Oj: Rails 6 (under Ruby 2.6.3): unexpected behaviour for Oj.dump

[swiknaba]

When dumping a hash with symbol-keys, under Rails 6, they hash-keys have : and ":
(everything run under ruby 2.6.3)

Rails 5

test = {foo: "hello from rails #{Rails.version}"}
# => {:foo=>"hello from rails 5.2.3"}

Oj.dump(test)
# => "{\"foo\":\"hello from rails 5.2.3\"}"

Rails 6

test = {foo: "hello from rails #{Rails.version}"}
# => {:foo=>"hello from rails 6.0.0.rc1"}

Oj.dump(test)
# => "{\":foo\":\"hello from rails 6.0.0.rc1\"}"
# note the additional `:` infront of the foo-key

Why is this a problem? MD5 hashing is broken in Rails 6 (Rails 5 returns the same digest, i.e. 9bb58f26192e4ba00f01e2e7b136bbd8):

test_2 = {foo: 'bar'}
# => {:foo=>"bar"}

md5 = Digest::MD5.new
# => #<Digest::MD5: d41d8cd98f00b204e9800998ecf8427e>

md5 << Oj.dump(test_2)
# => #<Digest::MD5: ac1fce2974bc71a06a0f1aafe21672f7>

md5.to_s
# => "ac1fce2974bc71a06a0f1aafe21672f7"


md5_2 = Digest::MD5.new
# => #<Digest::MD5: d41d8cd98f00b204e9800998ecf8427e>

irb(main):063:0> md5_2 << Oj.dump(test_2.stringify_keys)
# => #<Digest::MD5: 9bb58f26192e4ba00f01e2e7b136bbd8>

md5_2.to_s
# => "9bb58f26192e4ba00f01e2e7b136bbd8"

[ohler55]

I'll have to look at this. It appears as if Rails 6 is monkey patching Symbol#to_s or something along those lines.

[chulkilee]

What is the status of this? Is it still an issue?

[swiknaba]

What is the status of this? Is it still an issue?

A quick test with rails 6.0.0 & ruby 2.6.4:

test = { foo: "hello from rails #{Rails.version}" }
# => {:foo=>"hello from rails 6.0.0"}

Oj.dump(test)
# => "{\":foo\":\"hello from rails 6.0.0\"}"

RUBY_VERSION
# => "2.6.4"

it still seems to be an issue.

[ohler55]

To be honest there has been no progress. I'll try and get to it this week.

[ohler55]

Can you tell me how you are setting up the test? What is required and what calls were made to set the Oj defaults?

[swiknaba]

I did not configure anything. Just scaffold a new rails (API mode) app and throw in Oj into the Gemfile, run bundle install, then enter the rails console. That's it. Btw. Oj.load(Oj.dump({ foo: "bar" })) works, i.e. Oj.load correctly resolves the JSON string "{\":foo\":\"bar\"\}"

[ohler55]

I'm trying to reproduce it but I think I am making some bad assumptions. The default mode for Oj is :object mode. In that mode what you are seeing is expected. In :rails mode I don't see that behaviour. Can you check the Oj.default_options and see what the mode is? If it is not :compatible or :rails then I suspect the scaffolding does not include putting Oj into rails more. That is probably what you want.

[swiknaba]

Thanks! You are right. Oj.default_options.dig(:mode) returns :object. Most of my applications are still running on Rails 5.2.3, and for those, the mode is :compat by default (just adding the Oj gem to a rails application without further configuration as I did now for this Issue with Rails 6.0).

Reading about the existing issues with rails' ActiveSupport::JSON::Encoding vs. the JSON gem, I would tend to use :compat mode over :rails mode, but I didn't research much yet about how much of the implementation changed in Rails 6.

I've now added an initializer

# config/initializers/oj.rb

Oj.default_options = { mode: :compat }

which solves the problem; further reading on modes (for all the future readers): http://www.ohler.com/oj/doc/file.Options.html

[ohler55]

Super, glad it was an easy fix. The whole Rails vs JSON gem for JSON handling is a mess. Oj attempts to get the behaviour right depending on which is in control but some edge cases pop up every now and then.

Good to close?