Extract request HTTP headers for Rails

extract_request_http_headers_for_rails.rb

class ApplicationController < ActionController::Base
  private

  # @see [Rack::RequestでHTTPリクエストヘッダ一覧を書き出す - Qiita](https://qiita.com/mechamogera/items/9c620155e669b394d513)
  # @example
  #   {
  #     "Version"=>"HTTP/1.1",
  #     "Host"=>"localhost:3000",
  #     "User-Agent"=>"curl/7.54.0",
  #     "Accept"=>"*/*",
  #     "X-Forwarded-For"=>"192.0.0.1"
  #   }
  def request_http_header
    return @request_http_header if @request_http_header.present?
    @request_http_header = request.headers.env.select { |k, _| k =~ /^HTTP_/ }
    @request_http_header = @request_http_header.reduce({}) do |r, (k, v)|
      name = k
        .sub(/^HTTP_/, '')
        .downcase
        .split('_')
        .map(&:camelize)
        .join('-')
      r[name] = v
      r
    end
    @request_http_header
  end
end