MDL-53962 webservices: Make XML-RPC backwards compatible

webservice/upgrade.txt

@@ -17,6 +17,8 @@ This information is intended for authors of webservices, not people writing webs
   on the string returned by the getMessage() method of the thrown exception.
 * With Zend_SOAP dropped, moodle_zend_soap_server is now also deprecated.
 * As mentioned in the 2.9 notes, deprecated web service functions have now been removed.
+* Since our new XML-RPC server implementation does not support introspection, it is critical that all clients send
+  parameters in the correct order.
 
 === 3.0 ===
 

webservice/xmlrpc/lib.php

@@ -79,6 +79,8 @@ public function call($functionname, $params = array()) {
         );
 
         // Encode the request.
+        // See MDL-53962 - needed for backwards compatibility on <= 3.0
+        $params = array_values($params);
         $request = xmlrpc_encode_request($functionname, $params, $outputoptions);
 
         // Set the headers.

webservice/xmlrpc/locallib.php

@@ -78,16 +78,15 @@ protected function parse_request() {
 
         // Decode the request to get the decoded parameters and the name of the method to be called.
         $decodedparams = xmlrpc_decode_request($rawpostdata, $methodname);
+        $methodinfo = external_api::external_function_info($methodname);
+        $methodparams = array_keys($methodinfo->parameters_desc->keys);
 
         // Add the decoded parameters to the methodvariables array.
         if (is_array($decodedparams)) {
-            foreach ($decodedparams as $param) {
-                // Check if decoded param is an associative array.
-                if (is_array($param) && array_keys($param) !== range(0, count($param) - 1)) {
-                    $methodvariables = array_merge($methodvariables, $param);
-                } else {
-                    $methodvariables[] = $param;
-                }
+            foreach ($decodedparams as $index => $param) {
+                // See MDL-53962 - XML-RPC requests will usually be sent as an array (as in, one with indicies).
+                // We need to use a bit of "magic" to add the correct index back. Zend used to do this for us.
+                $methodvariables[$methodparams[$index]] = $param;
             }
         }