Provide more options for starting dehydration (#4664)

* provide more options for starting dehydration

* improve doc comments and tests

spec/unit/rust-crypto/rust-crypto.spec.ts

@@ -1894,6 +1894,193 @@ describe("RustCrypto", () => {
             await rehydrationCompletedPromise;
             await rustCrypto2.stop();
         });
+
+        describe("start dehydration options", () => {
+            let rustCrypto: RustCrypto;
+            let secretStorage: ServerSideSecretStorageImpl;
+            let dehydratedDeviceInfo: Record<string, any> | undefined;
+
+            // Function that is called when `GET /dehydrated_device` is called
+            // (i.e. when we try to rehydrate a device)
+            const getDehydratedDeviceMock = jest.fn(() => {
+                if (dehydratedDeviceInfo) {
+                    return {
+                        status: 200,
+                        body: dehydratedDeviceInfo,
+                    };
+                } else {
+                    return {
+                        status: 404,
+                        body: {
+                            errcode: "M_NOT_FOUND",
+                            error: "Not found",
+                        },
+                    };
+                }
+            });
+            // Function that is called when `PUT /dehydrated_device` is called
+            // (i.e. when we create a new dehydrated device)
+            const putDehydratedDeviceMock = jest.fn((path, opts) => {
+                const content = JSON.parse(opts.body as string);
+                dehydratedDeviceInfo = {
+                    device_id: content.device_id,
+                    device_data: content.device_data,
+                };
+                return {
+                    status: 200,
+                    body: {
+                        device_id: content.device_id,
+                    },
+                };
+            });
+
+            beforeEach(async () => {
+                // Set up a RustCrypto object with secret storage and cross-signing.
+                const secretStorageCallbacks = {
+                    getSecretStorageKey: async (keys: any, name: string) => {
+                        return [[...Object.keys(keys.keys)][0], new Uint8Array(32)];
+                    },
+                } as SecretStorageCallbacks;
+                secretStorage = new ServerSideSecretStorageImpl(new DummyAccountDataClient(), secretStorageCallbacks);
+
+                const e2eKeyReceiver = new E2EKeyReceiver("http://server");
+                const e2eKeyResponder = new E2EKeyResponder("http://server");
+                e2eKeyResponder.addKeyReceiver(TEST_USER, e2eKeyReceiver);
+                fetchMock.get("path:/_matrix/client/v3/room_keys/version", {
+                    status: 404,
+                    body: {
+                        errcode: "M_NOT_FOUND",
+                        error: "Not found",
+                    },
+                });
+                fetchMock.post("path:/_matrix/client/v3/keys/device_signing/upload", {
+                    status: 200,
+                    body: {},
+                });
+                fetchMock.post("path:/_matrix/client/v3/keys/signatures/upload", {
+                    status: 200,
+                    body: {},
+                });
+                rustCrypto = await makeTestRustCrypto(makeMatrixHttpApi(), TEST_USER, TEST_DEVICE_ID, secretStorage);
+
+                // dehydration requires secret storage and cross signing
+                async function createSecretStorageKey() {
+                    return {
+                        keyInfo: {} as AddSecretStorageKeyOpts,
+                        privateKey: new Uint8Array(32),
+                    };
+                }
+                await rustCrypto.bootstrapCrossSigning({ setupNewCrossSigning: true });
+                await rustCrypto.bootstrapSecretStorage({
+                    createSecretStorageKey,
+                    setupNewSecretStorage: true,
+                    setupNewKeyBackup: false,
+                });
+                // we need to process a sync so that the OlmMachine will upload keys
+                await rustCrypto.preprocessToDeviceMessages([]);
+                await rustCrypto.onSyncCompleted({});
+
+                // set up mocks needed for device dehydration
+                dehydratedDeviceInfo = undefined;
+                fetchMock.get(
+                    "path:/_matrix/client/unstable/org.matrix.msc3814.v1/dehydrated_device",
+                    getDehydratedDeviceMock,
+                );
+                fetchMock.put(
+                    "path:/_matrix/client/unstable/org.matrix.msc3814.v1/dehydrated_device",
+                    putDehydratedDeviceMock,
+                );
+                fetchMock.post(/_matrix\/client\/unstable\/org.matrix.msc3814.v1\/dehydrated_device\/.*\/events/, {
+                    status: 200,
+                    body: {
+                        events: [],
