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