Simulating Network Lag

[Lap]

Any thoughts on the best way to go about testing networking under varying conditions (packet loss, latency, etc.)?

I'm not finding any good external programs to help out.

[josefnpat]

The easiest way to simulate lag is to put a sleep in the server before responding. I suppose you could also do something along these lines:

Code: Select all

require "socket"

function sleep(sec)
    socket.select(nil, nil, sec)
end

function handle_data(data)
  sleep(0.120) -- 120 ms
  if math.random(1,10)>1 then
    -- properly handle the data
  else
    -- haha, packet loss!
end

[Lap]

I'm trying to figure out what else I might be missing by simulating it only within Love.

I guess I'd miss potential problems with testing packets of different sizes, as I've seen large ones get dropped before....maybe. So far this is the most difficult part of networking, as I never have problems with LAN's, but there have been plenty of bugs reported in the wild.

[Boolsheet]

There are all kind of fun things you have to look out for. As an example, here's a quote from the luasocket reference about udpsocket:receive.

If size is omitted, the maximum datagram size is used (which is currently limited by the implementation to 8192 bytes).

Linux has some tools to simulate stuff like that, but I forgot the name.

[bartbes]

And the worst part isn't fitting stuff in 8192 bytes, it's that what's sent with multiple send() calls can be received with one receive() call.

[ljdp]

If you've got OSX Lion and have installed Xcode then you already have a nice utility app called network link conditioner, I've been using it to test my RTS game.
It let's you change your bandwith, packet loss and latency.

http://joemiller.me/2011/07/25/network- ... -4-1-lion/