debian-mirror-gitlab/lib/declarative_policy/base.rb

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