How to add middleware in Rails 4.2 application

Question

I am trying to learn Middlewares and been practising how to mount it in the Rails application. I have followed the railscast

So far I have implemented these steps:

1) Created a new Rails 4.2 application called: Blog

2) Added a file in the lib folder named as response_timer.rb.

class ResponseTimer
  def initialize(app)
    @app = app
  end

  def call(env)
    [200, {"Content-Type" => "text/html"}, "Hello World"]
  end
end

3) Added config.middleware.use "ResponseTimer" in application.rb.

config.middleware.use "ResponseTimer"

But as i'm hitting the command rake middleware in the terminal, it is reporting this error:

rake aborted!
NameError: uninitialized constant ResponseTimer

I tried also to add the config.middleware.use "ResponseTimer" in the development.rb but again facing the same error.

What am i missing here?

Please help.

Referenced article: http://guides.rubyonrails.org/rails_on_rack.html

try adding your code along with the question, that will be helpful for others to understand this better. — Abhinay, Jan 19 '16 at 07:42
have you tried requiring the file in `application.rb`, ex: `require_relative '../lib/response_timer'` — Abhinay, Jan 19 '16 at 08:01
Updated the question. Also this answer helped me http://stackoverflow.com/a/24122424 — Hashmita Raut, Jan 19 '16 at 08:41
Exactly not my answer. As I told I followed this answer: [link](http://stackoverflow.com/a/24122424) :) — Hashmita Raut, Jan 19 '16 at 11:39

score 5 · Accepted Answer · edited May 23 '17 at 12:25

5

Middleware has to have an accompanying module / class, and needs to be loaded in the app before it can be referenced. The way to do this in Rails is with autoloading (lib files aren't autoloaded by default):

#config/application.rb
config.autoload_paths += Dir["#{config.root}/lib/**/"]
config.middleware.use "ResponseTimer"

The above should work for you.

edited May 23 '17 at 12:25

Community

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1

answered Jan 19 '16 at 09:03

Richard Peck

76,116
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`autoload_paths` is not working :( If I do `rails server` then `uninitialized constant Blog::Application::ResponseTimer (NameError)` And If I do `rake middleware` then `NameError: uninitialized constant Blog::Application::ResponseTimer ` – Hashmita Raut Jan 19 '16 at 10:44
Note, in Rails 5+ you can no longer use the String for the name of the middleware. You need to use the proper class name. Additionally, according to @rafaelfranca (Rails core), _"middleware can't be in app because they can't be reloaded. They should be in lib and if you put them in lib, require_relative will work."_ https://github.com/rails/rails/issues/25525#issuecomment-479941866 – Joshua Pinter Nov 02 '20 at 03:02

score -2 · Answer 2 · edited May 23 '17 at 12:17

-2

I followed this answer: https://stackoverflow.com/a/24122424

I tried it before but maybe missed something before.

In appliation.rb

require 'rails/all'
require_relative '../lib/response_timer'
module Blog
 class Application < Rails::Application
  ...
  config.middleware.use ResponseTimer
 end
end

edited May 23 '17 at 12:17

Community

1
1

answered Jan 19 '16 at 08:47

Hashmita Raut

171
1
7

You shouldn't have to include the file explicitly, it's an [antipattern](https://en.wikipedia.org/wiki/Anti-pattern). – Richard Peck Jan 19 '16 at 08:57
@RichPeck I am sure what you have pointed out is absolutely correct but `config.autoload_paths += Dir["#{config.root}/lib/**/"]` isn't this line doing the same stuff except its calling the entire `lib` folder where as in the given answer its just calling one file. can you please explain a bit. – Abhinay Jan 19 '16 at 09:35
It's autoloading the lib folder, so you don't need to explicitly call the files you need in your `application.rb`. – Richard Peck Jan 19 '16 at 09:37

How to add middleware in Rails 4.2 application

2 Answers2