the GAsyncResult that was provided to the callback.
a gsize to get the length of the data read in.
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. For UTF-8 conversion errors, the set error domain is G_CONVERT_ERROR. If there's no content to read, it will still return NULL, but error won't be set.
GException on failure.
2.30
Finish an asynchronous call started by DataInputStream.readLineAsync.