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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.
#
# <tt>rescue_from</tt> receives a series of exception classes or class
# names, and a trailing <tt>:with</tt> 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 <tt>exception.is_a?(klass)</tt> 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
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