td>
3410                 </tr>
3411               </table>or
3412
3413               <table border="0" bgcolor="#E0E0E0" width="90%">
3414                 <tr>
3415                   <td>
3416                     <pre class="SCREEN">
3417 +hide-referrer{http://www.yahoo.com/}
3418 </pre>
3419                   </td>
3420                 </tr>
3421               </table>
3422             </dd>
3423           </dl>
3424         </div>
3425       </div>
3426
3427       <div class="SECT3">
3428         <h4 class="SECT3"><a name="HIDE-USER-AGENT" id=
3429         "HIDE-USER-AGENT">8.5.25. hide-user-agent</a></h4>
3430
3431         <div class="VARIABLELIST">
3432           <dl>
3433             <dt>Typical use:</dt>
3434
3435             <dd>
3436               <p>Try to conceal your type of browser and client operating
3437               system</p>
3438             </dd>
3439
3440             <dt>Effect:</dt>
3441
3442             <dd>
3443               <p>Replaces the value of the <span class=
3444               "QUOTE">"User-Agent:"</span> HTTP header in client requests
3445               with the specified value.</p>
3446             </dd>
3447
3448             <dt>Type:</dt>
3449
3450             <dd>
3451               <p>Parameterized.</p>
3452             </dd>
3453
3454             <dt>Parameter:</dt>
3455
3456             <dd>
3457               <p>Any user-defined string.</p>
3458             </dd>
3459
3460             <dt>Notes:</dt>
3461
3462             <dd>
3463               <div class="WARNING">
3464                 <table class="WARNING" border="1" width="90%">
3465                   <tr>
3466                     <td align="center"><b>Warning</b></td>
3467                   </tr>
3468
3469                   <tr>
3470                     <td align="left">
3471                       <p>This can lead to problems on web sites that depend
3472                       on looking at this header in order to customize their
3473                       content for different browsers (which, by the way, is
3474                       <span class="emphasis"><i class=
3475                       "EMPHASIS">NOT</i></span> the right thing to do: good
3476                       web sites work browser-independently).</p>
3477                     </td>
3478                   </tr>
3479                 </table>
3480               </div>
3481
3482               <p>Using this action in multi-user setups or wherever different
3483               types of browsers will access the same <span class=
3484               "APPLICATION">Privoxy</span> is <span class=
3485               "emphasis"><i class="EMPHASIS">not recommended</i></span>. In
3486               single-user, single-browser setups, you might use it to delete
3487               your OS version information from the headers, because it is an
3488               invitation to exploit known bugs for your OS. It is also
3489               occasionally useful to forge this in order to access sites that
3490               won't let you in otherwise (though there may be a good reason
3491               in some cases).</p>
3492
3493               <p>More information on known user-agent strings can be found at
3494               <a href="http://www.user-agents.org/" target=
3495               "_top">http://www.user-agents.org/</a> and <a href=
3496               "http://en.wikipedia.org/wiki/User_agent" target=
3497               "_top">http://en.wikipedia.org/wiki/User_agent</a>.</p>
3498             </dd>
3499
3500             <dt>Example usage:</dt>
3501
3502             <dd>
3503               <table border="0" bgcolor="#E0E0E0" width="90%">
3504                 <tr>
3505                   <td>
3506                     <pre class="SCREEN">
3507 +hide-user-agent{Netscape 6.1 (X11; I; Linux 2.4.18 i686)}
3508 </pre>
3509                   </td>
3510                 </tr>
3511               </table>
3512             </dd>
3513           </dl>
3514         </div>
3515       </div>
3516
3517       <div class="SECT3">
3518         <h4 class="SECT3"><a name="LIMIT-CONNECT" id="LIMIT-CONNECT">8.5.26.
3519         limit-connect</a></h4>
3520
3521         <div class="VARIABLELIST">
3522           <dl>
3523             <dt>Typical use:</dt>
3524
3525             <dd>
3526               <p>Prevent abuse of <span class="APPLICATION">Privoxy</span> as
3527               a TCP proxy relay or disable SSL for untrusted sites</p>
3528             </dd>
3529
3530             <dt>Effect:</dt>
3531
3532             <dd>
3533               <p>Specifies to which ports HTTP CONNECT requests are
3534               allowable.</p>
3535             </dd>
3536
3537             <dt>Type:</dt>
3538
3539             <dd>
3540               <p>Parameterized.</p>
3541             </dd>
3542
3543             <dt>Parameter:</dt>
3544
3545             <dd>
3546               <p>A comma-separated list of ports or port ranges (the latter
3547               using dashes, with the minimum defaulting to 0 and the maximum
3548               to 65K).</p>
3549             </dd>
3550
3551             <dt>Notes:</dt>
3552
3553             <dd>
3554               <p>By default, i.e. if no <tt class=
3555               "LITERAL">limit-connect</tt> action applies, <span class=
3556               "APPLICATION">Privoxy</span> allows HTTP CONNECT requests to
3557               all ports. Use <tt class="LITERAL">limit-connect</tt> if
3558               fine-grained control is desired for some or all
3559               destinations.</p>
3560
3561               <p>The CONNECT methods exists in HTTP to allow access to secure
3562               websites (<span class="QUOTE">"https://"</span> URLs) through
3563               proxies. It works very simply: the proxy connects to the server
3564               on the specified port, and then short-circuits its connections
3565               to the client and to the remote server. This means
3566               CONNECT-enabled proxies can be used as TCP relays very
3567               easily.</p>
3568
3569               <p><span class="APPLICATION">Privoxy</span> relays HTTPS
3570               traffic without seeing the decoded content. Websites can
3571               leverage this limitation to circumvent <span class=
3572               "APPLICATION">Privoxy</span>'s filters. By specifying an
3573               invalid port range you can disable HTTPS entirely.</p>
3574             </dd>
3575
3576             <dt>Example usages:</dt>
3577
3578             <dd>
3579               <table border="0" bgcolor="#E0E0E0" width="90%">
3580                 <tr>
3581                   <td>
3582                     <pre class="SCREEN">
3583 +limit-connect{443}                   # Port 443 is OK.
3584 +limit-connect{80,443}                # Ports 80 and 443 are OK.
3585 +limit-connect{-3, 7, 20-100, 500-}   # Ports less than 3, 7, 20 to 100 and above 500 are OK.
3586 +limit-connect{-}                     # All ports are OK
3587 +limit-connect{,}                     # No HTTPS/SSL traffic is allowed
3588 </pre>
3589                   </td>
3590                 </tr>
3591               </table>
3592             </dd>
3593           </dl>
3594         </div>
3595       </div>
3596
3597       <div class="SECT3">
3598         <h4 class="SECT3"><a name="LIMIT-COOKIE-LIFETIME" id=
3599         "LIMIT-COOKIE-LIFETIME">8.5.27. limit-cookie-lifetime</a></h4>
3600
3601         <div class="VARIABLELIST">
3602           <dl>
3603             <dt>Typical use:</dt>
3604
3605             <dd>
3606               <p>Limit the lifetime of HTTP cookies to a couple of minutes or
3607               hours.</p>
3608             </dd>
3609
3610             <dt>Effect:</dt>
3611
3612             <dd>
3613               <p>Overwrites the expires field in Set-Cookie server headers if
3614               it's above the specified limit.</p>
3615             </dd>
3616
3617             <dt>Type:</dt>
3618
3619             <dd>
3620               <p>Parameterized.</p>
3621             </dd>
3622
3623             <dt>Parameter:</dt>
3624
3625             <dd>
3626               <p>The lifetime limit in minutes, or 0.</p>
3627             </dd>
3628
3629             <dt>Notes:</dt>
3630
3631             <dd>
3632               <p>This action reduces the lifetime of HTTP cookies coming from
3633               the server to the specified number of minutes, starting from
3634               the time the cookie passes Privoxy.</p>
3635
3636               <p>Cookies with a lifetime below the limit are not modified.
