Fix empty response body when streaming (#682)

## Summary
Fix a bug where streaming would send back an empty body. This happened
because we stringified an unawaited `Promise` within `createStream`

## Checklist
<!-- Tick these items off as you progress. -->
<!-- If an item isn't applicable, ideally please strikeout the item by
wrapping it in "~~"" and suffix it with "N/A My reason for skipping
this." -->
<!-- e.g. "- [ ] ~~Added tests~~ N/A Only touches docs" -->

- [ ] ~Added a [docs PR](https://github.com/inngest/website) that
references this PR~ N/A Bug fix
- [x] Added unit/integration tests
- [x] Added changesets if applicable

---------

Co-authored-by: Jack Williams <[email protected]>

.changeset/forty-elephants-think.md

@@ -0,0 +1,5 @@
+---
+"inngest": patch
+---
+
+Fix empty response body when streaming

.github/workflows/pr.yml

@@ -189,6 +189,12 @@ jobs:
       fail-fast: false
       matrix:
         example: ${{ fromJson(needs.examples-matrix.outputs.matrix) }}
+        streaming: [""]
+        include:
+          - example: framework-remix
+            streaming: force
+          - example: framework-nextjs-app-router
+            streaming: force
     steps:
       # Checkout the repo
       - name: Checkout SDK
@@ -204,3 +210,5 @@ jobs:
 
       - name: Run integration tests
         run: pnpm run itest ${{ matrix.example }}
+        env:
+          INNGEST_STREAMING: ${{ matrix.streaming }}

examples/framework-nextjs-app-router/src/app/api/inngest/route.ts

@@ -1,6 +1,14 @@
 import { functions, inngest } from "@/inngest";
 import { serve } from "inngest/next";
 
+/**
+ * Try to automatically choose the edge runtime if `INNGEST_STREAMING` is set.
+ *
+ * See https://innge.st/streaming.
+ */
+export const runtime =
+  process.env.INNGEST_STREAMING?.toLowerCase() === "force" ? "edge" : "nodejs";
+
 export const { GET, POST, PUT } = serve({
   client: inngest,
   functions,

packages/inngest/src/helpers/stream.ts

@@ -53,8 +53,14 @@ export const createStream = (opts?: {
 
           const finalize = (data: unknown) => {
             clearInterval(heartbeat);
-            controller.enqueue(encoder.encode(stringify(data)));
-            controller.close();
+
+            // `data` may be a `Promise`. If it is, we need to wait for it to
+            // resolve before sending it. To support this elegantly we'll always
+            // assume it's a promise and handle that case.
+            void Promise.resolve(data).then((resolvedData) => {
+              controller.enqueue(encoder.encode(stringify(resolvedData)));
+              controller.close();
+            });
           };
 
           passFinalize(finalize);