Prevent updating os_id of db items

Updating of db item's os_id should be disabled. But a special case (None
-> smth) should be allowed.

Change-Id: I9a38c99d1a5d024ef38339e8d41eff7856cb3ebe

ec2api/db/sqlalchemy/api.py

@@ -29,6 +29,7 @@ from sqlalchemy.sql import bindparam
 
 import ec2api.context
 from ec2api.db.sqlalchemy import models
+from ec2api import exception
 
 CONF = cfg.CONF
 
@@ -142,8 +143,12 @@ def add_item_id(context, kind, os_id, project_id=None):
 def update_item(context, item):
     item_ref = (model_query(context, models.Item).
                 filter_by(project_id=context.project_id,
-                          id=item["id"]).
+                          id=item['id']).
                 one())
+    if item_ref.os_id and item_ref.os_id != item['os_id']:
+        raise exception.EC2DBInvalidOsIdUpdate(item_id=item['id'],
+                                               old_os_id=item_ref.os_id,
+                                               new_os_id=item['os_id'])
     item_ref.update(_pack_item_data(item))
     item_ref.save()
     return _unpack_item_data(item_ref)

ec2api/exception.py

@@ -100,6 +100,11 @@ class EC2KeystoneDiscoverFailure(EC2APIException):
     msg_fmt = _("Could not discover keystone versions.")
 
 
+class EC2DBInvalidOsIdUpdate(EC2APIException):
+    msg_fmt = _('Invalid update of os_id of %(item_id)s item '
+                'from %(old_os_id)s to %(new_os_id)s')
+
+
 # Internal ec2api metadata exceptions
 
 class EC2MetadataException(EC2APIException):

ec2api/tests/unit/test_db_api.py

@@ -17,6 +17,7 @@ from sqlalchemy.orm import exc as orm_exception
 
 from ec2api.api import validator
 from ec2api.db import api as db_api
+from ec2api import exception
 from ec2api.tests.unit import base
 from ec2api.tests.unit import fakes
 from ec2api.tests.unit import matchers
@@ -142,6 +143,22 @@ class DbApiTestCase(base.DbTestCase):
                           {'id': fakes.random_ec2_id('fake'),
                            'key': 'val'})
 
+    def test_update_item_os_id(self):
+        item = db_api.add_item(self.context, 'fake', {})
+        item['os_id'] = 'fake_os_id'
+        db_api.update_item(self.context, item)
+        item = db_api.get_item_by_id(self.context, item['id'])
+        self.assertThat({'os_id': 'fake_os_id'},
+                        matchers.IsSubDictOf(item))
+        item['os_id'] = 'other_fake_os_id'
+        self.assertRaises(exception.EC2DBInvalidOsIdUpdate,
+                          db_api.update_item,
+                          self.context, item)
+        item['os_id'] = None
+        self.assertRaises(exception.EC2DBInvalidOsIdUpdate,
+                          db_api.update_item,
+                          self.context, item)
+
     def test_delete_item(self):
         item = db_api.add_item(self.context, 'fake', {})
         db_api.delete_item(self.context, item['id'])