Try optimising checking if server is allowed to see event

roomserver/internal/helpers/helpers.go

@@ -2,10 +2,7 @@ package helpers
 
 import (
 	"context"
-	"database/sql"
-	"errors"
 	"fmt"
-	"strings"
 
 	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/dendrite/roomserver/auth"
@@ -236,6 +233,7 @@ func LoadStateEvents(
 func CheckServerAllowedToSeeEvent(
 	ctx context.Context, db storage.Database, info *types.RoomInfo, eventID string, serverName gomatrixserverlib.ServerName, isServerInRoom bool,
 ) (bool, error) {
+	/*
 		roomState := state.NewStateResolution(db, info)
 		stateEntries, err := roomState.LoadStateAtEvent(ctx, eventID)
 		if err != nil {
@@ -284,7 +282,12 @@ func CheckServerAllowedToSeeEvent(
 		if err != nil {
 			return false, err
 		}
+	*/
 
+	stateAtEvent, err := db.GetHistoryVisibilityState(ctx, info, eventID, string(serverName))
+	if err != nil {
+		return false, err
+	}
 	return auth.IsServerAllowed(serverName, isServerInRoom, stateAtEvent), nil
 }
 

roomserver/state/state.go

@@ -124,6 +124,29 @@ func (v *StateResolution) LoadStateAtEvent(
 	return stateEntries, nil
 }
 
+// LoadStateAtEvent loads the full state of a room before a particular event.
+func (v *StateResolution) LoadStateAtEventForHistoryVisibility(
+	ctx context.Context, eventID string,
+) ([]types.StateEntry, error) {
+	span, ctx := opentracing.StartSpanFromContext(ctx, "StateResolution.LoadStateAtEvent")
+	defer span.Finish()
+
+	snapshotNID, err := v.db.SnapshotNIDFromEventID(ctx, eventID)
+	if err != nil {
+		return nil, fmt.Errorf("LoadStateAtEvent.SnapshotNIDFromEventID failed for event %s : %w", eventID, err)
+	}
+	if snapshotNID == 0 {
+		return nil, fmt.Errorf("LoadStateAtEvent.SnapshotNIDFromEventID(%s) returned 0 NID, was this event stored?", eventID)
+	}
+
+	stateEntries, err := v.LoadStateAtSnapshot(ctx, snapshotNID)
+	if err != nil {
+		return nil, err
+	}
+
+	return stateEntries, nil
+}
+
 // LoadCombinedStateAfterEvents loads a snapshot of the state after each of the events
 // and combines those snapshots together into a single list. At this point it is
 // possible to run into duplicate (type, state key) tuples.

roomserver/storage/interface.go

@@ -166,4 +166,6 @@ type Database interface {
 	GetKnownRooms(ctx context.Context) ([]string, error)
 	// ForgetRoom sets a flag in the membership table, that the user wishes to forget a specific room
 	ForgetRoom(ctx context.Context, userID, roomID string, forget bool) error
+
+	lityState(ctx context.Context, roomInfo *types.RoomInfo, eventID string, domain string) ([]*gomatrixserverlib.Event, error)
 }

roomserver/storage/postgres/state_snapshot_table.go

@@ -72,9 +72,32 @@ const bulkSelectStateBlockNIDsSQL = "" +
 	"SELECT state_snapshot_nid, state_block_nids FROM roomserver_state_snapshots" +
 	" WHERE state_snapshot_nid = ANY($1) ORDER BY state_snapshot_nid ASC"
 
+// Looks up both the history visibility event and relevant membership events from
+// a given domain name from a given state snapshot. This is used to optimise the
+// helpers.CheckServerAllowedToSeeEvent function.
+// TODO: There's a sequence scan here because of the hash join strategy, which is
+// probably O(n) on state key entries, so there must be a way to avoid that somehow.
+const bulkSelectStateForHistoryVisibilitySQL = `
+SELECT event_nid FROM (
+	SELECT event_nid, event_type_nid, event_state_key_nid FROM roomserver_events
+	WHERE (event_type_nid = 5 OR event_type_nid = 7)
+	AND event_nid = ANY(
+		SELECT UNNEST(event_nids) FROM roomserver_state_block
+		WHERE state_block_nid = ANY(
+			SELECT UNNEST(state_block_nids) FROM roomserver_state_snapshots
+			WHERE state_snapshot_nid = $1
+		)
+	)
+) AS roomserver_events
+INNER JOIN roomserver_event_state_keys
+	ON roomserver_events.event_state_key_nid = roomserver_event_state_keys.event_state_key_nid
+	AND (event_type_nid = 7 OR event_state_key LIKE '%:$2');
+`
+
 type stateSnapshotStatements struct {
 	insertStateStmt                         *sql.Stmt
 	bulkSelectStateBlockNIDsStmt            *sql.Stmt
+	bulkSelectStateForHistoryVisibilityStmt *sql.Stmt
 }
 
