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Cannot set headers after they are sent to the client, how do I stop Express from setting headers that have already been set?

I'm using Express, Node, and EJS to fetch data from Spotify Web API. Without EJS, I'm able to send a request from browser and fetch data no problem. With EJS, code crashes with code: 'ERR_HTTP_HEADERS_SENT' once I send a request in the browser. I'm lost on how to stop express from sending headers that have already been set.
const express = require("express");
const request = require("request");
const app = express();
const secret = require("./secret");
const redirect_uri = "http://localhost:8888/callback";
const client_id = secret.client_id;
const client_secret = secret.client_secret;
const querystring = require("querystring");
let state = "abc123";
let scope =
"user-read-private user-read-email user-read-recently-played user-top-read";
app.use(express.json());
app.use(express.urlencoded({ extended: true }));
app.set("view engine", "ejs");
// Request User Authorization
app.get("/login", function (req, res) {
return res.redirect(
"https://accounts.spotify.com/authorize?" +
querystring.stringify({
response_type: "code",
client_id: client_id,
scope: scope,
redirect_uri: redirect_uri,
state: state,
})
);
});
// Request Access Token
app.get("/callback", function (req, res) {
let code = req.query.code || null;
state = req.query.state || null;
if (state === null) {
return res.redirect(
"/#" +
querystring.stringify({
error: "state_mismatch",
})
);
} else {
authOptions = {
url: "https://accounts.spotify.com/api/token",
form: {
code: code,
redirect_uri: redirect_uri,
grant_type: "authorization_code",
},
headers: {
Authorization:
"Basic " +
new Buffer(client_id + ":" + client_secret).toString("base64"),
},
json: true,
};
}
// User Recently Played Tracks
request.post(authOptions, function (error, response, body) {
if (!error && response.statusCode === 200) {
let access_token = body.access_token;
let refresh_token = body.refresh_token;
let options = {
url: "https://api.spotify.com/v1/me/player/recently-played",
headers: { Authorization: "Bearer " + access_token },
json: true,
};
// use the access token to access the Spotify Web API
request.get(options, function (error, response, body) {
let items = body.items;
// Track Names
for (let i = 0; i < items.length; i++) {
let trackName = items[i].track.name;
console.log(trackName);
}
// Artist Names
for (let i = 0; i < items.length; i++) {
let artistName = items[i].track.artists[0].name;
console.log(artistName);
}
});
// we can also pass the token to the browser to make requests from there
return res.redirect(
"/#" +
querystring.stringify({
access_token: access_token,
refresh_token: refresh_token,
})
);
} else {
return res.redirect(
"/#" +
querystring.stringify({
error: "invalid_token",
})
);
}
});
return res.render("index");
});
// Refresh Token
app.get("/refresh_token", function (req, res) {
let refresh_token = req.query.refresh_token;
let authOptions = {
url: "https://accounts.spotify.com/api/token",
headers: {
Authorization:
"Basic " +
new Buffer(client_id + ":" + client_secret).toString("base64"),
},
form: {
grant_type: "refresh_token",
refresh_token: refresh_token,
},
json: true,
};
request.post(authOptions, function (error, response, body) {
if (!error && response.statusCode === 200) {
let access_token = body.access_token;
return res.send({
access_token: access_token,
});
}
});
});
app.listen(8888, () => console.log("Server started on port 8888"));

Can't access /playlists using express and app.get

I'm trying to access the app.get('/playlists') but it keeps coming up a 404 status code error and the browser is displaying cannot GET /playlists
I'm unsure what I'm doing tthat is isn't accessible here's the code:
var express = require('express'); // Express web server framework
var stateKey = 'spotify_auth_state';
var app = express();
app.use(express.static(__dirname + '/public'))
.use(cors())
.use(cookieParser());
app.get('/callback', function(req, res) {
// your application requests refresh and access tokens
// after checking the state parameter
var code = req.query.code || null;
var state = req.query.state || null;
var storedState = req.cookies ? req.cookies[stateKey] : null;
if (state === null || state !== storedState) {
res.redirect('/#' +
querystring.stringify({
error: 'state_mismatch'
}));
} else {
res.clearCookie(stateKey);
var authOptions = {
url: 'https://accounts.spotify.com/api/token',
form: {
code: code,
redirect_uri: redirect_uri,
grant_type: 'authorization_code'
},
headers: {
'Authorization': 'Basic ' + (new Buffer(client_id + ':' +
client_secret).toString('base64'))
},
json: true
};
request.post(authOptions, function(error, response, body) {
if (!error && response.statusCode === 200) {
var access_token = body.access_token,
refresh_token = body.refresh_token;
var options = {
url: 'https://api.spotify.com/v1/me',
headers: { 'Authorization': 'Bearer ' + access_token },
json: true
};
// use the access token to access the Spotify Web API
request.get(options, function(error, response, body) {
console.log(body);
});
// we can also pass the token to the browser to make requests from there
res.redirect('/#' +
querystring.stringify({
access_token: access_token,
refresh_token: refresh_token
}));
} else {
res.redirect('/#' +
querystring.stringify({
error: 'invalid_token'
}));
}
});
}
});
app.get('/refresh_token', function(req, res) {
// requesting access token from refresh token
var refresh_token = req.query.refresh_token;
var authOptions = {
url: 'https://accounts.spotify.com/api/token',
headers: { 'Authorization': 'Basic ' + (new Buffer(client_id + ':' + client_secret).toString('base64')) },
form: {
grant_type: 'refresh_token',
refresh_token: refresh_token
},
json: true
};
request.post(authOptions, function(error, response, body) {
if (!error && response.statusCode === 200) {
var access_token = body.access_token;
res.send({
'access_token': access_token
});
}
});
app.get('/playlists', (req, res) => {
console.log(request.url);
response.send('Hello, /');
});
});
console.log('Listening on 8888');
app.listen(8888);
I can't figure out why the route won't work

