Move pseudoID ClientEvent hotswapping to a common location (#3199)

Fixes a variety of issues where clients were receiving pseudoIDs in
places that should be userIDs.
This change makes pseudoIDs work with sliding sync & element x.

---------

Co-authored-by: Till <2353100+S7evinK@users.noreply.github.com>

13 files changed, 421 insertions, 328 deletions

diff --git a/clientapi/routing/state.go b/clientapi/routing/state.go
index 6f363349..18f9a0e9 100644
--- a/clientapi/routing/state.go
+++ b/clientapi/routing/state.go
@@ -172,23 +172,16 @@ func OnIncomingStateRequest(ctx context.Context, device *userapi.Device, rsAPI a
 			}
 		}
 		for _, ev := range stateAfterRes.StateEvents {
-			sender := spec.UserID{}
-			userID, err := rsAPI.QueryUserIDForSender(ctx, ev.RoomID(), ev.SenderID())
-			if err == nil && userID != nil {
-				sender = *userID
-			}
-
-			sk := ev.StateKey()
-			if sk != nil && *sk != "" {
-				skUserID, err := rsAPI.QueryUserIDForSender(ctx, ev.RoomID(), spec.SenderID(*ev.StateKey()))
-				if err == nil && skUserID != nil {
-					skString := skUserID.String()
-					sk = &skString
-				}
+			clientEvent, err := synctypes.ToClientEvent(ev, synctypes.FormatAll, func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+				return rsAPI.QueryUserIDForSender(ctx, roomID, senderID)
+			})
+			if err != nil {
+				util.GetLogger(ctx).WithError(err).Error("Failed converting to ClientEvent")
+				continue
 			}
 			stateEvents = append(
 				stateEvents,
-				synctypes.ToClientEvent(ev, synctypes.FormatAll, sender.String(), sk, ev.Unsigned()),
+				*clientEvent,
 			)
 		}
 	}
diff --git a/internal/eventutil/events.go b/internal/eventutil/events.go
index b3523e12..40d62fd6 100644
--- a/internal/eventutil/events.go
+++ b/internal/eventutil/events.go
@@ -176,11 +176,13 @@ func RedactEvent(ctx context.Context, redactionEvent, redactedEvent gomatrixserv
 		return fmt.Errorf("RedactEvent: redactionEvent isn't a redaction event, is '%s'", redactionEvent.Type())
 	}
 	redactedEvent.Redact()
-	senderID, err := querier.QueryUserIDForSender(ctx, redactedEvent.RoomID(), redactionEvent.SenderID())
+	clientEvent, err := synctypes.ToClientEvent(redactionEvent, synctypes.FormatSync, func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+		return querier.QueryUserIDForSender(ctx, roomID, senderID)
+	})
 	if err != nil {
 		return err
 	}
-	redactedBecause := synctypes.ToClientEvent(redactionEvent, synctypes.FormatSync, senderID.String(), redactionEvent.StateKey(), redactionEvent.Unsigned())
+	redactedBecause := clientEvent
 	if err := redactedEvent.SetUnsignedField("redacted_because", redactedBecause); err != nil {
 		return err
 	}
diff --git a/syncapi/routing/getevent.go b/syncapi/routing/getevent.go
index 886b1167..c089539f 100644
--- a/syncapi/routing/getevent.go
+++ b/syncapi/routing/getevent.go
@@ -118,25 +118,19 @@ func GetEvent(
 		}
 	}
 
-	senderUserID, err := rsAPI.QueryUserIDForSender(req.Context(), *roomID, events[0].SenderID())
-	if err != nil || senderUserID == nil {
-		util.GetLogger(req.Context()).WithError(err).WithField("senderID", events[0].SenderID()).WithField("roomID", *roomID).Error("QueryUserIDForSender errored or returned nil-user ID when user should be part of a room")
+	clientEvent, err := synctypes.ToClientEvent(events[0], synctypes.FormatAll, func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+		return rsAPI.QueryUserIDForSender(ctx, roomID, senderID)
+	})
+	if err != nil {
+		util.GetLogger(req.Context()).WithError(err).WithField("senderID", events[0].SenderID()).WithField("roomID", *roomID).Error("Failed converting to ClientEvent")
 		return util.JSONResponse{
 			Code: http.StatusInternalServerError,
 			JSON: spec.Unknown("internal server error"),
 		}
 	}
 
-	sk := events[0].StateKey()
-	if sk != nil && *sk != "" {
-		skUserID, err := rsAPI.QueryUserIDForSender(ctx, events[0].RoomID(), spec.SenderID(*events[0].StateKey()))
-		if err == nil && skUserID != nil {
-			skString := skUserID.String()
-			sk = &skString
-		}
-	}
 	return util.JSONResponse{
 		Code: http.StatusOK,
-		JSON: synctypes.ToClientEvent(events[0], synctypes.FormatAll, senderUserID.String(), sk, events[0].Unsigned()),
+		JSON: *clientEvent,
 	}
 }
diff --git a/syncapi/routing/relations.go b/syncapi/routing/relations.go
index b451a7e2..935ba83b 100644
--- a/syncapi/routing/relations.go
+++ b/syncapi/routing/relations.go
@@ -130,23 +130,16 @@ func Relations(
 	// type if it was specified.
 	res.Chunk = make([]synctypes.ClientEvent, 0, len(filteredEvents))
 	for _, event := range filteredEvents {
-		sender := spec.UserID{}
-		userID, err := rsAPI.QueryUserIDForSender(req.Context(), *roomID, event.SenderID())
-		if err == nil && userID != nil {
-			sender = *userID
-		}
-
-		sk := event.StateKey()
-		if sk != nil && *sk != "" {
-			skUserID, err := rsAPI.QueryUserIDForSender(req.Context(), *roomID, spec.SenderID(*event.StateKey()))
-			if err == nil && skUserID != nil {
-				skString := skUserID.String()
-				sk = &skString
-			}
+		clientEvent, err := synctypes.ToClientEvent(event.PDU, synctypes.FormatAll, func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+			return rsAPI.QueryUserIDForSender(req.Context(), roomID, senderID)
+		})
+		if err != nil {
+			util.GetLogger(req.Context()).WithError(err).WithField("senderID", events[0].SenderID()).WithField("roomID", *roomID).Error("Failed converting to ClientEvent")
+			continue
 		}
 		res.Chunk = append(
 			res.Chunk,
-			synctypes.ToClientEvent(event.PDU, synctypes.FormatAll, sender.String(), sk, event.Unsigned()),
+			*clientEvent,
 		)
 	}
 
