+ <p>By default <span class="APPLICATION">Privoxy</span> leaves the client headers in the order they were
+ sent by the client. Headers are modified in-place, new headers are added at the end of the already
+ existing headers.</p>
+ <p>The header order can be used to fingerprint client requests independently of other headers like the
+ User-Agent.</p>
+ <p>This directive allows to sort the headers differently to better mimic a different User-Agent. Client
+ headers will be emitted in the order given, headers whose name isn't explicitly specified are added at
+ the end.</p>
+ <p>Note that sorting headers in an uncommon way will make fingerprinting actually easier. Encrypted
+ headers are not affected by this directive.</p>
+ </dd>
+ </dl>
+ </div>
+ </div>
+ <div class="SECT3">
+ <h4 class="SECT3"><a name="CLIENT-SPECIFIC-TAG" id="CLIENT-SPECIFIC-TAG">7.6.16. client-specific-tag</a></h4>
+ <div class="VARIABLELIST">
+ <dl>
+ <dt>Specifies:</dt>
+ <dd>
+ <p>The name of a tag that will always be set for clients that requested it through the webinterface.</p>
+ </dd>
+ <dt>Type of value:</dt>
+ <dd>
+ <p><tt class="REPLACEABLE"><i>Tag name followed by a description that will be shown in the
+ webinterface</i></tt></p>
+ </dd>
+ <dt>Default value:</dt>
+ <dd>
+ <p>None</p>
+ </dd>
+ <dt>Notes:</dt>
+ <dd>
+ <div class="WARNING">
+ <table class="WARNING" border="1" width="90%">
+ <tr>
+ <td align="center"><b>Warning</b></td>
+ </tr>
+ <tr>
+ <td align="left">
+ <p>This is an experimental feature. The syntax is likely to change in future versions.</p>
+ </td>
+ </tr>
+ </table>
+ </div>
+ <p>Client-specific tags allow Privoxy admins to create different profiles and let the users chose which
+ one they want without impacting other users.</p>
+ <p>One use case is allowing users to circumvent certain blocks without having to allow them to circumvent
+ all blocks. This is not possible with the <a href="config.html#ENABLE-REMOTE-TOGGLE">enable-remote-toggle
+ feature</a> because it would bluntly disable all blocks for all users and also affect other actions like
+ filters. It also is set globally which renders it useless in most multi-user setups.</p>
+ <p>After a client-specific tag has been defined with the client-specific-tag directive, action sections
+ can be activated based on the tag by using a <a href="actions-file.html#CLIENT-TAG-PATTERN" target=
+ "_top">CLIENT-TAG</a> pattern. The CLIENT-TAG pattern is evaluated at the same priority as URL patterns,
+ as a result the last matching pattern wins. Tags that are created based on client or server headers are
+ evaluated later on and can overrule CLIENT-TAG and URL patterns!</p>
+ <p>The tag is set for all requests that come from clients that requested it to be set. Note that
+ "clients" are differentiated by IP address, if the IP address changes the tag has to be requested
+ again.</p>
+ <p>Clients can request tags to be set by using the CGI interface <a href=
+ "http://config.privoxy.org/client-tags" target="_top">http://config.privoxy.org/client-tags</a>. The
+ specific tag description is only used on the web page and should be phrased in away that the user
+ understand the effect of the tag.</p>
+ </dd>
+ <dt>Examples:</dt>
+ <dd>
+ <table border="0" bgcolor="#E0E0E0" width="90%">
+ <tr>
+ <td>
+ <pre class="SCREEN"> # Define a couple of tags, the described effect requires action sections
+ # that are enabled based on CLIENT-TAG patterns.
+ client-specific-tag circumvent-blocks Overrule blocks but do not affect other actions
+ client-specific-tag disable-content-filters Disable content-filters but do not affect other actions</pre>
+ </td>
+ </tr>
+ </table>
+ </dd>
+ </dl>
+ </div>
+ </div>
+ <div class="SECT3">
+ <h4 class="SECT3"><a name="CLIENT-TAG-LIFETIME" id="CLIENT-TAG-LIFETIME">7.6.17. client-tag-lifetime</a></h4>
+ <div class="VARIABLELIST">
+ <dl>
+ <dt>Specifies:</dt>
+ <dd>
+ <p>How long a temporarily enabled tag remains enabled.</p>
+ </dd>
+ <dt>Type of value:</dt>
+ <dd>
+ <p><tt class="REPLACEABLE"><i>Time in seconds.</i></tt></p>
+ </dd>
+ <dt>Default value:</dt>
+ <dd>
+ <p>60</p>
+ </dd>
+ <dt>Notes:</dt>
+ <dd>
+ <div class="WARNING">
+ <table class="WARNING" border="1" width="90%">
+ <tr>
+ <td align="center"><b>Warning</b></td>
+ </tr>
+ <tr>
+ <td align="left">
+ <p>This is an experimental feature. The syntax is likely to change in future versions.</p>
+ </td>
+ </tr>
+ </table>
+ </div>
+ <p>In case of some tags users may not want to enable them permanently, but only for a short amount of
+ time, for example to circumvent a block that is the result of an overly-broad URL pattern.</p>
+ <p>The CGI interface <a href="http://config.privoxy.org/client-tags" target=
+ "_top">http://config.privoxy.org/client-tags</a> therefore provides a "enable this tag temporarily"
+ option. If it is used, the tag will be set until the client-tag-lifetime is over.</p>
+ </dd>
+ <dt>Examples:</dt>
+ <dd>
+ <table border="0" bgcolor="#E0E0E0" width="90%">
+ <tr>
+ <td>
+ <pre class="SCREEN"> # Increase the time to life for temporarily enabled tags to 3 minutes
+ client-tag-lifetime 180</pre>
+ </td>
+ </tr>
+ </table>
+ </dd>
+ </dl>
+ </div>
+ </div>
+ <div class="SECT3">
+ <h4 class="SECT3"><a name="TRUST-X-FORWARDED-FOR" id="TRUST-X-FORWARDED-FOR">7.6.18.
