Parameter Contracts for Sinatra

REST conventions takes the guesswork out of designing and consuming web APIs. GET / POST / PATCH / DELETE resource endpoints and you get what you'd expect.

But figuring out what parameters are expected... well, all bets are off. This Sinatra extension takes a first step to solving this problem on the developer side

sinatra-param allows you to declare, validate, and transform endpoint parameters as you would in frameworks like ActiveModel or DataMapper.

require 'sinatra/param'
class App < Sinatra::Base
  helpers Sinatra::Param

  before do
    content_type :json
  end

  # GET /search?q=example
  # GET /search?q=example&categories=news
  # GET /search?q=example&sort=created_at&order=ASC
  get '/search' do
    param :q,           String, required: true
    param :categories,  Array
    param :sort,        String, default: "title"
    param :order,       String, in: ["ASC", "DESC"], transform: :upcase, default: "ASC"

    {...}.to_json
  end
end

By declaring parameter types, incoming parameters will automatically be transformed into an object of that type. For instance, if a param is Boolean, values of '1', 'true', 't', 'yes', and 'y' will be automatically transformed into true.

• String
• Integer
• Float
• Boolean ("1/0", "true/false", "t/f", "yes/no", "y/n")
• Array ("1,2,3,4,5")
• Hash (key1:value1,key2:value2)

Encapsulate business logic in a consistent way with validations. If a parameter does not satisfy a particular condition, a 406 error is returned with a message explaining the failure.

• required
• blank
• is
• in, within, range
• min / max

Passing a default option will provide a default value for a parameter if none is passed.

Use the transform option to take even more of the business logic of parameter I/O out of your code. Anything that responds to to_proc (including Procs and symbols) will do.

• Design by contract like this is great for developers, and with a little meta-programming, it could probably be exposed to users as well. The self-documenting dream of Hypermedia folks could well be within reach.

• Support for Rails-style Arrays ('key[]=value1&key[]=value2') and Hashes ('key[a]=value1&key[b]=value2). /via @manton

Mattt Thompson

• http://github.com/mattt
• http://twitter.com/mattt
• [email protected]

sinatra-param is available under the MIT license. See the LICENSE file for more info.