Add cache control settings

Things need to do local caching, which means they need to control
some settings about that. Add simple cache settings support.

Change-Id: I7b56cc25ebe7a803816d95b79d0329f8e42025ba

README.rst

@@ -45,11 +45,13 @@ and without the OS prefix. So, username is set with `username`.
 Service specific settings, like the nova service type, are set with the
 default service type as a prefix. For instance, to set a special service_type
 for trove (because you're using Rackspace) set:
+
 ::
 
   database_service_type: 'rax:database'
 
 An example config file is probably helpful:
+
 ::
 
   clouds:
@@ -90,6 +92,28 @@ the setting with the default service type. That might strike you funny when
 setting `service_type` and it does me too - but that's just the world we live
 in.
 
+Cache Settings
+--------------
+
+Accessing a cloud is often expensive, so it's quite common to want to do some
+client-side caching of those operations. To facilitate that, os-client-config
+understands a simple set of cache control settings.
+
+::
+
+  cache:
+    path: ~/.cache/openstack
+    max_age: 300
+  clouds:
+    mordred:
+      cloud: hp
+      username: mordred@inaugust.com
+      password: XXXXXXXXX
+      project_id: mordred@inaugust.com
+      region_name: region-b.geo-1
+      dns_service_type: hpext:dns
+
+
 Usage
 -----
 

os_client_config/config.py

@@ -28,6 +28,9 @@ CONFIG_HOME = os.path.join(os.path.expanduser(
 CONFIG_SEARCH_PATH = [os.getcwd(), CONFIG_HOME, '/etc/openstack']
 CONFIG_FILES = [
     os.path.join(d, 'clouds.yaml') for d in CONFIG_SEARCH_PATH]
+CACHE_PATH = os.path.join(os.path.expanduser(
+    os.environ.get('XDG_CACHE_PATH', os.path.join('~', '.cache'))),
+    'openstack')
 BOOL_KEYS = ('insecure', 'cache')
 REQUIRED_VALUES = ('auth_url', 'username', 'password', 'project_id')
 VENDOR_SEARCH_PATH = [os.getcwd(), CONFIG_HOME, '/etc/openstack']
@@ -70,6 +73,14 @@ class OpenStackConfig(object):
             self.cloud_config = dict(
                 clouds=dict(openstack=dict(self.defaults)))
 
+        self._cache_max_age = 300
+        self._cache_path = CACHE_PATH
+        if 'cache' in self.cloud_config:
+            self._cache_max_age = self.cloud_config['cache'].get(
+                'max_age', self._cache_max_age)
+            self._cache_path = os.path.expanduser(
+                self.cloud_config['cache'].get('path', self._cache_path))
+
     def _load_config_file(self):
         for path in self._config_files:
             if os.path.exists(path):
@@ -80,6 +91,12 @@ class OpenStackConfig(object):
             if os.path.exists(path):
                 return yaml.load(open(path, 'r'))
 
+    def get_cache_max_age(self):
+        return self._cache_max_age
+
+    def get_cache_path(self):
+        return self._cache_path
+
     def _get_regions(self, cloud):
         try:
             return self.cloud_config['clouds'][cloud]['region_name']