From 6063209fff19fe39d2669830ec9397e28b78c40c Mon Sep 17 00:00:00 2001
From: Andy Balaam <andy.balaam@matrix.org>
Date: Wed, 7 May 2025 12:24:43 +0100
Subject: [PATCH] Cache the key backup status whether enabled or not (#29886)

---
 src/DeviceListener.ts                  | 38 +++++++++++++++++++-------
 test/unit-tests/DeviceListener-test.ts |  4 ++-
 2 files changed, 31 insertions(+), 11 deletions(-)

diff --git a/src/DeviceListener.ts b/src/DeviceListener.ts
index 751e71dd9f..91ee0f284e 100644
--- a/src/DeviceListener.ts
+++ b/src/DeviceListener.ts
@@ -132,7 +132,7 @@ export default class DeviceListener {
         this.dismissedThisDeviceToast = false;
         this.keyBackupInfo = null;
         this.keyBackupFetchedAt = null;
-        this.keyBackupStatusChecked = false;
+        this.cachedKeyBackupStatus = undefined;
         this.ourDeviceIdsAtStart = null;
         this.displayingToastsForDeviceIds = new Set();
         this.client = undefined;
@@ -512,18 +512,36 @@ export default class DeviceListener {
      * trigger an auto-rageshake).
      */
     private checkKeyBackupStatus = async (): Promise<void> => {
-        if (this.keyBackupStatusChecked || !this.client) {
-            return;
-        }
-        const activeKeyBackupVersion = await this.client.getCrypto()?.getActiveSessionBackupVersion();
-        // if key backup is enabled, no need to check this ever again (XXX: why only when it is enabled?)
-        this.keyBackupStatusChecked = !!activeKeyBackupVersion;
-
-        if (!activeKeyBackupVersion) {
+        if (!(await this.getKeyBackupStatus())) {
             dis.dispatch({ action: Action.ReportKeyBackupNotEnabled });
         }
     };
-    private keyBackupStatusChecked = false;
+
+    /**
+     * Is key backup enabled? Use a cached answer if we have one.
+     */
+    private getKeyBackupStatus = async (): Promise<boolean> => {
+        if (!this.client) {
+            // To preserve existing behaviour, if there is no client, we
+            // pretend key storage is on.
+            //
+            // Someone looking to improve this code could try throwing an error
+            // here since we don't expect client to be undefined.
+            return true;
+        }
+
+        // If we've already cached the answer, return it.
+        if (this.cachedKeyBackupStatus !== undefined) {
+            return this.cachedKeyBackupStatus;
+        }
+
+        // Fetch the answer and cache it
+        const activeKeyBackupVersion = await this.client.getCrypto()?.getActiveSessionBackupVersion();
+        this.cachedKeyBackupStatus = !!activeKeyBackupVersion;
+
+        return this.cachedKeyBackupStatus;
+    };
+    private cachedKeyBackupStatus: boolean | undefined = undefined;
 
     private onRecordClientInformationSettingChange: CallbackFn = (
         _originalSettingName,
diff --git a/test/unit-tests/DeviceListener-test.ts b/test/unit-tests/DeviceListener-test.ts
index f58eccf586..09bc4cd18a 100644
--- a/test/unit-tests/DeviceListener-test.ts
+++ b/test/unit-tests/DeviceListener-test.ts
@@ -445,7 +445,9 @@ describe("DeviceListener", () => {
             it("dispatches keybackup event when key backup is not enabled", async () => {
                 mockCrypto.getActiveSessionBackupVersion.mockResolvedValue(null);
                 await createAndStart();
-                expect(mockDispatcher.dispatch).toHaveBeenCalledWith({ action: Action.ReportKeyBackupNotEnabled });
+                expect(mockDispatcher.dispatch).toHaveBeenCalledWith({
+                    action: Action.ReportKeyBackupNotEnabled,
+                });
             });
 
             it("does not check key backup status again after check is complete", async () => {