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| <modulesynopsis metafile="mod_ext_filter.xml.meta"> |
| |
| <name>mod_ext_filter</name> |
| <description>Pass the response body through an external program before |
| delivery to the client</description> |
| <status>Extension</status> |
| <sourcefile>mod_ext_filter.c</sourcefile> |
| <identifier>ext_filter_module</identifier> |
| |
| <summary> |
| <p><module>mod_ext_filter</module> presents a simple and familiar |
| programming model for <a href="../filter.html">filters</a>. With |
| this module, a program which reads from stdin and writes to stdout |
| (i.e., a Unix-style filter command) can be a filter for |
| Apache. This filtering mechanism is much slower than using a |
| filter which is specially written for the Apache API and runs |
| inside of the Apache server process, but it does have the |
| following benefits:</p> |
| |
| <ul> |
| <li>the programming model is much simpler</li> |
| |
| <li>any programming/scripting language can be used, provided |
| that it allows the program to read from standard input and |
| write to standard output</li> |
| |
| <li>existing programs can be used unmodified as Apache |
| filters</li> |
| </ul> |
| |
| <p>Even when the performance characteristics are not suitable |
| for production use, <module>mod_ext_filter</module> can be used as |
| a prototype environment for filters.</p> |
| |
| </summary> |
| <seealso><a href="../filter.html">Filters</a></seealso> |
| |
| <section id="examples"><title>Examples</title> |
| |
| <section><title>Generating HTML from some other type of response</title> |
| <example> |
| # mod_ext_filter directive to define a filter<br /> |
| # to HTML-ize text/c files using the external<br /> |
| # program /usr/bin/enscript, with the type of<br /> |
| # the result set to text/html<br /> |
| ExtFilterDefine c-to-html mode=output \<br /> |
| <indent> |
| intype=text/c outtype=text/html \<br /> |
| cmd="/usr/bin/enscript --color -W html -Ec -o - -"<br /> |
| </indent> |
| <br /> |
| <Directory "/export/home/trawick/apacheinst/htdocs/c"><br /> |
| <indent> |
| # core directive to cause the new filter to<br /> |
| # be run on output<br /> |
| SetOutputFilter c-to-html<br /> |
| <br /> |
| # mod_mime directive to set the type of .c<br /> |
| # files to text/c<br /> |
| AddType text/c .c<br /> |
| <br /> |
| # mod_ext_filter directive to set the debug<br /> |
| # level just high enough to see a log message<br /> |
| # per request showing the configuration in force<br /> |
| ExtFilterOptions DebugLevel=1<br /> |
| </indent> |
| </Directory> |
| </example> |
| </section> |
| |
| <section><title>Implementing a content encoding filter</title> |
| <p>Note: this gzip example is just for the purposes of illustration. |
| Please refer to <module>mod_deflate</module> for a practical |
| implementation.</p> |
| |
| <example> |
| # mod_ext_filter directive to define the external filter<br /> |
| ExtFilterDefine gzip mode=output cmd=/bin/gzip<br /> |
| <br /> |
| <Location /gzipped><br /> |
| <indent> |
| # core directive to cause the gzip filter to be<br /> |
| # run on output<br /> |
| SetOutputFilter gzip<br /> |
| <br /> |
| # mod_header directive to add<br /> |
| # "Content-Encoding: gzip" header field<br /> |
| Header set Content-Encoding gzip<br /> |
| </indent> |
| </Location> |
| </example> |
| </section> |
| |
| <section><title>Slowing down the server</title> |
| <example> |
| # mod_ext_filter directive to define a filter<br /> |
| # which runs everything through cat; cat doesn't<br /> |
| # modify anything; it just introduces extra pathlength<br /> |
| # and consumes more resources<br /> |
| ExtFilterDefine slowdown mode=output cmd=/bin/cat \<br /> |
| <indent> |
| preservescontentlength<br /> |
| </indent> |
| <br /> |
| <Location /><br /> |
| <indent> |
| # core directive to cause the slowdown filter to<br /> |
| # be run several times on output<br /> |
| #<br /> |
| SetOutputFilter slowdown;slowdown;slowdown<br /> |
| </indent> |
| </Location> |
| </example> |
| </section> |
| |
| <section><title>Using sed to replace text in the response</title> |
