An endpoint just to return what u have sent, using only native features.

node-api-mock.js

const http = require('http');

const port = 3349


const routes = {
    '/': handlePostReq
}
const server = http.createServer((req, res) => {
    routes[req.url](req, res);
})


function handlePostReq(req, res) {

    const size = parseInt(req.headers['content-length'], 10)
    const buffer = Buffer.allocUnsafe(size)
    var pos = 0 
    req.on('data', (chunk) => { 
      const offset = pos + chunk.length 
      if (offset > size) { 
        reject(413, 'Too Large', res) 
        return 
      } 
      chunk.copy(buffer, pos) 
      pos = offset 
    }) 
    .on('end', () => { 
      if (pos !== size) { 
        reject(400, 'Bad Request', res) 
        return 
      } 
      const data = JSON.parse(buffer.toString())
      
      res.setHeader('Content-Type', 'application/json;charset=utf-8');
      res.end(JSON.stringify(data))
    })
}


server.listen(port, () => {
    console.log(`Server listening on port ${port}`);
})