1 files changed, 31 insertions, 0 deletions
diff --git a/cloudinit/atomic_helper.py b/cloudinit/atomic_helper.py
new file mode 100644
index 00000000..a3cfd942
--- /dev/null
+++ b/cloudinit/atomic_helper.py
@@ -0,0 +1,31 @@
+#!/usr/bin/python
+# vi: ts=4 expandtab
+
+import json
+import os
+import tempfile
+
+_DEF_PERMS = 0o644
+
+
+def write_file(filename, content, mode=_DEF_PERMS, omode="wb"):
+    # open filename in mode 'omode', write content, set permissions to 'mode'
+    tf = None
+    try:
+        tf = tempfile.NamedTemporaryFile(dir=os.path.dirname(filename),
+                                         delete=False, mode=omode)
+        tf.write(content)
+        tf.close()
+        os.chmod(tf.name, mode)
+        os.rename(tf.name, filename)
+    except Exception as e:
+        if tf is not None:
+            os.unlink(tf.name)
+        raise e
+
+
+def write_json(filename, data, mode=_DEF_PERMS):
+    # dump json representation of data to file filename.
+    return write_file(
+        filename, json.dumps(data, indent=1, sort_keys=True) + "\n",
+        omode="w", mode=mode)