1 files changed, 99 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/encrypted_file.rb b/activesupport/lib/active_support/encrypted_file.rb
new file mode 100644
index 0000000000..c66f1b557e
--- /dev/null
+++ b/activesupport/lib/active_support/encrypted_file.rb
@@ -0,0 +1,99 @@
+# frozen_string_literal: true
+
+require "pathname"
+require "active_support/message_encryptor"
+
+module ActiveSupport
+  class EncryptedFile
+    class MissingContentError < RuntimeError
+      def initialize(content_path)
+        super "Missing encrypted content file in #{content_path}."
+      end
+    end
+
+    class MissingKeyError < RuntimeError
+      def initialize(key_path:, env_key:)
+        super \
+          "Missing encryption key to decrypt file with. " +
+          "Ask your team for your master key and write it to #{key_path} or put it in the ENV['#{env_key}']."
+      end
+    end
+
+    CIPHER = "aes-128-gcm"
+
+    def self.generate_key
+      SecureRandom.hex(ActiveSupport::MessageEncryptor.key_len(CIPHER))
+    end
+
+
+    attr_reader :content_path, :key_path, :env_key, :raise_if_missing_key
+
+    def initialize(content_path:, key_path:, env_key:, raise_if_missing_key:)
+      @content_path, @key_path = Pathname.new(content_path), Pathname.new(key_path)
+      @env_key, @raise_if_missing_key = env_key, raise_if_missing_key
+    end
+
+    def key
+      read_env_key || read_key_file || handle_missing_key
+    end
+
+    def read
+      if !key.nil? && content_path.exist?
+        decrypt content_path.binread
+      else
+        raise MissingContentError, content_path
+      end
+    end
+
+    def write(contents)
+      IO.binwrite "#{content_path}.tmp", encrypt(contents)
+      FileUtils.mv "#{content_path}.tmp", content_path
+    end
+
+    def change(&block)
+      writing read, &block
+    end
+
+
+    private
+      def writing(contents)
+        tmp_file = "#{Process.pid}.#{content_path.basename.to_s.chomp('.enc')}"
+        tmp_path = Pathname.new File.join(Dir.tmpdir, tmp_file)
+        tmp_path.binwrite contents
+
+        yield tmp_path
+
+        updated_contents = tmp_path.binread
+
+        write(updated_contents) if updated_contents != contents
+      ensure
+        FileUtils.rm(tmp_path) if tmp_path.exist?
+      end
+
+
+      def encrypt(contents)
+        encryptor.encrypt_and_sign contents
+      end
+
+      def decrypt(contents)
+        encryptor.decrypt_and_verify contents
+      end
+
+      def encryptor
+        @encryptor ||= ActiveSupport::MessageEncryptor.new([ key ].pack("H*"), cipher: CIPHER)
+      end
+
+
+      def read_env_key
+        ENV[env_key]
+      end
+
+      def read_key_file
+        key_path.binread.strip if key_path.exist?
+      end
+
+      def handle_missing_key
+        raise MissingKeyError, key_path: key_path, env_key: env_key if raise_if_missing_key
+      end
+  end
+end