module Padrino::Responders::Default

Default responder is responsible for exposing a resource to different mime requests, usually depending on the HTTP verb. The responder is triggered when respond is called. The simplest case to study is a GET request:

SampleApp.controllers :examples do 
  provides :html, :xml, :json

  get :index do 
    @examples = Example.find(:all)
    respond(@examples)
  end
end

When a request comes in, for example for an XML response, three steps happen:

1) the responder searches for a template at extensions/index.xml;
2) if the template is not available, it will invoke <code>#to_xml</code> on the given resource;
3) if the responder does not <code>respond_to :to_xml</code>, call <code>#to_format</code> on it.

Builtin HTTP verb semantics

Using this responder, a POST request for creating an object could be written as:

post :create do 
  @user = User.new(params[:user])
  @user.save
  respond(@user)
end

Which is exactly the same as:

post :create do 
  @user = User.new(params[:user])

  if @user.save
    flash[:notice] = 'User was successfully created.'
    case content_type
      when :html then redirect url(:users, :show, :id => @user.id)
      when :xml  then render :xml => @user, :status => :created, :location => url(:users, :show, :id => @user.id)
    end 
  else
    case content_type
      when :html then render 'index/new'
      when :xml  then render :xml => @user.errors, :status => :unprocessable_entity 
    end
  end
end

The same happens for PUT and DELETE requests.