dendrite/roomserver/internal/perform/perform_upgrade.go

// Copyright 2022 The Matrix.org Foundation C.I.C.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package perform

import (
	"context"
	"encoding/json"
	"fmt"
	"time"

	"github.com/matrix-org/dendrite/internal/eventutil"
	"github.com/matrix-org/dendrite/roomserver/api"
	"github.com/matrix-org/dendrite/roomserver/types"
	"github.com/matrix-org/dendrite/setup/config"
	"github.com/matrix-org/gomatrixserverlib"
	"github.com/matrix-org/gomatrixserverlib/spec"
	"github.com/matrix-org/util"
	"github.com/sirupsen/logrus"
)

type Upgrader struct {
	Cfg    *config.RoomServer
	URSAPI api.RoomserverInternalAPI
}

// PerformRoomUpgrade upgrades a room from one version to another
func (r *Upgrader) PerformRoomUpgrade(
	ctx context.Context,
	roomID string, userID spec.UserID, roomVersion gomatrixserverlib.RoomVersion,
) (newRoomID string, err error) {
	return r.performRoomUpgrade(ctx, roomID, userID, roomVersion)
}

func (r *Upgrader) performRoomUpgrade(
	ctx context.Context,
	roomID string, userID spec.UserID, roomVersion gomatrixserverlib.RoomVersion,
) (string, error) {
	evTime := time.Now()

	// Return an immediate error if the room does not exist
	if err := r.validateRoomExists(ctx, roomID); err != nil {
		return "", err
	}

	fullRoomID, err := spec.NewRoomID(roomID)
	if err != nil {
		return "", err
	}
	senderID, err := r.URSAPI.QuerySenderIDForUser(ctx, *fullRoomID, userID)
	if err != nil {
		util.GetLogger(ctx).WithError(err).Error("Failed getting senderID for user")
		return "", err
	}

	// 1. Check if the user is authorized to actually perform the upgrade (can send m.room.tombstone)
	if !r.userIsAuthorized(ctx, senderID, roomID) {
		return "", api.ErrNotAllowed{Err: fmt.Errorf("You don't have permission to upgrade the room, power level too low.")}
	}

	// TODO (#267): Check room ID doesn't clash with an existing one, and we
	//              probably shouldn't be using pseudo-random strings, maybe GUIDs?
	newRoomID := fmt.Sprintf("!%s:%s", util.RandomString(16), userID.Domain())

	// Get the existing room state for the old room.
	oldRoomReq := &api.QueryLatestEventsAndStateRequest{
		RoomID: roomID,
	}
	oldRoomRes := &api.QueryLatestEventsAndStateResponse{}
	if err := r.URSAPI.QueryLatestEventsAndState(ctx, oldRoomReq, oldRoomRes); err != nil {
		return "", fmt.Errorf("Failed to get latest state: %s", err)
	}

	// Make the tombstone event
	tombstoneEvent, pErr := r.makeTombstoneEvent(ctx, evTime, senderID, userID.Domain(), roomID, newRoomID)
	if pErr != nil {
		return "", pErr
	}

	// Generate the initial events we need to send into the new room. This includes copied state events and bans
	// as well as the power level events needed to set up the room
	eventsToMake, pErr := r.generateInitialEvents(ctx, oldRoomRes, senderID, roomID, roomVersion, tombstoneEvent)
	if pErr != nil {
		return "", pErr
	}

	// Send the setup events to the new room
	if pErr = r.sendInitialEvents(ctx, evTime, senderID, userID.Domain(), newRoomID, roomVersion, eventsToMake); pErr != nil {
		return "", pErr
	}

	// 5. Send the tombstone event to the old room
	if pErr = r.sendHeaderedEvent(ctx, userID.Domain(), tombstoneEvent, string(userID.Domain())); pErr != nil {
		return "", pErr
	}

