matrix-js-sdk/src/rust-crypto/rust-crypto.ts

/*
Copyright 2022-2023 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.
*/

import * as RustSdkCryptoJs from "@matrix-org/matrix-sdk-crypto-js";

import type { IEventDecryptionResult, IMegolmSessionData } from "../@types/crypto";
import type { IDeviceLists, IToDeviceEvent } from "../sync-accumulator";
import type { IEncryptedEventInfo } from "../crypto/api";
import { MatrixEvent } from "../models/event";
import { Room } from "../models/room";
import { RoomMember } from "../models/room-member";
import { CryptoBackend, OnSyncCompletedData } from "../common-crypto/CryptoBackend";
import { logger } from "../logger";
import { IHttpOpts, MatrixHttpApi, Method } from "../http-api";
import { UserTrustLevel } from "../crypto/CrossSigning";
import { RoomEncryptor } from "./RoomEncryptor";
import { OutgoingRequest, OutgoingRequestProcessor } from "./OutgoingRequestProcessor";
import { KeyClaimManager } from "./KeyClaimManager";
import { MapWithDefault } from "../utils";
import {
    BootstrapCrossSigningOpts,
    CrossSigningStatus,
    DeviceVerificationStatus,
    ImportRoomKeyProgressData,
    ImportRoomKeysOpts,
} from "../crypto-api";
import { deviceKeysToDeviceMap, rustDeviceToJsDevice } from "./device-converter";
import { IDownloadKeyResult, IQueryKeysRequest } from "../client";
import { Device, DeviceMap } from "../models/device";
import { ServerSideSecretStorage } from "../secret-storage";
import { CrossSigningKey } from "../crypto/api";
import { CrossSigningIdentity } from "./CrossSigningIdentity";
import { secretStorageContainsCrossSigningKeys } from "./secret-storage";

/**
 * An implementation of {@link CryptoBackend} using the Rust matrix-sdk-crypto.
 */
export class RustCrypto implements CryptoBackend {
    public globalErrorOnUnknownDevices = false;
    private _trustCrossSignedDevices = true;

    /** whether {@link stop} has been called */
    private stopped = false;

    /** whether {@link outgoingRequestLoop} is currently running */
    private outgoingRequestLoopRunning = false;

    /** mapping of roomId → encryptor class */
    private roomEncryptors: Record<string, RoomEncryptor> = {};

    private eventDecryptor: EventDecryptor;
    private keyClaimManager: KeyClaimManager;
    private outgoingRequestProcessor: OutgoingRequestProcessor;
    private crossSigningIdentity: CrossSigningIdentity;

    public constructor(
        /** The `OlmMachine` from the underlying rust crypto sdk. */
        private readonly olmMachine: RustSdkCryptoJs.OlmMachine,

        /**
         * Low-level HTTP interface: used to make outgoing requests required by the rust SDK.
         *
         * We expect it to set the access token, etc.
         */
        private readonly http: MatrixHttpApi<IHttpOpts & { onlyData: true }>,

        /** The local user's User ID. */
        private readonly userId: string,

        /** The local user's Device ID. */
        _deviceId: string,

        /** Interface to server-side secret storage */
        private readonly secretStorage: ServerSideSecretStorage,
    ) {
        this.outgoingRequestProcessor = new OutgoingRequestProcessor(olmMachine, http);
        this.keyClaimManager = new KeyClaimManager(olmMachine, this.outgoingRequestProcessor);
        this.eventDecryptor = new EventDecryptor(olmMachine);
        this.crossSigningIdentity = new CrossSigningIdentity(olmMachine, this.outgoingRequestProcessor);
    }

    ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    //
    // CryptoBackend implementation
    //
    ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////

    public stop(): void {
        // stop() may be called multiple times, but attempting to close() the OlmMachine twice
        // will cause an error.
        if (this.stopped) {
            return;
        }
        this.stopped = true;

        this.keyClaimManager.stop();

