NodeJS / Express: inconsistent [ERR_HTTP_HEADERS_SENT] occurring - node.js

Question

Here I have a POST method that gets called quite often.
app.post('/return_data', async (req, res) => {
var response, file
console.log("request recieved: " + req.body.room)
await readFile('Data/'+req.body.room+'.json').then((data) => {
console.log(data)
return res.send(data)
}).catch((e) => {
console.log(e)
})
})
For some reason the response is intermittent. Sometimes it will log the following error.
Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
at ServerResponse.setHeader (_http_outgoing.js:535:11)
at ServerResponse.header (/home/ec2-user/dc-floorplans/node_modules/express/lib/response.js:771:10)
at ServerResponse.send (/home/ec2-user/dc-floorplans/node_modules/express/lib/response.js:194:10)
at /home/ec2-user/dc-floorplans/app.js:127:13
at processTicksAndRejections (internal/process/task_queues.js:97:5)
at async /home/ec2-user/dc-floorplans/app.js:125:5 {
code: 'ERR_HTTP_HEADERS_SENT'
}
When I first start my web app, usually the first POST logs an error. After refreshing the page, the data comes through as intended. There is only one response in the function and so I'm puzzled as to why this error is occurring.
I know that readFile works because the data is logged in .then(). How can it be that sometimes data is sent to the client and other times it throws an error when the exact same process is happening?
Thanks in advance.
UPDATE -- FULL APP.JS:
app.set('view-engine', 'ejs');
app.use(express.urlencoded({ extended: false }))
app.use(cors())
app.use(flash())
app.use(session({
secret: process.env.SESSION_SECRET,
resave: false,
saveUninitialized: false
}))
app.use(passport.initialize())
app.use(passport.session())
app.use(methodOverride('_method'))
app.use(express.static(__dirname + '/static'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
app.get('/', checkAuthenticated, (req, res) => {
res.render('index.ejs');
});
app.get('/login', checkNotAuthenticated, function(req, res, next) {
res.render('login.ejs');
});
app.post('/login', checkNotAuthenticated, (req, res, next) => {
passport.authenticate('local', (err, user, info) => {
if(err) throw err
if(!user) return res.redirect('/login')
req.logIn(user, (err) => {
if(err) return next(err)
if(info.message==process.env.DEFAULTPW) {
console.log("Default password detected for: " + user.email)
return res.redirect('/')
}
return res.redirect('/')
})
})(req, res, next)
})
app.get('/update', checkAuthenticated, (req, res, next) => {
res.render('update.ejs')
})
app.post('/update', checkAuthenticated, async (req, res, next) => {
if(req.body.pw1 != req.body.pw2) { res.redirect('/update') }
if(req.body.pw2 == process.env.DEFAULTPW) { res.redirect('/update') }
const newpw = await encrypt(req.body.pw2)
var queryresult
await con.query("UPDATE login SET password = \'"+newpw+"\' WHERE email = \'"+req.body.email.toLowerCase()+"\'", (err, result, fields) => {
if (err) {
console.log(err)
return res.redirect('/update')
};
console.log(result)
queryresult = result
if(result.changedRows == 0) {
return res.redirect('/update')
}
})
return res.redirect('/')
});
app.post('/get_new_data', async (req, res) => {
console.log("New Data:")
await pollLM(req.body.room).then((data) => {
console.log(data)
return res.send(data)
}).catch((e) => {
console.log(e)
})
})
async function pollLM(room) {
return new Promise((resolve, reject) => {
const getData = pySpawn('python3.7', ['getData.py', room])
getData.stdout.on('data', (data) => {
resolve(data)
})
})
}
app.post('/return_data', async (req, res) => {
console.log("request recieved: " + req.body.room)
await readFile('Data/'+req.body.room+'.json').then((data) => {
console.log(data)
return res.send(data)
}).catch((e) => {
console.log(e)
})
})
async function readFile(path) {
return new Promise((resolve, reject) => {
fs.readFile(path, (err, data) => {
if (err) reject(err);
console.log(typeof(data))
resolve(data)
})
})
}
app.post('/update_reload_time', (req, res) => {
console.log("reload time updated to: " + req.body.time)
fs.writeFile('Data/delay.json', JSON.stringify(req.body), () => {
console.log("delay updated to: " + req.body.time)
})
})
app.get('/reload_time', async (req, res) => {
await readFile('Data/delay.json').then((data) => {
console.log(data)
return res.send(data)
}).catch((e) => {
console.log(e)
})
})
app.delete('/logout', (req, res) => {
req.logOut()
res.redirect('/login')
})
// Page routing...
function checkAuthenticated(req, res, next) {
if(req.isAuthenticated()) {
return next()
}
res.redirect('/login')
}
function checkNotAuthenticated(req, res, next) {
if(req.isAuthenticated()) {
return res.redirect('/')
}
next()
}
function encrypt(text) {
const key = crypto.scryptSync(process.env.CRYPTOPW, process.env.SALT, 24)
const cipher = crypto.createCipher('aes-192-cbc', key)
let encrypted = ''
cipher.on('readable', () => {
let chunk
while(null != (chunk = cipher.read())) {
encrypted += chunk.toString('hex')
}
})
cipher.write(text)
cipher.end()
return encrypted
}
function decrypt(text) {
const key = crypto.scryptSync(process.env.CRYPTOPW, process.env.SALT, 24)
const decipher = crypto.createDecipher('aes-192-cbc', key)
let decrypted = '';
decipher.on('readable', () => {
while(null !== (chunk = decipher.read())) {
decrypted += chunk.toString('utf8')
}
})
const encrypted = text
decipher.write(encrypted, 'hex')
decipher.end()
return decrypted
}

Answer 1

All you have to look for is where you response twice on the same call.
For example:
app.post('test', (req,res)=>{
res.send('1')
res.json('{1:2}')
})
will always return this error, because you are responding twice.
You have to investigate your routes one by one, I would start here:
app.post('/update', checkAuthenticated, async (req, res, next) => {
if(req.body.pw1 != req.body.pw2) { res.redirect('/update') }
if(req.body.pw2 == process.env.DEFAULTPW) { res.redirect('/update') }
const newpw = await encrypt(req.body.pw2)
var queryresult
await con.query("UPDATE login SET password = \'"+newpw+"\' WHERE email = \'"+req.body.email.toLowerCase()+"\'", (err, result, fields) => {
if (err) {
console.log(err)
return res.redirect('/update')
};
console.log(result)
queryresult = result
if(result.changedRows == 0) {
return res.redirect('/update')
}
})
return res.redirect('/')
});
You are calling res.redirect explicitly and on condition. Have you checked if both conditions meet simultaneously? I guess here is one weak point.
And I would check this one
app.post('/login', checkNotAuthenticated, (req, res, next) => {
passport.authenticate('local', (err, user, info) => {
if(err) throw err
if(!user) return res.redirect('/login')
req.logIn(user, (err) => {
if(err) return next(err)
if(info.message==process.env.DEFAULTPW) {
console.log("Default password detected for: " + user.email)
return res.redirect('/')
}
return res.redirect('/')
})
})(req, res, next)
})
Again there potentially meet two conditions. Check them out. Other parts look fine to me.