Updated 18 files, added 1692 files and deleted includes/system/compare.inc (automated)

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diff --git a/includes/external/matrix/node_modules/matrix-js-sdk/src/models/event.ts b/includes/external/matrix/node_modules/matrix-js-sdk/src/models/event.ts
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@@ -0,0 +1,1631 @@
+/*
+Copyright 2015 - 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.
+*/
+
+/**
+ * This is an internal module. See {@link MatrixEvent} and {@link RoomEvent} for
+ * the public classes.
+ */
+
+import { ExtensibleEvent, ExtensibleEvents, Optional } from "matrix-events-sdk";
+
+import type { IEventDecryptionResult } from "../@types/crypto";
+import { logger } from "../logger";
+import { VerificationRequest } from "../crypto/verification/request/VerificationRequest";
+import { EVENT_VISIBILITY_CHANGE_TYPE, EventType, MsgType, RelationType } from "../@types/event";
+import { Crypto } from "../crypto";
+import { deepSortedObjectEntries, internaliseString } from "../utils";
+import { RoomMember } from "./room-member";
+import { Thread, ThreadEvent, EventHandlerMap as ThreadEventHandlerMap, THREAD_RELATION_TYPE } from "./thread";
+import { IActionsObject } from "../pushprocessor";
+import { TypedReEmitter } from "../ReEmitter";
+import { MatrixError } from "../http-api";
+import { TypedEventEmitter } from "./typed-event-emitter";
+import { EventStatus } from "./event-status";
+import { DecryptionError } from "../crypto/algorithms";
+import { CryptoBackend } from "../common-crypto/CryptoBackend";
+import { WITHHELD_MESSAGES } from "../crypto/OlmDevice";
+
+export { EventStatus } from "./event-status";
+
+/* eslint-disable camelcase */
+export interface IContent {
+    [key: string]: any;
+    "msgtype"?: MsgType | string;
+    "membership"?: string;
+    "avatar_url"?: string;
+    "displayname"?: string;
+    "m.relates_to"?: IEventRelation;
+
+    "org.matrix.msc3952.mentions"?: IMentions;
+}
+
+type StrippedState = Required<Pick<IEvent, "content" | "state_key" | "type" | "sender">>;
+
+export interface IUnsigned {
+    "age"?: number;
+    "prev_sender"?: string;
+    "prev_content"?: IContent;
+    "redacted_because"?: IEvent;
+    "transaction_id"?: string;
+    "invite_room_state"?: StrippedState[];
+    "m.relations"?: Record<RelationType | string, any>; // No common pattern for aggregated relations
+}
+
+export interface IThreadBundledRelationship {
+    latest_event: IEvent;
+    count: number;
+    current_user_participated?: boolean;
+}
+
+export interface IEvent {
+    event_id: string;
+    type: string;
+    content: IContent;
+    sender: string;
+    room_id?: string;
+    origin_server_ts: number;
+    txn_id?: string;
+    state_key?: string;
+    membership?: string;
+    unsigned: IUnsigned;
+    redacts?: string;
+
+    /**
+     * @deprecated in favour of `sender`
+     */
+    user_id?: string;
+    /**
+     * @deprecated in favour of `unsigned.prev_content`
+     */
+    prev_content?: IContent;
+    /**
+     * @deprecated in favour of `origin_server_ts`
+     */
+    age?: number;
+}
+
+export interface IAggregatedRelation {
+    origin_server_ts: number;
+    event_id?: string;
+    sender?: string;
+    type?: string;
+    count?: number;
+    key?: string;
+}
+
+export interface IEventRelation {
+    "rel_type"?: RelationType | string;
+    "event_id"?: string;
+    "is_falling_back"?: boolean;
+    "m.in_reply_to"?: {
+        event_id?: string;
+    };
+    "key"?: string;
+}
+
+export interface IMentions {
+    user_ids?: string[];
+    room?: boolean;
+}
+
+/**
+ * When an event is a visibility change event, as per MSC3531,
+ * the visibility change implied by the event.
+ */
+export interface IVisibilityChange {
+    /**
+     * If `true`, the target event should be made visible.
+     * Otherwise, it should be hidden.
+     */
+    visible: boolean;
+
+    /**
+     * The event id affected.
+     */
+    eventId: string;
+
+    /**
+     * Optionally, a human-readable reason explaining why
+     * the event was hidden. Ignored if the event was made
+     * visible.
+     */
+    reason: string | null;
+}
+
+export interface IClearEvent {
+    room_id?: string;
+    type: string;
+    content: Omit<IContent, "membership" | "avatar_url" | "displayname" | "m.relates_to">;
+    unsigned?: IUnsigned;
+}
+/* eslint-enable camelcase */
+
+interface IKeyRequestRecipient {
+    userId: string;
+    deviceId: "*" | string;
+}
+
+export interface IDecryptOptions {
+    // Emits "event.decrypted" if set to true
+    emit?: boolean;
+    // True if this is a retry (enables more logging)
+    isRetry?: boolean;
+    // whether the message should be re-decrypted if it was previously successfully decrypted with an untrusted key
+    forceRedecryptIfUntrusted?: boolean;
+}
+
+/**
+ * Message hiding, as specified by https://github.com/matrix-org/matrix-doc/pull/3531.
+ */
+export type MessageVisibility = IMessageVisibilityHidden | IMessageVisibilityVisible;
+/**
+ * Variant of `MessageVisibility` for the case in which the message should be displayed.
+ */
+export interface IMessageVisibilityVisible {
+    readonly visible: true;
+}
+/**
+ * Variant of `MessageVisibility` for the case in which the message should be hidden.
+ */
+export interface IMessageVisibilityHidden {
+    readonly visible: false;
+    /**
+     * Optionally, a human-readable reason to show to the user indicating why the
+     * message has been hidden (e.g. "Message Pending Moderation").
+     */
+    readonly reason: string | null;
+}
+// A singleton implementing `IMessageVisibilityVisible`.
+const MESSAGE_VISIBLE: IMessageVisibilityVisible = Object.freeze({ visible: true });
+
+export enum MatrixEventEvent {
+    Decrypted = "Event.decrypted",
+    BeforeRedaction = "Event.beforeRedaction",
+    VisibilityChange = "Event.visibilityChange",
+    LocalEventIdReplaced = "Event.localEventIdReplaced",
+    Status = "Event.status",
+    Replaced = "Event.replaced",
+    RelationsCreated = "Event.relationsCreated",
+}
+
+export type MatrixEventEmittedEvents = MatrixEventEvent | ThreadEvent.Update;
+
+export type MatrixEventHandlerMap = {
+    /**
+     * Fires when an event is decrypted
+     *
+     * @param event - The matrix event which has been decrypted
+     * @param err - The error that occurred during decryption, or `undefined` if no error occurred.