        // make sure we close() the OlmMachine; doing so means that all the Rust objects will be
        // cleaned up; in particular, the indexeddb connections will be closed, which means they
        // can then be deleted.
        this.olmMachine.close();
    }

    public async encryptEvent(event: MatrixEvent, _room: Room): Promise<void> {
        const roomId = event.getRoomId()!;
        const encryptor = this.roomEncryptors[roomId];

        if (!encryptor) {
            throw new Error(`Cannot encrypt event in unconfigured room ${roomId}`);
        }

        await encryptor.encryptEvent(event);
    }

    public async decryptEvent(event: MatrixEvent): Promise<IEventDecryptionResult> {
        const roomId = event.getRoomId();
        if (!roomId) {
            // presumably, a to-device message. These are normally decrypted in preprocessToDeviceMessages
            // so the fact it has come back here suggests that decryption failed.
            //
            // once we drop support for the libolm crypto implementation, we can stop passing to-device messages
            // through decryptEvent and hence get rid of this case.
            throw new Error("to-device event was not decrypted in preprocessToDeviceMessages");
        }
        return await this.eventDecryptor.attemptEventDecryption(event);
    }

    public getEventEncryptionInfo(event: MatrixEvent): IEncryptedEventInfo {
        // TODO: make this work properly. Or better, replace it.

        const ret: Partial<IEncryptedEventInfo> = {};

        ret.senderKey = event.getSenderKey() ?? undefined;
        ret.algorithm = event.getWireContent().algorithm;

        if (!ret.senderKey || !ret.algorithm) {
            ret.encrypted = false;
            return ret as IEncryptedEventInfo;
        }
        ret.encrypted = true;
        ret.authenticated = true;
        ret.mismatchedSender = true;
        return ret as IEncryptedEventInfo;
    }

    public checkUserTrust(userId: string): UserTrustLevel {
        // TODO
        return new UserTrustLevel(false, false, false);
    }

    /**
     * Finds a DM verification request that is already in progress for the given room id
     *
     * @param roomId - the room to use for verification
     *
     * @returns the VerificationRequest that is in progress, if any
     */
    public findVerificationRequestDMInProgress(roomId: string): undefined {
        // TODO
        return;
    }

    /**
     * Get the cross signing information for a given user.
     *
     * The cross-signing API is currently UNSTABLE and may change without notice.
     *
     * @param userId - the user ID to get the cross-signing info for.
     *
     * @returns the cross signing information for the user.
     */
    public getStoredCrossSigningForUser(userId: string): null {
        // TODO
        return null;
    }

    ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    //
    // CryptoApi implementation
    //
    ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////

    public globalBlacklistUnverifiedDevices = false;

    public async userHasCrossSigningKeys(): Promise<boolean> {
        // TODO
        return false;
    }

    public prepareToEncrypt(room: Room): void {
        const encryptor = this.roomEncryptors[room.roomId];

        if (encryptor) {
            encryptor.ensureEncryptionSession();
        }
    }

    public forceDiscardSession(roomId: string): Promise<void> {
        return this.roomEncryptors[roomId]?.forceDiscardSession();
    }

    public async exportRoomKeys(): Promise<IMegolmSessionData[]> {
        const raw = await this.olmMachine.exportRoomKeys(() => true);
        return JSON.parse(raw);
    }

    public async importRoomKeys(keys: IMegolmSessionData[], opts?: ImportRoomKeysOpts): Promise<void> {
        // TODO when backup support will be added we would need to expose the `from_backup` flag in the bindings
        const jsonKeys = JSON.stringify(keys);
        await this.olmMachine.importRoomKeys(jsonKeys, (progress: BigInt, total: BigInt) => {
            const importOpt: ImportRoomKeyProgressData = {
                total: Number(total),
                successes: Number(progress),
                stage: "load_keys",
                failures: 0,
            };
            opts?.progressCallback?.(importOpt);
        });
    }

    /**
     * Get the device information for the given list of users.
     *
     * @param userIds - The users to fetch.
     * @param downloadUncached - If true, download the device list for users whose device list we are not
     *    currently tracking. Defaults to false, in which case such users will not appear at all in the result map.
     *
     * @returns A map `{@link DeviceMap}`.
     */
    public async getUserDeviceInfo(userIds: string[], downloadUncached = false): Promise<DeviceMap> {
        const deviceMapByUserId = new Map<string, Map<string, Device>>();
        const rustTrackedUsers: Set<RustSdkCryptoJs.UserId> = await this.olmMachine.trackedUsers();

        // Convert RustSdkCryptoJs.UserId to a `Set<string>`
        const trackedUsers = new Set<string>();
        rustTrackedUsers.forEach((rustUserId) => trackedUsers.add(rustUserId.toString()));