3637               The lifetime of session cookies is set to the specified
3638               limit.</p>
3639
3640               <p>The effect of this action depends on the server.</p>
3641
3642               <p>In case of servers which refresh their cookies with each
3643               response (or at least frequently), the lifetime limit set by
3644               this action is updated as well. Thus, a session associated with
3645               the cookie continues to work with this action enabled, as long
3646               as a new request is made before the last limit set is
3647               reached.</p>
3648
3649               <p>However, some servers send their cookies once, with a
3650               lifetime of several years (the year 2037 is a popular choice),
3651               and do not refresh them until a certain event in the future,
3652               for example the user logging out. In this case this action may
3653               limit the absolute lifetime of the session, even if requests
3654               are made frequently.</p>
3655
3656               <p>If the parameter is <span class="QUOTE">"0"</span>, this
3657               action behaves like <tt class="LITERAL"><a href=
3658               "actions-file.html#SESSION-COOKIES-ONLY">session-cookies-only</a></tt>.</p>
3659             </dd>
3660
3661             <dt>Example usages:</dt>
3662
3663             <dd>
3664               <table border="0" bgcolor="#E0E0E0" width="90%">
3665                 <tr>
3666                   <td>
3667                     <pre class="SCREEN">
3668 +limit-cookie-lifetime{60}
3669
3670 </pre>
3671                   </td>
3672                 </tr>
3673               </table>
3674             </dd>
3675           </dl>
3676         </div>
3677       </div>
3678
3679       <div class="SECT3">
3680         <h4 class="SECT3"><a name="PREVENT-COMPRESSION" id=
3681         "PREVENT-COMPRESSION">8.5.28. prevent-compression</a></h4>
3682
3683         <div class="VARIABLELIST">
3684           <dl>
3685             <dt>Typical use:</dt>
3686
3687             <dd>
3688               <p>Ensure that servers send the content uncompressed, so it can
3689               be passed through <tt class="LITERAL"><a href=
3690               "actions-file.html#FILTER">filter</a></tt>s.</p>
3691             </dd>
3692
3693             <dt>Effect:</dt>
3694
3695             <dd>
3696               <p>Removes the Accept-Encoding header which can be used to ask
3697               for compressed transfer.</p>
3698             </dd>
3699
3700             <dt>Type:</dt>
3701
3702             <dd>
3703               <p>Boolean.</p>
3704             </dd>
3705
3706             <dt>Parameter:</dt>
3707
3708             <dd>
3709               <p>N/A</p>
3710             </dd>
3711
3712             <dt>Notes:</dt>
3713
3714             <dd>
3715               <p>More and more websites send their content compressed by
3716               default, which is generally a good idea and saves bandwidth.
3717               But the <tt class="LITERAL"><a href=
3718               "actions-file.html#FILTER">filter</a></tt> and <tt class=
3719               "LITERAL"><a href=
3720               "actions-file.html#DEANIMATE-GIFS">deanimate-gifs</a></tt>
3721               actions need access to the uncompressed data.</p>
3722
3723               <p>When compiled with zlib support (available since
3724               <span class="APPLICATION">Privoxy</span> 3.0.7), content that
3725               should be filtered is decompressed on-the-fly and you don't
3726               have to worry about this action. If you are using an older
3727               <span class="APPLICATION">Privoxy</span> version, or one that
3728               hasn't been compiled with zlib support, this action can be used
3729               to convince the server to send the content uncompressed.</p>
3730
3731               <p>Most text-based instances compress very well, the size is
3732               seldom decreased by less than 50%, for markup-heavy instances
3733               like news feeds saving more than 90% of the original size isn't
3734               unusual.</p>
3735
3736               <p>Not using compression will therefore slow down the transfer,
3737               and you should only enable this action if you really need it.
3738               As of <span class="APPLICATION">Privoxy</span> 3.0.7 it's
3739               disabled in all predefined action settings.</p>
3740
3741               <p>Note that some (rare) ill-configured sites don't handle
3742               requests for uncompressed documents correctly. Broken PHP
3743               applications tend to send an empty document body, some IIS
3744               versions only send the beginning of the content. If you enable
3745               <tt class="LITERAL">prevent-compression</tt> per default, you
3746               might want to add exceptions for those sites. See the example
3747               for how to do that.</p>
3748             </dd>
3749
3750             <dt>Example usage (sections):</dt>
3751
3752             <dd>
3753               <table border="0" bgcolor="#E0E0E0" width="90%">
3754                 <tr>
3755                   <td>
3756                     <pre class="SCREEN">
3757 # Selectively turn off compression, and enable a filter
3758 #
3759 { +filter{tiny-textforms} +prevent-compression }
3760 # Match only these sites
3761  .google.
3762  sourceforge.net
3763  sf.net
3764
3765 # Or instead, we could set a universal default:
3766 #
3767 { +prevent-compression }
3768  / # Match all sites
3769
3770 # Then maybe make exceptions for broken sites:
3771 #
3772 { -prevent-compression }
3773 .compusa.com/
3774 </pre>
3775                   </td>
3776                 </tr>
3777               </table>
3778             </dd>
3779           </dl>
3780         </div>
3781       </div>
3782
3783       <div class="SECT3">
3784         <h4 class="SECT3"><a name="OVERWRITE-LAST-MODIFIED" id=
3785         "OVERWRITE-LAST-MODIFIED">8.5.29. overwrite-last-modified</a></h4>
3786
3787         <div class="VARIABLELIST">
3788           <dl>
3789             <dt>Typical use:</dt>
3790
3791             <dd>
3792               <p>Prevent yet another way to track the user's steps between
3793               sessions.</p>
3794             </dd>
3795
3796             <dt>Effect:</dt>
3797
3798             <dd>
3799               <p>Deletes the <span class="QUOTE">"Last-Modified:"</span> HTTP
3800               server header or modifies its value.</p>
3801             </dd>
3802
3803             <dt>Type:</dt>
3804
3805             <dd>
3806               <p>Parameterized.</p>
3807             </dd>
3808
3809             <dt>Parameter:</dt>
3810
3811             <dd>
3812               <p>One of the keywords: <span class="QUOTE">"block"</span>,
3813               <span class="QUOTE">"reset-to-request-time"</span> and
3814               <span class="QUOTE">"randomize"</span></p>
3815             </dd>
3816
3817             <dt>Notes:</dt>
3818
3819             <dd>
3820               <p>Removing the <span class="QUOTE">"Last-Modified:"</span>
3821               header is useful for filter testing, where you want to force a
3822               real reload instead of getting status code <span class=
3823               "QUOTE">"304"</span>, which would cause the browser to reuse
3824               the old version of the page.</p>
3825
3826               <p>The <span class="QUOTE">"randomize"</span> option overwrites
3827               the value of the <span class="QUOTE">"Last-Modified:"</span>
3828               header with a randomly chosen time between the original value
3829               and the current time. In theory the server could send each
3830               document with a different <span class=
3831               "QUOTE">"Last-Modified:"</span> header to track visits without
3832               using cookies. <span class="QUOTE">"Randomize"</span> makes it
3833               impossible and the browser can still revalidate cached
3834               documents.</p>
3835
3836               <p><span class="QUOTE">"reset-to-request-time"</span>
3837               overwrites the value of the <span class=
3838               "QUOTE">"Last-Modified:"</span> header with the current time.
3839               You could use this option together with <tt class=
3840               "LITERAL"><a href=
3841               "actions-file.html#HIDE-IF-MODIFIED-SINCE">hide-if-modified-since</a></tt>
3842               to further customize your random range.</p>
3843
3844               <p>The preferred parameter here is <span class=
3845               "QUOTE">"randomize"</span>. It is safe to use, as long as the
3846               time settings are more or less correct. If the server sets the
3847               <span class="QUOTE">"Last-Modified:"</span> header to the time
3848               of the request, the random range becomes zero and the value
3849               stays the same. Therefore you should later randomize it a
3850               second time with <tt class="LITERAL"><a href=
3851               "actions-file.html#HIDE-IF-MODIFIED-SINCE">hided-if-modified-since</a></tt>,
3852               just to be sure.</p>
3853
3854               <p>It is also recommended to use this action together with
3855               <tt class="LITERAL"><a href=
3856               "actions-file.html#CRUNCH-IF-NONE-MATCH">crunch-if-none-match</a></tt>.</p>
3857             </dd>
3858
3859             <dt>Example usage:</dt>
3860
3861             <dd>
3862               <table border="0" bgcolor="#E0E0E0" width="90%">
3863                 <tr>
3864                   <td>
3865                     <pre class="SCREEN">
3866 # Let the browser revalidate without being tracked across sessions
3867 { +hide-if-modified-since{-60} \
3868  +overwrite-last-modified{randomize} \
3869  +crunch-if-none-match}
3870 /
3871 </pre>
3872                   </td>
3873                 </tr>
3874               </table>
3875             </dd>
3876           </dl>
3877         </div>
3878       </div>
3879
3880       <div class="SECT3">
3881         <h4 class="SECT3"><a name="REDIRECT" id="REDIRECT">8.5.30.
