Implement ExtraPublicRoomsProvider for p2p demos (#1180)

* Change API and rename to ExtraPublicRoomsProvider

* Make dendritejs work again

* Maybe make libp2p demo work again

* Linting

2 files changed, 86 insertions, 3 deletions

diff --git a/cmd/dendritejs/main.go b/cmd/dendritejs/main.go
index 6e2bdafe..1443bc18 100644
--- a/cmd/dendritejs/main.go
+++ b/cmd/dendritejs/main.go
@@ -211,7 +211,7 @@ func main() {
 	)
 	fedSenderAPI := federationsender.NewInternalAPI(base, federation, rsAPI, &keyRing)
 	rsAPI.SetFederationSenderAPI(fedSenderAPI)
-	p2pPublicRoomProvider := NewLibP2PPublicRoomsProvider(node, fedSenderAPI)
+	p2pPublicRoomProvider := NewLibP2PPublicRoomsProvider(node, fedSenderAPI, federation)
 
 	stateAPI := currentstateserver.NewInternalAPI(base.Cfg, base.KafkaConsumer)
 
diff --git a/cmd/dendritejs/publicrooms.go b/cmd/dendritejs/publicrooms.go
index 5032bc15..a4623ba3 100644
--- a/cmd/dendritejs/publicrooms.go
+++ b/cmd/dendritejs/publicrooms.go
@@ -18,22 +18,29 @@ package main
 
 import (
 	"context"
+	"sync"
+	"time"
 
 	"github.com/matrix-org/dendrite/federationsender/api"
 	go_http_js_libp2p "github.com/matrix-org/go-http-js-libp2p"
 	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/util"
 )
 
 type libp2pPublicRoomsProvider struct {
 	node      *go_http_js_libp2p.P2pLocalNode
 	providers []go_http_js_libp2p.PeerInfo
 	fedSender api.FederationSenderInternalAPI
+	fedClient *gomatrixserverlib.FederationClient
 }
 
-func NewLibP2PPublicRoomsProvider(node *go_http_js_libp2p.P2pLocalNode, fedSender api.FederationSenderInternalAPI) *libp2pPublicRoomsProvider {
+func NewLibP2PPublicRoomsProvider(
+	node *go_http_js_libp2p.P2pLocalNode, fedSender api.FederationSenderInternalAPI, fedClient *gomatrixserverlib.FederationClient,
+) *libp2pPublicRoomsProvider {
 	p := &libp2pPublicRoomsProvider{
 		node:      node,
 		fedSender: fedSender,
+		fedClient: fedClient,
 	}
 	node.RegisterFoundProviders(p.foundProviders)
 	return p
@@ -62,10 +69,86 @@ func (p *libp2pPublicRoomsProvider) foundProviders(peerInfos []go_http_js_libp2p
 	p.providers = peerInfos
 }
 
-func (p *libp2pPublicRoomsProvider) Homeservers() []string {
+func (p *libp2pPublicRoomsProvider) Rooms() []gomatrixserverlib.PublicRoom {
+	return bulkFetchPublicRoomsFromServers(context.Background(), p.fedClient, p.homeservers())
+}
+
+func (p *libp2pPublicRoomsProvider) homeservers() []string {
 	result := make([]string, len(p.providers))
 	for i := range p.providers {
 		result[i] = p.providers[i].Id
 	}
 	return result
 }
+
+// bulkFetchPublicRoomsFromServers fetches public rooms from the list of homeservers.
+// Returns a list of public rooms.
+func bulkFetchPublicRoomsFromServers(
+	ctx context.Context, fedClient *gomatrixserverlib.FederationClient, homeservers []string,
+) (publicRooms []gomatrixserverlib.PublicRoom) {
+	limit := 200
+	// follow pipeline semantics, see https://blog.golang.org/pipelines for more info.
+	// goroutines send rooms to this channel
+	roomCh := make(chan gomatrixserverlib.PublicRoom, int(limit))
+	// signalling channel to tell goroutines to stop sending rooms and quit
+	done := make(chan bool)
+	// signalling to say when we can close the room channel
+	var wg sync.WaitGroup
+	wg.Add(len(homeservers))
+	// concurrently query for public rooms
+	for _, hs := range homeservers {
+		go func(homeserverDomain string) {
+			defer wg.Done()
+			util.GetLogger(ctx).WithField("hs", homeserverDomain).Info("Querying HS for public rooms")
+			fres, err := fedClient.GetPublicRooms(ctx, gomatrixserverlib.ServerName(homeserverDomain), int(limit), "", false, "")
+			if err != nil {
+				util.GetLogger(ctx).WithError(err).WithField("hs", homeserverDomain).Warn(
+					"bulkFetchPublicRoomsFromServers: failed to query hs",
+				)
+				return
+			}
+			for _, room := range fres.Chunk {
+				// atomically send a room or stop
+				select {
+				case roomCh <- room:
+				case <-done:
+					util.GetLogger(ctx).WithError(err).WithField("hs", homeserverDomain).Info("Interrupted whilst sending rooms")
+					return
+				}
+			}
+		}(hs)
+	}
+
+	// Close the room channel when the goroutines have quit so we don't leak, but don't let it stop the in-flight request.
+	// This also allows the request to fail fast if all HSes experience errors as it will cause the room channel to be
+	// closed.
+	go func() {
+		wg.Wait()
+		util.GetLogger(ctx).Info("Cleaning up resources")
+		close(roomCh)
+	}()
+
+	// fan-in results with timeout. We stop when we reach the limit.
+FanIn:
+	for len(publicRooms) < int(limit) || limit == 0 {
+		// add a room or timeout
+		select {
+		case room, ok := <-roomCh:
+			if !ok {
+				util.GetLogger(ctx).Info("All homeservers have been queried, returning results.")
+				break FanIn
+			}
+			publicRooms = append(publicRooms, room)
+		case <-time.After(15 * time.Second): // we've waited long enough, let's tell the client what we got.
+			util.GetLogger(ctx).Info("Waited 15s for federated public rooms, returning early")
+			break FanIn
+		case <-ctx.Done(): // the client hung up on us, let's stop.
+			util.GetLogger(ctx).Info("Client hung up, returning early")
+			break FanIn
+		}
+	}
+	// tell goroutines to stop
+	close(done)
+
+	return publicRooms
+}