crypto: Add new ClientEvent.ReceivedToDeviceMessage with proper OlmEncryptionInfo support (#4891)

* crypto: Add new ClientEvent.ReceivedToDeviceMessage

refactor rename ProcessedToDeviceEvent to ReceivedToDeviceEvent

* fix: Restore legacy isEncrypted() for to-device messages

* Update test for new preprocessToDeviceMessages API

* quick fix on doc

* quick update docs and renaming

* review: Better doc and names for OlmEncryptionInfo

* review: Remove IToDeviceMessage alias and only keep IToDeviceEvent

* review: improve comments of processToDeviceMessages

* review: pass up encrypted event when no crypto callbacks

* review: use single payload for ReceivedToDeviceMessage

* fix linter

* review: minor comment update

spec/integ/crypto/to-device-messages.spec.ts

@@ -17,13 +17,22 @@ limitations under the License.
 import fetchMock from "fetch-mock-jest";
 import "fake-indexeddb/auto";
 import { IDBFactory } from "fake-indexeddb";
+import Olm from "@matrix-org/olm";
 
 import { getSyncResponse, syncPromise } from "../../test-utils/test-utils";
-import { createClient, type MatrixClient } from "../../../src";
+import {
+    ClientEvent,
+    createClient,
+    type IToDeviceEvent,
+    type MatrixClient,
+    type MatrixEvent,
+    type ReceivedToDeviceMessage,
+} from "../../../src";
 import * as testData from "../../test-utils/test-data";
 import { E2EKeyResponder } from "../../test-utils/E2EKeyResponder";
 import { SyncResponder } from "../../test-utils/SyncResponder";
 import { E2EKeyReceiver } from "../../test-utils/E2EKeyReceiver";
+import { encryptOlmEvent, establishOlmSession, getTestOlmAccountKeys } from "./olm-utils.ts";
 
 afterEach(() => {
     // reset fake-indexeddb after each test, to make sure we don't leak connections
@@ -43,6 +52,8 @@ describe("to-device-messages", () => {
 
     /** an object which intercepts `/keys/query` requests on the test homeserver */
     let e2eKeyResponder: E2EKeyResponder;
+    let e2eKeyReceiver: E2EKeyReceiver;
+    let syncResponder: SyncResponder;
 
     beforeEach(
         async () => {
@@ -59,8 +70,8 @@ describe("to-device-messages", () => {
             });
 
             e2eKeyResponder = new E2EKeyResponder(homeserverUrl);
-            new E2EKeyReceiver(homeserverUrl);
-            const syncResponder = new SyncResponder(homeserverUrl);
+            e2eKeyReceiver = new E2EKeyReceiver(homeserverUrl);
+            syncResponder = new SyncResponder(homeserverUrl);
 
