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<title>[23281] branches/3.5: Try not to send Last-Modified, even with an empty value.</title>
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<dl class="meta">
<dt>Revision</dt> <dd><a href="http://core.trac.wordpress.org/changeset/23281">23281</a></dd>
<dt>Author</dt> <dd>ryan</dd>
<dt>Date</dt> <dd>2013-01-04 22:52:10 +0000 (Fri, 04 Jan 2013)</dd>
</dl>

<h3>Log Message</h3>
<pre>Try not to send Last-Modified, even with an empty value. Some servers interpret an empty value as the epoch.

Props nacin, slene, SergeyBiryukov, andy
fixes <a href="http://core.trac.wordpress.org/ticket/23021">#23021</a> for 3.5</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#branches35wpincludesclasswpphp">branches/3.5/wp-includes/class-wp.php</a></li>
<li><a href="#branches35wpincludesfunctionsphp">branches/3.5/wp-includes/functions.php</a></li>
</ul>

<h3>Property Changed</h3>
<ul>
<li><a href="#branches35">branches/3.5/</a></li>
<li><a href="#branches35wpadminincludesupdatecorephp">branches/3.5/wp-admin/includes/update-core.php</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="branches35"></a>
<div class="propset"><h4>Property changes: branches/3.5</h4>
<pre class="diff"><span>
</span></pre></div>
<a id="svnmergeinfo"></a>
<div class="modfile"><h4>Modified: svn:mergeinfo</h4></div>
<span class="cx">/branches/3.3:20543
</span><span class="cx">/branches/3.4:21757
</span><span class="cx">/trunk:18512,23133-23135,23139
</span><span class="cx">   + /branches/3.1:18031
</span><span class="cx">/branches/3.3:20543
</span><span class="cx">/branches/3.4:21757
</span><span class="cx">/trunk:18512,23133-23135,23139,23267
</span><a id="branches35wpadminincludesupdatecorephp"></a>
<div class="propset"><h4>Property changes: branches/3.5/wp-admin/includes/update-core.php</h4>
<pre class="diff"><span>
</span></pre></div>
<a id="svnmergeinfo"></a>
<div class="modfile"><h4>Modified: svn:mergeinfo</h4></div>
<span class="cx">/branches/3.3/wp-admin/includes/update-core.php:20543
</span><span class="cx">/branches/3.4/wp-admin/includes/update-core.php:21757
</span><span class="cx">/trunk/wp-admin/includes/update-core.php:18512,23133-23135,23139,23179
</span><span class="cx">   + /branches/3.1/wp-admin/includes/update-core.php:18031
</span><span class="cx">/branches/3.3/wp-admin/includes/update-core.php:20543
</span><span class="cx">/branches/3.4/wp-admin/includes/update-core.php:21757
</span><span class="cx">/trunk/wp-admin/includes/update-core.php:18512,23133-23135,23139,23179,23267
</span><a id="branches35wpincludesclasswpphp"></a>
<div class="modfile"><h4>Modified: branches/3.5/wp-includes/class-wp.php (23280 => 23281)</h4>
<pre class="diff"><span>
<span class="info">--- branches/3.5/wp-includes/class-wp.php        2013-01-04 22:36:35 UTC (rev 23280)
+++ branches/3.5/wp-includes/class-wp.php        2013-01-04 22:52:10 UTC (rev 23281)
</span><span class="lines">@@ -378,12 +378,29 @@
</span><span class="cx"> 
</span><span class="cx">                 if ( ! empty( $status ) )
</span><span class="cx">                         status_header( $status );
</span><ins>+
+                // If Last-Modified is set to false, it should not be sent (no-cache situation).
+                if ( isset( $headers['Last-Modified'] ) &amp;&amp; false === $headers['Last-Modified'] ) {
+                        unset( $headers['Last-Modified'] );
+
+                        // In PHP 5.3+, make sure we are not sending a Last-Modified header.
+                        if ( function_exists( 'header_remove' ) ) {
+                                @header_remove( 'Last-Modified' );
+                        } else {
+                                // In PHP 5.2, send an empty Last-Modified header, but only as a
