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26 <div id="page-content">
27 <div id="preamble"><h1>Apache Module mod_filter</h1>
29 <p><span>Available Languages: </span><a href="../en/mod/mod_filter.html" title="English"> en </a></p>
31 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Context-sensitive smart filter configuration module</td></tr>
32 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Base</td></tr>
33 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>filter_module</td></tr>
34 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_filter.c</td></tr></table>
37 <p>This module enables smart, context-sensitive configuration of
38 output content filters. For example, apache can be configured to
39 process different content-types through different filters, even
40 when the content-type is not known in advance (e.g. in a proxy).</p>
42 <p><code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> works by introducing indirection into
43 the filter chain. Instead of inserting filters in the chain, we insert
44 a filter harness which in turn dispatches conditionally
45 to a filter provider. Any content filter may be used as a provider
46 to <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code>; no change to existing filter modules is
47 required (although it may be possible to simplify them).</p>
49 <div id="quickview"><h3>Topics</h3>
51 <li><img alt="" src="../images/down.gif" /> <a href="#smart">Smart Filtering</a></li>
52 <li><img alt="" src="../images/down.gif" /> <a href="#terms">Filter Declarations, Providers and Chains</a></li>
53 <li><img alt="" src="../images/down.gif" /> <a href="#config">Configuring the Chain</a></li>
54 <li><img alt="" src="../images/down.gif" /> <a href="#errordocs">Filtering and Response Status</a></li>
55 <li><img alt="" src="../images/down.gif" /> <a href="#upgrade">Upgrading from Apache HTTP Server 2.2 Configuration</a></li>
56 <li><img alt="" src="../images/down.gif" /> <a href="#examples">Examples</a></li>
57 <li><img alt="" src="../images/down.gif" /> <a href="#protocol">Protocol Handling</a></li>
58 </ul><h3 class="directives">Directives</h3>
60 <li><img alt="" src="../images/down.gif" /> <a href="#addoutputfilterbytype">AddOutputFilterByType</a></li>
61 <li><img alt="" src="../images/down.gif" /> <a href="#filterchain">FilterChain</a></li>
62 <li><img alt="" src="../images/down.gif" /> <a href="#filterdeclare">FilterDeclare</a></li>
63 <li><img alt="" src="../images/down.gif" /> <a href="#filterprotocol">FilterProtocol</a></li>
64 <li><img alt="" src="../images/down.gif" /> <a href="#filterprovider">FilterProvider</a></li>
65 <li><img alt="" src="../images/down.gif" /> <a href="#filtertrace">FilterTrace</a></li>
67 <h3>Bugfix checklist</h3><ul class="seealso"><li><a href="https://www.apache.org/dist/httpd/CHANGES_2.4">httpd changelog</a></li><li><a href="https://bz.apache.org/bugzilla/buglist.cgi?bug_status=__open__&list_id=144532&product=Apache%20httpd-2&query_format=specific&order=changeddate%20DESC%2Cpriority%2Cbug_severity&component=mod_filter">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&component=mod_filter">Report a bug</a></li></ul><h3>See also</h3>
69 <li><a href="#comments_section">Comments</a></li></ul></div>
70 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
72 <h2><a name="smart" id="smart">Smart Filtering</a></h2>
73 <p>In the traditional filtering model, filters are inserted unconditionally
74 using <code class="directive"><a href="../mod/mod_mime.html#addoutputfilter">AddOutputFilter</a></code> and family.
