- added timestamp-based JSON caching of configuration for faster loading

[invirt/packages/invirt-base.git] / files / usr / share / python-support / sipb-xen-base / invirt / config.py

diff --git a/files/usr/share/python-support/sipb-xen-base/invirt/config.py b/files/usr/share/python-support/sipb-xen-base/invirt/config.py
index 37fafb4..dab9f20 100644 (file)
--- a/files/usr/share/python-support/sipb-xen-base/invirt/config.py
+++ b/files/usr/share/python-support/sipb-xen-base/invirt/config.py
@@ -1,13 +1,41 @@
-from __future__ import with_statement
-import yaml
+import json, yaml
+from os import error, makedirs
+from os.path import dirname, getmtime
 
-default_path = '/etc/invirt/master.yaml'
+default_src_path   = '/etc/invirt/master.yaml'
+default_cache_path = '/var/lib/invirt/invirt.json'
 
 try:    default_loader = yaml.CSafeLoader
 except: default_loader = yaml.SafeLoader
 
-def load( path = default_path ):
-    with file( path ) as f:
-        return yaml.load( f, default_loader )
+def wrap(rsrc, func):
+    "Utility to that emulates with Python 2.5's `with closing(rsrc)`."
+    try: return func(rsrc)
+    finally: rsrc.close()
+
+def load(src_path = default_src_path,
+         cache_path = default_cache_path,
+         force_refresh = False):
+    """
+    Try loading the configuration from the faster-to-load JSON cache at
+    cache_path.  If it doesn't exist or is outdated, load the configuration
+    instead from the original YAML file at src_path and regenerate the cache.
+    I assume I have the permissions to write to the cache directory.
+    """
+    if force_refresh:
+        do_refresh = True
+    else:
+        src_mtime = getmtime(src_path)
+        try:            cache_mtime = getmtime(cache_path)
+        except OSError: do_refresh  = True
+        else:           do_refresh  = src_mtime > cache_mtime
+
+    if do_refresh:
+        # reload the source and regenerate the cache
+        cfg = wrap(file(src_path), lambda f: yaml.load(f, default_loader))
+        wrap(file(cache_path, 'w'), lambda f: f.write(json.write(cfg)))
+    else:
+        cfg = wrap(file(cache_path), lambda f: json.read(f.read()))
+    return cfg
 
 # vim:et:sw=4:ts=4