fix: [nestjs integration] fastify HTTP adapter detection now works correctly for response headers (#938)

* fix: [nestjs integration] fastify HTTP adapter detection now works correctly for response headers

- fixed a bug where Fastify responses were incorrectly processed as Express due to overlapping method names.
- introduced type guards to differentiate between Express and Fastify response objects.
- bumping @trigger.dev/nestjs patch version to 2.3.19

* fix TS type check build error

Author: Eugene Yaroslavtsev

.changeset/lemon-jobs-repair.md

@@ -0,0 +1,5 @@
+---
+"@trigger.dev/nestjs": patch
+---
+
+fix: [nestjs integration] fastify HTTP adapter detection now works correctly for response headers

packages/nestjs/src/index.ts

@@ -16,7 +16,7 @@ import {
 } from "@nestjs/common";
 import { Headers as StandardHeaders, Request as StandardRequest } from "@remix-run/web-fetch";
 import { TriggerClient, TriggerClientOptions } from "@trigger.dev/sdk";
-import type { Response } from "express";
+import type { Response as ExpressResponse } from "express";
 import type { FastifyReply } from "fastify";
 
 const { ConfigurableModuleClass, MODULE_OPTIONS_TOKEN, OPTIONS_TYPE, ASYNC_OPTIONS_TYPE } =
@@ -192,15 +192,24 @@ function createControllerByPath(customProvider: InjectionToken, path: string) {
         throw new NotFoundException({ error: "Not found" });
       }
 
-      if (typeof res.status === "function") {
-        // express
-        (res as Response).status(response.status);
-        (res as Response).set(response.headers);
-      } else if (typeof res.code === "function") {
-        // fastify
-        (res as FastifyReply).code(response.status);
+      /**
+       * NestJS users mostly use either Express or Fastify, but they have
+       * different response object APIs, so we need to figure out which one
+       * is being used and set the status code and headers accordingly.
+       */
+      if (isExpressResponse(res)) {
+        res.status(response.status);
+
+        if (response.headers) {
+          // Merges the headers, so no need to iterate over them
+          res.set(response.headers);
+        }
+      } else if (isFastifyReply(res)) {
+        res.code(response.status);
+
         if (response.headers) {
-          (res as FastifyReply).headers(response.headers);
+          // Same merge behaviour as Express
+          res.headers(response.headers);
         }
       } else {
         throw new InternalServerErrorException(
@@ -214,3 +223,23 @@ function createControllerByPath(customProvider: InjectionToken, path: string) {
 
   return TriggerDevController;
 }
+
+/**
+ * Type guard for Express with unique checks
+ */
+function isExpressResponse(res: unknown): res is ExpressResponse {
+  return (
+    typeof (res as ExpressResponse)?.status === "function" &&
+    typeof (res as ExpressResponse)?.render === "function"
+  );
+}
+
+/**
+ * Type guard for Fastify with unique checks
+ */
+function isFastifyReply(res: unknown): res is FastifyReply {
+  return (
+    typeof (res as FastifyReply)?.code === "function" &&
+    typeof (res as FastifyReply)?.headers === "function"
+  );
+}