A controller concern to set the default format to JSON if none is provided, and enforce the requested formats

json_default.rb

# app/controllers/concerns/json_default.rb
# USAGE:
# Simply include into a controller that should be restricted to JSON format:
# `include JSONDefault`

module JSONDefault
  extend ActiveSupport::Concern

  included do
    before_action :set_default_format, :assert_valid_format!
  end

  private

    # Private: Ensure that the format is set if none is provided.
    #
    # Examples:
    #
    #   request format is JSON -> request format remains JSON
    #   request format is not set -> request format becomes JSON
    #   request format is XML -> request.format remains XML
    #
    # Returns the new request format
    def set_default_format
      request.format = 'json' unless params.key?(:format)
    end

    # Private: Assert that the format is set to JSON.
    #
    # If it is not, this will respond with a 406 Not Acceptable
    def assert_valid_format!
      raise ActionController::UnknownFormat unless request.format == 'json'
    end
end

json_default_spec.rb

describe JSONDefault, type: :controller do

  controller do
    include JSONDefault

    def index
      render nothing: true
    end
  end

  describe "ensure_default_format" do
    context "no format" do
      before { get :index }
      it { request.format.should eq "json" }
    end

    context "json format" do
      before { get :index, format: :json }
      it { request.format.should eq "json" }
    end

    context "unknown format" do
      before do
        controller.stub(assert_valid_format!: true)
        get :index, format: :xml
      end

      it { request.format.should eq 'xml' }
    end
  end

  describe "assert_valid_format!" do
    context "good format" do
      it { expect { get :index }.to_not raise_error }
    end
    context "bad format" do
      it { expect { get :index, format: :xml }.to raise_error(ActionController::UnknownFormat) }
    end
  end
end

spec_output.txt

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5 examples, 0 failures