Multer's GridFS storage engine

GridFS storage engine for Multer to store uploaded files directly to MongoDb.

�� Features

• Compatibility with MongoDb versions 2 and 3.
• Really simple api.
• Compatible with any current Node.js version.
• Caching of url based connections.
• Compatible with Mongoose connection objects.
• Promise support.
• Generator function support.
• Support for existing and promise based database connections.
• Storage operation buffering for incoming files while the connection is opening.
• Use it as a multer plugin or inside an express middleware function.
• Builtin Typescript support.

�� Installation

Using npm

$ npm install multer-gridfs-storage --save

Basic usage example:

const express = require('express');
const multer  = require('multer');
const {GridFsStorage} = require('multer-gridfs-storage');
const url = 'mongodb://yourhost:27017/database';

// Create a storage object with a given configuration
const storage = new GridFsStorage({ url });

// Set multer storage engine to the newly created object
const upload = multer({ storage });

const app = express();

// Upload your files as usual
app.post('/profile', upload.single('avatar'), (req, res, next) => { 
    /*....*/ 
});

app.post('/photos/upload', upload.array('photos', 12), (req, res, next) => {
    /*....*/ 
});

app.post('/cool-profile', upload.fields([{ name: 'avatar', maxCount: 1 }, { name: 'gallery', maxCount: 8 }]), (req, res, next) => {
    /*....*/ 
});

�� API

module(configuration): function

The module returns a function that can be invoked to create a Multer storage engine. It also works as a class. It is up to you to decide the best way to invoke it.

Check the wiki for an in depth guide on how to use this module.

Configuration

The configuration parameter is an object with the following properties.

url

Type: string

Required if db option is not present

An url pointing to the database used to store the incoming files.

With this option the module will create a mongodb connection for you. It must be a standard mongodb connection string.

If the db option is specified this setting is ignored.

Example:

const {GridFsStorage} = require('multer-gridfs-storage');

const storage = new GridFsStorage({
    url: 'mongodb://yourhost:27017/database'
});

The connected database is available in the storage.db property.

On mongodb v3 the client instance is also available in the storage.client property.

options

Type: object

Not required

This setting allows you to customize how this module establishes the connection if you are using the url option.

You can set this to an object like is specified in the MongoClient.connect documentation and change the default behavior without having to create the connection yourself using the db option.

cache

Type: boolean or string

Not required

Default value: false

Store this connection in the internal cache. You can also use a string to use a named cache. By default caching is disabled. See caching to learn more about reusing connections.

This option only applies when you use an url string to connect to MongoDb. Caching is not enabled when you create instances with a database object directly.

db

Type: DB or Promise

Required if url option is not present

The database connection to use, or a promise that resolves with the connection object. Mongoose Connection objects are supported too.

This is useful to reuse an existing connection to create more storage objects.

Example:

// using a database instance
const client = await MongoClient.connect('mongodb://yourhost:27017');
const database = client.db('database');
const storage = new GridFsStorage({ db: database });

// using a promise
const promise = MongoClient
  .connect('mongodb://yourhost:27017')
  .then(client => client.db('database'));
  
const storage = new GridFsStorage({ db: promise });

// using Mongoose

const connection = mongoose.connect('mongodb://yourhost:27017/database');

const storage = new GridFsStorage({ db: connection });

// mongodb v2
const {GridFsStorage} = require('multer-gridfs-storage');
 
// using a database instance
const database = await MongoClient.connect('mongodb://yourhost:27017/database');
const storage = new GridFsStorage({ db: database });

// using a promise
const promise = MongoClient.connect('mongodb://yourhost:27017/database');
const storage = new GridFsStorage({ db: promise });

client

If you used the db option to initialize the storage engine you can also include the client generated by calling the MongoClient.connect method in this option.

Using promises is also supported

// including the client in the storage
const client = await MongoClient.connect('mongodb://yourhost:27017');
const db = client.db('database');
const storage = new GridFsStorage({ db, client});

// using a promise
const client = MongoClient.connect('mongodb://yourhost:27017');
const db = client.then(cl => cl.db('database'));
const storage = new GridFsStorage({ db, client});

Using this feature is highly recommended in order to keep the storage in sync with the underlying connection status and to make your code more resilient to future changes in the mongodb library.

file

Type: function or function*

Not required

A function to control the file storage in the database. Is invoked per file with the parameters req and file, in that order.

This module uses GridFSBucket to store files in the database falling back to GridStore in case the previous class is not found like, for example, in earlier versions of MongoDb.

By default, naming behaves exactly like the default Multer disk storage, a 16 bytes long name in a hexadecimal format with no extension is generated for each file to guarantee that there are very low probabilities of collisions. You can override this by passing your own function.

The return value of this function is an object, or a promise that resolves to an object (this also applies to generators) with the following properties.

