MDL-31410 always send 200 in PayPal IPN response and hide all errors

enrol/paypal/ipn.php

@@ -28,6 +28,9 @@
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
+// Disable moodle specific debug messages and any errors in output,
+// comment out when debugging or better look into error log!
+define('NO_DEBUG_DISPLAY', true);
 
 require("../../config.php");
 require_once("lib.php");
@@ -35,6 +38,9 @@ require_once($CFG->libdir.'/eventslib.php');
 require_once($CFG->libdir.'/enrollib.php');
 require_once($CFG->libdir . '/filelib.php');
 
+// PayPal does not like when we return error messages here,
+// the custom handler just logs exceptions and stops.
+set_exception_handler('enrol_paypal_ipn_exception_handler');
 
 /// Keep out casual intruders
 if (empty($_POST) or !empty($_GET)) {
@@ -330,4 +336,20 @@ function message_paypal_error_to_admin($subject, $data) {
     message_send($eventdata);
 }
 
+/**
+ * Silent exception handler.
+ *
+ * @param Exception $ex
+ * @return void - does not return. Terminates execution!
+ */
+function enrol_paypal_ipn_exception_handler($ex) {
+    $info = get_exception_info($ex);
 
+    $logerrmsg = "enrol_paypal IPN exception handler: ".$info->message;
+    if (debugging('', DEBUG_NORMAL)) {
+        $logerrmsg .= ' Debug: '.$info->debuginfo."\n".format_backtrace($info->backtrace, true);
+    }
+    error_log($logerrmsg);
+
+    exit(0);
+}