如何在Rails 3.2中缓存gravatars？

Question

I wrote a gravatar helper to use in my learning app. The Users#index action lists all users with their gravatars, which can take a while even with pagination. Is there a way to cache the gravatars in Rails 3.2 with the following in mind:

1. Without using a Gravatar plugin that has a cache feature.

2. Without caching the users page itself; really, I'm only looking to cache the images themselves without having to grab them from gravatar.com again.

    def gravatar_for(user, options = { size: 50 }) gravatar_id = Digest::MD5::hexdigest(user.email.downcase) size = options[:size] gravatar_url = "http://gravatar.com/avatar/#{gravatar_id}.png?s=#{size}" image_tag(gravatar_url, alt: user.name) end 

Answer 1

If you view the source, you'll see SO doesn't do their own gravatar caching. Refresh the page a few times and you might see the gravatars are still the last elements to load.

Some things you can do to improve performance are:

• When run in production mode with cache control set up correctly, the browser will do some image caching for you (maybe watch the railscasts on that, episode 321 I think)
• Include the image dimensions in your img tag, the browser will reserve the right amount of screen space even before the image is available, it does fewer redraws and feels livelier
• Serve up your own placeholder instead of more expensive identicons etc.

Answer 2

My question is why you need this? You are putting image from external server and user browser and gravatar.com must cache it. It's reason why gravatar exists, for manage avatars without any work from developer. If you need to cache gravatars then why you really need it?

Answer 3

Caching the entire users page or fragment caching the image urls wouldn't make a difference anyway because the images will still be downloaded from Gravatar. Gravatar sets their Cache-Control header to have a max age of 5 minutes and there's not much else you can do about it.

One possibility is to save the images to another location where you have control over the response headers.

One minor thing you could do during development though is to not use a hard refresh on your pages. In some browsers CMD/CTRL + R or pressing the refresh button sends request headers with Cache-Control:max-age=0 which causes you to re-download all the images. You can do a soft refresh by simply visiting the page again (for example: pressing enter on the url in the addressbar) and it won't send that header.