# Get the mirror for the specified file by examining the file's metadata. Mirror names
# are stored in the 'app_metadata' by workgen when mirroring is enabled. If the file has
# a mirror, the name of the mirror is returned. Otherwise, the function returns None.
def get_mirror_file(db_dir, filename):

    connection = wiredtiger_open(db_dir, 'readonly')
    session = connection.open_session()
    c = session.open_cursor('metadata:', None, None)
    metadata = c[filename]
    c.close()

    result = re.findall('app_metadata="([^"]*)"', metadata)
    mirror = None

    if result:
        app_metadata = dict((a.strip(), b.strip())
            for a, b in (element.split('=')
                for element in result[0].split(',')))

        if app_metadata.get('workgen_dynamic_table') == 'true' and \
           app_metadata.get('workgen_table_mirror') != None :
            mirror = app_metadata['workgen_table_mirror']
            mirror = mirror.split(':')[1]

    session.close()
    connection.close()
    return mirror