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<div id="preamble"><h1>Apache Module mod_deflate</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="../en/mod/mod_deflate.html" title="English">&nbsp;en&nbsp;</a> |
<a href="../fr/mod/mod_deflate.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a> |
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<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Compress content before it is delivered to the
client</td></tr>
<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>deflate_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_deflate.c</td></tr></table>
<h3>Summary</h3>

    <p>The <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code> module provides
    the <code>DEFLATE</code> output filter that allows output from
    your server to be compressed before being sent to the client over
    the network.</p>
</div>
<div id="quickview"><a href="https://www.apache.org/foundation/contributing.html" class="badge"><img src="https://www.apache.org/images/SupportApache-small.png" alt="Support Apache!" /></a><h3>Topics</h3>
<ul id="topics">
<li><img alt="" src="../images/down.gif" /> <a href="#supportedencodings">Supported Encodings</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#recommended">Sample Configurations</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#enable">Enabling Compression</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#proxies">Dealing with proxy servers</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#precompressed">Serving pre-compressed
content</a></li>
</ul><h3 class="directives">Directives</h3>
<ul id="toc">
<li><img alt="" src="../images/down.gif" /> <a href="#deflatebuffersize">DeflateBufferSize</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#deflatecompressionlevel">DeflateCompressionLevel</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#deflatefilternote">DeflateFilterNote</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#deflateinflatelimitrequestbody">DeflateInflateLimitRequestBody</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#deflateinflateratioburst">DeflateInflateRatioBurst</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#deflateinflateratiolimit">DeflateInflateRatioLimit</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#deflatememlevel">DeflateMemLevel</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#deflatewindowsize">DeflateWindowSize</a></li>
</ul>
<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__&amp;list_id=144532&amp;product=Apache%20httpd-2&amp;query_format=specific&amp;order=changeddate%20DESC%2Cpriority%2Cbug_severity&amp;component=mod_deflate">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&amp;component=mod_deflate">Report a bug</a></li></ul><h3>See also</h3>
<ul class="seealso">
<li><a href="../filter.html">Filters</a></li>
<li><a href="#comments_section">Comments</a></li></ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="supportedencodings" id="supportedencodings">Supported Encodings</a></h2>
  <p>The <code>gzip</code> encoding is the only one supported to ensure complete compatibility
  with old browser implementations. The <code>deflate</code> encoding is not supported, 
  please check the <a href="https://zlib.net/zlib_faq.html#faq39">zlib's documentation</a>
  for a complete explanation.
  </p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="recommended" id="recommended">Sample Configurations</a></h2>
    <div class="warning"><h3>Compression and TLS</h3>
        <p>Some web applications are vulnerable to an information disclosure
        attack when a TLS connection carries deflate compressed data. For more
        information, review the details of the "BREACH" family of attacks.</p>
    </div>
    <p>This is a simple configuration that compresses common text-based content types.</p>

    <div class="example"><h3>Compress only a few types</h3><pre class="prettyprint lang-config">AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css text/javascript application/javascript</pre>
</div>

</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="enable" id="enable">Enabling Compression</a></h2>
    <div class="warning"><h3>Compression and TLS</h3>
        <p>Some web applications are vulnerable to an information disclosure
        attack when a TLS connection carries deflate compressed data. For more
        information, review the details of the "BREACH" family of attacks.</p>
    </div>

    <h3><a name="output" id="output">Output Compression</a></h3>
      <p>Compression is implemented by the <code>DEFLATE</code>
      <a href="../filter.html">filter</a>. The following directive
      will enable compression for documents in the container where it
      is placed:</p>

      <pre class="prettyprint lang-config">SetOutputFilter DEFLATE
SetEnvIfNoCase Request_URI "\.(?:gif|jpe?g|png)$" no-gzip</pre>


      <p>If you want to restrict the compression to particular MIME types
      in general, you may use the <code class="directive"><a href="../mod/mod_filter.html#addoutputfilterbytype">AddOutputFilterByType</a></code> directive. Here is an example of
      enabling compression only for the html files of the Apache
      documentation:</p>

