# GurusQ: Metal calling disparity-How to install metal in code

**URL:** <https://www.ruby-forum.com/t/gurusq-metal-calling-disparity-how-to-install-metal-in-code/186260>\
**Category:** Rails\
**Created:** [April 3, 2010, 4:07am UTC](https://www.ruby-forum.com/t/gurusq-metal-calling-disparity-how-to-install-metal-in-code/186260 "2010-04-03T04:07:39Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![magpie](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/45deac/32.png) [@magpie](https://www.ruby-forum.com/u/magpie)\
**Post date:** [April 3, 2010, 4:07am UTC](https://www.ruby-forum.com/t/gurusq-metal-calling-disparity-how-to-install-metal-in-code/186260/1 "2010-04-03T04:07:39Z")

</div>

I have a simple class that I want to install as Rails Metal. I don’t  
want to put it into a file in app/metal for reasons I don’t want to go  
into. It looks like this, and handler is defined elsewhere.

class UrlFilter  
ALLOW = [404]  
DENY = [403]  
def self.call(env)  
handler.call(env[“PATH\_INFO”]) ? ALLOW : DENY  
end  
end

I’ve tried installing it like this :  
ActionController::Dispatcher.middleware.use UrlFilter

but on the first request it crashes with :

Sat Apr 03 00:29:43 +0800 2010: Read error: #\<ArgumentError: wrong  
number of arguments (0 for 1)\>  
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.5/lib/action\_controller/middleware\_stack.rb:31:in  
`call' /Library/Ruby/Gems/1.8/gems/actionpack-2.3.5/lib/action_controller/middleware_stack.rb:31:in`klass’  
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.5/lib/action\_controller/middleware\_stack.rb:42:in  
`active?' /Library/Ruby/Gems/1.8/gems/actionpack-2.3.5/lib/action_controller/middleware_stack.rb:112:in`active’  
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.5/lib/action\_controller/dispatcher.rb:108:in  
`find_all' /Library/Ruby/Gems/1.8/gems/actionpack-2.3.5/lib/action_controller/middleware_stack.rb:112:in`each’  
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.5/lib/action\_controller/middleware\_stack.rb:112:in  
`find_all' /Library/Ruby/Gems/1.8/gems/actionpack-2.3.5/lib/action_controller/middleware_stack.rb:112:in`active’  
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.5/lib/action\_controller/middleware\_stack.rb:116:in  
`build' /Library/Ruby/Gems/1.8/gems/actionpack-2.3.5/lib/action_controller/dispatcher.rb:130:in`build\_middleware\_stack’  
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.5/lib/action\_controller/dispatcher.rb:113:in  
`call' /Library/Ruby/Gems/1.8/gems/actionpack-2.3.5/lib/action_controller/reloader.rb:34:in`run’  
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.5/lib/action\_controller/dispatcher.rb:108:in  
`call' /Library/Ruby/Gems/1.8/gems/rails-2.3.5/lib/rails/rack/static.rb:31:in`call’  
/Library/Ruby/Gems/1.8/gems/rack-1.0.1/lib/rack/urlmap.rb:46:in `call' /Library/Ruby/Gems/1.8/gems/rack-1.0.1/lib/rack/urlmap.rb:40:in`each’  
/Library/Ruby/Gems/1.8/gems/rack-1.0.1/lib/rack/urlmap.rb:40:in `call' /Library/Ruby/Gems/1.8/gems/rails-2.3.5/lib/rails/rack/log_tailer.rb:17:in`call’  
/Library/Ruby/Gems/1.8/gems/rack-1.0.1/lib/rack/content\_length.rb:13:in  
`call' /Library/Ruby/Gems/1.8/gems/rack-1.0.1/lib/rack/chunked.rb:15:in`call’  
/Library/Ruby/Gems/1.8/gems/rack-1.0.1/lib/rack/handler/mongrel.rb:64:in  
`process' /Library/Ruby/Gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:159:in`process\_client’  
/Library/Ruby/Gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:158:in `each' /Library/Ruby/Gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:158:in`process\_client’  
/Library/Ruby/Gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in `run' /Library/Ruby/Gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in`initialize’  
/Library/Ruby/Gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in `new' /Library/Ruby/Gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in`run’  
/Library/Ruby/Gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:268:in  
`initialize' /Library/Ruby/Gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:268:in`new’  
/Library/Ruby/Gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:268:in `run' /Library/Ruby/Gems/1.8/gems/rack-1.0.1/lib/rack/handler/mongrel.rb:34:in`run’  
/Library/Ruby/Gems/1.8/gems/rails-2.3.5/lib/commands/server.rb:111  
/Library/Ruby/Site/1.8/rubygems/custom\_require.rb:31:in  
`gem_original_require' /Library/Ruby/Site/1.8/rubygems/custom_require.rb:31:in`require’  
script/server:3

The rails calling code looks like this :

```
  def klass
    if @klass.respond_to?(:call)
      @klass.call
    elsif @klass.is_a?(Class)
      @klass
    else
      @klass.to_s.constantize
    end
  rescue NameError
    @klass
  end

  def active?
    return false unless klass

    if @conditional.respond_to?(:call)
      @conditional.call
    else
      @conditional
    end
  end

```

Notice when calling call no arguments are passed (twice!) ? Every metal  
example I’ve seen defines the entry method as

def self.call(env)

yet this calling code doesn’t pass any.

Whats going on ? How do I define and install a metal class in code ?