diff --git a/lib/php/src/TStringUtils.php b/lib/php/src/TStringUtils.php
new file mode 100644
index 0000000..69672e8
--- /dev/null
+++ b/lib/php/src/TStringUtils.php
@@ -0,0 +1,81 @@
+<?php
+
+interface TStringFunc {
+    public function substr($str, $start, $length = null);
+    public function strlen($str);
+}
+
+class TStringFunc_Core
+implements TStringFunc {
+    public function substr($str, $start, $length = null) {
+        // specifying a null $length would return an empty string
+        if($length === null) {
+            return substr($str, $start);
+        }
+        return substr($str, $start, $length);
+    }
+
+    public function strlen($str) {
+        return strlen($str);
+    }
+}
+
+class TStringFunc_Mbstring
+implements TStringFunc {
+    public function substr($str, $start, $length = null) {
+        /**
+         * We need to set the charset parameter, which is the second
+         * optional parameter and the first optional parameter can't
+         * be null or false as a "magic" value because that would
+         * cause an empty string to be returned, so we need to
+         * actually calculate the proper length value.
+         */
+        if($length === null) {
+            $length = $this->strlen($str) - $start;
+        }
+
+        return mb_substr($str, $start, $length, '8bit');
+    }
+
+    public function strlen($str) {
+        return mb_strlen($str, '8bit');
+    }
+}
+
+class TStringFuncFactory {
+    private static $_instance;
+
+    /**
+     * Get the Singleton instance of TStringFunc implementation that is
+     * compatible with the current system's mbstring.func_overload settings.
+     *
+     * @return TStringFunc
+     */
+    public static function create() {
+        if(!self::$_instance) {
+            self::_setInstance();
+        }
+
+        return self::$_instance;
+    }
+
+    private static function _setInstance() {
+        /**
+         * Cannot use str* functions for byte counting because multibyte
+         * characters will be read a single bytes.
+         *
+         * See: http://us.php.net/manual/en/mbstring.overload.php
+         */
+        if(ini_get('mbstring.func_overload') & 2) {
+            self::$_instance = new TStringFunc_Mbstring();
+        }
+        /**
+         * mbstring is not installed or does not have function overloading
+         * of the str* functions enabled so use PHP core str* functions for
+         * byte counting.
+         */
+        else {
+            self::$_instance = new TStringFunc_Core();
+        }
+    }
+}