Any missing properties will use the defaults. Also, note that each property must be supported by your installed version of MongoDb.

If you return null or undefined from the file function, the values for the current file will also be the defaults. This is useful when you want to conditionally change some files while leaving others untouched.

This example will use the collection 'photos' only for incoming files whose reported mime-type is image/jpeg, the others will be stored using default values.

const {GridFsStorage} = require('multer-gridfs-storage');

const storage = new GridFsStorage({
  url: 'mongodb://host:27017/database',
  file: (req, file) => {
    if (file.mimetype === 'image/jpeg') {
      return {
        bucketName: 'photos'
      };
    } else {
      return null;
    }
  }
});
const upload = multer({ storage });

This other example names every file something like 'file_1504287812377', using the date to change the number and to generate unique values

const {GridFsStorage} = require('multer-gridfs-storage');

const storage = new GridFsStorage({
  url: 'mongodb://host:27017/database',
  file: (req, file) => {
    return {
      filename: 'file_' + Date.now()
    };
  }
});
const upload = multer({ storage });

Is also possible to return values other than objects, like strings or numbers, in which case they will be used as the filename and the remaining properties will use the defaults. This is a simplified version of a previous example

const {GridFsStorage} = require('multer-gridfs-storage');

const storage = new GridFsStorage({
  url: 'mongodb://host:27017/database',
  file: (req, file) => {
    // instead of an object a string is returned
    return 'file_' + Date.now();
  }
});
const upload = multer({ storage });

Internally the function crypto.randomBytes is used to generate names. In this example, files are named using the same format plus the extension as received from the client, also changing the collection where to store files to uploads.

const crypto = require('crypto');
const path = require('path');
const {GridFsStorage} = require('multer-gridfs-storage');

var storage = new GridFsStorage({
  url: 'mongodb://host:27017/database',
  file: (req, file) => {
    return new Promise((resolve, reject) => {
      crypto.randomBytes(16, (err, buf) => {
        if (err) {
          return reject(err);
        }
        const filename = buf.toString('hex') + path.extname(file.originalname);
        const fileInfo = {
          filename: filename,
          bucketName: 'uploads'
        };
        resolve(fileInfo);
      });
    });
  }
});
const upload = multer({ storage });

File information

Each saved file located in req.file and req.files contain the following properties in addition to the ones that Multer create by default. Most of them can be set using the file configuration.

To see all the other properties of the file object, check the Multer's documentation.

Do not confuse contentType with Multer's mimetype. The first is the value in the database while the latter is the value in the request. You could choose to override the value at the moment of storing the file. In most cases both values should be equal.

�� Caching

You can enable caching by either using a boolean, or a non-empty string in the cache option, then, when the module is invoked again with the same url it will use the stored db instance instead of creating a new one.

The cache is not a simple object hash. It supports handling asynchronous connections. You could, for example, synchronously create two storage instances for the same cache one after the other and only one of them will try to open a connection.

This greatly simplifies managing instances in different files of your app. All you have to do now is to store a url string in a configuration file to share the same connection. Scaling your application with a load-balancer, for example, can lead to spawn a great number of database connections for each child process. With this feature no additional code is required to keep opened connections to the exact number you want without any effort.

You can also create named caches by using a string instead of a boolean value. In those cases, the module will uniquely identify the cache allowing for an arbitrary number of cached connections per url and giving you the ability to decide which connection to use and how many of them should be created.

The following code will create a new connection and store it under a cache named 'default'.

const {GridFsStorage} = require('multer-gridfs-storage');

const storage = new GridFsStorage({
    url: 'mongodb://yourhost:27017/database',
    cache: true
});

Other, more complex example, could be creating several files and only two connections to handle them.

// file 1
const {GridFsStorage} = require('multer-gridfs-storage');

const storage = new GridFsStorage({
   url: 'mongodb://yourhost:27017/database',
   cache: '1'
});

// file 2
const {GridFsStorage} = require('multer-gridfs-storage');

const storage = new GridFsStorage({
    url: 'mongodb://yourhost:27017/database',
    cache: '1'
});

 // file 3
const {GridFsStorage} = require('multer-gridfs-storage');

const storage = new GridFsStorage({
   url: 'mongodb://yourhost:27017/database',
   cache: '2'
});

// file 4
const {GridFsStorage} = require('multer-gridfs-storage');

const storage = new GridFsStorage({
    url: 'mongodb://yourhost:27017/database',
    cache: '2'
});

The files 1 and 2 will use the connection cached under the key '1' and the files 3 and 4 will use the cache named '2'. You don't have to worry about managing connections anymore. By setting a simple string value the module manages them for you automatically.

