class ActionDispatch::Http::Headers

def [](key)
  @env[env_name(key)]
end

def []=(key, value)
  @env[env_name(key)] = value
end

def each(&block)
  @env.each(&block)
end

def env_name(key)
  key = key.to_s
  if key =~ HTTP_HEADER
    key = key.upcase.tr('-', '_')
    key = "HTTP_" + key unless CGI_VARIABLES.include?(key)
  end
  key
end

def fetch(key, *args, &block)
  @env.fetch env_name(key), *args, &block
end

def initialize(env = {})
  @env = env
end

def key?(key); @env.key? key; end

def merge(headers_or_env)
  headers = Http::Headers.new(env.dup)
  headers.merge!(headers_or_env)
  headers
end

def merge!(headers_or_env)
  headers_or_env.each do |key, value|
    self[env_name(key)] = value
  end
end