	// If the old room was public, make sure the new one is too
	if pErr = r.publishIfOldRoomWasPublic(ctx, roomID, newRoomID); pErr != nil {
		return "", pErr
	}

	// If the old room had a canonical alias event, it should be deleted in the old room
	if pErr = r.clearOldCanonicalAliasEvent(ctx, oldRoomRes, evTime, senderID, userID.Domain(), roomID); pErr != nil {
		return "", pErr
	}

	// 4. Move local aliases to the new room
	if pErr = moveLocalAliases(ctx, roomID, newRoomID, senderID, r.URSAPI); pErr != nil {
		return "", pErr
	}

	// 6. Restrict power levels in the old room
	if pErr = r.restrictOldRoomPowerLevels(ctx, evTime, senderID, userID.Domain(), roomID); pErr != nil {
		return "", pErr
	}

	return newRoomID, nil
}

func (r *Upgrader) getRoomPowerLevels(ctx context.Context, roomID string) (*gomatrixserverlib.PowerLevelContent, error) {
	oldPowerLevelsEvent := api.GetStateEvent(ctx, r.URSAPI, roomID, gomatrixserverlib.StateKeyTuple{
		EventType: spec.MRoomPowerLevels,
		StateKey:  "",
	})
	return oldPowerLevelsEvent.PowerLevels()
}

func (r *Upgrader) restrictOldRoomPowerLevels(ctx context.Context, evTime time.Time, senderID spec.SenderID, userDomain spec.ServerName, roomID string) error {
	restrictedPowerLevelContent, pErr := r.getRoomPowerLevels(ctx, roomID)
	if pErr != nil {
		return pErr
	}

	// From: https://spec.matrix.org/v1.2/client-server-api/#server-behaviour-16
	// If possible, the power levels in the old room should also be modified to
	// prevent sending of events and inviting new users. For example, setting
	// events_default and invite to the greater of 50 and users_default + 1.
	restrictedDefaultPowerLevel := int64(50)
	if restrictedPowerLevelContent.UsersDefault+1 > restrictedDefaultPowerLevel {
		restrictedDefaultPowerLevel = restrictedPowerLevelContent.UsersDefault + 1
	}
	restrictedPowerLevelContent.EventsDefault = restrictedDefaultPowerLevel
	restrictedPowerLevelContent.Invite = restrictedDefaultPowerLevel

	restrictedPowerLevelsHeadered, resErr := r.makeHeaderedEvent(ctx, evTime, senderID, userDomain, roomID, gomatrixserverlib.FledglingEvent{
		Type:     spec.MRoomPowerLevels,
		StateKey: "",
		Content:  restrictedPowerLevelContent,
	})

	switch resErr.(type) {
	case api.ErrNotAllowed:
		util.GetLogger(ctx).WithField(logrus.ErrorKey, resErr).Warn("UpgradeRoom: Could not restrict power levels in old room")
	case nil:
		return r.sendHeaderedEvent(ctx, userDomain, restrictedPowerLevelsHeadered, api.DoNotSendToOtherServers)
	default:
		return resErr
	}
	return nil
}

func moveLocalAliases(ctx context.Context,
	roomID, newRoomID string, senderID spec.SenderID,
	URSAPI api.RoomserverInternalAPI,
) (err error) {

	aliasReq := api.GetAliasesForRoomIDRequest{RoomID: roomID}
	aliasRes := api.GetAliasesForRoomIDResponse{}
	if err = URSAPI.GetAliasesForRoomID(ctx, &aliasReq, &aliasRes); err != nil {
		return fmt.Errorf("Failed to get old room aliases: %w", err)
	}

