import Fastify, { FastifyRequest } from 'fastify';

const fastify = Fastify({
  logger: false,
  genReqIp: (req: FastifyRequest): string => {
    const ip = req.headers['cf-connecting-ip'];
    if (ip) {
      return ip;
    }

    return req.connection.remoteAddress ?? '0.0.0.0';
  },
});


fastify.get('/', function (req, reply) {
  reply.send(req.ip);
});


{
  const { statusCode, payload } = await fastify.inject({
    url: '/',
    headers: { 'Cf-Connecting-Ip': '1.2.3.4' },
  });
  console.log(statusCode, payload);
}