Propagate Durable Object transaction return values

Author: mrbbot

src/kv/do.ts

@@ -341,9 +341,9 @@ export class DurableObjectStorage implements DurableObjectOperator {
     return this.#transaction((txn) => txn.list(options));
   }
 
-  async transaction(
-    closure: (txn: DurableObjectTransaction) => Promise<void>
-  ): Promise<void> {
-    await this.#transaction(closure);
+  async transaction<T>(
+    closure: (txn: DurableObjectTransaction) => Promise<T>
+  ): Promise<T> {
+    return this.#transaction(closure);
   }
 }

test/kv/do.spec.ts

@@ -372,6 +372,15 @@ test("transaction: cannot perform more operations after rollback", async (t) =>
     await t.throws(() => txn.rollback(), { instanceOf: AssertionError });
   });
 });
+test("transaction: propagates return value", async (t) => {
+  const { backing, storage } = t.context;
+  await backing.put("a", storedValue(1));
+  const res = await storage.transaction(async (txn) => {
+    const value = (await txn.get<number>("a")) ?? 0;
+    return value + 2;
+  });
+  t.is(res, 3);
+});
 test("transaction: aborts all in-progress transactions", async (t) => {
   const { backing, storage } = t.context;
   await backing.put("key", storedValue("old"));