	// TODO: this should be spec.RoomID further up the call stack
	parsedNewRoomID, err := spec.NewRoomID(newRoomID)
	if err != nil {
		return err
	}

	for _, alias := range aliasRes.Aliases {
		aliasFound, aliasRemoved, err := URSAPI.RemoveRoomAlias(ctx, senderID, alias)
		if err != nil {
			return fmt.Errorf("Failed to remove old room alias: %w", err)
		} else if !aliasFound {
			return fmt.Errorf("Failed to remove old room alias: alias not found, possible race")
		} else if !aliasRemoved {
			return fmt.Errorf("Failed to remove old alias")
		}

		aliasAlreadyExists, err := URSAPI.SetRoomAlias(ctx, senderID, *parsedNewRoomID, alias)
		if err != nil {
			return fmt.Errorf("Failed to set new room alias: %w", err)
		} else if aliasAlreadyExists {
			return fmt.Errorf("Failed to set new room alias: alias exists when it should have just been removed")
		}
	}
	return nil
}

func (r *Upgrader) clearOldCanonicalAliasEvent(ctx context.Context, oldRoom *api.QueryLatestEventsAndStateResponse, evTime time.Time, senderID spec.SenderID, userDomain spec.ServerName, roomID string) error {
	for _, event := range oldRoom.StateEvents {
		if event.Type() != spec.MRoomCanonicalAlias || !event.StateKeyEquals("") {
			continue
		}
		var aliasContent struct {
			Alias      string   `json:"alias"`
			AltAliases []string `json:"alt_aliases"`
		}
		if err := json.Unmarshal(event.Content(), &aliasContent); err != nil {
			return fmt.Errorf("failed to unmarshal canonical aliases: %w", err)
		}
		if aliasContent.Alias == "" && len(aliasContent.AltAliases) == 0 {
			// There are no canonical aliases to clear, therefore do nothing.
			return nil
		}
	}

	emptyCanonicalAliasEvent, resErr := r.makeHeaderedEvent(ctx, evTime, senderID, userDomain, roomID, gomatrixserverlib.FledglingEvent{
		Type:    spec.MRoomCanonicalAlias,
		Content: map[string]interface{}{},
	})
	switch resErr.(type) {
	case api.ErrNotAllowed:
		util.GetLogger(ctx).WithField(logrus.ErrorKey, resErr).Warn("UpgradeRoom: Could not set empty canonical alias event in old room")
	case nil:
		return r.sendHeaderedEvent(ctx, userDomain, emptyCanonicalAliasEvent, api.DoNotSendToOtherServers)
	default:
		return resErr
	}
	return nil
}

func (r *Upgrader) publishIfOldRoomWasPublic(ctx context.Context, roomID, newRoomID string) error {
	// check if the old room was published
	var pubQueryRes api.QueryPublishedRoomsResponse
	err := r.URSAPI.QueryPublishedRooms(ctx, &api.QueryPublishedRoomsRequest{
		RoomID: roomID,
	}, &pubQueryRes)
	if err != nil {
		return err
	}

	// if the old room is published (was public), publish the new room
	if len(pubQueryRes.RoomIDs) == 1 {
		publishNewRoomAndUnpublishOldRoom(ctx, r.URSAPI, roomID, newRoomID)
	}
	return nil
}

func publishNewRoomAndUnpublishOldRoom(
	ctx context.Context,
	URSAPI api.RoomserverInternalAPI,
	oldRoomID, newRoomID string,
) {
	// expose this room in the published room list
	if err := URSAPI.PerformPublish(ctx, &api.PerformPublishRequest{
		RoomID:     newRoomID,
		Visibility: spec.Public,
	}); err != nil {
		// treat as non-fatal since the room is already made by this point
		util.GetLogger(ctx).WithError(err).Error("failed to publish room")
	}

