Node: Cannot set headers after they are sent to the client - node.js

Question

I did some research on the following error:
Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
I understood the idea and what's causing it but I am not sure how to fix it for my controller code:
exports.isServerOnline = (req, res, next) => {
const sock = new net.Socket();
sock.setTimeout(2500);
sock.on('connect', function () {
sock.destroy();
return res.json({
"server": "online"
});
}).on('error', function (e) {
return res.json({
"server": "offline"
});
}).on('timeout', function (e) {
return res.json({
"server": "offline"
});
}).connect(LS_PORT, LS_HOST);
}
I'm using socket to check if a remote host is up or down. Here is my client code (Vue.js):
created() {
this.getServerStatus();
},
methods: {
getServerStatus() {
axios
.get(`${process.env.VUE_APP_BACKEND_URL}/server/status`)
.then(response => {
if (response.data.server === "online") {
// no interesting code here
} else {
// no interesting code here
}
/* eslint-disable no-console */
})
.catch(error => {
console.log(error);
});
}
}
Complete error stack trace:
2020-07-02T07:40:47.743193+00:00 app[web.1]: _http_outgoing.js:518
2020-07-02T07:40:47.743201+00:00 app[web.1]: throw new ERR_HTTP_HEADERS_SENT('set');
2020-07-02T07:40:47.743202+00:00 app[web.1]: ^
2020-07-02T07:40:47.743202+00:00 app[web.1]:
2020-07-02T07:40:47.743204+00:00 app[web.1]: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
2020-07-02T07:40:47.743205+00:00 app[web.1]: at ServerResponse.setHeader (_http_outgoing.js:518:11)
2020-07-02T07:40:47.743206+00:00 app[web.1]: at ServerResponse.header (/app/node_modules/express/lib/response.js:771:10)
2020-07-02T07:40:47.743206+00:00 app[web.1]: at ServerResponse.json (/app/node_modules/express/lib/response.js:264:10)
2020-07-02T07:40:47.743206+00:00 app[web.1]: at Socket.<anonymous> (/app/src/controllers/status.js:15:20)
2020-07-02T07:40:47.743207+00:00 app[web.1]: at Socket.emit (events.js:315:20)
2020-07-02T07:40:47.743207+00:00 app[web.1]: at emitErrorNT (internal/streams/destroy.js:92:8)
2020-07-02T07:40:47.743208+00:00 app[web.1]: at emitErrorAndCloseNT (internal/streams/destroy.js:60:3)
2020-07-02T07:40:47.743208+00:00 app[web.1]: at processTicksAndRejections (internal/process/task_queues.js:84:21) {
2020-07-02T07:40:47.743209+00:00 app[web.1]: code: 'ERR_HTTP_HEADERS_SENT'
2020-07-02T07:40:47.743209+00:00 app[web.1]: }
I would highly appreciate if someone could point me on the right track.

Answer 1

I don't think that approach is correct mate. You are trying to create a socket inside http endpoint, that will not work. Here's gist I found that demonstrates using NodeJS Socket.
https://gist.github.com/tedmiston/5935757
I'll recommend using into something like Socket.io. They have good amount of documentation to get off the ground.