nodejs res.end not working in callback - mysql

Question

I'm trying to retrieve data from a database and send it back to the user, but since mysql queries work asynchronously, I can't just put the code that sends the response after the query code, I have to send the response within the callback function of the query.
var express = require('express');
var fs = require('fs');
var mysql = require('mysql')
var app = express();
var con = mysql.createConnection({
host:"localhost",
user:"root",
password:"",
database:"tempdb"
})
app.use(function (req, res, next) {
res.setHeader('Access-Control-Allow-Origin', 'http://localhost');
res.setHeader('Access-Control-Allow-Methods', 'GET, POST, OPTIONS, PUT,
PATCH, DELETE');
res.setHeader('Access-Control-Allow-Headers', 'X-Requested-With,content-
type');
res.setHeader('Access-Control-Allow-Credentials', true);
next();
});
app.get('/',function(req,res,next){
function foo(res){
con.query('SELECT * FROM `data` WHERE 1',function(err,result){
if (err) throw err;
res.end('weee',function(err){
if (err) throw err;
)}
})
}
foo(res)
next();
})
app.listen(1001)
Even with something as simple as this, when the data from the database isn't processed or used at all, the res.end function doesn't send any data.
I've tried many variations of this, using waterfall callbacks, putting the res.end in a function outside of the query and calling it, but nothing seems to work. The only time it works it when I put it outside the query, but since the query is async I can't get any data out of it that way. Is there a way to work around this or am I just missing something?
Thanks in advance!

Answer 1

Remove the call to next() in your app.get() handler.
You only want to do that when you are NOT handling the request and sending a response and you want to let other handlers have a crack at the request.
The way you have it, you are calling next() BEFORE the con.query() finishes so that lets the default handler in express handle the request and thus your res.end() doesn't actually do anything because a response has already been sent for this request.
Here's what I would suggest:
app.get('/', function(req, res){
con.query('SELECT * FROM `data` WHERE 1',function(err, result){
if (err) {
console.log(err);
res.status(500).end();
} else {
res.send('weee');
}
});
});
So, you only call next() if you are not going to be sending a response and you want someone else in the handler chain to send the response.

Answer 2

When using res in middlewares throw a return before res.
app.get('/',function(req,res,next){
function foo(res){
con.query('SELECT * FROM `data` WHERE 1',function(err,result){
if (err) throw err;
return res.end('weee',function(err){
if (err) throw err;
)}
})
}
foo(res)
next();
})
Hopefully this works...