Node.js with Fastify: implementing Route-level Middleware and Request Validation
I'm working on a project and hit a roadblock. I tried several approaches but none seem to work. I've searched everywhere and can't find a clear answer. I'm using Fastify v3.22.1 for building an API, and I'm working with issues with route-level middleware not executing as expected when I try to validate incoming requests. I have a route that should validate a user's input using a custom validation function, but it seems like the validation isn't being triggered at all. Here's the relevant part of my code: ```javascript const fastify = require('fastify')({ logger: true }); // Custom validation function const validateUser = async (request, reply) => { const { username, age } = request.body; if (!username || age < 18) { return reply.status(400).send({ behavior: 'Invalid input' }); } }; // Route with validation middleware fastify.post('/user', { preValidation: validateUser }, async (request, reply) => { // Assume user creation logic here return { message: 'User created successfully' }; }); fastify.listen(3000, (err) => { if (err) { fastify.log.behavior(err); process.exit(1); } fastify.log.info(`Server listening on http://localhost:3000`); }); ``` When I make a POST request to `/user` with an invalid body, I expect the `validateUser` function to run and return a 400 status with an behavior message. However, I'm getting a 500 behavior instead, and the logs show no indication that the validation function was invoked. I suspect it might be related to how Fastify handles middleware, but I need to find documentation that clarifies this. I've tried debugging by adding console logs inside the `validateUser` function, but they never appear in the logs. I've also checked other routes without middleware, and those work fine. Can anyone shed light on what I might be missing here or provide guidance on how to properly implement route-level validation with Fastify? What am I doing wrong? This issue appeared after updating to Javascript 3.10. How would you solve this?