3882         redirect</a></h4>
3883
3884         <div class="VARIABLELIST">
3885           <dl>
3886             <dt>Typical use:</dt>
3887
3888             <dd>
3889               <p>Redirect requests to other sites.</p>
3890             </dd>
3891
3892             <dt>Effect:</dt>
3893
3894             <dd>
3895               <p>Convinces the browser that the requested document has been
3896               moved to another location and the browser should get it from
3897               there.</p>
3898             </dd>
3899
3900             <dt>Type:</dt>
3901
3902             <dd>
3903               <p>Parameterized</p>
3904             </dd>
3905
3906             <dt>Parameter:</dt>
3907
3908             <dd>
3909               <p>An absolute URL or a single pcrs command.</p>
3910             </dd>
3911
3912             <dt>Notes:</dt>
3913
3914             <dd>
3915               <p>Requests to which this action applies are answered with a
3916               HTTP redirect to URLs of your choosing. The new URL is either
3917               provided as parameter, or derived by applying a single pcrs
3918               command to the original URL.</p>
3919
3920               <p>The syntax for pcrs commands is documented in the <a href=
3921               "filter-file.html">filter file</a> section.</p>
3922
3923               <p>This action will be ignored if you use it together with
3924               <tt class="LITERAL"><a href=
3925               "actions-file.html#BLOCK">block</a></tt>. It can be combined
3926               with <tt class="LITERAL"><a href=
3927               "actions-file.html#FAST-REDIRECTS">fast-redirects{check-decoded-url}</a></tt>
3928               to redirect to a decoded version of a rewritten URL.</p>
3929
3930               <p>Use this action carefully, make sure not to create
3931               redirection loops and be aware that using your own redirects
3932               might make it possible to fingerprint your requests.</p>
3933
3934               <p>In case of problems with your redirects, or simply to watch
3935               them working, enable <a href="config.html#DEBUG">debug
3936               128</a>.</p>
3937             </dd>
3938
3939             <dt>Example usages:</dt>
3940
3941             <dd>
3942               <table border="0" bgcolor="#E0E0E0" width="90%">
3943                 <tr>
3944                   <td>
3945                     <pre class="SCREEN">
3946 # Replace example.com's style sheet with another one
3947 { +redirect{http://localhost/css-replacements/example.com.css} }
3948  example.com/stylesheet\.css
3949
3950 # Create a short, easy to remember nickname for a favorite site
3951 # (relies on the browser to accept and forward invalid URLs to <span class=
3952 "APPLICATION">Privoxy</span>)
3953 { +redirect{http://www.privoxy.org/user-manual/actions-file.html} }
3954  a
3955
3956 # Always use the expanded view for Undeadly.org articles
3957 # (Note the $ at the end of the URL pattern to make sure
3958 # the request for the rewritten URL isn't redirected as well)
3959 {+redirect{s@$@&amp;mode=expanded@}}
3960 undeadly.org/cgi\?action=article&amp;sid=\d*$
3961
3962 # Redirect Google search requests to MSN
3963 {+redirect{s@^http://[^/]*/search\?q=([^&amp;]*).*@http://search.msn.com/results.aspx?q=$1@}}
3964 .google.com/search
3965
3966 # Redirect MSN search requests to Yahoo
3967 {+redirect{s@^http://[^/]*/results\.aspx\?q=([^&amp;]*).*@http://search.yahoo.com/search?p=$1@}}
3968 search.msn.com//results\.aspx\?q=
3969
3970 # Redirect remote requests for this manual
3971 # to the local version delivered by Privoxy
3972 {+redirect{s@^http://www@http://config@}}
3973 www.privoxy.org/user-manual/
3974 </pre>
3975                   </td>
3976                 </tr>
3977               </table>
3978             </dd>
3979           </dl>
3980         </div>
3981       </div>
3982
3983       <div class="SECT3">
3984         <h4 class="SECT3"><a name="SERVER-HEADER-FILTER" id=
3985         "SERVER-HEADER-FILTER">8.5.31. server-header-filter</a></h4>
3986
3987         <div class="VARIABLELIST">
3988           <dl>
3989             <dt>Typical use:</dt>
3990
3991             <dd>
3992               <p>Rewrite or remove single server headers.</p>
3993             </dd>
3994
3995             <dt>Effect:</dt>
3996
3997             <dd>
3998               <p>All server headers to which this action applies are filtered
3999               on-the-fly through the specified regular expression based
4000               substitutions.</p>
4001             </dd>
4002
4003             <dt>Type:</dt>
4004
4005             <dd>
4006               <p>Parameterized.</p>
4007             </dd>
4008
4009             <dt>Parameter:</dt>
4010
4011             <dd>
4012               <p>The name of a server-header filter, as defined in one of the
4013               <a href="filter-file.html">filter files</a>.</p>
4014             </dd>
4015
4016             <dt>Notes:</dt>
4017
4018             <dd>
4019               <p>Server-header filters are applied to each header on its own,
4020               not to all at once. This makes it easier to diagnose problems,
4021               but on the downside you can't write filters that only change
4022               header x if header y's value is z. You can do that by using
4023               tags though.</p>
4024
4025               <p>Server-header filters are executed after the other header
4026               actions have finished and use their output as input.</p>
4027
4028               <p>Please refer to the <a href="filter-file.html">filter file
4029               chapter</a> to learn which server-header filters are available
4030               by default, and how to create your own.</p>
4031             </dd>
4032
4033             <dt>Example usage (section):</dt>
4034
4035             <dd>
4036               <table border="0" bgcolor="#E0E0E0" width="90%">
4037                 <tr>
4038                   <td>
4039                     <pre class="SCREEN">
4040 {+server-header-filter{html-to-xml}}
4041 example.org/xml-instance-that-is-delivered-as-html
4042
4043 {+server-header-filter{xml-to-html}}
4044 example.org/instance-that-is-delivered-as-xml-but-is-not
4045
4046 </pre>
4047                   </td>
4048                 </tr>
4049               </table>
4050             </dd>
4051           </dl>
4052         </div>
4053       </div>
4054
4055       <div class="SECT3">
4056         <h4 class="SECT3"><a name="SERVER-HEADER-TAGGER" id=
4057         "SERVER-HEADER-TAGGER">8.5.32. server-header-tagger</a></h4>
4058
4059         <div class="VARIABLELIST">
4060           <dl>
4061             <dt>Typical use:</dt>
4062
4063             <dd>
4064               <p>Enable or disable filters based on the Content-Type
4065               header.</p>
4066             </dd>
4067
4068             <dt>Effect:</dt>
4069
4070             <dd>
4071               <p>Server headers to which this action applies are filtered
4072               on-the-fly through the specified regular expression based
4073               substitutions, the result is used as tag.</p>
4074             </dd>
4075
4076             <dt>Type:</dt>
4077
4078             <dd>
4079               <p>Parameterized.</p>
4080             </dd>
4081
4082             <dt>Parameter:</dt>
4083
4084             <dd>
4085               <p>The name of a server-header tagger, as defined in one of the
4086               <a href="filter-file.html">filter files</a>.</p>
4087             </dd>
4088
4089             <dt>Notes:</dt>
4090
4091             <dd>
4092               <p>Server-header taggers are applied to each header on its own,
4093               and as the header isn't modified, each tagger <span class=
4094               "QUOTE">"sees"</span> the original.</p>
4095
4096               <p>Server-header taggers are executed before all other header
4097               actions that modify server headers. Their tags can be used to
4098               control all of the other server-header actions, the content
4099               filters and the crunch actions (<a href=
4100               "actions-file.html#REDIRECT">redirect</a> and <a href=
4101               "actions-file.html#BLOCK">block</a>).</p>
4102
4103               <p>Obviously crunching based on tags created by server-header
4104               taggers doesn't prevent the request from showing up in the
4105               server's log file.</p>
4106             </dd>
4107
4108             <dt>Example usage (section):</dt>
4109
4110             <dd>
4111               <table border="0" bgcolor="#E0E0E0" width="90%">
4112                 <tr>
4113                   <td>
4114                     <pre class="SCREEN">
4115 # Tag every request with the content type declared by the server
4116 {+server-header-tagger{content-type}}
4117 /
4118
4119 </pre>
4120                   </td>
4121                 </tr>
4122               </table>
4123             </dd>
4124           </dl>
4125         </div>
4126       </div>
4127
4128       <div class="SECT3">
4129         <h4 class="SECT3"><a name="SESSION-COOKIES-ONLY" id=
4130         "SESSION-COOKIES-ONLY">8.5.33. session-cookies-only</a></h4>
4131
4132         <div class="VARIABLELIST">
4133           <dl>
4134             <dt>Typical use:</dt>
4135
4136             <dd>
4137               <p>Allow only temporary <span class="QUOTE">"session"</span>
4138               cookies (for the current browser session <span class=
4139               "emphasis"><i class="EMPHASIS">only</i></span>).</p>
4140             </dd>
4141
4142             <dt>Effect:</dt>
4143
4144             <dd>
4145               <p>Deletes the <span class="QUOTE">"expires"</span> field from
4146               <span class="QUOTE">"Set-Cookie:"</span> server headers. Most
4147               browsers will not store such cookies permanently and forget
4148               them in between sessions.</p>
4149             </dd>
4150
4151             <dt>Type:</dt>
4152
4153             <dd>
4154               <p>Boolean.</p>
4155             </dd>
4156
4157             <dt>Parameter:</dt>
4158
4159             <dd>
4160               <p>N/A</p>
4161             </dd>
4162
4163             <dt>Notes:</dt>
4164
4165             <dd>
4166               <p>This is less strict than <tt class="LITERAL"><a href=
4167               "actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a></tt>
4168               / <tt class="LITERAL"><a href=
4169               "actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a></tt>
4170               and allows you to browse websites that insist or rely on
4171               setting cookies, without compromising your privacy too
4172               badly.</p>
4173
4174               <p>Most browsers will not permanently store cookies that have
4175               been processed by <tt class="LITERAL">session-cookies-only</tt>
4176               and will forget about them between sessions. This makes
4177               profiling cookies useless, but won't break sites which require
4178               cookies so that you can log in for transactions. This is
4179               generally turned on for all sites, and is the recommended
4180               setting.</p>
4181
4182               <p>It makes <span class="emphasis"><i class="EMPHASIS">no sense
4183               at all</i></span> to use <tt class=
4184               "LITERAL">session-cookies-only</tt> together with <tt class=
4185               "LITERAL"><a href=
4186               "actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a></tt>
4187               or <tt class="LITERAL"><a href=
4188               "actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a></tt>.