75 Each filter then needs to determine whether to run, and there is little
76 flexibility available for server admins to allow the chain to be
77 configured dynamically.</p>
79 <p><code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> by contrast gives server administrators a
80 great deal of flexibility in configuring the filter chain. In fact,
81 filters can be inserted based on complex boolean
82 <a href="../expr.html">expressions</a> This generalises the limited
83 flexibility offered by <code class="directive">AddOutputFilterByType</code>.</p>
84 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
86 <h2><a name="terms" id="terms">Filter Declarations, Providers and Chains</a></h2>
88 <img src="../images/mod_filter_old.gif" width="160" height="310" alt="[This image displays the traditional filter model]" /><br />
89 <dfn>Figure 1:</dfn> The traditional filter model</p>
91 <p>In the traditional model, output filters are a simple chain
92 from the content generator (handler) to the client. This works well
93 provided the filter chain can be correctly configured, but presents
94 problems when the filters need to be configured dynamically based on
95 the outcome of the handler.</p>
98 <img src="../images/mod_filter_new.gif" width="423" height="331" alt="[This image shows the mod_filter model]" /><br />
99 <dfn>Figure 2:</dfn> The <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> model</p>
101 <p><code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> works by introducing indirection into
102 the filter chain. Instead of inserting filters in the chain, we insert
103 a filter harness which in turn dispatches conditionally
104 to a filter provider. Any content filter may be used as a provider
105 to <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code>; no change to existing filter modules
106 is required (although it may be possible to simplify them). There can be
107 multiple providers for one filter, but no more than one provider will
108 run for any single request.</p>
110 <p>A filter chain comprises any number of instances of the filter
111 harness, each of which may have any number of providers. A special
112 case is that of a single provider with unconditional dispatch: this
113 is equivalent to inserting the provider filter directly into the chain.</p>
114 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
115 <div class="section">
116 <h2><a name="config" id="config">Configuring the Chain</a></h2>
117 <p>There are three stages to configuring a filter chain with
118 <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code>. For details of the directives, see below.</p>
121 <dt>Declare Filters</dt>
122 <dd>The <code class="directive"><a href="#filterdeclare">FilterDeclare</a></code> directive
123 declares a filter, assigning it a name and filter type. Required
124 only if the filter is not the default type AP_FTYPE_RESOURCE.</dd>
126 <dt>Register Providers</dt>
127 <dd>The <code class="directive"><a href="#filterprovider">FilterProvider</a></code>
128 directive registers a provider with a filter. The filter may have
129 been declared with <code class="directive"><a href="#filterdeclare">FilterDeclare</a></code>; if not, FilterProvider will implicitly
130 declare it with the default type AP_FTYPE_RESOURCE. The provider
132 registered with <code>ap_register_output_filter</code> by some module.
133 The final argument to <code class="directive"><a href="#filterprovider">FilterProvider</a></code> is an expression: the provider will be
134 selected to run for a request if and only if the expression evaluates
135 to true. The expression may evaluate HTTP request or response
136 headers, environment variables, or the Handler used by this request.
137 Unlike earlier versions, mod_filter now supports complex expressions
138 involving multiple criteria with AND / OR logic (&& / ||)
139 and brackets. The details of the expression syntax are described in
140 the <a href="../expr.html">ap_expr documentation</a>.</dd>
142 <dt>Configure the Chain</dt>
143 <dd>The above directives build components of a smart filter chain,
144 but do not configure it to run. The <code class="directive"><a href="#filterchain">FilterChain</a></code> directive builds a filter chain from smart
145 filters declared, offering the flexibility to insert filters at the
146 beginning or end of the chain, remove a filter, or clear the chain.</dd>
148 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
149 <div class="section">
150 <h2><a name="errordocs" id="errordocs">Filtering and Response Status</a></h2>
151 <p>mod_filter normally only runs filters on responses with
152 HTTP status 200 (OK). If you want to filter documents with
153 other response statuses, you can set the <var>filter-errordocs</var>
154 environment variable, and it will work on all responses
155 regardless of status. To refine this further, you can use
156 expression conditions with <code class="directive">FilterProvider</code>.</p>
157 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
158 <div class="section">
159 <h2><a name="upgrade" id="upgrade">Upgrading from Apache HTTP Server 2.2 Configuration</a></h2>
160 <p>The <code class="directive"><a href="#filterprovider">FilterProvider</a></code>
161 directive has changed from httpd 2.2: the <var>match</var> and
162 <var>dispatch</var> arguments are replaced with a single but
163 more versatile <var>expression</var>. In general, you can convert
164 a match/dispatch pair to the two sides of an expression, using
166 <div class="example"><p><code>"dispatch = 'match'"</code></p></div>
167 <p>The Request headers, Response headers and Environment variables
168 are now interpreted from syntax <var>%{req:foo}</var>,
169 <var>%{resp:foo}</var> and <var>%{env:foo}</var> respectively.