+                        next_batch: "foo",
+                    },
+                });
+                getDehydratedDeviceMock.mockClear();
+                putDehydratedDeviceMock.mockClear();
+            });
+
+            afterEach(() => {
+                rustCrypto.stop();
+            });
+
+            // Several tests require a dehydrated device and dehydration key
+            // already set up.
+            async function setUpInitialDehydratedDevice() {
+                await rustCrypto.startDehydration();
+                getDehydratedDeviceMock.mockClear();
+                putDehydratedDeviceMock.mockClear();
+                return await secretStorage.get("org.matrix.msc3814");
+            }
+
+            it("should create a new key and dehydrate a device when no options given", async () => {
+                // With the default options, when we don't have an existing key ...
+                await rustCrypto.startDehydration();
+                // ... we create a new dehydration key ...
+                expect(await secretStorage.get("org.matrix.msc3814")).toBeTruthy();
+                // ... and create a new dehydrated device.
+                expect(putDehydratedDeviceMock).toHaveBeenCalled();
+            });
+
+            it("should rehydrate a device if available and keep existing key when no options given", async () => {
+                const origDehydrationKey = await setUpInitialDehydratedDevice();
+
+                // If we already have a dehydration key and dehydrated device...
+                await rustCrypto.startDehydration();
+                // ... we should fetch the device to rehydrate it ...
+                expect(getDehydratedDeviceMock).toHaveBeenCalled();
+                // ... create a new dehydrated device ...
+                expect(putDehydratedDeviceMock).toHaveBeenCalled();
+                // ... and keep the same dehydration key.
+                expect(await secretStorage.get("org.matrix.msc3814")).toEqual(origDehydrationKey);
+            });
+
+            it("should do nothing if onlyIfKeyCached is true and we have no key cached", async () => {
+                // Since there is no key cached, so should do nothing.  i.e. it
+                // should not make any HTTP requests and should not create a new key.
+                await rustCrypto.startDehydration({ onlyIfKeyCached: true });
+                expect(getDehydratedDeviceMock).not.toHaveBeenCalled();
+                expect(putDehydratedDeviceMock).not.toHaveBeenCalled();
+                expect(await secretStorage.get("org.matrix.msc3814")).toBeFalsy();
+            });
+
+            it("should start dehydration when onlyIfKeyCached is true, and we have a cached key", async () => {
+                const origDehydrationKey = await setUpInitialDehydratedDevice();
+
+                // If `onlyIfKeyCached` is `true`, and we already have have a
+                // key, we should behave the same as if no options were given.
+                await rustCrypto.startDehydration({ onlyIfKeyCached: true });
+                expect(getDehydratedDeviceMock).toHaveBeenCalled();
+                expect(putDehydratedDeviceMock).toHaveBeenCalled();
+                expect(await secretStorage.get("org.matrix.msc3814")).toEqual(origDehydrationKey);
+            });
+
+            it("should not rehydrate if rehydrate is set to false", async () => {
+                const origDehydrationKey = await setUpInitialDehydratedDevice();
+
+                // If `rehydrate` is set to `false` ...
+                await rustCrypto.startDehydration({ rehydrate: false });
+                // ... we should not try to rehydrate ...
+                expect(getDehydratedDeviceMock).not.toHaveBeenCalled();
+                // ... but we should still create a new dehydrated device ...
+                expect(putDehydratedDeviceMock).toHaveBeenCalled();
+                // ... and we should keep the same dehydration key.
+                expect(await secretStorage.get("org.matrix.msc3814")).toEqual(origDehydrationKey);
+            });
+
+            it("should create a new key if createNewKey is set to true", async () => {
+                const origDehydrationKey = await setUpInitialDehydratedDevice();
+
+                // If `createNewKey` is set to `true` ...
+                await rustCrypto.startDehydration({ createNewKey: true });
+                // ... we should rehydrate and dehydrate as normal ...
+                expect(getDehydratedDeviceMock).toHaveBeenCalled();
+                expect(putDehydratedDeviceMock).toHaveBeenCalled();
+                // ... and we should create a new dehydration key.
+                expect(await secretStorage.get("org.matrix.msc3814")).not.toEqual(origDehydrationKey);
+            });
+        });
     });
 
     describe("import & export secrets bundle", () => {

src/crypto-api/index.ts

@@ -41,6 +41,37 @@ import { MatrixEvent } from "../models/event.ts";
  * @packageDocumentation
  */
 