Connection strings are parsed and tested for similarities. In this example the urls are equivalent and only one connection will be created.

const {GridFsStorage} = require('multer-gridfs-storage');

// Both configurations are equivalent

const storage1 = new GridFsStorage({
    url: 'mongodb://host1:27017,host2:27017/database',
    cache: 'connections'
});

const storage2 = new GridFsStorage({
    url: 'mongodb://host2:27017,host1:27017/database',
    cache: 'connections'
});

Of course if you want to create more connections this is still possible. Caching is disabled by default so setting a cache: false or not setting any cache configuration at all will cause the module to ignore caching and create a new connection each time.

Using options has a particular side effect. The cache will spawn more connections only when they differ in their values. Objects provided here are not compared by reference as long as they are just plain objects. Falsey values like null and undefined are considered equal. This is required because various options can lead to completely different connections, for example when using replicas or server configurations. Only connections that are semantically equivalent are considered equal.

�� Utility methods

generateBytes

A shortcut for crypto.randomBytes which uses promises instead of callbacks to generate names and return the value in a property called filename.

const {GridFsStorage} = require('multer-gridfs-storage');
const {generateBytes} = GridFsStorage;
const result = await generateBytes();
// result will be something like {filename: '37492f9fe13c350667350bcacf0e5b19'}

fromStream

A function that pipe a readable stream to gridfs using the current storage configuration. Useful if you want to upload the received file in multiple storage devices.

const {GridFsStorage} = require('multer-gridfs-storage');
const multer = require('multer');
const upload = multer({ dest: 'uploads/' });
const app = express();
const storage = new GridFsStorage({url: 'mongodb://yourhost:27017/database'});

app.post('/profile', upload.single('avatar'), function (req, res, next) {
  const {file} = req;
  const stream = fs.createReadStream(file.path);
  storage.fromStream(stream, req, file)
    .then(() => res.send('File uploaded'))
    .catch(() => res.status(500).send('error'));
});

Storage ready

Each storage has a ready method that returns a promise. This allows you to watch for the MongoDb connection instead of using events. These two examples are equivalent.

// Using event emitters

const storage = new GridFsStorage({
  url: 'mongodb://yourhost:27017/database'
});

storage.on('connection', (db) => {
  // Db is the database instance
});

storage.on('connectionFailed', (err) => {
  // err is the error received from MongoDb
});

// Using the ready method

const storage = new GridFsStorage({
  url: 'mongodb://yourhost:27017/database'
});

try {
  const {db, client} = await storage.ready();
  // db is the database instance
  // client is the MongoClient instance
} catch (err) {
 // err is the error received from MongoDb
}

Remember that you don't need to wait for the connection to be ready to start uploading files. The module buffers every incoming file until the connection is ready and saves all of them as soon as possible.

The ready method is just a convenience function over code written using the connection events also with a couple of advantages. If you set up a listener after the connection or connectionFailed events are dispatched your code will not execute while using the ready method it will. The module keeps track of these events and resolves or rejects the promises accordingly. Promises in this case are more readable than events and more reliable.

⚡ Events

Each storage object is also a standard Node.js Event Emitter. This is done to ensure that some internal events can also be handled in user code.

Event: 'connection'

This event is emitted when the MongoDb connection is ready to use.

Event arguments

• result: Result is an object with the following properties:

  db: The MongoDb database pointing to the database

  client: The MongoClient instance that holds the connection

This event is triggered at most once.

Event: 'connectionFailed'

This event is emitted when the connection could not be opened.

• err: The connection error

This event only triggers at most once.

Only one of the events connection or connectionFailed will be emitted.

Event: 'file'

This event is emitted every time a new file is stored in the db.

Event arguments

• file: The uploaded file

Event: 'streamError'

This event is emitted when there is an error streaming the file to the database.

Event arguments

• error: The streaming error
• conf: The failed file configuration

Previously this event was named error but in Node error events are special and crash the process if one is emitted and there is no listener attached. You could choose to handle errors in an express middleware forcing you to set an empty error listener to avoid crashing. To simplify the issue this event was renamed to allow you to choose the best way to handle storage errors.

Event: 'dbError'

This event is emitted when the underlying connection emits an error.

Only available when the storage is created with the url option.

Event arguments

• error: The error emitted by the database connection

�� Notes

When using the url feature with the option {useUnifiedTopology:true} to create a MongoDb connection like this:

const storage = new GridFsStorage({
  url: 'mongodb://yourhost:27017/database',
  options: {useUnifiedTopology: true},
});

In this case the internal client always report that the connection is open even when is not. This is a known bug that you can track here.

Is recommended that you only use this option with a MongoDb version that has the bug resolved, otherwise the storage instance cannot track the connection status and features like buffering could not work properly in some scenarios.

�� Test

To run the test suite, first install the dependencies, then run npm test:

$ npm install
$ npm test

Tests are written with the ava testing framework.

Code coverage thanks to istanbul

$ npm run coverage

�� License

MIT