Bring back the completable promise from the past

Author: slinkydeveloper

packages/restate-sdk/src/endpoint/handlers/generic.ts

@@ -291,8 +291,8 @@ export class GenericHandler implements RestateHandler {
         (bytes) => {
           coreVm.sys_write_output_success(bytes);
           coreVm.sys_end();
-        },
-        (e) => {
+        })
+        .catch((e) => {
           const error = ensureError(e);
           console.warn("Function completed with an error.\n", error);
 

packages/restate-sdk/src/utils/completable_promise.ts

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2023-2024 - Restate Software, Inc., Restate GmbH
+ *
+ * This file is part of the Restate SDK for Node.js/TypeScript,
+ * which is released under the MIT license.
+ *
+ * You can find a copy of the license in file LICENSE in the root
+ * directory of this repository or package, or at
+ * https://github.com/restatedev/sdk-typescript/blob/main/LICENSE
+ */
+
+// Like https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/withResolvers
+// (not yet available in node)
+export class CompletablePromise<T> {
+    private success!: (value: T | PromiseLike<T>) => void;
+    private failure!: (reason?: unknown) => void;
+
+    public readonly promise: Promise<T>;
+
+    constructor() {
+        this.promise = new Promise((resolve, reject) => {
+            this.success = resolve;
+            this.failure = reject;
+        });
+    }
+
+    public resolve(value: T) {
+        this.success(value);
+    }
+
+    public reject(reason?: unknown) {
+        this.failure(reason);
+    }
+}