+     */
+    [MatrixEventEvent.Decrypted]: (event: MatrixEvent, err?: Error) => void;
+    [MatrixEventEvent.BeforeRedaction]: (event: MatrixEvent, redactionEvent: MatrixEvent) => void;
+    [MatrixEventEvent.VisibilityChange]: (event: MatrixEvent, visible: boolean) => void;
+    [MatrixEventEvent.LocalEventIdReplaced]: (event: MatrixEvent) => void;
+    [MatrixEventEvent.Status]: (event: MatrixEvent, status: EventStatus | null) => void;
+    [MatrixEventEvent.Replaced]: (event: MatrixEvent) => void;
+    [MatrixEventEvent.RelationsCreated]: (relationType: string, eventType: string) => void;
+} & Pick<ThreadEventHandlerMap, ThreadEvent.Update>;
+
+export class MatrixEvent extends TypedEventEmitter<MatrixEventEmittedEvents, MatrixEventHandlerMap> {
+    private pushActions: IActionsObject | null = null;
+    private _replacingEvent: MatrixEvent | null = null;
+    private _localRedactionEvent: MatrixEvent | null = null;
+    private _isCancelled = false;
+    private clearEvent?: IClearEvent;
+
+    /* Message hiding, as specified by https://github.com/matrix-org/matrix-doc/pull/3531.
+
+    Note: We're returning this object, so any value stored here MUST be frozen.
+    */
+    private visibility: MessageVisibility = MESSAGE_VISIBLE;
+
+    // Not all events will be extensible-event compatible, so cache a flag in
+    // addition to a falsy cached event value. We check the flag later on in
+    // a public getter to decide if the cache is valid.
+    private _hasCachedExtEv = false;
+    private _cachedExtEv: Optional<ExtensibleEvent> = undefined;
+
+    /* curve25519 key which we believe belongs to the sender of the event. See
+     * getSenderKey()
+     */
+    private senderCurve25519Key: string | null = null;
+
+    /* ed25519 key which the sender of this event (for olm) or the creator of
+     * the megolm session (for megolm) claims to own. See getClaimedEd25519Key()
+     */
+    private claimedEd25519Key: string | null = null;
+
+    /* curve25519 keys of devices involved in telling us about the
+     * senderCurve25519Key and claimedEd25519Key.
+     * See getForwardingCurve25519KeyChain().
+     */
+    private forwardingCurve25519KeyChain: string[] = [];
+
+    /* where the decryption key is untrusted
+     */
+    private untrusted: boolean | null = null;
+
+    /* if we have a process decrypting this event, a Promise which resolves
+     * when it is finished. Normally null.
+     */
+    private decryptionPromise: Promise<void> | null = null;
+
+    /* flag to indicate if we should retry decrypting this event after the
+     * first attempt (eg, we have received new data which means that a second
+     * attempt may succeed)
+     */
+    private retryDecryption = false;
+
+    /* The txnId with which this event was sent if it was during this session,
+     * allows for a unique ID which does not change when the event comes back down sync.
+     */
+    private txnId?: string;
+
+    /**
+     * A reference to the thread this event belongs to
+     */
+    private thread?: Thread;
+    private threadId?: string;
+
+    /*
+     * True if this event is an encrypted event which we failed to decrypt, the receiver's device is unverified and
+     * the sender has disabled encrypting to unverified devices.
+     */
+    private encryptedDisabledForUnverifiedDevices = false;
+
+    /* Set an approximate timestamp for the event relative the local clock.
+     * This will inherently be approximate because it doesn't take into account
+     * the time between the server putting the 'age' field on the event as it sent
+     * it to us and the time we're now constructing this event, but that's better
+     * than assuming the local clock is in sync with the origin HS's clock.
+     */
+    public localTimestamp: number;
+
+    /**
+     * The room member who sent this event, or null e.g.
+     * this is a presence event. This is only guaranteed to be set for events that
+     * appear in a timeline, ie. do not guarantee that it will be set on state
+     * events.
+     * @privateRemarks
+     * Should be read-only
+     */
+    public sender: RoomMember | null = null;
+    /**
+     * The room member who is the target of this event, e.g.
+     * the invitee, the person being banned, etc.
+     * @privateRemarks
+     * Should be read-only
+     */
+    public target: RoomMember | null = null;
+    /**
+     * The sending status of the event.
+     * @privateRemarks
+     * Should be read-only
+     */
+    public status: EventStatus | null = null;
+    /**
+     * most recent error associated with sending the event, if any
+     * @privateRemarks
+     * Should be read-only
+     */
+    public error: MatrixError | null = null;
+    /**
+     * True if this event is 'forward looking', meaning
+     * that getDirectionalContent() will return event.content and not event.prev_content.
+     * Only state events may be backwards looking
+     * Default: true. <strong>This property is experimental and may change.</strong>
+     * @privateRemarks
+     * Should be read-only
+     */
+    public forwardLooking = true;
+
+    /* If the event is a `m.key.verification.request` (or to_device `m.key.verification.start`) event,
+     * `Crypto` will set this the `VerificationRequest` for the event
+     * so it can be easily accessed from the timeline.
+     */
+    public verificationRequest?: VerificationRequest;
+
+    private readonly reEmitter: TypedReEmitter<MatrixEventEmittedEvents, MatrixEventHandlerMap>;
+
+    /**
+     * Construct a Matrix Event object
+     *
+     * @param event - The raw (possibly encrypted) event. <b>Do not access
+     * this property</b> directly unless you absolutely have to. Prefer the getter
+     * methods defined on this class. Using the getter methods shields your app
+     * from changes to event JSON between Matrix versions.
+     */
+    public constructor(public event: Partial<IEvent> = {}) {
+        super();
+
+        // intern the values of matrix events to force share strings and reduce the
+        // amount of needless string duplication. This can save moderate amounts of
+        // memory (~10% on a 350MB heap).
+        // 'membership' at the event level (rather than the content level) is a legacy
+        // field that Element never otherwise looks at, but it will still take up a lot
+        // of space if we don't intern it.
+        (["state_key", "type", "sender", "room_id", "membership"] as const).forEach((prop) => {
+            if (typeof event[prop] !== "string") return;
+            event[prop] = internaliseString(event[prop]!);
+        });
+
+        (["membership", "avatar_url", "displayname"] as const).forEach((prop) => {
+            if (typeof event.content?.[prop] !== "string") return;
+            event.content[prop] = internaliseString(event.content[prop]!);
+        });
+
+        (["rel_type"] as const).forEach((prop) => {
+            if (typeof event.content?.["m.relates_to"]?.[prop] !== "string") return;
+            event.content["m.relates_to"][prop] = internaliseString(event.content["m.relates_to"][prop]!);
+        });
+
+        this.txnId = event.txn_id;
+        this.localTimestamp = Date.now() - (this.getAge() ?? 0);
+        this.reEmitter = new TypedReEmitter(this);
+    }
+
+    /**
+     * Unstable getter to try and get an extensible event. Note that this might
+     * return a falsy value if the event could not be parsed as an extensible
+     * event.
+     *
+     * @deprecated Use stable functions where possible.
