From 5ebd1fb9768969956c9131df4274f9cdff7f0134 Mon Sep 17 00:00:00 2001
From: Brendan Heywood <brendan@catalyst-au.net>
Date: Thu, 6 Oct 2016 22:27:58 +1100
Subject: [PATCH] MDL-53978 core: Added callbacks for all major render stages

---
 lib/outputrenderers.php | 60 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 59 insertions(+), 1 deletion(-)

diff --git a/lib/outputrenderers.php b/lib/outputrenderers.php
index 977fa6984e5..550b09887a1 100644
--- a/lib/outputrenderers.php
+++ b/lib/outputrenderers.php
@@ -513,9 +513,30 @@ class core_renderer extends renderer_base {
      */
     public function htmlattributes() {
         $return = get_html_lang(true);
+        $attributes = array();
         if ($this->page->theme->doctype !== 'html5') {
-            $return .= ' xmlns="http://www.w3.org/1999/xhtml"';
+            $attributes['xmlns'] = 'http://www.w3.org/1999/xhtml';
         }
+
+        // Give plugins an opportunity to add things like xml namespaces to the html element.
+        // This function should return an array of html attribute names => values.
+        $pluginswithfunction = get_plugins_with_function('add_htmlattributes', 'lib.php');
+        foreach ($pluginswithfunction as $plugins) {
+            foreach ($plugins as $function) {
+                $newattrs = $function();
+                unset($newattrs['dir']);
+                unset($newattrs['lang']);
+                unset($newattrs['xmlns']);
+                unset($newattrs['xml:lang']);
+                $attributes += $newattrs;
+            }
+        }
+
+        foreach ($attributes as $key => $val) {
+            $val = s($val);
+            $return .= " $key=\"$val\"";
+        }
+
         return $return;
     }
 
@@ -540,6 +561,15 @@ class core_renderer extends renderer_base {
 
         $output = '';
 
+        // Give plugins an opportunity to add any head elements. The callback
+        // must always return a string containing valid html head content.
+        $pluginswithfunction = get_plugins_with_function('before_standard_html_head', 'lib.php');
+        foreach ($pluginswithfunction as $plugins) {
+            foreach ($plugins as $function) {
+                $output .= $function();
+            }
+        }
+
         // Allow a url_rewrite plugin to setup any dynamic head content.
         if (isset($CFG->urlrewriteclass) && !isset($CFG->upgraderunning)) {
             $class = $CFG->urlrewriteclass;
@@ -628,7 +658,18 @@ class core_renderer extends renderer_base {
         if ($this->page->pagelayout !== 'embedded' && !empty($CFG->additionalhtmltopofbody)) {
             $output .= "\n".$CFG->additionalhtmltopofbody;
         }
+
+        // Give plugins an opportunity to inject extra html content. The callback
+        // must always return a string containing valid html.
+        $pluginswithfunction = get_plugins_with_function('before_standard_top_of_body_html', 'lib.php');
+        foreach ($pluginswithfunction as $plugins) {
+            foreach ($plugins as $function) {
+                $output .= $function();
+            }
+        }
+
         $output .= $this->maintenance_warning();
+
         return $output;
     }
 
@@ -1001,6 +1042,15 @@ class core_renderer extends renderer_base {
     public function header() {
         global $USER, $CFG, $SESSION;
 
+        // Give plugins an opportunity touch things before the http headers are sent
+        // such as adding additional headers. The return value is ignored.
+        $pluginswithfunction = get_plugins_with_function('before_http_headers', 'lib.php');
+        foreach ($pluginswithfunction as $plugins) {
+            foreach ($plugins as $function) {
+                $function();
+            }
+        }
+
         if (\core\session\manager::is_loggedinas()) {
             $this->page->add_body_class('userloggedinas');
         }
@@ -1112,6 +1162,14 @@ class core_renderer extends renderer_base {
     public function footer() {
         global $CFG, $DB, $PAGE;
 
+        // Give plugins an opportunity to touch the page before JS is finalized.
+        $pluginswithfunction = get_plugins_with_function('before_footer', 'lib.php');
+        foreach ($pluginswithfunction as $plugins) {
+            foreach ($plugins as $function) {
+                $function();
+            }
+        }
+
         $output = $this->container_end_all(true);
 
         $footer = $this->opencontainers->pop('header/footer');