Pass CryptoBackend into SyncApi (#3010)

I need to start calling back into the new rust crypto implementation from the /sync loops, so I need to pass it into SyncApi. To reduce the coupling, I've defined a new interface specifying the methods which exist for that purpose. Currently it's only onSyncCompleted.

spec/integ/sliding-sync-sdk.spec.ts

@@ -119,7 +119,7 @@ describe("SlidingSyncSdk", () => {
         if (testOpts.withCrypto) {
             httpBackend!.when("GET", "/room_keys/version").respond(404, {});
             await client!.initCrypto();
-            syncOpts.crypto = client!.crypto;
+            syncOpts.cryptoCallbacks = syncOpts.crypto = client!.crypto;
         }
         httpBackend!.when("GET", "/_matrix/client/r0/pushrules").respond(200, {});
         sdk = new SlidingSyncSdk(mockSlidingSync, client, testOpts, syncOpts);

src/client.ts

@@ -1453,6 +1453,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
     protected buildSyncApiOptions(): SyncApiOptions {
         return {
             crypto: this.crypto,
+            cryptoCallbacks: this.cryptoBackend,
             canResetEntireTimeline: (roomId: string): boolean => {
                 if (!this.canResetTimelineCallback) {
                     return false;

src/common-crypto/CryptoBackend.ts

@@ -20,7 +20,7 @@ import { MatrixEvent } from "../models/event";
 /**
  * Common interface for the crypto implementations
  */
-export interface CryptoBackend {
+export interface CryptoBackend extends SyncCryptoCallbacks {
     /**
      * Global override for whether the client should ever send encrypted
      * messages to unverified devices. This provides the default for rooms which
@@ -71,3 +71,27 @@ export interface CryptoBackend {
      */
     exportRoomKeys(): Promise<IMegolmSessionData[]>;
 }
+
+/** The methods which crypto implementations should expose to the Sync api */
+export interface SyncCryptoCallbacks {
+    /**
+     * Called by the /sync loop after each /sync response is processed.
+     *
+     * Used to complete batch processing, or to initiate background processes
+     *
+     * @param syncState - information about the completed sync.
+     */
+    onSyncCompleted(syncState: OnSyncCompletedData): void;
+}
+
+export interface OnSyncCompletedData {
+    /**
+     * The 'next_batch' result from /sync, which will become the 'since' token for the next call to /sync.
+     */
+    nextSyncToken?: string;
+
+    /**
+     * True if we are working our way through a backlog of events after connecting.
+     */
+    catchingUp?: boolean;
+}

src/crypto/index.ts

@@ -88,7 +88,7 @@ import { IContent } from "../models/event";
 import { ISyncResponse } from "../sync-accumulator";
 import { ISignatures } from "../@types/signed";
 import { IMessage } from "./algorithms/olm";
-import { CryptoBackend } from "../common-crypto/CryptoBackend";
+import { CryptoBackend, OnSyncCompletedData } from "../common-crypto/CryptoBackend";
 import { RoomState, RoomStateEvent } from "../models/room-state";
 
 const DeviceVerification = DeviceInfo.DeviceVerification;
@@ -3013,7 +3013,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
      *
      * @param syncData -  the data from the 'MatrixClient.sync' event
      */
-    public async onSyncCompleted(syncData: ISyncStateData): Promise<void> {
+    public async onSyncCompleted(syncData: OnSyncCompletedData): Promise<void> {
         this.deviceList.setSyncToken(syncData.nextSyncToken ?? null);
         this.deviceList.saveIfDirty();
 

src/rust-crypto/rust-crypto.ts

@@ -18,7 +18,7 @@ import * as RustSdkCryptoJs from "@matrix-org/matrix-sdk-crypto-js";
 
 import type { IEventDecryptionResult, IMegolmSessionData } from "../@types/crypto";
 import { MatrixEvent } from "../models/event";
-import { CryptoBackend } from "../common-crypto/CryptoBackend";
+import { CryptoBackend, OnSyncCompletedData } from "../common-crypto/CryptoBackend";
 
 // import { logger } from "../logger";
 
@@ -62,4 +62,12 @@ export class RustCrypto implements CryptoBackend {
         // TODO
         return [];
     }
+
+    /** 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 {}
 }

src/sync.ts

@@ -25,6 +25,7 @@ limitations under the License.
 
 import { Optional } from "matrix-events-sdk";
 
+import type { SyncCryptoCallbacks } from "./common-crypto/CryptoBackend";
 import { User, UserEvent } from "./models/user";
 import { NotificationCountType, Room, RoomEvent } from "./models/room";
 import * as utils from "./utils";
@@ -115,9 +116,18 @@ function debuglog(...params: any[]): void {
  * Options passed into the constructor of SyncApi by MatrixClient
  */
 export interface SyncApiOptions {
-    // Crypto manager
+    /**
+     * Crypto manager
+     *
+     * @deprecated in favour of cryptoCallbacks
+     */
     crypto?: Crypto;
 
+    /**
+     * If crypto is enabled on our client, callbacks into the crypto module
+     */
+    cryptoCallbacks?: SyncCryptoCallbacks;
+
     /**
      * A function which is called
      * with a room ID and returns a boolean. It should return 'true' if the SDK can
@@ -925,8 +935,8 @@ export class SyncApi {
 
             // tell the crypto module to do its processing. It may block (to do a
             // /keys/changes request).
-            if (this.syncOpts.crypto) {
-                await this.syncOpts.crypto.onSyncCompleted(syncEventData);
+            if (this.syncOpts.cryptoCallbacks) {
+                await this.syncOpts.cryptoCallbacks.onSyncCompleted(syncEventData);
             }
 
             // keep emitting SYNCING -> SYNCING for clients who want to do bulk updates