Adds a [QSD] flag to RewriteRule to discard unwanted query strings

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<manualpage metafile="flags.xml.meta">
<parentdocument href="./">Rewrite</parentdocument>

  <title>Apache mod_rewrite Flags</title>

<summary>
<p>This document discusses the flags which are available to the
<directive module="mod_rewrite">RewriteRule</directive> directive,
providing detailed explanations and examples. This is not necessarily
a comprehensive list of all flags available, so be sure to also
consult the reference documentation.</p>
</summary>

<seealso><a href="../mod/mod_rewrite.html">Module documentation</a></seealso>
<seealso><a href="tech.html">Technical details</a></seealso>

<section id="introduction"><title>Introduction</title>
<p><directive module="mod_rewrite">RewriteRule</directive>s can have
their behavior modified by one or more flags. Flags are included in
square brackets at the end of the rule, and multiple flags are separated
by commas.</p>
<example>
RewriteRule pattern target [Flag1,Flag2,Flag3]
</example>

<p>The flags all have a short form, such as <code>CO</code>, as well as
a longer form, such as <code>cookie</code>. Some flags take one or more
arguments. Flags are not case sensitive.</p>

</section>

<section id="flags"><title>The flags</title>

<p>Each flag has a long and short form. While it is most common to use
the short form, it is recommended that you familiarize yourself with the
long form, so that you remember what each flag is supposed to do.</p>

<p>Presented here are each of the available flags, along with an example
of how you might use them.</p>

<section id="flag_b"><title>B</title>
<p>The [B] flag instructs <directive
module="mod_rewrite">RewriteRule</directive> to escape non-alphanumeric
characters before applying the transformation.
</p>
</section>

<section id="flag_c"><title>C|chain</title>
<p>The [C] or [chain] flag indicates that the <directive
module="mod_rewrite">RewriteRule</directive> is chained to the next
rule. That is, if the rule matches, then it is processed as usual and
control moves on to the next rule. However, if it does not match, then
the next rule, and any other rules that are chained together, will be
skipped.</p>

</section>

<section id="flag_co"><title>CO|cookie</title>
<p>The [CO], or [cookie] flag, allows you to set a cookie when a
particular <directive module="mod_rewrite">RewriteRule</directive>
matches. The argument consists of three required fields and two optional
fields.</p>
<p>You must declare a name and value for the cookie to be set, and the
domain for which you wish the cookie to be valid. You may optionally set
the lifetime of the cookie, and the path for which it should be
returned.</p>
<p>By default, the lifetime of the cookie is the current browser
session.</p>
<p>By default, the path for which the cookie will be valid is "/" - that
is, the entire website.</p>
<p>Several examples are offered here:</p>

<example>
RewriteEngine On<br />
RewriteRule ^/index\.html - [CO=frontdoor:yes:.apache.org:1440:/]
</example>

<p>In the example give, the rule doesn't rewrite the request.
The "-" rewrite target tells mod_rewrite to pass the request
through unchanged. Instead, it sets a cookie
called 'frontdoor' to a value of 'yes'. The cookie is valid for any host
in the <code>.apache.org</code> domain. It will be set to expire in 1440
minutes (24 hours) and will be returned for all URIs.</p>

</section>

<section id="flag_dpi"><title>DPI|discardpathinfo</title>
<p>The DPI flag causes the PATH_INFO portion of the rewritten URI to be
discarded.</p>
</section>

<section id="flag_e"><title>E|env</title>
<p>With the [E], or [env] flag, you can set the value of an environment
variable. Note that some environment variables may be set after the rule
is run, thus unsetting what you have set. See <a href="../env.html">the
Environment Variables document</a> for more details on how Environment
variables work.</p>

<p>The following example sets an evironment variable called 'image' to a
value of '1' if the requested URI is an image file. Then, that
environment variable is used to exclude those requests from the access
log.</p>

<example>
RewriteRule \.(png|gif|jpg) - [E=image:1]<br />
CustomLog logs/access_log combined env=!image
</example>