        // Keep untracked user to download their keys after
        const untrackedUsers: Set<string> = new Set();

        for (const userId of userIds) {
            // if this is a tracked user, we can just fetch the device list from the rust-sdk
            // (NB: this is probably ok even if we race with a leave event such that we stop tracking the user's
            // devices: the rust-sdk will return the last-known device list, which will be good enough.)
            if (trackedUsers.has(userId)) {
                deviceMapByUserId.set(userId, await this.getUserDevices(userId));
            } else {
                untrackedUsers.add(userId);
            }
        }

        // for any users whose device lists we are not tracking, fall back to downloading the device list
        // over HTTP.
        if (downloadUncached && untrackedUsers.size >= 1) {
            const queryResult = await this.downloadDeviceList(untrackedUsers);
            Object.entries(queryResult.device_keys).forEach(([userId, deviceKeys]) =>
                deviceMapByUserId.set(userId, deviceKeysToDeviceMap(deviceKeys)),
            );
        }

        return deviceMapByUserId;
    }

    /**
     * Get the device list for the given user from the olm machine
     * @param userId - Rust SDK UserId
     */
    private async getUserDevices(userId: string): Promise<Map<string, Device>> {
        const rustUserId = new RustSdkCryptoJs.UserId(userId);
        const devices: RustSdkCryptoJs.UserDevices = await this.olmMachine.getUserDevices(rustUserId);
        return new Map(
            devices
                .devices()
                .map((device: RustSdkCryptoJs.Device) => [
                    device.deviceId.toString(),
                    rustDeviceToJsDevice(device, rustUserId),
                ]),
        );
    }

    /**
     * Download the given user keys by calling `/keys/query` request
     * @param untrackedUsers - download keys of these users
     */
    private async downloadDeviceList(untrackedUsers: Set<string>): Promise<IDownloadKeyResult> {
        const queryBody: IQueryKeysRequest = { device_keys: {} };
        untrackedUsers.forEach((user) => (queryBody.device_keys[user] = []));

        return await this.http.authedRequest(Method.Post, "/_matrix/client/v3/keys/query", undefined, queryBody, {
            prefix: "",
        });
    }

    /**
     * Implementation of {@link CryptoApi#getTrustCrossSignedDevices}.
     */
    public getTrustCrossSignedDevices(): boolean {
        return this._trustCrossSignedDevices;
    }

    /**
     * Implementation of {@link CryptoApi#setTrustCrossSignedDevices}.
     */
    public setTrustCrossSignedDevices(val: boolean): void {
        this._trustCrossSignedDevices = val;
        // TODO: legacy crypto goes through the list of known devices and emits DeviceVerificationChanged
        //  events. Maybe we need to do the same?
    }

    /**
     * Implementation of {@link CryptoApi#getDeviceVerificationStatus}.
     */
    public async getDeviceVerificationStatus(
        userId: string,
        deviceId: string,
    ): Promise<DeviceVerificationStatus | null> {
        const device: RustSdkCryptoJs.Device | undefined = await this.olmMachine.getDevice(
            new RustSdkCryptoJs.UserId(userId),
            new RustSdkCryptoJs.DeviceId(deviceId),
        );

        if (!device) return null;

        return new DeviceVerificationStatus({
            signedByOwner: device.isCrossSignedByOwner(),
            crossSigningVerified: device.isCrossSigningTrusted(),
            localVerified: device.isLocallyTrusted(),
            trustCrossSignedDevices: this._trustCrossSignedDevices,
        });
    }

    /**
     * Implementation of {@link CryptoApi#isCrossSigningReady}
     */
    public async isCrossSigningReady(): Promise<boolean> {
        const { publicKeysOnDevice, privateKeysInSecretStorage, privateKeysCachedLocally } =
            await this.getCrossSigningStatus();
        const hasKeysInCache =
            Boolean(privateKeysCachedLocally.masterKey) &&
            Boolean(privateKeysCachedLocally.selfSigningKey) &&
            Boolean(privateKeysCachedLocally.userSigningKey);

        // The cross signing is ready if the public and private keys are available
        return publicKeysOnDevice && (hasKeysInCache || privateKeysInSecretStorage);
    }

    /**
     * Implementation of {@link CryptoApi#getCrossSigningKeyId}
     */
    public async getCrossSigningKeyId(type: CrossSigningKey = CrossSigningKey.Master): Promise<string | null> {
        // TODO
        return null;
    }

