support different and user-suppliable merging algorithms for cloud-config

This adds a very useful mechanism for merging cloud-config, allowing
the user to append to lists (ie, just add more 'run_cmd') or other
things.

See doc/merging.txt for more information, it is intended to be backwards
compatible by default.

LP: #1023179

1 files changed, 39 insertions, 0 deletions

diff --git a/cloudinit/mergers/str.py b/cloudinit/mergers/str.py
new file mode 100644
index 00000000..291c91c2
--- /dev/null
+++ b/cloudinit/mergers/str.py
@@ -0,0 +1,39 @@
+# vi: ts=4 expandtab
+#
+#    Copyright (C) 2012 Yahoo! Inc.
+#
+#    Author: Joshua Harlow <harlowja@yahoo-inc.com>
+#
+#    This program is free software: you can redistribute it and/or modify
+#    it under the terms of the GNU General Public License version 3, as
+#    published by the Free Software Foundation.
+#
+#    This program is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#    GNU General Public License for more details.
+#
+#    You should have received a copy of the GNU General Public License
+#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+
+class Merger(object):
+    def __init__(self, _merger, opts):
+        self._append = 'append' in opts
+
+    # On encountering a unicode object to merge value with
+    # we will for now just proxy into the string method to let it handle it.
+    def _on_unicode(self, value, merge_with):
+        return self._on_str(value, merge_with)
+
+    # On encountering a string object to merge with we will
+    # perform the following action, if appending we will
+    # merge them together, otherwise we will just return value.
+    def _on_str(self, value, merge_with):
+        if not self._append:
+            return value
+        else:
+            if isinstance(value, (unicode)):
+                return value + unicode(merge_with)
+            else:
+                return value + str(merge_with)