Long story short:
Should be mimic to asyncio.StreamReader counterpart: https://docs.python.org/3/library/asyncio-stream.html#asyncio.StreamReader.readuntil

(Re-opening #1151)

This solution is great to have in the toolbox dealing with pulling high-load data from servers that don't declare their response content-length. Currently I run into partial content.read() intermittently under high-load situations e.g. (#3881).