Don't send `adds_state_events` in roomserver output events anymore (#2258)

* Don't send `adds_state_events` in roomserver output events anymore

* Set `omitempty` on some output fields that aren't always set

* Add `AddsState` helper function

* No-op if no added state event IDs

* Revert "No-op if no added state event IDs"

This reverts commit 71a0ef3df10e0d94234d916246c30b0a4e82b26e.

* Revert "Add `AddsState` helper function"

This reverts commit c9fbe45475eb12ae44d2a8da7c0fc3a002ad9819.

2 files changed, 11 insertions, 77 deletions

diff --git a/roomserver/api/output.go b/roomserver/api/output.go
index d60d1cc8..767611ec 100644
--- a/roomserver/api/output.go
+++ b/roomserver/api/output.go
@@ -105,7 +105,7 @@ type OutputNewRoomEvent struct {
 	Event *gomatrixserverlib.HeaderedEvent `json:"event"`
 	// Does the event completely rewrite the room state? If so, then AddsStateEventIDs
 	// will contain the entire room state.
-	RewritesState bool `json:"rewrites_state"`
+	RewritesState bool `json:"rewrites_state,omitempty"`
 	// The latest events in the room after this event.
 	// This can be used to set the prev events for new events in the room.
 	// This also can be used to get the full current state after this event.
@@ -113,16 +113,9 @@ type OutputNewRoomEvent struct {
 	// The state event IDs that were added to the state of the room by this event.
 	// Together with RemovesStateEventIDs this allows the receiver to keep an up to date
 	// view of the current state of the room.
-	AddsStateEventIDs []string `json:"adds_state_event_ids"`
-	// All extra newly added state events. This is only set if there are *extra* events
-	// other than `Event`. This can happen when forks get merged because state resolution
-	// may decide a bunch of state events on one branch are now valid, so they will be
-	// present in this list. This is useful when trying to maintain the current state of a room
-	// as to do so you need to include both these events and `Event`.
-	AddStateEvents []*gomatrixserverlib.HeaderedEvent `json:"adds_state_events"`
-
+	AddsStateEventIDs []string `json:"adds_state_event_ids,omitempty"`
 	// The state event IDs that were removed from the state of the room by this event.
-	RemovesStateEventIDs []string `json:"removes_state_event_ids"`
+	RemovesStateEventIDs []string `json:"removes_state_event_ids,omitempty"`
 	// The ID of the event that was output before this event.
 	// Or the empty string if this is the first event output for this room.
 	// This is used by consumers to check if they can safely update their
@@ -145,10 +138,10 @@ type OutputNewRoomEvent struct {
 	//
 	// The state is given as a delta against the current state because they are
 	// usually either the same state, or differ by just a couple of events.
-	StateBeforeAddsEventIDs []string `json:"state_before_adds_event_ids"`
+	StateBeforeAddsEventIDs []string `json:"state_before_adds_event_ids,omitempty"`
 	// The state event IDs that are part of the current state, but not part
 	// of the state at the event.
-	StateBeforeRemovesEventIDs []string `json:"state_before_removes_event_ids"`
+	StateBeforeRemovesEventIDs []string `json:"state_before_removes_event_ids,omitempty"`
 	// The server name to use to push this event to other servers.
 	// Or empty if this event shouldn't be pushed to other servers.
 	//
@@ -167,27 +160,7 @@ type OutputNewRoomEvent struct {
 	SendAsServer string `json:"send_as_server"`
 	// The transaction ID of the send request if sent by a local user and one
 	// was specified
-	TransactionID *TransactionID `json:"transaction_id"`
-}
-
-// AddsState returns all added state events from this event.
-//
-// This function is needed because `AddStateEvents` will not include a copy of
-// the original event to save space, so you cannot use that slice alone.
-// Instead, use this function which will add the original event if it is present
-// in `AddsStateEventIDs`.
-func (ore *OutputNewRoomEvent) AddsState() []*gomatrixserverlib.HeaderedEvent {
-	includeOutputEvent := false
-	for _, id := range ore.AddsStateEventIDs {
-		if id == ore.Event.EventID() {
-			includeOutputEvent = true
-			break
-		}
-	}
-	if !includeOutputEvent {
-		return ore.AddStateEvents
-	}
-	return append(ore.AddStateEvents, ore.Event)
+	TransactionID *TransactionID `json:"transaction_id,omitempty"`
 }
 