4189               If you do, cookies will be plainly killed.</p>
4190
4191               <p>Note that it is up to the browser how it handles such
4192               cookies without an <span class="QUOTE">"expires"</span> field.
4193               If you use an exotic browser, you might want to try it out to
4194               be sure.</p>
4195
4196               <p>This setting also has no effect on cookies that may have
4197               been stored previously by the browser before starting
4198               <span class="APPLICATION">Privoxy</span>. These would have to
4199               be removed manually.</p>
4200
4201               <p><span class="APPLICATION">Privoxy</span> also uses the
4202               <a href=
4203               "actions-file.html#FILTER-CONTENT-COOKIES">content-cookies
4204               filter</a> to block some types of cookies. Content cookies are
4205               not effected by <tt class=
4206               "LITERAL">session-cookies-only</tt>.</p>
4207             </dd>
4208
4209             <dt>Example usage:</dt>
4210
4211             <dd>
4212               <table border="0" bgcolor="#E0E0E0" width="90%">
4213                 <tr>
4214                   <td>
4215                     <pre class="SCREEN">
4216 +session-cookies-only
4217 </pre>
4218                   </td>
4219                 </tr>
4220               </table>
4221             </dd>
4222           </dl>
4223         </div>
4224       </div>
4225
4226       <div class="SECT3">
4227         <h4 class="SECT3"><a name="SET-IMAGE-BLOCKER" id=
4228         "SET-IMAGE-BLOCKER">8.5.34. set-image-blocker</a></h4>
4229
4230         <div class="VARIABLELIST">
4231           <dl>
4232             <dt>Typical use:</dt>
4233
4234             <dd>
4235               <p>Choose the replacement for blocked images</p>
4236             </dd>
4237
4238             <dt>Effect:</dt>
4239
4240             <dd>
4241               <p>This action alone doesn't do anything noticeable. If
4242               <span class="emphasis"><i class="EMPHASIS">both</i></span>
4243               <tt class="LITERAL"><a href=
4244               "actions-file.html#BLOCK">block</a></tt> <span class=
4245               "emphasis"><i class="EMPHASIS">and</i></span> <tt class=
4246               "LITERAL"><a href=
4247               "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a></tt>
4248               <span class="emphasis"><i class="EMPHASIS">also</i></span>
4249               apply, i.e. if the request is to be blocked as an image,
4250               <span class="emphasis"><i class="EMPHASIS">then</i></span> the
4251               parameter of this action decides what will be sent as a
4252               replacement.</p>
4253             </dd>
4254
4255             <dt>Type:</dt>
4256
4257             <dd>
4258               <p>Parameterized.</p>
4259             </dd>
4260
4261             <dt>Parameter:</dt>
4262
4263             <dd>
4264               <ul>
4265                 <li>
4266                   <p><span class="QUOTE">"pattern"</span> to send a built-in
4267                   checkerboard pattern image. The image is visually decent,
4268                   scales very well, and makes it obvious where banners were
4269                   busted.</p>
4270                 </li>
4271
4272                 <li>
4273                   <p><span class="QUOTE">"blank"</span> to send a built-in
4274                   transparent image. This makes banners disappear completely,
4275                   but makes it hard to detect where <span class=
4276                   "APPLICATION">Privoxy</span> has blocked images on a given
4277                   page and complicates troubleshooting if <span class=
4278                   "APPLICATION">Privoxy</span> has blocked innocent images,
4279                   like navigation icons.</p>
4280                 </li>
4281
4282                 <li>
4283                   <p><span class="QUOTE">"<tt class=
4284                   "REPLACEABLE"><i>target-url</i></tt>"</span> to send a
4285                   redirect to <tt class="REPLACEABLE"><i>target-url</i></tt>.
4286                   You can redirect to any image anywhere, even in your local
4287                   filesystem via <span class="QUOTE">"file:///"</span> URL.
4288                   (But note that not all browsers support redirecting to a
4289                   local file system).</p>
4290
4291                   <p>A good application of redirects is to use special
4292                   <span class="APPLICATION">Privoxy</span>-built-in URLs,
4293                   which send the built-in images, as <tt class=
4294                   "REPLACEABLE"><i>target-url</i></tt>. This has the same
4295                   visual effect as specifying <span class=
4296                   "QUOTE">"blank"</span> or <span class=
4297                   "QUOTE">"pattern"</span> in the first place, but enables
4298                   your browser to cache the replacement image, instead of
4299                   requesting it over and over again.</p>
4300                 </li>
4301               </ul>
4302             </dd>
4303
4304             <dt>Notes:</dt>
4305
4306             <dd>
4307               <p>The URLs for the built-in images are <span class=
4308               "QUOTE">"http://config.privoxy.org/send-banner?type=<tt class=
4309               "REPLACEABLE"><i>type</i></tt>"</span>, where <tt class=
4310               "REPLACEABLE"><i>type</i></tt> is either <span class=
4311               "QUOTE">"blank"</span> or <span class=
4312               "QUOTE">"pattern"</span>.</p>
4313
4314               <p>There is a third (advanced) type, called <span class=
4315               "QUOTE">"auto"</span>. It is <span class="emphasis"><i class=
4316               "EMPHASIS">NOT</i></span> to be used in <tt class=
4317               "LITERAL">set-image-blocker</tt>, but meant for use from
4318               <a href="filter-file.html">filters</a>. Auto will select the
4319               type of image that would have applied to the referring page,
4320               had it been an image.</p>
4321             </dd>
4322
4323             <dt>Example usage:</dt>
4324
4325             <dd>
4326               <p>Built-in pattern:</p>
4327
4328               <table border="0" bgcolor="#E0E0E0" width="90%">
4329                 <tr>
4330                   <td>
4331                     <pre class="SCREEN">
4332 +set-image-blocker{pattern}
4333 </pre>
4334                   </td>
4335                 </tr>
4336               </table>
4337
4338               <p>Redirect to the BSD daemon:</p>
4339
4340               <table border="0" bgcolor="#E0E0E0" width="90%">
4341                 <tr>
4342                   <td>
4343                     <pre class="SCREEN">
4344 +set-image-blocker{http://www.freebsd.org/gifs/dae_up3.gif}
4345 </pre>
4346                   </td>
4347                 </tr>
4348               </table>
4349
4350               <p>Redirect to the built-in pattern for better caching:</p>
4351
4352               <table border="0" bgcolor="#E0E0E0" width="90%">
4353                 <tr>
4354                   <td>
4355                     <pre class="SCREEN">
4356 +set-image-blocker{http://config.privoxy.org/send-banner?type=pattern}
4357 </pre>
4358                   </td>
4359                 </tr>
4360               </table>
4361             </dd>
4362           </dl>
4363         </div>
4364       </div>
4365
4366       <div class="SECT3">
4367         <h3 class="SECT3"><a name="AEN4847" id="AEN4847">8.5.35.
