Express - Error: Can't set headers after they are sent. - express

Question

When I test my application with siege siege -b -r 1 -c 100 https://*****/RTC/stats/rank
I get this error in my nodeJS console
_http_outgoing.js:491
throw new Error('Can\'t set headers after they are sent.');
^
Error: Can't set headers after they are sent.
at validateHeader (_http_outgoing.js:491:11)
at ServerResponse.setHeader (_http_outgoing.js:498:3)
at ServerResponse.header (/home/nodeJS/RTC-stats/node_modules/express/lib/response.js:767:10)
at ServerResponse.send (/home/nodeJS/RTC-stats/node_modules/express/lib/response.js:170:12)
at ServerResponse.json (/home/nodeJS/RTC-stats/node_modules/express/lib/response.js:267:15)
at ServerResponse.send (/home/nodeJS/RTC-stats/node_modules/express/lib/response.js:158:21)
at Request._callback (/home/nodeJS/RTC-stats/server.js:46:14)
at Request.self.callback (/home/nodeJS/RTC-stats/node_modules/request/request.js:186:22)
at emitTwo (events.js:126:13)
at Request.emit (events.js:214:7)
Here you can find the code I used:
const request = require('request');
const express = require('express');
const app = express();
let players = [
"df6c767a-c4a9-4a42-bbbc-e34c7b4f1e16",
"22366c4f-744a-422b-81ff-e21608dd5950",
"c553f6b4-da31-4879-88a6-5dfa28cae1ac",
"5e5cfb2e-29a5-407e-972b-9999fcd567af",
"5fcc4c0e-13ca-49d2-a949-b74ef17d146f",
"094fd818-f794-404c-a2a4-674d3be5e7d3",
];
let responses = [];
let completed_requests = 0;
app.get('/RTC/stats/rank', function (ereq, eres) {
for (var i = 0, len = players.length; i < len; i++) {
var playerUUID = players[i];
var options = {
url: 'https://r6db.com/api/v2/players/' + playerUUID + '?platform=PC',
headers: {
'x-app-id': '5e23d930-edd3-4240-b9a9-723c673fb648'
},
};
request(options, function(err, res, body) {
if (err) { return console.log(err); }
var playerInfo = JSON.parse(body);
responses.push(playerInfo.rank.emea);
completed_requests++;
if (completed_requests === players.length) {
completed_requests = 0;
eres.send(responses);
responses = [];
}
});
}
});
app.listen(3000)
I think there is a problem with the way I send the request to the api. My biggest gues is that it has to do with timing and the sending of the result back to the client. Or is using siege a bad way of testing this application.

Answer 1

const players = [];
app.get(`/`, async (ereq, eres) => {
const http = (options) => {
return new Promise((resolve, reject) => {
request(options, (err, res, body) => {
if (err) {
return reject(err);
}
return resolve(JSON.parse(body));
});
});
};
for(let i = 0; i < players.length; i++) {
var playerUUID = players[i];
var options = {
url: 'https://r6db.com/api/v2/players/' + playerUUID + '?platform=PC',
headers: {
'x-app-id': '5e23d930-edd3-4240-b9a9-723c673fb648'
},
};
try {
let playerInfo = await http(options);
response.push(playerInfo.rank.emea);
} catch (e) {
console.log(e); // I think that you should handle this a better way than just console.logging...
}
}
return eres.json(response);
});
Just make sure that you use promises. Promises will slow down the for loop in order for you to get a proper response and also allowing you to check whatever you need to before returning. If you need to return a response in the for loop, then I would recommend that you go ahead and break; out of the for loop before it continues to try and send data to a response that is already sent.