p2p: de-dupe and shuffle public rooms; implement keydb (#1074)

- We don't want a serverKeyAPI as fetching keys doesn't need a DB.
- De-dupe rooms so we don't see them multiple times, but shuffle the
  alias we join via so we don't all flood a single server.

cmd/dendritejs/keyfetcher.go

@@ -82,3 +82,8 @@ func (f *libp2pKeyFetcher) FetchKeys(
 func (f *libp2pKeyFetcher) FetcherName() string {
 	return "libp2pKeyFetcher"
 }
+
+// no-op function for storing keys - we don't do any work to fetch them so don't bother storing.
+func (f *libp2pKeyFetcher) StoreKeys(ctx context.Context, results map[gomatrixserverlib.PublicKeyLookupRequest]gomatrixserverlib.PublicKeyLookupResult) error {
+	return nil
+}

cmd/dendritejs/main.go

@@ -37,7 +37,6 @@ import (
 	"github.com/matrix-org/dendrite/publicroomsapi"
 	"github.com/matrix-org/dendrite/publicroomsapi/storage"
 	"github.com/matrix-org/dendrite/roomserver"
-	"github.com/matrix-org/dendrite/serverkeyapi"
 	"github.com/matrix-org/dendrite/syncapi"
 	go_http_js_libp2p "github.com/matrix-org/go-http-js-libp2p"
 	"github.com/matrix-org/gomatrixserverlib"
@@ -197,14 +196,12 @@ func main() {
 	deviceDB := base.CreateDeviceDB()
 	federation := createFederationClient(cfg, node)
 
-	serverKeyAPI := serverkeyapi.SetupServerKeyAPIComponent(
-		base, federation,
-	)
+	fetcher := &libp2pKeyFetcher{}
 	keyRing := gomatrixserverlib.KeyRing{
 		KeyFetchers: []gomatrixserverlib.KeyFetcher{
-			&libp2pKeyFetcher{},
+			fetcher,
 		},
-		KeyDatabase: serverKeyAPI,
+		KeyDatabase: fetcher,
 	}
 	p2pPublicRoomProvider := NewLibP2PPublicRoomsProvider(node)