Support UTF-8 data when using the JSON serializer

Closes #38

lib/rack/session/encryptor.rb

@@ -32,12 +32,12 @@ module Serializable
         def serialize_payload(message)
           serialized_data = serializer.dump(message)
 
-          return "#{[0].pack('v')}#{serialized_data}" if @options[:pad_size].nil?
+          return "#{[0].pack('v')}#{serialized_data.force_encoding('BINARY')}" if @options[:pad_size].nil?
 
           padding_bytes = @options[:pad_size] - (2 + serialized_data.size) % @options[:pad_size]
           padding_data = SecureRandom.random_bytes(padding_bytes)
 
-          "#{[padding_bytes].pack('v')}#{padding_data}#{serialized_data}"
+          "#{[padding_bytes].pack('v')}#{padding_data}#{serialized_data.force_encoding('BINARY')}"
         end
 
         # Return the deserialized message. The first 2 bytes will be read as the

test/spec_session_encryptor.rb

@@ -58,6 +58,18 @@ def self.included(_base)
         encryptor.decrypt(message).must_equal({ 'foo' => 'bar' })
       end
 
+      # The V1 encryptor defaults to the Marshal serializer, while the V2
+      # encryptor always uses the JSON serializer. This means that we are
+      # indirectly covering both serializers.
+      it 'decrypts an encrypted message with UTF-8 data' do
+        encryptor = encryptor_class.new(@secret)
+
+        encrypted_message = encryptor.encrypt({ 'foo' => '😀' })
+        decrypted_message = encryptor.decrypt(encrypted_message)
+
+        decrypted_message.must_equal({ 'foo' => '😀' })
+      end
+
       it 'decrypts raises InvalidSignature without purpose' do
         encryptor = encryptor_class.new(@secret, purpose: 'testing')
         other_encryptor = encryptor_class.new(@secret)