From 271e0f7742c129c52f7662157ab327cedf2cca69 Mon Sep 17 00:00:00 2001
From: Peter Westwood <westi@git.wordpress.org>
Date: Sat, 21 Feb 2009 21:39:06 +0000
Subject: [PATCH] Allow for the HTTP headers returned by WordPress to be
 filtered by a plugin. Fixes #9205 props filosofo.

git-svn-id: https://develop.svn.wordpress.org/trunk@10619 602fd350-edb4-49c9-b593-d223f7449a82
---
 wp-includes/classes.php   | 28 ++++++++++++++++++----------
 wp-includes/functions.php | 30 +++++++++++++++++++++++++-----
 2 files changed, 43 insertions(+), 15 deletions(-)

diff --git a/wp-includes/classes.php b/wp-includes/classes.php
index d91dd3e4d3..9b5efd7af4 100644
--- a/wp-includes/classes.php
+++ b/wp-includes/classes.php
@@ -302,16 +302,17 @@ class WP {
 	 * @since 2.0.0
 	 */
 	function send_headers() {
-		@header('X-Pingback: '. get_bloginfo('pingback_url'));
+		$headers = array('X-Pingback' => get_bloginfo('pingback_url'));
+		$status = null;
 		if ( is_user_logged_in() )
-			nocache_headers();
+			$headers = array_merge($headers, wp_get_nocache_headers());
 		if ( !empty($this->query_vars['error']) && '404' == $this->query_vars['error'] ) {
-			status_header( 404 );
+			$status = 404;
 			if ( !is_user_logged_in() )
-				nocache_headers();
-			@header('Content-Type: ' . get_option('html_type') . '; charset=' . get_option('blog_charset'));
+				$headers = array_merge($headers, wp_get_nocache_headers());
+			$headers['Content-Type'] = get_option('html_type') . '; charset=' . get_option('blog_charset');
 		} else if ( empty($this->query_vars['feed']) ) {
-			@header('Content-Type: ' . get_option('html_type') . '; charset=' . get_option('blog_charset'));
+			$headers['Content-Type'] = get_option('html_type') . '; charset=' . get_option('blog_charset');
 		} else {
 			// We're showing a feed, so WP is indeed the only thing that last changed
 			if ( !empty($this->query_vars['withcomments'])
@@ -329,8 +330,8 @@ class WP {
 			else
 				$wp_last_modified = mysql2date('D, d M Y H:i:s', get_lastpostmodified('GMT'), 0).' GMT';
 			$wp_etag = '"' . md5($wp_last_modified) . '"';
-			@header("Last-Modified: $wp_last_modified");
-			@header("ETag: $wp_etag");
+			$headers['Last-Modified'] = $wp_last_modified;
+			$headers['ETag'] = $wp_etag;
 
 			// Support for Conditional GET
 			if (isset($_SERVER['HTTP_IF_NONE_MATCH']))
@@ -347,11 +348,18 @@ class WP {
 			if ( ($client_last_modified && $client_etag) ?
 					 (($client_modified_timestamp >= $wp_modified_timestamp) && ($client_etag == $wp_etag)) :
 					 (($client_modified_timestamp >= $wp_modified_timestamp) || ($client_etag == $wp_etag)) ) {
-				status_header( 304 );
-				exit;
+				$status = 304;
+				add_action('send_headers', 'exit', 1);
 			}
 		}
 
+		$headers = apply_filters('wp_headers', $headers, $this); 
+
+		if ( ! empty( $status ) ) 
+			status_header( $status );
+		foreach( (array) $headers as $name => $field_value )
+			@header("{$name}: {$field_value}");
+
 		do_action_ref_array('send_headers', array(&$this));
 	}
 
diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index 067d66ebb0..3aed0597f6 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -1459,6 +1459,27 @@ function status_header( $header ) {
 	return @header( $status_header, true, $header );
 }
 
+/**
+ * Gets the header information to prevent caching.
+ *
+ * The several different headers cover the different ways cache prevention is handled
+ * by different browsers
+ *
+ * @since 2.8
+ *
+ * @uses apply_filters()
+ * @return array The associative array of header names and field values.
+ */
+function wp_get_nocache_headers() {
+	$headers = array(
+		'Expires' => 'Wed, 11 Jan 1984 05:00:00 GMT',
+		'Last-Modified' => gmdate( 'D, d M Y H:i:s' ) . ' GMT',
+		'Cache-Control' => 'no-cache, must-revalidate, max-age=0',
+		'Pragma' => 'no-cache',
+	);
+	return apply_filters('nocache_headers', $headers);	
+}
+
 /**
  * Sets the headers to prevent caching for the different browsers.
  *
@@ -1466,13 +1487,12 @@ function status_header( $header ) {
  * be sent so that all of them get the point that no caching should occur.
  *
  * @since 2.0.0
+ * @uses wp_get_nocache_headers()
  */
 function nocache_headers() {
-	// why are these @-silenced when other header calls aren't?
-	@header( 'Expires: Wed, 11 Jan 1984 05:00:00 GMT' );
-	@header( 'Last-Modified: ' . gmdate( 'D, d M Y H:i:s' ) . ' GMT' );
-	@header( 'Cache-Control: no-cache, must-revalidate, max-age=0' );
-	@header( 'Pragma: no-cache' );
+	$headers = wp_get_nocache_headers();
+	foreach( (array) $headers as $name => $field_value ) 
+		@header("{$name}: {$field_value}");		
 }
 
 /**