Switch crypto.spec.ts away from TestClient and matrix-mock-request. (#3142)

I became sufficiently annoyed with matrix-mock-request that I decided to replace it with fetch-mock, which is what we use in matrix-react-sdk and is generally more powerful, easier to use, and actually maintained.

Unfortunately, we have a TestClient utility which is widely used and quite tightly integrated with matrix-mock-request. It wasn't going to be possible to change TestClient without changing all the tests that use it.

I also don't find TestClient particularly easy to use - it does a lot of stuff which I'm not convinced ought to be done for every single test.

So... I've introduced a couple of new classes (SyncResponder, E2EKeyReceiver) which do some of the useful bits of TestClient, but in a more granular way, and have switched crypto.spec.ts over so that rather than instantiating a TestClient for each test, it creates a MatrixClient directly and intercepts the endpoints necessary.

spec/test-utils/SyncResponder.ts

@@ -0,0 +1,131 @@
+/*
+Copyright 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.
+*/
+
+import debugFunc from "debug";
+import { Debugger } from "debug";
+import fetchMock from "fetch-mock-jest";
+import { MockResponse } from "fetch-mock";
+
+/** Interface implemented by classes that intercept `/sync` requests from test clients
+ *
+ * Common interface implemented by {@link TestClient} and {@link SyncResponder}
+ */
+export interface ISyncResponder {
+    /** Next time we see a sync request (or immediately, if there is one waiting), send the given response
+     *
+     * @param response - response to /sync request
+     */
+    sendOrQueueSyncResponse(response: object): void;
+}
+
+enum SyncResponderState {
+    IDLE,
+    WAITING_FOR_REQUEST,
+    WAITING_FOR_RESPONSE,
+}
+
+/** SyncResponder: An object which intercepts `/sync` fetches via fetch-mock.
+ *
+ * Two modes are possible:
+ *  * A response can be queued up; the next call to `/sync` will return it.
+ *  * If a call to `/sync` arrives before a response is queued, it will block until a call to {@link #sendOrQueueSyncResponse}.
+ */
+export class SyncResponder implements ISyncResponder {
+    private readonly debug: Debugger;
+    private state: SyncResponderState = SyncResponderState.IDLE;
+
+    /*
+     * properties that are only valid in WAITING_FOR_REQUEST
+     */
+
+    /** the response to be sent when the request is made */
+    private pendingResponse: object | null = null;
+
+    /*
+     * properties that are only valid in WAITING_FOR_RESPONSE
+     */
+
+    /** a callback to be called with a response once one is registered.
+     *
+     * It will release the /sync request and update the state.
+     */
+    private onResponseReceived: ((response: object) => void) | null = null;
+
+    /**
+     * Construct a new SyncResponder.
+     *
+     * It will immediately register an intercept of `/sync` requests for the given homeserverUrl.
+     * Only /sync requests made to this server will be intercepted: this allows a single test to use more than one
+     * client and have overlapping /sync requests.
+     *
+     * @param homeserverUrl - the Homeserver Url of the client under test.
+     */
+    public constructor(homeserverUrl: string) {
+        this.debug = debugFunc(`sync-responder:[${homeserverUrl}]`);
+        fetchMock.get("begin:" + new URL("/_matrix/client/r0/sync?", homeserverUrl).toString(), (_url, _options) =>
+            this.onSyncRequest(),
+        );
+    }
+
+    private async onSyncRequest(): Promise<MockResponse> {
+        switch (this.state) {
+            case SyncResponderState.IDLE: {
+                this.debug("Got /sync request: waiting for response to be ready");
+                const res = await new Promise<object>((resolve) => {
+                    this.onResponseReceived = resolve;
+                    this.state = SyncResponderState.WAITING_FOR_RESPONSE;
+                });
+                this.debug("Responding to /sync");
+                this.state = SyncResponderState.IDLE;
+                this.onResponseReceived = null;
+                return res;
+            }
+
+            case SyncResponderState.WAITING_FOR_REQUEST: {
+                this.debug("Got /sync request: responding immediately with queued response");
+                const res = this.pendingResponse!;
+                this.state = SyncResponderState.IDLE;
+                this.pendingResponse = null;
+                return res;
+            }
+
+            default:
+                // we must already be in WAITING_FOR_RESPONSE, ie we already have a /sync request in progress
+                throw new Error(`Got unexpected /sync request in state ${this.state}`);
+        }
+    }
+
+    /** Next time we see a sync request (or immediately, if there is one waiting), send the given response
+     *
+     * @param response - response to /sync request
+     */
+    public sendOrQueueSyncResponse(response: object): void {
+        switch (this.state) {
+            case SyncResponderState.IDLE:
+                this.pendingResponse = response;
+                this.state = SyncResponderState.WAITING_FOR_REQUEST;
+                break;
+
+            case SyncResponderState.WAITING_FOR_RESPONSE:
+                this.onResponseReceived!(response);
+                break;
+
+            default:
+                // we already have a response queued
+                throw new Error(`Cannot queue more than one /sync response`);
+        }
+    }
+}