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Diffstat (limited to 'lib/declarative_policy.rb')
-rw-r--r-- | lib/declarative_policy.rb | 94 |
1 files changed, 94 insertions, 0 deletions
diff --git a/lib/declarative_policy.rb b/lib/declarative_policy.rb new file mode 100644 index 00000000000..ae65653645b --- /dev/null +++ b/lib/declarative_policy.rb @@ -0,0 +1,94 @@ +require_dependency 'declarative_policy/cache' +require_dependency 'declarative_policy/condition' +require_dependency 'declarative_policy/dsl' +require_dependency 'declarative_policy/preferred_scope' +require_dependency 'declarative_policy/rule' +require_dependency 'declarative_policy/runner' +require_dependency 'declarative_policy/step' + +require_dependency 'declarative_policy/base' + +require 'thread' + +module DeclarativePolicy + CLASS_CACHE_MUTEX = Mutex.new + CLASS_CACHE_IVAR = :@__DeclarativePolicy_CLASS_CACHE + + class << self + def policy_for(user, subject, opts = {}) + cache = opts[:cache] || {} + key = Cache.policy_key(user, subject) + + cache[key] ||= class_for(subject).new(user, subject, opts) + end + + def class_for(subject) + return GlobalPolicy if subject == :global + return NilPolicy if subject.nil? + + subject = find_delegate(subject) + + policy_class = class_for_class(subject.class) + raise "no policy for #{subject.class.name}" if policy_class.nil? + policy_class + end + + def has_policy?(subject) + !class_for_class(subject.class).nil? + end + + private + + # This method is heavily cached because there are a lot of anonymous + # modules in play in a typical rails app, and #name performs quite + # slowly for anonymous classes and modules. + # + # See https://bugs.ruby-lang.org/issues/11119 + # + # if the above bug is resolved, this caching could likely be removed. + def class_for_class(subject_class) + unless subject_class.instance_variable_defined?(CLASS_CACHE_IVAR) + CLASS_CACHE_MUTEX.synchronize do + # re-check in case of a race + break if subject_class.instance_variable_defined?(CLASS_CACHE_IVAR) + + policy_class = compute_class_for_class(subject_class) + subject_class.instance_variable_set(CLASS_CACHE_IVAR, policy_class) + end + end + + subject_class.instance_variable_get(CLASS_CACHE_IVAR) + end + + def compute_class_for_class(subject_class) + subject_class.ancestors.each do |klass| + next unless klass.name + + begin + policy_class = "#{klass.name}Policy".constantize + + # NOTE: the < operator here tests whether policy_class + # inherits from Base. We can't use #is_a? because that + # tests for *instances*, not *subclasses*. + return policy_class if policy_class < Base + rescue NameError + nil + end + end + + nil + end + + def find_delegate(subject) + seen = Set.new + + while subject.respond_to?(:declarative_policy_delegate) + raise ArgumentError, "circular delegations" if seen.include?(subject.object_id) + seen << subject.object_id + subject = subject.declarative_policy_delegate + end + + subject + end + end +end |