'Retrieve diff file from the server.
Args:
definitions: datastore_index.IndexDefinitions as loaded from users
index.yaml file.
Returns:
A pair of datastore_index.IndexDefinitions objects.  The first record
is the set of indexes that are present in the index.yaml file but missing
from the server.  The second record is the set of indexes that are
present on the server but missing from the index.yaml file (indicating
that these indexes should probably be vacuumed).'

def DoDiff(self, definitions):

    StatusUpdate('Fetching    index    definitions    diff.', self.error_fh)
    with TempChangeField(definitions, 'application', None) as app_id:
        response = self.rpcserver.Send('/api/datastore/index/diff', app_id=app_id, payload=definitions.ToYAML())
    return datastore_index.ParseMultipleIndexDefinitions(response)
