stored files directly in mongodb with gridfs-strea

I need save some files like: images,video,pdf... into mongodb, so i use gridfs-stream and express.js

var file = req.files.file; 
req.pipe(gfs.createWriteStream({
    filename:file.originalname,
    mode:"w",
    chunkSize:1024*4,
    content_type:file.mimetype,
    root:"fs"
})
res.send(200);

for testing i use postman and set an POST request this way:

 POST /fs/upload HTTP/1.1
 Host: localhost:5000
 Cache-Control: no-cache

 ----WebKitFormBoundaryE19zNvXGzXaLvS5C
 Content-Disposition: form-data; name="file"; filename="epic.png"
 Content-Type: image/png


  ----WebKitFormBoundaryE19zNvXGzXaLvS5C

the problem is that this way just store the data of the file:

{
    "_id" : ObjectId("54d14ec5b102fe401519a3c1"),
    "filename" : "epic.png",
    "contentType" : "image/png",
    "length" : 0,
    "chunkSize" : 4096,
    "uploadDate" : ISODate("2015-02-03T22:42:14.730Z"),
    "aliases" : null,
    "metadata" : null,
    "md5" : "993fb9ce262a96a81c79a38106147e95"
}

but not the content i mean de binary data for it, into mongodb is store for it the propety length is equal to 0, bacause has not any chunks in fs.chucks.

Reading in blogs found the answer to streaming data directly at database with express.js,gridfs-stream.js and multer middleware that way:

var multer = require('multer');

app.post('/fs/upload', multer({
    upload: null,// take uploading process 

    onFileUploadStart: function (file) {
        //set upload with WritableStream        
        this.upload = gfs.createWriteStream({
            filename: file.originalname,
            mode: "w",
            chunkSize: 1024*4,
            content_type: file.mimetype,
            root: "fs"
        });
     },

     onFileUploadData: function (file, data) {
        //put the chucks into db 
        this.upload.write(data);
     },

     onFileUploadComplete: function (file) {
        //end process 
        this.upload.on('drain', function () {
            this.upload.end();
        });
     }
}), function (req, res) {
   res.sendStatus(200);
});

For testing this:

app.route('/fs/download/:file').get(function (req, res) {
   var readstream = gfs.createReadStream({_id: req.params.file});
   readstream.pipe(res);
});