This is a showcase for a new API framework under development. Code is not yet publicly available.

01_kraftwerk-example.rb

require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'
  gem 'kraftwerk', path: 'kraftwerk'
end

DATABASE = []

module Measures
  class Index
    include Kraftwerk::Endpoint

    def call(_params)
      DATABASE
    end
  end

  class Create
    include Kraftwerk::Endpoint

    validate do
      required(:value) { filled? & int? }
      optional(:tag) { str? }
    end

    def call(params)
      DATABASE << params
    end
  end

  class Average
    include Kraftwerk::Endpoint

    validate do
      optional(:last) { int? }
      optional(:tag) { str? }
    end

    def call(params)
      values = DATABASE
      values = values.select { |v| v[:tag] == params[:tag] } if params[:tag]
      values = values.last(params[:last]) if params[:last]

      if !values.empty?
        avg = values.map { |v| v[:value] }.reduce(:+) / values.size.to_f
        { average: avg } # normal object returned
      else
        # response object
        Kraftwerk::Response.new(code: 404, body: { error: 'No elements to calculate average from' })
      end
    end
  end
end

app = Kraftwerk::App.new
app.routing do
  get  '/measures', to: Measures::Index
  post '/measures', to: Measures::Create
  get  '/measures/average', to: Measures::Average
end

Rack::Server.start app: app.rack_app, Port: 2300

02_tree

This is how it would look like in application structure:

.
├── config.ru
├── endpoints
│   └── measures
│       ├── average.rb
│       ├── create.rb
│       └── index.rb
├── Gemfile
├── Gemfile.lock
└── routes.rb

2 directories, 7 files

03_curls

> curl -i localhost:2300

HTTP/1.1 404 Not Found 
X-Cascade: pass
Content-Type: application/json
Server: WEBrick/1.4.2 (Ruby/2.5.1/2018-03-29)
Date: Sat, 05 Jan 2019 18:01:14 GMT
Content-Length: 21
Connection: Keep-Alive

{"error":"not found"}

---------------------------------------------------------
> curl -i localhost:2300/measures

HTTP/1.1 200 OK 
Server: WEBrick/1.4.2 (Ruby/2.5.1/2018-03-29)
Date: Sat, 05 Jan 2019 18:01:17 GMT
Content-Length: 2
Connection: Keep-Alive

[]

---------------------------------------------------------
> curl -i localhost:2300/measures/average

HTTP/1.1 404 Not Found 
Server: WEBrick/1.4.2 (Ruby/2.5.1/2018-03-29)
Date: Sat, 05 Jan 2019 18:02:13 GMT
Content-Length: 49
Connection: Keep-Alive

{"error":"No elements to calculate average from"}

---------------------------------------------------------
> curl -XPOST localhost:2300/measures -H 'Content-Type: application/json' -d '{}' -i

HTTP/1.1 400 Bad Request 
Server: WEBrick/1.4.2 (Ruby/2.5.1/2018-03-29)
Date: Sat, 05 Jan 2019 18:02:54 GMT
Content-Length: 24
Connection: Keep-Alive

{"value":["is missing"]}

---------------------------------------------------------
> url -XPOST localhost:2300/measures -H 'Content-Type: application/json' -d '{"value": 100}' -i

HTTP/1.1 201 Created 
Server: WEBrick/1.4.2 (Ruby/2.5.1/2018-03-29)
Date: Sat, 05 Jan 2019 18:03:24 GMT
Content-Length: 15
Connection: Keep-Alive

[{"value":100}]

---------------------------------------------------------
> curl -XPOST localhost:2300/measures -H 'Content-Type: application/json' -d '{"value": 100, "tag": "test"}' -i

HTTP/1.1 201 Created 
Server: WEBrick/1.4.2 (Ruby/2.5.1/2018-03-29)
Date: Sat, 05 Jan 2019 18:03:57 GMT
Content-Length: 42
Connection: Keep-Alive

[{"value":100},{"value":100,"tag":"test"}]

---------------------------------------------------------
> curl -XPOST localhost:2300/measures -H 'Content-Type: application/json' -d '{"value": 100, "tag": "test", "admin": true}' -i

HTTP/1.1 201 Created 
Server: WEBrick/1.4.2 (Ruby/2.5.1/2018-03-29)
Date: Sat, 05 Jan 2019 18:04:36 GMT
Content-Length: 69
Connection: Keep-Alive

[{"value":100},{"value":100,"tag":"test"},{"value":100,"tag":"test"}]

---------------------------------------------------------
> curl -i localhost:2300/measures/average

HTTP/1.1 200 OK 
Server: WEBrick/1.4.2 (Ruby/2.5.1/2018-03-29)
Date: Sat, 05 Jan 2019 18:05:09 GMT
Content-Length: 17
Connection: Keep-Alive

{"average":100.0}