Use TCP_NODELAY on the server socket

[stefantalpalaru]

Rationale: https://news.ycombinator.com/item?id=40310896

[mathiascode]

Sure, why not. We already have our own buffer, so Nagle's algorithm doesn't really benefit us anyway.

Could you set TCP_NODELAY on the peer sockets as well?

[mathiascode]

I believe TCP_NODELAY should be available on every OS we support. Do you know one that doesn't have it?

[stefantalpalaru]

Not aware of any without it. I was just copying the safety checks in

nicotine-plus/pynicotine/slskproto.py

Lines 1144 to 1177 in 5ecf2df

	if hasattr(socket, "SO_KEEPALIVE"):
	server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1) # pylint: disable=no-member
	if hasattr(socket, "TCP_KEEPINTVL"):
	server_socket.setsockopt(socket.IPPROTO_TCP,
	socket.TCP_KEEPINTVL, interval) # pylint: disable=no-member
	if hasattr(socket, "TCP_KEEPCNT"):
	server_socket.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPCNT, count) # pylint: disable=no-member
	if hasattr(socket, "TCP_KEEPIDLE"):
	server_socket.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPIDLE, idle) # pylint: disable=no-member
	elif hasattr(socket, "TCP_KEEPALIVE"):
	# macOS fallback
	server_socket.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPALIVE, idle) # pylint: disable=no-member
	elif hasattr(socket, "SIO_KEEPALIVE_VALS"):
	# Windows fallback
	# Probe count is set to 10 on a system level, and can't be modified.
	# https://docs.microsoft.com/en-us/windows/win32/winsock/so-keepalive
	server_socket.ioctl(
	socket.SIO_KEEPALIVE_VALS, # pylint: disable=no-member
	(
	1,
	idle * 1000,
	interval * 1000
	)
	)
	if hasattr(socket, "TCP_USER_TIMEOUT"):
	server_socket.setsockopt(socket.IPPROTO_TCP, socket.TCP_USER_TIMEOUT, timeout_seconds * 1000)

[mathiascode]

I think we can leave the check out for now.

[stefantalpalaru]

The CPython code itself checks for the corresponding C define: https://github.com/python/cpython/blob/7e894c2f38f64aed9b259c8fd31880f1142a259d/Modules/socketmodule.c#L8561

[slook]

I also think we should leave all the if hasattr(socket, "TCP_NODELAY"): checks out for now, because it is probably not required.

It can be added again if any testers report a Critical Error thown by the exception handler.

[stefantalpalaru]

OK. Check removed.

[stefantalpalaru]

Could you set TCP_NODELAY on the peer sockets as well?

No. Those are UDP.

[mathiascode]

Could you set TCP_NODELAY on the peer sockets as well?

No. Those are UDP.

The Soulseek protocol uses TCP, not UDP. Peer sockets are created here:

nicotine-plus/pynicotine/slskproto.py

Line 1710 in f8ecc7b

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

and here:

nicotine-plus/pynicotine/slskproto.py

Line 2386 in f8ecc7b

incoming_sock, incoming_addr = sock.accept()

[stefantalpalaru]

I stand corrected. Also added for peer sockets.