General: Check to see that the PHP-XML module is enabled before using XML functions.

There are a handful of places where we don't check that the XML functions exist before we use them. Ubuntu's PHP 7 packages don't include PHP-XML by default, increasing the chance of this causing issues.

Props kraftbj, markoheijnen.
Fixes #37122.



git-svn-id: https://develop.svn.wordpress.org/trunk@38883 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/IXR/class-IXR-message.php

@@ -44,6 +44,11 @@ class IXR_Message
 
     function parse()
     {
+        if ( ! function_exists( 'xml_parser_create' ) ) {
+            trigger_error( __( "PHP's XML extension is not available. Please contact your hosting provider to enable PHP's XML" ) );
+            return false;
+        }
+
         // first remove the XML declaration
         // merged from WP #10698 - this method avoids the RAM usage of preg_replace on very large messages
         $header = preg_replace( '/<\?xml.*?\?'.'>/s', '', substr( $this->message, 0, 100 ), 1 );