headers.rb

# Currently in Rails 2 and 3...
# https://github.com/rails/rails/blob/3-2-stable/actionpack/lib/action_dispatch/http/headers.rb
# 
# headers = ActionDispatch::Http::Headers.new
# headers['HTTP_FOO_BAR'] = 'a1b2c3'
# puts headers['foo-bar']              #=> 'a1b2c3'
# puts headers.has_key? 'foo-bar'      #=> false
# puts headers.has_key? 'HTTP_FOO_BAR' #=> true
#
# I found this pseudo hash syntax, where the array [] lookup returned a value,
# but include?, has_key? and friends don't work, confusing, inconsistent and surprising.
#
# Below is a possible fix.
 
module ActionDispatch
  module Http
    class Headers < ::Hash
      @@env_cache = Hash.new { |h,k| h[k] = "HTTP_#{k.upcase.gsub(/-/, '_')}" }

      def initialize(*args)

        if args.size == 1 && args[0].is_a?(Hash)
          super()
          update(args[0])
        else
          super
        end
      end

      def [](header_name)
        super || super(env_name(header_name))
      end

      def key?(header_name)
        !!self[header_name]
      end
      alias_method :include?, :key?
      alias_method :has_key?, :key?
      alias_method :member?, :key?

      private
        # Converts a HTTP header name to an environment variable name.
        def env_name(header_name)
          @@env_cache[header_name]
        end
    end
  end
end

# ====================
# Testing....
# ====================
headers = ActionDispatch::Http::Headers.new
headers['HTTP_FOO_BAR'] = 'ab123cd'

puts headers['foo-bar'] #=> 'ab123cd'
puts headers['HTTP_FOO_BAR'] #=> 'ab123cd'

puts headers.has_key? 'foo-bar'       # => true
puts headers.has_key? 'HTTP_FOO_BAR'  # => true

puts headers.key? 'foo-bar'           # => true
puts headers.key? 'HTTP_FOO_BAR'      # => true

puts headers.member? 'foo-bar'        # => true
puts headers.member? 'HTTP_FOO_BAR'   # => true