gistfile1.js

//Uploading file directly on mongodb with gridfs-stream and multer express middleware 
var multer = require('multer');
var express = require('express');
var mongoose = require('mongoose')
var Grid = require('gridfs-stream');

var conecction = function() {
  var conn = mongoose.createConnection('localhost', 'fs_model', 27017).once('open', function() {
    console.log('CONECTADO A fs_model');
  })//end open connection
  return Grid(conn.db, mongoose.mongo);            
}
  
var gfs = connection();  
  



var dispatch = function(gfs) {
	var stacks = [];//take all files 
	return multer({
		onFileUploadStart:function(file){		 
			stacks.push(gfs.createWriteStream({
				filename:file.name,
				mode:"w",
				chunkSize:1024*4,
				content_type:file.mimetype,
				root:"fs",
				metadata:{name:file.originalname}
			}));//put writable stream at stacks array for handler
			
		},
		onFileUploadData:function(file,data) {
		  //this function is async for that we have to check with what file are working 
			stacks.forEach(function(stack) {
				if(stack.name === file.name) stack.write(data);//writing in memory to mongodb 
			})
		},
		onFileUploadComplete:function(file) {
			stacks.forEach(function(stack,index) {
		  //this function is async for that we have to check with what file are workin
				if(stack.name === file.name) {
					stack.end();
					stacks.splice(index,1);//delete the files ready
				}
			})//stack 
		}
	})
}//end dispatch files 

app..use(dispatch(gfs))//middleware post and file request

app.post("/upload",function(req,res) {
  res.send(req.files);
})

this code work to upload multiples o singles files but i am not sure if the memory overflow cause the writable stream dont use the event drain, for short the pipe functionality