+/**
+ * The options to start device dehydration.
+ */
+export interface StartDehydrationOpts {
+    /**
+     * Force creation of a new dehydration key, even if there is already an
+     * existing dehydration key. If `false`, and `onlyIfKeyCached` is `false`, a
+     * new key will be created if there is no existing dehydration key, whether
+     * already cached in our local storage or stored in Secret Storage.
+     *
+     * Checking for the presence of the key in Secret Storage may result in the
+     * `getSecretStorageKey` callback being called.
+     *
+     * Defaults to `false`.
+     */
+    createNewKey?: boolean;
+    /**
+     * Only start dehydration if we have a dehydration key cached in our local
+     * storage. If `true`, Secret Storage will not be checked. Defaults to
+     * `false`.
+     */
+    onlyIfKeyCached?: boolean;
+    /**
+     * Try to rehydrate a device before creating a new dehydrated device.
+     * Setting this to `false` may be useful for situations where the client is
+     * known to pre-date the dehydrated device, and so rehydration is
+     * unnecessary. Defaults to `true`.
+     */
+    rehydrate?: boolean;
+}
+
 /**
  * Public interface to the cryptography parts of the js-sdk
  *
@@ -649,10 +680,11 @@ export interface CryptoApi {
     /**
      * Start using device dehydration.
      *
-     * - Rehydrates a dehydrated device, if one is available.
+     * - Rehydrates a dehydrated device, if one is available and `opts.rehydrate`
+     *   is `true`.
      * - Creates a new dehydration key, if necessary, and stores it in Secret
      *   Storage.
-     *   - If `createNewKey` is set to true, always creates a new key.
+     *   - If `opts.createNewKey` is set to true, always creates a new key.
      *   - If a dehydration key is not available, creates a new one.
      * - Creates a new dehydrated device, and schedules periodically creating
      *   new dehydrated devices.
@@ -661,11 +693,11 @@ export interface CryptoApi {
      * `true`, and must not be called until after cross-signing and secret
      * storage have been set up.
      *
-     * @param createNewKey - whether to force creation of a new dehydration key.
-     *   This can be used, for example, if Secret Storage is being reset.  Defaults
-     *   to false.
+     * @param opts - options for device dehydration. For backwards compatibility
+     *     with old code, a boolean can be given here, which will be treated as
+     *     the `createNewKey` option. However, this is deprecated.
      */
-    startDehydration(createNewKey?: boolean): Promise<void>;
+    startDehydration(opts?: StartDehydrationOpts | boolean): Promise<void>;
 
     ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////
     //

src/crypto/index.ts

@@ -105,6 +105,7 @@ import {
     CryptoEventHandlerMap as CryptoApiCryptoEventHandlerMap,
     KeyBackupRestoreResult,
     KeyBackupRestoreOpts,
+    StartDehydrationOpts,
 } from "../crypto-api/index.ts";
 import { Device, DeviceMap } from "../models/device.ts";
 import { deviceInfoToDevice } from "./device-converter.ts";
@@ -4327,7 +4328,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
     /**
      * Stub function -- dehydration is not implemented here, so throw error
      */
-    public async startDehydration(createNewKey?: boolean): Promise<void> {
+    public async startDehydration(createNewKey?: StartDehydrationOpts | boolean): Promise<void> {
         throw new Error("Not implemented");
     }
 

src/rust-crypto/DehydratedDeviceManager.ts

@@ -23,7 +23,7 @@ import { IToDeviceEvent } from "../sync-accumulator.ts";
 import { ServerSideSecretStorage } from "../secret-storage.ts";
 import { decodeBase64 } from "../base64.ts";
 import { Logger } from "../logger.ts";
-import { CryptoEvent, CryptoEventHandlerMap } from "../crypto-api/index.ts";
+import { CryptoEvent, CryptoEventHandlerMap, StartDehydrationOpts } from "../crypto-api/index.ts";
 import { TypedEventEmitter } from "../models/typed-event-emitter.ts";
 
