Controller tricks: API on Metal
Sooner or later each Rails developer come to a point when he wants to build his first API. Among the first things you have to take care of are your controllers. If you want your API to be fast (and I bet you do) then you should consider using ActionController::Metal. The trick is that
ActionController::Base
has many Middlewares that are not necessary for the API, by using Metal controller with minimum modules included, the one can achieve up to 40% speedup. Lets see what your basic metal controller may looks like:class Api::V1::BaseController < ActionController::Metal
include ActionController::Rendering # enables rendering
include ActionController::MimeResponds # enables serving different content types like :xml or :json
include AbstractController::Callbacks # callbacks for your authentication logic
append_view_path "#{Rails.root}/app/views" # you have to specify your views location as well
end
Unfortunately NewRelic doesn’t support Metal by default, so you have to add monitoring manually.Routing: use versioning
Nobody’s perfect. So are we. Your API will definitely be changed and extended multiple times in the future so you better take care of your versioning at the beginning. As you noticed,BaseController
wrapped in V1
namespace. Use something like this in your routes:namespace :api do
namespace :v1 do
# put your routes here
end
end
Views tricks: RABL ’em all
You don’t want to burden your code with logic of exposing different model fields for different API actions, right? In this case you should use some template engine. RABL is at your service. Here’s an example of your view:object @object
attribute :public_id => :id
attributes :title, :created_at, :source
child :contacts do
attributes :title
end
child :files do
attributes :filename, :content_type, :size
end
Also that will save you time by getting rid of ugly respond_to
blocks. Instead ofdef show
@object = Object.find(params[:id])
respond_to do |f|
f.json { render json: @object.to_json }
f.xml { render xml: @object.to_xml }
end
end
You can simple do literally Nothingdef show
@object = Object.find(params[:id])
end
Just make sure you have a RABL view in a corresponding directory.Security
There’re plenty of articles about securing your API with OAuth. Another convenient way is to simply use token passed in the query string. If you ended up with token keep in mind that you can easily generate it by callingSecureRandom.urlsafe_base64
. To make sure token is unique you can use something like this:def build_token
begin
token = SecureRandom.urlsafe_base64
end while User.exists?(api_token: token)
token
end
Hiding your IDs with GUIDs
By default Rails uses incremental integer for primary key. Common practice is not to expose these kind of IDs to the public via your API because users can guess other IDs in your database and that might be a potential risk. To solve this you can come up with a simple algorithm that will convert your IDs into some “safe” form and back. But still it’s not super safe because someone can find out what the algorithm is. Another possible solution is to expose GUIDs to the public. It’s a 128 entity that typically looks like this:a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11
To generate it in Ruby use SecureRandom.uuid
(generates V4 GUID). You can store it as a simple string column but if you are using Postgresql then you can utilize it’s built in uuid
type – this can save you a lot of space. Rails, however falls back to :string
for the uuid
Postgresql native type. To workaround this you can create column manually in your migration (index should be added as well):execute "ALTER TABLE objects add COLUMN public_id uuid NOT NULL DEFAULT uuid_generate_v4()"
add_index :objects, [:public_id], name: "index_objects_on_public_id", unique: true
To use uuid_generate_v4
function you have to add Postgresql extension:create extension "uuid-ossp"
And don’t forget to change your schema format to :sql
in config/application.rb
config.active_record.schema_format = :sql
Testing your API
You definitely want to cover up your new shiny API with some sort of tests. See example below that usesRack::Test::Methods
# spec_helper
module ApiHelper
include Rack::Test::Methods
def app
Rails.application
end
end
RSpec.configure do |config|
config.include ApiHelper, api: true
end
# spec
require 'spec_helper'
describe "api/v1/objects", api: true do
let(:url) { "api/v1/objects" }
let(:object) { Factory.create(:object) }
let(:token) { "YOUR_SECRET_TOKEN" }
let(:data) { JSON.parse(last_response.body) }
before(:each) { get url, token: token } # here's where API call made
subject { data }
it { should have(1).object }
end
Conclusion
We’ve just gone through the following tricks:- Minimum usable Metal controller
- Simple versioning
- Easy API views with RABL
- Postresql native
uuid
type - API spec sample
render json: your_json
you should include ActionController::Renderers::All
in your base API controller. Thanks Divya Kunnath for pointing that out.