Add delay before revoking URL on Android (#51299)

src/panels/config/automation/ha-automation-trace.ts

@@ -464,7 +464,6 @@ export class HaAutomationTrace extends LitElement {
       url,
       `trace ${this._entityId} ${this._trace!.timestamp.start}.json`
     );
-    URL.revokeObjectURL(url);
   }
 
   private _importTrace() {

src/panels/config/integrations/integration-panels/zwave_js/zwave_js-config-dashboard.ts

@@ -806,7 +806,6 @@ class ZWaveJSConfigDashboard extends SubscribeMixin(LitElement) {
           url,
           `zwave_js_backup_${new Date().toISOString().replace(/[:.]/g, "-")}.bin`
         );
-        URL.revokeObjectURL(url);
       } catch (err: any) {
         showAlertDialog(this, {
           title: this.hass.localize(

src/panels/config/script/ha-script-trace.ts

@@ -479,7 +479,6 @@ export class HaScriptTrace extends LitElement {
       url,
       `trace ${this._entityId} ${this._trace!.timestamp.start}.json`
     );
-    URL.revokeObjectURL(url);
   }
 
   private _importTrace() {

src/util/file_download.ts

@@ -1,3 +1,9 @@
+// 10 seconds gives the Android WebView download listener enough time
+// to open the blob before it is revoked, while still freeing memory
+// promptly. Revoking immediately would invalidate the URL before the
+// native layer can read it.
+const BLOB_REVOKE_DELAY_MS = 10_000;
+
 export const fileDownload = (href: string, filename = ""): void => {
   const element = document.createElement("a");
   element.target = "_blank";
@@ -7,4 +13,14 @@ export const fileDownload = (href: string, filename = ""): void => {
   document.body.appendChild(element);
   element.dispatchEvent(new MouseEvent("click"));
   document.body.removeChild(element);
+
+  if (href.startsWith("blob:")) {
+    // Revoke blob URLs after a delay on Android so the WebView download
+    // listener has time to fetch the blob before it becomes invalid.
+    if (window.externalApp) {
+      setTimeout(() => URL.revokeObjectURL(href), BLOB_REVOKE_DELAY_MS);
+    } else {
+      URL.revokeObjectURL(href);
+    }
+  }
 };

test/util/file_download.test.ts

@@ -0,0 +1,68 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { fileDownload } from "../../src/util/file_download";
+
+describe("fileDownload", () => {
+  let appendChildSpy: ReturnType<typeof vi.spyOn>;
+  let removeChildSpy: ReturnType<typeof vi.spyOn>;
+  let dispatchEventSpy: ReturnType<typeof vi.spyOn>;
+  let createdElement: HTMLAnchorElement;
+
+  beforeEach(() => {
+    vi.useFakeTimers();
+    vi.spyOn(URL, "revokeObjectURL").mockImplementation(() => undefined);
+    createdElement = document.createElement("a");
+    vi.spyOn(createdElement, "dispatchEvent");
+    vi.spyOn(document, "createElement").mockReturnValue(createdElement);
+    appendChildSpy = vi
+      .spyOn(document.body, "appendChild")
+      .mockImplementation((node) => node);
+    removeChildSpy = vi
+      .spyOn(document.body, "removeChild")
+      .mockImplementation((node) => node);
+    dispatchEventSpy = vi.spyOn(createdElement, "dispatchEvent");
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+    delete (window as any).externalApp;
+  });
+
+  it("sets href, download, and triggers a click", () => {
+    fileDownload("https://example.com/file.json", "file.json");
+
+    expect(createdElement.href).toBe("https://example.com/file.json");
+    expect(createdElement.download).toBe("file.json");
+    expect(appendChildSpy).toHaveBeenCalledWith(createdElement);
+    expect(dispatchEventSpy).toHaveBeenCalledWith(expect.any(MouseEvent));
+    expect(removeChildSpy).toHaveBeenCalledWith(createdElement);
+  });
+
+  it("defaults filename to empty string", () => {
+    fileDownload("https://example.com/file.json");
+    expect(createdElement.download).toBe("");
+  });
+
+  it("does not revoke non-blob URLs", () => {
+    fileDownload("https://example.com/file.json", "file.json");
+    vi.runAllTimers();
+    expect(URL.revokeObjectURL).not.toHaveBeenCalled();
+  });
+
+  it("revokes blob URLs immediately outside Android", () => {
+    fileDownload("blob:http://localhost/abc-123", "file.json");
+    expect(URL.revokeObjectURL).toHaveBeenCalledWith(
+      "blob:http://localhost/abc-123"
+    );
+  });
+
+  it("revokes blob URL after delay on Android", () => {
+    (window as any).externalApp = {};
+    fileDownload("blob:http://localhost/abc-123", "file.json");
+    vi.advanceTimersByTime(9_999);
+    expect(URL.revokeObjectURL).not.toHaveBeenCalled();
+    vi.advanceTimersByTime(1);
+    expect(URL.revokeObjectURL).toHaveBeenCalledWith(
+      "blob:http://localhost/abc-123"
+    );
+  });
+});