+ trust-x-forwarded-for</a></h4>
+ <div class="VARIABLELIST">
+ <dl>
+ <dt>Specifies:</dt>
+ <dd>
+ <p>Whether or not Privoxy should use IP addresses specified with the X-Forwarded-For header</p>
+ </dd>
+ <dt>Type of value:</dt>
+ <dd>
+ <p><tt class="REPLACEABLE"><i>0 or one</i></tt></p>
+ </dd>
+ <dt>Default value:</dt>
+ <dd>
+ <p>0</p>
+ </dd>
+ <dt>Notes:</dt>
+ <dd>
+ <div class="WARNING">
+ <table class="WARNING" border="1" width="90%">
+ <tr>
+ <td align="center"><b>Warning</b></td>
+ </tr>
+ <tr>
+ <td align="left">
+ <p>This is an experimental feature. The syntax is likely to change in future versions.</p>
+ </td>
+ </tr>
+ </table>
+ </div>
+ <p>If clients reach Privoxy through another proxy, for example a load balancer, Privoxy can't tell the
+ client's IP address from the connection. If multiple clients use the same proxy, they will share the same
+ client tag settings which is usually not desired.</p>
+ <p>This option lets Privoxy use the X-Forwarded-For header value as client IP address. If the proxy sets
+ the header, multiple clients using the same proxy do not share the same client tag settings.</p>
+ <p>This option should only be enabled if Privoxy can only be reached through a proxy and if the proxy can
+ be trusted to set the header correctly. It is recommended that ACL are used to make sure only trusted
+ systems can reach Privoxy.</p>
+ <p>If access to Privoxy isn't limited to trusted systems, this option would allow malicious clients to
+ change the client tags for other clients or increase Privoxy's memory requirements by registering lots of
+ client tag settings for clients that don't exist.</p>
+ </dd>
+ <dt>Examples:</dt>
+ <dd>
+ <table border="0" bgcolor="#E0E0E0" width="90%">
+ <tr>
+ <td>
+ <pre class="SCREEN"> # Allow systems that can reach Privoxy to provide the client
+ # IP address with a X-Forwarded-For header.
+ trust-x-forwarded-for 1</pre>
+ </td>
+ </tr>
+ </table>
+ </dd>
+ </dl>
+ </div>
+ </div>
+ <div class="SECT3">
+ <h4 class="SECT3"><a name="RECEIVE-BUFFER-SIZE" id="RECEIVE-BUFFER-SIZE">7.6.19. receive-buffer-size</a></h4>
+ <div class="VARIABLELIST">
+ <dl>
+ <dt>Specifies:</dt>
+ <dd>
+ <p>The size of the buffer Privoxy uses to receive data from the server.</p>
+ </dd>
+ <dt>Type of value:</dt>
+ <dd>
+ <p><tt class="REPLACEABLE"><i>Size in bytes</i></tt></p>
+ </dd>
+ <dt>Default value:</dt>
+ <dd>
+ <p>5000</p>
+ </dd>
+ <dt>Notes:</dt>
+ <dd>
+ <p>Increasing the receive-buffer-size increases Privoxy's memory usage but can lower the number of
+ context switches and thereby reduce the cpu usage and potentially increase the throughput.</p>
+ <p>This is mostly relevant for fast network connections and large downloads that don't require
+ filtering.</p>
+ <p>Reducing the buffer size reduces the amount of memory Privoxy needs to handle the request but
+ increases the number of systemcalls and may reduce the throughput.</p>
+ <p>A dtrace command like: <span class="QUOTE">"sudo dtrace -n 'syscall::read:return /execname ==
+ "privoxy"/ { @[execname] = llquantize(arg0, 10, 0, 5, 20); @m = max(arg0)}'"</span> can be used to
+ properly tune the receive-buffer-size. On systems without dtrace, strace or truss may be used as less
+ convenient alternatives.</p>
+ <p>If the buffer is too large it will increase Privoxy's memory footprint without any benefit. As the
+ memory is (currently) cleared before using it, a buffer that is too large can actually reduce the
+ throughput.</p>
+ </dd>
+ <dt>Examples:</dt>
+ <dd>
+ <table border="0" bgcolor="#E0E0E0" width="90%">
+ <tr>
+ <td>
+ <pre class="SCREEN"> # Increase the receive buffer size
+ receive-buffer-size 32768</pre>
+ </td>
+ </tr>
+ </table>