<p>Note that this same effect can be obtained using <directive
module="mod_setenvif">SetEnvIf</directive>. This technique is offered as
an example, not as a recommendation.</p>
</section>

<section id="flag_f"><title>F|forbidden</title>
<p>Using the [F] flag causes Apache to return a 403 Forbidden status
code to the client. While the same behavior can be accomplished using
the <directive module="mod_access">Deny</directive> directive, this 
allows more flexibility in assigning a Forbidden status.</p>

<p>The following rule will forbid <code>.exe</code> files from being
downloaded from your server.</p>

<example>
RewriteRule \.exe - [F]
</example>

<p>This example uses the "-" syntax for the rewrite target, which means
that the requested URI is not modified. There's no reason to rewrite to
another URI, if you're going to forbid the request.</p>

</section>

<section id="flag_g"><title>G|gone</title>
<p>The [G] flag forces Apache to return a 410 Gone status with the
response. This indicates that a resource used to be available, but is no
longer available.</p>

<p>As with the [F] flag, you will typically use the "-" syntax for the
rewrite target when using the [G] flag:</p>

<example>
RewriteRule oldproduct - [G,NC]
</example>
</section>

<section id="flag_h"><title>H|handler</title>
<p>Forces the resulting request to be handled with the specified
handler. For example, one might use this to force all files without a
file extension to be parsed by the php handler:</p>

<example>
RewriteRule !\. - [H=application/x-httpd-php]
</example>

<p>
The regular expression above - <code>!\.</code> - will match any request
that does not contain the literal <code>.</code> character.
</p>

<p>This can be also used to force the handler based on some conditions.
For example, the following snippet used in per-server context allows
<code>.php</code> files to be <em>displayed</em> by <code>mod_php</code>
if they are requested with the <code>.phps</code> extension:</p>

<example>
RewriteRule ^(/source/.+\.php)s$ $1 [H=application/x-httpd-php-source]
</example>

<p>The regular expression above - <code>^(/source/.+\.php)s$</code> - will
match any request that starts with <code>/source/</code> followed by 1 or
n characters followed by <code>.phps</code> literally. The backreference
$1 referrers to the captured match within parenthesis of the regular
expression.</p>
</section>

<section id="flag_l"><title>L|last</title>
<p>The [L] flag causes <module>mod_rewrite</module> to stop processing
the rule set. In most contexts, this means that if the rule matches, no
further rules will be processed.</p>

<p>If you are using <directive
module="mod_rewrite">RewriteRule</directive> in either
<code>.htaccess</code> files or in 
<directive type="section" module="core">Directory</directive> sections,
it is important to have some understanding of how the rules are
processed.  The simplified form of this is that once the rules have been
processed, the rewritten request is handed back to the URL parsing
engine to do what it may with it. It is possible that as the rewritten
request is handled, the <code>.htaccess</code> file or 
<directive type="section" module="core">Directory</directive> section
may be encountered again, and thus the ruleset may be run again from the
start. Most commonly this will happen if one of the rules causes a
redirect - either internal or external - causing the request process to
start over.</p>

<p>It is therefore important, if you are using <directive
module="mod_rewrite">RewriteRule</directive> directives in one of these
contexts, that you take explicit steps to avoid rules looping, and not
count solely on the [L] flag to terminate execution of a series of
rules, as shown below.</p>

<p>The example given here will rewrite any request to
<code>index.php</code>, giving the original request as a query string
argument to <code>index.php</code>, however, the <directive
module="mod_rewrite">RewriteCond</directive> ensures that if the request 
is already for <code>index.php</code>, the <directive
module="mod_rewrite">RewriteRule</directive> will be skipped.</p>

<example>
RewriteCond %{REQUEST_URI} !=index.php<br />
RewriteRule ^(.*) index.php?req=$1 [L]
</example>
</section>

