dendrite/roomserver/storage/shared/storage.go

package shared

import (
	"context"
	"database/sql"
	"encoding/json"
	"fmt"

	"github.com/matrix-org/dendrite/internal/sqlutil"
	"github.com/matrix-org/dendrite/roomserver/api"
	"github.com/matrix-org/dendrite/roomserver/storage/tables"
	"github.com/matrix-org/dendrite/roomserver/types"
	"github.com/matrix-org/gomatrixserverlib"
	"github.com/tidwall/gjson"
)

// Ideally, when we have both events we should redact the event JSON and forget about the redaction, but we currently
// don't because the redaction code is brand new. When we are more certain that redactions don't misbehave or are
// vulnerable to attacks from remote servers (e.g a server bypassing event auth rules shouldn't redact our data)
// then we should flip this to true. This will mean redactions /actually delete information irretrievably/ which
// will be necessary for compliance with the law. Note that downstream components (syncapi) WILL delete information
// in their database on receipt of a redaction. Also note that we still modify the event JSON to set the field
// unsigned.redacted_because - we just don't clear out the content fields yet.
//
// If this hasn't been done by 09/2020 this should be flipped to true.
const redactionsArePermanent = false

type Database struct {
	DB                  *sql.DB
	EventsTable         tables.Events
	EventJSONTable      tables.EventJSON
	EventTypesTable     tables.EventTypes
	EventStateKeysTable tables.EventStateKeys
	RoomsTable          tables.Rooms
	TransactionsTable   tables.Transactions
	StateSnapshotTable  tables.StateSnapshot
	StateBlockTable     tables.StateBlock
	RoomAliasesTable    tables.RoomAliases
	PrevEventsTable     tables.PreviousEvents
	InvitesTable        tables.Invites
	MembershipTable     tables.Membership
	PublishedTable      tables.Published
	RedactionsTable     tables.Redactions
}

func (d *Database) EventTypeNIDs(
	ctx context.Context, eventTypes []string,
) (map[string]types.EventTypeNID, error) {
	return d.EventTypesTable.BulkSelectEventTypeNID(ctx, eventTypes)
}

func (d *Database) EventStateKeys(
	ctx context.Context, eventStateKeyNIDs []types.EventStateKeyNID,
) (map[types.EventStateKeyNID]string, error) {
	return d.EventStateKeysTable.BulkSelectEventStateKey(ctx, eventStateKeyNIDs)
}

func (d *Database) EventStateKeyNIDs(
	ctx context.Context, eventStateKeys []string,
) (map[string]types.EventStateKeyNID, error) {
	return d.EventStateKeysTable.BulkSelectEventStateKeyNID(ctx, eventStateKeys)
}

func (d *Database) StateEntriesForEventIDs(
	ctx context.Context, eventIDs []string,
) ([]types.StateEntry, error) {
	return d.EventsTable.BulkSelectStateEventByID(ctx, eventIDs)
}

func (d *Database) StateEntriesForTuples(
	ctx context.Context,
	stateBlockNIDs []types.StateBlockNID,
	stateKeyTuples []types.StateKeyTuple,
) ([]types.StateEntryList, error) {
	return d.StateBlockTable.BulkSelectFilteredStateBlockEntries(
		ctx, stateBlockNIDs, stateKeyTuples,
	)
}

func (d *Database) AddState(
	ctx context.Context,
	roomNID types.RoomNID,
	stateBlockNIDs []types.StateBlockNID,
	state []types.StateEntry,
) (stateNID types.StateSnapshotNID, err error) {
	err = sqlutil.WithTransaction(d.DB, func(txn *sql.Tx) error {
		if len(state) > 0 {
			var stateBlockNID types.StateBlockNID
			stateBlockNID, err = d.StateBlockTable.BulkInsertStateData(ctx, txn, state)
			if err != nil {
				return err
			}
			stateBlockNIDs = append(stateBlockNIDs[:len(stateBlockNIDs):len(stateBlockNIDs)], stateBlockNID)
		}
		stateNID, err = d.StateSnapshotTable.InsertState(ctx, txn, roomNID, stateBlockNIDs)
		return err
	})
	if err != nil {
		return 0, err
	}
	return
}

func (d *Database) EventNIDs(
	ctx context.Context, eventIDs []string,
) (map[string]types.EventNID, error) {
	return d.EventsTable.BulkSelectEventNID(ctx, eventIDs)
}

