Save bandwidth for HTTP partially download case -

i have such special requirement:

1. download big file server http.
2. if detect network not good, giveup current download download smaller file.

but per test, seems if send http server, download file continuously if read 1024 bytes, try close connection after detect bandwidth low, download bytes larger request.

to save bandwidth, wish server not send more data request, sounds impossible. what's mechanism stop send data client if request partially? e.g. 1024 bytes? if not disconnect, server sent data client till whole file finished?