+     */
+    public get unstableExtensibleEvent(): Optional<ExtensibleEvent> {
+        if (!this._hasCachedExtEv) {
+            this._cachedExtEv = ExtensibleEvents.parse(this.getEffectiveEvent());
+        }
+        return this._cachedExtEv;
+    }
+
+    private invalidateExtensibleEvent(): void {
+        // just reset the flag - that'll trick the getter into parsing a new event
+        this._hasCachedExtEv = false;
+    }
+
+    /**
+     * Gets the event as though it would appear unencrypted. If the event is already not
+     * encrypted, it is simply returned as-is.
+     * @returns The event in wire format.
+     */
+    public getEffectiveEvent(): IEvent {
+        const content = Object.assign({}, this.getContent()); // clone for mutation
+
+        if (this.getWireType() === EventType.RoomMessageEncrypted) {
+            // Encrypted events sometimes aren't symmetrical on the `content` so we'll copy
+            // that over too, but only for missing properties. We don't copy over mismatches
+            // between the plain and decrypted copies of `content` because we assume that the
+            // app is relying on the decrypted version, so we want to expose that as a source
+            // of truth here too.
+            for (const [key, value] of Object.entries(this.getWireContent())) {
+                // Skip fields from the encrypted event schema though - we don't want to leak
+                // these.
+                if (["algorithm", "ciphertext", "device_id", "sender_key", "session_id"].includes(key)) {
+                    continue;
+                }
+
+                if (content[key] === undefined) content[key] = value;
+            }
+        }
+
+        // clearEvent doesn't have all the fields, so we'll copy what we can from this.event.
+        // We also copy over our "fixed" content key.
+        return Object.assign({}, this.event, this.clearEvent, { content }) as IEvent;
+    }
+
+    /**
+     * Get the event_id for this event.
+     * @returns The event ID, e.g. <code>$143350589368169JsLZx:localhost
+     * </code>
+     */
+    public getId(): string | undefined {
+        return this.event.event_id;
+    }
+
+    /**
+     * Get the user_id for this event.
+     * @returns The user ID, e.g. `@alice:matrix.org`
+     */
+    public getSender(): string | undefined {
+        return this.event.sender || this.event.user_id; // v2 / v1
+    }
+
+    /**
+     * Get the (decrypted, if necessary) type of event.
+     *
+     * @returns The event type, e.g. `m.room.message`
+     */
+    public getType(): EventType | string {
+        if (this.clearEvent) {
+            return this.clearEvent.type;
+        }
+        return this.event.type!;
+    }
+
+    /**
+     * Get the (possibly encrypted) type of the event that will be sent to the
+     * homeserver.
+     *
+     * @returns The event type.
+     */
+    public getWireType(): EventType | string {
+        return this.event.type!;
+    }
+
+    /**
+     * Get the room_id for this event. This will return `undefined`
+     * for `m.presence` events.
+     * @returns The room ID, e.g. <code>!cURbafjkfsMDVwdRDQ:matrix.org
+     * </code>
+     */
+    public getRoomId(): string | undefined {
+        return this.event.room_id;
+    }
+
+    /**
+     * Get the timestamp of this event.
+     * @returns The event timestamp, e.g. `1433502692297`
+     */
+    public getTs(): number {
+        return this.event.origin_server_ts!;
+    }
+
+    /**
+     * Get the timestamp of this event, as a Date object.
+     * @returns The event date, e.g. `new Date(1433502692297)`
+     */
+    public getDate(): Date | null {
+        return this.event.origin_server_ts ? new Date(this.event.origin_server_ts) : null;
+    }
+
+    /**
+     * Get a string containing details of this event
+     *
+     * This is intended for logging, to help trace errors. Example output:
+     *
+     * @example
+     * ```
+     * id=$HjnOHV646n0SjLDAqFrgIjim7RCpB7cdMXFrekWYAn type=m.room.encrypted
+     * sender=@user:example.com room=!room:example.com ts=2022-10-25T17:30:28.404Z
+     * ```
+     */
+    public getDetails(): string {
+        let details = `id=${this.getId()} type=${this.getWireType()} sender=${this.getSender()}`;
+        const room = this.getRoomId();
+        if (room) {
+            details += ` room=${room}`;
+        }
+        const date = this.getDate();
+        if (date) {
+            details += ` ts=${date.toISOString()}`;
+        }
+        return details;
+    }
+
+    /**
+     * Get the (decrypted, if necessary) event content JSON, even if the event
+     * was replaced by another event.
+     *
+     * @returns The event content JSON, or an empty object.
+     */
+    public getOriginalContent<T = IContent>(): T {
+        if (this._localRedactionEvent) {
+            return {} as T;
+        }
+        if (this.clearEvent) {
+            return (this.clearEvent.content || {}) as T;
+        }
+        return (this.event.content || {}) as T;
+    }
+
+    /**
+     * Get the (decrypted, if necessary) event content JSON,
+     * or the content from the replacing event, if any.
+     * See `makeReplaced`.
+     *
+     * @returns The event content JSON, or an empty object.
+     */
+    public getContent<T extends IContent = IContent>(): T {
+        if (this._localRedactionEvent) {
+            return {} as T;
+        } else if (this._replacingEvent) {
+            return this._replacingEvent.getContent()["m.new_content"] || {};
+        } else {
+            return this.getOriginalContent();
+        }
+    }
+
+    /**
+     * Get the (possibly encrypted) event content JSON that will be sent to the
+     * homeserver.
+     *
+     * @returns The event content JSON, or an empty object.
+     */
+    public getWireContent(): IContent {
+        return this.event.content || {};
+    }
+
+    /**
+     * Get the event ID of the thread head
+     */
+    public get threadRootId(): string | undefined {
+        const relatesTo = this.getWireContent()?.["m.relates_to"];
+        if (relatesTo?.rel_type === THREAD_RELATION_TYPE.name) {
+            return relatesTo.event_id;
+        } else {
+            return this.getThread()?.id || this.threadId;
+        }
+    }
+
+    /**
+     * A helper to check if an event is a thread's head or not
+     */
+    public get isThreadRoot(): boolean {
+        const threadDetails = this.getServerAggregatedRelation<IThreadBundledRelationship>(THREAD_RELATION_TYPE.name);
+
+        // Bundled relationships only returned when the sync response is limited
+        // hence us having to check both bundled relation and inspect the thread
+        // model
+        return !!threadDetails || this.getThread()?.id === this.getId();
+    }
+
+    public get replyEventId(): string | undefined {
+        return this.getWireContent()["m.relates_to"]?.["m.in_reply_to"]?.event_id;
+    }
+
+    public get relationEventId(): string | undefined {
+        return this.getWireContent()?.["m.relates_to"]?.event_id;
+    }
+
+    /**
+     * Get the previous event content JSON. This will only return something for
+     * state events which exist in the timeline.
+     * @returns The previous event content JSON, or an empty object.
