Pop extra keys from context in from_dict()

RequestContext.to_dict() adds user/tenant keys, but from_dict() spews
this warning a "Arguments dropped when creating context" if you pass a
dict which contains user/tenant keys.

Seems to make perfect sense that from_dict() would remove these extra
keys. A test case ensures this won't happen for new arguments.

This is import for oslo.messaging because we deserialize request context
dicts into nova's RequestContext using from_dict().

blueprint: oslo-messaging
Change-Id: I0938f3c7c581383cbebc3a973d64454250f6ab8e

nova/context.py

@@ -139,6 +139,8 @@ def to_dict(self):
 
     @classmethod
     def from_dict(cls, values):
+        values.pop('user', None)
+        values.pop('tenant', None)
         return cls(**values)
 
     def elevated(self, read_deleted=None, overwrite=False):

nova/tests/test_context.py

@@ -101,3 +101,21 @@ def test_service_catalog_cinder_only(self):
         ctxt = context.RequestContext('111', '222',
                 service_catalog=service_catalog)
         self.assertEquals(ctxt.service_catalog, volume_catalog)
+
+    def test_to_dict_from_dict_no_log(self):
+        warns = []
+
+        def stub_warn(msg, *a, **kw):
+            if (a and len(a) == 1 and isinstance(a[0], dict) and a[0]):
+                a = a[0]
+            warns.append(str(msg) % a)
+
+        self.stubs.Set(context.LOG, 'warn', stub_warn)
+
+        ctxt = context.RequestContext('111',
+                                      '222',
+                                      roles=['admin', 'weasel'])
+
+        ctxt = context.RequestContext.from_dict(ctxt.to_dict())
+
+        self.assertEqual(len(warns), 0, warns)