diff --git a/syncapi/routing/search.go b/syncapi/routing/search.go
index f574781a..4a8be9f4 100644
--- a/syncapi/routing/search.go
+++ b/syncapi/routing/search.go
@@ -230,20 +230,14 @@ func Search(req *http.Request, device *api.Device, syncDB storage.Database, fts
 			profileInfos[userID.String()] = profile
 		}
 
-		sender := spec.UserID{}
-		userID, err := rsAPI.QueryUserIDForSender(req.Context(), event.RoomID(), event.SenderID())
-		if err == nil && userID != nil {
-			sender = *userID
+		clientEvent, err := synctypes.ToClientEvent(event, synctypes.FormatAll, func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+			return rsAPI.QueryUserIDForSender(ctx, roomID, senderID)
+		})
+		if err != nil {
+			util.GetLogger(req.Context()).WithError(err).WithField("senderID", event.SenderID()).Error("Failed converting to ClientEvent")
+			continue
 		}
 
-		sk := event.StateKey()
-		if sk != nil && *sk != "" {
-			skUserID, err := rsAPI.QueryUserIDForSender(req.Context(), event.RoomID(), spec.SenderID(*event.StateKey()))
-			if err == nil && skUserID != nil {
-				skString := skUserID.String()
-				sk = &skString
-			}
-		}
 		results = append(results, Result{
 			Context: SearchContextResponse{
 				Start: startToken.String(),
@@ -257,7 +251,7 @@ func Search(req *http.Request, device *api.Device, syncDB storage.Database, fts
 				ProfileInfo: profileInfos,
 			},
 			Rank:   eventScore[event.EventID()].Score,
-			Result: synctypes.ToClientEvent(event, synctypes.FormatAll, sender.String(), sk, event.Unsigned()),
+			Result: *clientEvent,
 		})
 		roomGroup := groups[event.RoomID().String()]
 		roomGroup.Results = append(roomGroup.Results, event.EventID())
diff --git a/syncapi/streams/stream_invite.go b/syncapi/streams/stream_invite.go
index 1424dc2e..a3634c03 100644
--- a/syncapi/streams/stream_invite.go
+++ b/syncapi/streams/stream_invite.go
@@ -75,20 +75,15 @@ func (p *InviteStreamProvider) IncrementalSync(
 			user = *sender
 		}
 
-		sk := inviteEvent.StateKey()
-		if sk != nil && *sk != "" {
-			skUserID, err := p.rsAPI.QueryUserIDForSender(ctx, inviteEvent.RoomID(), spec.SenderID(*inviteEvent.StateKey()))
-			if err == nil && skUserID != nil {
-				skString := skUserID.String()
-				sk = &skString
-			}
-		}
-
 		// skip ignored user events
 		if _, ok := req.IgnoredUsers.List[user.String()]; ok {
 			continue
 		}
-		ir := types.NewInviteResponse(inviteEvent, user, sk, eventFormat)
+		ir, err := types.NewInviteResponse(ctx, p.rsAPI, inviteEvent, eventFormat)
+		if err != nil {
+			req.Log.WithError(err).Error("failed creating invite response")
+			continue
+		}
 		req.Response.Rooms.Invite[roomID] = ir
 	}
 
diff --git a/syncapi/streams/stream_pdu.go b/syncapi/streams/stream_pdu.go
index eb1f0ef2..3abb0b3c 100644
--- a/syncapi/streams/stream_pdu.go
+++ b/syncapi/streams/stream_pdu.go
@@ -3,7 +3,6 @@ package streams
 import (
 	"context"
 	"database/sql"
-	"encoding/json"
 	"fmt"
 	"time"
 
@@ -16,8 +15,6 @@ import (
 	"github.com/matrix-org/dendrite/syncapi/types"
 	userapi "github.com/matrix-org/dendrite/userapi/api"
 	"github.com/matrix-org/gomatrixserverlib/spec"
-	"github.com/tidwall/gjson"
-	"github.com/tidwall/sjson"
 
 	"github.com/matrix-org/dendrite/syncapi/notifier"
 	"github.com/matrix-org/gomatrixserverlib"
@@ -359,23 +356,6 @@ func (p *PDUStreamProvider) addRoomDeltaToResponse(
 	// Now that we've filtered the timeline, work out which state events are still
 	// left. Anything that appears in the filtered timeline will be removed from the
 	// "state" section and kept in "timeline".
-
-	// update the powerlevel event for timeline events
-	for i, ev := range events {
-		if ev.Version() != gomatrixserverlib.RoomVersionPseudoIDs {
-			continue
-		}
-		if ev.Type() != spec.MRoomPowerLevels || !ev.StateKeyEquals("") {
-			continue
-		}
-		var newEvent gomatrixserverlib.PDU
-		newEvent, err = p.updatePowerLevelEvent(ctx, ev, eventFormat)
-		if err != nil {
-			return r.From, err
-		}
-		events[i] = &rstypes.HeaderedEvent{PDU: newEvent}
-	}
-
 	sEvents := gomatrixserverlib.HeaderedReverseTopologicalOrdering(
 		gomatrixserverlib.ToPDUs(removeDuplicates(delta.StateEvents, events)),
 		gomatrixserverlib.TopologicalOrderByAuthEvents,
@@ -390,15 +370,6 @@ func (p *PDUStreamProvider) addRoomDeltaToResponse(
 			continue
 		}
 		delta.StateEvents[i-skipped] = he
-		// update the powerlevel event for state events
-		if ev.Version() == gomatrixserverlib.RoomVersionPseudoIDs && ev.Type() == spec.MRoomPowerLevels && ev.StateKeyEquals("") {
-			var newEvent gomatrixserverlib.PDU
-			newEvent, err = p.updatePowerLevelEvent(ctx, he, eventFormat)
-			if err != nil {
-				return r.From, err
-			}
-			delta.StateEvents[i-skipped] = &rstypes.HeaderedEvent{PDU: newEvent}
-		}
 	}
 	delta.StateEvents = delta.StateEvents[:len(sEvents)-skipped]
 
