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# Copyright 2011-2013 Amazon.com, Inc. or its affiliates. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License"). You
# may not use this file except in compliance with the License. A copy of
# the License is located at
#
# http://aws.amazon.com/apache2.0/
#
# or in the "license" file accompanying this file. This file is
# distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
# ANY KIND, either express or implied. See the License for the specific
# language governing permissions and limitations under the License.
require 'thread'
module AWS
module Core
# Provides lazy creation of error classes via {#const_missing}.
#
# Extend this module provides 3 benefits to another module:
#
# * A method that accepts strings and returns error classes.
# * Thread-safe dynamic error class creation via {#const_missing}
# * An error grammar for parsing AWS xml errors
#
# Here is an example of how it works:
#
# Class Foo
# module Errors
# extend AWS::Core::LazyErrorClasses
# end
# end
#
# Foo::Errors.error_class('NoSuchKey')
# #=> Foo::Errors::NoSuckKey
#
# Foo::Errors.error_class('Nested.Error.Klasses')
# #=> Foo::Errors::Nested::Error::Klasses
#
# The errors returned from {#error_class} are subclasses
# of {AWS::Errors::Base}.
#
module LazyErrorClasses
# This grammar parses the defualt AWS XML error format
BASE_ERROR_GRAMMAR = XML::Grammar.customize do
element("Error") do
ignore
end
end
# @api private
def self.extended base
unless base.const_defined?(:GRAMMAR)
base.const_set(:GRAMMAR, BASE_ERROR_GRAMMAR)
end
mutex = Mutex.new
MetaUtils.extend_method(base, :const_missing_mutex) { mutex }
end
# Defines a new error class.
# @param [String,Symbol] constant
# @return [nil]
def const_missing constant
const_missing_mutex.synchronize do
# It's possible the constant was defined by another thread while
# this thread was waiting on the mutex, check before setting.
if error_const_set?(constant)
const_get(constant)
else
const_set(constant, Class.new(Errors::Base) { extend LazyErrorClasses })
end
end
end
# Converts the error code into an error class constant.
#
# AWS::EC2::Errors.error_class('Non.Existent.Error')
# #=> AWS::EC2::Errors::Non::Existent::Error
#
# @param [String] code An AWS error code.
#
# @return [Class] Returns the error class defiend by the error code.
#
def error_class code
module_eval("#{self}::#{code.gsub('.Range','Range').gsub(".","::")}")
end
private
# @return [Boolean] Returns true if the constant is defined in the
# current module.
def error_const_set?(constant)
# Not using #const_defined? because in Ruby 1.9+, it returns true for
# constants not defined directly on the current module.
constant = constant.to_sym
# In Ruby 1.8, #constants returns an array of strings,
# in Ruby 1.9+, #constants returns an array of symbols.
constants.any? { |c| c.to_sym == constant }
end
end
end
end
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