Estoy construyendo una API de Ruby on Rails con Ruby 2.0 y Rails 4.0. Mi aplicación es casi exclusivamente una API JSON, por lo que si se produce un error (500, 404), quiero capturar ese error y devolver un mensaje de error JSON bien formateado.

He intentadoesta y también:

rescue_from ActionController::RoutingError, :with => :error_render_method

def error_render_method
  puts "HANDLING ERROR"
  render :json => { :errors => "Method not found." }, :status => :not_found
  true
end

En mi ApplicationController.

Ninguno de estos hace el truco (las excepciones no se capturan en absoluto). Mi búsqueda en Google muestra que esto cambió mucho entre 3.1, 3.2 y no puedo encontrar ninguna buena documentación sobre cómo hacer esto en Rails 4.0.

Alguien sabe?

Editar Aquí está el seguimiento de la pila cuando voy a una página 404:

Started GET "/testing" for 127.0.0.1 at 2013-08-21 09:50:42 -0400

ActionController::RoutingError (No route matches [GET] "/testing"):
actionpack (4.0.0) lib/action_dispatch/middleware/debug_exceptions.rb:21:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
railties (4.0.0) lib/rails/rack/logger.rb:38:in `call_app'
railties (4.0.0) lib/rails/rack/logger.rb:21:in `block in call'
activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `block in tagged'
activesupport (4.0.0) lib/active_support/tagged_logging.rb:25:in `tagged'
activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `tagged'
railties (4.0.0) lib/rails/rack/logger.rb:21:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/request_id.rb:21:in `call'
rack (1.5.2) lib/rack/methodoverride.rb:21:in `call'
rack (1.5.2) lib/rack/runtime.rb:17:in `call'
activesupport (4.0.0) lib/active_support/cache/strategy/local_cache.rb:83:in `call'
rack (1.5.2) lib/rack/lock.rb:17:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/static.rb:64:in `call'
railties (4.0.0) lib/rails/engine.rb:511:in `call'
railties (4.0.0) lib/rails/application.rb:97:in `call'
rack (1.5.2) lib/rack/lock.rb:17:in `call'
rack (1.5.2) lib/rack/content_length.rb:14:in `call'
rack (1.5.2) lib/rack/handler/webrick.rb:60:in `service'
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/webrick/httpserver.rb:138:in `service'
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/webrick/httpserver.rb:94:in `run'
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/webrick/server.rb:295:in `block in start_thread'


Rendered /Library/Ruby/Gems/2.0.0/gems/actionpack-4.0.0/lib/action_dispatch/middleware/templates/rescues/_trace.erb (1.0ms)
Rendered /Library/Ruby/Gems/2.0.0/gems/actionpack-4.0.0/lib/action_dispatch/middleware/templates/routes/_route.html.erb (2.9ms)
Rendered /Library/Ruby/Gems/2.0.0/gems/actionpack-4.0.0/lib/action_dispatch/middleware/templates/routes/_route.html.erb (0.9ms)
Rendered /Library/Ruby/Gems/2.0.0/gems/actionpack-4.0.0/lib/action_dispatch/middleware/templates/routes/_table.html.erb (1.1ms)
Rendered /Library/Ruby/Gems/2.0.0/gems/actionpack-4.0.0/lib/action_dispatch/middleware/templates/rescues/routing_error.erb within rescues/layout (38.3ms)

No creo que quiera llegar nunca tan lejos, algo debería atraparlo y devolver la respuesta de error json adecuada.