func (d *Database) SetState(
	ctx context.Context, eventNID types.EventNID, stateNID types.StateSnapshotNID,
) error {
	return d.EventsTable.UpdateEventState(ctx, eventNID, stateNID)
}

func (d *Database) StateAtEventIDs(
	ctx context.Context, eventIDs []string,
) ([]types.StateAtEvent, error) {
	return d.EventsTable.BulkSelectStateAtEventByID(ctx, eventIDs)
}

func (d *Database) SnapshotNIDFromEventID(
	ctx context.Context, eventID string,
) (types.StateSnapshotNID, error) {
	_, stateNID, err := d.EventsTable.SelectEvent(ctx, nil, eventID)
	return stateNID, err
}

func (d *Database) EventIDs(
	ctx context.Context, eventNIDs []types.EventNID,
) (map[types.EventNID]string, error) {
	return d.EventsTable.BulkSelectEventID(ctx, eventNIDs)
}

func (d *Database) EventsFromIDs(ctx context.Context, eventIDs []string) ([]types.Event, error) {
	nidMap, err := d.EventNIDs(ctx, eventIDs)
	if err != nil {
		return nil, err
	}

	var nids []types.EventNID
	for _, nid := range nidMap {
		nids = append(nids, nid)
	}

	return d.Events(ctx, nids)
}

func (d *Database) RoomNID(ctx context.Context, roomID string) (types.RoomNID, error) {
	roomNID, err := d.RoomsTable.SelectRoomNID(ctx, nil, roomID)
	if err == sql.ErrNoRows {
		return 0, nil
	}
	return roomNID, err
}

func (d *Database) RoomNIDExcludingStubs(ctx context.Context, roomID string) (roomNID types.RoomNID, err error) {
	roomNID, err = d.RoomNID(ctx, roomID)
	if err != nil {
		return
	}
	latestEvents, _, err := d.RoomsTable.SelectLatestEventNIDs(ctx, nil, roomNID)
	if err != nil {
		return
	}
	if len(latestEvents) == 0 {
		roomNID = 0
		return
	}
	return
}

func (d *Database) LatestEventIDs(
	ctx context.Context, roomNID types.RoomNID,
) (references []gomatrixserverlib.EventReference, currentStateSnapshotNID types.StateSnapshotNID, depth int64, err error) {
	err = sqlutil.WithTransaction(d.DB, func(txn *sql.Tx) error {
		var eventNIDs []types.EventNID
		eventNIDs, currentStateSnapshotNID, err = d.RoomsTable.SelectLatestEventNIDs(ctx, txn, roomNID)
		if err != nil {
			return err
		}
		references, err = d.EventsTable.BulkSelectEventReference(ctx, txn, eventNIDs)
		if err != nil {
			return err
		}
		depth, err = d.EventsTable.SelectMaxEventDepth(ctx, txn, eventNIDs)
		if err != nil {
			return err
		}
		return nil
	})
	return
}

func (d *Database) StateBlockNIDs(
	ctx context.Context, stateNIDs []types.StateSnapshotNID,
) ([]types.StateBlockNIDList, error) {
	return d.StateSnapshotTable.BulkSelectStateBlockNIDs(ctx, stateNIDs)
}

func (d *Database) StateEntries(
	ctx context.Context, stateBlockNIDs []types.StateBlockNID,
) ([]types.StateEntryList, error) {
	return d.StateBlockTable.BulkSelectStateBlockEntries(ctx, stateBlockNIDs)
}

func (d *Database) GetRoomVersionForRoom(
	ctx context.Context, roomID string,
) (gomatrixserverlib.RoomVersion, error) {
	return d.RoomsTable.SelectRoomVersionForRoomID(
		ctx, nil, roomID,
	)
}

func (d *Database) GetRoomVersionForRoomNID(
	ctx context.Context, roomNID types.RoomNID,
) (gomatrixserverlib.RoomVersion, error) {
	return d.RoomsTable.SelectRoomVersionForRoomNID(
		ctx, roomNID,
	)
}

func (d *Database) SetRoomAlias(ctx context.Context, alias string, roomID string, creatorUserID string) error {
	return d.RoomAliasesTable.InsertRoomAlias(ctx, alias, roomID, creatorUserID)
}

