Method LoadCombinedStateAfterEvents

roomserver/state/state.go:153–225

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.

(
	ctx context.Context, prevStates []types.StateAtEvent,
)

// and combines those snapshots together into a single list. At this point it is
// possible to run into duplicate (type, state key) tuples.
func (v *StateResolution) LoadCombinedStateAfterEvents(
	ctx context.Context, prevStates []types.StateAtEvent,
) ([]types.StateEntry, error) {
	span, ctx := opentracing.StartSpanFromContext(ctx, "StateResolution.LoadCombinedStateAfterEvents")
	defer span.Finish()

	stateNIDs := make([]types.StateSnapshotNID, len(prevStates))
	for i, state := range prevStates {
		stateNIDs[i] = state.BeforeStateSnapshotNID
	}
	// Fetch the state snapshots for the state before the each prev event from the database.
	// Deduplicate the IDs before passing them to the database.
	// There could be duplicates because the events could be state events where
	// the snapshot of the room state before them was the same.
	stateBlockNIDLists, err := v.db.StateBlockNIDs(ctx, UniqueStateSnapshotNIDs(stateNIDs))
	if err != nil {
		return nil, fmt.Errorf("v.db.StateBlockNIDs: %w", err)
	}

	var stateBlockNIDs []types.StateBlockNID
	for _, list := range stateBlockNIDLists {
		stateBlockNIDs = append(stateBlockNIDs, list.StateBlockNIDs...)
	}
	// Fetch the state entries that will be combined to create the snapshots.
	// Deduplicate the IDs before passing them to the database.
	// There could be duplicates because a block of state entries could be reused by
	// multiple snapshots.
	stateEntryLists, err := v.db.StateEntries(ctx, uniqueStateBlockNIDs(stateBlockNIDs))
	if err != nil {
		return nil, fmt.Errorf("v.db.StateEntries: %w", err)
	}
	stateBlockNIDsMap := stateBlockNIDListMap(stateBlockNIDLists)
	stateEntriesMap := stateEntryListMap(stateEntryLists)

	// Combine the entries from all the snapshots of state after each prev event into a single list.
	var combined []types.StateEntry
	for _, prevState := range prevStates {
		// Grab the list of state data NIDs for this snapshot.
		stateBlockNIDs, ok := stateBlockNIDsMap.lookup(prevState.BeforeStateSnapshotNID)
		if !ok {
			// This should only get hit if the database is corrupt.
			// It should be impossible for an event to reference a NID that doesn't exist
			panic(fmt.Errorf("corrupt DB: Missing state snapshot numeric ID %d", prevState.BeforeStateSnapshotNID))
		}

		// Combine all the state entries for this snapshot.
		// The order of state block NIDs in the list tells us the order to combine them in.
		var fullState []types.StateEntry
		for _, stateBlockNID := range stateBlockNIDs {
			entries, ok := stateEntriesMap.lookup(stateBlockNID)
			if !ok {
				// This should only get hit if the database is corrupt.
				// It should be impossible for an event to reference a NID that doesn't exist
				panic(fmt.Errorf("corrupt DB: Missing state block numeric ID %d", stateBlockNID))
			}
			fullState = append(fullState, entries...)
		}
		if prevState.IsStateEvent() && !prevState.IsRejected {