@@ -468,79 +439,6 @@ func (p *PDUStreamProvider) addRoomDeltaToResponse(
 	return latestPosition, nil
 }
 
-func (p *PDUStreamProvider) updatePowerLevelEvent(ctx context.Context, ev *rstypes.HeaderedEvent, eventFormat synctypes.ClientEventFormat) (gomatrixserverlib.PDU, error) {
-	pls, err := gomatrixserverlib.NewPowerLevelContentFromEvent(ev)
-	if err != nil {
-		return nil, err
-	}
-	newPls := make(map[string]int64)
-	var userID *spec.UserID
-	for user, level := range pls.Users {
-		if eventFormat != synctypes.FormatSyncFederation {
-			userID, err = p.rsAPI.QueryUserIDForSender(ctx, ev.RoomID(), spec.SenderID(user))
-			if err != nil {
-				return nil, err
-			}
-			user = userID.String()
-		}
-		newPls[user] = level
-	}
-	var newPlBytes, newEv []byte
-	newPlBytes, err = json.Marshal(newPls)
-	if err != nil {
-		return nil, err
-	}
-	newEv, err = sjson.SetRawBytes(ev.JSON(), "content.users", newPlBytes)
-	if err != nil {
-		return nil, err
-	}
-
-	// do the same for prev content
-	prevContent := gjson.GetBytes(ev.JSON(), "unsigned.prev_content")
-	if !prevContent.Exists() {
-		var evNew gomatrixserverlib.PDU
-		evNew, err = gomatrixserverlib.MustGetRoomVersion(ev.Version()).NewEventFromTrustedJSONWithEventID(ev.EventID(), newEv, false)
-		if err != nil {
-			return nil, err
-		}
-
-		return evNew, err
-	}
-	pls = gomatrixserverlib.PowerLevelContent{}
-	err = json.Unmarshal([]byte(prevContent.Raw), &pls)
-	if err != nil {
-		return nil, err
-	}
-
-	newPls = make(map[string]int64)
-	for user, level := range pls.Users {
-		if eventFormat != synctypes.FormatSyncFederation {
-			userID, err = p.rsAPI.QueryUserIDForSender(ctx, ev.RoomID(), spec.SenderID(user))
-			if err != nil {
-				return nil, err
-			}
-			user = userID.String()
-		}
-		newPls[user] = level
-	}
-	newPlBytes, err = json.Marshal(newPls)
-	if err != nil {
-		return nil, err
-	}
-	newEv, err = sjson.SetRawBytes(newEv, "unsigned.prev_content.users", newPlBytes)
-	if err != nil {
-		return nil, err
-	}
-
-	var evNew gomatrixserverlib.PDU
-	evNew, err = gomatrixserverlib.MustGetRoomVersion(ev.Version()).NewEventFromTrustedJSONWithEventID(ev.EventID(), newEv, false)
-	if err != nil {
-		return nil, err
-	}
-
-	return evNew, err
-}
-
 // applyHistoryVisibilityFilter gets the current room state and supplies it to ApplyHistoryVisibilityFilter, to make
 // sure we always return the required events in the timeline.
 func applyHistoryVisibilityFilter(
@@ -690,35 +588,6 @@ func (p *PDUStreamProvider) getJoinResponseForCompleteSync(
 		prevBatch.Decrement()
 	}
 
-	// Update powerlevel events for timeline events
-	for i, ev := range events {
-		if ev.Version() != gomatrixserverlib.RoomVersionPseudoIDs {
-			continue
-		}
-		if ev.Type() != spec.MRoomPowerLevels || !ev.StateKeyEquals("") {
-			continue
-		}
-		newEvent, err := p.updatePowerLevelEvent(ctx, ev, eventFormat)
-		if err != nil {
-			return nil, err
-		}
-		events[i] = &rstypes.HeaderedEvent{PDU: newEvent}
-	}
-	// Update powerlevel events for state events
-	for i, ev := range stateEvents {
-		if ev.Version() != gomatrixserverlib.RoomVersionPseudoIDs {
-			continue
-		}
-		if ev.Type() != spec.MRoomPowerLevels || !ev.StateKeyEquals("") {
-			continue
-		}
-		newEvent, err := p.updatePowerLevelEvent(ctx, ev, eventFormat)
-		if err != nil {
-			return nil, err
-		}
-		stateEvents[i] = &rstypes.HeaderedEvent{PDU: newEvent}
-	}
-
 	jr.Timeline.PrevBatch = prevBatch
 	jr.Timeline.Events = synctypes.ToClientEvents(gomatrixserverlib.ToPDUs(events), eventFormat, func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
 		return p.rsAPI.QueryUserIDForSender(ctx, roomID, senderID)
diff --git a/syncapi/synctypes/clientevent.go b/syncapi/synctypes/clientevent.go
index e0616e11..6812f833 100644
--- a/syncapi/synctypes/clientevent.go
+++ b/syncapi/synctypes/clientevent.go
@@ -22,6 +22,8 @@ import (
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/gomatrixserverlib/spec"
 	"github.com/sirupsen/logrus"
+	"github.com/tidwall/gjson"
+	"github.com/tidwall/sjson"
 )
 