func (d *Database) GetRoomIDForAlias(ctx context.Context, alias string) (string, error) {
	return d.RoomAliasesTable.SelectRoomIDFromAlias(ctx, alias)
}

func (d *Database) GetAliasesForRoomID(ctx context.Context, roomID string) ([]string, error) {
	return d.RoomAliasesTable.SelectAliasesFromRoomID(ctx, roomID)
}

func (d *Database) GetCreatorIDForAlias(
	ctx context.Context, alias string,
) (string, error) {
	return d.RoomAliasesTable.SelectCreatorIDFromAlias(ctx, alias)
}

func (d *Database) RemoveRoomAlias(ctx context.Context, alias string) error {
	return d.RoomAliasesTable.DeleteRoomAlias(ctx, alias)
}

func (d *Database) GetMembership(
	ctx context.Context, roomNID types.RoomNID, requestSenderUserID string,
) (membershipEventNID types.EventNID, stillInRoom bool, err error) {
	requestSenderUserNID, err := d.assignStateKeyNID(ctx, nil, requestSenderUserID)
	if err != nil {
		return
	}

	senderMembershipEventNID, senderMembership, err :=
		d.MembershipTable.SelectMembershipFromRoomAndTarget(
			ctx, roomNID, requestSenderUserNID,
		)
	if err == sql.ErrNoRows {
		// The user has never been a member of that room
		return 0, false, nil
	} else if err != nil {
		return
	}

	return senderMembershipEventNID, senderMembership == tables.MembershipStateJoin, nil
}

func (d *Database) GetMembershipEventNIDsForRoom(
	ctx context.Context, roomNID types.RoomNID, joinOnly bool, localOnly bool,
) ([]types.EventNID, error) {
	if joinOnly {
		return d.MembershipTable.SelectMembershipsFromRoomAndMembership(
			ctx, roomNID, tables.MembershipStateJoin, localOnly,
		)
	}

	return d.MembershipTable.SelectMembershipsFromRoom(ctx, roomNID, localOnly)
}

func (d *Database) GetInvitesForUser(
	ctx context.Context,
	roomNID types.RoomNID,
	targetUserNID types.EventStateKeyNID,
) (senderUserIDs []types.EventStateKeyNID, eventIDs []string, err error) {
	return d.InvitesTable.SelectInviteActiveForUserInRoom(ctx, targetUserNID, roomNID)
}

func (d *Database) Events(
	ctx context.Context, eventNIDs []types.EventNID,
) ([]types.Event, error) {
	eventJSONs, err := d.EventJSONTable.BulkSelectEventJSON(ctx, eventNIDs)
	if err != nil {
		return nil, err
	}
	results := make([]types.Event, len(eventJSONs))
	for i, eventJSON := range eventJSONs {
		var roomNID types.RoomNID
		var roomVersion gomatrixserverlib.RoomVersion
		result := &results[i]
		result.EventNID = eventJSON.EventNID
		roomNID, err = d.EventsTable.SelectRoomNIDForEventNID(ctx, eventJSON.EventNID)
		if err != nil {
			return nil, err
		}
		roomVersion, err = d.RoomsTable.SelectRoomVersionForRoomNID(ctx, roomNID)
		if err != nil {
			return nil, err
		}
		result.Event, err = gomatrixserverlib.NewEventFromTrustedJSON(
			eventJSON.EventJSON, false, roomVersion,
		)
		if err != nil {
			return nil, err
		}
	}
	if !redactionsArePermanent {
		d.applyRedactions(results)
	}
	return results, nil
}

func (d *Database) GetTransactionEventID(
	ctx context.Context, transactionID string,
	sessionID int64, userID string,
) (string, error) {
	eventID, err := d.TransactionsTable.SelectTransactionEventID(ctx, transactionID, sessionID, userID)
	if err == sql.ErrNoRows {
		return "", nil
	}
	return eventID, err
}

func (d *Database) MembershipUpdater(
	ctx context.Context, roomID, targetUserID string,
	targetLocal bool, roomVersion gomatrixserverlib.RoomVersion,
) (types.MembershipUpdater, error) {
	return NewMembershipUpdater(ctx, d, roomID, targetUserID, targetLocal, roomVersion, true)
}

func (d *Database) GetLatestEventsForUpdate(
	ctx context.Context, roomNID types.RoomNID,
) (types.RoomRecentEventsUpdater, error) {
	return NewRoomRecentEventsUpdater(d, ctx, roomNID, true)
}