| <example> |
| # mod_ext_filter directive to define a filter which<br /> |
| # replaces text in the response<br /> |
| #<br /> |
| ExtFilterDefine fixtext mode=output intype=text/html \<br /> |
| <indent> |
| cmd="/bin/sed s/verdana/arial/g"<br /> |
| </indent> |
| <br /> |
| <Location /><br /> |
| <indent> |
| # core directive to cause the fixtext filter to<br /> |
| # be run on output<br /> |
| SetOutputFilter fixtext<br /> |
| </indent> |
| </Location> |
| </example> |
| </section> |
| |
| <section><title>Tracing another filter</title> |
| <example> |
| # Trace the data read and written by mod_deflate<br /> |
| # for a particular client (IP 192.168.1.31)<br /> |
| # experiencing compression problems.<br /> |
| # This filter will trace what goes into mod_deflate.<br /> |
| ExtFilterDefine tracebefore \<br /> |
| <indent> |
| cmd="/bin/tracefilter.pl /tmp/tracebefore" \<br /> |
| EnableEnv=trace_this_client<br /> |
| </indent> |
| <br /> |
| # This filter will trace what goes after mod_deflate.<br /> |
| # Note that without the ftype parameter, the default<br /> |
| # filter type of AP_FTYPE_RESOURCE would cause the<br /> |
| # filter to be placed *before* mod_deflate in the filter<br /> |
| # chain. Giving it a numeric value slightly higher than<br /> |
| # AP_FTYPE_CONTENT_SET will ensure that it is placed<br /> |
| # after mod_deflate.<br /> |
| ExtFilterDefine traceafter \<br /> |
| <indent> |
| cmd="/bin/tracefilter.pl /tmp/traceafter" \<br /> |
| EnableEnv=trace_this_client ftype=21<br /> |
| </indent> |
| <br /> |
| <Directory /usr/local/docs><br /> |
| <indent> |
| SetEnvIf Remote_Addr 192.168.1.31 trace_this_client<br /> |
| SetOutputFilter tracebefore;deflate;traceafter<br /> |
| </indent> |
| </Directory> |
| </example> |
| |
| <example><title>Here is the filter which traces the data:</title> |
| #!/usr/local/bin/perl -w<br /> |
| use strict;<br /> |
| <br /> |
| open(SAVE, ">$ARGV[0]")<br /> |
| <indent> |
| or die "can't open $ARGV[0]: $?";<br /> |
| </indent> |
| <br /> |
| while (<STDIN>) {<br /> |
| <indent> |
| print SAVE $_;<br /> |
| print $_;<br /> |
| </indent> |
| }<br /> |
| <br /> |
| close(SAVE); |
| </example> |
| </section> |
| </section> <!-- /Examples --> |
| |
| <directivesynopsis> |
| <name>ExtFilterDefine</name> |
| <description>Define an external filter</description> |
| <syntax>ExtFilterDefine <var>filtername</var> <var>parameters</var></syntax> |
| <contextlist><context>server config</context></contextlist> |
| |
| <usage> |
| <p>The <directive>ExtFilterDefine</directive> directive defines the |
| characteristics of an external filter, including the program to |
| run and its arguments.</p> |
| |
| <p><var>filtername</var> specifies the name of the filter being |
| defined. This name can then be used in SetOutputFilter |
| directives. It must be unique among all registered filters. |
| <em>At the present time, no error is reported by the |
| register-filter API, so a problem with duplicate names isn't |
| reported to the user.</em></p> |
| |
| <p>Subsequent parameters can appear in any order and define the |
| external command to run and certain other characteristics. The |
| only required parameter is <code>cmd=</code>. These parameters |
| are:</p> |
| |
| <dl> |
| <dt><code>cmd=<var>cmdline</var></code></dt> |
| |
| <dd>The <code>cmd=</code> keyword allows you to specify the |
| external command to run. If there are arguments after the |
| program name, the command line should be surrounded in |
| quotation marks (<em>e.g.</em>, <code>cmd="<var>/bin/mypgm</var> |
| <var>arg1</var> <var>arg2</var>"</code>. Normal shell quoting is |
| not necessary since the program is run directly, bypassing the shell. |
| Program arguments are blank-delimited. A backslash can be used to |
| escape blanks which should be part of a program argument. Any |
| backslashes which are part of the argument must be escaped with |
| backslash themselves. In addition to the standard CGI environment |
| variables, DOCUMENT_URI, DOCUMENT_PATH_INFO, and |
| QUERY_STRING_UNESCAPED will also be set for the program.</dd> |
| |
