gh-157418: Correct the IocpProactor.recvfrom_into() parameter name

[lpyu001]

• Issue: asyncio: IocpProactor.recvfrom_into() misnames its receive-size parameter as flags #157418

[picnixz]

That's a breaking change strictly speaking. If we are not sure about how people are calling the APIs, we should be more careful.

[picnixz]

Note that socket.recvfrom_into expects a flags not a number of bytes as its last parameter so I don't know what would be correct here (it's surprising that we don't have a flag anymore actually).

[picnixz]

to be clear: I acknowledge this is a bug but I don't know if changing the parameter name is safe without a warning or whatever. Can you check the call sites and browse OSS repos?

[lpyu001]

I couldn't find any OSS calls using IocpProactor.recvfrom_into(..., flags=...) as a keyword argument.

qasync overrides the method using the old flags name, but forwards the argument positionally:

def recvfrom_into(self, conn, buf, flags=0):
    return self._proactor.recvfrom_into(conn, buf, flags)

https://github.com/CabbageDevelopment/qasync/blob/master/src/qasync/_windows.py#L99-L101

CPython is unaffected because it has always treated the third argument as the receive length, rather than as actual socket flags:

return await self._proactor.recvfrom_into(sock, buf, nbytes)

https://github.com/python/cpython/blob/main/Lib/asyncio/proactor_events.py#L718-L720

[picnixz]

Let's add a NEWS entry then just in case. This could trip people accidently and could be very annoying.