added utility to read and cache remote metadata feeds.

src/utility/metadata.py

@@ -0,0 +1,36 @@
+import os.path, sys, time, urllib
+from time import strftime
+import logging
+
+__author__ = 'rhoerbe'
+
+logger = logging.getLogger(__name__)
+
+def fetch_metadata(url, path, maxage=600):
+    """
+    :param url:  metadata remote location
+    :param path: metdata file name
+    :param maxage: if max age of existing metadata file (s) is exceeded,
+     the file will be fetched from the remote location
+    """
+    fetch = False
+    if not os.path.isfile(path):
+        fetch = True
+        logger.debug("metadata file %s not found" % path)
+    elif (os.path.getmtime(path) + maxage) < time.time():
+        fetch = True
+        logger.debug("metadata file %s from %s is more than %s s old" %
+                     (path,
+                      strftime("%Y-%m-%d %H:%M:%S", time.localtime(os.path.getmtime(path))),
+                      maxage))
+    else:
+        logger.debug("metadata file %s is less than %s s old" % (path, maxage))
+    if fetch:
+        f=urllib.URLopener()
+        try:
+            f.retrieve(url, path)
+            logger.debug("downloaded metadata from %s into %s" % (url, path))
+        except:
+            logger.debug("downloaded metadata from %s failed: %s" %
+                         (url, sys.exc_info()[0]))
+