| <dt><code>mode=<var>mode</var></code></dt> |
| |
| <dd>Use <code>mode=output</code> (the default) for filters which |
| process the response. Use <code>mode=input</code> for filters |
| which process the request. <code>mode=input</code> is new with |
| Apache 2.1.</dd> |
| |
| <dt><code>intype=<var>imt</var></code></dt> |
| |
| <dd>This parameter specifies the internet media type (<em>i.e.</em>, |
| MIME type) of documents which should be filtered. By default, |
| all documents are filtered. If <code>intype=</code> is |
| specified, the filter will be disabled for documents of other |
| types.</dd> |
| |
| <dt><code>outtype=<var>imt</var></code></dt> |
| |
| <dd>This parameter specifies the internet media type (<em>i.e.</em>, |
| MIME type) of filtered documents. It is useful when the |
| filter changes the internet media type as part of the |
| filtering operation. By default, the internet media type is |
| unchanged.</dd> |
| |
| <dt><code>PreservesContentLength</code></dt> |
| |
| <dd>The <code>PreservesContentLength</code> keyword specifies |
| that the filter preserves the content length. This is not the |
| default, as most filters change the content length. In the |
| event that the filter doesn't modify the length, this keyword |
| should be specified.</dd> |
| |
| <dt><code>ftype=<var>filtertype</var></code></dt> |
| |
| <dd>This parameter specifies the numeric value for filter type |
| that the filter should be registered as. The default value, |
| AP_FTYPE_RESOURCE, is sufficient in most cases. If the filter |
| needs to operate at a different point in the filter chain than |
| resource filters, then this parameter will be necessary. See |
| the AP_FTYPE_foo definitions in util_filter.h for appropriate |
| values.</dd> |
| |
| <dt><code>disableenv=<var>env</var></code></dt> |
| |
| <dd>This parameter specifies the name of an environment variable |
| which, if set, will disable the filter.</dd> |
| |
| <dt><code>enableenv=<var>env</var></code></dt> |
| |
| <dd>This parameter specifies the name of an environment variable |
| which must be set, or the filter will be disabled.</dd> |
| </dl> |
| </usage> |
| </directivesynopsis> |
| |
| <directivesynopsis> |
| <name>ExtFilterOptions</name> |
| <description>Configure <module>mod_ext_filter</module> options</description> |
| <syntax>ExtFilterOptions <var>option</var> [<var>option</var>] ...</syntax> |
| <default>ExtFilterOptions DebugLevel=0 NoLogStderr</default> |
| <contextlist><context>directory</context></contextlist> |
| |
| <usage> |
| <p>The <directive>ExtFilterOptions</directive> directive specifies |
| special processing options for <module>mod_ext_filter</module>. |
| <var>Option</var> can be one of</p> |
| |
| <dl> |
| <dt><code>DebugLevel=<var>n</var></code></dt> |
| |
| <dd> |
| The <code>DebugLevel</code> keyword allows you to specify |
| the level of debug messages generated by |
| <module>mod_ext_filter</module>. By default, no debug messages |
| are generated. This is equivalent to |
| <code>DebugLevel=0</code>. With higher numbers, more debug |
| messages are generated, and server performance will be |
| degraded. The actual meanings of the numeric values are |
| described with the definitions of the DBGLVL_ constants |
| near the beginning of <code>mod_ext_filter.c</code>. |
| |
| <p>Note: The core directive <directive module="core" |
| >LogLevel</directive> should be used to cause debug messages to |
| be stored in the Apache error log.</p> |
| </dd> |
| |
| <dt><code>LogStderr | NoLogStderr</code></dt> |
| |
| <dd>The <code>LogStderr</code> keyword specifies that |
| messages written to standard error by the external filter |
| program will be saved in the Apache error log. |
| <code>NoLogStderr</code> disables this feature.</dd> |
| </dl> |
| |
| <example><title>Example</title> |
| ExtFilterOptions LogStderr DebugLevel=0 |
| </example> |
| |
| <p>Messages written to the filter's standard error will be stored |
| in the Apache error log. No debug messages will be generated by |
| <module>mod_ext_filter</module>. </p> |
| </usage> |
| </directivesynopsis> |
| |
| </modulesynopsis> |
