Optionally add extension to checked out files based on MIME type

If available, gdatastore will now use sugar.mime to guess an extension
to add to checked out files, based on their MIME type.

The outside world (including emacs) is still surprisingly focused on
file extensions rather than MIME types. By adding an extension to the
file names returned by gdatastore we help other software that has to
interface with legacy components. The alternative would be to add code
to every piece of glue code to guess the extension and rename the
file in a race-free way. Doing it in gdatastore reduces the overall
complexity of the software system.

1 files changed, 22 insertions, 3 deletions

diff --git a/gdatastore/datastore.py b/gdatastore/datastore.py
index 72bf832..0fd7765 100644
--- a/gdatastore/datastore.py
+++ b/gdatastore/datastore.py
@@ -32,6 +32,13 @@ import dbus
 import dbus.service
 import gconf
 
+try:
+    from sugar import mime as sugar_mime
+except ImportError:
+    # Only used for helping legacy applications that use the file
+    # extension rather than the MIME type
+    sugar_mime = None
+
 from gdatastore.index import Index
 
 
@@ -534,13 +541,16 @@ class InternalApi(object):
     def get_data_path(self, (tree_id, version_id), sender=None):
         logging.debug('get_data_path((%r, %r), %r)', tree_id, version_id,
                       sender)
+        metadata = self._index.retrieve((tree_id, version_id))
         ref_name = _format_ref(tree_id, version_id)
         top_level_entries = self._git_call('ls-tree',
                                            [ref_name]).splitlines()
         if len(top_level_entries) == 1 and \
            top_level_entries[0].endswith('\tdata'):
             blob_hash = top_level_entries[0].split('\t')[0].split(' ')[2]
-            return self._checkout_file(blob_hash)
+            mime_type = metadata.get('mime_type', '')
+            return self._checkout_file(blob_hash,
+                                       suffix=_guess_extension(mime_type))
 
         return self._checkout_dir(ref_name)
 
@@ -661,8 +671,8 @@ class InternalApi(object):
         for entry in old_versions:
             self.delete((entry['tree_id'], entry['version_id']))
 
-    def _checkout_file(self, blob_hash):
-        fd, file_name = tempfile.mkstemp(dir=self._checkouts_dir)
+    def _checkout_file(self, blob_hash, suffix=''):
+        fd, file_name = tempfile.mkstemp(dir=self._checkouts_dir, suffix=suffix)
         try:
             self._git_call('cat-file', ['blob', blob_hash], stdout_fd=fd)
         finally:
@@ -855,3 +865,12 @@ def to_native(value):
 
 def _format_ref(tree_id, version_id):
     return 'refs/gdatastore/%s/%s' % (tree_id, version_id)
+
+
+def _guess_extension(mime_type):
+    if sugar_mime is None:
+        return ''
+    extension = sugar_mime.get_primary_extension(mime_type)
+    if not extension:
+        return ''
+    return '.' + extension