Add clear error if Durable Object missing fetch handler, closes #164

Author: mrbbot

packages/durable-objects/src/error.ts

@@ -4,6 +4,7 @@ export type DurableObjectErrorCode =
   | "ERR_SCRIPT_NOT_FOUND" // Missing mounted script for object
   | "ERR_CLASS_NOT_FOUND" // Missing constructor for object
   | "ERR_RESPONSE_TYPE" // Fetch handler returned non-Response object;
-  | "ERR_DESERIALIZATION"; // Unable to deserialize stored value (likely loading data created in Miniflare 1)
+  | "ERR_DESERIALIZATION" // Unable to deserialize stored value (likely loading data created in Miniflare 1)
+  | "ERR_NO_HANDLER"; // No fetch handler for object
 
 export class DurableObjectError extends MiniflareError<DurableObjectErrorCode> {}

packages/durable-objects/src/namespace.ts

@@ -82,7 +82,16 @@ export class DurableObjectState {
     // TODO: catch, reset object on error
     const outputGate = new OutputGate();
     return outputGate.runWith(() =>
-      this.#inputGate.runWith(() => this[kInstance]!.fetch(request))
+      this.#inputGate.runWith(() => {
+        const instance = this[kInstance];
+        if (!instance?.fetch) {
+          throw new DurableObjectError(
+            "ERR_NO_HANDLER",
+            "No fetch handler defined in Durable Object"
+          );
+        }
+        return instance.fetch(request);
+      })
     );
   }
 }

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

@@ -147,6 +147,25 @@ test("DurableObjectState: kFetch: waits for writes to be confirmed before return
   assert(value);
   t.is(deserialize(value), "value");
 });
+test("DurableObjectState: kFetch: throws clear error if missing fetch handler", async (t) => {
+  // https://github.com/cloudflare/miniflare/issues/164
+  const factory = new MemoryStorageFactory();
+  const plugin = new DurableObjectsPlugin(ctx, {
+    durableObjects: { TEST: "TestObject" },
+  });
+
+  class TestObject {}
+  plugin.beforeReload();
+  plugin.reload({}, { TestObject }, new Map());
+
+  const ns = plugin.getNamespace(factory, "TEST");
+  const id = ns.newUniqueId();
+  await t.throwsAsync(ns.get(id).fetch("http://localhost"), {
+    instanceOf: DurableObjectError,
+    code: "ERR_NO_HANDLER",
+    message: "No fetch handler defined in Durable Object",
+  });
+});
 test("DurableObjectState: hides implementation details", async (t) => {
   const [ns, plugin, factory] = getTestObjectNamespace();
   const state = await plugin.getObject(factory, ns.newUniqueId());