Add a config flag to enable the rust crypto-sdk (#9759)

This PR adds an option to `config.json` which will make the js-sdk use the rust crypto sdk, instead of the libolm implementation.

To use it, you need to add something like this to `config.json`:

```
    "features": {
        "feature_rust_crypto": true
    },
```

We don't (yet) have any way to migrate a device between implementations, so the setting that was in use when you log in is persisted to the device; it is *visible* via the labs section but cannot currently be changed.

This is part of https://github.com/vector-im/element-web/issues/21972, and enables the functionality added to the js-sdk in https://github.com/matrix-org/matrix-js-sdk/pull/2969.

test/MatrixClientPeg-test.ts

@@ -14,8 +14,11 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+import { logger } from "matrix-js-sdk/src/logger";
+
 import { advanceDateAndTime, stubClient } from "./test-utils";
-import { MatrixClientPeg as peg } from "../src/MatrixClientPeg";
+import { IMatrixClientPeg, MatrixClientPeg as peg } from "../src/MatrixClientPeg";
+import SettingsStore from "../src/settings/SettingsStore";
 
 jest.useFakeTimers();
 
@@ -57,4 +60,71 @@ describe("MatrixClientPeg", () => {
         expect(peg.userRegisteredWithinLastHours(1)).toBe(false);
         expect(peg.userRegisteredWithinLastHours(24)).toBe(false);
     });
+
+    describe(".start", () => {
+        let testPeg: IMatrixClientPeg;
+
+        beforeEach(() => {
+            // instantiate a MatrixClientPegClass instance, with a new MatrixClient
+            const PegClass = Object.getPrototypeOf(peg).constructor;
+            testPeg = new PegClass();
+            testPeg.replaceUsingCreds({
+                accessToken: "SEKRET",
+                homeserverUrl: "http://example.com",
+                userId: "@user:example.com",
+                deviceId: "TEST_DEVICE_ID",
+            });
+
+            // stub out Logger.log which gets called a lot and clutters up the test output
+            jest.spyOn(logger, "log").mockImplementation(() => {});
+        });
+
+        it("should initialise client crypto", async () => {
+            const mockInitCrypto = jest.spyOn(testPeg.get(), "initCrypto").mockResolvedValue(undefined);
+            const mockSetTrustCrossSignedDevices = jest
+                .spyOn(testPeg.get(), "setCryptoTrustCrossSignedDevices")
+                .mockImplementation(() => {});
+            const mockStartClient = jest.spyOn(testPeg.get(), "startClient").mockResolvedValue(undefined);
+
+            await testPeg.start();
+            expect(mockInitCrypto).toHaveBeenCalledTimes(1);
+            expect(mockSetTrustCrossSignedDevices).toHaveBeenCalledTimes(1);
+            expect(mockStartClient).toHaveBeenCalledTimes(1);
+        });
+
+        it("should carry on regardless if there is an error initialising crypto", async () => {
+            const e2eError = new Error("nope nope nope");
+            const mockInitCrypto = jest.spyOn(testPeg.get(), "initCrypto").mockRejectedValue(e2eError);
+            const mockSetTrustCrossSignedDevices = jest
+                .spyOn(testPeg.get(), "setCryptoTrustCrossSignedDevices")
+                .mockImplementation(() => {});
+            const mockStartClient = jest.spyOn(testPeg.get(), "startClient").mockResolvedValue(undefined);
+            const mockWarning = jest.spyOn(logger, "warn").mockReturnValue(undefined);
+
+            await testPeg.start();
+            expect(mockInitCrypto).toHaveBeenCalledTimes(1);
+            expect(mockSetTrustCrossSignedDevices).not.toHaveBeenCalled();
+            expect(mockStartClient).toHaveBeenCalledTimes(1);
+            expect(mockWarning).toHaveBeenCalledWith(expect.stringMatching("Unable to initialise e2e"), e2eError);
+        });
+
+        it("should initialise the rust crypto library, if enabled", async () => {
+            const originalGetValue = SettingsStore.getValue;
+            jest.spyOn(SettingsStore, "getValue").mockImplementation(
+                (settingName: string, roomId: string | null = null, excludeDefault = false) => {
+                    if (settingName === "feature_rust_crypto") {
+                        return true;
+                    }
+                    return originalGetValue(settingName, roomId, excludeDefault);
+                },
+            );
+
+            const mockInitCrypto = jest.spyOn(testPeg.get(), "initCrypto").mockResolvedValue(undefined);
+            const mockInitRustCrypto = jest.spyOn(testPeg.get(), "initRustCrypto").mockResolvedValue(undefined);
+
+            await testPeg.start();
+            expect(mockInitCrypto).not.toHaveBeenCalled();
+            expect(mockInitRustCrypto).toHaveBeenCalledTimes(1);
+        });
+    });
 });