From 55b4e4a4deca00cba9e3ec5b9b65ebb101c7267b Mon Sep 17 00:00:00 2001
From: Samuel Macleod <smacleod@cloudflare.com>
Date: Wed, 25 Sep 2024 18:58:31 +0100
Subject: [PATCH] Use symbol to identify internal classes

---
 .../miniflare/src/workers/core/proxy.worker.ts   | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/packages/miniflare/src/workers/core/proxy.worker.ts b/packages/miniflare/src/workers/core/proxy.worker.ts
index 99c3e2db1cb1..8e5556aa3c18 100644
--- a/packages/miniflare/src/workers/core/proxy.worker.ts
+++ b/packages/miniflare/src/workers/core/proxy.worker.ts
@@ -91,14 +91,20 @@ function objectContainsFunctions(
 	return false;
 }
 
-function isObject(value: unknown) {
-	return value && typeof value === "object";
+function isObject(
+	value: unknown
+): value is Record<string | number | symbol, unknown> {
+	return !!value && typeof value === "object";
 }
 
 function getType(value: unknown) {
 	return Object.prototype.toString.call(value).slice(8, -1); // `[object <type>]`
 }
 
+function isInternal(value: unknown) {
+	return isObject(value) && value[Symbol.for("cloudflare:internal-class")];
+}
+
 type Env = Record<string, unknown> & {
 	[CoreBindings.DATA_PROXY_SECRET]: ArrayBuffer;
 };
@@ -119,7 +125,11 @@ export class ProxyServer implements DurableObject {
 			// should only ever return `Object`, as none override `Symbol.toStringTag`
 			// https://tc39.es/ecma262/multipage/fundamental-objects.html#sec-object.prototype.tostring
 			const type = getType(value);
-			if ((type === "Object" && !isPlainObject(value)) || type === "Promise") {
+			const isInternalClass = isInternal(value);
+			if (
+				((type === "Object" || isInternalClass) && !isPlainObject(value)) ||
+				type === "Promise"
+			) {
 				const address = this.nextHeapAddress++;
 				this.heap.set(address, value);
 				assert(value !== null);