using express and sqlite3

Question

so I have a database called user.db and the table are user_id, username, hashpassword.

when I call this function from the main thread it works find

function check_login(username, hashpassword){
 user_db.all("SELECT * FROM users", [], (err, rows)=>{
     console.log(rows)
 });}

but when im calling it from the express funcation

app.post("/log_in/:cookie", (req, res) =>{
let cookie = req.params.cookie;
if (cookie != "")
{
    let user_id = check_login(req.body.username, req.body.hashpassword);
    console.log(user_id);
    if( user_id != ""){
        let code = create_code(get_info_by_cookie(cookie, user_id));
        res.json({"code":code})
    }
    else{
        res.json({"error":"username or password doesn't match"})
    }

}
else{
    res.json({"error":"no cookie was given"})
}
    });

it's printing undefined

can someone please tell me why when I call the function from another script or in the main thread it works fine but when it from the app.post() it doesn't work

Answer 1

SQLite3 functions are asynchronous, so your code can't assume it gets a return value. But more important than that, you forgot to work with Express's concept of middleware functions. Let's fix that. First, let's define our user check function as a middleware function, using normal JS conventions for naming things, not Python conventions.

First, checking for a cookie value:

function checkCookie(req, res, next) {
  let cookie = req.params.cookie;
  if (!cookie)  return next(new Error("no cookie found"));
  next();
}

Then, checking the user's login:

function checkLogin(req, res, next) {
  let username = req.body.username,
      hashpassword = req.body.hashpassword;

  user_db.all("SELECT * FROM users", [], (err, rows) => {
    if (err) return next(err);
    // ...
    // You code goes here. You didn't show any, so I'm not inventing any either.
    // ...
    if (hasAccess) return next();
    return next(new Error(`user ${username} does not have access`);
  });
}

And now we can use this in a proper express chain:

app.post("/log_in/:cookie", checkCookie, checkLogin, (req, res) => {
    // We KNOW this user has a cookie set, and the their login is good.
    // So all this function has to do is form whatever response you need
    // given that those two things are true
});