the #GAsyncResult that was provided to the callback
a #gsize to get the length of the data read in
a string with the data that was read before encountering any of the stop characters. Set @length to a #gsize to get the length of the string. This function will return %NULL on an error.
GException on failure.
2.24
Finish an asynchronous call started by g_data_input_stream_read_upto_async().
Note that this function does not consume the stop character. You have to use g_data_input_stream_read_byte() to get it before calling g_data_input_stream_read_upto_async() again.
The returned string will always be nul-terminated on success.