From b5311ce466aa12322f71ee4c5dd6e40123471f39 Mon Sep 17 00:00:00 2001
From: sam marshall <s.marshall@open.ac.uk>
Date: Tue, 14 Aug 2018 13:32:06 +0100
Subject: [PATCH] MDL-63131 Web services: Callback to allow web service
 overrides

---
 lib/externallib.php | 25 +++++++++++++++++++++----
 webservice/lib.php  | 20 +++++++++++++++++++-
 2 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/lib/externallib.php b/lib/externallib.php
index 44fbd297a17..50a88f1b078 100644
--- a/lib/externallib.php
+++ b/lib/externallib.php
@@ -221,11 +221,28 @@ class external_api {
             $params = call_user_func($callable,
                                      $externalfunctioninfo->parameters_desc,
                                      $args);
+            $params = array_values($params);
 
-            // Execute - gulp!
-            $callable = array($externalfunctioninfo->classname, $externalfunctioninfo->methodname);
-            $result = call_user_func_array($callable,
-                                           array_values($params));
+            // Allow any Moodle plugin a chance to override this call. This is a convenient spot to
+            // make arbitrary behaviour customisations. The overriding plugin could call the 'real'
+            // function first and then modify the results, or it could do a completely separate
+            // thing.
+            $callbacks = get_plugins_with_function('override_webservice_execution');
+            $result = false;
+            foreach ($callbacks as $plugintype => $plugins) {
+                foreach ($plugins as $plugin => $callback) {
+                    $result = $callback($externalfunctioninfo, $params);
+                    if ($result !== false) {
+                        break;
+                    }
+                }
+            }
+
+            // If the function was not overridden, call the real one.
+            if ($result === false) {
+                $callable = array($externalfunctioninfo->classname, $externalfunctioninfo->methodname);
+                $result = call_user_func_array($callable, $params);
+            }
 
             // Validate the return parameters.
             if ($externalfunctioninfo->returns_desc !== null) {
diff --git a/webservice/lib.php b/webservice/lib.php
index 5da1bba99bb..fedfbc8e46b 100644
--- a/webservice/lib.php
+++ b/webservice/lib.php
@@ -1392,9 +1392,27 @@ abstract class webservice_base_server extends webservice_server {
     protected function execute() {
         // validate params, this also sorts the params properly, we need the correct order in the next part
         $params = call_user_func(array($this->function->classname, 'validate_parameters'), $this->function->parameters_desc, $this->parameters);
+        $params = array_values($params);
+
+        // Allow any Moodle plugin a chance to override this call. This is a convenient spot to
+        // make arbitrary behaviour customisations, for example to affect the mobile app behaviour.
+        // The overriding plugin could call the 'real' function first and then modify the results,
+        // or it could do a completely separate thing.
+        $callbacks = get_plugins_with_function('override_webservice_execution');
+        foreach ($callbacks as $plugintype => $plugins) {
+            foreach ($plugins as $plugin => $callback) {
+                $result = $callback($this->function, $params);
+                if ($result !== false) {
+                    // If the callback returns anything other than false, we assume it replaces the
+                    // real function.
+                    $this->returns = $result;
+                    return;
+                }
+            }
+        }
 
         // execute - yay!
-        $this->returns = call_user_func_array(array($this->function->classname, $this->function->methodname), array_values($params));
+        $this->returns = call_user_func_array(array($this->function->classname, $this->function->methodname), $params);
     }
 
     /**