1 <?xml version="1.0" encoding="ISO-8859-1"?>
2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
3 <html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!--
4 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
5 This file is generated from xml source: DO NOT EDIT
6 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
8 <title>mod_filter - Apache HTTP Server</title>
9 <link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
10 <link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
11 <link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" />
12 <link href="../images/favicon.ico" rel="shortcut icon" /></head>
14 <div id="page-header">
15 <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
16 <p class="apache">Apache HTTP Server Version 2.3</p>
17 <img alt="" src="../images/feather.gif" /></div>
18 <div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
20 <a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.3</a> > <a href="./">Modules</a></div>
21 <div id="page-content">
22 <div id="preamble"><h1>Apache Module mod_filter</h1>
24 <p><span>Available Languages: </span><a href="../en/mod/mod_filter.html" title="English"> en </a></p>
26 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Context-sensitive smart filter configuration module</td></tr>
27 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Base</td></tr>
28 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>filter_module</td></tr>
29 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_filter.c</td></tr>
30 <tr><th><a href="module-dict.html#Compatibility">Compatibility:</a></th><td>Version 2.1 and later</td></tr></table>
33 <p>This module enables smart, context-sensitive configuration of
34 output content filters. For example, apache can be configured to
35 process different content-types through different filters, even
36 when the content-type is not known in advance (e.g. in a proxy).</p>
38 <p><code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> works by introducing indirection into
39 the filter chain. Instead of inserting filters in the chain, we insert
40 a filter harness which in turn dispatches conditionally
41 to a filter provider. Any content filter may be used as a provider
42 to <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code>; no change to existing filter modules is
43 required (although it may be possible to simplify them).</p>
45 <div id="quickview"><h3 class="directives">Directives</h3>
47 <li><img alt="" src="../images/down.gif" /> <a href="#filterchain">FilterChain</a></li>
48 <li><img alt="" src="../images/down.gif" /> <a href="#filterdeclare">FilterDeclare</a></li>
49 <li><img alt="" src="../images/down.gif" /> <a href="#filterprotocol">FilterProtocol</a></li>
50 <li><img alt="" src="../images/down.gif" /> <a href="#filterprovider">FilterProvider</a></li>
51 <li><img alt="" src="../images/down.gif" /> <a href="#filtertrace">FilterTrace</a></li>
55 <li><img alt="" src="../images/down.gif" /> <a href="#smart">Smart Filtering</a></li>
56 <li><img alt="" src="../images/down.gif" /> <a href="#terms">Filter Declarations, Providers and Chains</a></li>
57 <li><img alt="" src="../images/down.gif" /> <a href="#config">Configuring the Chain</a></li>
58 <li><img alt="" src="../images/down.gif" /> <a href="#errordocs">Filtering and Response Status</a></li>
59 <li><img alt="" src="../images/down.gif" /> <a href="#upgrade">Upgrading from HTTPD 2.2 Configuration</a></li>
60 <li><img alt="" src="../images/down.gif" /> <a href="#examples">Examples</a></li>
61 <li><img alt="" src="../images/down.gif" /> <a href="#protocol">Protocol Handling</a></li>
63 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
65 <h2><a name="smart" id="smart">Smart Filtering</a></h2>
66 <p>In the traditional filtering model, filters are inserted unconditionally
67 using <code class="directive"><a href="../mod/mod_mime.html#addoutputfilter">AddOutputFilter</a></code> and family.