 // PrevEventRef represents a reference to a previous event in a state event upgrade
@@ -78,59 +80,62 @@ func ToClientEvents(serverEvs []gomatrixserverlib.PDU, format ClientEventFormat,
 		if se == nil {
 			continue // TODO: shouldn't happen?
 		}
-		if format == FormatSyncFederation {
-			evs = append(evs, ToClientEvent(se, format, string(se.SenderID()), se.StateKey(), spec.RawJSON(se.Unsigned())))
+		ev, err := ToClientEvent(se, format, userIDForSender)
+		if err != nil {
+			logrus.WithError(err).Warn("Failed converting event to ClientEvent")
 			continue
 		}
+		evs = append(evs, *ev)
+	}
+	return evs
+}
 
-		sender := spec.UserID{}
-		userID, err := userIDForSender(se.RoomID(), se.SenderID())
-		if err == nil && userID != nil {
-			sender = *userID
-		}
+// ToClientEventDefault converts a single server event to a client event.
+// It provides default logic for event.SenderID & event.StateKey -> userID conversions.
+func ToClientEventDefault(userIDQuery spec.UserIDForSender, event gomatrixserverlib.PDU) ClientEvent {
+	ev, err := ToClientEvent(event, FormatAll, userIDQuery)
+	if err != nil {
+		return ClientEvent{}
+	}
+	return *ev
+}
 
-		sk := se.StateKey()
-		if sk != nil && *sk != "" {
-			skUserID, err := userIDForSender(se.RoomID(), spec.SenderID(*sk))
-			if err == nil && skUserID != nil {
-				skString := skUserID.String()
-				sk = &skString
-			}
+// If provided state key is a user ID (state keys beginning with @ are reserved for this purpose)
+// fetch it's associated sender ID and use that instead. Otherwise returns the same state key back.
+//
+// # This function either returns the state key that should be used, or an error
+//
+// TODO: handle failure cases better (e.g. no sender ID)
+func FromClientStateKey(roomID spec.RoomID, stateKey string, senderIDQuery spec.SenderIDForUser) (*string, error) {
+	if len(stateKey) >= 1 && stateKey[0] == '@' {
+		parsedStateKey, err := spec.NewUserID(stateKey, true)
+		if err != nil {
+			// If invalid user ID, then there is no associated state event.
+			return nil, fmt.Errorf("Provided state key begins with @ but is not a valid user ID: %w", err)
 		}
-
-		unsigned := se.Unsigned()
-		var prev PrevEventRef
-		if err := json.Unmarshal(se.Unsigned(), &prev); err == nil && prev.PrevSenderID != "" {
-			prevUserID, err := userIDForSender(se.RoomID(), spec.SenderID(prev.PrevSenderID))
-			if err == nil && userID != nil {
-				prev.PrevSenderID = prevUserID.String()
-			} else {
-				errString := "userID unknown"
-				if err != nil {
-					errString = err.Error()
-				}
-				logrus.Warnf("Failed to find userID for prev_sender in ClientEvent: %s", errString)
-				// NOTE: Not much can be done here, so leave the previous value in place.
-			}
-			unsigned, err = json.Marshal(prev)
-			if err != nil {
-				logrus.Errorf("Failed to marshal unsigned content for ClientEvent: %s", err.Error())
-				continue
-			}
+		senderID, err := senderIDQuery(roomID, *parsedStateKey)
+		if err != nil {
+			return nil, fmt.Errorf("Failed to query sender ID: %w", err)
+		}
+		if senderID == nil {
+			// If no sender ID, then there is no associated state event.
+			return nil, fmt.Errorf("No associated sender ID found.")
 		}
-		evs = append(evs, ToClientEvent(se, format, sender.String(), sk, spec.RawJSON(unsigned)))
+		newStateKey := string(*senderID)
+		return &newStateKey, nil
+	} else {
+		return &stateKey, nil
 	}
-	return evs
 }
 
 // ToClientEvent converts a single server event to a client event.
-func ToClientEvent(se gomatrixserverlib.PDU, format ClientEventFormat, sender string, stateKey *string, unsigned spec.RawJSON) ClientEvent {
+func ToClientEvent(se gomatrixserverlib.PDU, format ClientEventFormat, userIDForSender spec.UserIDForSender) (*ClientEvent, error) {
 	ce := ClientEvent{
-		Content:        spec.RawJSON(se.Content()),
-		Sender:         sender,
+		Content:        se.Content(),
+		Sender:         string(se.SenderID()),
 		Type:           se.Type(),
-		StateKey:       stateKey,
-		Unsigned:       unsigned,
+		StateKey:       se.StateKey(),
+		Unsigned:       se.Unsigned(),
 		OriginServerTS: se.OriginServerTS(),
 		EventID:        se.EventID(),
 		Redacts:        se.Redacts(),
@@ -148,58 +153,268 @@ func ToClientEvent(se gomatrixserverlib.PDU, format ClientEventFormat, sender st
 		// TODO: Set Signatures & Hashes fields
 	}
 
-	if format != FormatSyncFederation {
-		if se.Version() == gomatrixserverlib.RoomVersionPseudoIDs {
-			ce.SenderKey = se.SenderID()
+	if format != FormatSyncFederation && se.Version() == gomatrixserverlib.RoomVersionPseudoIDs {
+		err := updatePseudoIDs(&ce, se, userIDForSender, format)
+		if err != nil {
+			return nil, err
 		}
 	}
-	return ce
+
+	return &ce, nil
 }
 
-// ToClientEvent converts a single server event to a client event.
-// It provides default logic for event.SenderID & event.StateKey -> userID conversions.
-func ToClientEventDefault(userIDQuery spec.UserIDForSender, event gomatrixserverlib.PDU) ClientEvent {
-	sender := spec.UserID{}
-	userID, err := userIDQuery(event.RoomID(), event.SenderID())
+func updatePseudoIDs(ce *ClientEvent, se gomatrixserverlib.PDU, userIDForSender spec.UserIDForSender, format ClientEventFormat) error {
+	ce.SenderKey = se.SenderID()
+
+	userID, err := userIDForSender(se.RoomID(), se.SenderID())
 	if err == nil && userID != nil {
-		sender = *userID
+		ce.Sender = userID.String()
 	}
 
