extract_host: Handle empty host string input

This fixes an HTTP 500 error caused by the assumption
that this field is always populated for a volume.

Closes-Bug: #1628536

Change-Id: I19df26c37c03f8220fb3d87395f32b5ddef6bf9d

cinder/tests/unit/test_volume_utils.py

@@ -716,6 +716,11 @@ class VolumeUtilsTestCase(test.TestCase):
         self.assertEqual(pool,
                          volume_utils.extract_host(host, 'pool', True))
 
+    def test_extract_host_none_string(self):
+        self.assertRaises(exception.InvalidVolume,
+                          volume_utils.extract_host,
+                          None)
+
     def test_get_volume_rpc_host(self):
         host = 'Host@backend'
         # default level is 'backend'

cinder/volume/utils.py

@@ -648,7 +648,8 @@ def extract_host(host, level='backend', default_pool_name=False):
                               string.  default_pool_name=True will return
                               DEFAULT_POOL_NAME, otherwise we return None.
                               Default value of this parameter is False.
-    :return: expected level of information
+    :return: expected information, string or None
+    :raises: exception.InvalidVolume
 
     For example:
         host = 'HostA@BackendB#PoolC'
@@ -665,6 +666,11 @@ def extract_host(host, level='backend', default_pool_name=False):
         ret = extract_host(host, 'pool', True)
         # ret is '_pool0'
     """
+
+    if host is None:
+        msg = _LE("volume is not assigned to a host")
+        raise exception.InvalidVolume(reason=msg)
+
     if level == 'host':
         # make sure pool is not included
         hst = host.split('#')[0]