68 Each filter then needs to determine whether to run, and there is little
69 flexibility available for server admins to allow the chain to be
70 configured dynamically.</p>
72 <p><code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> by contrast gives server administrators a
73 great deal of flexibility in configuring the filter chain. In fact,
74 filters can be inserted based on any Request Header, Response Header
75 or Environment Variable. This generalises the limited flexibility offered
76 by <code class="directive"><a href="../mod/core.html#addoutputfilterbytype">AddOutputFilterByType</a></code>, and fixes
77 it to work correctly with dynamic content, regardless of the
78 content generator. The ability to dispatch based on Environment
79 Variables offers the full flexibility of configuration with
80 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> to anyone who needs it.</p>
81 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
83 <h2><a name="terms" id="terms">Filter Declarations, Providers and Chains</a></h2>
85 <img src="../images/mod_filter_old.gif" width="160" height="310" alt="[This image displays the traditional filter model]" /><br />
86 <dfn>Figure 1:</dfn> The traditional filter model</p>
88 <p>In the traditional model, output filters are a simple chain
89 from the content generator (handler) to the client. This works well
90 provided the filter chain can be correctly configured, but presents
91 problems when the filters need to be configured dynamically based on
92 the outcome of the handler.</p>
95 <img src="../images/mod_filter_new.gif" width="423" height="331" alt="[This image shows the mod_filter model]" /><br />
96 <dfn>Figure 2:</dfn> The <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> model</p>
98 <p><code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> works by introducing indirection into
99 the filter chain. Instead of inserting filters in the chain, we insert
100 a filter harness which in turn dispatches conditionally
101 to a filter provider. Any content filter may be used as a provider
102 to <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code>; no change to existing filter modules
103 is required (although it may be possible to simplify them). There can be
104 multiple providers for one filter, but no more than one provider will
105 run for any single request.</p>
107 <p>A filter chain comprises any number of instances of the filter
108 harness, each of which may have any number of providers. A special
109 case is that of a single provider with unconditional dispatch: this
110 is equivalent to inserting the provider filter directly into the chain.</p>
111 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
112 <div class="section">
113 <h2><a name="config" id="config">Configuring the Chain</a></h2>
114 <p>There are three stages to configuring a filter chain with
115 <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code>. For details of the directives, see below.</p>
118 <dt>Declare Filters</dt>
119 <dd>The <code class="directive"><a href="#filterdeclare">FilterDeclare</a></code> directive
120 declares a filter, assigning it a name and filter type. Required
121 only if the filter is not the default type AP_FTYPE_RESOURCE.</dd>
123 <dt>Register Providers</dt>
124 <dd>The <code class="directive"><a href="#filterprovider">FilterProvider</a></code>
125 directive registers a provider with a filter. The filter may have
126 been declared with <code class="directive"><a href="#filterdeclare">FilterDeclare</a></code>; if not, FilterProvider will implicitly
127 declare it with the default type AP_FTYPE_RESOURCE. The provider
129 registered with <code>ap_register_output_filter</code> by some module.
130 The final argument to <code class="directive"><a href="#filterprovider">FilterProvider</a></code> is an expression: the provider will be
131 selected to run for a request if and only if the expression evaluates
132 to true. The expression may evaluate HTTP request or response
133 headers, environment variables, or the Handler used by this request.
134 Unlike earlier versions, mod_filter now supports complex expressions
135 involving multiple criteria with AND / OR logic (&& / ||)
138 <dt>Configure the Chain</dt>
139 <dd>The above directives build components of a smart filter chain,
140 but do not configure it to run. The <code class="directive"><a href="#filterchain">FilterChain</a></code> directive builds a filter chain from smart
141 filters declared, offering the flexibility to insert filters at the
142 beginning or end of the chain, remove a filter, or clear the chain.</dd>
144 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
145 <div class="section">
146 <h2><a name="errordocs" id="errordocs">Filtering and Response Status</a></h2>
147 <p>mod_filter normally only runs filters on responses with
148 HTTP status 200 (OK). If you want to filter documents with
149 other response statuses, you can set the <var>filter-errordocs</var>
150 environment variable, and it will work on all responses
151 regardless of status. To refine this further, you can use
152 expression conditions with <code class="directive">FilterProvider</code>.</p>
153 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
154 <div class="section">
155 <h2><a name="upgrade" id="upgrade">Upgrading from HTTPD 2.2 Configuration</a></h2>
156 <p>The <code class="directive"><a href="#filterprovider">FilterProvider</a></code>
157 directive has changed from HTTPD 2.2: the <var>match</var> and
158 <var>dispatch</var> arguments are replaced with a single but
159 more versatile <var>expression</var>. In general, you can convert
160 a match/dispatch pair to the two sides of an expression, using
162 <div class="example"><p><code>"dispatch = match"</code></p></div>
163 <p>The Request headers, Response headers and Environment variables
164 are now interpreted from syntax <var>$req{foo}</var>,
165 <var>$resp{foo}</var> and <var>$env{foo}</var> respectively.
