CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
"><LINK
REL="HOME"
-TITLE="Privoxy 3.0.6 User Manual"
+TITLE="Privoxy 3.0.7 User Manual"
HREF="index.html"><LINK
REL="PREVIOUS"
TITLE="Actions Files"
><TH
COLSPAN="3"
ALIGN="center"
->Privoxy 3.0.6 User Manual</TH
+>Privoxy 3.0.7 User Manual</TH
></TR
><TR
><TD
></A
>9. Filter Files</H1
><P
-> On-the-fly text substitutions that can be invoked through the
- <TT
-CLASS="LITERAL"
-><A
-HREF="actions-file.html#FILTER"
->filter</A
-></TT
-> action need
+> On-the-fly text substitutions need
to be defined in a <SPAN
CLASS="QUOTE"
>"filter file"</SPAN
can then be invoked as an <SPAN
CLASS="QUOTE"
>"action"</SPAN
->. Multiple filter files can be
- defined through the <TT
+>.</P
+><P
+> <SPAN
+CLASS="APPLICATION"
+>Privoxy</SPAN
+> supports three different filter actions:
+ <TT
+CLASS="LITERAL"
+><A
+HREF="actions-file.html#FILTER"
+>filter</A
+></TT
+> to
+ rewrite the content that is send to the client,
+ <TT
+CLASS="LITERAL"
+><A
+HREF="actions-file.html#CLIENT-HEADER-FILTER"
+>client-header-filter</A
+></TT
+>
+ to rewrite headers that are send by the client, and
+ <TT
+CLASS="LITERAL"
+><A
+HREF="actions-file.html#SERVER-HEADER-FILTER"
+>server-header-filter</A
+></TT
+>
+ to rewrite headers that are send by the server, and</P
+><P
+> <SPAN
+CLASS="APPLICATION"
+>Privoxy</SPAN
+> also supports two tagger actions:
+ <TT
+CLASS="LITERAL"
+><A
+HREF="actions-file.html#CLIENT-HEADER-TAGGER"
+>client-header-tagger</A
+></TT
+>
+ and
+ <TT
+CLASS="LITERAL"
+><A
+HREF="actions-file.html#SERVER-HEADER-TAGGER"
+>server-header-tagger</A
+></TT
+>.
+ Taggers and filters use the same syntax in the filter files, the differnce
+ is that taggers don't modify the text they are filtering, but use a rewritten
+ version of the filtered text as tag. The tags can then be used to change the
+ applying actions through sections with <A
+HREF="actions-file.html#TAG-PATTERN"
+>tag-patterns</A
+>.</P
+><P
+> Multiple filter files can be defined through the <TT
CLASS="LITERAL"
> <A
HREF="config.html#FILTERFILE"
>.
</P
><P
-> Typical reasons for doing these kinds of substitutions are to eliminate
- common annoyances in HTML and JavaScript, such as pop-up windows,
+> Command tasks for content filters are to eliminate common annoyances in
+ HTML and JavaScript, such as pop-up windows,
exit consoles, crippled windows without navigation tools, the
infamous <BLINK> tag etc, to suppress images with certain
width and height attributes (standard banner sizes or web-bugs),
- or just to have fun. The possibilities are endless.</P
+ or just to have fun.</P
><P
-> Filtering works on any text-based document type, including
+> Content filtering works on any text-based document type, including
HTML, JavaScript, CSS etc. (all <TT
CLASS="LITERAL"
>text/*</TT
>"roll
your own"</SPAN
> filters, you should first be familiar with HTML syntax,
- and, of course, regular expressions. By default, filters are only applied
- to the raw document content, but can be extended to the HTTP headers with
- the supplemental actions:
- <A
-HREF="actions-file.html#FILTER-CLIENT-HEADERS"
->filter-client-headers</A
-> and
- <A
-HREF="actions-file.html#FILTER-SERVER-HEADERS"
->filter-server-headers</A
->.</P
+ and, of course, regular expressions.</P
><P
> Just like the <A
HREF="actions-file.html"
>filters</I
></SPAN
>
- here. Each filter consists of a heading line, that starts with the
+ here. Each filter consists of a heading line, that starts with one of the
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
->keyword</I
+>keywords</I
></SPAN
> <TT
CLASS="LITERAL"
>FILTER:</TT
->, followed by
- the filter's <SPAN
+>,
+ <TT
+CLASS="LITERAL"
+>CLIENT-HEADER-FILTER:</TT
+> or <TT
+CLASS="LITERAL"
+>SERVER-HEADER-FILTER:</TT
+>
+ followed by the filter's <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>actions file</A
>.</P
><P
-> A filter header line for a filter called <SPAN
+> Filter definitions start with a header line that contains the filter
+ type, the filter name and the filter description.