+     */
+    public getPrevContent(): IContent {
+        // v2 then v1 then default
+        return this.getUnsigned().prev_content || this.event.prev_content || {};
+    }
+
+    /**
+     * Get either 'content' or 'prev_content' depending on if this event is
+     * 'forward-looking' or not. This can be modified via event.forwardLooking.
+     * In practice, this means we get the chronologically earlier content value
+     * for this event (this method should surely be called getEarlierContent)
+     * <strong>This method is experimental and may change.</strong>
+     * @returns event.content if this event is forward-looking, else
+     * event.prev_content.
+     */
+    public getDirectionalContent(): IContent {
+        return this.forwardLooking ? this.getContent() : this.getPrevContent();
+    }
+
+    /**
+     * Get the age of this event. This represents the age of the event when the
+     * event arrived at the device, and not the age of the event when this
+     * function was called.
+     * Can only be returned once the server has echo'ed back
+     * @returns The age of this event in milliseconds.
+     */
+    public getAge(): number | undefined {
+        return this.getUnsigned().age || this.event.age; // v2 / v1
+    }
+
+    /**
+     * Get the age of the event when this function was called.
+     * This is the 'age' field adjusted according to how long this client has
+     * had the event.
+     * @returns The age of this event in milliseconds.
+     */
+    public getLocalAge(): number {
+        return Date.now() - this.localTimestamp;
+    }
+
+    /**
+     * Get the event state_key if it has one. This will return <code>undefined
+     * </code> for message events.
+     * @returns The event's `state_key`.
+     */
+    public getStateKey(): string | undefined {
+        return this.event.state_key;
+    }
+
+    /**
+     * Check if this event is a state event.
+     * @returns True if this is a state event.
+     */
+    public isState(): boolean {
+        return this.event.state_key !== undefined;
+    }
+
+    /**
+     * Replace the content of this event with encrypted versions.
+     * (This is used when sending an event; it should not be used by applications).
+     *
+     * @internal
+     *
+     * @param cryptoType - type of the encrypted event - typically
+     * <tt>"m.room.encrypted"</tt>
+     *
+     * @param cryptoContent - raw 'content' for the encrypted event.
+     *
+     * @param senderCurve25519Key - curve25519 key to record for the
+     *   sender of this event.
+     *   See {@link MatrixEvent#getSenderKey}.
+     *
+     * @param claimedEd25519Key - claimed ed25519 key to record for the
+     *   sender if this event.
+     *   See {@link MatrixEvent#getClaimedEd25519Key}
+     */
+    public makeEncrypted(
+        cryptoType: string,
+        cryptoContent: object,
+        senderCurve25519Key: string,
+        claimedEd25519Key: string,
+    ): void {
+        // keep the plain-text data for 'view source'
+        this.clearEvent = {
+            type: this.event.type!,
+            content: this.event.content!,
+        };
+        this.event.type = cryptoType;
+        this.event.content = cryptoContent;
+        this.senderCurve25519Key = senderCurve25519Key;
+        this.claimedEd25519Key = claimedEd25519Key;
+    }
+
+    /**
+     * Check if this event is currently being decrypted.
+     *
+     * @returns True if this event is currently being decrypted, else false.
+     */
+    public isBeingDecrypted(): boolean {
+        return this.decryptionPromise != null;
+    }
+
+    public getDecryptionPromise(): Promise<void> | null {
+        return this.decryptionPromise;
+    }
+
+    /**
+     * Check if this event is an encrypted event which we failed to decrypt
+     *
+     * (This implies that we might retry decryption at some point in the future)
+     *
+     * @returns True if this event is an encrypted event which we
+     *     couldn't decrypt.
+     */
+    public isDecryptionFailure(): boolean {
+        return this.clearEvent?.content?.msgtype === "m.bad.encrypted";
+    }
+
+    /*
+     * True if this event is an encrypted event which we failed to decrypt, the receiver's device is unverified and
+     * the sender has disabled encrypting to unverified devices.
+     */
+    public get isEncryptedDisabledForUnverifiedDevices(): boolean {
+        return this.isDecryptionFailure() && this.encryptedDisabledForUnverifiedDevices;
+    }
+
+    public shouldAttemptDecryption(): boolean {
+        if (this.isRedacted()) return false;
+        if (this.isBeingDecrypted()) return false;
+        if (this.clearEvent) return false;
+        if (!this.isEncrypted()) return false;
+
+        return true;
+    }
+
+    /**
+     * Start the process of trying to decrypt this event.
+     *
+     * (This is used within the SDK: it isn't intended for use by applications)
+     *
+     * @internal
+     *
+     * @param crypto - crypto module
+     *
+     * @returns promise which resolves (to undefined) when the decryption
+     * attempt is completed.
+     */
+    public async attemptDecryption(crypto: CryptoBackend, options: IDecryptOptions = {}): Promise<void> {
+        // start with a couple of sanity checks.
+        if (!this.isEncrypted()) {
+            throw new Error("Attempt to decrypt event which isn't encrypted");
+        }
+
+        const alreadyDecrypted = this.clearEvent && !this.isDecryptionFailure();
+        const forceRedecrypt = options.forceRedecryptIfUntrusted && this.isKeySourceUntrusted();
+        if (alreadyDecrypted && !forceRedecrypt) {
+            // we may want to just ignore this? let's start with rejecting it.
+            throw new Error("Attempt to decrypt event which has already been decrypted");
+        }
+
+        // if we already have a decryption attempt in progress, then it may
+        // fail because it was using outdated info. We now have reason to
+        // succeed where it failed before, but we don't want to have multiple
+        // attempts going at the same time, so just set a flag that says we have
+        // new info.
+        //
+        if (this.decryptionPromise) {
+            logger.log(`Event ${this.getId()} already being decrypted; queueing a retry`);
+            this.retryDecryption = true;
+            return this.decryptionPromise;
+        }
+
+        this.decryptionPromise = this.decryptionLoop(crypto, options);
+        return this.decryptionPromise;
+    }
+
+    /**
+     * Cancel any room key request for this event and resend another.
+     *
+     * @param crypto - crypto module
+     * @param userId - the user who received this event
+     *
+     * @returns a promise that resolves when the request is queued
+     */
+    public cancelAndResendKeyRequest(crypto: Crypto, userId: string): Promise<void> {
+        const wireContent = this.getWireContent();
+        return crypto.requestRoomKey(
+            {
+                algorithm: wireContent.algorithm,
+                room_id: this.getRoomId()!,
+                session_id: wireContent.session_id,
+                sender_key: wireContent.sender_key,
+            },
+            this.getKeyRequestRecipients(userId),
+            true,
+        );
+    }
+
+    /**
+     * Calculate the recipients for keyshare requests.
+     *
+     * @param userId - the user who received this event.
