From 868f2d5a806b5d363ce04b2033f12668cdbd8d71 Mon Sep 17 00:00:00 2001
From: Neil Alexander <neilalexander@users.noreply.github.com>
Date: Mon, 12 Oct 2020 11:20:11 +0100
Subject: [PATCH] Recursively fetch auth events if needed

---
 federationapi/routing/send.go | 92 ++++++++++++++++++++---------------
 1 file changed, 54 insertions(+), 38 deletions(-)

diff --git a/federationapi/routing/send.go b/federationapi/routing/send.go
index fe4295213..49a6a6728 100644
--- a/federationapi/routing/send.go
+++ b/federationapi/routing/send.go
@@ -112,6 +112,8 @@ type txnReq struct {
 	haveEvents map[string]*gomatrixserverlib.HeaderedEvent
 	// new events which the roomserver does not know about
 	newEvents map[string]bool
+	// servers which we should fetch missing events from
+	servers []gomatrixserverlib.ServerName
 }
 
 // A subset of FederationClient functionality that txn requires. Useful for testing.
@@ -350,7 +352,7 @@ func (t *txnReq) processEvent(ctx context.Context, e gomatrixserverlib.Event, is
 	}
 	var stateResp api.QueryMissingAuthPrevEventsResponse
 	if err := t.rsAPI.QueryMissingAuthPrevEvents(ctx, &stateReq, &stateResp); err != nil {
-		return err
+		return fmt.Errorf("t.rsAPI.QueryMissingAuthPrevEvents: %w", err)
 	}
 
 	if !stateResp.RoomExists {
@@ -366,45 +368,20 @@ func (t *txnReq) processEvent(ctx context.Context, e gomatrixserverlib.Event, is
 	if len(stateResp.MissingAuthEventIDs) > 0 {
 		logger.Infof("Event refers to %d unknown auth_events", len(stateResp.MissingAuthEventIDs))
 
-		servers := []gomatrixserverlib.ServerName{t.Origin}
-		serverReq := &api.QueryServerJoinedToRoomRequest{
-			RoomID: e.RoomID(),
-		}
-		serverRes := &api.QueryServerJoinedToRoomResponse{}
-		if err := t.rsAPI.QueryServerJoinedToRoom(ctx, serverReq, serverRes); err == nil {
-			servers = append(servers, serverRes.ServerNames...)
-			logger.Infof("Found %d server(s) to query for missing events", len(servers))
+		if len(t.servers) == 0 {
+			t.servers = []gomatrixserverlib.ServerName{t.Origin}
+			serverReq := &api.QueryServerJoinedToRoomRequest{
+				RoomID: e.RoomID(),
+			}
+			serverRes := &api.QueryServerJoinedToRoomResponse{}
+			if err := t.rsAPI.QueryServerJoinedToRoom(ctx, serverReq, serverRes); err == nil {
+				t.servers = append(t.servers, serverRes.ServerNames...)
+				logger.Infof("Found %d server(s) to query for missing events", len(t.servers))
+			}
 		}
 
-	getAuthEvent:
-		for _, missingAuthEventID := range stateResp.MissingAuthEventIDs {
-			for _, server := range servers {
-				logger.Infof("Retrieving missing auth event %q from %q", missingAuthEventID, server)
-				tx, err := t.federation.GetEvent(ctx, server, missingAuthEventID)
-				if err != nil {
-					continue // try the next server
-				}
-				ev, err := gomatrixserverlib.NewEventFromUntrustedJSON(tx.PDUs[0], stateResp.RoomVersion)
-				if err != nil {
-					logger.WithError(err).Errorf("Failed to unmarshal auth event %q", missingAuthEventID)
-					continue // try the next server
-				}
-				if err = api.SendInputRoomEvents(
-					context.Background(),
-					t.rsAPI,
-					[]api.InputRoomEvent{
-						{
-							Kind:         api.KindOutlier,
-							Event:        ev.Headered(stateResp.RoomVersion),
-							AuthEventIDs: ev.AuthEventIDs(),
-							SendAsServer: api.DoNotSendToOtherServers,
-						},
-					},
-				); err != nil {
-					logger.WithError(err).Errorf("Failed to send auth event %q to roomserver", missingAuthEventID)
-					continue getAuthEvent // move onto the next event
-				}
-			}
+		if err := t.retrieveMissingAuthEvents(ctx, e, &stateResp); err != nil {
+			return fmt.Errorf("t.retrieveMissingAuthEvents: %w", err)
 		}
 	}
 
@@ -427,6 +404,45 @@ func (t *txnReq) processEvent(ctx context.Context, e gomatrixserverlib.Event, is
 	)
 }
 
+func (t *txnReq) retrieveMissingAuthEvents(
+	ctx context.Context, e gomatrixserverlib.Event, stateResp *api.QueryMissingAuthPrevEventsResponse,
+) error {
+	logger := util.GetLogger(ctx).WithField("event_id", e.EventID()).WithField("room_id", e.RoomID())
+
+	missingAuthEvents := make(map[string]struct{})
+	for _, missingAuthEventID := range stateResp.MissingAuthEventIDs {
+		missingAuthEvents[missingAuthEventID] = struct{}{}
+	}
+
+withNextEvent:
+	for missingAuthEventID := range missingAuthEvents {
+	withNextServer:
+		for _, server := range t.servers {
+			logger.Infof("Retrieving missing auth event %q from %q", missingAuthEventID, server)
+			tx, err := t.federation.GetEvent(ctx, server, missingAuthEventID)
+			if err != nil {
+				logger.WithError(err).Warnf("Failed to retrieve auth event %q", missingAuthEventID)
+				continue withNextServer
+			}
+			ev, err := gomatrixserverlib.NewEventFromUntrustedJSON(tx.PDUs[0], stateResp.RoomVersion)
+			if err != nil {
+				logger.WithError(err).Warnf("Failed to unmarshal auth event %q", missingAuthEventID)
+				continue withNextServer
+			}
+			if err = t.processEvent(ctx, ev, false); err != nil {
+				return fmt.Errorf("recursive t.processEvent: %w", err)
+			}
+			delete(missingAuthEvents, missingAuthEventID)
+			continue withNextEvent
+		}
+	}
+
+	if missing := len(missingAuthEvents); missing > 0 {
+		return fmt.Errorf("Event refers to %d auth_events which we failed to fetch", missing)
+	}
+	return nil
+}
+
 func checkAllowedByState(e gomatrixserverlib.Event, stateEvents []gomatrixserverlib.Event) error {
 	authUsingState := gomatrixserverlib.NewAuthEvents(nil)
 	for i := range stateEvents {