require 'active_support/concern' require 'active_support/core_ext/class/attribute' require 'active_support/core_ext/string/inflections' module ActiveSupport # Rescuable module adds support for easier exception handling. module Rescuable extend Concern included do class_attribute :rescue_handlers self.rescue_handlers = [] 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 # # Exceptions raised inside exception handlers are not propagated up. def rescue_from(*klasses, with: nil, &block) unless with if block_given? with = block else raise ArgumentError, 'Need a handler. Pass the with: keyword argument or provide a block.' end end klasses.each do |klass| key = if klass.is_a?(Module) && klass.respond_to?(:===) klass.name elsif klass.is_a?(String) klass else raise ArgumentError, "#{klass.inspect} must be an Exception class or a String referencing an Exception class" end # Put the new handler at the end because the list is read in reverse. self.rescue_handlers += [[key, with]] end end # Matches an exception to a handler based on the exception class. # # If no handler matches the exception, check for a handler matching the # (optional) exception.cause. If no handler matches the exception or its # cause, this returns nil so you can deal with unhandled exceptions. # Be sure to re-raise unhandled exceptions if this is what you expect. # # begin # … # rescue => exception # rescue_with_handler(exception) || raise # end # # Returns the exception if it was handled and nil if it was not. def rescue_with_handler(exception, object: self) if handler = handler_for_rescue(exception, object: object) handler.call exception exception end end def handler_for_rescue(exception, object: self) #:nodoc: case rescuer = find_rescue_handler(exception) when Symbol method = object.method(rescuer) if method.arity == 0 -> e { method.call } else method end when Proc if rescuer.arity == 0 -> e { object.instance_exec(&rescuer) } else -> e { object.instance_exec(e, &rescuer) } end end end private def find_rescue_handler(exception) if exception # Handlers are in order of declaration but the most recently declared # is the highest priority match, so we search for matching handlers # in reverse. _, handler = rescue_handlers.reverse_each.detect do |class_or_name, _| if klass = constantize_rescue_handler_class(class_or_name) klass === exception end end handler || find_rescue_handler(exception.cause) end end def constantize_rescue_handler_class(class_or_name) case class_or_name when String, Symbol begin # Try a lexical lookup first since we support # # class Super # rescue_from 'Error', with: … # end # # class Sub # class Error < StandardError; end # end # # so an Error raised in Sub will hit the 'Error' handler. const_get class_or_name rescue NameError class_or_name.safe_constantize end else class_or_name end end end # Delegates to the class method, but uses the instance as the subject for # rescue_from handlers (method calls, instance_exec blocks). def rescue_with_handler(exception) self.class.rescue_with_handler exception, object: self end # Internal handler lookup. Delegates to class method. Some libraries call # this directly, so keeping it around for compatibility. def handler_for_rescue(exception) #:nodoc: self.class.handler_for_rescue exception, object: self end end end