add Limited, an API limiting/versioning wrapper

2 files changed, 43 insertions, 0 deletions

diff --git a/bin/nova-direct-api b/bin/nova-direct-api
index 1a78fb0c0..ac0b5b51c 100755
--- a/bin/nova-direct-api
+++ b/bin/nova-direct-api
@@ -53,12 +53,19 @@ flags.DEFINE_flag(flags.HelpXMLFlag())
 
 
 
+class ReadOnlyCompute(direct.Limited):
+    """Read-only Compute API."""
+
+    _allowed = ['get', 'get_all', 'get_console_output']
+
+
 if __name__ == '__main__':
     utils.default_flagfile()
     FLAGS(sys.argv)
     logging.setup()
 
     direct.register_service('compute', compute.API())
+    direct.register_service('compute-readonly', ReadOnlyCompute(compute.API()))
     direct.register_service('volume', volume.API())
     direct.register_service('network', network.API())
     direct.register_service('reflect', direct.Reflection())
diff --git a/nova/api/direct.py b/nova/api/direct.py
index dfca250e0..1011091a6 100644
--- a/nova/api/direct.py
+++ b/nova/api/direct.py
@@ -211,6 +211,42 @@ class ServiceWrapper(wsgi.Controller):
             return result
 
 
+class Limited(object):
+    __notdoc = """Limit the available methods on a given object.
+
+    (Not a docstring so that the docstring can be conditionally overriden.)
+
+    Useful when defining a public API that only exposes a subset of an
+    internal API.
+
+    Expected usage of this class is to define a subclass that lists the allowed
+    methods in the 'allowed' variable.
+
+    Additionally where appropriate methods can be added or overwritten, for
+    example to provide backwards compatibility.
+
+    """
+
+    _allowed = None
+
+    def __init__(self, proxy):
+        self._proxy = proxy
+        if not self.__doc__:
+            self.__doc__ = proxy.__doc__
+        if not self._allowed:
+            self._allowed = []
+
+    def __getattr__(self, key):
+        """Only return methods that are named in self._allowed."""
+        if key not in self._allowed:
+            raise AttributeError()
+        return getattr(self._proxy, key)
+
+    def __dir__(self):
+        """Only return methods that are named in self._allowed."""
+        return [x for x in dir(self._proxy) if x in self._allowed]
+
+
 class Proxy(object):
     """Pretend a Direct API endpoint is an object."""
     def __init__(self, app, prefix=None):