329 lines
9.6 KiB
Ruby
329 lines
9.6 KiB
Ruby
module DeclarativePolicy
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class Base
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# A map of ability => list of rules together with :enable
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# or :prevent actions. Used to look up which rules apply to
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# a given ability. See Base.ability_map
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class AbilityMap
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attr_reader :map
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def initialize(map = {})
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@map = map
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end
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# This merge behavior is different than regular hashes - if both
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# share a key, the values at that key are concatenated, rather than
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# overridden.
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def merge(other)
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conflict_proc = proc { |key, my_val, other_val| my_val + other_val }
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AbilityMap.new(@map.merge(other.map, &conflict_proc))
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end
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def actions(key)
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@map[key] ||= []
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end
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def enable(key, rule)
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actions(key) << [:enable, rule]
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end
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def prevent(key, rule)
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actions(key) << [:prevent, rule]
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end
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end
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class << self
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# The `own_ability_map` vs `ability_map` distinction is used so that
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# the data structure is properly inherited - with subclasses recursively
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# merging their parent class.
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#
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# This pattern is also used for conditions, global_actions, and delegations.
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def ability_map
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if self == Base
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own_ability_map
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else
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superclass.ability_map.merge(own_ability_map)
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end
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end
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def own_ability_map
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@own_ability_map ||= AbilityMap.new
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end
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# an inheritable map of conditions, by name
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def conditions
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if self == Base
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own_conditions
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else
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superclass.conditions.merge(own_conditions)
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end
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end
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def own_conditions
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@own_conditions ||= {}
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end
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# a list of global actions, generated by `prevent_all`. these aren't
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# stored in `ability_map` because they aren't indexed by a particular
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# ability.
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def global_actions
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if self == Base
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own_global_actions
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else
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superclass.global_actions + own_global_actions
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end
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end
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def own_global_actions
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@own_global_actions ||= []
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end
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# an inheritable map of delegations, indexed by name (which may be
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# autogenerated)
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def delegations
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if self == Base
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own_delegations
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else
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superclass.delegations.merge(own_delegations)
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end
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end
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def own_delegations
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@own_delegations ||= {}
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end
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# all the [rule, action] pairs that apply to a particular ability.
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# we combine the specific ones looked up in ability_map with the global
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# ones.
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def configuration_for(ability)
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ability_map.actions(ability) + global_actions
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end
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### declaration methods ###
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def delegate(name = nil, &delegation_block)
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if name.nil?
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@delegate_name_counter ||= 0
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@delegate_name_counter += 1
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name = :"anonymous_#{@delegate_name_counter}"
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end
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name = name.to_sym
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if delegation_block.nil?
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delegation_block = proc { @subject.__send__(name) }
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end
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own_delegations[name] = delegation_block
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end
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# Declares a rule, constructed using RuleDsl, and returns
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# a PolicyDsl which is used for registering the rule with
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# this class. PolicyDsl will call back into Base.enable_when,
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# Base.prevent_when, and Base.prevent_all_when.
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def rule(&b)
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rule = RuleDsl.new(self).instance_eval(&b)
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PolicyDsl.new(self, rule)
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end
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# A hash in which to store calls to `desc` and `with_scope`, etc.
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def last_options
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@last_options ||= {}.with_indifferent_access
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end
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# retrieve and zero out the previously set options (used in .condition)
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def last_options!
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last_options.tap { @last_options = nil }
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end
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# Declare a description for the following condition. Currently unused,
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# but opens the potential for explaining to users why they were or were
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# not able to do something.
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def desc(description)
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last_options[:description] = description
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end
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def with_options(opts = {})
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last_options.merge!(opts)
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end
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def with_scope(scope)
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with_options scope: scope
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end
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def with_score(score)
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with_options score: score
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end
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# Declares a condition. It gets stored in `own_conditions`, and generates
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# a query method based on the condition's name.
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def condition(name, opts = {}, &value)
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name = name.to_sym
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opts = last_options!.merge(opts)
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opts[:context_key] ||= self.name
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condition = Condition.new(name, opts, &value)
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self.own_conditions[name] = condition
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define_method(:"#{name}?") { condition(name).pass? }
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end
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# These next three methods are mainly called from PolicyDsl,
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# and are responsible for "inverting" the relationship between
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# an ability and a rule. We store in `ability_map` a map of
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# abilities to rules that affect them, together with a
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# symbol indicating :prevent or :enable.
