http_servlet_handler.rb

class PHPHandler 
  def initialize(app)  
    @app = app  
  end  

  def call(env) 
    if env["PATH_INFO"] =~ /\/$/
      env["PATH_INFO"] += "index.php"
    end

    if env["PATH_INFO"] =~ /\.php$/
      php_path =  env["PATH_INFO"][1..-1]
      body = %x{php #{php_path}}
      [200, {"Content-Type" => "text/html"}, [body]]
    else
      status, headers, body = @app.call(env)
      [status, headers, body]
    end 
  end  
end

use PHPHandler