Your /playlists endpoint is declared inside of the /refresh_token endpoint. Moving it outside of that should work.

Spotify authorization code grant: Bad Request

I am trying to create a website that uses the Spotify APIs and I am stuck trying to get the authorization code flow to work. Below is the code that I am using.
app.get('/login', function(req, res) {
var scope = 'user-read-private';
res.redirect('https://accounts.spotify.com/authorize?' +
querystring.stringify({
response_type: 'code',
client_id: clientId,
scope: scope,
redirect_uri: redirectUri,
state: state
}));
});
app.get('/callback', function(req, res) {
res.status(200);
var code = req.query.code;
console.log('\ncode:', code, '\n');
spotify.authorizationCodeGrant(code).then(
function(data) {
console.log('The access token expires in ' + data.body['expires_in']);
console.log('The access token is ' + data.body['access_token']);
spotify.setAccessToken(data.body['access_token']);
spotify.setRefreshToken(data.body['refresh_token']);
},
function(err) {
console.log('Could not login!', err);
}
);
res.redirect('/');
});
The problem that I am having is that when it gets to the authorizeCodeGrant call it just fails and gives me a 400 bad request error and I am not sure why because I know that I am getting a code from Spotify, the code just does not seem to work.
var path = require('path');
var express = require('express');
var request = require('request');
var exphbs = require('express-handlebars');
var querystring = require('querystring');
var url = require('url');
var Spotify = require('spotify-web-api-node');
var keys = require('./keys');
var scopes = ['playlist-modify-private', 'user-read-private'],
redirectUri = 'http://localhost:3000/callback',
clientId = 'client_id',
clientSecret = 'client_secret',
state = 'some-state-of-my-choice';
var spotify = new Spotify({
redirectUri: redirectUri,
clientId: clientId,
redirectUri: redirectUri
});
var results = [];
var login = 1;//keeps track if logged into spotify
var tokenExpiration;
var app = express();
var port = process.env.PORT || 3000;
app.engine('handlebars', exphbs({ defaultLayout: 'main'}));
app.set('view engine', 'handlebars');
app.get('/', function(req, res, next){
res.status(200);
res.render('searchPage', {
login: login,
results: results
});
});
app.get('/login', function(req, res) {
var scope = 'user-read-private';
res.redirect('https://accounts.spotify.com/authorize?' +
querystring.stringify({
response_type: 'code',
client_id: clientId,
scope: scope,
redirect_uri: redirectUri,
state: state
}));
});
app.get('/callback', function(req, res) {
var code = req.query.code;
console.log('\ncode:', code, '\n');
spotify.authorizationCodeGrant(code).then(
function(data) {
console.log('The access token expires in ' + data.body['expires_in']);
console.log('The access token is ' + data.body['access_token']);
spotify.setAccessToken(data.body['access_token']);
spotify.setRefreshToken(data.body['refresh_token']);
tokenExpiration = new Data().getTime()/1000 + data.body['expires_in'];
login = 0;
},
function(err) {
console.log('Could not login!', err);
}
);
if(login == 0){
res.redirect('/#' +
querystring.stringify({
access_token: spotify.getAccessToken(),
refresh_token: spotify.getRefreshToken()
}));
}else{
res.redirect('/');
}
});
var numberOfTimesUpdated = 0;
setInterval(function() {
if(++numberOfTimesUpdated > 5 && login == 0) {
clearInterval(this);
spotify.refreshAccessToken().then(
function(data) {
tokenExpiration = new Data().getTime()/1000 + data.body['expires_in'];
spotify.setAccessToken(data.body['access_token']);
},
function(err) {
console.log('Could not refresh the token!', err.message);
}
);
}
}, 1000);
app.post('/search/:title', function(req, res) {
var search = req.params.title.toLowerCase();//req.body.search;
console.log('search', search);
resutls = [];
spotify.searchTracks(search, function(err, data) {
if(err) {
console.error('something went wrong...');
return;
}
console.log('I got' + search.body.tracks.total + 'results!');
search.body.tracks.items.forEach(function(track){
results.push({
artist: track.artist[0].name,
song: track.name,
preview: track.external_urls.sp,
album: track.album.name
});
res.render('searchPage', {
login: login,
results: results
});
});
});
});
app.use(express.static('public'));
app.listen(port, function(err){
console.log("== Server is listening on port", port);
});
Above is the full code for the server.