170 The variables <var>%{HANDLER}</var> and <var>%{CONTENT_TYPE}</var>
171 are also supported.</p>
172 <p>Note that the match no longer support substring matches. They can be
173 replaced by regular expression matches.</p>
174 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
175 <div class="section">
176 <h2><a name="examples" id="examples">Examples</a></h2>
178 <dt>Server side Includes (SSI)</dt>
179 <dd>A simple case of replacing <code class="directive">AddOutputFilterByType</code>
180 <pre class="prettyprint lang-config">FilterDeclare SSI
181 FilterProvider SSI INCLUDES "%{CONTENT_TYPE} =~ m|^text/html|"
182 FilterChain SSI</pre>
186 <dt>Server side Includes (SSI)</dt>
187 <dd>The same as the above but dispatching on handler (classic
188 SSI behaviour; .shtml files get processed).
189 <pre class="prettyprint lang-config">FilterProvider SSI INCLUDES "%{HANDLER} = 'server-parsed'"
190 FilterChain SSI</pre>
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 <pre class="prettyprint lang-config">FilterDeclare gzip CONTENT_SET
198 FilterProvider gzip inflate "%{req:Accept-Encoding} !~ /gzip/"
199 FilterChain gzip</pre>
203 <dt>Image Downsampling</dt>
204 <dd>Suppose we want to downsample all web images, and have filters
205 for GIF, JPEG and PNG.
206 <pre class="prettyprint lang-config">FilterProvider unpack jpeg_unpack "%{CONTENT_TYPE} = 'image/jpeg'"
207 FilterProvider unpack gif_unpack "%{CONTENT_TYPE} = 'image/gif'"
208 FilterProvider unpack png_unpack "%{CONTENT_TYPE} = 'image/png'"
210 FilterProvider downsample downsample_filter "%{CONTENT_TYPE} = m|^image/(jpeg|gif|png)|"
211 FilterProtocol downsample "change=yes"
213 FilterProvider repack jpeg_pack "%{CONTENT_TYPE} = 'image/jpeg'"
214 FilterProvider repack gif_pack "%{CONTENT_TYPE} = 'image/gif'"
215 FilterProvider repack png_pack "%{CONTENT_TYPE} = 'image/png'"
216 <Location "/image-filter">
217 FilterChain unpack downsample repack
218 </Location></pre>
222 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
223 <div class="section">
224 <h2><a name="protocol" id="protocol">Protocol Handling</a></h2>
225 <p>Historically, each filter is responsible for ensuring that whatever
226 changes it makes are correctly represented in the HTTP response headers,
227 and that it does not run when it would make an illegal change. This
228 imposes a burden on filter authors to re-implement some common
229 functionality in every filter:</p>
232 <li>Many filters will change the content, invalidating existing content
233 tags, checksums, hashes, and lengths.</li>
235 <li>Filters that require an entire, unbroken response in input need to
236 ensure they don't get byteranges from a backend.</li>
238 <li>Filters that transform output in a filter need to ensure they don't
239 violate a <code>Cache-Control: no-transform</code> header from the
242 <li>Filters may make responses uncacheable.</li>
245 <p><code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> aims to offer generic handling of these
246 details of filter implementation, reducing the complexity required of
247 content filter modules. This is work-in-progress; the
248 <code class="directive"><a href="#filterprotocol">FilterProtocol</a></code> implements
249 some of this functionality for back-compatibility with Apache 2.0
250 modules. For httpd 2.1 and later, the
251 <code>ap_register_output_filter_protocol</code> and
252 <code>ap_filter_protocol</code> API enables filter modules to
253 declare their own behaviour.</p>
255 <p>At the same time, <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> should not interfere
256 with a filter that wants to handle all aspects of the protocol. By
257 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>
258 will leave the headers untouched.</p>
260 <p>At the time of writing, this feature is largely untested,
261 as modules in common use are designed to work with 2.0.
262 Modules using it should test it carefully.</p>
264 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
265 <div class="directive-section"><h2><a name="AddOutputFilterByType" id="AddOutputFilterByType">AddOutputFilterByType</a> <a name="addoutputfilterbytype" id="addoutputfilterbytype">Directive</a></h2>
266 <table class="directive">
267 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>assigns an output filter to a particular media-type</td></tr>
268 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>AddOutputFilterByType <var>filter</var>[;<var>filter</var>...]