+     *
+     * @returns array of recipients
+     */
+    public getKeyRequestRecipients(userId: string): IKeyRequestRecipient[] {
+        // send the request to all of our own devices
+        const recipients = [
+            {
+                userId,
+                deviceId: "*",
+            },
+        ];
+
+        return recipients;
+    }
+
+    private async decryptionLoop(crypto: CryptoBackend, options: IDecryptOptions = {}): Promise<void> {
+        // make sure that this method never runs completely synchronously.
+        // (doing so would mean that we would clear decryptionPromise *before*
+        // it is set in attemptDecryption - and hence end up with a stuck
+        // `decryptionPromise`).
+        await Promise.resolve();
+
+        // eslint-disable-next-line no-constant-condition
+        while (true) {
+            this.retryDecryption = false;
+
+            let res: IEventDecryptionResult;
+            let err: Error | undefined = undefined;
+            try {
+                if (!crypto) {
+                    res = this.badEncryptedMessage("Encryption not enabled");
+                } else {
+                    res = await crypto.decryptEvent(this);
+                    if (options.isRetry === true) {
+                        logger.info(`Decrypted event on retry (${this.getDetails()})`);
+                    }
+                }
+            } catch (e) {
+                const detailedError = e instanceof DecryptionError ? (<DecryptionError>e).detailedString : String(e);
+
+                err = e as Error;
+
+                // see if we have a retry queued.
+                //
+                // NB: make sure to keep this check in the same tick of the
+                //   event loop as `decryptionPromise = null` below - otherwise we
+                //   risk a race:
+                //
+                //   * A: we check retryDecryption here and see that it is
+                //        false
+                //   * B: we get a second call to attemptDecryption, which sees
+                //        that decryptionPromise is set so sets
+                //        retryDecryption
+                //   * A: we continue below, clear decryptionPromise, and
+                //        never do the retry.
+                //
+                if (this.retryDecryption) {
+                    // decryption error, but we have a retry queued.
+                    logger.log(`Error decrypting event (${this.getDetails()}), but retrying: ${detailedError}`);
+                    continue;
+                }
+
+                // decryption error, no retries queued. Warn about the error and
+                // set it to m.bad.encrypted.
+                //
+                // the detailedString already includes the name and message of the error, and the stack isn't much use,
+                // so we don't bother to log `e` separately.
+                logger.warn(`Error decrypting event (${this.getDetails()}): ${detailedError}`);
+
+                res = this.badEncryptedMessage(String(e));
+            }
+
+            // at this point, we've either successfully decrypted the event, or have given up
+            // (and set res to a 'badEncryptedMessage'). Either way, we can now set the
+            // cleartext of the event and raise Event.decrypted.
+            //
+            // make sure we clear 'decryptionPromise' before sending the 'Event.decrypted' event,
+            // otherwise the app will be confused to see `isBeingDecrypted` still set when
+            // there isn't an `Event.decrypted` on the way.
+            //
+            // see also notes on retryDecryption above.
+            //
+            this.decryptionPromise = null;
+            this.retryDecryption = false;
+            this.setClearData(res);
+
+            // Before we emit the event, clear the push actions so that they can be recalculated
+            // by relevant code. We do this because the clear event has now changed, making it
+            // so that existing rules can be re-run over the applicable properties. Stuff like
+            // highlighting when the user's name is mentioned rely on this happening. We also want
+            // to set the push actions before emitting so that any notification listeners don't
+            // pick up the wrong contents.
+            this.setPushActions(null);
+
+            if (options.emit !== false) {
+                this.emit(MatrixEventEvent.Decrypted, this, err);
+            }
+
+            return;
+        }
+    }
+
+    private badEncryptedMessage(reason: string): IEventDecryptionResult {
+        return {
+            clearEvent: {
+                type: EventType.RoomMessage,
+                content: {
+                    msgtype: "m.bad.encrypted",
+                    body: "** Unable to decrypt: " + reason + " **",
+                },
+            },
+            encryptedDisabledForUnverifiedDevices: reason === `DecryptionError: ${WITHHELD_MESSAGES["m.unverified"]}`,
+        };
+    }
+
+    /**
+     * Update the cleartext data on this event.
+     *
+     * (This is used after decrypting an event; it should not be used by applications).
+     *
+     * @internal
+     *
+     * @param decryptionResult - the decryption result, including the plaintext and some key info
+     *
+     * @remarks
+     * Fires {@link MatrixEventEvent.Decrypted}
+     */
+    private setClearData(decryptionResult: IEventDecryptionResult): void {
+        this.clearEvent = decryptionResult.clearEvent;
+        this.senderCurve25519Key = decryptionResult.senderCurve25519Key ?? null;
+        this.claimedEd25519Key = decryptionResult.claimedEd25519Key ?? null;
+        this.forwardingCurve25519KeyChain = decryptionResult.forwardingCurve25519KeyChain || [];
+        this.untrusted = decryptionResult.untrusted || false;
+        this.encryptedDisabledForUnverifiedDevices = decryptionResult.encryptedDisabledForUnverifiedDevices || false;
+        this.invalidateExtensibleEvent();
+    }
+
+    /**
+     * Gets the cleartext content for this event. If the event is not encrypted,
+     * or encryption has not been completed, this will return null.
+     *
+     * @returns The cleartext (decrypted) content for the event
+     */
+    public getClearContent(): IContent | null {
+        return this.clearEvent ? this.clearEvent.content : null;
+    }
+
+    /**
+     * Check if the event is encrypted.
+     * @returns True if this event is encrypted.
+     */
+    public isEncrypted(): boolean {
+        return !this.isState() && this.event.type === EventType.RoomMessageEncrypted;
+    }
+
+    /**
+     * The curve25519 key for the device that we think sent this event
+     *
+     * For an Olm-encrypted event, this is inferred directly from the DH
+     * exchange at the start of the session: the curve25519 key is involved in
+     * the DH exchange, so only a device which holds the private part of that
+     * key can establish such a session.
+     *
+     * For a megolm-encrypted event, it is inferred from the Olm message which
+     * established the megolm session
+     */
+    public getSenderKey(): string | null {
+        return this.senderCurve25519Key;
+    }
+
+    /**
+     * The additional keys the sender of this encrypted event claims to possess.
+     *
+     * Just a wrapper for #getClaimedEd25519Key (q.v.)
+     */
+    public getKeysClaimed(): Partial<Record<"ed25519", string>> {
+        if (!this.claimedEd25519Key) return {};
+
+        return {
+            ed25519: this.claimedEd25519Key,
+        };
+    }
+
+    /**
+     * Get the ed25519 the sender of this event claims to own.
+     *
+     * For Olm messages, this claim is encoded directly in the plaintext of the
+     * event itself. For megolm messages, it is implied by the m.room_key event
+     * which established the megolm session.
+     *
+     * Until we download the device list of the sender, it's just a claim: the
+     * device list gives a proof that the owner of the curve25519 key used for
+     * this event (and returned by #getSenderKey) also owns the ed25519 key by
+     * signing the public curve25519 key with the ed25519 key.
+     *
+     * In general, applications should not use this method directly, but should
+     * instead use MatrixClient.getEventSenderDeviceInfo.