-	sk := event.StateKey()
+	sk := se.StateKey()
 	if sk != nil && *sk != "" {
-		skUserID, err := userIDQuery(event.RoomID(), spec.SenderID(*event.StateKey()))
+		skUserID, err := userIDForSender(se.RoomID(), spec.SenderID(*sk))
 		if err == nil && skUserID != nil {
 			skString := skUserID.String()
-			sk = &skString
+			ce.StateKey = &skString
 		}
 	}
-	return ToClientEvent(event, FormatAll, sender.String(), sk, event.Unsigned())
+
+	var prev PrevEventRef
+	if err := json.Unmarshal(se.Unsigned(), &prev); err == nil && prev.PrevSenderID != "" {
+		prevUserID, err := userIDForSender(se.RoomID(), spec.SenderID(prev.PrevSenderID))
+		if err == nil && userID != nil {
+			prev.PrevSenderID = prevUserID.String()
+		} else {
+			errString := "userID unknown"
+			if err != nil {
+				errString = err.Error()
+			}
+			logrus.Warnf("Failed to find userID for prev_sender in ClientEvent: %s", errString)
+			// NOTE: Not much can be done here, so leave the previous value in place.
+		}
+		ce.Unsigned, err = json.Marshal(prev)
+		if err != nil {
+			err = fmt.Errorf("Failed to marshal unsigned content for ClientEvent: %w", err)
+			return err
+		}
+	}
+
+	switch se.Type() {
+	case spec.MRoomCreate:
+		updatedContent, err := updateCreateEvent(se.Content(), userIDForSender, se.RoomID())
+		if err != nil {
+			err = fmt.Errorf("Failed to update m.room.create event for ClientEvent: %w", err)
+			return err
+		}
+		ce.Content = updatedContent
+	case spec.MRoomMember:
+		updatedEvent, err := updateInviteEvent(userIDForSender, se, format)
+		if err != nil {
+			err = fmt.Errorf("Failed to update m.room.member event for ClientEvent: %w", err)
+			return err
+		}
+		if updatedEvent != nil {
+			ce.Unsigned = updatedEvent.Unsigned()
+		}
+	case spec.MRoomPowerLevels:
+		updatedEvent, err := updatePowerLevelEvent(userIDForSender, se, format)
+		if err != nil {
+			err = fmt.Errorf("Failed update m.room.power_levels event for ClientEvent: %w", err)
+			return err
+		}
+		if updatedEvent != nil {
+			ce.Content = updatedEvent.Content()
+			ce.Unsigned = updatedEvent.Unsigned()
+		}
+	}
+
+	return nil
 }
 
