aboutsummaryrefslogtreecommitdiffstats
path: root/actionpack/lib/action_dispatch/http/feature_policy.rb
blob: 592b6e4393a5f1a582bca54805a643fa44d2e654 (plain) (blame)
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
# frozen_string_literal: true

require "active_support/core_ext/object/deep_dup"

module ActionDispatch #:nodoc:
  class FeaturePolicy
    class Middleware
      CONTENT_TYPE = "Content-Type"
      POLICY       = "Feature-Policy"

      def initialize(app)
        @app = app
      end

      def call(env)
        request = ActionDispatch::Request.new(env)
        _, headers, _ = response = @app.call(env)

        return response unless html_response?(headers)
        return response if policy_present?(headers)

        if policy = request.feature_policy
          headers[POLICY] = policy.build(request.controller_instance)
        end

        if policy_empty?(policy)
          headers.delete(POLICY)
        end

        response
      end

      private
        def html_response?(headers)
          if content_type = headers[CONTENT_TYPE]
            content_type =~ /html/
          end
        end

        def policy_present?(headers)
          headers[POLICY]
        end

        def policy_empty?(policy)
          policy.try(:directives) && policy.directives.empty?
        end
    end

    module Request
      POLICY = "action_dispatch.feature_policy"

      def feature_policy
        get_header(POLICY)
      end

      def feature_policy=(policy)
        set_header(POLICY, policy)
      end
    end

    MAPPINGS = {
      self: "'self'",
      none: "'none'",
    }.freeze

    # List of available features can be found at
    # https://github.com/WICG/feature-policy/blob/master/features.md#policy-controlled-features
    DIRECTIVES = {
      accelerometer:        "accelerometer",
      ambient_light_sensor: "ambient-light-sensor",
      autoplay:             "autoplay",
      camera:               "camera",
      encrypted_media:      "encrypted-media",
      fullscreen:           "fullscreen",
      geolocation:          "geolocation",
      gyroscope:            "gyroscope",
      magnetometer:         "magnetometer",
      microphone:           "microphone",
      midi:                 "midi",
      payment:              "payment",
      picture_in_picture:   "picture-in-picture",
      speaker:              "speaker",
      usb:                  "usb",
      vibrate:              "vibrate",
      vr:                   "vr",
    }.freeze

    private_constant :MAPPINGS, :DIRECTIVES

    attr_reader :directives

    def initialize
      @directives = {}
      yield self if block_given?
    end

    def initialize_copy(other)
      @directives = other.directives.deep_dup
    end

    DIRECTIVES.each do |name, directive|
      define_method(name) do |*sources|
        if sources.first
          @directives[directive] = apply_mappings(sources)
        else
          @directives.delete(directive)
        end
      end
    end

    def build(context = nil)
      build_directives(context).compact.join("; ")
    end

    private
      def apply_mappings(sources)
        sources.map do |source|
          case source
          when Symbol
            apply_mapping(source)
          when String, Proc
            source
          else
            raise ArgumentError, "Invalid HTTP feature policy source: #{source.inspect}"
          end
        end
      end

      def apply_mapping(source)
        MAPPINGS.fetch(source) do
          raise ArgumentError, "Unknown HTTP feature policy source mapping: #{source.inspect}"
        end
      end

      def build_directives(context)
        @directives.map do |directive, sources|
          if sources.is_a?(Array)
            "#{directive} #{build_directive(sources, context).join(' ')}"
          elsif sources
            directive
          else
            nil
          end
        end
      end

      def build_directive(sources, context)
        sources.map { |source| resolve_source(source, context) }
      end

      def resolve_source(source, context)
        case source
        when String
          source
        when Symbol
          source.to_s
        when Proc
          if context.nil?
            raise RuntimeError, "Missing context for the dynamic feature policy source: #{source.inspect}"
          else
            context.instance_exec(&source)
          end
        else
          raise RuntimeError, "Unexpected feature policy source: #{source.inspect}"
        end
      end
  end
end