Write static status HTML page via temporary fileliw/status-write-via-temp-file

This will avoid the file being truncated if the disk fills up.

1 files changed, 26 insertions, 1 deletions

diff --git a/lorrycontroller/status.py b/lorrycontroller/status.py
index b0a3807..22bdb0b 100644
--- a/lorrycontroller/status.py
+++ b/lorrycontroller/status.py
@@ -16,6 +16,7 @@
 
 import logging
 import os
+import tempfile
 import time
 
 import bottle
@@ -49,13 +50,37 @@ class StatusRenderer(object):
         modified_status = dict(status)
         modified_status['links'] = False
         html = self.render_status_as_html(template, modified_status)
+
+        # We write the file first to a temporary file and then
+        # renaming it into place. If there are any problems, such as
+        # the disk getting full, we won't truncate an existing file.
+
         try:
-            with open(filename, 'w') as f:
+            temp_filename = self.temp_filename_in_same_dir_as(filename)
+            with open(temp_filename, 'w') as f:
                 f.write(html)
+            os.rename(temp_filename, filename)
         except (OSError, IOError) as e:
+            self.remove_temp_file(temp_filename)
             status['warning_msg'] = (
                 'ERROR WRITING STATUS HTML TO DISK: %s' % str(e))
 
+    def temp_filename_in_same_dir_as(self, filename):
+        dirname = os.path.dirname(filename)
+        fd, temp_filename = tempfile.mkstemp(dir=dirname)
+        os.fchmod(fd, 0644)
+        os.close(fd)
+        return temp_filename
+
+    def remove_temp_file(self, temp_filename):
+        try:
+            os.remove(temp_filename)
+        except OSError:
+            # Ignore a problem with removing. Don't ignore all
+            # exceptions to avoid catching variable names being
+            # mistyped, etc.
+            pass
+
     def get_free_disk_space(self, dirname):
         result = os.statvfs(dirname)
         free_bytes = result.f_bavail * result.f_bsize