-// If provided state key is a user ID (state keys beginning with @ are reserved for this purpose)
-// fetch it's associated sender ID and use that instead. Otherwise returns the same state key back.
-//
-// # This function either returns the state key that should be used, or an error
-//
-// TODO: handle failure cases better (e.g. no sender ID)
-func FromClientStateKey(roomID spec.RoomID, stateKey string, senderIDQuery spec.SenderIDForUser) (*string, error) {
-	if len(stateKey) >= 1 && stateKey[0] == '@' {
-		parsedStateKey, err := spec.NewUserID(stateKey, true)
+func updateCreateEvent(content spec.RawJSON, userIDForSender spec.UserIDForSender, roomID spec.RoomID) (spec.RawJSON, error) {
+	if creator := gjson.GetBytes(content, "creator"); creator.Exists() {
+		oldCreator := creator.Str
+		userID, err := userIDForSender(roomID, spec.SenderID(oldCreator))
 		if err != nil {
-			// If invalid user ID, then there is no associated state event.
-			return nil, fmt.Errorf("Provided state key begins with @ but is not a valid user ID: %s", err.Error())
+			err = fmt.Errorf("Failed to find userID for creator in ClientEvent: %w", err)
+			return nil, err
 		}
-		senderID, err := senderIDQuery(roomID, *parsedStateKey)
+
+		if userID != nil {
+			var newCreatorBytes, newContent []byte
+			newCreatorBytes, err = json.Marshal(userID.String())
+			if err != nil {
+				err = fmt.Errorf("Failed to marshal new creator for ClientEvent: %w", err)
+				return nil, err
+			}
+
+			newContent, err = sjson.SetRawBytes([]byte(content), "creator", newCreatorBytes)
+			if err != nil {
+				err = fmt.Errorf("Failed to set new creator for ClientEvent: %w", err)
+				return nil, err
+			}
+
+			return newContent, nil
+		}
+	}
+
+	return content, nil
+}
+
+func updateInviteEvent(userIDForSender spec.UserIDForSender, ev gomatrixserverlib.PDU, eventFormat ClientEventFormat) (gomatrixserverlib.PDU, error) {
+	if inviteRoomState := gjson.GetBytes(ev.Unsigned(), "invite_room_state"); inviteRoomState.Exists() {
+		userID, err := userIDForSender(ev.RoomID(), ev.SenderID())
+		if err != nil || userID == nil {
+			if err != nil {
+				err = fmt.Errorf("invalid userID found when updating invite_room_state: %w", err)
+			}
+			return nil, err
+		}
+
+		newState, err := GetUpdatedInviteRoomState(userIDForSender, inviteRoomState, ev, ev.RoomID(), eventFormat)
 		if err != nil {
-			return nil, fmt.Errorf("Failed to query sender ID: %s", err.Error())
+			return nil, err
 		}
-		if senderID == nil {
-			// If no sender ID, then there is no associated state event.
-			return nil, fmt.Errorf("No associated sender ID found.")
+
+		var newEv []byte
+		newEv, err = sjson.SetRawBytes(ev.JSON(), "unsigned.invite_room_state", newState)
+		if err != nil {
+			return nil, err
 		}
-		newStateKey := string(*senderID)
-		return &newStateKey, nil
-	} else {
-		return &stateKey, nil
+
+		return gomatrixserverlib.MustGetRoomVersion(ev.Version()).NewEventFromTrustedJSON(newEv, false)
+	}
+
+	return ev, nil
+}
+
+type InviteRoomStateEvent struct {
+	Content  spec.RawJSON `json:"content"`
+	SenderID string       `json:"sender"`
+	StateKey *string      `json:"state_key"`
+	Type     string       `json:"type"`
+}
+
+func GetUpdatedInviteRoomState(userIDForSender spec.UserIDForSender, inviteRoomState gjson.Result, event gomatrixserverlib.PDU, roomID spec.RoomID, eventFormat ClientEventFormat) (spec.RawJSON, error) {
+	var res spec.RawJSON
+	inviteStateEvents := []InviteRoomStateEvent{}
+	err := json.Unmarshal([]byte(inviteRoomState.Raw), &inviteStateEvents)
+	if err != nil {
+		return nil, err
 	}
+
+	if event.Version() == gomatrixserverlib.RoomVersionPseudoIDs && eventFormat != FormatSyncFederation {
+		for i, ev := range inviteStateEvents {
+			userID, userIDErr := userIDForSender(roomID, spec.SenderID(ev.SenderID))
+			if userIDErr != nil {
+				return nil, userIDErr
+			}
+			if userID != nil {
+				inviteStateEvents[i].SenderID = userID.String()
+			}
+
+			if ev.StateKey != nil && *ev.StateKey != "" {
+				userID, senderErr := userIDForSender(roomID, spec.SenderID(*ev.StateKey))
+				if senderErr != nil {
+					return nil, senderErr
+				}
+				if userID != nil {
+					user := userID.String()
+					inviteStateEvents[i].StateKey = &user
+				}
+			}
+
+			updatedContent, updateErr := updateCreateEvent(ev.Content, userIDForSender, roomID)
+			if updateErr != nil {
+				updateErr = fmt.Errorf("Failed to update m.room.create event for ClientEvent: %w", userIDErr)
+				return nil, updateErr
+			}
+			inviteStateEvents[i].Content = updatedContent
+		}
+	}
+
+	res, err = json.Marshal(inviteStateEvents)
+	if err != nil {
+		return nil, err
+	}
+
+	return res, nil
+}
+
+func updatePowerLevelEvent(userIDForSender spec.UserIDForSender, se gomatrixserverlib.PDU, eventFormat ClientEventFormat) (gomatrixserverlib.PDU, error) {
+	if !se.StateKeyEquals("") {
+		return se, nil
+	}
+
+	pls, err := gomatrixserverlib.NewPowerLevelContentFromEvent(se)
+	if err != nil {
+		return nil, err
+	}
+	newPls := make(map[string]int64)
+	var userID *spec.UserID
+	for user, level := range pls.Users {
+		if eventFormat != FormatSyncFederation {
+			userID, err = userIDForSender(se.RoomID(), spec.SenderID(user))
+			if err != nil {
+				return nil, err
+			}
+			user = userID.String()
+		}
+		newPls[user] = level
+	}
+	var newPlBytes, newEv []byte
+	newPlBytes, err = json.Marshal(newPls)
+	if err != nil {
+		return nil, err
+	}
+	newEv, err = sjson.SetRawBytes(se.JSON(), "content.users", newPlBytes)
+	if err != nil {
+		return nil, err
+	}
+
+	// do the same for prev content
+	prevContent := gjson.GetBytes(se.JSON(), "unsigned.prev_content")
+	if !prevContent.Exists() {
+		var evNew gomatrixserverlib.PDU
+		evNew, err = gomatrixserverlib.MustGetRoomVersion(se.Version()).NewEventFromTrustedJSON(newEv, false)
+		if err != nil {
+			return nil, err
+		}
+
+		return evNew, err
+	}
+	pls = gomatrixserverlib.PowerLevelContent{}
+	err = json.Unmarshal([]byte(prevContent.Raw), &pls)
+	if err != nil {
+		return nil, err
+	}
+
+	newPls = make(map[string]int64)
+	for user, level := range pls.Users {
+		if eventFormat != FormatSyncFederation {
+			userID, err = userIDForSender(se.RoomID(), spec.SenderID(user))
+			if err != nil {
+				return nil, err
+			}
+			user = userID.String()
+		}
+		newPls[user] = level
+	}
+	newPlBytes, err = json.Marshal(newPls)
+	if err != nil {
+		return nil, err
+	}
+	newEv, err = sjson.SetRawBytes(newEv, "unsigned.prev_content.users", newPlBytes)
+	if err != nil {
+		return nil, err
+	}
+
+	var evNew gomatrixserverlib.PDU
+	evNew, err = gomatrixserverlib.MustGetRoomVersion(se.Version()).NewEventFromTrustedJSONWithEventID(se.EventID(), newEv, false)
+	if err != nil {
+		return nil, err
+	}
+
+	return evNew, err
 }
diff --git a/syncapi/synctypes/clientevent_test.go b/syncapi/synctypes/clientevent_test.go
index 202c185f..662f9ea4 100644
--- a/syncapi/synctypes/clientevent_test.go
+++ b/syncapi/synctypes/clientevent_test.go
@@ -26,6 +26,14 @@ import (
 	"github.com/matrix-org/gomatrixserverlib/spec"
 )
 
+func queryUserIDForSender(senderID spec.SenderID) (*spec.UserID, error) {
+	if senderID == "" {
+		return nil, nil
+	}
+
+	return spec.NewUserID(string(senderID), true)
+}
+
 const testSenderID = "testSenderID"
 const testUserID = "@test:localhost"
 