func (d *Database) StoreEvent(
	ctx context.Context, event gomatrixserverlib.Event,
	txnAndSessionID *api.TransactionID, authEventNIDs []types.EventNID,
) (types.RoomNID, types.StateAtEvent, *gomatrixserverlib.Event, string, error) {
	var (
		roomNID          types.RoomNID
		eventTypeNID     types.EventTypeNID
		eventStateKeyNID types.EventStateKeyNID
		eventNID         types.EventNID
		stateNID         types.StateSnapshotNID
		redactionEvent   *gomatrixserverlib.Event
		redactedEventID  string
		err              error
	)

	err = sqlutil.WithTransaction(d.DB, func(txn *sql.Tx) error {
		if txnAndSessionID != nil {
			if err = d.TransactionsTable.InsertTransaction(
				ctx, txn, txnAndSessionID.TransactionID,
				txnAndSessionID.SessionID, event.Sender(), event.EventID(),
			); err != nil {
				return fmt.Errorf("d.TransactionsTable.InsertTransaction: %w", err)
			}
		}

		// TODO: Here we should aim to have two different code paths for new rooms
		// vs existing ones.

		// Get the default room version. If the client doesn't supply a room_version
		// then we will use our configured default to create the room.
		// https://matrix.org/docs/spec/client_server/r0.6.0#post-matrix-client-r0-createroom
		// Note that the below logic depends on the m.room.create event being the
		// first event that is persisted to the database when creating or joining a
		// room.
		var roomVersion gomatrixserverlib.RoomVersion
		if roomVersion, err = extractRoomVersionFromCreateEvent(event); err != nil {
			return fmt.Errorf("extractRoomVersionFromCreateEvent: %w", err)
		}

		if roomNID, err = d.assignRoomNID(ctx, txn, event.RoomID(), roomVersion); err != nil {
			return fmt.Errorf("d.assignRoomNID: %w", err)
		}

		if eventTypeNID, err = d.assignEventTypeNID(ctx, txn, event.Type()); err != nil {
			return fmt.Errorf("d.assignEventTypeNID: %w", err)
		}

		eventStateKey := event.StateKey()
		// Assigned a numeric ID for the state_key if there is one present.
		// Otherwise set the numeric ID for the state_key to 0.
		if eventStateKey != nil {
			if eventStateKeyNID, err = d.assignStateKeyNID(ctx, txn, *eventStateKey); err != nil {
				return fmt.Errorf("d.assignStateKeyNID: %w", err)
			}
		}

		if eventNID, stateNID, err = d.EventsTable.InsertEvent(
			ctx,
			txn,
			roomNID,
			eventTypeNID,
			eventStateKeyNID,
			event.EventID(),
			event.EventReference().EventSHA256,
			authEventNIDs,
			event.Depth(),
		); err != nil {
			if err == sql.ErrNoRows {
				// We've already inserted the event so select the numeric event ID
				eventNID, stateNID, err = d.EventsTable.SelectEvent(ctx, txn, event.EventID())
				if err != nil {
					return fmt.Errorf("d.EventsTable.SelectEvent: %w", err)
				}
			}
			if err != nil {
				return fmt.Errorf("d.EventsTable.InsertEvent: %w", err)
			}
		}

		if err = d.EventJSONTable.InsertEventJSON(ctx, txn, eventNID, event.JSON()); err != nil {
			return fmt.Errorf("d.EventJSONTable.InsertEventJSON: %w", err)
		}
		redactionEvent, redactedEventID, err = d.handleRedactions(ctx, txn, eventNID, event)
		return nil
	})
	if err != nil {
		return 0, types.StateAtEvent{}, nil, "", err
	}

	return roomNID, types.StateAtEvent{
		BeforeStateSnapshotNID: stateNID,
		StateEntry: types.StateEntry{
			StateKeyTuple: types.StateKeyTuple{
				EventTypeNID:     eventTypeNID,
				EventStateKeyNID: eventStateKeyNID,
			},
			EventNID: eventNID,
		},
	}, redactionEvent, redactedEventID, nil
}

func (d *Database) PublishRoom(ctx context.Context, roomID string, publish bool) error {
	return d.PublishedTable.UpsertRoomPublished(ctx, roomID, publish)
}

