Fix Instrumentation not inheriting Feature

[paul]

Fixes #505. There was a bug because the Instrumenter was getting initialized twice because the shortcut on https://github.com/httprb/http/blob/master/lib/http/options.rb#L111 wasn't hit without Instrumenter inheriting Feature.

I also fixed the docs a mentioned in the issue.

@ixti @tarcieri WDYT about adding activesupport as a dev dependency, so I can write a real test that exercises it being called correctly?

[paul]

@joshuaflanagan Can you check if this works for you?

require "pp"
require "active_support/notifications"
ActiveSupport::Notifications.subscribe(/.*/) do |name, start, finish, id, payload|
  pp :name => name, :start => start.to_f, :finish => finish.to_f, :id => id, :payload => payload
end

HTTP.use(instrumentation: {instrumenter: ActiveSupport::Notifications.instrumenter}).get("https://httpbin.org/get")

{:name=>"start_request.http",
 :start=>1540825224.790576,
 :finish=>1540825224.7905908,
 :id=>"a1ecae467ff9e7c58964",
 :payload=>
  {:request=>
    #<HTTP::Request:0x000055e547d9bbb0
     @body=#<HTTP::Request::Body:0x000055e547d98758 @source=nil>,
     @headers=
      #<HTTP::Headers {"Connection"=>"close", "Host"=>"httpbin.org", "User-Agent"=>"http.rb/4.0.0"}>,
     @proxy={},
     @scheme=:https,
     @uri=#<HTTP::URI:0x0055e547d98de8 URI:https://httpbin.org/get>,
     @verb=:get,
     @version="1.1">}}

{:name=>"request.http",
 :start=>1540825224.792291,
 :finish=>1540825225.0600104,
 :id=>"a1ecae467ff9e7c58964",
 :payload=>
  {:response=>
    #<HTTP::Response/1.1 200 OK {"Connection"=>"close", "Server"=>"gunicorn/19.9.0", "Date"=>"Mon, 29 Oct 2018 15:00:25 GMT", "Content-Type"=>"application/json", "Content-Length"=>"195", "Access-Control-Allow-Origin"=>"*", "Access-Control-Allow-Credentials"=>"true", "Via"=>"1.1 vegur"}>}}

# => #<HTTP::Response/1.1 200 OK {"Connection"=>"close", "Server"=>"gunicorn/19.9.0", "Date"=>"Mon, 29 Oct 2018 15:00:25 GMT", "Content-Type"=>"application/json", "Content-Length"=>"195", "Access-Control-Allow-Origin"=>"*", "Access-Control-Allow-Credentials"=>"true", "Via"=>"1.1 vegur"}>

[ixti]

I dislike this part. I see reason behind this but it feels like trying to use instrumenter for something it's not supposed to be used.

[paul]

It's a common pattern in Rails itself: https://github.com/rails/rails/blob/b2eb1d1c55a59fee1e6c4cba7030d8ceb524267c/actionpack/lib/action_controller/metal/instrumentation.rb#L30-L32

I'm not a big fan of it either (I wish the instrument call would just automatically emit events at both the start and end of the block), but I assume this is how it was intended to be used.

[joshuaflanagan]

Doesn't it? https://github.com/rails/rails/blob/405aef3dede8938c8eb9789f6d6722864faddb09/activesupport/lib/active_support/notifications/instrumenter.rb#L21-L29
line 21 - start
line 29 - finish

[paul]

@joshuaflanagan I dug through the overly-complicated code for a few minutes, and I can't figure out why, but the subscribers don't receive any calls at the start of the block, just the end.

[joshuaflanagan]

Ok, you're right. I misinterpreted that code. Line 21 is marking the start of the event, but nothing is published until the finish on line 29.

Confirmed in the docs (https://guides.rubyonrails.org/active_support_instrumentation.html#creating-custom-events):

Simply call instrument with a name, payload and a block. The notification will be sent after the block returns.

[ixti]

We have activemodel dev dependency due to certificate of authority but we were thinking about getting rid of this. I would say that it's OK to add AS dependency for now, but I have a feeling that probably we should extract this feature into a separate gem, probably, e.g. http-rails or such. Have no strong feelings one way or the other thogh. @tarcieri would really like to know your thoughts.

[tarcieri]

I don't mind activesupport as a dev dependency. I agree extracting the functionality into a separate crate would probably be best.

[ixti]

Merged into 4-x-stable, will be released as part of v4.0.2