From 60cabb3bcb62e4c1b3f8e5cec1e4de81ed28d784 Mon Sep 17 00:00:00 2001
From: Tomas Krejci <tk@tomaskrejci.com>
Date: Wed, 17 Jun 2026 19:37:59 +0200
Subject: [PATCH] Add dinosaur API error handler

---
 lecture_5/dinosaurs/src/app.js                  |  3 +++
 .../dinosaurs/src/validation/errorHandler.js    | 17 +++++++++++++++++
 2 files changed, 20 insertions(+)
 create mode 100644 lecture_5/dinosaurs/src/validation/errorHandler.js

diff --git a/lecture_5/dinosaurs/src/app.js b/lecture_5/dinosaurs/src/app.js
index 3286f3d..1ebd2ef 100644
--- a/lecture_5/dinosaurs/src/app.js
+++ b/lecture_5/dinosaurs/src/app.js
@@ -1,9 +1,12 @@
 import express from "express";
 import { dinosaurRouter } from "./routes/dinosaurRoutes.js";
+import { errorHandler } from "./validation/errorHandler.js";
 
 const app = express();
 
 app.use(express.json());
 app.use(dinosaurRouter);
+// Error middleware must be registered after routes so it can handle rejected route handlers.
+app.use(errorHandler);
 
 export { app };
diff --git a/lecture_5/dinosaurs/src/validation/errorHandler.js b/lecture_5/dinosaurs/src/validation/errorHandler.js
new file mode 100644
index 0000000..56abc8d
--- /dev/null
+++ b/lecture_5/dinosaurs/src/validation/errorHandler.js
@@ -0,0 +1,17 @@
+import { ZodError } from "zod";
+
+// Centralized Express error middleware for validation and unexpected runtime errors.
+export const errorHandler = (error, _request, response, _next) => {
+	console.error(error);
+
+	if (error instanceof ZodError) {
+		return response.status(400).json({
+			message: "Validation error",
+			errors: error.issues,
+		});
+	}
+
+	return response.status(500).json({
+		message: "Internal server error",
+	});
+};