    /**
     * Implementation of {@link CryptoApi#boostrapCrossSigning}
     */
    public async bootstrapCrossSigning(opts: BootstrapCrossSigningOpts): Promise<void> {
        await this.crossSigningIdentity.bootstrapCrossSigning(opts);
    }

    /**
     * Implementation of {@link CryptoApi#isSecretStorageReady}
     */
    public async isSecretStorageReady(): Promise<boolean> {
        return false;
    }

    /**
     * Implementation of {@link CryptoApi#getCrossSigningStatus}
     */
    public async getCrossSigningStatus(): Promise<CrossSigningStatus> {
        const userIdentity: RustSdkCryptoJs.OwnUserIdentity | null = await this.olmMachine.getIdentity(
            new RustSdkCryptoJs.UserId(this.userId),
        );
        const publicKeysOnDevice =
            Boolean(userIdentity?.masterKey) &&
            Boolean(userIdentity?.selfSigningKey) &&
            Boolean(userIdentity?.userSigningKey);
        const privateKeysInSecretStorage = await secretStorageContainsCrossSigningKeys(this.secretStorage);
        const crossSigningStatus: RustSdkCryptoJs.CrossSigningStatus | null =
            await this.olmMachine.crossSigningStatus();

        return {
            publicKeysOnDevice,
            privateKeysInSecretStorage,
            privateKeysCachedLocally: {
                masterKey: Boolean(crossSigningStatus?.hasMaster),
                userSigningKey: Boolean(crossSigningStatus?.hasUserSigning),
                selfSigningKey: Boolean(crossSigningStatus?.hasSelfSigning),
            },
        };
    }

    ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    //
    // SyncCryptoCallbacks implementation
    //
    ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////

    /**
     * Apply sync changes to the olm machine
     * @param events - the received to-device messages
     * @param oneTimeKeysCounts - the received one time key counts
     * @param unusedFallbackKeys - the received unused fallback keys
     * @param devices - the received device list updates
     * @returns A list of preprocessed to-device messages.
     */
    private async receiveSyncChanges({
        events,
        oneTimeKeysCounts = new Map<string, number>(),
        unusedFallbackKeys,
        devices = new RustSdkCryptoJs.DeviceLists(),
    }: {
        events?: IToDeviceEvent[];
        oneTimeKeysCounts?: Map<string, number>;
        unusedFallbackKeys?: Set<string>;
        devices?: RustSdkCryptoJs.DeviceLists;
    }): Promise<IToDeviceEvent[]> {
        const result = await this.olmMachine.receiveSyncChanges(
            events ? JSON.stringify(events) : "[]",
            devices,
            oneTimeKeysCounts,
            unusedFallbackKeys,
        );

        // receiveSyncChanges returns a JSON-encoded list of decrypted to-device messages.
        return JSON.parse(result);
    }

    /** called by the sync loop to preprocess incoming to-device messages
     *
     * @param events - the received to-device messages
     * @returns A list of preprocessed to-device messages.
     */
    public preprocessToDeviceMessages(events: IToDeviceEvent[]): Promise<IToDeviceEvent[]> {
        // send the received to-device messages into receiveSyncChanges. We have no info on device-list changes,
        // one-time-keys, or fallback keys, so just pass empty data.
        return this.receiveSyncChanges({ events });
    }

    /** called by the sync loop to process one time key counts and unused fallback keys
     *
     * @param oneTimeKeysCounts - the received one time key counts
     * @param unusedFallbackKeys - the received unused fallback keys
     */
    public async processKeyCounts(
        oneTimeKeysCounts?: Record<string, number>,
        unusedFallbackKeys?: string[],
    ): Promise<void> {
        const mapOneTimeKeysCount = oneTimeKeysCounts && new Map<string, number>(Object.entries(oneTimeKeysCounts));
        const setUnusedFallbackKeys = unusedFallbackKeys && new Set<string>(unusedFallbackKeys);

        if (mapOneTimeKeysCount !== undefined || setUnusedFallbackKeys !== undefined) {
            await this.receiveSyncChanges({
                oneTimeKeysCounts: mapOneTimeKeysCount,
                unusedFallbackKeys: setUnusedFallbackKeys,
            });
        }
    }

