How do I access the Rack environment from within Rails?

Question

I have a Rack application that looks like this:

class Foo   def initialize(app)     @app = app   end   def call(env)     env["hello"] = "world"     @app.call(env)   end end 

After hooking my Rack application into Rails, how do I get access to env["hello"] from within Rails?

Update: Thanks to Gaius for the answer. Rack and Rails let you store things for the duration of the request, or the duration of the session:

# in middleware def call(env)   Rack::Request.new(env)["foo"] = "bar"  # sticks around for one request    env["rack.session"] ||= {}   env["rack.session"]["hello"] = "world" # sticks around for duration of session end  # in Rails def index   if params["foo"] == "bar"     ...   end   if session["hello"] == "world"     ...   end end 

Answer 1

I'm pretty sure you can use the Rack::Request object for passing request-scope variables:

# middleware: def call(env)   request = Rack::Request.new(env) # no matter how many times you do 'new' you always get the same object   request[:foo] = 'bar'   @app.call(env) end  # Controller: def index   if params[:foo] == 'bar'     ...   end end 

Alternatively, you can get at that "env" object directly:

# middleware: def call(env)   env['foo'] = 'bar'   @app.call(env) end  # controller: def index   if request.env['foo'] == 'bar'     ...   end end