+     */
+    public getClaimedEd25519Key(): string | null {
+        return this.claimedEd25519Key;
+    }
+
+    /**
+     * Get the curve25519 keys of the devices which were involved in telling us
+     * about the claimedEd25519Key and sender curve25519 key.
+     *
+     * Normally this will be empty, but in the case of a forwarded megolm
+     * session, the sender keys are sent to us by another device (the forwarding
+     * device), which we need to trust to do this. In that case, the result will
+     * be a list consisting of one entry.
+     *
+     * If the device that sent us the key (A) got it from another device which
+     * it wasn't prepared to vouch for (B), the result will be [A, B]. And so on.
+     *
+     * @returns base64-encoded curve25519 keys, from oldest to newest.
+     */
+    public getForwardingCurve25519KeyChain(): string[] {
+        return this.forwardingCurve25519KeyChain;
+    }
+
+    /**
+     * Whether the decryption key was obtained from an untrusted source. If so,
+     * we cannot verify the authenticity of the message.
+     */
+    public isKeySourceUntrusted(): boolean | undefined {
+        return !!this.untrusted;
+    }
+
+    public getUnsigned(): IUnsigned {
+        return this.event.unsigned || {};
+    }
+
+    public setUnsigned(unsigned: IUnsigned): void {
+        this.event.unsigned = unsigned;
+    }
+
+    public unmarkLocallyRedacted(): boolean {
+        const value = this._localRedactionEvent;
+        this._localRedactionEvent = null;
+        if (this.event.unsigned) {
+            this.event.unsigned.redacted_because = undefined;
+        }
+        return !!value;
+    }
+
+    public markLocallyRedacted(redactionEvent: MatrixEvent): void {
+        if (this._localRedactionEvent) return;
+        this.emit(MatrixEventEvent.BeforeRedaction, this, redactionEvent);
+        this._localRedactionEvent = redactionEvent;
+        if (!this.event.unsigned) {
+            this.event.unsigned = {};
+        }
+        this.event.unsigned.redacted_because = redactionEvent.event as IEvent;
+    }
+
+    /**
+     * Change the visibility of an event, as per https://github.com/matrix-org/matrix-doc/pull/3531 .
+     *
+     * @param visibilityChange - event holding a hide/unhide payload, or nothing
+     *   if the event is being reset to its original visibility (presumably
+     *   by a visibility event being redacted).
+     *
+     * @remarks
+     * Fires {@link MatrixEventEvent.VisibilityChange} if `visibilityEvent`
+     *   caused a change in the actual visibility of this event, either by making it
+     *   visible (if it was hidden), by making it hidden (if it was visible) or by
+     *   changing the reason (if it was hidden).
+     */
+    public applyVisibilityEvent(visibilityChange?: IVisibilityChange): void {
+        const visible = visibilityChange?.visible ?? true;
+        const reason = visibilityChange?.reason ?? null;
+        let change = false;
+        if (this.visibility.visible !== visible) {
+            change = true;
+        } else if (!this.visibility.visible && this.visibility["reason"] !== reason) {
+            change = true;
+        }
+        if (change) {
+            if (visible) {
+                this.visibility = MESSAGE_VISIBLE;
+            } else {
+                this.visibility = Object.freeze({
+                    visible: false,
+                    reason,
+                });
+            }
+            this.emit(MatrixEventEvent.VisibilityChange, this, visible);
+        }
+    }
+
+    /**
+     * Return instructions to display or hide the message.
+     *
+     * @returns Instructions determining whether the message
+     * should be displayed.
+     */
+    public messageVisibility(): MessageVisibility {
+        // Note: We may return `this.visibility` without fear, as
+        // this is a shallow frozen object.
+        return this.visibility;
+    }
+
+    /**
+     * Update the content of an event in the same way it would be by the server
+     * if it were redacted before it was sent to us
+     *
+     * @param redactionEvent - event causing the redaction
+     */
+    public makeRedacted(redactionEvent: MatrixEvent): void {
+        // quick sanity-check
+        if (!redactionEvent.event) {
+            throw new Error("invalid redactionEvent in makeRedacted");
+        }
+
+        this._localRedactionEvent = null;
+
+        this.emit(MatrixEventEvent.BeforeRedaction, this, redactionEvent);
+
+        this._replacingEvent = null;
+        // we attempt to replicate what we would see from the server if
+        // the event had been redacted before we saw it.
+        //
+        // The server removes (most of) the content of the event, and adds a
+        // "redacted_because" key to the unsigned section containing the
+        // redacted event.
+        if (!this.event.unsigned) {
+            this.event.unsigned = {};
+        }
+        this.event.unsigned.redacted_because = redactionEvent.event as IEvent;
+
+        for (const key in this.event) {
+            if (this.event.hasOwnProperty(key) && !REDACT_KEEP_KEYS.has(key)) {
+                delete this.event[key as keyof IEvent];
+            }
+        }
+
+        // If the event is encrypted prune the decrypted bits
+        if (this.isEncrypted()) {
+            this.clearEvent = undefined;
+        }
+
+        const keeps =
+            this.getType() in REDACT_KEEP_CONTENT_MAP
+                ? REDACT_KEEP_CONTENT_MAP[this.getType() as keyof typeof REDACT_KEEP_CONTENT_MAP]
+                : {};
+        const content = this.getContent();
+        for (const key in content) {
+            if (content.hasOwnProperty(key) && !keeps[key]) {
+                delete content[key];
+            }
+        }
+
+        this.invalidateExtensibleEvent();
+    }
+
+    /**
+     * Check if this event has been redacted
+     *
+     * @returns True if this event has been redacted
+     */
+    public isRedacted(): boolean {
+        return Boolean(this.getUnsigned().redacted_because);
+    }
+
+    /**
+     * Check if this event is a redaction of another event
+     *
+     * @returns True if this event is a redaction
+     */
+    public isRedaction(): boolean {
+        return this.getType() === EventType.RoomRedaction;
+    }
+
+    /**
+     * Return the visibility change caused by this event,
+     * as per https://github.com/matrix-org/matrix-doc/pull/3531.
+     *
+     * @returns If the event is a well-formed visibility change event,
+     * an instance of `IVisibilityChange`, otherwise `null`.
+     */
+    public asVisibilityChange(): IVisibilityChange | null {
+        if (!EVENT_VISIBILITY_CHANGE_TYPE.matches(this.getType())) {
+            // Not a visibility change event.
+            return null;
+        }
+        const relation = this.getRelation();
+        if (!relation || relation.rel_type != "m.reference") {
+            // Ill-formed, ignore this event.
+            return null;
+        }
+        const eventId = relation.event_id;
+        if (!eventId) {
+            // Ill-formed, ignore this event.
+            return null;
+        }
+        const content = this.getWireContent();
+        const visible = !!content.visible;
+        const reason = content.reason;
+        if (reason && typeof reason != "string") {
+            // Ill-formed, ignore this event.
