http request with node.js fail Can\'t set headers after they are sent

Question

I try to request a server with https/http and display the result in a web page. It's work as a script on a server but fail with i return the result with a get request. ``` var express = require('express'); var app = express(); var port = 1337; var https = require('https'); app.get('/', function(req, response, next) { doRequest(function(resp){ response.send("response" + resp); // FAIL ON REQUEST ! }); }); function doRequest(callback){ var post_data"query=test"; var post_options = { host: 'mySite.com', path: '/path/to/source', method: 'POST', secureProtocol: 'SSLv3_method' }; // Set up the request var post_req = https.request(post_options, function(res) { res.setEncoding('utf8'); res.on('data', function (chunk) { callback(chunk); }); }); // post the data post_req.write(post_data); post_req.end(); } doRequest(console.log); // WORKS ! ``` I get this error: ``` http.js:707 throw new Error('Can\'t set headers after they are sent.'); ^ Error: Can't set headers after they are sent. at ServerR…

Accepted Answer

JavaScript is asynchronous so

```
// post the data
post_req.write(post_data);
post_req.end();
```

Will most likely be executed before

```
// Set up the request
var post_req = https.request(post_options, function(res) {
    res.setEncoding('utf8');
    res.on('data', function (chunk) {
        callback(chunk);
    });
});
```

Is finished, causing your logic to fail.

http request with node.js fail Can\'t set headers after they are sent

Solution

Problem