4368         Summary</a></h3>
4369
4370         <p>Note that many of these actions have the potential to cause a page
4371         to misbehave, possibly even not to display at all. There are many
4372         ways a site designer may choose to design his site, and what HTTP
4373         header content, and other criteria, he may depend on. There is no way
4374         to have hard and fast rules for all sites. See the <a href=
4375         "appendix.html#ACTIONSANAT">Appendix</a> for a brief example on
4376         troubleshooting actions.</p>
4377       </div>
4378     </div>
4379
4380     <div class="SECT2">
4381       <h2 class="SECT2"><a name="ALIASES" id="ALIASES">8.6. Aliases</a></h2>
4382
4383       <p>Custom <span class="QUOTE">"actions"</span>, known to <span class=
4384       "APPLICATION">Privoxy</span> as <span class="QUOTE">"aliases"</span>,
4385       can be defined by combining other actions. These can in turn be invoked
4386       just like the built-in actions. Currently, an alias name can contain
4387       any character except space, tab, <span class="QUOTE">"="</span>,
4388       <span class="QUOTE">"{"</span> and <span class="QUOTE">"}"</span>, but
4389       we <span class="emphasis"><i class="EMPHASIS">strongly
4390       recommend</i></span> that you only use <span class="QUOTE">"a"</span>
4391       to <span class="QUOTE">"z"</span>, <span class="QUOTE">"0"</span> to
4392       <span class="QUOTE">"9"</span>, <span class="QUOTE">"+"</span>, and
4393       <span class="QUOTE">"-"</span>. Alias names are not case sensitive, and
4394       are not required to start with a <span class="QUOTE">"+"</span> or
4395       <span class="QUOTE">"-"</span> sign, since they are merely textually
4396       expanded.</p>
4397
4398       <p>Aliases can be used throughout the actions file, but they
4399       <span class="emphasis"><i class="EMPHASIS">must be defined in a special
4400       section at the top of the file!</i></span> And there can only be one
4401       such section per actions file. Each actions file may have its own alias
4402       section, and the aliases defined in it are only visible within that
4403       file.</p>
4404
4405       <p>There are two main reasons to use aliases: One is to save typing for
4406       frequently used combinations of actions, the other one is a gain in
4407       flexibility: If you decide once how you want to handle shops by
4408       defining an alias called <span class="QUOTE">"shop"</span>, you can
4409       later change your policy on shops in <span class="emphasis"><i class=
4410       "EMPHASIS">one</i></span> place, and your changes will take effect
4411       everywhere in the actions file where the <span class=
4412       "QUOTE">"shop"</span> alias is used. Calling aliases by their purpose
4413       also makes your actions files more readable.</p>
4414
4415       <p>Currently, there is one big drawback to using aliases, though:
4416       <span class="APPLICATION">Privoxy</span>'s built-in web-based action
4417       file editor honors aliases when reading the actions files, but it
4418       expands them before writing. So the effects of your aliases are of
4419       course preserved, but the aliases themselves are lost when you edit
4420       sections that use aliases with it.</p>
4421
4422       <p>Now let's define some aliases...</p>
4423
4424       <table border="0" bgcolor="#E0E0E0" width="100%">
4425         <tr>
4426           <td>
4427             <pre class="SCREEN">
4428  # Useful custom aliases we can use later.
4429  #
4430  # Note the (required!) section header line and that this section
4431  # must be at the top of the actions file!
4432  #
4433  {{alias}}
4434
4435  # These aliases just save typing later:
4436  # (Note that some already use other aliases!)
4437  #
4438  +crunch-all-cookies = +<a href=
4439 "actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a> +<a href="actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a>
4440  -crunch-all-cookies = -<a href=
4441 "actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a> -<a href="actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a>
4442  +block-as-image      = +block{Blocked image.} +handle-as-image
4443  allow-all-cookies   = -crunch-all-cookies -<a href=
4444 "actions-file.html#SESSION-COOKIES-ONLY">session-cookies-only</a> -<a href=
4445 "actions-file.html#FILTER-CONTENT-COOKIES">filter{content-cookies}</a>
4446
4447  # These aliases define combinations of actions
4448  # that are useful for certain types of sites:
4449  #
4450  fragile     = -<a href="actions-file.html#BLOCK">block</a> -<a href=
4451 "actions-file.html#FILTER">filter</a> -crunch-all-cookies -<a href=
4452 "actions-file.html#FAST-REDIRECTS">fast-redirects</a> -<a href=
4453 "actions-file.html#HIDE-REFERER">hide-referrer</a> -<a href=
4454 "actions-file.html#PREVENT-COMPRESSION">prevent-compression</a>
4455
4456  shop        = -crunch-all-cookies -<a href=
4457 "actions-file.html#FILTER-ALL-POPUPS">filter{all-popups}</a>
4458
4459  # Short names for other aliases, for really lazy people ;-)
4460  #
4461  c0 = +crunch-all-cookies
4462  c1 = -crunch-all-cookies
4463 </pre>
4464           </td>
4465         </tr>
4466       </table>
4467
4468       <p>...and put them to use. These sections would appear in the lower
4469       part of an actions file and define exceptions to the default actions
4470       (as specified further up for the <span class="QUOTE">"/"</span>
4471       pattern):</p>
4472
4473       <table border="0" bgcolor="#E0E0E0" width="100%">
4474         <tr>
4475           <td>
4476             <pre class="SCREEN">
4477  # These sites are either very complex or very keen on
4478  # user data and require minimal interference to work:
4479  #
4480  {fragile}
4481  .office.microsoft.com
4482  .windowsupdate.microsoft.com
4483  # Gmail is really mail.google.com, not gmail.com
4484  mail.google.com
4485
4486  # Shopping sites:
4487  # Allow cookies (for setting and retrieving your customer data)
4488  #
4489  {shop}
4490  .quietpc.com
4491  .worldpay.com   # for quietpc.com
4492  mybank.example.com
4493
4494  # These shops require pop-ups:
4495  #
4496  {-filter{all-popups} -filter{unsolicited-popups}}
4497   .dabs.com
4498   .overclockers.co.uk
4499 </pre>
4500           </td>
4501         </tr>
4502       </table>
4503
4504       <p>Aliases like <span class="QUOTE">"shop"</span> and <span class=
4505       "QUOTE">"fragile"</span> are typically used for <span class=
4506       "QUOTE">"problem"</span> sites that require more than one action to be
4507       disabled in order to function properly.</p>
4508     </div>
4509
4510     <div class="SECT2">
4511       <h2 class="SECT2"><a name="ACT-EXAMPLES" id="ACT-EXAMPLES">8.7. Actions
4512       Files Tutorial</a></h2>
4513
4514       <p>The above chapters have shown <a href="actions-file.html">which
4515       actions files there are and how they are organized</a>, how actions are
4516       <a href="actions-file.html#ACTIONS">specified</a> and <a href=
4517       "actions-file.html#ACTIONS-APPLY">applied to URLs</a>, how <a href=
4518       "actions-file.html#AF-PATTERNS">patterns</a> work, and how to define
4519       and use <a href="actions-file.html#ALIASES">aliases</a>. Now, let's
4520       look at an example <tt class="FILENAME">match-all.action</tt>,
4521       <tt class="FILENAME">default.action</tt> and <tt class=
4522       "FILENAME">user.action</tt> file and see how all these pieces come
4523       together:</p>
4524
4525       <div class="SECT3">
4526         <h3 class="SECT3"><a name="AEN4911" id="AEN4911">8.7.1.
4527         match-all.action</a></h3>
4528
4529         <p>Remember <span class="emphasis"><i class="EMPHASIS">all actions
4530         are disabled when matching starts</i></span>, so we have to
4531         explicitly enable the ones we want.</p>
4532
4533         <p>While the <tt class="FILENAME">match-all.action</tt> file only
4534         contains a single section, it is probably the most important one. It
4535         has only one pattern, <span class="QUOTE">"<tt class=
4536         "LITERAL">/</tt>"</span>, but this pattern <a href=
4537         "actions-file.html#AF-PATTERNS">matches all URLs</a>. Therefore, the
4538         set of actions used in this <span class="QUOTE">"default"</span>
4539         section <span class="emphasis"><i class="EMPHASIS">will be applied to
4540         all requests as a start</i></span>. It can be partly or wholly
4541         overridden by other actions files like <tt class=
4542         "FILENAME">default.action</tt> and <tt class=
4543         "FILENAME">user.action</tt>, but it will still be largely responsible
4544         for your overall browsing experience.</p>
4545
4546         <p>Again, at the start of matching, all actions are disabled, so
4547         there is no need to disable any actions here. (Remember: a
4548         <span class="QUOTE">"+"</span> preceding the action name enables the
4549         action, a <span class="QUOTE">"-"</span> disables!). Also note how
4550         this long line has been made more readable by splitting it into
4551         multiple lines with line continuation.</p>
4552
4553         <table border="0" bgcolor="#E0E0E0" width="100%">
4554           <tr>
4555             <td>
4556               <pre class="SCREEN">
4557 { \
4558  +<a href=
4559 "actions-file.html#CHANGE-X-FORWARDED-FOR">change-x-forwarded-for{block}</a> \
4560  +<a href="actions-file.html#HIDE-FROM-HEADER">hide-from-header{block}</a> \
4561  +<a href=
4562 "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker{pattern}</a> \
4563 }
4564 / # Match all URLs
4565
4566 </pre>
4567             </td>
4568           </tr>
4569         </table>
4570
4571         <p>The default behavior is now set.</p>
4572       </div>
4573
4574       <div class="SECT3">
4575         <h3 class="SECT3"><a name="AEN4933" id="AEN4933">8.7.2.
4576         default.action</a></h3>
4577
4578         <p>If you aren't a developer, there's no need for you to edit the
4579         <tt class="FILENAME">default.action</tt> file. It is maintained by
4580         the <span class="APPLICATION">Privoxy</span> developers and if you
4581         disagree with some of the sections, you should overrule them in your
4582         <tt class="FILENAME">user.action</tt>.</p>
4583
4584         <p>Understanding the <tt class="FILENAME">default.action</tt> file
4585         can help you with your <tt class="FILENAME">user.action</tt>,
4586         though.</p>
4587
4588         <p>The first section in this file is a special section for internal
4589         use that prevents older <span class="APPLICATION">Privoxy</span>
4590         versions from reading the file:</p>
4591
4592         <table border="0" bgcolor="#E0E0E0" width="100%">
4593           <tr>
4594             <td>
4595               <pre class="SCREEN">
4596 ##########################################################################
4597 # Settings -- Don't change! For internal Privoxy use ONLY.
