Peeking via MSC2753 (#1370)

Initial implementation of MSC2753, as tested by https://github.com/matrix-org/sytest/pull/944.
Doesn't yet handle unpeeks, peeked EDUs, or history viz changing during a peek - these will follow.
https://github.com/matrix-org/dendrite/pull/1370 has full details.

syncapi/consumers/roomserver.go

@@ -17,6 +17,7 @@ package consumers
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 
 	"github.com/Shopify/sarama"
 	"github.com/matrix-org/dendrite/internal"
@@ -26,11 +27,13 @@ import (
 	"github.com/matrix-org/dendrite/syncapi/sync"
 	"github.com/matrix-org/dendrite/syncapi/types"
 	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/sirupsen/logrus"
 	log "github.com/sirupsen/logrus"
 )
 
 // OutputRoomEventConsumer consumes events that originated in the room server.
 type OutputRoomEventConsumer struct {
+	cfg        *config.SyncAPI
 	rsAPI      api.RoomserverInternalAPI
 	rsConsumer *internal.ContinualConsumer
 	db         storage.Database
@@ -55,6 +58,7 @@ func NewOutputRoomEventConsumer(
 		PartitionStore: store,
 	}
 	s := &OutputRoomEventConsumer{
+		cfg:        cfg,
 		rsConsumer: &consumer,
 		db:         store,
 		notifier:   n,
@@ -100,6 +104,8 @@ func (s *OutputRoomEventConsumer) onMessage(msg *sarama.ConsumerMessage) error {
 		return s.onNewInviteEvent(context.TODO(), *output.NewInviteEvent)
 	case api.OutputTypeRetireInviteEvent:
 		return s.onRetireInviteEvent(context.TODO(), *output.RetireInviteEvent)
+	case api.OutputTypeNewPeek:
+		return s.onNewPeek(context.TODO(), *output.NewPeek)
 	case api.OutputTypeRedactedEvent:
 		return s.onRedactEvent(context.TODO(), *output.RedactedEvent)
 	default:
@@ -162,6 +168,12 @@ func (s *OutputRoomEventConsumer) onNewRoomEvent(
 		}).Panicf("roomserver output log: write event failure")
 		return nil
 	}
+
+	if pduPos, err = s.notifyJoinedPeeks(ctx, &ev, pduPos); err != nil {
+		logrus.WithError(err).Errorf("Failed to notifyJoinedPeeks for PDU pos %d", pduPos)
+		return err
+	}
+
 	s.notifier.OnNewEvent(&ev, "", nil, types.NewStreamToken(pduPos, 0, nil))
 
 	s.notifyKeyChanges(&ev)
@@ -184,6 +196,37 @@ func (s *OutputRoomEventConsumer) notifyKeyChanges(ev *gomatrixserverlib.Headere
 	}
 }
 
+func (s *OutputRoomEventConsumer) notifyJoinedPeeks(ctx context.Context, ev *gomatrixserverlib.HeaderedEvent, sp types.StreamPosition) (types.StreamPosition, error) {
+	if ev.Type() != gomatrixserverlib.MRoomMember {
+		return sp, nil
+	}
+	membership, err := ev.Membership()
+	if err != nil {
+		return sp, fmt.Errorf("ev.Membership: %w", err)
+	}
+	// TODO: check that it's a join and not a profile change (means unmarshalling prev_content)
+	if membership == gomatrixserverlib.Join {
+		// check it's a local join
+		_, domain, err := gomatrixserverlib.SplitID('@', *ev.StateKey())
+		if err != nil {
+			return sp, fmt.Errorf("gomatrixserverlib.SplitID: %w", err)
+		}
+		if domain != s.cfg.Matrix.ServerName {
+			return sp, nil
+		}
+
+		// cancel any peeks for it
+		peekSP, peekErr := s.db.DeletePeeks(ctx, ev.RoomID(), *ev.StateKey())
+		if peekErr != nil {
+			return sp, fmt.Errorf("s.db.DeletePeeks: %w", peekErr)
+		}
+		if peekSP > 0 {
+			sp = peekSP
+		}
+	}
+	return sp, nil
+}
+
 func (s *OutputRoomEventConsumer) onNewInviteEvent(
 	ctx context.Context, msg api.OutputNewInviteEvent,
 ) error {
@@ -219,6 +262,26 @@ func (s *OutputRoomEventConsumer) onRetireInviteEvent(
 	return nil
 }
 
+func (s *OutputRoomEventConsumer) onNewPeek(
+	ctx context.Context, msg api.OutputNewPeek,
+) error {
+	sp, err := s.db.AddPeek(ctx, msg.RoomID, msg.UserID, msg.DeviceID)
+	if err != nil {
+		// panic rather than continue with an inconsistent database
+		log.WithFields(log.Fields{
+			log.ErrorKey: err,
+		}).Panicf("roomserver output log: write peek failure")
+		return nil
+	}
+	// tell the notifier about the new peek so it knows to wake up new devices
+	s.notifier.OnNewPeek(msg.RoomID, msg.UserID, msg.DeviceID)
+
+	// we need to wake up the users who might need to now be peeking into this room,
+	// so we send in a dummy event to trigger a wakeup
+	s.notifier.OnNewEvent(nil, msg.RoomID, nil, types.NewStreamToken(sp, 0, nil))
+	return nil
+}
+
 func (s *OutputRoomEventConsumer) updateStateEvent(event gomatrixserverlib.HeaderedEvent) (gomatrixserverlib.HeaderedEvent, error) {
 	if event.StateKey() == nil {
 		return event, nil