166 The variables <var>$handler</var> and <var>$Content-Type</var>
167 are also supported.</p>
168 <p>Note that the match no longer supports integer comparisons
169 or substring matches. The latter can be replaced by regular
170 expression matches.</p>
171 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
172 <div class="section">
173 <h2><a name="examples" id="examples">Examples</a></h2>
175 <dt>Server side Includes (SSI)</dt>
176 <dd>A simple case of using <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> in place of
177 <code class="directive"><a href="../mod/core.html#addoutputfilterbytype">AddOutputFilterByType</a></code>
178 <div class="example"><p><code>
179 FilterDeclare SSI<br />
180 FilterProvider SSI INCLUDES "$resp{Content-Type} = /^text\/html/"<br />
185 <dt>Server side Includes (SSI)</dt>
186 <dd>The same as the above but dispatching on handler (classic
187 SSI behaviour; .shtml files get processed).
188 <div class="example"><p><code>
189 FilterProvider SSI INCLUDES "Handler = server-parsed"<br />
194 <dt>Emulating mod_gzip with mod_deflate</dt>
195 <dd>Insert INFLATE filter only if "gzip" is NOT in the
196 Accept-Encoding header. This filter runs with ftype CONTENT_SET.
197 <div class="example"><p><code>
198 FilterDeclare gzip CONTENT_SET<br />
199 FilterProvider gzip inflate "$req{Accept-Encoding} != /gzip/"<br />
204 <dt>Image Downsampling</dt>
205 <dd>Suppose we want to downsample all web images, and have filters
206 for GIF, JPEG and PNG.
207 <div class="example"><p><code>
208 FilterProvider unpack jpeg_unpack "$resp{Content-Type} = image/jpeg"<br />
209 FilterProvider unpack gif_unpack "$resp{Content-Type} = image/gif"<br />
210 FilterProvider unpack png_unpack "$resp{Content-Type} = image/png"<br />
212 FilterProvider downsample downsample_filter "$resp{Content-Type} = /image\/(jpeg|gif|png)/"<br />
213 FilterProtocol downsample "change=yes"<br />
215 FilterProvider repack jpeg_pack "$resp{Content-Type} = image/jpeg"<br />
216 FilterProvider repack gif_pack "$resp{Content-Type} = image/gif"<br />
217 FilterProvider repack png_pack "$resp{Content-Type} = image/png"<br />
218 <Location /image-filter><br />
219 <span class="indent">
220 FilterChain unpack downsample repack<br />
226 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
227 <div class="section">
228 <h2><a name="protocol" id="protocol">Protocol Handling</a></h2>
229 <p>Historically, each filter is responsible for ensuring that whatever
230 changes it makes are correctly represented in the HTTP response headers,
231 and that it does not run when it would make an illegal change. This
232 imposes a burden on filter authors to re-implement some common
233 functionality in every filter:</p>
236 <li>Many filters will change the content, invalidating existing content
237 tags, checksums, hashes, and lengths.</li>
239 <li>Filters that require an entire, unbroken response in input need to
240 ensure they don't get byteranges from a backend.</li>
242 <li>Filters that transform output in a filter need to ensure they don't
243 violate a <code>Cache-Control: no-transform</code> header from the
246 <li>Filters may make responses uncacheable.</li>
249 <p><code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> aims to offer generic handling of these
250 details of filter implementation, reducing the complexity required of
251 content filter modules. This is work-in-progress; the
252 <code class="directive"><a href="#filterprotocol">FilterProtocol</a></code> implements
253 some of this functionality for back-compatibility with Apache 2.0
254 modules. For httpd 2.1 and later, the
255 <code>ap_register_output_filter_protocol</code> and
256 <code>ap_filter_protocol</code> API enables filter modules to
257 declare their own behaviour.</p>
259 <p>At the same time, <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> should not interfere
260 with a filter that wants to handle all aspects of the protocol. By
261 default (i.e. in the absence of any <code class="directive"><a href="#filterprotocol">FilterProtocol</a></code> directives), <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code>
262 will leave the headers untouched.</p>
264 <p>At the time of writing, this feature is largely untested,
265 as modules in common use are designed to work with 2.0.
