Merge pull request #4419 from element-hq/valere/backport-config-fix

Backport fix: Uncaught exception in downloadConfig

src/config/Config.test.ts

@@ -95,6 +95,19 @@ describe("Config.initWith", () => {
     expect(Config.get().ssla).toBe("https://example.invalid/ssla");
   });
 
+  it("falls back to the defaults when fetching config.json rejects", async () => {
+    // A rejected promise is what a webview gives for a missing local file.
+    vi.spyOn(globalThis, "fetch").mockRejectedValue(
+      new TypeError("Load failed"),
+    );
+    vi.spyOn(logger, "info").mockImplementation(() => {});
+    Reflect.set(Config, "internalInstance", undefined);
+
+    await expect(Config.init()).resolves.toBeUndefined();
+
+    expect(Config.get().media_quality).toEqual(DEFAULT_CONFIG.media_quality);
+  });
+
   it("replaces a config initialized earlier", () => {
     Config.initWith({ ssla: "https://first.invalid/ssla" });
     Config.initWith({ ssla: "https://second.invalid/ssla" });

src/config/Config.ts

@@ -140,13 +140,20 @@ export function validateConfig(config: ConfigOptions): ConfigOptions {
 }
 
 async function downloadConfig(fetchTarget: string): Promise<ConfigOptions> {
-  const response = await fetch(fetchTarget);
+  let response: Response;
+  try {
+    response = await fetch(fetchTarget);
+  } catch (e) {
+    // The embedded package ships no config.json, and some webviews (Element X
+    // iOS) reject the fetch of a missing local file rather than answering 404.
+    logger.info(`No config at ${fetchTarget}, using defaults`, e);
+    // resolveConfig merges in the defaults.
+    return {};
+  }
 
   if (isFailure(response)) {
-    // Lack of a config isn't an error, we should just use the defaults.
-    // Also treat a blank config as no config, assuming the status code is 0, because we don't get 404s from file:
-    // URIs so this is the only way we can not fail if the file doesn't exist when loading from a file:// URI.
-    return DEFAULT_CONFIG;
+    // resolveConfig merges in the defaults.
+    return {};
   }
 
   return response.json();