将标头发送到客户端后无法设置标头 node.js 中的错误

Question

Cannot set headers after they are sent to the client I'm getting this error. I did some study and I think it's because of more than one callbacks but I'm unable to solve this issue. Please help me fix this issue. I'm attaching herewith my routes.js code. Any help will be highly appreciable. Thank you.

Here's my routes.js code

const {
   con,g
   sessionStore
 } = require('./config/db');
const { route } = require('./routes/auth');
exports.new = function(req, res){
    message = '';
   if(req.method == "POST"){
      const post  = req.body;
      const username= post.username;
      const title= post.title;
      const state= post.state;
      const category= post.category;
      const description= post.description;
 
      if (!req.files)
                return res.status(400).send('No files were uploaded.');
 
      const file = req.files.uploaded_image;
      var img_name=file.name;
 
         if(file.mimetype == "image/jpeg" ||file.mimetype == "image/png"||file.mimetype == "image/gif" ){
                                 
              file.mv('public/imgs/uploads/'+file.name, function(err) {
                             
               var sql = "INSERT INTO `nt_data`(`username`,`title`,`state`,`category`, `images` ,`description`) VALUES (?,?,?,?,?,?)";
               var query = con.query(sql, [username, title, state, category, img_name, description], function(err) {
                  console.log(err)
                 if (!err) {
                   res.redirect('show/' + username);
                 }
                 else {
                  message = "This format is not allowed , please upload file with '.png','.gif','.jpg'";
                  res.render('new.ejs',{message: message});
                }
               }); 
            }); 
          
   } 
}
   else {
      res.render('new');
   }
 
};

exports.show = function(req, res){
    let message = '';
    var username = req.params.username;
    const sql="SELECT * FROM `nt_data` WHERE `username`='"+username+"'"; 
    con.query(sql, function(err, result){
       console.log(err)
      if(result.length <= 0){
      message = "show not found!";
      
      res.render('show.ejs',{data:result, message: message});
     }else{
      res.redirect('/places');
     }
     res.render('show', {data:result, message: message});
   });
  
};
 
exports.places=function (req,res){
   let message = '';
   var username = req.params.username;
    const sql="SELECT * FROM `nt_data` WHERE `username`='"+username+"'"; 
    con.query(sql, function(err, result){
       console.log(err)
       if(result.length <= 0)
         message = "places not found!";
   res.render('places.ejs',{data:result, message: message});
    });
}

Answer 1

In your show function you execute a database query, inside the callback you have an if else statement with a res.render and a res.redirect. So one way or the other a result is sent. So you cannot send a result when the if statement is completed. Remove this res.render('show', {data:result, message: message}); . line and you are good to go!