             // add bob as known user
             syncResponder.sendOrQueueSyncResponse(getSyncResponse([testData.BOB_TEST_USER_ID]));
@@ -149,4 +160,111 @@ describe("to-device-messages", () => {
             // for future: check that bob's device can decrypt the ciphertext?
         });
     });
+
+    describe("receive to-device-messages", () => {
+        it("Should receive decrypted to-device message via ClientEvent", async () => {
+            // create a test olm device which we will use to communicate with alice. We use libolm to implement this.
+            await Olm.init();
+            const testOlmAccount = new Olm.Account();
+            testOlmAccount.create();
+
+            const testDeviceKeys = getTestOlmAccountKeys(testOlmAccount, "@bob:xyz", "DEVICE_ID");
+            e2eKeyResponder.addDeviceKeys(testDeviceKeys);
+
+            await aliceClient.startClient();
+            await syncPromise(aliceClient);
+
+            syncResponder.sendOrQueueSyncResponse(getSyncResponse(["@bob:xyz"]));
+            await syncPromise(aliceClient);
+
+            const p2pSession = await establishOlmSession(aliceClient, e2eKeyReceiver, syncResponder, testOlmAccount);
+
+            const toDeviceEvent = encryptOlmEvent({
+                sender: "@bob:xyz",
+                senderKey: testDeviceKeys.keys[`curve25519:DEVICE_ID`],
+                senderSigningKey: testDeviceKeys.keys[`ed25519:DEVICE_ID`],
+                p2pSession: p2pSession,
+                recipient: aliceClient.getUserId()!,
+                recipientCurve25519Key: e2eKeyReceiver.getDeviceKey(),
+                recipientEd25519Key: e2eKeyReceiver.getSigningKey(),
+                plaincontent: {
+                    body: "foo",
+                },
+                plaintype: "m.test.type",
+            });
+
+            const processedToDeviceResolver: PromiseWithResolvers<ReceivedToDeviceMessage> = Promise.withResolvers();
+
+            aliceClient.on(ClientEvent.ReceivedToDeviceMessage, (payload) => {
+                processedToDeviceResolver.resolve(payload);
+            });
+
+            const oldToDeviceResolver: PromiseWithResolvers<MatrixEvent> = Promise.withResolvers();
+
+            aliceClient.on(ClientEvent.ToDeviceEvent, (event) => {
+                oldToDeviceResolver.resolve(event);
+            });
+
+            expect(toDeviceEvent.type).toBe("m.room.encrypted");
+
+            syncResponder.sendOrQueueSyncResponse({ to_device: { events: [toDeviceEvent] } });
+            await syncPromise(aliceClient);
+
+            const { message, encryptionInfo } = await processedToDeviceResolver.promise;
+
+            expect(message.type).toBe("m.test.type");
+            expect(message.content["body"]).toBe("foo");
+
+            expect(encryptionInfo).not.toBeNull();
+            expect(encryptionInfo!.senderVerified).toBe(false);
+            expect(encryptionInfo!.sender).toBe("@bob:xyz");
+            expect(encryptionInfo!.senderDevice).toBe("DEVICE_ID");
+
+            const oldFormat = await oldToDeviceResolver.promise;
+            expect(oldFormat.isEncrypted()).toBe(true);
+            expect(oldFormat.getType()).toBe("m.test.type");
+            expect(oldFormat.getContent()["body"]).toBe("foo");
+        });
+
+        it("Should receive clear to-device message via ClientEvent", async () => {
+            await aliceClient.startClient();
+            await syncPromise(aliceClient);
+
+            const toDeviceEvent: IToDeviceEvent = {
+                sender: "@bob:xyz",
+                type: "m.test.type",
+                content: {
+                    body: "foo",
+                },
+            };
+
+            const processedToDeviceResolver: PromiseWithResolvers<ReceivedToDeviceMessage> = Promise.withResolvers();
+
+            aliceClient.on(ClientEvent.ReceivedToDeviceMessage, (payload) => {
+                processedToDeviceResolver.resolve(payload);
+            });
+
+            const oldToDeviceResolver: PromiseWithResolvers<MatrixEvent> = Promise.withResolvers();
+
+            aliceClient.on(ClientEvent.ToDeviceEvent, (event) => {
+                oldToDeviceResolver.resolve(event);
+            });
+
+            syncResponder.sendOrQueueSyncResponse({ to_device: { events: [toDeviceEvent] } });
+            await syncPromise(aliceClient);
+
+            const { message, encryptionInfo } = await processedToDeviceResolver.promise;
+
+            expect(message.type).toBe("m.test.type");
+            expect(message.content["body"]).toBe("foo");
+
+            // When the message is not encrypted, we don't have the encryptionInfo.
+            expect(encryptionInfo).toBeNull();
+
+            const oldFormat = await oldToDeviceResolver.promise;
+            expect(oldFormat.isEncrypted()).toBe(false);
+            expect(oldFormat.getType()).toBe("m.test.type");
+            expect(oldFormat.getContent()["body"]).toBe("foo");
+        });
+    });
 });