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def enable_when(abilities, rule)
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abilities.each { |a| own_ability_map.enable(a, rule) }
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end
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def prevent_when(abilities, rule)
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abilities.each { |a| own_ability_map.prevent(a, rule) }
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end
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# we store global prevents (from `prevent_all`) separately,
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# so that they can be combined into every decision made.
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def prevent_all_when(rule)
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own_global_actions << [:prevent, rule]
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end
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end
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# A policy object contains a specific user and subject on which
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# to compute abilities. For this reason it's sometimes called
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# "context" within the framework.
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#
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# It also stores a reference to the cache, so it can be used
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# to cache computations by e.g. ManifestCondition.
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attr_reader :user, :subject, :cache
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def initialize(user, subject, opts = {})
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@user = user
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@subject = subject
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@cache = opts[:cache] || {}
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end
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# helper for checking abilities on this and other subjects
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# for the current user.
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def can?(ability, new_subject = :_self)
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return allowed?(ability) if new_subject == :_self
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policy_for(new_subject).allowed?(ability)
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end
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# This is the main entry point for permission checks. It constructs
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# or looks up a Runner for the given ability and asks it if it passes.
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def allowed?(*abilities)
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abilities.all? { |a| runner(a).pass? }
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end
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# The inverse of #allowed?, used mainly in specs.
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def disallowed?(*abilities)
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abilities.all? { |a| !runner(a).pass? }
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end
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# computes the given ability and prints a helpful debugging output
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# showing which
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def debug(ability, *a)
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runner(ability).debug(*a)
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end
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desc "Unknown user"
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condition(:anonymous, scope: :user, score: 0) { @user.nil? }
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desc "By default"
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condition(:default, scope: :global, score: 0) { true }
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def repr
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subject_repr =
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if @subject.respond_to?(:id)
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"#{@subject.class.name}/#{@subject.id}"
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else
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@subject.inspect
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end
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user_repr =
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if @user
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@user.to_reference
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else
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"<anonymous>"
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end
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"(#{user_repr} : #{subject_repr})"
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end
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def inspect
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"#<#{self.class.name} #{repr}>"
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end
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# returns a Runner for the given ability, capable of computing whether
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# the ability is allowed. Runners are cached on the policy (which itself
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# is cached on @cache), and caches its result. This is how we perform caching
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# at the ability level.
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def runner(ability)
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ability = ability.to_sym
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@runners ||= {}
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@runners[ability] ||=
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begin
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delegated_runners = delegated_policies.values.compact.map { |p| p.runner(ability) }
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own_runner = Runner.new(own_steps(ability))
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delegated_runners.inject(own_runner, &:merge_runner)
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end
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end
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# Helpers for caching. Used by ManifestCondition in performing condition
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# computation.
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#
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# NOTE we can't use ||= here because the value might be the
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# boolean `false`
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def cache(key, &b)
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return @cache[key] if cached?(key)
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@cache[key] = yield
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end
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def cached?(key)
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!@cache[key].nil?
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end
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# returns a ManifestCondition capable of computing itself. The computation
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# will use our own @cache.
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def condition(name)
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name = name.to_sym
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@_conditions ||= {}
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@_conditions[name] ||=
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begin
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raise "invalid condition #{name}" unless self.class.conditions.key?(name)
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ManifestCondition.new(self.class.conditions[name], self)
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end
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end
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# used in specs - returns true if there is no possible way for any action
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# to be allowed, determined only by the global :prevent_all rules.
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def banned?
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global_steps = self.class.global_actions.map { |(action, rule)| Step.new(self, rule, action) }
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!Runner.new(global_steps).pass?
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end
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# A list of other policies that we've delegated to (see `Base.delegate`)
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def delegated_policies
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@delegated_policies ||= self.class.delegations.transform_values do |block|
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new_subject = instance_eval(&block)
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# never delegate to nil, as that would immediately prevent_all
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next if new_subject.nil?
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policy_for(new_subject)
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end
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end
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def policy_for(other_subject)
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DeclarativePolicy.policy_for(@user, other_subject, cache: @cache)
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end
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protected
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# constructs steps that come from this policy and not from any delegations
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def own_steps(ability)
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rules = self.class.configuration_for(ability)
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rules.map { |(action, rule)| Step.new(self, rule, action) }
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end
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end
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end
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