@@ -106,7 +114,12 @@ func TestToClientEvent(t *testing.T) { // nolint: gocyclo
 		t.Fatalf("failed to create userID: %s", err)
 	}
 	sk := ""
-	ce := ToClientEvent(ev, FormatAll, userID.String(), &sk, ev.Unsigned())
+	ce, err := ToClientEvent(ev, FormatAll, func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+		return queryUserIDForSender(senderID)
+	})
+	if err != nil {
+		t.Fatalf("failed to create ClientEvent: %s", err)
+	}
 
 	verifyEventFields(t,
 		EventFieldsToVerify{
@@ -161,12 +174,12 @@ func TestToClientFormatSync(t *testing.T) {
 	if err != nil {
 		t.Fatalf("failed to create Event: %s", err)
 	}
-	userID, err := spec.NewUserID("@test:localhost", true)
+	ce, err := ToClientEvent(ev, FormatSync, func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+		return queryUserIDForSender(senderID)
+	})
 	if err != nil {
-		t.Fatalf("failed to create userID: %s", err)
+		t.Fatalf("failed to create ClientEvent: %s", err)
 	}
-	sk := ""
-	ce := ToClientEvent(ev, FormatSync, userID.String(), &sk, ev.Unsigned())
 	if ce.RoomID != "" {
 		t.Errorf("ClientEvent.RoomID: wanted '', got %s", ce.RoomID)
 	}
@@ -206,7 +219,12 @@ func TestToClientEventFormatSyncFederation(t *testing.T) { // nolint: gocyclo
 		t.Fatalf("failed to create userID: %s", err)
 	}
 	sk := ""
-	ce := ToClientEvent(ev, FormatSyncFederation, userID.String(), &sk, ev.Unsigned())
+	ce, err := ToClientEvent(ev, FormatSyncFederation, func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+		return queryUserIDForSender(senderID)
+	})
+	if err != nil {
+		t.Fatalf("failed to create ClientEvent: %s", err)
+	}
 
 	verifyEventFields(t,
 		EventFieldsToVerify{
diff --git a/syncapi/types/types.go b/syncapi/types/types.go
index b90c128c..bca11855 100644
--- a/syncapi/types/types.go
+++ b/syncapi/types/types.go
@@ -15,6 +15,7 @@
 package types
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -532,7 +533,7 @@ type InviteResponse struct {
 }
 
 // NewInviteResponse creates an empty response with initialised arrays.
-func NewInviteResponse(event *types.HeaderedEvent, userID spec.UserID, stateKey *string, eventFormat synctypes.ClientEventFormat) *InviteResponse {
+func NewInviteResponse(ctx context.Context, rsAPI api.QuerySenderIDAPI, event *types.HeaderedEvent, eventFormat synctypes.ClientEventFormat) (*InviteResponse, error) {
 	res := InviteResponse{}
 	res.InviteState.Events = []json.RawMessage{}
 
@@ -540,18 +541,42 @@ func NewInviteResponse(event *types.HeaderedEvent, userID spec.UserID, stateKey
 	// If there is then unmarshal it into the response. This will contain the
 	// partial room state such as join rules, room name etc.
 	if inviteRoomState := gjson.GetBytes(event.Unsigned(), "invite_room_state"); inviteRoomState.Exists() {
-		_ = json.Unmarshal([]byte(inviteRoomState.Raw), &res.InviteState.Events)
+		if event.Version() == gomatrixserverlib.RoomVersionPseudoIDs && eventFormat != synctypes.FormatSyncFederation {
+			updatedInvite, err := synctypes.GetUpdatedInviteRoomState(func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+				return rsAPI.QueryUserIDForSender(ctx, roomID, senderID)
+			}, inviteRoomState, event.PDU, event.RoomID(), eventFormat)
+			if err != nil {
+				return nil, err
+			}
+			_ = json.Unmarshal(updatedInvite, &res.InviteState.Events)
+		} else {
+			_ = json.Unmarshal([]byte(inviteRoomState.Raw), &res.InviteState.Events)
+		}
+	}
+
+	// Clear unsigned so it doesn't have pseudoIDs converted during ToClientEvent
+	eventNoUnsigned, err := event.SetUnsigned(nil)
+	if err != nil {
+		return nil, err
 	}
 
 	// Then we'll see if we can create a partial of the invite event itself.
 	// This is needed for clients to work out *who* sent the invite.
-	inviteEvent := synctypes.ToClientEvent(event.PDU, eventFormat, userID.String(), stateKey, event.Unsigned())
+	inviteEvent, err := synctypes.ToClientEvent(eventNoUnsigned, eventFormat, func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+		return rsAPI.QueryUserIDForSender(ctx, roomID, senderID)
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	// Ensure unsigned field is empty so it isn't marshalled into the final JSON
 	inviteEvent.Unsigned = nil
-	if ev, err := json.Marshal(inviteEvent); err == nil {
+
+	if ev, err := json.Marshal(*inviteEvent); err == nil {
 		res.InviteState.Events = append(res.InviteState.Events, ev)
 	}
 
-	return &res
+	return &res, nil
 }
 
 // LeaveResponse represents a /sync response for a room which is under the 'leave' key.
diff --git a/syncapi/types/types_test.go b/syncapi/types/types_test.go
index a79b9fc5..35e1882c 100644
--- a/syncapi/types/types_test.go
+++ b/syncapi/types/types_test.go
@@ -1,6 +1,7 @@
 package types
 
 import (
+	"context"
 	"encoding/json"
 	"reflect"
 	"testing"
@@ -11,8 +12,19 @@ import (
 	"github.com/matrix-org/gomatrixserverlib/spec"
 )
 