266 Modules using it should test it carefully.</p>
268 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
269 <div class="directive-section"><h2><a name="FilterChain" id="FilterChain">FilterChain</a> <a name="filterchain" id="filterchain">Directive</a></h2>
270 <table class="directive">
271 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configure the filter chain</td></tr>
272 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>FilterChain [+=-@!]<var>filter-name</var> <var>...</var></code></td></tr>
273 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
274 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Options</td></tr>
275 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
276 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_filter</td></tr>
278 <p>This configures an actual filter chain, from declared filters.
279 <code class="directive">FilterChain</code> takes any number of arguments,
280 each optionally preceded with a single-character control that
281 determines what to do:</p>
284 <dt><code>+<var>filter-name</var></code></dt>
285 <dd>Add <var>filter-name</var> to the end of the filter chain</dd>
287 <dt><code>@<var>filter-name</var></code></dt>
288 <dd>Insert <var>filter-name</var> at the start of the filter chain</dd>
290 <dt><code>-<var>filter-name</var></code></dt>
291 <dd>Remove <var>filter-name</var> from the filter chain</dd>
293 <dt><code>=<var>filter-name</var></code></dt>
294 <dd>Empty the filter chain and insert <var>filter-name</var></dd>
296 <dt><code>!</code></dt>
297 <dd>Empty the filter chain</dd>
299 <dt><code><var>filter-name</var></code></dt>
300 <dd>Equivalent to <code>+<var>filter-name</var></code></dd>
304 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
305 <div class="directive-section"><h2><a name="FilterDeclare" id="FilterDeclare">FilterDeclare</a> <a name="filterdeclare" id="filterdeclare">Directive</a></h2>
306 <table class="directive">
307 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Declare a smart filter</td></tr>
308 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>FilterDeclare <var>filter-name</var> <var>[type]</var></code></td></tr>
309 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
310 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Options</td></tr>
311 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
312 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_filter</td></tr>
314 <p>This directive declares an output filter together with a
315 header or environment variable that will determine runtime
316 configuration. The first argument is a <var>filter-name</var>
317 for use in <code class="directive"><a href="#filterprovider">FilterProvider</a></code>,
318 <code class="directive"><a href="#filterchain">FilterChain</a></code> and
319 <code class="directive"><a href="#filterprotocol">FilterProtocol</a></code> directives.</p>
321 <p>The final (optional) argument
322 is the type of filter, and takes values of <code>ap_filter_type</code>
323 - namely <code>RESOURCE</code> (the default), <code>CONTENT_SET</code>,
324 <code>PROTOCOL</code>, <code>TRANSCODE</code>, <code>CONNECTION</code>
325 or <code>NETWORK</code>.</p>
328 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
329 <div class="directive-section"><h2><a name="FilterProtocol" id="FilterProtocol">FilterProtocol</a> <a name="filterprotocol" id="filterprotocol">Directive</a></h2>
330 <table class="directive">
331 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Deal with correct HTTP protocol handling</td></tr>
332 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>FilterProtocol <var>filter-name</var> [<var>provider-name</var>]
333 <var>proto-flags</var></code></td></tr>
334 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
335 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Options</td></tr>
336 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
337 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_filter</td></tr>
339 <p>This directs <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> to deal with ensuring the
340 filter doesn't run when it shouldn't, and that the HTTP response
341 headers are correctly set taking into account the effects of the
344 <p>There are two forms of this directive. With three arguments, it
345 applies specifically to a <var>filter-name</var> and a
346 <var>provider-name</var> for that filter.
347 With two arguments it applies to a <var>filter-name</var> whenever the
348 filter runs <em>any</em> provider.</p>
350 <p><var>proto-flags</var> is one or more of</p>
353 <dt><code>change=yes</code></dt>
354 <dd>The filter changes the content, including possibly the content
357 <dt><code>change=1:1</code></dt>
358 <dd>The filter changes the content, but will not change the content
361 <dt><code>byteranges=no</code></dt>
362 <dd>The filter cannot work on byteranges and requires complete input</dd>
364 <dt><code>proxy=no</code></dt>
365 <dd>The filter should not run in a proxy context</dd>
367 <dt><code>proxy=transform</code></dt>
368 <dd>The filter transforms the response in a manner incompatible with
369 the HTTP <code>Cache-Control: no-transform</code> header.</dd>
371 <dt><code>cache=no</code></dt>
372 <dd>The filter renders the output uncacheable (eg by introducing randomised
373 content changes)</dd>
377 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
378 <div class="directive-section"><h2><a name="FilterProvider" id="FilterProvider">FilterProvider</a> <a name="filterprovider" id="filterprovider">Directive</a></h2>
379 <table class="directive">
380 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Register a content filter</td></tr>
381 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>FilterProvider <var>filter-name</var> <var>provider-name</var>
382 <var>expression</var></code></td></tr>
383 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
384 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Options</td></tr>
385 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
386 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_filter</td></tr>
388 <p>This directive registers a <em>provider</em> for the smart filter.
