nodejs write after request end error

Question

I am facing problem of write after request end in nodejs : I have a server.js file , which sends request to other js file (say abc.js) which sends response back to server.js file and then server.js file writes the resoponse and then end response.

my problem is if I write response in abc.js and end it there only it works fine, but if it is in sererconf.js it doesn't.

Let me make it clear that I get this bug only when i send 20-30 requests at a time. I want to know the logic behind it, I searched a lot, but no nice answer found, any help will be appreciated.

    server.js full code:

    /* create HTTP server */
    var httpd = http.createServer(function(req, res) {
    res.setHeader('Access-Control-Allow-Origin', '*');
    res.writeHead(200, {"Content-Type" : "application/json"});
    }).listen(3800);

/* send request to the file mentioned in url*/
httpd.on('request', function(req, res) {
    urll = __dirname + '/..' + req.url;

    fs.exists(urll, function (exists) {
      if(exists){
        var server = require(urll);
        server.get(req,res);
      }
    });

    module.exports = {
        result : function(result){
            if(Array.isArray(result)){
                for(var key in result){
                    result[key] = JSON.parse(result[key]);
                }
            }

            result = JSON.stringify(result);            
                res.write(result ,function(err) { if(!err) res.end(); });
        },
            };
});


**apps.js code**:

var constants   =  require('./lib/constant.js');
var APP_PATH    =    constants.APP_PATH;
module.exports = {

 get : function(req) {  
  req.on('data', function(chunk) {

    var hash = chunk;
        hash = JSON.parse(hash);
    var id   = hash.id;

        dirPath = APP_PATH + id;

        fs.exists( dirPath, function (exists) {
            if(exists)
                read_app_dir(dirPath);
            else
                taskDone([]);       
        });

  });   
 }
};

function read_app_dir(app_dir){
 fs.readdir(app_dir,function(err, list){
     if (err) {
            httpd.log.info('cannot read apps dir at s_apps = '+err);
     }else{     
        create_new_obj(list,app_dir);
    }
 });

}

function create_new_obj(list, app_dir){
 appFilesObj = [];
 var i       = 0;

 list.forEach(function(file) {
  i=i+1;

        file = app_dir +'/' +file;
        appFilesObj.push(file);

        if(i == Object.keys(list).length)
        read_app_files(appFilesObj);       
  });   
}

function read_app_files(appFilesObj,app_dir){
var apps = [];
var i    = 0;

 if(Object.keys(appFilesObj).length > 0){
   appFilesObj.forEach(function(appfile) {
         read_file(appfile,function(data){ i=i+1; 
             apps.push(data);                       
             if(i == Object.keys(appFilesObj).length)
             taskDone(apps);                            
        });
    });
 }else{
    taskDone([]);                               
 }
}


function read_file(file,callback){
 fs.readFile(file,'utf8', function (err, data) {
    if (err)
         httpd.log.info('cannot read file at s_apps = '+err);     
    else
          callback(data);
 });
}

function taskDone(apps){
  var httpd = require(__dirname + '/server.js');
      httpd.result(apps);
}

if I do res.write and res.end in this file in taskDone() then it works fine.

Thanks in advance :)

Answer 1

The problem with above code was, that I was sending back response by calling an exported function of server.js like this:

var httpd = require(__dirname + '/server.js');
    httpd.result(apps);

where result() is the function which I have exported in server.js to write response and end response

Instead of this, now I added a callback support while calling function of other files (ex-apps.js), so that I "res.write" and "res.end()" only when the actually called function gives back the response. (I am not writing the whole code , please refer above code for difference in both) httpd.on('request', function(req, res) { urll = __dirname + '/..' + req.url;

    fs.exists(urll, function (exists) {
      if(exists){
        var server = require(urll);
        server.get(req,res,function(result){
          res.write(result);
          res.end();
         });
      }
    });

**apps.js**


   get : function(req, callback) {  
    req.on('data', function(chunk) {
//when task is done and taskDone() function is called I just callback() the result
     function taskDone(result){
       callback(result);
     }
  }
 }

When I was sending result back by calling a function of server.js and then writing the response...I don't know how..but somehow server was getting confused in multiple requests and saying "write after end" error...while the end was called by some other user's request.

I may be wrong, but this is what I concluded from this :) I hope this may help others.