| <?xml version="1.0"?> |
| <!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd"> |
| <?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?> |
| <!-- $LastChangedRevision$ --> |
| |
| <!-- |
| Licensed to the Apache Software Foundation (ASF) under one or more |
| contributor license agreements. See the NOTICE file distributed with |
| this work for additional information regarding copyright ownership. |
| The ASF licenses this file to You under the Apache License, Version 2.0 |
| (the "License"); you may not use this file except in compliance with |
| the License. You may obtain a copy of the License at |
| |
| http://www.apache.org/licenses/LICENSE-2.0 |
| |
| Unless required by applicable law or agreed to in writing, software |
| distributed under the License is distributed on an "AS IS" BASIS, |
| WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| See the License for the specific language governing permissions and |
| limitations under the License. |
| --> |
| |
| <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> |
| <highlight language="config"> |
| # mod_ext_filter directive to define a filter |
| # to HTML-ize text/c files using the external |
| # program /usr/bin/enscript, with the type of |
| # the result set to text/html |
| ExtFilterDefine c-to-html mode=output \ |
| intype=text/c outtype=text/html \ |
| cmd="/usr/bin/enscript --color -w html -Ec -o -" |
| |
| <Directory "/export/home/trawick/apacheinst/htdocs/c"> |
| # core directive to cause the new filter to |
| # be run on output |
| SetOutputFilter c-to-html |
| |
| # mod_mime directive to set the type of .c |
| # files to text/c |
| AddType text/c .c |
| </Directory> |
| </highlight> |
| </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> |
| |
| <highlight language="config"> |
| # mod_ext_filter directive to define the external filter |
| ExtFilterDefine gzip mode=output cmd=/bin/gzip |
| |
| <Location "/gzipped"> |
| |
| # core directive to cause the gzip filter to be |
| # run on output |
| SetOutputFilter gzip |
| |
| # mod_headers directive to add |
| # "Content-Encoding: gzip" header field |
| Header set Content-Encoding gzip |
| </Location> |
| </highlight> |
| </section> |
| |
| <section><title>Slowing down the server</title> |
| <highlight language="config"> |
| # mod_ext_filter directive to define a filter |
| # which runs everything through cat; cat doesn't |
| # modify anything; it just introduces extra pathlength |
| # and consumes more resources |
| ExtFilterDefine slowdown mode=output cmd=/bin/cat \ |
| preservescontentlength |
| |
| <Location "/"> |
| # core directive to cause the slowdown filter to |
| # be run several times on output |
| # |
| SetOutputFilter slowdown;slowdown;slowdown |
| </Location> |
| </highlight> |
| </section> |
| |
| <section><title>Using sed to replace text in the response</title> |
| <highlight language="config"> |
| # mod_ext_filter directive to define a filter which |
| # replaces text in the response |
| # |
| ExtFilterDefine fixtext mode=output intype=text/html \ |
| cmd="/bin/sed s/verdana/arial/g" |
| |
| <Location "/"> |
| # core directive to cause the fixtext filter to |
| # be run on output |
| SetOutputFilter fixtext |
| </Location> |
| </highlight> |
| |
| <note> |
| <p>You can do the same thing using <module>mod_substitute</module> |
| without invoking an external process.</p> |
| </note> |
| </section> |
| |
| <section><title>Tracing another filter</title> |
| <highlight language="config"> |
| # Trace the data read and written by mod_deflate |
| # for a particular client (IP 192.168.1.31) |
| # experiencing compression problems. |
| # This filter will trace what goes into mod_deflate. |
| ExtFilterDefine tracebefore \ |
| cmd="/bin/tracefilter.pl /tmp/tracebefore" \ |
| EnableEnv=trace_this_client |
| |
| # This filter will trace what goes after mod_deflate. |
| # Note that without the ftype parameter, the default |
| # filter type of AP_FTYPE_RESOURCE would cause the |
| # filter to be placed *before* mod_deflate in the filter |
| # chain. Giving it a numeric value slightly higher than |
| # AP_FTYPE_CONTENT_SET will ensure that it is placed |
| # after mod_deflate. |
| ExtFilterDefine traceafter \ |
| cmd="/bin/tracefilter.pl /tmp/traceafter" \ |
| EnableEnv=trace_this_client ftype=21 |
| |
| <Directory "/usr/local/docs"> |
| SetEnvIf Remote_Addr 192.168.1.31 trace_this_client |
| SetOutputFilter tracebefore;deflate;traceafter |
| </Directory> |
| </highlight> |
| |
| <example><title>Here is the filter which traces the data:</title> |
| <highlight language="perl"> |
| #!/usr/local/bin/perl -w |
| use strict; |
| |
| open(SAVE, ">$ARGV[0]") |
| or die "can't open $ARGV[0]: $?"; |
| |
| while (<STDIN>) { |
| print SAVE $_; |
| print $_; |
| } |
| |
| close(SAVE); |
| </highlight> |
| </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 <directive module="core" |
| >SetOutputFilter</directive> |
| 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 available |
| in Apache 2.1 and later.</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 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>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> |
| |
| <dt><code>Onfail=[abort|remove]</code></dt> |
| <dd>Determines how to proceed if the external filter program |
| cannot be started. With <code>abort</code> (the default value) |
| the request will be aborted. With <code>remove</code>, the |
| filter is removed and the request continues without it.</dd> |
| </dl> |
| |
| <highlight language="config"> |
| ExtFilterOptions LogStderr |
| </highlight> |
| |
| <p>Messages written to the filter's standard error will be stored |
| in the Apache error log.</p> |
| </usage> |
| </directivesynopsis> |
| |
| </modulesynopsis> |