Add threading headers to change notification mails as proposed in PR #120

inc/subscription.php

@@ -424,9 +424,14 @@ class Subscription {
         $trep['DIFF'] = $tdiff;
         $hrep['DIFF'] = $hdiff;
 
+        $headers = array('Message-Id' => $this->getMessageID($id));
+        if ($rev) {
+            $headers['In-Reply-To'] =  $this->getMessageID($id, $rev);
+        }
+
         return $this->send(
             $subscriber_mail, $subject, $id,
-            $template, $trep, $hrep
+            $template, $trep, $hrep, $headers
         );
     }
 
@@ -542,9 +547,10 @@ class Subscription {
      *                                template (in text format)
      * @param array  $hrep            Predefined parameters used to parse the
      *                                template (in HTML format), null to default to $trep
+     * @param array  $headers         Additional mail headers in the form 'name' => 'value'
      * @return bool
      */
-    protected function send($subscriber_mail, $subject, $context, $template, $trep, $hrep = null) {
+    protected function send($subscriber_mail, $subject, $context, $template, $trep, $hrep = null, $headers = array()) {
         global $lang;
         global $conf;
 
@@ -560,9 +566,36 @@ class Subscription {
         if(isset($trep['SUBSCRIBE'])) {
             $mail->setHeader('List-Unsubscribe', '<'.$trep['SUBSCRIBE'].'>', false);
         }
+
+        foreach ($headers as $header => $value) {
+            $mail->setHeader($header, $value);
+        }
+
         return $mail->send();
     }
 
+    /**
+     * Get a valid message id for a certain $id and revision (or the current revision)
+     * @param string $id  The id of the page (or media file) the message id should be for
+     * @param string $rev The revision of the page, set to the current revision of the page $id if not set
+     * @return string
+     */
+    protected function getMessageID($id, $rev = NULL) {
+        static $listid = null;
+        if (is_null($listid)) {
+            $server = parse_url(DOKU_URL, PHP_URL_HOST);
+            $listid = join('.', array_reverse(explode('/', DOKU_BASE))).$server;
+            $listid = urlencode($listid);
+            $listid = strtolower(trim($listid, '.'));
+        }
+
+        if (is_null($rev)) {
+            $rev = @filemtime(wikiFN($id));
+        }
+
+        return "<$id?rev=$rev@$listid>";
+    }
+
     /**
      * Default callback for COMMON_NOTIFY_ADDRESSLIST
      *