the #GAsyncResult that was provided to the callback.
a #gsize to get the length of the data read in.
Return: a NUL-terminated byte array 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.
GException on failure.
2.20
Finish an asynchronous call started by g_data_input_stream_read_line_async(). Note the warning about string encoding in g_data_input_stream_read_line() applies here as well.