    /** called by the sync loop to process the notification that device lists have
     * been changed.
     *
     * @param deviceLists - device_lists field from /sync
     */
    public async processDeviceLists(deviceLists: IDeviceLists): Promise<void> {
        const devices = new RustSdkCryptoJs.DeviceLists(
            deviceLists.changed?.map((userId) => new RustSdkCryptoJs.UserId(userId)),
            deviceLists.left?.map((userId) => new RustSdkCryptoJs.UserId(userId)),
        );
        await this.receiveSyncChanges({ devices });
    }

    /** called by the sync loop on m.room.encrypted events
     *
     * @param room - in which the event was received
     * @param event - encryption event to be processed
     */
    public async onCryptoEvent(room: Room, event: MatrixEvent): Promise<void> {
        const config = event.getContent();

        const existingEncryptor = this.roomEncryptors[room.roomId];
        if (existingEncryptor) {
            existingEncryptor.onCryptoEvent(config);
        } else {
            this.roomEncryptors[room.roomId] = new RoomEncryptor(
                this.olmMachine,
                this.keyClaimManager,
                this.outgoingRequestProcessor,
                room,
                config,
            );
        }

        // start tracking devices for any users already known to be in this room.
        const members = await room.getEncryptionTargetMembers();
        logger.debug(
            `[${room.roomId} encryption] starting to track devices for: `,
            members.map((u) => `${u.userId} (${u.membership})`),
        );
        await this.olmMachine.updateTrackedUsers(members.map((u) => new RustSdkCryptoJs.UserId(u.userId)));
    }

    /** called by the sync loop after processing each sync.
     *
     * TODO: figure out something equivalent for sliding sync.
     *
     * @param syncState - information on the completed sync.
     */
    public onSyncCompleted(syncState: OnSyncCompletedData): void {
        // Processing the /sync may have produced new outgoing requests which need sending, so kick off the outgoing
        // request loop, if it's not already running.
        this.outgoingRequestLoop();
    }

    ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    //
    // Other public functions
    //
    ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////

    /** called by the MatrixClient on a room membership event
     *
     * @param event - The matrix event which caused this event to fire.
     * @param member - The member whose RoomMember.membership changed.
     * @param oldMembership - The previous membership state. Null if it's a new member.
     */
    public onRoomMembership(event: MatrixEvent, member: RoomMember, oldMembership?: string): void {
        const enc = this.roomEncryptors[event.getRoomId()!];
        if (!enc) {
            // not encrypting in this room
            return;
        }
        enc.onRoomMembership(member);
    }

    /** Callback for OlmMachine.registerRoomKeyUpdatedCallback
     *
     * Called by the rust-sdk whenever there is an update to (megolm) room keys. We
     * check if we have any events waiting for the given keys, and schedule them for
     * a decryption retry if so.
     *
     * @param keys - details of the updated keys
     */
    public async onRoomKeysUpdated(keys: RustSdkCryptoJs.RoomKeyInfo[]): Promise<void> {
        for (const key of keys) {
            this.onRoomKeyUpdated(key);
        }
    }

    private onRoomKeyUpdated(key: RustSdkCryptoJs.RoomKeyInfo): void {
        logger.debug(`Got update for session ${key.senderKey.toBase64()}|${key.sessionId} in ${key.roomId.toString()}`);
        const pendingList = this.eventDecryptor.getEventsPendingRoomKey(key);
        if (pendingList.length === 0) return;

        logger.debug(
            "Retrying decryption on events:",
            pendingList.map((e) => `${e.getId()}`),
        );

        // Have another go at decrypting events with this key.
        //
        // We don't want to end up blocking the callback from Rust, which could otherwise end up dropping updates,
        // so we don't wait for the decryption to complete. In any case, there is no need to wait:
        // MatrixEvent.attemptDecryption ensures that there is only one decryption attempt happening at once,
        // and deduplicates repeated attempts for the same event.
        for (const ev of pendingList) {
            ev.attemptDecryption(this, { isRetry: true }).catch((_e) => {
                logger.info(`Still unable to decrypt event ${ev.getId()} after receiving key`);
            });
        }
    }

    ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    //
    // Outgoing requests
    //
    ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////

    private async outgoingRequestLoop(): Promise<void> {
        if (this.outgoingRequestLoopRunning) {
            return;
        }
        this.outgoingRequestLoopRunning = true;
        try {
            while (!this.stopped) {
                const outgoingRequests: Object[] = await this.olmMachine.outgoingRequests();
                if (outgoingRequests.length == 0 || this.stopped) {
                    // no more messages to send (or we have been told to stop): exit the loop
                    return;
                }
                for (const msg of outgoingRequests) {
                    await this.outgoingRequestProcessor.makeOutgoingRequest(msg as OutgoingRequest);
                }
            }
        } catch (e) {
            logger.error("Error processing outgoing-message requests from rust crypto-sdk", e);
        } finally {
            this.outgoingRequestLoopRunning = false;
        }
    }
}

class EventDecryptor {
    /**
     * Events which we couldn't decrypt due to unknown sessions / indexes.
     *
     * Map from senderKey to sessionId to Set of MatrixEvents
     */
    private eventsPendingKey = new MapWithDefault<string, MapWithDefault<string, Set<MatrixEvent>>>(
        () => new MapWithDefault<string, Set<MatrixEvent>>(() => new Set()),
    );

    public constructor(private readonly olmMachine: RustSdkCryptoJs.OlmMachine) {}

    public async attemptEventDecryption(event: MatrixEvent): Promise<IEventDecryptionResult> {
        logger.info("Attempting decryption of event", event);
        // add the event to the pending list *before* attempting to decrypt.
        // then, if the key turns up while decryption is in progress (and
        // decryption fails), we will schedule a retry.
        // (fixes https://github.com/vector-im/element-web/issues/5001)
        this.addEventToPendingList(event);

        const res = (await this.olmMachine.decryptRoomEvent(
            JSON.stringify({
                event_id: event.getId(),
                type: event.getWireType(),
                sender: event.getSender(),
                state_key: event.getStateKey(),
                content: event.getWireContent(),
                origin_server_ts: event.getTs(),
            }),
            new RustSdkCryptoJs.RoomId(event.getRoomId()!),
        )) as RustSdkCryptoJs.DecryptedRoomEvent;

        // Success. We can remove the event from the pending list, if
        // that hasn't already happened.
        this.removeEventFromPendingList(event);

        return {
            clearEvent: JSON.parse(res.event),
            claimedEd25519Key: res.senderClaimedEd25519Key,
            senderCurve25519Key: res.senderCurve25519Key,
            forwardingCurve25519KeyChain: res.forwardingCurve25519KeyChain,
        };
    }

    /**
     * Look for events which are waiting for a given megolm session
     *
     * Returns a list of events which were encrypted by `session` and could not be decrypted
     *
     * @param session -
     */
    public getEventsPendingRoomKey(session: RustSdkCryptoJs.RoomKeyInfo): MatrixEvent[] {
        const senderPendingEvents = this.eventsPendingKey.get(session.senderKey.toBase64());
        if (!senderPendingEvents) return [];

        const sessionPendingEvents = senderPendingEvents.get(session.sessionId);
        if (!sessionPendingEvents) return [];

        const roomId = session.roomId.toString();
        return [...sessionPendingEvents].filter((ev) => ev.getRoomId() === roomId);
    }

    /**
     * Add an event to the list of those awaiting their session keys.
     */
    private addEventToPendingList(event: MatrixEvent): void {
        const content = event.getWireContent();
        const senderKey = content.sender_key;
        const sessionId = content.session_id;

        const senderPendingEvents = this.eventsPendingKey.getOrCreate(senderKey);
        const sessionPendingEvents = senderPendingEvents.getOrCreate(sessionId);
        sessionPendingEvents.add(event);
    }

    /**
     * Remove an event from the list of those awaiting their session keys.
     */
    private removeEventFromPendingList(event: MatrixEvent): void {
        const content = event.getWireContent();
        const senderKey = content.sender_key;
        const sessionId = content.session_id;

        const senderPendingEvents = this.eventsPendingKey.get(senderKey);
        if (!senderPendingEvents) return;

        const sessionPendingEvents = senderPendingEvents.get(sessionId);
        if (!sessionPendingEvents) return;

        sessionPendingEvents.delete(event);

        // also clean up the higher-level maps if they are now empty
        if (sessionPendingEvents.size === 0) {
            senderPendingEvents.delete(sessionId);
            if (senderPendingEvents.size === 0) {
                this.eventsPendingKey.delete(senderKey);
            }
        }
    }
}