+                                // last resort to override a header already sent. #WP23021
+                                foreach ( headers_list() as $header ) {
+                                        if ( 0 === stripos( $header, 'Last-Modified' ) ) {
+                                                $headers['Last-Modified'] = '';
+                                                break;
+                                        }
+                                }
+                        }
+                }
+
</ins><span class="cx">                 foreach( (array) $headers as $name =&gt; $field_value )
</span><span class="cx">                         @header(&quot;{$name}: {$field_value}&quot;);
</span><span class="cx"> 
</span><del>-                if ( isset( $headers['Last-Modified'] ) &amp;&amp; empty( $headers['Last-Modified'] ) &amp;&amp; function_exists( 'header_remove' ) )
-                        @header_remove( 'Last-Modified' );
-
</del><span class="cx">                 if ( $exit_required )
</span><span class="cx">                         exit();
</span><span class="cx"> 
</span></span></pre></div>
<a id="branches35wpincludesfunctionsphp"></a>
<div class="modfile"><h4>Modified: branches/3.5/wp-includes/functions.php (23280 => 23281)</h4>
<pre class="diff"><span>
<span class="info">--- branches/3.5/wp-includes/functions.php        2013-01-04 22:36:35 UTC (rev 23280)
+++ branches/3.5/wp-includes/functions.php        2013-01-04 22:52:10 UTC (rev 23281)
</span><span class="lines">@@ -902,7 +902,6 @@
</span><span class="cx"> function wp_get_nocache_headers() {
</span><span class="cx">         $headers = array(
</span><span class="cx">                 'Expires' =&gt; 'Wed, 11 Jan 1984 05:00:00 GMT',
</span><del>-                'Last-Modified' =&gt; '',
</del><span class="cx">                 'Cache-Control' =&gt; 'no-cache, must-revalidate, max-age=0',
</span><span class="cx">                 'Pragma' =&gt; 'no-cache',
</span><span class="cx">         );
</span><span class="lines">@@ -910,6 +909,7 @@
</span><span class="cx">         if ( function_exists('apply_filters') ) {
</span><span class="cx">                 $headers = (array) apply_filters('nocache_headers', $headers);
</span><span class="cx">         }
</span><ins>+        $headers['Last-Modified'] = false;
</ins><span class="cx">         return $headers;
</span><span class="cx"> }
</span><span class="cx"> 
</span><span class="lines">@@ -924,10 +924,25 @@
</span><span class="cx">  */
</span><span class="cx"> function nocache_headers() {
</span><span class="cx">         $headers = wp_get_nocache_headers();
</span><ins>+
+        unset( $headers['Last-Modified'] );
+
+        // In PHP 5.3+, make sure we are not sending a Last-Modified header.
+        if ( function_exists( 'header_remove' ) ) {
+                @header_remove( 'Last-Modified' );
+        } else {
+                // In PHP 5.2, send an empty Last-Modified header, but only as a
+                // last resort to override a header already sent. #WP23021
+                foreach ( headers_list() as $header ) {
+                        if ( 0 === stripos( $header, 'Last-Modified' ) ) {
+                                $headers['Last-Modified'] = '';
+                                break;
+                        }
+                }
+        }
+
</ins><span class="cx">         foreach( $headers as $name =&gt; $field_value )
</span><span class="cx">                 @header(&quot;{$name}: {$field_value}&quot;);
</span><del>-        if ( empty( $headers['Last-Modified'] ) &amp;&amp; function_exists( 'header_remove' ) )
-                @header_remove( 'Last-Modified' );
</del><span class="cx"> }
</span><span class="cx"> 
</span><span class="cx"> /**
</span></span></pre>
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