From 2e4afde68dae7f410af8c9e3a0664fcf97ce8a3d Mon Sep 17 00:00:00 2001
From: Aidan Woods <aidantwoods@gmail.com>
Date: Fri, 5 May 2017 21:55:58 +0100
Subject: [PATCH] faster check substr at beginning of string

---
 Parsedown.php | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/Parsedown.php b/Parsedown.php
index 6ef12d3bb..096c399a0 100644
--- a/Parsedown.php
+++ b/Parsedown.php
@@ -1533,7 +1533,7 @@ protected function sanitiseElement(array $Element)
                     unset($Element['attributes'][$att]);
                 }
                 # dump onevent attribute
-                elseif (preg_match('/^on/i', $att))
+                elseif (self::striAtStart($att, 'on'))
                 {
                     unset($Element['attributes'][$att]);
                 }
@@ -1551,7 +1551,7 @@ protected function filterUnsafeUrlInAttribute(array $Element, $attribute)
 
             foreach ($this->safeLinksWhitelist as $scheme)
             {
-                if (stripos($Element['attributes'][$attribute], $scheme) === 0)
+                if (self::striAtStart($Element['attributes'][$attribute], $scheme))
                 {
                     $safe = true;
 
@@ -1584,6 +1584,20 @@ protected static function escape($text, $allowQuotes = false)
         return htmlspecialchars($text, $allowQuotes ? ENT_NOQUOTES : ENT_QUOTES, 'UTF-8');
     }
 
+    protected static function striAtStart($string, $needle)
+    {
+        $len = strlen($needle);
+
+        if ($len > strlen($string))
+        {
+            return false;
+        }
+        else
+        {
+            return strtolower(substr($string, 0, $len)) === strtolower($needle);
+        }
+    }
+
     static function instance($name = 'default')
     {
         if (isset(self::$instances[$name]))