the GAsyncResult that was provided to the callback.
a string with the line that was read in (without the newlines). Set length to a gsize to get the length of the read line. On an error, it will return NULL and error will be set. If there's no content to read, it will still return NULL, but error won't be set. [transfer full]
GException on failure.
Finish an asynchronous call started by g_data_input_stream_read_line_async(). Since 2.20