Make SendEvents return the correct event ID

src/github.com/matrix-org/dendrite/clientapi/producers/roomserver.go

@@ -37,7 +37,7 @@ func NewRoomserverProducer(inputAPI api.RoomserverInputAPI) *RoomserverProducer
 func (c *RoomserverProducer) SendEvents(
 	ctx context.Context, events []gomatrixserverlib.Event, sendAsServer gomatrixserverlib.ServerName,
 	txnID *api.TransactionID,
-) error {
+) (string, error) {
 	ires := make([]api.InputRoomEvent, len(events))
 	for i, event := range events {
 		ires[i] = api.InputRoomEvent{
@@ -55,10 +55,10 @@ func (c *RoomserverProducer) SendEvents(
 // with the state at the event as KindOutlier before it.
 func (c *RoomserverProducer) SendEventWithState(
 	ctx context.Context, state gomatrixserverlib.RespState, event gomatrixserverlib.Event,
-) error {
+) (string, error) {
 	outliers, err := state.Events()
 	if err != nil {
-		return err
+		return "", err
 	}
 
 	ires := make([]api.InputRoomEvent, len(outliers)+1)
@@ -87,16 +87,22 @@ func (c *RoomserverProducer) SendEventWithState(
 }
 
 // SendInputRoomEvents writes the given input room events to the roomserver input API.
-func (c *RoomserverProducer) SendInputRoomEvents(ctx context.Context, ires []api.InputRoomEvent) error {
+func (c *RoomserverProducer) SendInputRoomEvents(
+	ctx context.Context, ires []api.InputRoomEvent,
+) (eventID string, err error) {
 	request := api.InputRoomEventsRequest{InputRoomEvents: ires}
 	var response api.InputRoomEventsResponse
-	return c.InputAPI.InputRoomEvents(ctx, &request, &response)
+	err = c.InputAPI.InputRoomEvents(ctx, &request, &response)
+	eventID = response.EventID
+	return
 }
 
 // SendInvite writes the invite event to the roomserver input API.
 // This should only be needed for invite events that occur outside of a known room.
 // If we are in the room then the event should be sent using the SendEvents method.
-func (c *RoomserverProducer) SendInvite(ctx context.Context, inviteEvent gomatrixserverlib.Event) error {
+func (c *RoomserverProducer) SendInvite(
+	ctx context.Context, inviteEvent gomatrixserverlib.Event,
+) error {
 	request := api.InputRoomEventsRequest{
 		InputInviteEvents: []api.InputInviteEvent{{Event: inviteEvent}},
 	}

src/github.com/matrix-org/dendrite/clientapi/routing/sendevent.go

@@ -107,16 +107,18 @@ func SendEvent(
 		}
 	}
 
-	// pass the new event to the roomserver
-	if err := producer.SendEvents(
+	// pass the new event to the roomserver and receive the correct event ID
+	// event ID in case of duplicate transaction is discarded
+	eventID, err := producer.SendEvents(
 		req.Context(), []gomatrixserverlib.Event{*e}, cfg.Matrix.ServerName, txnAndDeviceID,
-	); err != nil {
+	)
+	if err != nil {
 		return httputil.LogThenError(req, err)
 	}
 
 	res := util.JSONResponse{
 		Code: http.StatusOK,
-		JSON: sendEventResponse{e.EventID()},
+		JSON: sendEventResponse{eventID},
 	}
 	// Add response to transactionsCache
 	if txnID != nil {

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

@@ -94,7 +94,9 @@ type InputRoomEventsRequest struct {
 }
 
 // InputRoomEventsResponse is a response to InputRoomEvents
-type InputRoomEventsResponse struct{}
+type InputRoomEventsResponse struct {
+	EventID string `json:"event_id"`
+}
 
 // RoomserverInputAPI is used to write events to the room server.
 type RoomserverInputAPI interface {

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

@@ -87,42 +87,38 @@ func processRoomEvent(
 	db RoomEventDatabase,
 	ow OutputRoomEventWriter,
 	input api.InputRoomEvent,
-) error {
+) (eventID string, err error) {
 	// Parse and validate the event JSON
 	event := input.Event
 
 	// Check that the event passes authentication checks and work out the numeric IDs for the auth events.
 	authEventNIDs, err := checkAuthEvents(ctx, db, event, input.AuthEventIDs)
 	if err != nil {
-		return err
+		return
 	}
 
 	if input.TransactionID != nil {
-		var eventID string
 		tdID := input.TransactionID
 		eventID, err = db.GetTransactionEventID(
 			ctx, tdID.TransactionID, tdID.DeviceID, input.Event.Sender(),
 		)
-		if err != nil {
-			return err
-		}
-
-		if eventID != "" {
-			return nil
+		// On error OR event with the transaction already processed/processesing
+		if err != nil || eventID != "" {
+			return
 		}
 	}
 
 	// Store the event
 	roomNID, stateAtEvent, err := db.StoreEvent(ctx, event, input.TransactionID, authEventNIDs)
 	if err != nil {
-		return err
+		return
 	}
 
 	if input.Kind == api.KindOutlier {
 		// For outliers we can stop after we've stored the event itself as it
 		// doesn't have any associated state to store and we don't need to
 		// notify anyone about it.
-		return nil
+		return event.EventID(), nil
 	}
 
 	if stateAtEvent.BeforeStateSnapshotNID == 0 {
@@ -130,7 +126,7 @@ func processRoomEvent(
 		// Lets calculate one.
 		err = calculateAndSetState(ctx, db, input, roomNID, &stateAtEvent, event)
 		if err != nil {
-			return err
+			return
 		}
 	}
 
@@ -140,7 +136,9 @@ func processRoomEvent(
 	}
 
 	// Update the extremities of the event graph for the room
-	return updateLatestEvents(ctx, db, ow, roomNID, stateAtEvent, event, input.SendAsServer, input.TransactionID)
+	return event.EventID(), updateLatestEvents(
+		ctx, db, ow, roomNID, stateAtEvent, event, input.SendAsServer, input.TransactionID,
+	)
 }
 
 func calculateAndSetState(

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

@@ -60,17 +60,17 @@ func (r *RoomserverInputAPI) InputRoomEvents(
 	ctx context.Context,
 	request *api.InputRoomEventsRequest,
 	response *api.InputRoomEventsResponse,
-) error {
+) (err error) {
 	// We lock as processRoomEvent can only be called once at a time
 	r.mutex.Lock()
 	defer r.mutex.Unlock()
 	for i := range request.InputRoomEvents {
-		if err := processRoomEvent(ctx, r.DB, r, request.InputRoomEvents[i]); err != nil {
+		if response.EventID, err = processRoomEvent(ctx, r.DB, r, request.InputRoomEvents[i]); err != nil {
 			return err
 		}
 	}
 	for i := range request.InputInviteEvents {
-		if err := processInviteEvent(ctx, r.DB, r, request.InputInviteEvents[i]); err != nil {
+		if err = processInviteEvent(ctx, r.DB, r, request.InputInviteEvents[i]); err != nil {
 			return err
 		}
 	}