NodeJs Error: Can't set headers after they are sent - node.js

Question

I am new to nodejs and stuck up with this Error:Can't set headers after they are sent. Below is my code. Please help. I used postman to test this code. It is working for the first 2 hits but on the 3rd hit this error is coming.
const http = require('http');
const fs = require('fs')
module.exports.verifyPyeval5 = function(request, response){
let filePath = "D:/PyEval/NewPyEvalRequests/solution.txt";
fs.readFile(filePath, 'utf8', function (err,data) {
var json = JSON.parse(data);
post_call(json,function(res){
response.status(200)
.json(res);
});
});
};
var post_call = function(new_val,callback){
var post_req = http.request(post_options, function(res) {
res.setEncoding('utf8');
res.on('data', function (chunk) {
callback(chunk);
});
});
post_req.write(JSON.stringify(new_val));
post_req.end();
};
var post_options = {
host: 'acclabserv',
port: '8080',
path: '/generate',
method: 'POST',
headers: {
'Content-Type': 'application/json'
}
};

Answer 1

I got it the issue is with callback function it gets called more then once.
var post_call = function(new_val,callback){
var post_req = http.request(post_options, function(res) {
res.setEncoding('utf8');
var str = null;
res.on('data', function (chunk) {
str += chunk;
});
res.on('end', function () {
callback(str);
});
});
post_req.write(JSON.stringify(new_val));
post_req.end();
};
One more thing to note here I dont know the type of chuck if its an object and you want array of object in response then you can use this
var str = []; //in req.on('data') str.push(chunck)