dcutr: consider more than just external addresses

[thomaseizinger]

Description

At the moment, the dcutr::Behaviour only sends external addresses to the remote. See

rust-libp2p/protocols/dcutr/src/behaviour_impl.rs

Line 202 in 411a049

handler::relayed::Handler::new(connected_point, self.observed_addresses());

and

rust-libp2p/protocols/dcutr/src/behaviour_impl.rs

Lines 103 to 110 in 411a049

	fn observed_addresses(&self) -> Vec<Multiaddr> {
	self.external_addresses
	.iter()
	.cloned()
	.filter(|a| !a.iter().any(|p| p == Protocol::P2pCircuit))
	.map(|a| a.with(Protocol::P2p(self.local_peer_id)))
	.collect()
	}

I'd argue this is kind of flawed. We don't need hole punching if we have external addresses. Instead, we should likely gather and use external address candidates as well as allow the user to add their own candidates to the this list.

Likely, this is a left-over from before we landed #3954.

[thomaseizinger]

cc @mxinden @jxs

[mxinden]

You are right. Good catch @thomaseizinger! libp2p-dcutr should use address candidates, e.g. reported through libp2p-identify.

[thomaseizinger]

You are right. Good catch @thomaseizinger! libp2p-dcutr should use address candidates, e.g. reported through libp2p-identify.

FTR: Instead of using ExternalAddresses, we should be taking addresses from FromSwarm::NewExternalAddrCandidate.