4598 ##########################################################################
4599 {{settings}}
4600 for-privoxy-version=3.0.11
4601 </pre>
4602             </td>
4603           </tr>
4604         </table>
4605
4606         <p>After that comes the (optional) alias section. We'll use the
4607         example section from the above <a href=
4608         "actions-file.html#ALIASES">chapter on aliases</a>, that also
4609         explains why and how aliases are used:</p>
4610
4611         <table border="0" bgcolor="#E0E0E0" width="100%">
4612           <tr>
4613             <td>
4614               <pre class="SCREEN">
4615 ##########################################################################
4616 # Aliases
4617 ##########################################################################
4618 {{alias}}
4619
4620  # These aliases just save typing later:
4621  # (Note that some already use other aliases!)
4622  #
4623  +crunch-all-cookies = +<a href=
4624 "actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a> +<a href="actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a>
4625  -crunch-all-cookies = -<a href=
4626 "actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a> -<a href="actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a>
4627  +block-as-image      = +block{Blocked image.} +handle-as-image
4628  mercy-for-cookies   = -crunch-all-cookies -<a href=
4629 "actions-file.html#SESSION-COOKIES-ONLY">session-cookies-only</a> -<a href=
4630 "actions-file.html#FILTER-CONTENT-COOKIES">filter{content-cookies}</a>
4631
4632  # These aliases define combinations of actions
4633  # that are useful for certain types of sites:
4634  #
4635  fragile     = -<a href="actions-file.html#BLOCK">block</a> -<a href=
4636 "actions-file.html#FILTER">filter</a> -crunch-all-cookies -<a href=
4637 "actions-file.html#FAST-REDIRECTS">fast-redirects</a> -<a href=
4638 "actions-file.html#HIDE-REFERER">hide-referrer</a>
4639  shop        = -crunch-all-cookies -<a href=
4640 "actions-file.html#FILTER-ALL-POPUPS">filter{all-popups}</a>
4641 </pre>
4642             </td>
4643           </tr>
4644         </table>
4645
4646         <p>The first of our specialized sections is concerned with
4647         <span class="QUOTE">"fragile"</span> sites, i.e. sites that require
4648         minimum interference, because they are either very complex or very
4649         keen on tracking you (and have mechanisms in place that make them
4650         unusable for people who avoid being tracked). We will simply use our
4651         pre-defined <tt class="LITERAL">fragile</tt> alias instead of stating
4652         the list of actions explicitly:</p>
4653
4654         <table border="0" bgcolor="#E0E0E0" width="100%">
4655           <tr>
4656             <td>
4657               <pre class="SCREEN">
4658 ##########################################################################
4659 # Exceptions for sites that'll break under the default action set:
4660 ##########################################################################
4661
4662 # "Fragile" Use a minimum set of actions for these sites (see alias above):
4663 #
4664 { fragile }
4665 .office.microsoft.com           # surprise, surprise!
4666 .windowsupdate.microsoft.com
4667 mail.google.com
4668 </pre>
4669             </td>
4670           </tr>
4671         </table>
4672
4673         <p>Shopping sites are not as fragile, but they typically require
4674         cookies to log in, and pop-up windows for shopping carts or item
4675         details. Again, we'll use a pre-defined alias:</p>
4676
4677         <table border="0" bgcolor="#E0E0E0" width="100%">
4678           <tr>
4679             <td>
4680               <pre class="SCREEN">
4681 # Shopping sites:
4682 #
4683 { shop }
4684 .quietpc.com
4685 .worldpay.com   # for quietpc.com
4686 .jungle.com
4687 .scan.co.uk
4688 </pre>
4689             </td>
4690           </tr>
4691         </table>
4692
4693         <p>The <tt class="LITERAL"><a href=
4694         "actions-file.html#FAST-REDIRECTS">fast-redirects</a></tt> action,
4695         which may have been enabled in <tt class=
4696         "FILENAME">match-all.action</tt>, breaks some sites. So disable it
4697         for popular sites where we know it misbehaves:</p>
4698
4699         <table border="0" bgcolor="#E0E0E0" width="100%">
4700           <tr>
4701             <td>
4702               <pre class="SCREEN">
4703 { -<a href="actions-file.html#FAST-REDIRECTS">fast-redirects</a> }
4704 login.yahoo.com
4705 edit.*.yahoo.com
4706 .google.com
4707 .altavista.com/.*(like|url|link):http
4708 .altavista.com/trans.*urltext=http
4709 .nytimes.com
4710 </pre>
4711             </td>
4712           </tr>
4713         </table>
4714
4715         <p>It is important that <span class="APPLICATION">Privoxy</span>
4716         knows which URLs belong to images, so that <span class=
4717         "emphasis"><i class="EMPHASIS">if</i></span> they are to be blocked,
4718         a substitute image can be sent, rather than an HTML page. Contacting
4719         the remote site to find out is not an option, since it would destroy
4720         the loading time advantage of banner blocking, and it would feed the
4721         advertisers information about you. We can mark any URL as an image
4722         with the <tt class="LITERAL"><a href=
4723         "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a></tt> action,
4724         and marking all URLs that end in a known image file extension is a
4725         good start:</p>
4726
4727         <table border="0" bgcolor="#E0E0E0" width="100%">
4728           <tr>
4729             <td>
4730               <pre class="SCREEN">
4731 ##########################################################################
4732 # Images:
4733 ##########################################################################
4734
4735 # Define which file types will be treated as images, in case they get
4736 # blocked further down this file:
4737 #
4738 { +<a href="actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a> }
4739 /.*\.(gif|jpe?g|png|bmp|ico)$
4740 </pre>
4741             </td>
4742           </tr>
4743         </table>
4744
4745         <p>And then there are known banner sources. They often use scripts to
4746         generate the banners, so it won't be visible from the URL that the
4747         request is for an image. Hence we block them <span class=
4748         "emphasis"><i class="EMPHASIS">and</i></span> mark them as images in
4749         one go, with the help of our <tt class="LITERAL">+block-as-image</tt>
4750         alias defined above. (We could of course just as well use <tt class=
4751         "LITERAL">+<a href="actions-file.html#BLOCK">block</a> +<a href=
4752         "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a></tt> here.)
4753         Remember that the type of the replacement image is chosen by the
4754         <tt class="LITERAL"><a href=
4755         "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a></tt>
4756         action. Since all URLs have matched the default section with its
4757         <tt class="LITERAL">+<a href=
4758         "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a>{pattern}</tt>
4759         action before, it still applies and needn't be repeated:</p>
4760
4761         <table border="0" bgcolor="#E0E0E0" width="100%">
4762           <tr>
4763             <td>
4764               <pre class="SCREEN">
4765 # Known ad generators:
4766 #
4767 { +block-as-image }
4768 ar.atwola.com
4769 .ad.doubleclick.net
4770 .ad.*.doubleclick.net
4771 .a.yimg.com/(?:(?!/i/).)*$
4772 .a[0-9].yimg.com/(?:(?!/i/).)*$
4773 bs*.gsanet.com
4774 .qkimg.net
4775 </pre>
4776             </td>
4777           </tr>
4778         </table>
4779
4780         <p>One of the most important jobs of <span class=
4781         "APPLICATION">Privoxy</span> is to block banners. Many of these can
4782         be <span class="QUOTE">"blocked"</span> by the <tt class=
4783         "LITERAL"><a href=
4784         "actions-file.html#FILTER">filter</a>{banners-by-size}</tt> action,
4785         which we enabled above, and which deletes the references to banner
4786         images from the pages while they are loaded, so the browser doesn't
4787         request them anymore, and hence they don't need to be blocked here.
4788         But this naturally doesn't catch all banners, and some people choose
4789         not to use filters, so we need a comprehensive list of patterns for
4790         banner URLs here, and apply the <tt class="LITERAL"><a href=
4791         "actions-file.html#BLOCK">block</a></tt> action to them.</p>
4792
4793         <p>First comes many generic patterns, which do most of the work, by
4794         matching typical domain and path name components of banners. Then
4795         comes a list of individual patterns for specific sites, which is
4796         omitted here to keep the example short:</p>
4797
4798         <table border="0" bgcolor="#E0E0E0" width="100%">
4799           <tr>
4800             <td>
4801               <pre class="SCREEN">
4802 ##########################################################################
4803 # Block these fine banners:
4804 ##########################################################################
4805 { <a href="actions-file.html#BLOCK">+block{Banner ads.}</a> }
4806
4807 # Generic patterns:
4808 #
4809 ad*.
4810 .*ads.
4811 banner?.
4812 count*.
