read_line_utf8_async
  
  Description:
  [ 
CCode ( cname = 
"g_data_input_stream_read_line_async" ,  finish_name = 
"g_data_input_stream_read_line_finish_utf8" ) ]
public async string? 
read_line_utf8_async (
int io_priority = 
DEFAULT, 
Cancellable? cancellable = 
null, 
out size_t length = 
null) 
throws IOError