Avoid polluting the original object in case of Object.create

.changeset/plenty-walls-clap.md

@@ -0,0 +1,5 @@
+---
+'@whatwg-node/server': patch
+---
+
+Avoid polluting the original object in case of \`Object.create\`

packages/server/src/utils.ts

@@ -527,75 +527,17 @@ export function isolateObject<TIsolatedObject extends object>(
     if (waitUntilPromises == null) {
       return {} as TIsolatedObject;
     }
-    originalCtx = {} as TIsolatedObject;
-  }
-  const extraProps: Partial<TIsolatedObject> = {};
-  const deletedProps = new Set<string | symbol>();
-  return new Proxy(originalCtx, {
-    get(originalCtx, prop) {
-      if (waitUntilPromises != null && prop === 'waitUntil') {
-        return function waitUntil(promise: Promise<unknown>) {
-          waitUntilPromises.push(promise.catch(err => console.error(err)));
-        };
-      }
-      const extraPropVal = (extraProps as any)[prop];
-      if (extraPropVal != null) {
-        if (typeof extraPropVal === 'function') {
-          return extraPropVal.bind(extraProps);
-        }
-        return extraPropVal;
-      }
-      if (deletedProps.has(prop)) {
-        return undefined;
-      }
-      return (originalCtx as any)[prop];
-    },
-    set(_originalCtx, prop, value) {
-      (extraProps as any)[prop] = value;
-      return true;
-    },
-    has(originalCtx, prop) {
-      if (waitUntilPromises != null && prop === 'waitUntil') {
-        return true;
-      }
-      if (deletedProps.has(prop)) {
-        return false;
-      }
-      if (prop in extraProps) {
-        return true;
-      }
-      return prop in originalCtx;
-    },
-    defineProperty(_originalCtx, prop, descriptor) {
-      return Reflect.defineProperty(extraProps, prop, descriptor);
-    },
-    deleteProperty(_originalCtx, prop) {
-      if (prop in extraProps) {
-        return Reflect.deleteProperty(extraProps, prop);
-      }
-      deletedProps.add(prop);
-      return true;
-    },
-    ownKeys(originalCtx) {
-      const extraKeys = Reflect.ownKeys(extraProps);
-      const originalKeys = Reflect.ownKeys(originalCtx);
-      const deletedKeys = Array.from(deletedProps);
-      const allKeys = new Set(
-        extraKeys.concat(originalKeys.filter(keys => !deletedKeys.includes(keys))),
-      );
-      if (waitUntilPromises != null) {
-        allKeys.add('waitUntil');
-      }
-      return Array.from(allKeys);
-    },
-    getOwnPropertyDescriptor(originalCtx, prop) {
-      if (prop in extraProps) {
-        return Reflect.getOwnPropertyDescriptor(extraProps, prop);
-      }
-      if (deletedProps.has(prop)) {
-        return undefined;
-      }
-      return Reflect.getOwnPropertyDescriptor(originalCtx, prop);
+    return {
+      waitUntil(promise: Promise<unknown>) {
+        waitUntilPromises?.push(promise.catch(err => console.error(err)));
+      },
+    } as TIsolatedObject;
+  }
+  return Object.create(originalCtx, {
+    waitUntil: {
+      value(promise: Promise<unknown>) {
+        waitUntilPromises?.push(promise.catch(err => console.error(err)));
+      },
     },
   });
 }

packages/server/test/server-context.spec.ts

@@ -31,6 +31,40 @@ describe('Server Context', () => {
         expect(res.status).toBe(200);
         expect(await res.json()).toEqual({ foo: 'bar', bar: 'baz' });
       });
+      it('Do not pollute the original object in case of `Object.create`', async () => {
+        const serverAdapter = createServerAdapter((_req, context0: any) => {
+          context0.i = 0;
+          const context1 = Object.create(context0);
+          context1.i = 1;
+          const context2 = Object.create(context0);
+          context2.i = 2;
+          return Response.json({
+            i0: context0.i,
+            i1: context1.i,
+            i2: context2.i,
+          });
+        });
+        const res = await serverAdapter.fetch('http://localhost');
+        const resJson = await res.json();
+        expect(resJson).toEqual({
+          i0: 0,
+          i1: 1,
+          i2: 2,
+        });
+      });
+      it('retains the prototype in case of `Object.create`', async () => {
+        class MyContext {}
+        const serverAdapter = createServerAdapter((_req, context0: MyContext) => {
+          return Response.json({
+            isMyContext: context0 instanceof MyContext,
+          });
+        });
+        const res = await serverAdapter.fetch('http://localhost', new MyContext());
+        const resJson = await res.json();
+        expect(resJson).toEqual({
+          isMyContext: true,
+        });
+      });
     },
     { noLibCurl: true },
   );

packages/server/test/utils.spec.ts

@@ -0,0 +1,11 @@
+import { isolateObject } from '../src/utils';
+
+describe('isolateObject', () => {
+  test('Object.create does not share property assignments', () => {
+    const origin = isolateObject({});
+    const a = Object.create(origin);
+    const b = Object.create(origin);
+    a.a = 1;
+    expect(b.a).toEqual(undefined);
+  });
+});