-func UserIDForSender(roomID string, senderID string) (*spec.UserID, error) {
-	return spec.NewUserID(senderID, true)
+type FakeRoomserverAPI struct{}
+
+func (f *FakeRoomserverAPI) QueryUserIDForSender(ctx context.Context, roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+	if senderID == "" {
+		return nil, nil
+	}
+
+	return spec.NewUserID(string(senderID), true)
+}
+
+func (f *FakeRoomserverAPI) QuerySenderIDForUser(ctx context.Context, roomID spec.RoomID, userID spec.UserID) (*spec.SenderID, error) {
+	sender := spec.SenderID(userID.String())
+	return &sender, nil
 }
 
 func TestSyncTokens(t *testing.T) {
@@ -61,25 +73,18 @@ func TestNewInviteResponse(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	sender, err := spec.NewUserID("@neilalexander:matrix.org", true)
+	rsAPI := FakeRoomserverAPI{}
+	res, err := NewInviteResponse(context.Background(), &rsAPI, &types.HeaderedEvent{PDU: ev}, synctypes.FormatSync)
 	if err != nil {
 		t.Fatal(err)
 	}
-	skUserID, err := spec.NewUserID("@neilalexander:dendrite.neilalexander.dev", true)
-	if err != nil {
-		t.Fatal(err)
-	}
-	skString := skUserID.String()
-	sk := &skString
-
-	res := NewInviteResponse(&types.HeaderedEvent{PDU: ev}, *sender, sk, synctypes.FormatSync)
 	j, err := json.Marshal(res)
 	if err != nil {
 		t.Fatal(err)
 	}
 
 	if string(j) != expected {
-		t.Fatalf("Invite response didn't contain correct info")
+		t.Fatalf("Invite response didn't contain correct info, \nexpected: %s \ngot: %s", expected, string(j))
 	}
 }
 
diff --git a/userapi/consumers/roomserver.go b/userapi/consumers/roomserver.go
index dca09193..047fe921 100644
--- a/userapi/consumers/roomserver.go
+++ b/userapi/consumers/roomserver.go
@@ -301,25 +301,14 @@ func (s *OutputRoomEventConsumer) processMessage(ctx context.Context, event *rst
 
 	switch {
 	case event.Type() == spec.MRoomMember:
-		sender := spec.UserID{}
-		userID, queryErr := s.rsAPI.QueryUserIDForSender(ctx, event.RoomID(), event.SenderID())
-		if queryErr == nil && userID != nil {
-			sender = *userID
-		}
-
-		sk := event.StateKey()
-		if sk != nil && *sk != "" {
-			skUserID, queryErr := s.rsAPI.QueryUserIDForSender(ctx, event.RoomID(), spec.SenderID(*sk))
-			if queryErr == nil && skUserID != nil {
-				skString := skUserID.String()
-				sk = &skString
-			} else {
-				return fmt.Errorf("queryUserIDForSender: userID unknown for %s", *sk)
-			}
+		cevent, clientEvErr := synctypes.ToClientEvent(event, synctypes.FormatAll, func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+			return s.rsAPI.QueryUserIDForSender(ctx, roomID, senderID)
+		})
+		if clientEvErr != nil {
+			return clientEvErr
 		}
-		cevent := synctypes.ToClientEvent(event, synctypes.FormatAll, sender.String(), sk, event.Unsigned())
 		var member *localMembership
-		member, err = newLocalMembership(&cevent)
+		member, err = newLocalMembership(cevent)
 		if err != nil {
 			return fmt.Errorf("newLocalMembership: %w", err)
 		}
@@ -538,27 +527,19 @@ func (s *OutputRoomEventConsumer) notifyLocal(ctx context.Context, event *rstype
 	if err != nil {
 		return fmt.Errorf("s.localPushDevices: %w", err)
 	}
-
-	sender := spec.UserID{}
-	userID, err := s.rsAPI.QueryUserIDForSender(ctx, event.RoomID(), event.SenderID())
-	if err == nil && userID != nil {
-		sender = *userID
+	clientEvent, err := synctypes.ToClientEvent(event, synctypes.FormatSync, func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+		return s.rsAPI.QueryUserIDForSender(ctx, roomID, senderID)
+	})
+	if err != nil {
+		return err
 	}
 
-	sk := event.StateKey()
-	if sk != nil && *sk != "" {
-		skUserID, queryErr := s.rsAPI.QueryUserIDForSender(ctx, event.RoomID(), spec.SenderID(*event.StateKey()))
-		if queryErr == nil && skUserID != nil {
-			skString := skUserID.String()
-			sk = &skString
-		}
-	}
 	n := &api.Notification{
 		Actions: actions,
 		// UNSPEC: the spec doesn't say this is a ClientEvent, but the
 		// fields seem to match. room_id should be missing, which
 		// matches the behaviour of FormatSync.
-		Event: synctypes.ToClientEvent(event, synctypes.FormatSync, sender.String(), sk, event.Unsigned()),
+		Event: *clientEvent,
 		// TODO: this is per-device, but it's not part of the primary
 		// key. So inserting one notification per profile tag doesn't
 		// make sense. What is this supposed to be? Sytests require it
diff --git a/userapi/util/notify_test.go b/userapi/util/notify_test.go
index 27e77cf7..2ea978d6 100644
--- a/userapi/util/notify_test.go
+++ b/userapi/util/notify_test.go
@@ -23,6 +23,14 @@ import (
 	userUtil "github.com/matrix-org/dendrite/userapi/util"
 )
 
+func queryUserIDForSender(senderID spec.SenderID) (*spec.UserID, error) {
+	if senderID == "" {
+		return nil, nil
+	}
+
+	return spec.NewUserID(string(senderID), true)
+}
+
 func TestNotifyUserCountsAsync(t *testing.T) {
 	alice := test.NewUser(t)
 	aliceLocalpart, serverName, err := gomatrixserverlib.SplitID('@', alice.ID)
@@ -100,13 +108,14 @@ func TestNotifyUserCountsAsync(t *testing.T) {
 		}
 
 		// Insert a dummy event
-		sender, err := spec.NewUserID(alice.ID, true)
+		ev, err := synctypes.ToClientEvent(dummyEvent, synctypes.FormatAll, func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+			return queryUserIDForSender(senderID)
+		})
 		if err != nil {
 			t.Error(err)
 		}
-		sk := ""
 		if err := db.InsertNotification(ctx, aliceLocalpart, serverName, dummyEvent.EventID(), 0, nil, &api.Notification{
-			Event: synctypes.ToClientEvent(dummyEvent, synctypes.FormatAll, sender.String(), &sk, dummyEvent.Unsigned()),
+			Event: *ev,
 		}); err != nil {
 			t.Error(err)
 		}