XML datastore: add file rotation for backup purpose

nemubot/datastore/xml.py

@@ -14,7 +14,9 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-import fcntl, os
+import fcntl
+import os
+import xml.parsers.expat
 
 from nemubot.datastore.abstract import Abstract
 
@@ -23,8 +25,17 @@ class XML(Abstract):
 
     """A concrete implementation of a data store that relies on XML files"""
 
-    def __init__(self, basedir):
+    def __init__(self, basedir, rotate=True):
+        """Initialize the datastore
+
+        Arguments:
+        basedir -- path to directory containing XML files
+        rotate -- auto-backup files?
+        """
+
         self.basedir = basedir
+        self.rotate = rotate
+        self.nb_save = 0
 
     def open(self):
         """Lock the directory"""
@@ -83,6 +94,22 @@ class XML(Abstract):
         else:
             return Abstract.load(self, module)
 
+    def _rotate(self, path):
+        """Backup given path
+
+        Argument:
+        path -- location of the file to backup
+        """
+
+        self.nb_save += 1
+
+        for i in range(10):
+            if self.nb_save % (1 << i) == 0:
+                src = path + "." + str(i-1) if i != 0 else path
+                dst = path + "." + str(i)
+                if os.path.isfile(src):
+                    os.rename(src, dst)
+
     def save(self, module, data):
         """Load data for the given module
 
@@ -91,4 +118,9 @@ class XML(Abstract):
         data -- the new data to save
         """
 
-        return data.save(self._get_data_file_path(module))
+        path = self._get_data_file_path(module)
+
+        if self.rotate:
+            self._rotate(path)
+
+        return data.save(path)