Method loadStateAtSnapshotForNumericTuples

roomserver/state/state.go:352–395

loadStateAtSnapshotForNumericTuples loads the state for a list of event type and state key pairs at a snapshot. This is used when we only want to load a subset of the room state at a snapshot. If there is no entry for a given event type and state key pair then it will be discarded. This is typically

(
	ctx context.Context,
	stateNID types.StateSnapshotNID,
	stateKeyTuples []types.StateKeyTuple,
)

// This is typically the state before an event or the current state of a room.
// Returns a sorted list of state entries or an error if there was a problem talking to the database.
func (v *StateResolution) loadStateAtSnapshotForNumericTuples(
	ctx context.Context,
	stateNID types.StateSnapshotNID,
	stateKeyTuples []types.StateKeyTuple,
) ([]types.StateEntry, error) {
	span, ctx := opentracing.StartSpanFromContext(ctx, "StateResolution.loadStateAtSnapshotForNumericTuples")
	defer span.Finish()

	stateBlockNIDLists, err := v.db.StateBlockNIDs(ctx, []types.StateSnapshotNID{stateNID})
	if err != nil {
		return nil, err
	}
	// We've asked for exactly one snapshot from the db so we should have exactly one entry in the result.
	stateBlockNIDList := stateBlockNIDLists[0]

	stateEntryLists, err := v.db.StateEntriesForTuples(
		ctx, stateBlockNIDList.StateBlockNIDs, stateKeyTuples,
	)
	if err != nil {
		return nil, err
	}
	stateEntriesMap := stateEntryListMap(stateEntryLists)

	// 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 stateBlockNIDList.StateBlockNIDs {
		entries, ok := stateEntriesMap.lookup(stateBlockNID)
		if !ok {
			// If the block is missing from the map it means that none of its entries matched a requested tuple.
			// This can happen if the block doesn't contain an update for one of the requested tuples.
			// If none of the requested tuples are in the block then it can be safely skipped.
			continue
		}
		fullState = append(fullState, entries...)
	}

	// Stable sort so that the most recent entry for each state key stays
	// remains later in the list than the older entries for the same state key.
	sort.Stable(stateEntryByStateKeySorter(fullState))
	// Unique returns the last entry and hence the most recent entry for each state key.
	fullState = fullState[:util.Unique(stateEntryByStateKeySorter(fullState))]
	return fullState, nil
}

// LoadStateAfterEventsForStringTuples loads the state for a list of event type
// and state key pairs after list of events.