+            return null;
+        }
+        // Well-formed visibility change event.
+        return {
+            visible,
+            reason,
+            eventId,
+        };
+    }
+
+    /**
+     * Check if this event alters the visibility of another event,
+     * as per https://github.com/matrix-org/matrix-doc/pull/3531.
+     *
+     * @returns True if this event alters the visibility
+     * of another event.
+     */
+    public isVisibilityEvent(): boolean {
+        return EVENT_VISIBILITY_CHANGE_TYPE.matches(this.getType());
+    }
+
+    /**
+     * Get the (decrypted, if necessary) redaction event JSON
+     * if event was redacted
+     *
+     * @returns The redaction event JSON, or an empty object
+     */
+    public getRedactionEvent(): IEvent | {} | null {
+        if (!this.isRedacted()) return null;
+
+        if (this.clearEvent?.unsigned) {
+            return this.clearEvent?.unsigned.redacted_because ?? null;
+        } else if (this.event.unsigned?.redacted_because) {
+            return this.event.unsigned.redacted_because;
+        } else {
+            return {};
+        }
+    }
+
+    /**
+     * Get the push actions, if known, for this event
+     *
+     * @returns push actions
+     */
+    public getPushActions(): IActionsObject | null {
+        return this.pushActions;
+    }
+
+    /**
+     * Set the push actions for this event.
+     *
+     * @param pushActions - push actions
+     */
+    public setPushActions(pushActions: IActionsObject | null): void {
+        this.pushActions = pushActions;
+    }
+
+    /**
+     * Replace the `event` property and recalculate any properties based on it.
+     * @param event - the object to assign to the `event` property
+     */
+    public handleRemoteEcho(event: object): void {
+        const oldUnsigned = this.getUnsigned();
+        const oldId = this.getId();
+        this.event = event;
+        // if this event was redacted before it was sent, it's locally marked as redacted.
+        // At this point, we've received the remote echo for the event, but not yet for
+        // the redaction that we are sending ourselves. Preserve the locally redacted
+        // state by copying over redacted_because so we don't get a flash of
+        // redacted, not-redacted, redacted as remote echos come in
+        if (oldUnsigned.redacted_because) {
+            if (!this.event.unsigned) {
+                this.event.unsigned = {};
+            }
+            this.event.unsigned.redacted_because = oldUnsigned.redacted_because;
+        }
+        // successfully sent.
+        this.setStatus(null);
+        if (this.getId() !== oldId) {
+            // emit the event if it changed
+            this.emit(MatrixEventEvent.LocalEventIdReplaced, this);
+        }
+
+        this.localTimestamp = Date.now() - this.getAge()!;
+    }
+
+    /**
+     * Whether the event is in any phase of sending, send failure, waiting for
+     * remote echo, etc.
+     */
+    public isSending(): boolean {
+        return !!this.status;
+    }
+
+    /**
+     * Update the event's sending status and emit an event as well.
+     *
+     * @param status - The new status
+     */
+    public setStatus(status: EventStatus | null): void {
+        this.status = status;
+        this.emit(MatrixEventEvent.Status, this, status);
+    }
+
+    public replaceLocalEventId(eventId: string): void {
+        this.event.event_id = eventId;
+        this.emit(MatrixEventEvent.LocalEventIdReplaced, this);
+    }
+
+    /**
+     * Get whether the event is a relation event, and of a given type if
+     * `relType` is passed in. State events cannot be relation events
+     *
+     * @param relType - if given, checks that the relation is of the
+     * given type
+     */
+    public isRelation(relType?: string): boolean {
+        // Relation info is lifted out of the encrypted content when sent to
+        // encrypted rooms, so we have to check `getWireContent` for this.
+        const relation = this.getWireContent()?.["m.relates_to"];
+        if (this.isState() && relation?.rel_type === RelationType.Replace) {
+            // State events cannot be m.replace relations
+            return false;
+        }
+        return !!(relation?.rel_type && relation.event_id && (relType ? relation.rel_type === relType : true));
+    }
+
+    /**
+     * Get relation info for the event, if any.
+     */
+    public getRelation(): IEventRelation | null {
+        if (!this.isRelation()) {
+            return null;
+        }
+        return this.getWireContent()["m.relates_to"] ?? null;
+    }
+
+    /**
+     * Set an event that replaces the content of this event, through an m.replace relation.
+     *
+     * @param newEvent - the event with the replacing content, if any.
+     *
+     * @remarks
+     * Fires {@link MatrixEventEvent.Replaced}
+     */
+    public makeReplaced(newEvent?: MatrixEvent): void {
+        // don't allow redacted events to be replaced.
+        // if newEvent is null we allow to go through though,
+        // as with local redaction, the replacing event might get
+        // cancelled, which should be reflected on the target event.
+        if (this.isRedacted() && newEvent) {
+            return;
+        }
+        // don't allow state events to be replaced using this mechanism as per MSC2676
+        if (this.isState()) {
+            return;
+        }
+        if (this._replacingEvent !== newEvent) {
+            this._replacingEvent = newEvent ?? null;
+            this.emit(MatrixEventEvent.Replaced, this);
+            this.invalidateExtensibleEvent();
+        }
+    }
+
+    /**
+     * Returns the status of any associated edit or redaction
+     * (not for reactions/annotations as their local echo doesn't affect the original event),
+     * or else the status of the event.
+     */
+    public getAssociatedStatus(): EventStatus | null {
+        if (this._replacingEvent) {
+            return this._replacingEvent.status;
+        } else if (this._localRedactionEvent) {
+            return this._localRedactionEvent.status;
+        }
+        return this.status;
+    }
+
+    public getServerAggregatedRelation<T>(relType: RelationType | string): T | undefined {
+        return this.getUnsigned()["m.relations"]?.[relType];
+    }
+
+    /**
+     * Returns the event ID of the event replacing the content of this event, if any.
+     */
+    public replacingEventId(): string | undefined {
+        const replaceRelation = this.getServerAggregatedRelation<IAggregatedRelation>(RelationType.Replace);
+        if (replaceRelation) {
+            return replaceRelation.event_id;
+        } else if (this._replacingEvent) {
+            return this._replacingEvent.getId();
+        }
+    }
+
+    /**
+     * Returns the event replacing the content of this event, if any.
+     * Replacements are aggregated on the server, so this would only
+     * return an event in case it came down the sync, or for local echo of edits.
+     */
+    public replacingEvent(): MatrixEvent | null {
+        return this._replacingEvent;
+    }
+
+    /**
+     * Returns the origin_server_ts of the event replacing the content of this event, if any.
+     */
+    public replacingEventDate(): Date | undefined {
+        const replaceRelation = this.getServerAggregatedRelation<IAggregatedRelation>(RelationType.Replace);
+        if (replaceRelation) {
+            const ts = replaceRelation.origin_server_ts;
+            if (Number.isFinite(ts)) {
+                return new Date(ts);
+            }
+        } else if (this._replacingEvent) {
+            return this._replacingEvent.getDate() ?? undefined;
+        }
+    }
+
+    /**
+     * Returns the event that wants to redact this event, but hasn't been sent yet.