      <pre class="prettyprint lang-config">&lt;Directory "/your-server-root/manual"&gt;
    AddOutputFilterByType DEFLATE text/html
&lt;/Directory&gt;</pre>


      <div class="note"><h3>Note</h3>
        The <code>DEFLATE</code> filter is always inserted after RESOURCE
        filters like PHP or SSI. It never touches internal subrequests.
      </div>
      <div class="note"><h3>Note</h3>
        There is an environment variable <code>force-gzip</code>,
        set via <code class="directive"><a href="../mod/mod_env.html#setenv">SetEnv</a></code>, which
        will ignore the accept-encoding setting of your browser and will
        send compressed output.
      </div>

    
    <h3><a name="inflate" id="inflate">Output Decompression</a></h3>
      <p>The <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code> module also provides a filter for
      inflating/uncompressing a gzip compressed response body. In order to activate
      this feature you have to insert the <code>INFLATE</code> filter into
      the output filter chain using <code class="directive"><a href="../mod/core.html#setoutputfilter">SetOutputFilter</a></code> or <code class="directive"><a href="../mod/mod_mime.html#addoutputfilter">AddOutputFilter</a></code>, for example:</p>

      <pre class="prettyprint lang-config">&lt;Location "/dav-area"&gt;
    ProxyPass "http://example.com/"
    SetOutputFilter INFLATE
&lt;/Location&gt;</pre>


      <p>This Example will uncompress gzip'ed output from example.com, so other
      filters can do further processing with it.
      </p>

    
    <h3><a name="input" id="input">Input Decompression</a></h3>
      <p>The <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code> module also provides a filter for
      decompressing a gzip compressed request body . In order to activate
      this feature you have to insert the <code>DEFLATE</code> filter into
      the input filter chain using <code class="directive"><a href="../mod/core.html#setinputfilter">SetInputFilter</a></code> or <code class="directive"><a href="../mod/mod_mime.html#addinputfilter">AddInputFilter</a></code>, for example:</p>

      <pre class="prettyprint lang-config">&lt;Location "/dav-area"&gt;
    SetInputFilter DEFLATE
&lt;/Location&gt;</pre>


      <p>Now if a request contains a <code>Content-Encoding:
      gzip</code> header, the body will be automatically decompressed.
      Few browsers have the ability to gzip request bodies. However,
      some special applications actually do support request
      compression, for instance some <a href="http://www.webdav.org">WebDAV</a> clients.</p>

      <div class="warning"><h3>Note on Content-Length</h3>
        <p>If you evaluate the request body yourself, <em>don't trust
        the <code>Content-Length</code> header!</em>
        The Content-Length header reflects the length of the
        incoming data from the client and <em>not</em> the byte count of
        the decompressed data stream.</p>
      </div>
    
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="proxies" id="proxies">Dealing with proxy servers</a></h2>

    <p>The <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code> module sends a <code>Vary:
    Accept-Encoding</code> HTTP response header to alert proxies that
    a cached response should be sent only to clients that send the
    appropriate <code>Accept-Encoding</code> request header.  This
    prevents compressed content from being sent to a client that will
    not understand it.</p>

    <p>If you use some special exclusions dependent
    on, for example, the <code>User-Agent</code> header, you must
    manually configure an addition to the <code>Vary</code> header
    to alert proxies of the additional restrictions.  For example,
    in a typical configuration where the addition of the <code>DEFLATE</code>
    filter depends on the <code>User-Agent</code>, you should add:</p>

    <pre class="prettyprint lang-config">Header append Vary User-Agent</pre>


    <p>If your decision about compression depends on other information
    than request headers (<em>e.g.</em> HTTP version), you have to set the
    <code>Vary</code> header to the value <code>*</code>. This prevents
    compliant proxies from caching entirely.</p>

