We could create a middleware that allows us to validate the body of a request with a Zod schema.

const validateBody =
	(schema: ZodSchema) => (request: Request, response: Response, next: NextFunction) => {
		try {
			schema.parse(request.body);
			next();
		} catch (error) {
			return handleError(request, response, error);
		}
	};

Even better, we could try to hold on to the type.

const validateBody =
	<T>(schema: ZodSchema<T>): RequestHandler<NonNullable<unknown>, NonNullable<unknown>, T> =>
	(request: Request, response: Response, next: NextFunction) => {
		try {
			schema.parse(request.body);
			next();
		} catch (error) {
			return handleError(request, response, error);
		}
	};

Validating POST

app.post('/tasks', validateBody(NewTaskSchema), async (req, res) => {
	try {
		const task = NewTaskSchema.parse(req.body);
		await createTask.run([task.title, task.description]);
		return res.sendStatus(201);
	} catch (error) {
		return handleError(req, res, error);
	}
});

Validating PUT

app.put('/tasks/:id', validateBody(UpdateTaskSchema), async (req, res) => {
	try {
		const { id } = TaskParamsSchema.parse(req.params);

		const previous = TaskSchema.parse(await getTask.get([id]));
		const updates = req.body;
		const task = { ...previous, ...updates };

		await updateTask.run([task.title, task.description, task.completed, id]);
		return res.sendStatus(200);
	} catch (error) {
		return handleError(req, res, error);
	}
});

Next: Validating Query and Path Parameters with Middleware