aiohttp_bug.py

from aiohttp.client import ClientSession
from aiohttp.streams import AsyncStreamIterator
from functools import partial
import asyncio


async def main():
    async with ClientSession() as session:
        # use the file from gist below
        url = "https://gist.githubusercontent.com/vitaliihonta/b9be77deb0dfea1e9a411e695e6f15c9/raw/5fbf72842bff7f74ce06479d7e0d06f5af334f86/example.txt"
        async with session.get(url) as resp:
            async for line in AsyncStreamIterator(partial(resp.content.readuntil, b'ab')):
                print(line)


if __name__ == '__main__':
    asyncio.get_event_loop().run_until_complete(main())

example.txt

11ab
22ab
33ab