summaryrefslogtreecommitdiff
path: root/lib/declarative_policy/base.rb
blob: b028169f500ffc00c98ea06de278c5350b8d1408 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
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?
          delegation_block = proc { @subject.__send__(name) } # rubocop:disable GitlabSecurity/PublicSend
        end

        own_delegations[name] = delegation_block
      end

      # 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.
      def rule(&b)
        rule = RuleDsl.new(self).instance_eval(&b)
        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.
    attr_reader :user, :subject, :cache
    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
    # showing which
    def debug(ability, *a)
      runner(ability).debug(*a)
    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
          delegated_runners = delegated_policies.values.compact.map { |p| p.runner(ability) }
          own_runner = Runner.new(own_steps(ability))
          delegated_runners.inject(own_runner, &:merge_runner)
        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`
    def cache(key, &b)
      return @cache[key] if cached?(key)
      @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)
          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