Check for the existing of a header attribute in rails before invoking an action

Question

I am building an API in rails 4. Before invoking an action, I am trying first to check whether an attribute exist in the http header. Is there a way to do that instead of checking each in all actions of the controllers. The rails documentation mentions something like

constraints(lambda { |req| req.env["HTTP_CUSTOM_HEADER"] =~ /value/ }) do
  #controller, action mapping
end

but I still want to give the user consuming my API a feedback. something like sending a json with a message stating: missing the custom attribute in the header

Habit

Answer 1

You can add before_action to the controller and check a header attribute, for example:

class SomeController < ApplicationController
  before_action :render_message, unless: :check_header

  def check_header
    request.env["HTTP_CUSTOM_HEADER"] =~ /foo/
  end

  def render_message
    render json: { message: "missing the custom attribute in the header" }
  end
end

If check_attribute filter returns nil, then render_message action render desired message.

Saudra

I have many controllers and I don't want to use that in each controller. I basicaly have 4 controllers and each one of them has to do this checking – Habit

ok, thanks, I think adding your code to the action controller will work perfectly. thanks for the inspiration :) – Habit

Answer 2

You can check controller actions using before_action filter:

For example in APIController:

class APIController < ApplicationController
  before_action :check_headers

  private

  def check_header
    # do whatever is required here
  end
end

Ahem

Answer 3

If the header existence acts as an authentication mechanism there is no point to hit backend for that, try to avoid it earlier on reverse-proxy side:

nginx.conf

server {
  location / {
    if ($http_x_custom_header) {
      return 200 'missing the custom attribute in the header'; 
    }
    proxy_pass...
  }
}

Egomania

well since I am building an api for that, I would not want to do that as the api might get changed in the next versions. I still want to have full controll in my code base – Habit

Ok, makes sense to have the header detection on application layer if it behaves beyond than simple check and may change later – Egomania