+     * @returns the event
+     */
+    public localRedactionEvent(): MatrixEvent | null {
+        return this._localRedactionEvent;
+    }
+
+    /**
+     * For relations and redactions, returns the event_id this event is referring to.
+     */
+    public getAssociatedId(): string | undefined {
+        const relation = this.getRelation();
+        if (this.replyEventId) {
+            return this.replyEventId;
+        } else if (relation) {
+            return relation.event_id;
+        } else if (this.isRedaction()) {
+            return this.event.redacts;
+        }
+    }
+
+    /**
+     * Checks if this event is associated with another event. See `getAssociatedId`.
+     * @deprecated use hasAssociation instead.
+     */
+    public hasAssocation(): boolean {
+        return !!this.getAssociatedId();
+    }
+
+    /**
+     * Checks if this event is associated with another event. See `getAssociatedId`.
+     */
+    public hasAssociation(): boolean {
+        return !!this.getAssociatedId();
+    }
+
+    /**
+     * Update the related id with a new one.
+     *
+     * Used to replace a local id with remote one before sending
+     * an event with a related id.
+     *
+     * @param eventId - the new event id
+     */
+    public updateAssociatedId(eventId: string): void {
+        const relation = this.getRelation();
+        if (relation) {
+            relation.event_id = eventId;
+        } else if (this.isRedaction()) {
+            this.event.redacts = eventId;
+        }
+    }
+
+    /**
+     * Flags an event as cancelled due to future conditions. For example, a verification
+     * request event in the same sync transaction may be flagged as cancelled to warn
+     * listeners that a cancellation event is coming down the same pipe shortly.
+     * @param cancelled - Whether the event is to be cancelled or not.
+     */
+    public flagCancelled(cancelled = true): void {
+        this._isCancelled = cancelled;
+    }
+
+    /**
+     * Gets whether or not the event is flagged as cancelled. See flagCancelled() for
+     * more information.
+     * @returns True if the event is cancelled, false otherwise.
+     */
+    public isCancelled(): boolean {
+        return this._isCancelled;
+    }
+
+    /**
+     * Get a copy/snapshot of this event. The returned copy will be loosely linked
+     * back to this instance, though will have "frozen" event information. Other
+     * properties of this MatrixEvent instance will be copied verbatim, which can
+     * mean they are in reference to this instance despite being on the copy too.
+     * The reference the snapshot uses does not change, however members aside from
+     * the underlying event will not be deeply cloned, thus may be mutated internally.
+     * For example, the sender profile will be copied over at snapshot time, and
+     * the sender profile internally may mutate without notice to the consumer.
+     *
+     * This is meant to be used to snapshot the event details themselves, not the
+     * features (such as sender) surrounding the event.
+     * @returns A snapshot of this event.
+     */
+    public toSnapshot(): MatrixEvent {
+        const ev = new MatrixEvent(JSON.parse(JSON.stringify(this.event)));
+        for (const [p, v] of Object.entries(this)) {
+            if (p !== "event") {
+                // exclude the thing we just cloned
+                // @ts-ignore - XXX: this is just nasty
+                ev[p as keyof MatrixEvent] = v;
+            }
+        }
+        return ev;
+    }
+
+    /**
+     * Determines if this event is equivalent to the given event. This only checks
+     * the event object itself, not the other properties of the event. Intended for
+     * use with toSnapshot() to identify events changing.
+     * @param otherEvent - The other event to check against.
+     * @returns True if the events are the same, false otherwise.
+     */
+    public isEquivalentTo(otherEvent: MatrixEvent): boolean {
+        if (!otherEvent) return false;
+        if (otherEvent === this) return true;
+        const myProps = deepSortedObjectEntries(this.event);
+        const theirProps = deepSortedObjectEntries(otherEvent.event);
+        return JSON.stringify(myProps) === JSON.stringify(theirProps);
+    }
+
+    /**
+     * Summarise the event as JSON. This is currently used by React SDK's view
+     * event source feature and Seshat's event indexing, so take care when
+     * adjusting the output here.
+     *
+     * If encrypted, include both the decrypted and encrypted view of the event.
+     *
+     * This is named `toJSON` for use with `JSON.stringify` which checks objects
+     * for functions named `toJSON` and will call them to customise the output
+     * if they are defined.
+     */
+    public toJSON(): object {
+        const event = this.getEffectiveEvent();
+
+        if (!this.isEncrypted()) {
+            return event;
+        }
+
+        return {
+            decrypted: event,
+            encrypted: this.event,
+        };
+    }
+
+    public setVerificationRequest(request: VerificationRequest): void {
+        this.verificationRequest = request;
+    }
+
+    public setTxnId(txnId: string): void {
+        this.txnId = txnId;
+    }
+
+    public getTxnId(): string | undefined {
+        return this.txnId;
+    }
+
+    /**
+     * Set the instance of a thread associated with the current event
+     * @param thread - the thread
+     */
+    public setThread(thread?: Thread): void {
+        if (this.thread) {
+            this.reEmitter.stopReEmitting(this.thread, [ThreadEvent.Update]);
+        }
+        this.thread = thread;
+        this.setThreadId(thread?.id);
+        if (thread) {
+            this.reEmitter.reEmit(thread, [ThreadEvent.Update]);
+        }
+    }
+
+    /**
+     * Get the instance of the thread associated with the current event
+     */
+    public getThread(): Thread | undefined {
+        return this.thread;
+    }
+
+    public setThreadId(threadId?: string): void {
+        this.threadId = threadId;
+    }
+}
+
+/* REDACT_KEEP_KEYS gives the keys we keep when an event is redacted
+ *
+ * This is specified here:
+ *  http://matrix.org/speculator/spec/HEAD/client_server/latest.html#redactions
+ *
+ * Also:
+ *  - We keep 'unsigned' since that is created by the local server
+ *  - We keep user_id for backwards-compat with v1
+ */
+const REDACT_KEEP_KEYS = new Set([
+    "event_id",
+    "type",
+    "room_id",
+    "user_id",
+    "sender",
+    "state_key",
+    "prev_state",
+    "content",
+    "unsigned",
+    "origin_server_ts",
+]);
+
+// a map from state event type to the .content keys we keep when an event is redacted
+const REDACT_KEEP_CONTENT_MAP: Record<string, Record<string, 1>> = {
+    [EventType.RoomMember]: { membership: 1 },
+    [EventType.RoomCreate]: { creator: 1 },
+    [EventType.RoomJoinRules]: { join_rule: 1 },
+    [EventType.RoomPowerLevels]: {
+        ban: 1,
+        events: 1,
+        events_default: 1,
+        kick: 1,
+        redact: 1,
+        state_default: 1,
+        users: 1,
+        users_default: 1,
+    },
+} as const;