	// remove the old room from the published room list
	if err := URSAPI.PerformPublish(ctx, &api.PerformPublishRequest{
		RoomID:     oldRoomID,
		Visibility: "private",
	}); err != nil {
		// treat as non-fatal since the room is already made by this point
		util.GetLogger(ctx).WithError(err).Error("failed to un-publish room")
	}
}

func (r *Upgrader) validateRoomExists(ctx context.Context, roomID string) error {
	if _, err := r.URSAPI.QueryRoomVersionForRoom(ctx, roomID); err != nil {
		return eventutil.ErrRoomNoExists{}
	}
	return nil
}

func (r *Upgrader) userIsAuthorized(ctx context.Context, senderID spec.SenderID, roomID string,
) bool {
	plEvent := api.GetStateEvent(ctx, r.URSAPI, roomID, gomatrixserverlib.StateKeyTuple{
		EventType: spec.MRoomPowerLevels,
		StateKey:  "",
	})
	if plEvent == nil {
		return false
	}
	pl, err := plEvent.PowerLevels()
	if err != nil {
		return false
	}
	// Check for power level required to send tombstone event (marks the current room as obsolete),
	// if not found, use the StateDefault power level
	return pl.UserLevel(senderID) >= pl.EventLevel("m.room.tombstone", true)
}

// nolint:gocyclo
func (r *Upgrader) generateInitialEvents(ctx context.Context, oldRoom *api.QueryLatestEventsAndStateResponse, senderID spec.SenderID, roomID string, newVersion gomatrixserverlib.RoomVersion, tombstoneEvent *types.HeaderedEvent) ([]gomatrixserverlib.FledglingEvent, error) {
	state := make(map[gomatrixserverlib.StateKeyTuple]*types.HeaderedEvent, len(oldRoom.StateEvents))
	for _, event := range oldRoom.StateEvents {
		if event.StateKey() == nil {
			// This shouldn't ever happen, but better to be safe than sorry.
			continue
		}
		if event.Type() == spec.MRoomMember && !event.StateKeyEquals(string(senderID)) {
			// With the exception of bans which we do want to copy, we
			// should ignore membership events that aren't our own, as event auth will
			// prevent us from being able to create membership events on behalf of other
			// users anyway unless they are invites or bans.
			membership, err := event.Membership()
			if err != nil {
				continue
			}
			switch membership {
			case spec.Ban:
			default:
				continue
			}
		}
		// skip events that rely on a specific user being present
		// TODO: What to do here for pseudoIDs? It's checking non-member events for state keys with userIDs.
		sKey := *event.StateKey()
		if event.Type() != spec.MRoomMember && len(sKey) > 0 && sKey[:1] == "@" {
			continue
		}
		state[gomatrixserverlib.StateKeyTuple{EventType: event.Type(), StateKey: *event.StateKey()}] = event
	}

	// The following events are ones that we are going to override manually
	// in the following section.
	override := map[gomatrixserverlib.StateKeyTuple]struct{}{
		{EventType: spec.MRoomCreate, StateKey: ""}:               {},
		{EventType: spec.MRoomMember, StateKey: string(senderID)}: {},
		{EventType: spec.MRoomPowerLevels, StateKey: ""}:          {},
		{EventType: spec.MRoomJoinRules, StateKey: ""}:            {},
	}

	// The overridden events are essential events that must be present in the
	// old room state. Check that they are there.
	for tuple := range override {
		if _, ok := state[tuple]; !ok {
			return nil, fmt.Errorf("essential event of type %q state key %q is missing", tuple.EventType, tuple.StateKey)
		}
	}

	oldCreateEvent := state[gomatrixserverlib.StateKeyTuple{EventType: spec.MRoomCreate, StateKey: ""}]
	oldMembershipEvent := state[gomatrixserverlib.StateKeyTuple{EventType: spec.MRoomMember, StateKey: string(senderID)}]
	oldPowerLevelsEvent := state[gomatrixserverlib.StateKeyTuple{EventType: spec.MRoomPowerLevels, StateKey: ""}]
	oldJoinRulesEvent := state[gomatrixserverlib.StateKeyTuple{EventType: spec.MRoomJoinRules, StateKey: ""}]