func (d *Database) GetPublishedRooms(ctx context.Context) ([]string, error) {
	return d.PublishedTable.SelectAllPublishedRooms(ctx, true)
}

func (d *Database) assignRoomNID(
	ctx context.Context, txn *sql.Tx,
	roomID string, roomVersion gomatrixserverlib.RoomVersion,
) (types.RoomNID, error) {
	// Check if we already have a numeric ID in the database.
	roomNID, err := d.RoomsTable.SelectRoomNID(ctx, txn, roomID)
	if err == sql.ErrNoRows {
		// We don't have a numeric ID so insert one into the database.
		roomNID, err = d.RoomsTable.InsertRoomNID(ctx, txn, roomID, roomVersion)
		if err == sql.ErrNoRows {
			// We raced with another insert so run the select again.
			roomNID, err = d.RoomsTable.SelectRoomNID(ctx, txn, roomID)
		}
	}
	return roomNID, err
}

func (d *Database) assignEventTypeNID(
	ctx context.Context, txn *sql.Tx, eventType string,
) (eventTypeNID types.EventTypeNID, err error) {
	// Check if we already have a numeric ID in the database.
	eventTypeNID, err = d.EventTypesTable.SelectEventTypeNID(ctx, txn, eventType)
	if err == sql.ErrNoRows {
		// We don't have a numeric ID so insert one into the database.
		eventTypeNID, err = d.EventTypesTable.InsertEventTypeNID(ctx, txn, eventType)
		if err == sql.ErrNoRows {
			// We raced with another insert so run the select again.
			eventTypeNID, err = d.EventTypesTable.SelectEventTypeNID(ctx, txn, eventType)
		}
	}
	return
}

func (d *Database) assignStateKeyNID(
	ctx context.Context, txn *sql.Tx, eventStateKey string,
) (types.EventStateKeyNID, error) {
	// Check if we already have a numeric ID in the database.
	eventStateKeyNID, err := d.EventStateKeysTable.SelectEventStateKeyNID(ctx, txn, eventStateKey)
	if err == sql.ErrNoRows {
		// We don't have a numeric ID so insert one into the database.
		eventStateKeyNID, err = d.EventStateKeysTable.InsertEventStateKeyNID(ctx, txn, eventStateKey)
		if err == sql.ErrNoRows {
			// We raced with another insert so run the select again.
			eventStateKeyNID, err = d.EventStateKeysTable.SelectEventStateKeyNID(ctx, txn, eventStateKey)
		}
	}
	return eventStateKeyNID, err
}

func extractRoomVersionFromCreateEvent(event gomatrixserverlib.Event) (
	gomatrixserverlib.RoomVersion, error,
) {
	var err error
	var roomVersion gomatrixserverlib.RoomVersion
	// Look for m.room.create events.
	if event.Type() != gomatrixserverlib.MRoomCreate {
		return gomatrixserverlib.RoomVersion(""), nil
	}
	roomVersion = gomatrixserverlib.RoomVersionV1
	var createContent gomatrixserverlib.CreateContent
	// The m.room.create event contains an optional "room_version" key in
	// the event content, so we need to unmarshal that first.
	if err = json.Unmarshal(event.Content(), &createContent); err != nil {
		return gomatrixserverlib.RoomVersion(""), err
	}
	// A room version was specified in the event content?
	if createContent.RoomVersion != nil {
		roomVersion = gomatrixserverlib.RoomVersion(*createContent.RoomVersion)
	}
	return roomVersion, err
}

// handleRedactions manages the redacted status of events. There's two cases to consider in order to comply with the spec:
// "servers should not apply or send redactions to clients until both the redaction event and original event have been seen, and are valid."
// https://matrix.org/docs/spec/rooms/v3#authorization-rules-for-events
// These cases are:
//  - This is a redaction event, redact the event it references if we know about it.
//  - This is a normal event which may have been previously redacted.
// In the first case, check if we have the referenced event then apply the redaction, else store it
// in the redactions table with validated=FALSE. In the second case, check if there is a redaction for it:
// if there is then apply the redactions and set validated=TRUE.
//
// When an event is redacted, the redacted event JSON is modified to add an `unsigned.redacted_because` field. We use this field
// when loading events to determine whether to apply redactions. This keeps the hot-path of reading events quick as we don't need
// to cross-reference with other tables when loading.
//
// Returns the redaction event and the event ID of the redacted event if this call resulted in a redaction.
func (d *Database) handleRedactions(
	ctx context.Context, txn *sql.Tx, eventNID types.EventNID, event gomatrixserverlib.Event,
) (*gomatrixserverlib.Event, string, error) {
	var err error
	isRedactionEvent := event.Type() == gomatrixserverlib.MRoomRedaction && event.StateKey() == nil
	if isRedactionEvent {
		// an event which redacts itself should be ignored
		if event.EventID() == event.Redacts() {
			return nil, "", nil
		}

