[Ruby] allow encode json options to be an object that responds to to_hash

[lukad]

fixes #9500

[haberman]

What is an example of how this arises in real code?

What is a json::Ext::Generator::State object, and why is your code passing that in instead of Hash?

[lukad]

We ran into this in a Rails application that serves a JSON api and calls out to a GRPC Service. The JSON response is supposed to include the protobuf message.

msg = protobuf_message # returned from a GRPC service
{
  msg: protobuf_message,
  # and other fields
}.to_json

json::Ext::Generator::State holds Ruby's json generator options (like identation or space). This will always be created when calling to_json on a Hash and it will be passed down as opts to all subsequent to_json calls on the Hash's values values values as opts.

It is not safe for protobuf to assume that the opts passed to a message's to_json are always a hash.

Links:

• https://github.com/ruby/ruby/blob/v3_1_1/ext/json/generator/generator.c#L414
• https://github.com/ruby/ruby/blob/v3_1_1/ext/json/generator/generator.h#L87
• https://github.com/ruby/ruby/blob/v3_1_1/ext/json/generator/generator.c#L1031

[haberman]

Maybe I am missing something, but this test doesn't seem to exercise the new code. We need a test that calls encode_json with a second parameter that response to to_h but is not itself a Hash.

[lukad]

[m].to_json will do exactly that. Ruby's #to_json creates a json::Ext::Generator::State which is not a Hash. That state object will then be passed to m.to_json which in turn passes the state to encode_json.

Withouth my changes the assert fails.

[lukad]

An ArgumentError: Expected hash arguments is raised without my changes.

Error: test_protobuf_encode_decode_json_helpers(BasicTest::MessageContainerTest): ArgumentError: Expected hash arguments.
/Users/luka/code/protobuf/ruby/lib/google/protobuf/message_exts.rb:44:in `encode_json'
/Users/luka/code/protobuf/ruby/lib/google/protobuf/message_exts.rb:44:in `to_json'
/Users/luka/code/protobuf/ruby/tests/common_tests.rb:874:in `to_json'
/Users/luka/code/protobuf/ruby/tests/common_tests.rb:874:in `test_protobuf_encode_decode_json_helpers'
     871:     decoded_msg = Google::Protobuf.decode_json(proto_module::TestMessage, encoded_msg)
     872:     assert_equal proto_module::TestMessage.decode_json(m.to_json), decoded_msg
     873:
  => 874:     assert_equal [m].to_json, Google::Protobuf.encode_json([m])
     875:     assert_equal proto_module::TestMessage.decode_json([m.to_json].first), decoded_msg
     876:   end
     877: