Add bootstrap.php checking environment (MB_OVERLOAD_STRING).

composer.json

@@ -61,6 +61,9 @@
     },
     "include-path": ["phpseclib/"],
     "autoload": {
+        "files": [
+            "phpseclib/bootstrap.php"
+        ],
         "psr-4": {
             "phpseclib\\": "phpseclib/"
         }

composer.lock

@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file",
         "This file is @generated automatically"
     ],
-    "hash": "b24ab20be15b6312e532ee2ffa18d5fa",
+    "hash": "98a14889a81b2d6ecbb029483e954dec",
     "packages": [],
     "packages-dev": [
         {

phpseclib/bootstrap.php

@@ -0,0 +1,16 @@
+<?php
+/**
+ * Bootstrapping File for phpseclib
+ *
+ * @license http://www.opensource.org/licenses/mit-license.html MIT License
+ */
+
+if (extension_loaded('mbstring')) {
+    // 2 - MB_OVERLOAD_STRING
+    if (ini_get('mbstring.func_overload') & 2) {
+        throw new \UnexpectedValueException(
+            'Overloading of string functions using mbstring.func_overload ' .
+            'is not supported by phpseclib.'
+        );
+    }
+}