		err = d.RedactionsTable.InsertRedaction(ctx, txn, tables.RedactionInfo{
			Validated:        false,
			RedactionEventID: event.EventID(),
			RedactsEventID:   event.Redacts(),
		})
		if err != nil {
			return nil, "", err
		}
	}

	redactionEvent, redactedEvent, validated, err := d.loadRedactionPair(ctx, txn, eventNID, event)
	if err != nil {
		return nil, "", err
	}
	if validated || redactedEvent == nil || redactionEvent == nil {
		// we've seen this redaction before or there is nothing to redact
		return nil, "", nil
	}
	if redactedEvent.RoomID() != redactionEvent.RoomID() {
		// redactions across rooms aren't allowed
		return nil, "", nil
	}

	// mark the event as redacted
	err = redactedEvent.SetUnsignedField("redacted_because", redactionEvent)
	if err != nil {
		return nil, "", err
	}
	if redactionsArePermanent {
		redactedEvent.Event = redactedEvent.Redact()
	}
	// overwrite the eventJSON table
	err = d.EventJSONTable.InsertEventJSON(ctx, txn, redactedEvent.EventNID, redactedEvent.JSON())
	if err != nil {
		return nil, "", err
	}

	return &redactionEvent.Event, redactedEvent.EventID(), d.RedactionsTable.MarkRedactionValidated(ctx, txn, redactionEvent.EventID(), true)
}

// loadRedactionPair returns both the redaction event and the redacted event, else nil.
func (d *Database) loadRedactionPair(
	ctx context.Context, txn *sql.Tx, eventNID types.EventNID, event gomatrixserverlib.Event,
) (*types.Event, *types.Event, bool, error) {
	var redactionEvent, redactedEvent *types.Event
	var info *tables.RedactionInfo
	var err error
	isRedactionEvent := event.Type() == gomatrixserverlib.MRoomRedaction && event.StateKey() == nil

	var eventBeingRedacted string
	if isRedactionEvent {
		eventBeingRedacted = event.Redacts()
		redactionEvent = &types.Event{
			EventNID: eventNID,
			Event:    event,
		}
	} else {
		eventBeingRedacted = event.EventID() // maybe, we'll see if we have info
		redactedEvent = &types.Event{
			EventNID: eventNID,
			Event:    event,
		}
	}

	info, err = d.RedactionsTable.SelectRedactionInfoByEventBeingRedacted(ctx, txn, eventBeingRedacted)
	if err != nil {
		return nil, nil, false, err
	}
	if info == nil {
		// this event hasn't been redacted or we don't have the redaction for it yet
		return nil, nil, false, nil
	}

	if isRedactionEvent {
		redactedEvent = d.loadEvent(ctx, info.RedactsEventID)
	} else {
		redactionEvent = d.loadEvent(ctx, info.RedactionEventID)
	}

	return redactionEvent, redactedEvent, info.Validated, nil
}

// applyRedactions will redact events that have an `unsigned.redacted_because` field.
func (d *Database) applyRedactions(events []types.Event) {
	for i := range events {
		if result := gjson.GetBytes(events[i].Unsigned(), "redacted_because"); result.Exists() {
			events[i].Event = events[i].Redact()
		}
	}
}

// loadEvent loads a single event or returns nil on any problems/missing event
func (d *Database) loadEvent(ctx context.Context, eventID string) *types.Event {
	nids, err := d.EventNIDs(ctx, []string{eventID})
	if err != nil {
		return nil
	}
	if len(nids) == 0 {
		return nil
	}
	evs, err := d.Events(ctx, []types.EventNID{nids[eventID]})
	if err != nil {
		return nil
	}
	if len(evs) != 1 {
		return nil
	}
	return &evs[0]
}