	// Create the new room create event. Using a map here instead of CreateContent
	// means that we preserve any other interesting fields that might be present
	// in the create event (such as for the room types MSC).
	newCreateContent := map[string]interface{}{}
	_ = json.Unmarshal(oldCreateEvent.Content(), &newCreateContent)
	newCreateContent["creator"] = string(senderID)
	newCreateContent["room_version"] = newVersion
	newCreateContent["predecessor"] = gomatrixserverlib.PreviousRoom{
		EventID: tombstoneEvent.EventID(),
		RoomID:  roomID,
	}
	newCreateEvent := gomatrixserverlib.FledglingEvent{
		Type:     spec.MRoomCreate,
		StateKey: "",
		Content:  newCreateContent,
	}

	// Now create the new membership event. Same rules apply as above, so
	// that we preserve fields we don't otherwise know about. We'll always
	// set the membership to join though, because that is necessary to auth
	// the events after it.
	newMembershipContent := map[string]interface{}{}
	_ = json.Unmarshal(oldMembershipEvent.Content(), &newMembershipContent)
	newMembershipContent["membership"] = spec.Join
	newMembershipEvent := gomatrixserverlib.FledglingEvent{
		Type:     spec.MRoomMember,
		StateKey: string(senderID),
		Content:  newMembershipContent,
	}

	// We might need to temporarily give ourselves a higher power level
	// than we had in the old room in order to be able to send all of
	// the relevant state events. This function will return whether we
	// had to override the power level events or not — if we did, we
	// need to send the original power levels again later on.
	powerLevelContent, err := oldPowerLevelsEvent.PowerLevels()
	if err != nil {
		util.GetLogger(ctx).WithError(err).Error()
		return nil, fmt.Errorf("Power level event content was invalid")
	}

	tempPowerLevelsEvent, powerLevelsOverridden := createTemporaryPowerLevels(powerLevelContent, senderID)

	// Now do the join rules event, same as the create and membership
	// events. We'll set a sane default of "invite" so that if the
	// existing join rules contains garbage, the room can still be
	// upgraded.
	newJoinRulesContent := map[string]interface{}{
		"join_rule": spec.Invite, // sane default
	}
	_ = json.Unmarshal(oldJoinRulesEvent.Content(), &newJoinRulesContent)
	newJoinRulesEvent := gomatrixserverlib.FledglingEvent{
		Type:     spec.MRoomJoinRules,
		StateKey: "",
		Content:  newJoinRulesContent,
	}

	eventsToMake := make([]gomatrixserverlib.FledglingEvent, 0, len(state))
	eventsToMake = append(
		eventsToMake, newCreateEvent, newMembershipEvent,
		tempPowerLevelsEvent, newJoinRulesEvent,
	)

	// For some reason Sytest expects there to be a guest access event.
	// Create one if it doesn't exist.
	if _, ok := state[gomatrixserverlib.StateKeyTuple{EventType: spec.MRoomGuestAccess, StateKey: ""}]; !ok {
		eventsToMake = append(eventsToMake, gomatrixserverlib.FledglingEvent{
			Type: spec.MRoomGuestAccess,
			Content: map[string]string{
				"guest_access": "forbidden",
			},
		})
	}

	// Duplicate all of the old state events into the new room.
	for tuple, event := range state {
		if _, ok := override[tuple]; ok {
			// Don't duplicate events we have overridden already. They
			// are already in `eventsToMake`.
			continue
		}
		newEvent := gomatrixserverlib.FledglingEvent{
			Type:     tuple.EventType,
			StateKey: tuple.StateKey,
		}
		if err = json.Unmarshal(event.Content(), &newEvent.Content); err != nil {
			logrus.WithError(err).Error("Failed to unmarshal old event")
			continue
		}
		eventsToMake = append(eventsToMake, newEvent)
	}

