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.
Finish an asynchronous call started by gio.data_input_stream.DataInputStream.readUptoAsync.
Note that this function does not consume the stop character. You have to use gio.data_input_stream.DataInputStream.readByteData to get it before calling gio.data_input_stream.DataInputStream.readUptoAsync again.
The returned string will always be nul-terminated on success.