+ A content filter header line for a filter called <SPAN
CLASS="QUOTE"
>"foo"</SPAN
> could look
><H2
CLASS="SECT2"
><A
-NAME="AEN4346"
+NAME="AEN4528"
></A
>9.1. Filter File Tutorial</H2
><P
> Now, let's complete our <SPAN
CLASS="QUOTE"
>"foo"</SPAN
-> filter. We have already defined
+> content filter. We have already defined
the heading, but the jobs are still missing. Since all it does is to replace
<SPAN
CLASS="QUOTE"
></DT
><DD
><P
-> Header filter to change the Content-Type from xml to html.
+> Server-header filter to change the Content-Type from xml to html.
</P
></DD
><DT
></DT
><DD
><P
-> Header filter to change the Content-Type from html to xml.
+> Server-header filter to change the Content-Type from html to xml.
</P
></DD
><DT
></DT
><DD
><P
-> Header filter to remove the <B
+> Client-header filter to remove the <B
CLASS="COMMAND"
>Tor</B
> exit node notation
found in Host and Referer headers.
</P
+><P
+> If <SPAN
+CLASS="APPLICATION"
+>Privoxy</SPAN
+> and <B
+CLASS="COMMAND"
+>Tor</B
+> are chained and <SPAN
+CLASS="APPLICATION"
+>Privoxy</SPAN
+>
+ is configured to use socks4a, one can use <SPAN
+CLASS="QUOTE"
+>"http://www.example.org.foobar.exit/"</SPAN
+>
+ to access the host <SPAN
+CLASS="QUOTE"
+>"www.example.org"</SPAN
+> through the
+ <B
+CLASS="COMMAND"
+>Tor</B
+> exit node <SPAN
+CLASS="QUOTE"
+>"foobar"</SPAN
+>.
+ </P
+><P
+> As the HTTP client isn't aware of this notation, it treats the
+ whole string <SPAN
+CLASS="QUOTE"
+>"www.example.org.foobar.exit"</SPAN
+> as host and uses it
+ for the <SPAN
+CLASS="QUOTE"
+>"Host"</SPAN
+> and <SPAN
+CLASS="QUOTE"
+>"Referer"</SPAN
+> headers. From the
+ server's point of view the resulting headers are invalid and can cause problems.
+ </P
+><P
+> An invalid <SPAN
+CLASS="QUOTE"
+>"Referer"</SPAN
+> header can trigger <SPAN
+CLASS="QUOTE"
+>"hot-linking"</SPAN
+>
+ protections, an invalid <SPAN
+CLASS="QUOTE"
+>"Host"</SPAN
+> header will make it impossible for
+ the server to find the right vhost (several domains hosted on the same IP address).
+ </P
+><P
+> This client-header filter removes the <SPAN
+CLASS="QUOTE"
+>"foo.exit"</SPAN
+> part in those headers
+ to prevent the mentioned problems. Note that it only modifies
+ the HTTP headers, it doesn't make it impossible for the server
+ to detect your <B
+CLASS="COMMAND"
+>Tor</B
+> exit node based on the IP address
+ the request is coming from.
+ </P
></DD
></DL
></DIV
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