4813 /.*count(er)?\.(pl|cgi|exe|dll|asp|php[34]?)
4814 /(?:.*/)?(publicite|werbung|rekla(ma|me|am)|annonse|maino(kset|nta|s)?)/
4815
4816 # Site-specific patterns (abbreviated):
4817 #
4818 .hitbox.com
4819 </pre>
4820             </td>
4821           </tr>
4822         </table>
4823
4824         <p>It's quite remarkable how many advertisers actually call their
4825         banner servers ads.<tt class="REPLACEABLE"><i>company</i></tt>.com,
4826         or call the directory in which the banners are stored simply
4827         <span class="QUOTE">"banners"</span>. So the above generic patterns
4828         are surprisingly effective.</p>
4829
4830         <p>But being very generic, they necessarily also catch URLs that we
4831         don't want to block. The pattern <tt class="LITERAL">.*ads.</tt> e.g.
4832         catches <span class="QUOTE">"nasty-<span class="emphasis"><i class=
4833         "EMPHASIS">ads</i></span>.nasty-corp.com"</span> as intended, but
4834         also <span class="QUOTE">"downlo<span class="emphasis"><i class=
4835         "EMPHASIS">ads</i></span>.sourcefroge.net"</span> or <span class=
4836         "QUOTE">"<span class="emphasis"><i class=
4837         "EMPHASIS">ads</i></span>l.some-provider.net."</span> So here come
4838         some well-known exceptions to the <tt class="LITERAL">+<a href=
4839         "actions-file.html#BLOCK">block</a></tt> section above.</p>
4840
4841         <p>Note that these are exceptions to exceptions from the default!
4842         Consider the URL <span class=
4843         "QUOTE">"downloads.sourcefroge.net"</span>: Initially, all actions
4844         are deactivated, so it wouldn't get blocked. Then comes the defaults
4845         section, which matches the URL, but just deactivates the <tt class=
4846         "LITERAL"><a href="actions-file.html#BLOCK">block</a></tt> action
4847         once again. Then it matches <tt class="LITERAL">.*ads.</tt>, an
4848         exception to the general non-blocking policy, and suddenly <tt class=
4849         "LITERAL"><a href="actions-file.html#BLOCK">+block</a></tt> applies.
4850         And now, it'll match <tt class="LITERAL">.*loads.</tt>, where
4851         <tt class="LITERAL"><a href="actions-file.html#BLOCK">-block</a></tt>
4852         applies, so (unless it matches <span class="emphasis"><i class=
4853         "EMPHASIS">again</i></span> further down) it ends up with no
4854         <tt class="LITERAL"><a href="actions-file.html#BLOCK">block</a></tt>
4855         action applying.</p>
4856
4857         <table border="0" bgcolor="#E0E0E0" width="100%">
4858           <tr>
4859             <td>
4860               <pre class="SCREEN">
4861 ##########################################################################
4862 # Save some innocent victims of the above generic block patterns:
4863 ##########################################################################
4864
4865 # By domain:
4866 #
4867 { -<a href="actions-file.html#BLOCK">block</a> }
4868 adv[io]*.  # (for advogato.org and advice.*)
4869 adsl.      # (has nothing to do with ads)
4870 adobe.     # (has nothing to do with ads either)
4871 ad[ud]*.   # (adult.* and add.*)
4872 .edu       # (universities don't host banners (yet!))
4873 .*loads.   # (downloads, uploads etc)
4874
4875 # By path:
4876 #
4877 /.*loads/
4878
4879 # Site-specific:
4880 #
4881 www.globalintersec.com/adv # (adv = advanced)
4882 www.ugu.com/sui/ugu/adv
4883 </pre>
4884             </td>
4885           </tr>
4886         </table>
4887
4888         <p>Filtering source code can have nasty side effects, so make an
4889         exception for our friends at sourceforge.net, and all paths with
4890         <span class="QUOTE">"cvs"</span> in them. Note that <tt class=
4891         "LITERAL">-<a href="actions-file.html#FILTER">filter</a></tt>
4892         disables <span class="emphasis"><i class="EMPHASIS">all</i></span>
4893         filters in one fell swoop!</p>
4894
4895         <table border="0" bgcolor="#E0E0E0" width="100%">
4896           <tr>
4897             <td>
4898               <pre class="SCREEN">
4899 # Don't filter code!
4900 #
4901 { -<a href="actions-file.html#FILTER">filter</a> }
4902 /(.*/)?cvs
4903 bugzilla.
4904 developer.
4905 wiki.
4906 .sourceforge.net
4907 </pre>
4908             </td>
4909           </tr>
4910         </table>
4911
4912         <p>The actual <tt class="FILENAME">default.action</tt> is of course
4913         much more comprehensive, but we hope this example made clear how it
4914         works.</p>
4915       </div>
4916
4917       <div class="SECT3">
4918         <h3 class="SECT3"><a name="AEN5046" id="AEN5046">8.7.3.
4919         user.action</a></h3>
4920
4921         <p>So far we are painting with a broad brush by setting general
4922         policies, which would be a reasonable starting point for many people.
4923         Now, you might want to be more specific and have customized rules
4924         that are more suitable to your personal habits and preferences. These
4925         would be for narrowly defined situations like your ISP or your bank,
4926         and should be placed in <tt class="FILENAME">user.action</tt>, which
4927         is parsed after all other actions files and hence has the last word,
4928         over-riding any previously defined actions. <tt class=
4929         "FILENAME">user.action</tt> is also a <span class=
4930         "emphasis"><i class="EMPHASIS">safe</i></span> place for your
4931         personal settings, since <tt class="FILENAME">default.action</tt> is
4932         actively maintained by the <span class="APPLICATION">Privoxy</span>
4933         developers and you'll probably want to install updated versions from
4934         time to time.</p>
4935
4936         <p>So let's look at a few examples of things that one might typically
4937         do in <tt class="FILENAME">user.action</tt>:</p>
4938
4939         <table border="0" bgcolor="#E0E0E0" width="100%">
4940           <tr>
4941             <td>
4942               <pre class="SCREEN">
4943 # My user.action file. &lt;fred@example.com&gt;
4944 </pre>
4945             </td>
4946           </tr>
4947         </table>
4948
4949         <p>As <a href="actions-file.html#ALIASES">aliases</a> are local to
4950         the actions file that they are defined in, you can't use the ones
4951         from <tt class="FILENAME">default.action</tt>, unless you repeat them
4952         here:</p>
4953
4954         <table border="0" bgcolor="#E0E0E0" width="100%">
4955           <tr>
4956             <td>
4957               <pre class="SCREEN">
4958 # Aliases are local to the file they are defined in.
4959 # (Re-)define aliases for this file:
4960 #
4961 {{alias}}
4962 #
4963 # These aliases just save typing later, and the alias names should
4964 # be self explanatory.
4965 #
4966 +crunch-all-cookies = +crunch-incoming-cookies +crunch-outgoing-cookies
4967 -crunch-all-cookies = -crunch-incoming-cookies -crunch-outgoing-cookies
4968  allow-all-cookies  = -crunch-all-cookies -session-cookies-only
4969  allow-popups       = -filter{all-popups}
4970 +block-as-image     = +block{Blocked as image.} +handle-as-image
4971 -block-as-image     = -block
4972
4973 # These aliases define combinations of actions that are useful for
4974 # certain types of sites:
4975 #
4976 fragile     = -block -crunch-all-cookies -filter -fast-redirects -hide-referrer
4977 shop        = -crunch-all-cookies allow-popups
4978
4979 # Allow ads for selected useful free sites:
4980 #
4981 allow-ads   = -block -filter{banners-by-size} -filter{banners-by-link}
4982
4983 # Alias for specific file types that are text, but might have conflicting
4984 # MIME types. We want the browser to force these to be text documents.