 func CreateStateSnapshotTable(db *sql.DB) error {
@@ -88,6 +111,7 @@ func PrepareStateSnapshotTable(db *sql.DB) (tables.StateSnapshot, error) {
 	return s, sqlutil.StatementList{
 		{&s.insertStateStmt, insertStateSQL},
 		{&s.bulkSelectStateBlockNIDsStmt, bulkSelectStateBlockNIDsSQL},
+		{&s.bulkSelectStateForHistoryVisibilityStmt, bulkSelectStateForHistoryVisibilitySQL},
 	}.Prepare(db)
 }
 
@@ -136,3 +160,26 @@ func (s *stateSnapshotStatements) BulkSelectStateBlockNIDs(
 	}
 	return results, nil
 }
+
+func (s *stateSnapshotStatements) BulkSelectStateForHistoryVisibility(
+	ctx context.Context, txn *sql.Tx, stateSnapshotNID types.StateSnapshotNID, domain string,
+) ([]types.EventNID, error) {
+	stmt := sqlutil.TxStmt(txn, s.bulkSelectStateForHistoryVisibilityStmt)
+	rows, err := stmt.QueryContext(ctx, stateSnapshotNID, domain)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close() // nolint: errcheck
+	results := make([]types.EventNID, 0, 16)
+	for i := 0; rows.Next(); i++ {
+		var eventNID types.EventNID
+		if err = rows.Scan(&eventNID); err != nil {
+			return nil, err
+		}
+		results = append(results, eventNID)
+	}
+	if err = rows.Err(); err != nil {
+		return nil, err
+	}
+	return results, nil
+}

roomserver/storage/shared/storage.go

@@ -988,6 +988,34 @@ func (d *Database) loadEvent(ctx context.Context, eventID string) *types.Event {
 	return &evs[0]
 }
 
+func (d *Database) GetHistoryVisibilityState(ctx context.Context, roomInfo *types.RoomInfo, eventID string, domain string) ([]*gomatrixserverlib.Event, error) {
+	eventStates, err := d.EventsTable.BulkSelectStateAtEventByID(ctx, nil, []string{eventID})
+	if err != nil {
+		return nil, err
+	}
+	eventNIDs, err := d.StateSnapshotTable.BulkSelectStateForHistoryVisibility(ctx, nil, eventStates[0].BeforeStateSnapshotNID, domain)
+	if err != nil {
+		return nil, err
+	}
+	eventIDs, _ := d.EventsTable.BulkSelectEventID(ctx, nil, eventNIDs)
+	if err != nil {
+		eventIDs = map[types.EventNID]string{}
+	}
+	events := make([]*gomatrixserverlib.Event, 0, len(eventNIDs))
+	for _, eventNID := range eventNIDs {
+		data, err := d.EventJSONTable.BulkSelectEventJSON(ctx, nil, []types.EventNID{eventNID})
+		if err != nil {
+			return nil, err
+		}
+		ev, err := gomatrixserverlib.NewEventFromTrustedJSONWithEventID(eventIDs[eventNID], data[0].EventJSON, false, roomInfo.RoomVersion)
+		if err != nil {
+			return nil, err
+		}
+		events = append(events, ev)
+	}
+	return events, nil
+}
+
 // GetStateEvent returns the current state event of a given type for a given room with a given state key
 // If no event could be found, returns nil
 // If there was an issue during the retrieval, returns an error

roomserver/storage/sqlite3/state_snapshot_table.go

@@ -140,3 +140,9 @@ func (s *stateSnapshotStatements) BulkSelectStateBlockNIDs(
 	}
 	return results, nil
 }
+
+func (s *stateSnapshotStatements) BulkSelectStateForHistoryVisibility(
+	ctx context.Context, txn *sql.Tx, stateSnapshotNID types.StateSnapshotNID, domain string,
+) ([]types.EventNID, error) {
+	return nil, nil
+}

roomserver/storage/tables/interface.go

@@ -80,6 +80,7 @@ type Rooms interface {
 type StateSnapshot interface {
 	InsertState(ctx context.Context, txn *sql.Tx, roomNID types.RoomNID, stateBlockNIDs types.StateBlockNIDs) (stateNID types.StateSnapshotNID, err error)
 	BulkSelectStateBlockNIDs(ctx context.Context, txn *sql.Tx, stateNIDs []types.StateSnapshotNID) ([]types.StateBlockNIDList, error)
+	BulkSelectStateForHistoryVisibility(ctx context.Context, txn *sql.Tx, stateSnapshotNID types.StateSnapshotNID, domain string) ([]types.EventNID, error)
 }
 
 type StateBlock interface {