@@ -- Add Express V4 Support to @salesforce/mrt-utilities package. (#334)

* Initial Commit

* Update CHANGELOG.md

* Change peer to have a wider support range for 4.x

* Revert manual changelog update; replace with changeset

* Add some docs to better understand this pattern

* No monkey patching

Author: bendvc

.changeset/mrt-utilities-express-4-support.md

@@ -0,0 +1,5 @@
+---
+'@salesforce/mrt-utilities': patch
+---
+
+Add Express 4 support, improve middleware error handling, and add dual-version Express test coverage.

packages/mrt-utilities/package.json

@@ -115,6 +115,7 @@
     "eslint-plugin-header": "catalog:",
     "eslint-plugin-prettier": "catalog:",
     "express": "5.1.0",
+    "express4": "npm:express@4.21.2",
     "mocha": "catalog:",
     "prettier": "catalog:",
     "shx": "catalog:",
@@ -124,7 +125,7 @@
     "typescript-eslint": "catalog:"
   },
   "peerDependencies": {
-    "express": "5.1.0"
+    "express": "^4.0.0 || ^5.0.0"
   },
   "engines": {
     "node": ">=22.16.0"

packages/mrt-utilities/src/middleware/middleware.ts

@@ -272,7 +272,7 @@ export const createMRTRequestProcessorMiddleware = (
     req.headers[X_MOBIFY_REQUEST_PROCESSOR_LOCAL] = 'true'; // Mark the request as processed by the request processor
   };
 
-  const ssrRequestProcessorMiddleware = async (req: Request, res: Response, next: NextFunction) => {
+  const ssrRequestProcessorMiddleware = (req: Request, res: Response, next: NextFunction) => {
     // If the path is /, we enforce that the only methods
     // allowed are GET, HEAD or OPTIONS. This is a restriction
     // imposed by API Gateway: we enforce it here so that the
@@ -282,17 +282,21 @@ export const createMRTRequestProcessorMiddleware = (
       return;
     }
 
-    // Apply custom query parameter parsing.
-    await processIncomingRequest(req, res);
-
-    // Strip out API Gateway headers from the incoming request. We
-    // do that now so that the rest of the code don't have to deal
-    // with these headers, which can be large and may be accidentally
-    // forwarded to other servers.
-    cleanUpHeaders(req, false);
-
-    // Hand off to the next middleware
-    next();
+    // Apply custom query parameter parsing and forward errors via next()
+    processIncomingRequest(req, res)
+      .then(() => {
+        // Strip out API Gateway headers from the incoming request. We
+        // do that now so that the rest of the code don't have to deal
+        // with these headers, which can be large and may be accidentally
+        // forwarded to other servers.
+        cleanUpHeaders(req, false);
+
+        // Hand off to the next middleware
+        next();
+      })
+      .catch((err) => {
+        next(err);
+      });
   };
 
   return ssrRequestProcessorMiddleware;

packages/mrt-utilities/test/helpers/express-versions.ts

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2025, Salesforce, Inc.
+ * SPDX-License-Identifier: Apache-2
+ * For full license text, see the license.txt file in the repo root or http://www.apache.org/licenses/LICENSE-2.0
+ */
+
+import express5 from 'express';
+import {createRequire} from 'node:module';
+
+/*
+ * Load Express v4 via an npm alias so tests can run against v4 and v5
+ * in the same process without altering production imports.
+ */
+const require = createRequire(import.meta.url);
+const express4 = require('express4') as typeof express5;
+
+/*
+ * Export both versions for parameterized test suites.
+ */
+export const expressVersions = [
+  {label: 'express4', express: express4},
+  {label: 'express5', express: express5},
+];