app.js

    var express = require('express'); 
    var app = express(); 
    var bodyParser = require('body-parser');
    var mongoose = require('mongoose');
    mongoose.connect('mongodb://127.0.0.1/gridfstest');
    var conn = mongoose.connection;
    var multer = require('multer');
    var GridFsStorage = require('multer-gridfs-storage');
    var Grid = require('gridfs-stream');
    Grid.mongo = mongoose.mongo;
    var gfs = Grid(conn.db);

    /** Seting up server to accept cross-origin browser requests */
    app.use(function(req, res, next) { //allow cross origin requests
        res.setHeader("Access-Control-Allow-Methods", "POST, PUT, OPTIONS, DELETE, GET");
        res.header("Access-Control-Allow-Origin", "http://localhost:3000");
        res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
        res.header("Access-Control-Allow-Credentials", true);
        next();
    });

    app.use(bodyParser.json());

    /** Setting up storage using multer-gridfs-storage */
    var storage = GridFsStorage({
        gfs : gfs,
        filename: function (req, file, cb) {
            var datetimestamp = Date.now();
            cb(null, file.fieldname + '-' + datetimestamp + '.' + file.originalname.split('.')[file.originalname.split('.').length -1]);
        },
        /** With gridfs we can store aditional meta-data along with the file */
        metadata: function(req, file, cb) {
            cb(null, { originalname: file.originalname });
        },
        root: 'ctFiles' //root name for collection to store files into
    });

    var upload = multer({ //multer settings for single upload
        storage: storage
    }).single('file');

    /** API path that will upload the files */
    app.post('/upload', function(req, res) {
        upload(req,res,function(err){
            if(err){
                 res.json({error_code:1,err_desc:err});
                 return;
            }
             res.json({error_code:0,err_desc:null});
        });
    });

    app.get('/file/:filename', function(req, res){
        gfs.collection('ctFiles'); //set collection name to lookup into

        /** First check if file exists */
        gfs.files.find({filename: req.params.filename}).toArray(function(err, files){
            if(!files || files.length === 0){
                return res.status(404).json({
                    responseCode: 1,
                    responseMessage: "error"
                });
            }
            /** create read stream */
            var readstream = gfs.createReadStream({
                filename: files[0].filename,
                root: "ctFiles"
            });
            /** set the proper content type */
            res.set('Content-Type', files[0].contentType)
            /** return response */
            return readstream.pipe(res);
        });
    });

    app.listen('3002', function(){
        console.log('running on 3002...');
    });