Fix empty ini files not including DEFAULT section

Empty files and subsequent modification by adding, removing,
setting and changing keys then outputting those files seems
to cause iniparse to ignore the whole DEFAULT section. To fix
this modify the write() function to correctly output the DEFAULT
section when it exists (but does not exist in the read data).

Fixes bug 1303968

Change-Id: I1b4133bc6f876e9e5e39045f46054db13bd4634f

anvil/ini_parser.py

@@ -15,16 +15,18 @@
 #    under the License.
 
 import ConfigParser
+from ConfigParser import DEFAULTSECT
 from ConfigParser import NoOptionError
 from ConfigParser import NoSectionError
 from StringIO import StringIO
 
 import iniparse
+from iniparse import ini
+
 import re
 
 from anvil import log as logging
 from anvil import utils
-from iniparse import ini
 
 LOG = logging.getLogger(__name__)
 
@@ -125,6 +127,7 @@ class AnvilConfigParser(iniparse.RawConfigParser):
     2. Override set option behavior to insert option right
     after same commented option, if present, otherwise insert
     in the section beginning.
+    3. Includes [DEFAULT] section if present (but not present in original).
     """
 
     # commented option regexp
@@ -141,6 +144,11 @@ class AnvilConfigParser(iniparse.RawConfigParser):
             $       # then line ends
         """, re.VERBOSE)
 
+    def __init__(self, defaults=None, dict_type=dict, include_defaults=True):
+        super(AnvilConfigParser, self).__init__(defaults=defaults,
+                                                dict_type=dict_type)
+        self._include_defaults = include_defaults
+
     def readfp(self, fp, filename=None):
         super(AnvilConfigParser, self).readfp(fp, filename)
         self._on_after_file_read()
@@ -152,6 +160,44 @@ class AnvilConfigParser(iniparse.RawConfigParser):
         except KeyError:
             raise NoSectionError(section)
 
+    def _sections(self):
+        """Gets all the underlying sections (including DEFAULT). The underlying
+        iniparse library seems to exclude the DEFAULT section which makes it
+        hard to tell if we should include the DEFAULT section in output or
+        whether the library will include it for us (which it will do if the
+        origin data had a DEFAULT section).
+        """
+        sections = set()
+        for x in self.data._data.contents:
+            if isinstance(x, ini.LineContainer):
+                sections.add(x.name)
+        return sections
+
+    def write(self, fp):
+        """Writes sections to the provided file object, and also includes the
+        default section if it is not present in the origin data but should be
+        present in the output data.
+        """
+        if self.data._bom:
+            fp.write(u'\ufeff')
+        default_added = False
+        if self._include_defaults and DEFAULTSECT not in self._sections():
+            try:
+                sect = self.data[DEFAULTSECT]
+            except KeyError:
+                pass
+            else:
+                default_added = True
+                fp.write("%s\n" % (ini.SectionLine(DEFAULTSECT)))
+                for lines in sect._lines:
+                    fp.write("%s\n" % (lines))
+        data = "%s" % (self.data._data)
+        if default_added and data:
+            # Remove extra spaces since we added a section before this.
+            data = data.lstrip()
+            data = "\n" + data
+        fp.write(data)
+
     def _on_after_file_read(self):
         """This function is called after reading config file
         to move all commented lines into section they belong to,
@@ -233,7 +279,7 @@ class DefaultConf(object):
     a large DEFAULT section.
     """
 
-    current_section = "DEFAULT"
+    current_section = DEFAULTSECT
 
     def __init__(self, backing, current_section=None):
         self.backing = backing