Reduce duplicated code related to policies

This patch adds some logic that is currently duplicated throughout
Openstack. As part of this de-duplication, the patch also modifies
current implementation.

Major Changes:
    * check, set_rules, reset, init are now part of the Enforcer class
    * check was renamed into enforce
    * init was renamed into load_rules
    * It is now possible to load multiple files and have per instance
      rules instead of global rules.
    * There's a global instance of the Enforcer class that can be used as
      main enforcer.

        from openstack.common import policy
        ENFORCER = policy.ENFORCER
        ENFORCER.enforce(rule, target, creds)

Minor Changes:
    * Added do_raise to the enforce method
    * Enforcer instance is now passed to the Check call.

NOTE: If / once this patch gets in, I'll update other projects and port
them to the latest version.

Change-Id: Ife909bdf3277ef33c2fb1eae16ae261fa6374c63

1 files changed, 32 insertions, 0 deletions

diff --git a/openstack/common/fileutils.py b/openstack/common/fileutils.py
index b988ad0..bb2ef61 100644
--- a/openstack/common/fileutils.py
+++ b/openstack/common/fileutils.py
@@ -19,6 +19,13 @@
 import errno
 import os
 
+from openstack.common.gettextutils import _
+from openstack.common import log as logging
+
+LOG = logging.getLogger(__name__)
+
+_FILE_CACHE = {}
+
 
 def ensure_tree(path):
     """Create a directory (and any ancestor directories required)
@@ -33,3 +40,28 @@ def ensure_tree(path):
                 raise
         else:
             raise
+
+
+def read_cached_file(filename, force_reload=False):
+    """Read from a file if it has been modified.
+
+    :param force_reload: Whether to reload the file.
+    :returns: A tuple with a boolean specifying if the data is fresh
+              or not.
+    """
+    global _FILE_CACHE
+
+    if force_reload and filename in _FILE_CACHE:
+        del _FILE_CACHE[filename]
+
+    reloaded = False
+    mtime = os.path.getmtime(filename)
+    cache_info = _FILE_CACHE.setdefault(filename, {})
+
+    if not cache_info or mtime > cache_info.get('mtime', 0):
+        LOG.debug(_("Reloading cached file %s") % filename)
+        with open(filename) as fap:
+            cache_info['data'] = fap.read()
+        cache_info['mtime'] = mtime
+        reloaded = True
+    return (reloaded, cache_info['data'])