 /**
@@ -121,28 +121,39 @@ export class DehydratedDeviceManager extends TypedEventEmitter<DehydratedDevices
     /**
      * Start using device dehydration.
      *
-     * - Rehydrates a dehydrated device, if one is available.
+     * - Rehydrates a dehydrated device, if one is available and `opts.rehydrate`
+     *   is `true`.
      * - Creates a new dehydration key, if necessary, and stores it in Secret
      *   Storage.
-     *   - If `createNewKey` is set to true, always creates a new key.
+     *   - If `opts.createNewKey` is set to true, always creates a new key.
      *   - If a dehydration key is not available, creates a new one.
      * - Creates a new dehydrated device, and schedules periodically creating
      *   new dehydrated devices.
      *
-     * @param createNewKey - whether to force creation of a new dehydration key.
-     *   This can be used, for example, if Secret Storage is being reset.
+     * @param opts - options for device dehydration. For backwards compatibility
+     *     with old code, a boolean can be given here, which will be treated as
+     *     the `createNewKey` option. However, this is deprecated.
      */
-    public async start(createNewKey?: boolean): Promise<void> {
-        this.stop();
-        try {
-            await this.rehydrateDeviceIfAvailable();
-        } catch (e) {
-            // If rehydration fails, there isn't much we can do about it.  Log
-            // the error, and create a new device.
-            this.logger.info("dehydration: Error rehydrating device:", e);
-            this.emit(CryptoEvent.RehydrationError, (e as Error).message);
+    public async start(opts: StartDehydrationOpts | boolean = {}): Promise<void> {
+        if (typeof opts === "boolean") {
+            opts = { createNewKey: opts };
         }
-        if (createNewKey) {
+
+        if (opts.onlyIfKeyCached && !(await this.olmMachine.dehydratedDevices().getDehydratedDeviceKey())) {
+            return;
+        }
+        this.stop();
+        if (opts.rehydrate !== false) {
+            try {
+                await this.rehydrateDeviceIfAvailable();
+            } catch (e) {
+                // If rehydration fails, there isn't much we can do about it.  Log
+                // the error, and create a new device.
+                this.logger.info("dehydration: Error rehydrating device:", e);
+                this.emit(CryptoEvent.RehydrationError, (e as Error).message);
+            }
+        }
+        if (opts.createNewKey) {
             await this.resetKey();
         }
         await this.scheduleDeviceDehydration();

src/rust-crypto/rust-crypto.ts

@@ -67,6 +67,7 @@ import {
     CryptoEventHandlerMap,
     KeyBackupRestoreOpts,
     KeyBackupRestoreResult,
+    StartDehydrationOpts,
 } from "../crypto-api/index.ts";
 import { deviceKeysToDeviceMap, rustDeviceToJsDevice } from "./device-converter.ts";
 import { IDownloadKeyResult, IQueryKeysRequest } from "../client.ts";
@@ -1425,11 +1426,11 @@ export class RustCrypto extends TypedEventEmitter<RustCryptoEvents, CryptoEventH
     /**
      * Implementation of {@link CryptoApi#startDehydration}.
      */
-    public async startDehydration(createNewKey?: boolean): Promise<void> {
+    public async startDehydration(opts: StartDehydrationOpts | boolean = {}): Promise<void> {
         if (!(await this.isCrossSigningReady()) || !(await this.isSecretStorageReady())) {
             throw new Error("Device dehydration requires cross-signing and secret storage to be set up");
         }
-        return await this.dehydratedDeviceManager.start(createNewKey);
+        return await this.dehydratedDeviceManager.start(opts || {});
     }
 
     /**