Compatibility with Puma master branch

[adamlogic]

I just attempted to use Puma master, and requests were failing with the following:

/app/vendor/ruby-2.6.5/lib/ruby/2.6.0/json/common.rb:156:in `initialize': no implicit conversion of Hash into String (TypeError)
	from /app/vendor/ruby-2.6.5/lib/ruby/2.6.0/json/common.rb:156:in `new'
	from /app/vendor/ruby-2.6.5/lib/ruby/2.6.0/json/common.rb:156:in `parse'
	from /app/vendor/bundle/ruby/2.6.0/gems/multi_json-1.14.1/lib/multi_json/adapters/json_common.rb:14:in `load'
	from /app/vendor/bundle/ruby/2.6.0/gems/multi_json-1.14.1/lib/multi_json/adapter.rb:21:in `load'
	from /app/vendor/bundle/ruby/2.6.0/gems/multi_json-1.14.1/lib/multi_json.rb:122:in `load'
	from /app/vendor/bundle/ruby/2.6.0/gems/barnes-0.0.8/lib/barnes/instruments/puma_instrument.rb:24:in `json_stats'
	from /app/vendor/bundle/ruby/2.6.0/gems/barnes-0.0.8/lib/barnes/instruments/puma_instrument.rb:36:in `instrument!'
	from /app/vendor/bundle/ruby/2.6.0/gems/barnes-0.0.8/lib/barnes/panel.rb:46:in `block in instrument!'
	from /app/vendor/bundle/ruby/2.6.0/gems/barnes-0.0.8/lib/barnes/panel.rb:45:in `each'
	from /app/vendor/bundle/ruby/2.6.0/gems/barnes-0.0.8/lib/barnes/panel.rb:45:in `instrument!'
	from /app/vendor/bundle/ruby/2.6.0/gems/barnes-0.0.8/lib/barnes/periodic.rb:58:in `block (3 levels) in initialize'
	from /app/vendor/bundle/ruby/2.6.0/gems/barnes-0.0.8/lib/barnes/periodic.rb:57:in `each'
	from /app/vendor/bundle/ruby/2.6.0/gems/barnes-0.0.8/lib/barnes/periodic.rb:57:in `block (2 levels) in initialize'
	from /app/vendor/bundle/ruby/2.6.0/gems/barnes-0.0.8/lib/barnes/periodic.rb:46:in `loop'
	from /app/vendor/bundle/ruby/2.6.0/gems/barnes-0.0.8/lib/barnes/periodic.rb:46:in `block in initialize'Exception

In puma/puma#2086, Puma.stats was changed to return a Hash instead of a String. I'm assuming this line needs to be updated to support that.

barnes/lib/barnes/instruments/puma_instrument.rb

Line 24 in 62e99ba

MultiJson.load(::Puma.stats || "{}")

[nateberkopec]

Puma 5.0 will return a hash here, so I think you should just only attempt JSON conversion if Puma.stats is a String.

[schneems]

Can we have it give a different API? Maybe Puma.stats_hash ?

[nateberkopec]

I think we had a strong case to change it. Exposing a string is not extensible by external consumers, which is what this API is intended for. A hash is a much better object for this purpose.

[schneems]

A proposal in puma/puma#2253 to expose this as a hash without breaking backward compat.

[schneems]

This is resolved