    <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">Header set Vary *</pre>
</div>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="precompressed" id="precompressed">Serving pre-compressed
content</a></h2>

    <p>Since <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code> re-compresses content each
    time a request is made, some performance benefit can be derived by
    pre-compressing the content and telling <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code> to serve them
    without re-compressing them. This may be accomplished using a
    configuration like the following:</p>

    <pre class="prettyprint lang-config">&lt;IfModule mod_headers.c&gt;
    # Serve gzip compressed CSS and JS files if they exist
    # and the client accepts gzip.
    RewriteCond "%{HTTP:Accept-encoding}" "gzip"
    RewriteCond "%{REQUEST_FILENAME}\.gz" -s
    RewriteRule "^(.*)\.(css|js)"         "$1\.$2\.gz" [QSA]

    # Serve correct content types, and prevent mod_deflate double gzip.
    RewriteRule "\.css\.gz$" "-" [T=text/css,E=no-gzip:1]
    RewriteRule "\.js\.gz$"  "-" [T=text/javascript,E=no-gzip:1]


    &lt;FilesMatch "(\.js\.gz|\.css\.gz)$"&gt;
      # Serve correct encoding type.
      Header append Content-Encoding gzip

      # Force proxies to cache gzipped &amp;
      # non-gzipped css/js files separately.
      Header append Vary Accept-Encoding
    &lt;/FilesMatch&gt;
&lt;/IfModule&gt;</pre>


</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DeflateBufferSize" id="DeflateBufferSize">DeflateBufferSize</a> <a name="deflatebuffersize" id="deflatebuffersize">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Fragment size to be compressed at one time by zlib</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateBufferSize <var>value</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>DeflateBufferSize 8096</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
</table>
    <p>The <code class="directive">DeflateBufferSize</code> directive specifies
    the size in bytes of the fragments that zlib should compress at one
    time. If the compressed response size is bigger than the one specified
    by this directive then httpd will switch to chunked encoding 
    (HTTP header <code>Transfer-Encoding</code> set to <code>Chunked</code>), with the
    side effect of not setting any <code>Content-Length</code> HTTP header. This is particularly 
    important when httpd works behind reverse caching proxies or when httpd is configured with 
    <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> and <code class="module"><a href="../mod/mod_cache_disk.html">mod_cache_disk</a></code> because
    HTTP responses without any <code>Content-Length</code> header might not be cached.
  </p>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DeflateCompressionLevel" id="DeflateCompressionLevel">DeflateCompressionLevel</a> <a name="deflatecompressionlevel" id="deflatecompressionlevel">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>How much compression do we apply to the output</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateCompressionLevel <var>value</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>Zlib's default</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
</table>
    <p>The <code class="directive">DeflateCompressionLevel</code> directive specifies
        what level of compression should be used, the higher the value,
        the better the compression, but the more CPU time is required to
        achieve this.</p>
    <p>The value must between 1 (less compression) and 9 (more compression).</p>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DeflateFilterNote" id="DeflateFilterNote">DeflateFilterNote</a> <a name="deflatefilternote" id="deflatefilternote">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Places the compression ratio in a note for logging</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateFilterNote [<var>type</var>] <var>notename</var></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
</table>
    <p>The <code class="directive">DeflateFilterNote</code> directive
    specifies that a note about compression ratios should be attached
    to the request. The name of the note is the value specified for
    the directive. You can use that note for statistical purposes by
    adding the value to your <a href="../logs.html#accesslog">access log</a>.</p>

    <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">DeflateFilterNote ratio

LogFormat '"%r" %b (%{ratio}n) "%{User-agent}i"' deflate
CustomLog "logs/deflate_log" deflate</pre>
</div>

    <p>If you want to extract more accurate values from your logs, you
    can use the <var>type</var> argument to specify the type of data
    left as a note for logging. <var>type</var> can be one of:</p>

    <dl>
      <dt><code>Input</code></dt>
      <dd>Store the byte count of the filter's input stream in the note.</dd>

