fix(core): Read __sentry_original__ as own property to avoid overflow on cyclic Proxy prototype chains

CHANGELOG.md

@@ -14,6 +14,10 @@
 
   When Next.js serves a page from its cache, for example an ISR page or a `cacheComponents` shell, the pageload now has the `page.server_rendering.type` attribute. It is `static` if the whole page came from the cache, and `partially_static` if parts of it rendered for this request. Then the pageload stays connected to this request, as before. If the request that rendered the cached page was sampled, the pageload also links to it. So in Sentry, a cached page no longer looks like missing server instrumentation.
 
+### Other Changes
+
+- fix(core): Read `__sentry_original__` as an own property in `getOriginalFunction` ([#25964](https://github.com/getsentry/sentry-javascript/pull/25964))
+
 Work in this release was contributed by @lazerg and @chiliec. Thank you for your contributions!
 
 ## 11.10.0

packages/core/src/utils/object.ts

@@ -120,7 +120,7 @@ export function wrapMethod<O extends {}, T extends string & keyof O>(
  */
 // eslint-disable-next-line @typescript-eslint/ban-types
 export function getOriginalFunction<T extends Function>(func: WrappedFunction<T>): T | undefined {
-  return func.__sentry_original__;
+  return Object.prototype.hasOwnProperty.call(func, '__sentry_original__') ? func.__sentry_original__ : undefined;
 }
 
 /**

packages/core/test/lib/integrations/functiontostring.test.ts

@@ -120,6 +120,18 @@ describe('FunctionToString', () => {
     expect(Reflect.apply(Function.prototype.toString, inspectedFunction, new Array(100_000))).toBe(expected);
   });
 
+  it('does not overflow the stack when the prototype chain loops through a Proxy', () => {
+    function inspectedFunction(): void {}
+    Object.setPrototypeOf(inspectedFunction, Object.create(new Proxy(inspectedFunction, {})));
+    const callToString = Function.prototype.call.bind(Function.prototype.toString) as (thisArg: unknown) => string;
+    const expected = callToString(inspectedFunction);
+
+    const fts = functionToStringIntegration();
+    getClient()?.addIntegration(fts);
+
+    expect(callToString(inspectedFunction)).toBe(expected);
+  });
+
   it('falls back to native toString and does not throw when the carrier read throws', () => {
     const foo = {
       bar(wat: boolean): boolean {