269 <var>media-type</var> [<var>media-type</var>] ...</code></td></tr>
270 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
271 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
272 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
273 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_filter</td></tr>
274 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Had severe limitations before
275 being moved to <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> in version 2.3.7</td></tr>
277 <p>This directive activates a particular output <a href="../filter.html">filter</a> for a request depending on the
278 response <a class="glossarylink" href="../glossary.html#media-type" title="see glossary">media-type</a>.</p>
280 <p>The following example uses the <code>DEFLATE</code> filter, which
281 is provided by <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code>. It will compress all
282 output (either static or dynamic) which is labeled as
283 <code>text/html</code> or <code>text/plain</code> before it is sent
286 <pre class="prettyprint lang-config">AddOutputFilterByType DEFLATE text/html text/plain</pre>
289 <p>If you want the content to be processed by more than one filter, their
290 names have to be separated by semicolons. It's also possible to use one
291 <code class="directive">AddOutputFilterByType</code> directive for each of
294 <p>The configuration below causes all script output labeled as
295 <code>text/html</code> to be processed at first by the
296 <code>INCLUDES</code> filter and then by the <code>DEFLATE</code>
299 <pre class="prettyprint lang-config"><Location "/cgi-bin/">
301 AddOutputFilterByType INCLUDES;DEFLATE text/html
302 </Location></pre>
308 <li><code class="directive"><a href="../mod/mod_mime.html#addoutputfilter">AddOutputFilter</a></code></li>
309 <li><code class="directive"><a href="../mod/core.html#setoutputfilter">SetOutputFilter</a></code></li>
310 <li><a href="../filter.html">filters</a></li>
313 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
314 <div class="directive-section"><h2><a name="FilterChain" id="FilterChain">FilterChain</a> <a name="filterchain" id="filterchain">Directive</a></h2>
315 <table class="directive">
316 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configure the filter chain</td></tr>
317 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>FilterChain [+=-@!]<var>filter-name</var> <var>...</var></code></td></tr>
318 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
319 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Options</td></tr>
320 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
321 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_filter</td></tr>
323 <p>This configures an actual filter chain, from declared filters.
324 <code class="directive">FilterChain</code> takes any number of arguments,
325 each optionally preceded with a single-character control that
326 determines what to do:</p>
329 <dt><code>+<var>filter-name</var></code></dt>
330 <dd>Add <var>filter-name</var> to the end of the filter chain</dd>
332 <dt><code>@<var>filter-name</var></code></dt>
333 <dd>Insert <var>filter-name</var> at the start of the filter chain</dd>
335 <dt><code>-<var>filter-name</var></code></dt>
336 <dd>Remove <var>filter-name</var> from the filter chain</dd>
338 <dt><code>=<var>filter-name</var></code></dt>
339 <dd>Empty the filter chain and insert <var>filter-name</var></dd>
341 <dt><code>!</code></dt>
342 <dd>Empty the filter chain</dd>
344 <dt><code><var>filter-name</var></code></dt>
345 <dd>Equivalent to <code>+<var>filter-name</var></code></dd>
349 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
350 <div class="directive-section"><h2><a name="FilterDeclare" id="FilterDeclare">FilterDeclare</a> <a name="filterdeclare" id="filterdeclare">Directive</a></h2>
351 <table class="directive">
352 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Declare a smart filter</td></tr>
353 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>FilterDeclare <var>filter-name</var> <var>[type]</var></code></td></tr>
354 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
355 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Options</td></tr>
356 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
357 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_filter</td></tr>
359 <p>This directive declares an output filter together with a
360 header or environment variable that will determine runtime
361 configuration. The first argument is a <var>filter-name</var>
362 for use in <code class="directive"><a href="#filterprovider">FilterProvider</a></code>,
363 <code class="directive"><a href="#filterchain">FilterChain</a></code> and
364 <code class="directive"><a href="#filterprotocol">FilterProtocol</a></code> directives.</p>
366 <p>The final (optional) argument
367 is the type of filter, and takes values of <code>ap_filter_type</code>
368 - namely <code>RESOURCE</code> (the default), <code>CONTENT_SET</code>,
369 <code>PROTOCOL</code>, <code>TRANSCODE</code>, <code>CONNECTION</code>
370 or <code>NETWORK</code>.</p>
373 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
374 <div class="directive-section"><h2><a name="FilterProtocol" id="FilterProtocol">FilterProtocol</a> <a name="filterprotocol" id="filterprotocol">Directive</a></h2>
375 <table class="directive">
376 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Deal with correct HTTP protocol handling</td></tr>
377 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>FilterProtocol <var>filter-name</var> [<var>provider-name</var>]
378 <var>proto-flags</var></code></td></tr>
379 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
380 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Options</td></tr>
381 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
382 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_filter</td></tr>
384 <p>This directs <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> to deal with ensuring the
385 filter doesn't run when it shouldn't, and that the HTTP response
386 headers are correctly set taking into account the effects of the
389 <p>There are two forms of this directive. With three arguments, it
390 applies specifically to a <var>filter-name</var> and a
391 <var>provider-name</var> for that filter.