<section id="flag_n"><title>N|next</title>
<p>
The [N] flag causes the ruleset to start over again from the top. Use
with extreme caution, as it may result in loop.
</p>
<p>
The [Next] flag could be used, for example, if you wished to replace a
certain string or letter repeatedly in a request. The example shown here
will replace A with B everywhere in a request, and will continue doing
so until there are no more As to be replaced.
</p>

<example>
RewriteRule (.*)A(.*) $1B$2 [N]
</example>

<p>You can think of this as a <code>while</code> loop: While this
pattern still matches (i.e., while the URI still contains an
<code>A</code>), perform this substitution (i.e., replace the
<code>A</code> with a <code>B</code>).</p>

</section>

<section id="flag_nc"><title>NC|nocase</title>
<p>Use of the [NC] flag causes the <directive
module="mod_rewrite">RewriteRule</directive> to be matched in a
case-insensitive manner. That is, it doesn't care whether letters appear
as upper-case or lower-case in the matched URI.</p>

<p>In the example below, any request for an image file will be proxied
to your dedicated image server. The match is case-insensitive, so that
<code>.jpg</code> and <code>.JPG</code> files are both acceptable, for
example.</p>

<example>
RewriteRule (.*\.(jpg|gif|png))$ http://images.example.com$1 [P,NC]
</example>
</section>

<section id="flag_ne"><title>NE|noescape</title>
<p>By default, special characters, such as <code>&amp;</code> and
<code>?</code>, for example, will be converted to their hexcode
equivalent. Using the [NE] flag prevents that from happening.
</p>

<example>
RewriteRule ^/anchor/(.+) /bigpage.html#$1 [NE,R]
</example>

<p>
The above example will redirect <code>/anchor/xyz</code> to
<code>/bigpage.html#xyz</code>. Omitting the [NE] will result in the #
being converted to its hexcode equivalent, <code>%23</code>, which will
then result in a 404 Not Found error condition.
</p>

</section>

<section id="flag_ns"><title>NS|nosubreq</title>
<p>Use of the [NS] flag prevents the rule from being used on
subrequests. For example, a page which is included using an SSI (Server
Side Include) is a subrequest, and you may want to avoid rewrites
happening on those subrequests.</p>

<p>
Images, javascript files, or css files, loaded as part of an HTML page,
are not subrequests - the browser requests them as separate HTTP
requests.
</p>
</section>

<section id="flag_p"><title>P|proxy</title>
<p>Use of the [P] flag causes the request to be handled by
<module>mod_proxy</module>, and handled via a proxy request. For
example, if you wanted all image requests to be handled by a back-end
image server, you might do something like the following:</p>

<example>
RewriteRule (.*)\.(jpg|gif|png) http://images.example.com$1.$2 [P]
</example>

<p>Use of the [P] flag implies [L] - that is, the request is immediatly
pushed through the proxy, and any following rules will not be
considered.</p>

</section>

<section id="flag_pt"><title>PT|passthrough</title>

<p>
The target (or substitution string) in a RewriteRule is assumed to be a
file path, by default. The use of the [PT] flag causes it to be treated
as a URI instead. That is to say, the
use of the [PT] flag causes the result of the <directive
module="mod_rewrite">RewriteRule</directive> to be passed back through
URL mapping, so that location-based mappings, such as <directive
module="mod_alias">Alias</directive>, for example, might have a chance to take
effect.
</p>

<p>
If, for example, you have an 
<directive module="mod_alias">Alias</directive>
for /icons, and have a <directive
module="mod_rewrite">RewriteRule</directive> pointing there, you should
use the [PT] flag to ensure that the 
<directive module="mod_alias">Alias</directive> is evaluated.
</p>

<example>
Alias /icons /usr/local/apache/icons<br />
RewriteRule /pics/(.+)\.jpg /icons/$1.gif [PT]
</example>

<p>
Omission of the [PT] flag in this case will cause the Alias to be
ignored, resulting in a 'File not found' error being returned.
</p>

</section>

<section id="flag_qsa"><title>QSA|qsappend</title>
<p>
When the replacement URI contains a query string, the default behavior
of <directive module="mod_rewrite">RewriteRule</directive> is to discard
the existing query string, and replace it with the newly generated one.
Using the [QSA] flag causes the query strings to be combined.
</p>

