Correct decoding of JSON response

The old version assumed `json_decode` would return an associative array.
While it can do so if an extra option is specified, the default
behaviour is to return an object. Therefore, a successful password
change resulted in an error while parsing the response.

The new code is accessing the response as object instead. The method
is now covered by a unit test.

plugins/password/drivers/cpanel_webmail.php

@@ -70,13 +70,17 @@ class rcube_cpanel_webmail_password
      */
     public static function decode_response($response)
     {
+        if (!$response) {
+            return PASSWORD_CONNECT_ERROR;
+        }
+
         $result = json_decode($response);
 
-        if ($result['status'] === 1) {
+        if ($result->status === 1) {
             return PASSWORD_SUCCESS;
         }
 
-        $errors = $result['errors'];
+        $errors = $result->errors;
         if (is_array($errors) && count($errors) > 0) {
             return array(
                 'code'    => PASSWORD_ERROR,

plugins/password/tests/Password.php

@@ -19,5 +19,28 @@ class Password_Plugin extends PHPUnit_Framework_TestCase
         $this->assertInstanceOf('password', $plugin);
         $this->assertInstanceOf('rcube_plugin', $plugin);
     }
-}
 
+    function test_driver_cpanel_webmail()
+    {
+        $driver = 'cpanel_webmail';
+        include_once __DIR__ . "/../drivers/$driver.php";
+        $driver_class = "rcube_${driver}_password";
+        $this->assertTrue(class_exists($driver_class));
+
+        $json_response_fail = '{"data":null,"errors":'
+                . '["Execution of Email::passwdpop (api version:3) is not '
+                . 'permitted inside of webmail"],"status":0,"metadata":{},'
+                . '"messages":null}';
+        $result = $driver_class::decode_response($json_response_fail);
+        $this->assertTrue(is_array($result));
+        $this->assertEquals($result['code'], PASSWORD_ERROR);
+        $expected_message = 'Execution of Email::passwdpop (api version:3) is'
+                . ' not permitted inside of webmail';
+        $this->assertEquals($result['message'], $expected_message);
+
+        $json_response_success = '{"metadata":{},"data":null,"messages":null,'
+                . '"errors":null,"status":1}';
+        $result = $driver_class::decode_response($json_response_success);
+        $this->assertEquals($result, PASSWORD_SUCCESS);
+    }
+}