392 With two arguments it applies to a <var>filter-name</var> whenever the
393 filter runs <em>any</em> provider.</p>
395 <p>Flags specified with this directive are merged with the flags
396 that underlying providers may have registerd with
397 <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code>. For example, a filter may internally specify
398 the equivalent of <code>change=yes</code>, but a particular
399 configuration of the module can override with <code>change=no</code>.
402 <p><var>proto-flags</var> is one or more of</p>
405 <dt><code>change=yes|no</code></dt>
406 <dd>Specifies whether the filter changes the content, including possibly
407 the content length. The "no" argument is supported in 2.4.7 and later.</dd>
409 <dt><code>change=1:1</code></dt>
410 <dd>The filter changes the content, but will not change the content
413 <dt><code>byteranges=no</code></dt>
414 <dd>The filter cannot work on byteranges and requires complete input</dd>
416 <dt><code>proxy=no</code></dt>
417 <dd>The filter should not run in a proxy context</dd>
419 <dt><code>proxy=transform</code></dt>
420 <dd>The filter transforms the response in a manner incompatible with
421 the HTTP <code>Cache-Control: no-transform</code> header.</dd>
423 <dt><code>cache=no</code></dt>
424 <dd>The filter renders the output uncacheable (eg by introducing randomised
425 content changes)</dd>
429 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
430 <div class="directive-section"><h2><a name="FilterProvider" id="FilterProvider">FilterProvider</a> <a name="filterprovider" id="filterprovider">Directive</a></h2>
431 <table class="directive">
432 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Register a content filter</td></tr>
433 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>FilterProvider <var>filter-name</var> <var>provider-name</var>
434 <var>expression</var></code></td></tr>
435 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
436 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Options</td></tr>
437 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
438 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_filter</td></tr>
440 <p>This directive registers a <em>provider</em> for the smart filter.
441 The provider will be called if and only if the <var>expression</var>
442 declared evaluates to true when the harness is first called.</p>
445 <var>provider-name</var> must have been registered by loading
446 a module that registers the name with
447 <code>ap_register_output_filter</code>.
450 <p><var>expression</var> is an
451 <a href="../expr.html">ap_expr</a>.</p>
456 <li><a href="../expr.html">Expressions in Apache HTTP Server</a>,
457 for a complete reference and examples.</li>
458 <li><code class="module"><a href="../mod/mod_include.html">mod_include</a></code></li>
461 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
462 <div class="directive-section"><h2><a name="FilterTrace" id="FilterTrace">FilterTrace</a> <a name="filtertrace" id="filtertrace">Directive</a></h2>
463 <table class="directive">
464 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Get debug/diagnostic information from
465 <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code></td></tr>
466 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>FilterTrace <var>filter-name</var> <var>level</var></code></td></tr>
467 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory</td></tr>
468 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Base</td></tr>
469 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_filter</td></tr>
471 <p>This directive generates debug information from
472 <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code>.
473 It is designed to help test and debug providers (filter modules), although
474 it may also help with <code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> itself.</p>
476 <p>The debug output depends on the <var>level</var> set:</p>
478 <dt><code>0</code> (default)</dt>
479 <dd>No debug information is generated.</dd>
481 <dt><code>1</code></dt>
482 <dd><code class="module"><a href="../mod/mod_filter.html">mod_filter</a></code> will record buckets and brigades
483 passing through the filter to the error log, before the provider has
484 processed them. This is similar to the information generated by
485 <a href="http://apache.webthing.com/mod_diagnostics/">mod_diagnostics</a>.
488 <dt><code>2</code> (not yet implemented)</dt>
489 <dd>Will dump the full data passing through to a tempfile before the
490 provider. <strong>For single-user debug only</strong>; this will not
491 support concurrent hits.</dd>
496 <div class="bottomlang">
497 <p><span>Available Languages: </span><a href="../en/mod/mod_filter.html" title="English"> en </a></p>
498 </div><div class="top"><a href="#page-header"><img src="../images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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