<p>Consider the following rule:</p>

<example>
RewriteRule /pages/(.+) /page.php?page=$1 [QSA]
</example>

<p>With the [QSA] flag, a request for <code>/pages/123?one=two</code> will be
mapped to <code>/page.php?page=123&amp;one=two</code>. Without the [QSA]
flag, that same request will be mapped to
<code>/page.php?page=123</code> - that is, the existing query string
will be discarded.
</p>
</section>

<section id="flag_qsd"><title>QSD|qsdiscard</title>
<p>
When the requested URI contains a query string, and the target URI does
not, the default behavior of <directive
module="mod_rewrite">RewriteRule</directive> is to copy that query
string to the target URI. Using the [QSD] flag causes the query string
to be discarded.
</p>

<p>
Using [QSD] and [QSA] together will result in [QSD] taking preference.
</p>

<p>
If the target URI has a query string, the default behavior will be
observed - that is, the original query string will be discarded and
replaced with the query string in the <code>RewriteRule</code> target
URI.
</p>

</section>

<section id="flag_r"><title>R|redirect</title>
<p>
Use of the [R] flag causes a HTTP redirect to be issued to the browser.
If a fully-qualified URL is specified (that is, including
<code>http://servername/</code>) then a redirect will be issued to that
location. Otherwise, the current servername will be used to generate the
URL sent with the redirect.
</p>

<p>
<em>Any</em> status code may be specified, that is a valid HTTP Response,
with a 302 status code being used by default if none is specified.
</p>

<p>
You will almost always want to use [R] in conjunction with [L] (that is,
use [R,L]) because on its own, the [R] flag prepends
<code>http://thishost[:thisport]</code> to the URI, but then passes this
on to the next rule in the ruleset, which can often result in 'Invalid
URI in request' warnings.
</p>

</section>

<section id="flag_s"><title>S|skip</title>
<p>The [S] flag is used to skip rules that you don't want to run. This
can be thought of as a <code>goto</code> statement in your rewrite
ruleset. In the following example, we only want to run the <directive
module="mod_rewrite">RewriteRule</directive> if the requested URI
doesn't correspond with an actual file.</p>

<example>
# Is the request for a non-existent file?<br />
RewriteCond %{REQUEST_FILENAME} !-f<br />
RewriteCond %{REQUEST_FILENAME} !-d<br />
# If so, skip these two RewriteRules<br />
RewriteRule .? - [S=2]<br />
<br />
RewriteRule (.*\.gif) images.php?$1<br />
RewriteRule (.*\.html) docs.php?$1
</example>

<p>This technique is useful because a <directive
module="mod_rewrite">RewriteCond</directive> only applies to the
<directive module="mod_rewrite">RewriteRule</directive> immediately
following it. Thus, if you want to make a <code>RewriteCond</code> apply
to several <code>RewriteRule</code>s, one possible technique is to
negate those conditions and use a [Skip] flag.</p>

</section>

<section id="flag_t"><title>T|type</title>
<p>Sets the MIME type with which the resulting response will be
sent. This has the same effect as the <directive
module="mod_mime">AddType</directive> directive.</p>

<p>For example, you might use the following technique to serve Perl
source code as plain text, if requested in a particular way:</p>

<example>
# Serve .pl files as plain text<br />
RewriteRule \.pl$ - [T=text/plain]
</example>

<p>Or, perhaps, if you have a camera that produces jpeg images without
file extensions, you could force those images to be served with the
correct MIME type by virtue of their file names:</p>

<example>
# Files with 'IMG' in the name are jpg images.<br />
RewriteRule IMG - [T=image/jpg]
</example>

<p>Please note that this is a trivial example, and could be better done
using <directive type="section" module="core">FilesMatch</directive>
instead. Always consider the alternate
solutions to a problem before resorting to rewrite, which will
invariably be a less efficient solution than the alternatives.</p>
</section>

</section>
</manualpage>