Request & Reply Objects

request and reply

request contains the incoming HTTP request details (URL, headers, body, params, query). reply is an object with methods to send the response—it's pooled for performance.

Reading request data

Access path params, query strings, headers, and body from the request object.

fastify.get('/users/:id', async (request, reply) => {
  const { id } = request.params;
  const { filter } = request.query;
  const token = request.headers.authorization;
  
  return { userId: id, filter, hasToken: !!token };
});

Sending replies

Return an object (auto-serialized to JSON) or use reply methods for custom status codes and headers.

fastify.post('/items', async (request, reply) => {
  // Auto-JSON serialization
  return { id: 1, status: 'created' };
});

fastify.delete('/items/:id', async (request, reply) => {
  // Custom status and location header
  return reply.status(204).send();
});

Return or send, not both

In an async handler, either return the payload or call reply.send(). Doing both logs a warning about the reply being already sent.

Quick check

Quick check: Which sets a status code and sends JSON in one chain?

• `reply.code(201).send({id: 1})`
• `request.code(201)`
• `reply.json(201)`