	// If we sent a temporary power level event into the room before,
	// override that now by restoring the original power levels.
	if powerLevelsOverridden {
		eventsToMake = append(eventsToMake, gomatrixserverlib.FledglingEvent{
			Type:    spec.MRoomPowerLevels,
			Content: powerLevelContent,
		})
	}
	return eventsToMake, nil
}

func (r *Upgrader) sendInitialEvents(ctx context.Context, evTime time.Time, senderID spec.SenderID, userDomain spec.ServerName, newRoomID string, newVersion gomatrixserverlib.RoomVersion, eventsToMake []gomatrixserverlib.FledglingEvent) error {
	var err error
	var builtEvents []*types.HeaderedEvent
	authEvents := gomatrixserverlib.NewAuthEvents(nil)
	for i, e := range eventsToMake {
		depth := i + 1 // depth starts at 1

		proto := gomatrixserverlib.ProtoEvent{
			SenderID: string(senderID),
			RoomID:   newRoomID,
			Type:     e.Type,
			StateKey: &e.StateKey,
			Depth:    int64(depth),
		}
		err = proto.SetContent(e.Content)
		if err != nil {
			return fmt.Errorf("failed to set content of new %q event: %w", proto.Type, err)
		}
		if i > 0 {
			proto.PrevEvents = []string{builtEvents[i-1].EventID()}
		}

		var verImpl gomatrixserverlib.IRoomVersion
		verImpl, err = gomatrixserverlib.GetRoomVersion(newVersion)
		if err != nil {
			return err
		}
		builder := verImpl.NewEventBuilderFromProtoEvent(&proto)
		if err = builder.AddAuthEvents(&authEvents); err != nil {
			return err
		}

		var event gomatrixserverlib.PDU
		event, err = builder.Build(evTime, userDomain, r.Cfg.Matrix.KeyID, r.Cfg.Matrix.PrivateKey)
		if err != nil {
			return fmt.Errorf("failed to build new %q event: %w", builder.Type, err)

		}

		if err = gomatrixserverlib.Allowed(event, &authEvents, func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
			return r.URSAPI.QueryUserIDForSender(ctx, roomID, senderID)
		}); err != nil {
			return fmt.Errorf("Failed to auth new %q event: %w", builder.Type, err)
		}

		// Add the event to the list of auth events
		builtEvents = append(builtEvents, &types.HeaderedEvent{PDU: event})
		err = authEvents.AddEvent(event)
		if err != nil {
			return fmt.Errorf("failed to add new %q event to auth set: %w", builder.Type, err)
		}
	}

	inputs := make([]api.InputRoomEvent, 0, len(builtEvents))
	for _, event := range builtEvents {
		inputs = append(inputs, api.InputRoomEvent{
			Kind:         api.KindNew,
			Event:        event,
			Origin:       userDomain,
			SendAsServer: api.DoNotSendToOtherServers,
		})
	}
	if err = api.SendInputRoomEvents(ctx, r.URSAPI, userDomain, inputs, false); err != nil {
		return fmt.Errorf("failed to send new room %q to roomserver: %w", newRoomID, err)
	}
	return nil
}

func (r *Upgrader) makeTombstoneEvent(
	ctx context.Context,
	evTime time.Time,
	senderID spec.SenderID, senderDomain spec.ServerName, roomID, newRoomID string,
) (*types.HeaderedEvent, error) {
	content := map[string]interface{}{
		"body":             "This room has been replaced",
		"replacement_room": newRoomID,
	}
	event := gomatrixserverlib.FledglingEvent{
		Type:    "m.room.tombstone",
		Content: content,
	}
	return r.makeHeaderedEvent(ctx, evTime, senderID, senderDomain, roomID, event)
}

