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Rack middleware for adding HTTP endpoints for files stored in MongoDB GridFS
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Rack::GridFS is a Rack middleware for creating HTTP endpoints for files stored in MongoDB's GridFS. You can configure a prefix string which will be used to match the path of a request, and further look up GridFS files based on either their ObjectId or filename field.

For example,

GET '/gridfs/someobjectid'

If the prefix is "gridfs", then the id will be be "someobjectid".

You can also use Rack::GridFS::Endpoint as a rack endpoint if you want to handle routing another way.


The library hasn't been updated for some time and is in the process of being brought up to modern standards on the master branch. It does not yet work with 2.x versions of the mongo driver gem, which means that you will not be able to use it together with Mongoid 5.x (patches welcome if you need it faster than we can deliver it). Since Mongoid 3.x and 4.x use the moped gem instead of mongo, though, you may be able to use the current rack-gridfs release in apps still using one of these older Mongoid versions. rack-gridfs should support the latest 1.x mongo releases, which support MongoDB 3.0.

If your head is spinning, this official blog post gives a good breakdown of driver version history and the future.


  • Use as rack middleware or mount as a rack endpoint
  • File lookup using a path or object id
  • Chunked transfer encoding, keeps memory usage low
  • Content-Type header set using 'mime-types' gem
  • Last-Modified and Etag headers set automatically for conditional get support
  • Cache-Control header support
  • High availability when using replication sets


$ gem install rack-gridfs

Or in a Bundler project, add to your Gemfile:

gem 'rack-gridfs', '~> 0.4'


require 'rack/gridfs'

use Rack::GridFS, :prefix => 'gridfs',
                  :hostname => 'localhost',
                  :port => 27017,
                  :database => 'test'


  • prefix: a string used to match against incoming paths and route to through the middleware. Default 'gridfs'.
  • lookup: whether to look up a file based on :id or :path (example below). Default is :id.
  • fs_name: collection name for the file system, if not using the Mongo driver default ("fs").

You must also specify MongoDB database details:

  • hostname: the hostname/IP where the MongoDB server is running. Default 'localhost'.
  • port: the port of the MongoDB server. Default 27017.
  • database: the name of the MongoDB database to connect to.
  • username and password: if you need to authenticate to MongoDB.

Alternatively you can pass in a Mongo::DB instance instead:

  • db: MongoMapper.database, or Mongoid.database for example.

Simple Sinatra Example

require 'rubygems'
require 'sinatra'

require 'rack/gridfs'
use Rack::GridFS, :database => 'test', :prefix => 'gridfs'

get /.*/ do
  "The URL did not match a file in GridFS."

Usage with Rails 2

To use Rack::GridFS in a Rails application, add it as middleware in application.rb or config/environments/* with something like this:

config.middleware.insert_after Rack::Runtime, Rack::GridFS,
  :prefix => 'uploads', :database => "my_app_#{Rails.env}"

Run rake middleware to decide for yourself where to best place it in the middleware stack for your app using the Rails convenience methods, taking into consideration that it can probably be near the top since it simply returns a "static" file or a 404.

Usage with Rails 3

To use in Rails 3, you can insert into the middleware stack as above, or mount the app directly in your routes (recommended). In config/routes.rb:

mount => Mongoid.database), :at => "gridfs"

This allows for much more straightforward and sensible configuration, if you do not require other middleware in front of GridFS (Rack-based authorization, for instance).

Path (filename) Lookup

The :lookup => :path option causes files to be looked up from the GridFS store based on their filename field (which can be a full file path) rather than ObjectId (requests still need to match the prefix you've set). This allows you to find files based on essentially arbitrary URLs such as:

GET '/prefix/media/images/jane_avatar.jpg'

How filenames are set is specific to your application. We'll look at an example with Carrierwave below.

NOTE: The Mongo Ruby driver will try to create an index on the filename field for you automatically, but if you are using filename lookup you'll want to double-check that it is created appropriately (on slaves only if you have a master-slave architecture, etc.).

Carrierwave Example

Path lookup works well for usage with Carrierwave. As a minimal example with Mongoid:

# config/initializers/carrierwave.rb
CarrierWave.configure do |config| = :grid_fs
  config.grid_fs_connection = Mongoid.database
  config.grid_fs_access_url = "/uploads"

# app/uploaders/avatar_uploader.rb
class AvatarUploader < CarrierWave::Uploader::Base
  # (Virtual) path where uploaded files will be stored, appended to the
  # gridfs_access_url by methods used with view helpers
  def store_dir

# app/models/user.rb
class User
  include Mongoid::Document
  mount_uploader :avatar, AvatarUploader
<%# app/views/user/show.html.erb %>
<%= image_tag(@user.avatar.url) if @user.avatar? %>

This will result in URL paths like /uploads/user/avatar/4d250d04a8f41c0a31000006/original_filename.jpg being generated for the view helpers, and Carrierwave will store user/avatar/4d250d04a8f41c0a31000006/original_filename.jpg as the filename in GridFS. Thus, you can configure Rack::GridFS to serve these files as such:

config.middleware.insert_after Rack::Runtime, Rack::GridFS,
  :prefix => 'uploads', :lookup => :path, :database => "my_app_#{Rails.env}"

Ruby Version and Mongo Driver Compatibility Notes

If for some reason you need support for ancient versions of the mongo driver prior to v1.2, these were supported in rack-gridfs 0.3.0 and below. 0.4.x supports mongo 1.2+ which made substantial changes to the earlier GridFS API.

Support for Ruby 1.8 is no longer being tested and will be dropped in the next version that supports mongo 2.x (the driver itself officially drops 1.8 support). It was supported up to rack-gridfs gem release/git tag v0.4.2.

Development and Contributing

Running the project and unit tests in development follows typical procedure for a Ruby project:

$ git clone
$ cd rack-gridfs
$ bundle install
$ bundle exec rake test

Note that the test suite expects that you have MongoDB running locally on the default port and will use a database called test.


Copyright (c) 2010-2015 Blake Carlson. See LICENSE for details.

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