Use fastify in firebase function

fastify-in-firebase-function.js

'use strict';

const functions = require('firebase-functions');

const fastify = require('./fastify');
exports.greetFromFastify = functions.https.onRequest(fastify);

fastify.js

'use strict';

const http = require('http');
const Fastify = require('fastify');

let handleRequest = null;

const serverFactory = (handler, opts) => {
  handleRequest = handler;
  console.log('server factory opts: %j', opts);
  return http.createServer();
};
const fastify = Fastify({
  serverFactory,
  logger: true,
  // skipHandleTrustProxy: true // proposed addition to the options
});

fastify.get('/get', (req, reply) => {
  reply.send('[Fastify] Response from GET request');
});

fastify.post('/post', (req, reply) => {
  reply.send('[Fastify] Response from POST request');
});

module.exports = (req, res) => {
  console.log('req.ip: %s', req.ip);  // req.ip: 127.0.0.1
  /*
   Without the next line, an error would occur
   error: /Users/shwei/Work/workspace/cf-fastify-restify-express/functions/node_modules/fastify/fastify.js:249
    req.ip = req.connection.remoteAddress
           ^
    TypeError: Cannot set property ip of [object Object] which has only a getter
        at _ipAsRemoteAddress (/Users/shwei/Work/workspace/cf-fastify-restify-express/functions/node_modules/fastify/fastify.js:249:12)
  */
  req = Object.assign({ip: ''}, {...req}); 
  
  fastify.ready(err => {
    if (err) throw err;
    handleRequest(req, res);
  });
};

Any Suggestion/help how to send data in a post request, even defining a schema also is not helping???
Above example works only if you don't send any json data in body. Once you send the it gives error:
payload.setEncoding('utf8')

         ^

TypeError: payload.setEncoding is not a function
at rawBody (/Users/manasaranjanmishra/rize/fastify-env/functions/node_modules/fastify/lib/contentTypeParser.js:150:13)
at ContentTypeParser.run (/Users/manasaranjanmishra/rize/fastify-env/functions/node_modules/fastify/lib/contentTypeParser.js:101:5)
at handleRequest (/Users/manasaranjanmishra/rize/fastify-env/functions/node_modules/fastify/lib/handleRequest.js:35:39)
at runPreParsing (/Users/manasaranjanmishra/rize/fastify-env/functions/node_modules/fastify/lib/route.js:385:5)
at Object.routeHandler [as handler] (/Users/manasaranjanmishra/rize/fastify-env/functions/node_modules/fastify/lib/route.js:343:7)
at Router.lookup (/Users/manasaranjanmishra/rize/fastify-env/functions/node_modules/find-my-way/index.js:356:14)
at /Users/manasaranjanmishra/rize/fastify-env/functions/src/index.js:39:5
at manageErr (/Users/manasaranjanmishra/rize/fastify-env/functions/node_modules/fastify/fastify.js:392:11)
at exit (/Users/manasaranjanmishra/rize/fastify-env/functions/node_modules/fastify/lib/hooks.js:90:5)
at next (/Users/manasaranjanmishra/rize/fastify-env/functions/node_modules/fastify/lib/hooks.js:101:9)
Any Suggestion/help how to send data in a post request, even defining a schema also is not helping.