Require Response return for Durable Object fetches

Author: mrbbot

packages/durable-objects/package.json

@@ -38,7 +38,8 @@
   "dependencies": {
     "@miniflare/core": "2.0.0-next.3",
     "@miniflare/shared": "2.0.0-next.3",
-    "@miniflare/storage-memory": "2.0.0-next.3"
+    "@miniflare/storage-memory": "2.0.0-next.3",
+    "undici": "^4.9.3"
   },
   "devDependencies": {
     "@miniflare/shared-test": "2.0.0-next.3"

packages/durable-objects/src/namespace.ts

@@ -9,6 +9,8 @@ import {
   withInputGating,
 } from "@miniflare/core";
 import { Awaitable, Context, InputGate, OutputGate } from "@miniflare/shared";
+import { Response as BaseResponse } from "undici";
+import { DurableObjectError } from "./plugin";
 import { DurableObjectStorage } from "./storage";
 
 function hexEncode(value: Uint8Array): string {
@@ -107,7 +109,21 @@ export class DurableObjectStub {
     // noinspection SuspiciousTypeOfGuard
     const request =
       input instanceof Request && !init ? input : new Request(input, init);
-    return state[kFetch](withInputGating(withImmutableHeaders(request)));
+    const res = await state[kFetch](
+      withInputGating(withImmutableHeaders(request))
+    );
+
+    // noinspection SuspiciousTypeOfGuard
+    const validRes =
+      res instanceof Response || (res as any) instanceof BaseResponse;
+    if (!validRes) {
+      throw new DurableObjectError(
+        "ERR_RESPONSE_TYPE",
+        "Durable Object fetch handler didn't respond with a Response object"
+      );
+    }
+
+    return res;
   }
 }
 

packages/durable-objects/src/plugin.ts

@@ -37,7 +37,9 @@ interface ProcessedDurableObject {
   scriptName?: string;
 }
 
-export type DurableObjectErrorCode = "ERR_CLASS_NOT_FOUND"; // Missing constructor for object
+export type DurableObjectErrorCode =
+  | "ERR_CLASS_NOT_FOUND" // Missing constructor for object
+  | "ERR_RESPONSE_TYPE"; // Fetch handler returned non-Response object;
 
 export class DurableObjectError extends MiniflareError<DurableObjectErrorCode> {}
 

packages/durable-objects/test/namespace.spec.ts

@@ -3,6 +3,7 @@ import { deserialize } from "v8";
 import { Request, Response, fetch } from "@miniflare/core";
 import {
   DurableObject,
+  DurableObjectError,
   DurableObjectId,
   DurableObjectNamespace,
   DurableObjectState,
@@ -207,6 +208,29 @@ test("DurableObjectStub: fetch: passes through web socket requests", async (t) =
   webSocket.send("test message");
   t.is(await dataPromise, "test message");
 });
+test("DurableObjectStub: fetch: throws if handler doesn't return Response", async (t) => {
+  const factory = new MemoryStorageFactory();
+  const plugin = new DurableObjectsPlugin(log, compat, {
+    durableObjects: { TEST: "TestObject" },
+  });
+
+  class TestObject implements DurableObject {
+    fetch(): Response {
+      return "definitely a response" as any;
+    }
+  }
+  plugin.beforeReload();
+  plugin.reload({ TestObject }, {});
+
+  const ns = plugin.getNamespace(factory, "TEST");
+  const stub = ns.get(testId);
+  await t.throwsAsync(stub.fetch("http://localhost"), {
+    instanceOf: DurableObjectError,
+    code: "ERR_RESPONSE_TYPE",
+    message:
+      "Durable Object fetch handler didn't respond with a Response object",
+  });
+});
 test("DurableObjectStub: hides implementation details", async (t) => {
   const [ns] = getTestObjectNamespace();
   const stub = ns.get(testId);