How to send a POST request from node.js Express?

Could someone show me the simplest way to send a post request from node.js Express, including how to pass and retrieve some data? I am expecting something similar to cURL in PHP.

var request = require('request');
function updateClient(postData){
var clientServerOptions = {
uri: 'http://'+clientHost+''+clientContext,
body: JSON.stringify(postData),
method: 'POST',
headers: {
'Content-Type': 'application/json'
}
}
request(clientServerOptions, function (error, response) {
console.log(error,response.body);
return;
});
}
For this to work, your server must be something like:
var express = require('express');
var bodyParser = require('body-parser');
var app = express();
app.use(bodyParser.urlencoded({ extended: false }));
app.use(bodyParser.json())
var port = 9000;
app.post('/sample/put/data', function(req, res) {
console.log('receiving data ...');
console.log('body is ',req.body);
res.send(req.body);
});
// start the server
app.listen(port);
console.log('Server started! At http://localhost:' + port);

As described here for a post request :
var http = require('http');
var options = {
host: 'www.host.com',
path: '/',
port: '80',
method: 'POST'
};
callback = function(response) {
var str = ''
response.on('data', function (chunk) {
str += chunk;
});
response.on('end', function () {
console.log(str);
});
}
var req = http.request(options, callback);
//This is the data we are posting, it needs to be a string or a buffer
req.write("data");
req.end();

you can try like this:
var request = require('request');
request.post({ headers: {'content-type' : 'application/json'}
, url: <your URL>, body: <req_body in json> }
, function(error, response, body){
console.log(body);
});

in your server side the code looks like:
var request = require('request');
app.post('/add', function(req, res){
console.log(req.body);
request.post(
{
url:'http://localhost:6001/add',
json: {
unit_name:req.body.unit_name,
unit_price:req.body.unit_price
},
headers: {
'Content-Type': 'application/json'
}
},
function(error, response, body){
// console.log(error);
// console.log(response);
console.log(body);
res.send(body);
});
// res.send("body");
});
in receiving end server code looks like:
app.post('/add', function(req, res){
console.log('received request')
console.log(req.body);
let adunit = new AdUnit(req.body);
adunit.save()
.then(game => {
res.status(200).json({'adUnit':'AdUnit is added successfully'})
})
.catch(err => {
res.status(400).send('unable to save to database');
})
});
Schema is just two properties unit_name and unit_price.

I use superagent, which is simliar to jQuery.
Here is the docs
And the demo like:
var sa = require('superagent');
sa.post('url')
.send({key: value})
.end(function(err, res) {
//TODO
});

Try this. It works for me.
const express = require("express");
const app = express();
app.use(express.json());
const PORT = 3000;
const jobTypes = [
{ id: 1, type: "Interior" },
{ id: 2, type: "Etterior" },
{ id: 3, type: "Roof" },
{ id: 4, type: "Renovations" },
{ id: 5, type: "Roof" },
];
app.post("/api/jobtypes", (req, res) => {
const jobtype = { id: jobTypes.length + 1, type: req.body.type };
jobTypes.push(jobtype);
res.send(jobtype);
});
app.listen(PORT, console.log(`Listening on port ${PORT}....`));

how to send the response to browser fromm http.request in node.js?

I am using the sample code from nodejs.org and trying to send the response to the browser .
var http = require("http");
var port = 8001;
http.createServer().listen(port);
var options = {
host: "xxx",
port: 5984,
//path: "/_all_dbs",
path: "xxxxx",
method: "GET"
};
var req = http.request(options, function(res) {
console.log('STATUS: ' + res.statusCode);
console.log('HEADERS: ' + JSON.stringify(res.headers));
res.setEncoding('utf8');
res.on('data', function (chunk) {
console.log('BODY: ' + chunk);
var buffer = "";
buffer += chunk;
var parsedData = JSON.parse(buffer);
console.log(parsedData);
console.log("Name of the contact "+parsedData.name);
});
});
req.on('error', function(e) {
console.log('problem with request: ' + e.message);
});
req.write("hello");
req.end();
But req.write("hello") just does not output the string to the browser ?
Is this not the right way ? can someone also tell me how to output the response to the html in views folder so that i can populate the response to the static html .

Try this:
var http = require('http');
var options = {
host: "127.0.0.1",
port: 5984,
path: "/_all_dbs",
method: "GET"
};
http.createServer(function(req,res){
var rq = http.request(options, function(rs) {
rs.on('data', function (chunk) {
res.write(chunk);
});
rs.on('end', function () {
res.end();
});
});
rq.end();
}).listen(8001);
Edit:
This node script saves the output to a file:
var http = require('http');
var fs=require('fs');
var options = {
host: "127.0.0.1",
port: 5984,
path: "/_all_dbs",
method: "GET"
};
var buffer="";
var rq = http.request(options, function(rs) {
rs.on('data', function (chunk) {
buffer+=chunk;
});
rs.on('end', function () {
fs.writeFile('/path/to/viewsfolder/your.html',buffer,function(err){
if (err) throw err;
console.log('It\'s saved!');
});
});
});
rq.end();