Include the state before the event in roomserver output

src/github.com/matrix-org/dendrite/roomserver/api/output.go

@@ -22,9 +22,6 @@ import (
 type OutputRoomEvent struct {
 	// The JSON bytes of the event.
 	Event []byte
-	// The state event IDs needed to determine who can see this event.
-	// This can be used to tell which users to send the event to.
-	VisibilityEventIDs []string
 	// 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.
@@ -43,6 +40,14 @@ type OutputRoomEvent struct {
 	// If the LastSentEventID doesn't match what they were expecting it to be
 	// they can use the LatestEventIDs to request the full current state.
 	LastSentEventID string
+	// The state event IDs that are part of the state at the event, but not
+	// part of the current state. Together with the StateBeforeRemovesEventIDs
+	// this can be used to construct the state before the event from the
+	// current state.
+	StateBeforeAddsEventIDs []string
+	// The state event IDs that are part of the current state, but not part
+	// of the state at the event.
+	StateBeforeRemovesEventIDs []string
 }
 
 // UnmarshalJSON implements json.Unmarshaller
@@ -52,12 +57,14 @@ func (ore *OutputRoomEvent) UnmarshalJSON(data []byte) error {
 	// We use json.RawMessage so that the event JSON is sent as JSON rather than
 	// being base64 encoded which is the default for []byte.
 	var content struct {
-		Event                *json.RawMessage
+		Event                      *json.RawMessage
-		VisibilityEventIDs   []string
+		VisibilityEventIDs         []string
-		LatestEventIDs       []string
+		LatestEventIDs             []string
-		AddsStateEventIDs    []string
+		AddsStateEventIDs          []string
-		RemovesStateEventIDs []string
+		RemovesStateEventIDs       []string
-		LastSentEventID      string
+		LastSentEventID            string
+		StateBeforeAddsEventIDs    []string
+		StateBeforeRemovesEventIDs []string
 	}
 	if err := json.Unmarshal(data, &content); err != nil {
 		return err
@@ -65,11 +72,12 @@ func (ore *OutputRoomEvent) UnmarshalJSON(data []byte) error {
 	if content.Event != nil {
 		ore.Event = []byte(*content.Event)
 	}
-	ore.VisibilityEventIDs = content.VisibilityEventIDs
 	ore.LatestEventIDs = content.LatestEventIDs
 	ore.AddsStateEventIDs = content.AddsStateEventIDs
 	ore.RemovesStateEventIDs = content.RemovesStateEventIDs
 	ore.LastSentEventID = content.LastSentEventID
+	ore.StateBeforeAddsEventIDs = content.StateBeforeAddsEventIDs
+	ore.StateBeforeRemovesEventIDs = content.StateBeforeRemovesEventIDs
 	return nil
 }
 
@@ -81,19 +89,22 @@ func (ore OutputRoomEvent) MarshalJSON() ([]byte, error) {
 	// being base64 encoded which is the default for []byte.
 	event := json.RawMessage(ore.Event)
 	content := struct {
-		Event                *json.RawMessage
+		Event                      *json.RawMessage
-		VisibilityEventIDs   []string
+		VisibilityEventIDs         []string
-		LatestEventIDs       []string
+		LatestEventIDs             []string
-		AddsStateEventIDs    []string
+		AddsStateEventIDs          []string
-		RemovesStateEventIDs []string
+		RemovesStateEventIDs       []string
-		LastSentEventID      string
+		LastSentEventID            string
+		StateBeforeAddsEventIDs    []string
+		StateBeforeRemovesEventIDs []string
 	}{
-		Event:                &event,
+		Event:                      &event,
-		VisibilityEventIDs:   ore.VisibilityEventIDs,
+		LatestEventIDs:             ore.LatestEventIDs,
-		LatestEventIDs:       ore.LatestEventIDs,
+		AddsStateEventIDs:          ore.AddsStateEventIDs,
-		AddsStateEventIDs:    ore.AddsStateEventIDs,
+		RemovesStateEventIDs:       ore.RemovesStateEventIDs,
-		RemovesStateEventIDs: ore.RemovesStateEventIDs,
+		LastSentEventID:            ore.LastSentEventID,
-		LastSentEventID:      ore.LastSentEventID,
+		StateBeforeAddsEventIDs:    ore.StateBeforeAddsEventIDs,
+		StateBeforeRemovesEventIDs: ore.StateBeforeRemovesEventIDs,
 	}
 	return json.Marshal(&content)
 }

