Improve UtfString handling of invalid strings

First check whether string is actually utf-8 before trying to process it
as it.

Fixes phpmyadmin/phpmyadmin#13385

Signed-off-by: Michal Čihař <michal@cihar.com>

Author: nijel

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## [Unreleased]
 
 * Fixed parsing SQL comment at the end of query.
+* Improved handing of non utf-8 strings.
 
 ## [4.1.7] - 2017-06-06
 

src/UtfString.php

@@ -75,7 +75,11 @@ public function __construct($str)
         $this->byteIdx = 0;
         $this->charIdx = 0;
         $this->byteLen = mb_strlen($str, '8bit');
-        $this->charLen = mb_strlen($str, 'UTF-8');
+        if (! mb_check_encoding($str, 'UTF-8')) {
+            $this->charLen = 0;
+        } else {
+            $this->charLen = mb_strlen($str, 'UTF-8');
+        }
     }
 
     /**

tests/Misc/UtfStringTest.php

@@ -82,4 +82,35 @@ public function testToString()
         $str = new UtfString(static::TEST_PHRASE);
         $this->assertEquals(static::TEST_PHRASE, (string) $str);
     }
+
+    /**
+     * Test access to string
+     *
+     * @dataProvider utf8_strings
+     */
+    public function testAccess($text, $pos10, $pos20)
+    {
+        $str = new UtfString($text);
+        $this->assertEquals($pos10, $str->offsetGet(10));
+        $this->assertEquals($pos20, $str->offsetGet(20));
+        $this->assertEquals($pos10, $str->offsetGet(10));
+    }
+
+    public function utf8_strings()
+    {
+        return array(
+            'ascii' => array(
+                'abcdefghijklmnopqrstuvwxyz', 'k', 'u'
+            ),
+            'unicode' => array(
+                'áéíóúýěřťǔǐǒǎšďȟǰǩľžčǚň', 'ǐ', 'č'
+            ),
+            'emoji' => array(
+                '😂😄😃😀😊😉😍😘😚😗😂👿😮😨😱😠😡😤😖😆😋👯', '😂', '😋'
+            ),
+            'iso' => array(
+                "P\xf8\xed\xb9ern\xec \xbelu\xbbou\xe8k\xfd k\xf3d \xfap\xecl \xef\xe1belsk\xe9 k\xf3dy", null, null
+            ),
+        );
+    }
 }