Allow to have more than min_peers/2 outbound peers

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Default value is 8, so we allow only 4 outbound peers, unfortunately if a node is behind NAT it can't get inbound peers and it stucks with 4 peers as maximum.
This PR allows a number of outbound peers to be between min_peers and max_peers/2. Node behind NAT will eventually have just min_peers number of peers.

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Another option is to keep the second condition as peers.peer_outbound_count() >= p2p.config.peer_min_preferred_count() / 2, as I said a node behind NAT will eventually have min_peers anyway, but in this case we can save a few slots for inbound peers of a node with public ip.

[antiochp]

We do something similar to what you propose in monitor_peers (but looking at preferred counts in both cases) -

grin/servers/src/grin/seed.rs

Lines 189 to 194 in 1f7ea49

	// We have enough peers, both total connected and outbound connected so we are good.
	if peers.peer_count() >= config.peer_min_preferred_count()
	&& peers.peer_outbound_count() >= config.peer_min_preferred_count() / 2
	{
	return;
	}

Here we keep the "total peer count" below peer_min_preferred_count and the "total outbound peer count" below peer_min_preferred_count / 2.

I wonder if we should look at both "total peer count" and "total outbound peer count" as you suggest, in listen_for_addrs, but comparing to preferred count (and preferred / 2)?

i.e. We go try and connect to more outbound peers if -

• we have less than peer_min_preferred_count / 2 outbound peers
• or, we have less than peer_min_preferred_count total peers

That way we handle nodes behind NAT by just looking at total peers (we will never have inbound peers)
but for public nodes we default to looking at outbound peer counts.

I think it may make sense to keep the listen_for_addrs and monitor_peers peer counting logic consistent.

[antiochp]

Good catch by the way - I don't think the NAT case was fully considered here when we split out default 8 slots into inbound/outbound.

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I tested the latest version of this PR - after 20 mins a node behind NAT oscillates around 8 peers in total (all outbound), a node with a public IP has 4 outbounds (55 in the first seconds) and 100+ inbounds.

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Ah, I pushed to the origin by mistake, removed the branch but Travis noticed it and now tries to build this removed branch too, please ignore push build

[antiochp]

Yeah this looks good.

[antiochp]

Nice.