      <dt><code>Output</code></dt>
      <dd>Store the byte count of the filter's output stream in the note.</dd>

      <dt><code>Ratio</code></dt>
      <dd>Store the compression ratio (<code>output/input * 100</code>)
      in the note. This is the default, if the <var>type</var> argument
      is omitted.</dd>
    </dl>

    <p>Thus you may log it this way:</p>

    <div class="example"><h3>Accurate Logging</h3><pre class="prettyprint lang-config">DeflateFilterNote Input instream
DeflateFilterNote Output outstream
DeflateFilterNote Ratio ratio

LogFormat '"%r" %{outstream}n/%{instream}n (%{ratio}n%%)' deflate
CustomLog "logs/deflate_log" deflate</pre>
</div>

<h3>See also</h3>
<ul>
<li><code class="module"><a href="../mod/mod_log_config.html">mod_log_config</a></code></li>
</ul>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DeflateInflateLimitRequestBody" id="DeflateInflateLimitRequestBody">DeflateInflateLimitRequestBody</a> <a name="deflateinflatelimitrequestbody" id="deflateinflatelimitrequestbody">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum size of inflated request bodies</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateInflateLimitRequestBody <var>value</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>None, but LimitRequestBody applies after deflation</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>2.4.10 and later</td></tr>
</table>
    <p>The <code class="directive">DeflateInflateLimitRequestBody</code> directive
        specifies the maximum size of an inflated request body. If it is unset,
        <code class="directive"><a href="../mod/core.html#limitrequestbody">LimitRequestBody</a></code> is applied to the
        inflated body.</p>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DeflateInflateRatioBurst" id="DeflateInflateRatioBurst">DeflateInflateRatioBurst</a> <a name="deflateinflateratioburst" id="deflateinflateratioburst">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of times the inflation ratio for request bodies
             can be crossed</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateInflateRatioBurst <var>value</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>DeflateInflateRatioBurst 3</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>2.4.10 and later</td></tr>
</table>
    <p>The <code class="directive">DeflateInflateRatioBurst</code> directive
       specifies the maximum number of times the
       <code class="directive"><a href="#deflateinflateratiolimit">DeflateInflateRatioLimit</a></code> can
       be crossed before terminating the request.</p>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DeflateInflateRatioLimit" id="DeflateInflateRatioLimit">DeflateInflateRatioLimit</a> <a name="deflateinflateratiolimit" id="deflateinflateratiolimit">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum inflation ratio for request bodies</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateInflateRatioLimit <var>value</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>DeflateInflateRatioLimit 200</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>2.4.10 and later</td></tr>
</table>
    <p>The <code class="directive">DeflateInflateRatioLimit</code> directive
        specifies the maximum ratio of deflated to inflated size of an
        inflated request body. This ratio is checked as the body is
        streamed in, and if crossed more than
        <code class="directive"><a href="#deflateinflateratioburst">DeflateInflateRatioBurst</a></code>
        times, the request will be terminated.</p>

</div>
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<div class="directive-section"><h2><a name="DeflateMemLevel" id="DeflateMemLevel">DeflateMemLevel</a> <a name="deflatememlevel" id="deflatememlevel">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>How much memory should be used by zlib for compression</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateMemLevel <var>value</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>DeflateMemLevel 9</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
</table>
    <p>The <code class="directive">DeflateMemLevel</code> directive specifies
    how much memory should be used by zlib for compression
    (a value between 1 and 9).</p>

</div>
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<div class="directive-section"><h2><a name="DeflateWindowSize" id="DeflateWindowSize">DeflateWindowSize</a> <a name="deflatewindowsize" id="deflatewindowsize">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Zlib compression window size</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateWindowSize <var>value</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>DeflateWindowSize 15</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
</table>
    <p>The <code class="directive">DeflateWindowSize</code> directive specifies the
    zlib compression window size (a value between 1 and 15). Generally, the
    higher the window size, the higher can the compression ratio be expected.</p>

</div>
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