Implement Dual DHT

[dennis-tra]

Research how this relates to routing.Routing

[guillaumemichel]

The Dual DHT is essentially a wrapper around two IpfsDHT, one local and one global.

type DHT struct {
    WAN *dht.IpfsDHT
    LAN *dht.IpfsDHT
}

The dual DHT implements the following interfaces from the github.com/libp2p/go-libp2p/core/routing package.

ContentRouting
Routing
PeerRouting
PubKeyFetcher
ValueStore

The Dual DHT takes dht.Option for (1) the global, (2) the local and (3) both DHTs. We want to adapt the following the match the Config from v2.

// WanDHTOption applies the given DHT options to the WAN DHT.
func WanDHTOption(opts ...dht.Option) Option {
    return func(c *config) error {
        c.wan = append(c.wan, opts...)
        return nil
    }
}

// LanDHTOption applies the given DHT options to the LAN DHT.
func LanDHTOption(opts ...dht.Option) Option {
    return func(c *config) error {
        c.lan = append(c.lan, opts...)
        return nil
    }
}

// DHTOption applies the given DHT options to both the WAN and the LAN DHTs.
func DHTOption(opts ...dht.Option) Option {
    return func(c *config) error {
        c.lan = append(c.lan, opts...)
        c.wan = append(c.wan, opts...)
        return nil
    }
}

The routing methods (e.g FindPeer, FindProvidersAsync, Provide etc.) essentially define the Dual DHT behavior wrt. the two active DHTs, so most of the code can be copied over to v2.

[guillaumemichel]

As per 2023-09-29, we agreed not to implement the Dual DHT. The Dual DHT has no reason to exist as it can now be implemented easily with https://github.com/libp2p/go-libp2p-routing-helpers.