module ActiveSupport # Rescuable module adds support for easier exception handling. module Rescuable def self.included(base) # :nodoc: base.class_inheritable_accessor :rescue_handlers base.rescue_handlers = [] base.extend(ClassMethods) end module ClassMethods # Rescue exceptions raised in controller actions. # # rescue_from receives a series of exception classes or class # names, and a trailing :with option with the name of a method # or a Proc object to be called to handle them. Alternatively a block can # be given. # # Handlers that take one argument will be called with the exception, so # that the exception can be inspected when dealing with it. # # Handlers are inherited. They are searched from right to left, from # bottom to top, and up the hierarchy. The handler of the first class for # which exception.is_a?(klass) holds true is the one invoked, if # any. # # class ApplicationController < ActionController::Base # rescue_from User::NotAuthorized, :with => :deny_access # self defined exception # rescue_from ActiveRecord::RecordInvalid, :with => :show_errors # # rescue_from 'MyAppError::Base' do |exception| # render :xml => exception, :status => 500 # end # # protected # def deny_access # ... # end # # def show_errors(exception) # exception.record.new_record? ? ... # end # end def rescue_from(*klasses, &block) options = klasses.extract_options! unless options.has_key?(:with) if block_given? options[:with] = block else raise ArgumentError, "Need a handler. Supply an options hash that has a :with key as the last argument." end end klasses.each do |klass| key = if klass.is_a?(Class) && klass <= Exception klass.name elsif klass.is_a?(String) klass else raise ArgumentError, "#{klass} is neither an Exception nor a String" end # put the new handler at the end because the list is read in reverse rescue_handlers << [key, options[:with]] end end end # Tries to rescue the exception by looking up and calling a registered handler. def rescue_with_handler(exception) if handler = handler_for_rescue(exception) handler.arity != 0 ? handler.call(exception) : handler.call true # don't rely on the return value of the handler end end def handler_for_rescue(exception) # We go from right to left because pairs are pushed onto rescue_handlers # as rescue_from declarations are found. _, rescuer = Array(rescue_handlers).reverse.detect do |klass_name, handler| # The purpose of allowing strings in rescue_from is to support the # declaration of handler associations for exception classes whose # definition is yet unknown. # # Since this loop needs the constants it would be inconsistent to # assume they should exist at this point. An early raised exception # could trigger some other handler and the array could include # precisely a string whose corresponding constant has not yet been # seen. This is why we are tolerant to unknown constants. # # Note that this tolerance only matters if the exception was given as # a string, otherwise a NameError will be raised by the interpreter # itself when rescue_from CONSTANT is executed. klass = self.class.const_get(klass_name) rescue nil klass ||= klass_name.constantize rescue nil exception.is_a?(klass) if klass end case rescuer when Symbol method(rescuer) when Proc rescuer.bind(self) end end end end