Calling setsockopt on sockets to peers

[viciious]

Hi!

I would like to ask a question on how it would be best to approach the following task. For the purpose of optimizing throughput and prioritizing P2P traffic in our LAN, we'd like to be able to set the Type-of-Service option for the associated network packets. Here's the C code equivalent of what we'd like to do:

int iptos = IPTOS_THROUGHPUT;

setsockopt(sockfd, IPPROTO_IP, IP_TOS,  &iptos, sizeof(iptos));

What would be the best place in the library's source code to hook into? Note that the option should be set for both incoming and outgoing traffic.

Would you be interested in providing an out-of-the-box method for doing such thing?

Thanks!

[anacrolix]

There's an exposed Diallers and Listeners that lets you provide custom socket implementations. I would start there. I will follow up if I look before you do

[viciious]

Yeah, I spotted the Dialers interface too. However, I'm not entirely about the order in which the dialers are called. It seems like a new Dialer is added to the tail of the list and of NewClient has actually populated the list with sockets - have a lesser chance of actually doing anything.

[anacrolix]

Yeah you would disable all the default ones and bring your own in this case. Sorry I haven't had a chance to look yet. Another option might be a hook to configure the default listeners and dialers after they're inited for you.

[viciious]

Ideally there should be a client option that would somehow be passed all the way down to socket.go that would make the call to setSockOpt on the socket if set to true. Although I can't think of a good implementation of this approach yet.

[anacrolix]

See

torrent/client.go

Lines 711 to 724 in 6cdcac8

	func dialFromSocket(ctx context.Context, s Dialer, addr string) net.Conn {
	c, err := s.Dial(ctx, addr)
	if err != nil {
	log.ContextLogger(ctx).Levelf(log.Debug, "error dialing %q: %v", addr, err)
	}
	// This is a bit optimistic, but it looks non-trivial to thread this through the proxy code. Set
	// it now in case we close the connection forthwith. Note this is also done in the TCP dialer
	// code to increase the chance it's done.
	if tc, ok := c.(*net.TCPConn); ok {
	tc.SetLinger(0)
	}
	countDialResult(err)
	return c
	}

for where it calls the custom dialer interface. See https://github.com/anacrolix/torrent/blob/v1.58.1/client.go#L360 for where to add your own dialer, which looks like it will do the right thing (add your setsockopt after you do the dial successfully internally to your dialer.T. Likewise

torrent/client.go

Lines 422 to 427 in 6cdcac8

	func (cl *Client) AddListener(l Listener) {
	cl.listeners = append(cl.listeners, l)
	if cl.config.AcceptPeerConnections {
	go cl.acceptConnections(l)
	}
	}

also does the right thing, set your sockopts the same way.

Disable all the builtin networks using

torrent/client.go

Lines 441 to 455 in 6cdcac8

	func (cl *Client) listenOnNetwork(n network) bool {
	if n.Ipv4 && cl.config.DisableIPv4 {
	return false
	}
	if n.Ipv6 && cl.config.DisableIPv6 {
	return false
	}
	if n.Tcp && cl.config.DisableTCP {
	return false
	}
	if n.Udp && cl.config.DisableUTP && cl.config.NoDHT {
	return false
	}
	return true
	}

. You'll need to register your DHT server manually if you're using it, see

torrent/client.go

Lines 345 to 356 in 6cdcac8

	if !cfg.NoDHT {
	for _, s := range sockets {
	if pc, ok := s.(net.PacketConn); ok {
	ds, err := cl.NewAnacrolixDhtServer(pc)
	if err != nil {
	panic(err)
	}
	cl.dhtServers = append(cl.dhtServers, AnacrolixDhtServerWrapper{ds})
	cl.onClose = append(cl.onClose, func() { ds.Close() })
	}
	}
	}

.

If you run into any corner cases where the client refuses to proceed, please report an issue! This should be supported. For excample it looks like the client might error if there are no sockets during NewClient init, which would be incorrect behaviour. And an option could be added to just disable all builtin networks, and helpers for registering dhts and doing port forwarding lazily.

[viciious]

Thanks! I went ahead and created a PR that adds a global option to the library instead - the approach above seems unnecessarily complicated: #1017