 // An OutputOldRoomEvent is written when the roomserver receives an old event.
diff --git a/roomserver/internal/input/input_latest_events.go b/roomserver/internal/input/input_latest_events.go
index f4a52031..7e58ef9d 100644
--- a/roomserver/internal/input/input_latest_events.go
+++ b/roomserver/internal/input/input_latest_events.go
@@ -365,6 +365,7 @@ func (u *latestEventsUpdater) makeOutputNewRoomEvent() (*api.OutputEvent, error)
 		LastSentEventID: u.lastEventIDSent,
 		LatestEventIDs:  latestEventIDs,
 		TransactionID:   u.transactionID,
+		SendAsServer:    u.sendAsServer,
 	}
 
 	eventIDMap, err := u.stateEventMap()
@@ -384,51 +385,17 @@ func (u *latestEventsUpdater) makeOutputNewRoomEvent() (*api.OutputEvent, error)
 		ore.StateBeforeAddsEventIDs = append(ore.StateBeforeAddsEventIDs, eventIDMap[entry.EventNID])
 	}
 
-	ore.SendAsServer = u.sendAsServer
-
-	// include extra state events if they were added as nearly every downstream component will care about it
-	// and we'd rather not have them all hit QueryEventsByID at the same time!
-	if len(ore.AddsStateEventIDs) > 0 {
-		var err error
-		if ore.AddStateEvents, err = u.extraEventsForIDs(u.roomInfo.RoomVersion, ore.AddsStateEventIDs); err != nil {
-			return nil, fmt.Errorf("failed to load add_state_events from db: %w", err)
-		}
-	}
-
 	return &api.OutputEvent{
 		Type:         api.OutputTypeNewRoomEvent,
 		NewRoomEvent: &ore,
 	}, nil
 }
 
-// extraEventsForIDs returns the full events for the event IDs given, but does not include the current event being
-// updated.
-func (u *latestEventsUpdater) extraEventsForIDs(roomVersion gomatrixserverlib.RoomVersion, eventIDs []string) ([]*gomatrixserverlib.HeaderedEvent, error) {
-	var extraEventIDs []string
-	for _, e := range eventIDs {
-		if e == u.event.EventID() {
-			continue
-		}
-		extraEventIDs = append(extraEventIDs, e)
-	}
-	if len(extraEventIDs) == 0 {
-		return nil, nil
-	}
-	extraEvents, err := u.updater.UnsentEventsFromIDs(u.ctx, extraEventIDs)
-	if err != nil {
-		return nil, err
-	}
-	var h []*gomatrixserverlib.HeaderedEvent
-	for _, e := range extraEvents {
-		h = append(h, e.Headered(roomVersion))
-	}
-	return h, nil
-}
-
 // retrieve an event nid -> event ID map for all events that need updating
 func (u *latestEventsUpdater) stateEventMap() (map[types.EventNID]string, error) {
-	var stateEventNIDs []types.EventNID
-	var allStateEntries []types.StateEntry
+	cap := len(u.added) + len(u.removed) + len(u.stateBeforeEventRemoves) + len(u.stateBeforeEventAdds)
+	stateEventNIDs := make(types.EventNIDs, 0, cap)
+	allStateEntries := make([]types.StateEntry, 0, cap)
 	allStateEntries = append(allStateEntries, u.added...)
 	allStateEntries = append(allStateEntries, u.removed...)
 	allStateEntries = append(allStateEntries, u.stateBeforeEventRemoves...)
@@ -436,12 +403,6 @@ func (u *latestEventsUpdater) stateEventMap() (map[types.EventNID]string, error)
 	for _, entry := range allStateEntries {
 		stateEventNIDs = append(stateEventNIDs, entry.EventNID)
 	}
-	stateEventNIDs = stateEventNIDs[:util.SortAndUnique(eventNIDSorter(stateEventNIDs))]
+	stateEventNIDs = stateEventNIDs[:util.SortAndUnique(stateEventNIDs)]
 	return u.updater.EventIDs(u.ctx, stateEventNIDs)
 }
-
-type eventNIDSorter []types.EventNID
-
-func (s eventNIDSorter) Len() int           { return len(s) }
-func (s eventNIDSorter) Less(i, j int) bool { return s[i] < s[j] }
-func (s eventNIDSorter) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }