NodeJs Error: Can't set headers after they are sent

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'
      }
  };

why are you using this line `post_req.write(JSON.stringify(new_val));` what it is for ? — Arpit Solanki, Jul 17 '17 at 13:35
Possible duplicate of [Error: Can't set headers after they are sent to the client](https://stackoverflow.com/questions/7042340/error-cant-set-headers-after-they-are-sent-to-the-client) — George, Jul 17 '17 at 13:53
**post_req.write(JSON.stringify(new_val));** This is for writing a json to the request. — Chandan Kumar, Jul 18 '17 at 05:22

Yash Ganatra · Accepted Answer · 2017-07-17T13:50:15.480

2

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)

edited Jul 17 '17 at 13:50

answered Jul 17 '17 at 13:26

Yash Ganatra

468
2
12

I have used status and send in chain only. – Chandan Kumar Jul 17 '17 at 13:30
Updated my answer yes you have used it in chain but there is no need and check the answer. – Yash Ganatra Jul 17 '17 at 13:34
I tried by removing status. but issue persists. I am not able to find where callback is getting called twice. can you please help? – Chandan Kumar Jul 17 '17 at 13:38
1

req.on('data') this gets called many time use terminating callback like req.on('end') – Yash Ganatra Jul 17 '17 at 13:39
Thanks for help. I will check the solution and update accordingly. – Chandan Kumar Jul 17 '17 at 13:41
OP has modularized the code keep the way it is. don't try to remove the function and keep in main. Its not a good practice anyway. @YashGanatra – Arpit Solanki Jul 17 '17 at 13:41
sorry I didn't get you @ArpitSolanki – Yash Ganatra Jul 17 '17 at 13:42
Oh yes, You are right @ArpitSolanki I was just giving the example not trying to change his structure – Yash Ganatra Jul 17 '17 at 13:43
Its better for the readers if you keep the structure as it. Example is ok but if you point out the problem without changing the structure then it would be nice – Arpit Solanki Jul 17 '17 at 13:45
I will keep that in mind. I haven't done it though. As I just replaced status.json to send and updated the end callback there's nothing to deal with modularization. – Yash Ganatra Jul 17 '17 at 13:49
btw the web service is giving exact same response every time. How is it working for first 2 times and failing 3rd time exactly. – Chandan Kumar Jul 17 '17 at 13:50

NodeJs Error: Can't set headers after they are sent

1 Answers1