session_id_in_header.rb

# This module offers the way to get session_id from HTTP_X_SID
# in the request headers for Rack application.
# 
# This is only work memcache and dalli
# (Rack::Session::Cookie implements 'extract_session_id' by itself.)
# Put this file in config/initializers when used with Rails.
#
# I don't know why this module exists because the default way is
# using cookies, but cookie is even put in HTTP Request and response
# headers too.
#
# License : MIT License
# Kazuya NUMATA <numata@gmail.com>

require 'rack/session/abstract/id'

module SessionHeader
  module Rack
    module Session
      module ID
        ENV_SESSION_KEY = 'rack.session'.freeze
        def self.included(base)
          base.class_eval do
            include ::SessionHeader::Rack::Session::ID::InstanceMethods
            alias_method_chain :extract_session_id, :session_id_header
            alias_method_chain :commit_session, :session_id_header
          end
        end
        module InstanceMethods
          private

          def extract_session_id_with_session_id_header(env)
            sid = env["HTTP_X_SID"]
            sid ||= extract_session_id_without_session_id_header(env)
            sid
          end

          def commit_session_with_session_id_header(env, status, headers, body)
            status, headers, body = commit_session_without_session_id_header(env, status, headers, body)
            session = env[ENV_SESSION_KEY]
            headers["X-Sid"] = session.id
            [status, headers, body]
          end
        end
      end
    end
  end
end

::Rack::Session::Abstract::ID.class_eval do
  include ::SessionHeader::Rack::Session::ID
end