func (r *Upgrader) makeHeaderedEvent(ctx context.Context, evTime time.Time, senderID spec.SenderID, senderDomain spec.ServerName, roomID string, event gomatrixserverlib.FledglingEvent) (*types.HeaderedEvent, error) {
	proto := gomatrixserverlib.ProtoEvent{
		SenderID: string(senderID),
		RoomID:   roomID,
		Type:     event.Type,
		StateKey: &event.StateKey,
	}
	err := proto.SetContent(event.Content)
	if err != nil {
		return nil, fmt.Errorf("failed to set new %q event content: %w", proto.Type, err)
	}
	// Get the sender domain.
	identity, err := r.Cfg.Matrix.SigningIdentityFor(senderDomain)
	if err != nil {
		return nil, fmt.Errorf("failed to get signing identity for %q: %w", senderDomain, err)
	}
	var queryRes api.QueryLatestEventsAndStateResponse
	headeredEvent, err := eventutil.QueryAndBuildEvent(ctx, &proto, identity, evTime, r.URSAPI, &queryRes)
	switch e := err.(type) {
	case nil:
	case eventutil.ErrRoomNoExists:
		return nil, e
	case gomatrixserverlib.BadJSONError:
		return nil, e
	case gomatrixserverlib.EventValidationError:
		return nil, e
	default:
		return nil, fmt.Errorf("failed to build new %q event: %w", proto.Type, err)
	}

	// check to see if this user can perform this operation
	stateEvents := make([]gomatrixserverlib.PDU, len(queryRes.StateEvents))
	for i := range queryRes.StateEvents {
		stateEvents[i] = queryRes.StateEvents[i].PDU
	}
	provider := gomatrixserverlib.NewAuthEvents(stateEvents)
	if err = gomatrixserverlib.Allowed(headeredEvent.PDU, &provider, func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
		return r.URSAPI.QueryUserIDForSender(ctx, roomID, senderID)
	}); err != nil {
		return nil, api.ErrNotAllowed{Err: fmt.Errorf("failed to auth new %q event: %w", proto.Type, err)} // TODO: Is this error string comprehensible to the client?
	}

	return headeredEvent, nil
}

func createTemporaryPowerLevels(powerLevelContent *gomatrixserverlib.PowerLevelContent, senderID spec.SenderID) (gomatrixserverlib.FledglingEvent, bool) {
	// Work out what power level we need in order to be able to send events
	// of all types into the room.
	neededPowerLevel := powerLevelContent.StateDefault
	for _, powerLevel := range powerLevelContent.Events {
		if powerLevel > neededPowerLevel {
			neededPowerLevel = powerLevel
		}
	}

	// Make a copy of the existing power level content.
	tempPowerLevelContent := *powerLevelContent
	powerLevelsOverridden := false

	// At this point, the "Users", "Events" and "Notifications" keys are all
	// pointing to the map of the original PL content, so we will specifically
	// override the users map with a new one and duplicate the values deeply,
	// so that we can modify them without modifying the original.
	tempPowerLevelContent.Users = make(map[string]int64, len(powerLevelContent.Users))
	for key, value := range powerLevelContent.Users {
		tempPowerLevelContent.Users[key] = value
	}

	// If the user who is upgrading the room doesn't already have sufficient
	// power, then elevate their power levels.
	if tempPowerLevelContent.UserLevel(senderID) < neededPowerLevel {
		tempPowerLevelContent.Users[string(senderID)] = neededPowerLevel
		powerLevelsOverridden = true
	}

	// Then return the temporary power levels event.
	return gomatrixserverlib.FledglingEvent{
		Type:    spec.MRoomPowerLevels,
		Content: tempPowerLevelContent,
	}, powerLevelsOverridden
}

func (r *Upgrader) sendHeaderedEvent(
	ctx context.Context,
	serverName spec.ServerName,
	headeredEvent *types.HeaderedEvent,
	sendAsServer string,
) error {
	var inputs []api.InputRoomEvent
	inputs = append(inputs, api.InputRoomEvent{
		Kind:         api.KindNew,
		Event:        headeredEvent,
		Origin:       serverName,
		SendAsServer: sendAsServer,
	})
	return api.SendInputRoomEvents(ctx, r.URSAPI, serverName, inputs, false)
}