module ActionView::Helpers::AssetUrlHelper

def compute_asset_host(source = "", options = {})

(proc or otherwise).
or the value returned from invoking call on an object responding to call
numbers 0-3 if it contains %d (the number is the source hash mod 4),
the host if no wildcard is set, the host interpolated with the
Pick an asset host for this source. Returns +nil+ if no host is set, 
def compute_asset_host(source = "", options = {})
  request = self.request if respond_to?(:request)
  host = options[:host]
  host ||= config.asset_host if defined? config.asset_host
  if host
    if host.respond_to?(:call)
      arity = host.respond_to?(:arity) ? host.arity : host.method(:call).arity
      args = [source]
      args << request if request && (arity > 1 || arity < 0)
      host = host.call(*args)
    elsif host.include?("%d")
      host = host % (Zlib.crc32(source) % 4)
    end
  end
  host ||= request.base_url if request && options[:protocol] == :request
  return unless host
  if URI_REGEXP.match?(host)
    host
  else
    protocol = options[:protocol] || config.default_asset_host_protocol || (request ? :request : :relative)
    case protocol
    when :relative
      "//#{host}"
    when :request
      "#{request.protocol}#{host}"
    else
      "#{protocol}://#{host}"
    end
  end
end