4985 handle-as-text = -<a href="actions-file.html#FILTER">filter</a> +-<a href=
4986 "actions-file.html#CONTENT-TYPE-OVERWRITE">content-type-overwrite{text/plain}</a> +-<a href="actions-file.html#FORCE-TEXT-MODE">force-text-mode</a> -<a href="actions-file.html#HIDE-CONTENT-DISPOSITION">hide-content-disposition</a>
4987 </pre>
4988             </td>
4989           </tr>
4990         </table>
4991
4992         <p>Say you have accounts on some sites that you visit regularly, and
4993         you don't want to have to log in manually each time. So you'd like to
4994         allow persistent cookies for these sites. The <tt class=
4995         "LITERAL">allow-all-cookies</tt> alias defined above does exactly
4996         that, i.e. it disables crunching of cookies in any direction, and the
4997         processing of cookies to make them only temporary.</p>
4998
4999         <table border="0" bgcolor="#E0E0E0" width="100%">
5000           <tr>
5001             <td>
5002               <pre class="SCREEN">
5003 { allow-all-cookies }
5004  sourceforge.net
5005  .yahoo.com
5006  .msdn.microsoft.com
5007  .redhat.com
5008 </pre>
5009             </td>
5010           </tr>
5011         </table>
5012
5013         <p>Your bank is allergic to some filter, but you don't know which, so
5014         you disable them all:</p>
5015
5016         <table border="0" bgcolor="#E0E0E0" width="100%">
5017           <tr>
5018             <td>
5019               <pre class="SCREEN">
5020 { -<a href="actions-file.html#FILTER">filter</a> }
5021  .your-home-banking-site.com
5022 </pre>
5023             </td>
5024           </tr>
5025         </table>
5026
5027         <p>Some file types you may not want to filter for various
5028         reasons:</p>
5029
5030         <table border="0" bgcolor="#E0E0E0" width="100%">
5031           <tr>
5032             <td>
5033               <pre class="SCREEN">
5034 # Technical documentation is likely to contain strings that might
5035 # erroneously get altered by the JavaScript-oriented filters:
5036 #
5037 .tldp.org
5038 /(.*/)?selfhtml/
5039
5040 # And this stupid host sends streaming video with a wrong MIME type,
5041 # so that Privoxy thinks it is getting HTML and starts filtering:
5042 #
5043 stupid-server.example.com/
5044 </pre>
5045             </td>
5046           </tr>
5047         </table>
5048
5049         <p>Example of a simple <a href="actions-file.html#BLOCK">block</a>
5050         action. Say you've seen an ad on your favourite page on example.com
5051         that you want to get rid of. You have right-clicked the image,
5052         selected <span class="QUOTE">"copy image location"</span> and pasted
5053         the URL below while removing the leading http://, into a <tt class=
5054         "LITERAL">{ +block{} }</tt> section. Note that <tt class="LITERAL">{
5055         +handle-as-image }</tt> need not be specified, since all URLs ending
5056         in <tt class="LITERAL">.gif</tt> will be tagged as images by the
5057         general rules as set in default.action anyway:</p>
5058
5059         <table border="0" bgcolor="#E0E0E0" width="100%">
5060           <tr>
5061             <td>
5062               <pre class="SCREEN">
5063 { +<a href="actions-file.html#BLOCK">block</a>{Nasty ads.} }
5064  www.example.com/nasty-ads/sponsor\.gif
5065  another.example.net/more/junk/here/
5066 </pre>
5067             </td>
5068           </tr>
5069         </table>
5070
5071         <p>The URLs of dynamically generated banners, especially from large
5072         banner farms, often don't use the well-known image file name
5073         extensions, which makes it impossible for <span class=
5074         "APPLICATION">Privoxy</span> to guess the file type just by looking
5075         at the URL. You can use the <tt class="LITERAL">+block-as-image</tt>
5076         alias defined above for these cases. Note that objects which match
5077         this rule but then turn out NOT to be an image are typically rendered
5078         as a <span class="QUOTE">"broken image"</span> icon by the browser.
5079         Use cautiously.</p>
5080
5081         <table border="0" bgcolor="#E0E0E0" width="100%">
5082           <tr>
5083             <td>
5084               <pre class="SCREEN">
5085 { +block-as-image }
5086  .doubleclick.net
5087  .fastclick.net
5088  /Realmedia/ads/
5089  ar.atwola.com/
5090 </pre>
5091             </td>
5092           </tr>
5093         </table>
5094
5095         <p>Now you noticed that the default configuration breaks Forbes
5096         Magazine, but you were too lazy to find out which action is the
5097         culprit, and you were again too lazy to give <a href=
5098         "contact.html">feedback</a>, so you just used the <tt class=
5099         "LITERAL">fragile</tt> alias on the site, and -- <span class=
5100         "emphasis"><i class="EMPHASIS">whoa!</i></span> -- it worked. The
5101         <tt class="LITERAL">fragile</tt> aliases disables those actions that
5102         are most likely to break a site. Also, good for testing purposes to
5103         see if it is <span class="APPLICATION">Privoxy</span> that is causing
5104         the problem or not. We later find other regular sites that misbehave,
5105         and add those to our personalized list of troublemakers:</p>
5106
5107         <table border="0" bgcolor="#E0E0E0" width="100%">
5108           <tr>
5109             <td>
5110               <pre class="SCREEN">
5111 { fragile }
5112  .forbes.com
5113  webmail.example.com
5114  .mybank.com
5115 </pre>
5116             </td>
5117           </tr>
5118         </table>
5119
5120         <p>You like the <span class="QUOTE">"fun"</span> text replacements in
5121         <tt class="FILENAME">default.filter</tt>, but it is disabled in the
5122         distributed actions file. So you'd like to turn it on in your
5123         private, update-safe config, once and for all:</p>
5124
5125         <table border="0" bgcolor="#E0E0E0" width="100%">
5126           <tr>
5127             <td>
5128               <pre class="SCREEN">
5129 { +<a href="actions-file.html#FILTER-FUN">filter{fun}</a> }
5130  / # For ALL sites!
5131 </pre>
5132             </td>
5133           </tr>
5134         </table>
5135
5136         <p>Note that the above is not really a good idea: There are
5137         exceptions to the filters in <tt class="FILENAME">default.action</tt>
5138         for things that really shouldn't be filtered, like code on
5139         CVS-&gt;Web interfaces. Since <tt class="FILENAME">user.action</tt>
5140         has the last word, these exceptions won't be valid for the
5141         <span class="QUOTE">"fun"</span> filtering specified here.</p>
5142
5143         <p>You might also worry about how your favourite free websites are
5144         funded, and find that they rely on displaying banner advertisements
5145         to survive. So you might want to specifically allow banners for those
5146         sites that you feel provide value to you:</p>
5147
5148         <table border="0" bgcolor="#E0E0E0" width="100%">
5149           <tr>
5150             <td>
5151               <pre class="SCREEN">
5152 { allow-ads }
5153  .sourceforge.net
5154  .slashdot.org
5155  .osdn.net
5156 </pre>
5157             </td>
5158           </tr>
5159         </table>
5160
5161         <p>Note that <tt class="LITERAL">allow-ads</tt> has been aliased to
5162         <tt class="LITERAL">-<a href=
5163         "actions-file.html#BLOCK">block</a></tt>, <tt class=
5164         "LITERAL">-<a href=
5165         "actions-file.html#FILTER-BANNERS-BY-SIZE">filter{banners-by-size}</a></tt>,
5166         and <tt class="LITERAL">-<a href=
5167         "actions-file.html#FILTER-BANNERS-BY-LINK">filter{banners-by-link}</a></tt>
5168         above.</p>
5169
5170         <p>Invoke another alias here to force an over-ride of the MIME type
5171         <tt class="LITERAL">application/x-sh</tt> which typically would open
5172         a download type dialog. In my case, I want to look at the shell
5173         script, and then I can save it should I choose to.</p>
5174
5175         <table border="0" bgcolor="#E0E0E0" width="100%">
5176           <tr>
5177             <td>
5178               <pre class="SCREEN">
5179 { handle-as-text }
5180  /.*\.sh$
5181 </pre>
5182             </td>
5183           </tr>
5184         </table>
5185
5186         <p><tt class="FILENAME">user.action</tt> is generally the best place
5187         to define exceptions and additions to the default policies of
5188         <tt class="FILENAME">default.action</tt>. Some actions are safe to
5189         have their default policies set here though. So let's set a default
5190         policy to have a <span class="QUOTE">"blank"</span> image as opposed
5191         to the checkerboard pattern for <span class="emphasis"><i class=
5192         "EMPHASIS">ALL</i></span> sites. <span class="QUOTE">"/"</span> of
5193         course matches all URL paths and patterns:</p>
5194
5195         <table border="0" bgcolor="#E0E0E0" width="100%">
5196           <tr>
5197             <td>
5198               <pre class="SCREEN">
5199 { +<a href=
5200 "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker{blank}</a> }
5201 / # ALL sites
5202 </pre>
5203             </td>
5204           </tr>
5205         </table>
5206       </div>
5207     </div>
5208   </div>
5209
5210   <div class="NAVFOOTER">
5211     <hr align="left" width="100%">
5212
5213     <table summary="Footer navigation table" width="100%" border="0"
5214     cellpadding="0" cellspacing="0">
5215       <tr>
5216         <td width="33%" align="left" valign="top"><a href="config.html"
5217         accesskey="P">Prev</a></td>
5218
5219         <td width="34%" align="center" valign="top"><a href="index.html"
5220         accesskey="H">Home</a></td>
5221
5222         <td width="33%" align="right" valign="top"><a href="filter-file.html"
5223         accesskey="N">Next</a></td>
5224       </tr>
5225
5226       <tr>
5227         <td width="33%" align="left" valign="top">The Main Configuration
5228         File</td>
5229
5230         <td width="34%" align="center" valign="top">&nbsp;</td>
5231
5232         <td width="33%" align="right" valign="top">Filter Files</td>
5233       </tr>
5234     </table>
5235   </div>
5236 </body>
5237 </html>