389 The provider will be called if and only if the <var>expression</var>
390 declared evaluates to true when the harness is first called.</p>
393 <var>provider-name</var> must have been registered by loading
394 a module that registers the name with
395 <code>ap_register_output_filter</code>.
398 <p><var>expression</var> can be any of the following:</p>
400 <dt><code><var>string</var></code></dt>
401 <dd>true if <var>string</var> is not empty</dd>
403 <dt><code><var>string1</var> = <var>string2</var><br />
404 <var>string1</var> == <var>string2</var><br />
405 <var>string1</var> != <var>string2</var></code></dt>
407 <dd><p>Compare <var>string1</var> with <var>string2</var>. If
408 <var>string2</var> has the form <code>/<var>string2</var>/</code>
409 then it is treated as a regular expression. Regular expressions are
410 implemented by the <a href="http://www.pcre.org">PCRE</a> engine and
411 have the same syntax as those in <a href="http://www.perl.com">perl
412 5</a>. Note that <code>==</code> is just an alias for <code>=</code>
413 and behaves exactly the same way.</p>
416 <dt><code><var>string1</var> < <var>string2</var><br />
417 <var>string1</var> <= <var>string2</var><br />
418 <var>string1</var> > <var>string2</var><br />
419 <var>string1</var> >= <var>string2</var></code></dt>
421 <dd>Compare <var>string1</var> with <var>string2</var>. Note, that
422 strings are compared <em>literally</em> (using
423 <code>strcmp(3)</code>). Therefore the string "100" is less than
426 <dt><code>( <var>expression</var> )</code></dt>
427 <dd>true if <var>expression</var> is true</dd>
429 <dt><code>! <var>expression</var></code></dt>
430 <dd>true if <var>expression</var> is false</dd>
432 <dt><code><var>expression1</var> &&
433 <var>expression2</var></code></dt>
434 <dd>true if both <var>expression1</var> and
435 <var>expression2</var> are true</dd>
437 <dt><code><var>expression1</var> ||
438 <var>expression2</var></code></dt>
439 <dd>true if either <var>expression1</var> or
440 <var>expression2</var> is true</dd>
445 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
446 <div class="directive-section"><h2><a name="FilterTrace" id="FilterTrace">FilterTrace</a> <a name="filtertrace" id="filtertrace">Directive</a></h2>
447 <table class="directive">
448 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Get debug/diagnostic information from
449 <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code></td></tr>
450 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>FilterTrace <var>filter-name</var> <var>level</var></code></td></tr>
451 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory</td></tr>
452 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
453 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_filter</td></tr>
455 <p>This directive generates debug information from
456 <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code>.
457 It is designed to help test and debug providers (filter modules), although
458 it may also help with <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> itself.</p>
460 <p>The debug output depends on the <var>level</var> set:</p>
462 <dt><code>0</code> (default)</dt>
463 <dd>No debug information is generated.</dd>
465 <dt><code>1</code></dt>
466 <dd><code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> will record buckets and brigades
467 passing through the filter to the error log, before the provider has
468 processed them. This is similar to the information generated by
469 <a href="http://apache.webthing.com/mod_diagnostics/">mod_diagnostics</a>.
472 <dt><code>2</code> (not yet implemented)</dt>
473 <dd>Will dump the full data passing through to a tempfile before the
474 provider. <strong>For single-user debug only</strong>; this will not
475 support concurrent hits.</dd>
480 <div class="bottomlang">
481 <p><span>Available Languages: </span><a href="../en/mod/mod_filter.html" title="English"> en </a></p>
482 </div><div id="footer">
483 <p class="apache">Copyright 2009 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
484 <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div>