Fetch missing auth events, implement QueryMissingAuthPrevEvents, try other servers in room for /event and /get_missing_events (#1450)

* Try to ask other servers in the room for missing events if the origin won't provide them

* Logging

* More logging

* Implement QueryMissingAuthPrevEvents

* Try to get missing auth events badly

* Use processEvent

* Logging

* Update QueryMissingAuthPrevEvents

* Try to find missing auth events

* Patchy fix for test

* Logging tweaks

* Send auth events as outliers

* Update check in QueryMissingAuthPrevEvents

* Error responses

* More return codes

* Don't return error on reject/soft-fail since it was ultimately handled

* More tweaks

* More error tweaks

roomserver/api/api.go

@@ -68,6 +68,13 @@ type RoomserverInternalAPI interface {
 		response *QueryStateAfterEventsResponse,
 	) error
 
+	// Query whether the roomserver is missing any auth or prev events.
+	QueryMissingAuthPrevEvents(
+		ctx context.Context,
+		request *QueryMissingAuthPrevEventsRequest,
+		response *QueryMissingAuthPrevEventsResponse,
+	) error
+
 	// Query a list of events by event ID.
 	QueryEventsByID(
 		ctx context.Context,

roomserver/api/api_trace.go

@@ -104,6 +104,16 @@ func (t *RoomserverInternalAPITrace) QueryStateAfterEvents(
 	return err
 }
 
+func (t *RoomserverInternalAPITrace) QueryMissingAuthPrevEvents(
+	ctx context.Context,
+	req *QueryMissingAuthPrevEventsRequest,
+	res *QueryMissingAuthPrevEventsResponse,
+) error {
+	err := t.Impl.QueryMissingAuthPrevEvents(ctx, req, res)
+	util.GetLogger(ctx).WithError(err).Infof("QueryMissingAuthPrevEvents req=%+v res=%+v", js(req), js(res))
+	return err
+}
+
 func (t *RoomserverInternalAPITrace) QueryEventsByID(
 	ctx context.Context,
 	req *QueryEventsByIDRequest,

roomserver/api/query.go

@@ -82,6 +82,27 @@ type QueryStateAfterEventsResponse struct {
 	StateEvents []gomatrixserverlib.HeaderedEvent `json:"state_events"`
 }
 
+type QueryMissingAuthPrevEventsRequest struct {
+	// The room ID to query the state in.
+	RoomID string `json:"room_id"`
+	// The list of auth events to check the existence of.
+	AuthEventIDs []string `json:"auth_event_ids"`
+	// The list of previous events to check the existence of.
+	PrevEventIDs []string `json:"prev_event_ids"`
+}
+
+type QueryMissingAuthPrevEventsResponse struct {
+	// Does the room exist on this roomserver?
+	// If the room doesn't exist all other fields will be empty.
+	RoomExists bool `json:"room_exists"`
+	// The room version of the room.
+	RoomVersion gomatrixserverlib.RoomVersion `json:"room_version"`
+	// The event IDs of the auth events that we don't know locally.
+	MissingAuthEventIDs []string `json:"missing_auth_event_ids"`
+	// The event IDs of the previous events that we don't know locally.
+	MissingPrevEventIDs []string `json:"missing_prev_event_ids"`
+}
+
 // QueryEventsByIDRequest is a request to QueryEventsByID
 type QueryEventsByIDRequest struct {
 	// The event IDs to look up.
@@ -154,6 +175,8 @@ type QueryServerJoinedToRoomResponse struct {
 	RoomExists bool `json:"room_exists"`
 	// True if we still believe that we are participating in the room
 	IsInRoom bool `json:"is_in_room"`
+	// List of servers that are also in the room
+	ServerNames []gomatrixserverlib.ServerName `json:"server_names"`
 }
 
 // QueryServerAllowedToSeeEventRequest is a request to QueryServerAllowedToSeeEvent