def fresh_when(object = nil, etag: nil, weak_etag: nil, strong_etag: nil, last_modified: nil, public: false, template: nil)
      weak_etag ||= etag || object unless strong_etag
      last_modified ||= object.try(:updated_at) || object.try(:maximum, :updated_at)

      if strong_etag
        response.strong_etag = combine_etags strong_etag,
          last_modified: last_modified, public: public, template: template
      elsif weak_etag || template
        response.weak_etag = combine_etags weak_etag,
          last_modified: last_modified, public: public, template: template
      end

      response.last_modified = last_modified if last_modified
      response.cache_control[:public] = true if public

      head :not_modified if request.fresh?(response)
    end
def fresh_when(object = nil, etag: nil, weak_etag: nil, strong_etag: nil, last_modified: nil, public: false, template: nil)
      weak_etag ||= etag || object unless strong_etag
      last_modified ||= object.try(:updated_at) || object.try(:maximum, :updated_at)

      if strong_etag
        response.strong_etag = combine_etags strong_etag,
          last_modified: last_modified, public: public, template: template
      elsif weak_etag || template
        response.weak_etag = combine_etags weak_etag,
          last_modified: last_modified, public: public, template: template
      end

      response.last_modified = last_modified if last_modified
      response.cache_control[:public] = true if public

      head :not_modified if request.fresh?(response)
    end
Sets the +etag+, +last_modified+, or both on the response and renders a
 <tt>304 Not Modified</tt> response if the request is already fresh.

 === Parameters:

 * <tt>:etag</tt> Sets a "weak" ETag validator on the response. See the
   +:weak_etag+ option.
 * <tt>:weak_etag</tt> Sets a "weak" ETag validator on the response.
   Requests that set If-None-Match header may return a 304 Not Modified
   response if it matches the ETag exactly. A weak ETag indicates semantic
   equivalence, not byte-for-byte equality, so they're good for caching
   HTML pages in browser caches. They can't be used for responses that
   must be byte-identical, like serving Range requests within a PDF file.
 * <tt>:strong_etag</tt> Sets a "strong" ETag validator on the response.
   Requests that set If-None-Match header may return a 304 Not Modified
   response if it matches the ETag exactly. A strong ETag implies exact
   equality: the response must match byte for byte. This is necessary for
   doing Range requests within a large video or PDF file, for example, or
   for compatibility with some CDNs that don't support weak ETags.
 * <tt>:last_modified</tt> Sets a "weak" last-update validator on the
   response. Subsequent requests that set If-Modified-Since may return a
   304 Not Modified response if last_modified <= If-Modified-Since.
 * <tt>:public</tt> By default the Cache-Control header is private, set this to
   +true+ if you want your application to be cacheable by other devices (proxy caches).
 * <tt>:template</tt> By default, the template digest for the current
   controller/action is included in ETags. If the action renders a
   different template, you can include its digest instead. If the action
   doesn't render a template at all, you can pass <tt>template: false</tt>
   to skip any attempt to check for a template digest.

 === Example:

   def show
     @article = Article.find(params[:id])
     fresh_when(etag: @article, last_modified: @article.updated_at, public: true)
   end

 This will render the show template if the request isn't sending a matching ETag or
 If-Modified-Since header and just a <tt>304 Not Modified</tt> response if there's a match.

 You can also just pass a record. In this case +last_modified+ will be set
 by calling +updated_at+ and +etag+ by passing the object itself.

   def show
     @article = Article.find(params[:id])
     fresh_when(@article)
   end

 You can also pass an object that responds to +maximum+, such as a
 collection of active records. In this case +last_modified+ will be set by
 calling <tt>maximum(:updated_at)</tt> on the collection (the timestamp of the
 most recently updated record) and the +etag+ by passing the object itself.

   def index
     @articles = Article.all
     fresh_when(@articles)
   end

 When passing a record or a collection, you can still set the public header:

   def show
     @article = Article.find(params[:id])
     fresh_when(@article, public: true)
   end

 When rendering a different template than the default controller/action
 style, you can indicate which digest to include in the ETag:

   before_action { fresh_when @article, template: 'widgets/show' }