Dual DHT shortcutting SearchValue for previously published records

[aschmahmann]

The dual DHT uses the parallel router SearchValue:

go-libp2p-kad-dht/dual/dual.go

Lines 345 to 348 in 57a258f

	func (dht *DHT) SearchValue(ctx context.Context, key string, opts ...routing.Option) (<-chan []byte, error) {
	p := helper.Parallel{Routers: []routing.Routing{dht.WAN, dht.LAN}, Validator: dht.WAN.Validator}
	return p.SearchValue(ctx, key, opts...)
	}

The parallel router aborts as soon as any of the routers have completed their search. This is problematic if we first we publish and then search because publishing will store a copy of the record in our datastore during the put

go-libp2p-kad-dht/routing.go

Line 62 in 57a258f

err = dht.putLocal(key, rec)

and then when we do a search we will get that record:

go-libp2p-kad-dht/routing.go

Line 298 in 57a258f

if rec, err := dht.getLocal(key); rec != nil && err == nil {

If the LAN DHT is much smaller than the WAN DHT (e.g. the normal online case) or the WAN DHT is much smaller than the LAN DHT (e.g. an offline case or one using a segregated network like CJDNS) then one of the DHTs will return immediately with a single record (the one previously published) and therefore cause an abort of the other DHT query.

@petar @Stebalien