module ActionController::Head

def head(status, options = {})

render
return head(:bad_request) unless valid_request?
return head(:method_not_allowed) unless request.post?

It can also be used to return exceptional conditions:

head :created, location: @person

head :created, location: person_path(@person)

significant headers:
This allows you to easily return a response that consists only of
argument is interpreted to be a hash of header names and values.
Return a response that has no content (merely headers). The options 
def head(status, options = {})
  options, status = status, nil if status.is_a?(Hash)
  status ||= options.delete(:status) || :ok
  location = options.delete(:location)
  content_type = options.delete(:content_type)
  options.each do |key, value|
    headers[key.to_s.dasherize.split('-').each { |v| v[0] = v[0].chr.upcase }.join('-')] = value.to_s
  end
  self.status = status
  self.location = url_for(location) if location
  if include_content?(self.status)
    self.content_type = content_type || (Mime[formats.first] if formats)
    self.response.charset = false if self.response
    self.response_body = " "
  else
    headers.delete('Content-Type')
    headers.delete('Content-Length')
    self.response_body = ""
  end
end

def include_content?(status)

:nodoc: 
def include_content?(status)
  case status
  when 100..199
    false
  when 204, 205, 304
    false
  else
    true
  end
end