src/github.com/matrix-org/dendrite/roomserver/input/latest_events.go

@@ -20,6 +20,7 @@ import (
 	"github.com/matrix-org/dendrite/roomserver/state"
 	"github.com/matrix-org/dendrite/roomserver/types"
 	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/util"
 )
 
 // updateLatestEvents updates the list of latest events for this room in the database and writes the
@@ -110,6 +111,13 @@ func doUpdateLatestEvents(
 		return err
 	}
 
+	stateBeforeEventRemoves, stateBeforeEventAdds, err := state.DifferenceBetweeenStateSnapshots(
+		db, newStateNID, stateAtEvent.BeforeStateSnapshotNID,
+	)
+	if err != nil {
+		return err
+	}
+
 	// Send the event to the output logs.
 	// We do this inside the database transaction to ensure that we only mark an event as sent if we sent it.
 	// (n.b. this means that it's possible that the same event will be sent twice if the transaction fails but
@@ -118,7 +126,10 @@ func doUpdateLatestEvents(
 	// send the event asynchronously but we would need to ensure that 1) the events are written to the log in
 	// the correct order, 2) that pending writes are resent across restarts. In order to avoid writing all the
 	// necessary bookkeeping we'll keep the event sending synchronous for now.
-	if err = writeEvent(db, ow, lastEventIDSent, event, newLatest, removed, added); err != nil {
+	if err = writeEvent(
+		db, ow, lastEventIDSent, event, newLatest, removed, added,
+		stateBeforeEventRemoves, stateBeforeEventAdds,
+	); err != nil {
 		return err
 	}
 
@@ -170,6 +181,7 @@ func writeEvent(
 	db RoomEventDatabase, ow OutputRoomEventWriter, lastEventIDSent string,
 	event gomatrixserverlib.Event, latest []types.StateAtEventAndReference,
 	removed, added []types.StateEntry,
+	stateBeforeEventRemoves, stateBeforeEventAdds []types.StateEntry,
 ) error {
 
 	latestEventIDs := make([]string, len(latest))
@@ -190,6 +202,13 @@ func writeEvent(
 	for _, entry := range removed {
 		stateEventNIDs = append(stateEventNIDs, entry.EventNID)
 	}
+	for _, entry := range stateBeforeEventRemoves {
+		stateEventNIDs = append(stateEventNIDs, entry.EventNID)
+	}
+	for _, entry := range stateBeforeEventAdds {
+		stateEventNIDs = append(stateEventNIDs, entry.EventNID)
+	}
+	stateEventNIDs = stateEventNIDs[:util.SortAndUnique(eventNIDSorter(stateEventNIDs))]
 	eventIDMap, err := db.EventIDs(stateEventNIDs)
 	if err != nil {
 		return err
@@ -200,7 +219,18 @@ func writeEvent(
 	for _, entry := range removed {
 		ore.RemovesStateEventIDs = append(ore.RemovesStateEventIDs, eventIDMap[entry.EventNID])
 	}
-
+	for _, entry := range stateBeforeEventRemoves {
+		ore.StateBeforeRemovesEventIDs = append(ore.StateBeforeRemovesEventIDs, eventIDMap[entry.EventNID])
+	}
+	for _, entry := range stateBeforeEventAdds {
+		ore.StateBeforeAddsEventIDs = append(ore.StateBeforeAddsEventIDs, eventIDMap[entry.EventNID])
+	}
 	// TODO: Fill out VisibilityStateIDs
 	return ow.WriteOutputRoomEvent(ore)
 }
+
+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] }