code tunes

When your application uses many static files (photos for example), you should consider placing these files on different hosts to improve the speed at which they are downloaded by web browsers.

Most web browsers have a limit on how many simultaneous connections can be made to a single named host. And this limit is usually two. It means that if you let’s say display many photos on a single page, user’s browser can only download two at a time. The broadband internet connection will be no help here. The browser will not fully use it, because it will keep opening and closing connections.

With little server and Rails configuration you pretend to be serving your files from different hosts and trick the browser (read more). This is easy if you keep all the files on your own server, but when you use Paperclip to upload files to Amazon’s S3 servers it gets more trickier. In fact Paperclip doesn’t support uploading to different hosts (buckets).

First, notice that these addresses means the same for Amazon’s S3:

• http://s3.amazonaws.com/bucket_name/filename.ext
• http://bucket_name.s3.amazonaws.com/filename.ext

So all we need to do is to make Paperclip upload to different buckets and return attachment’s url of the latter type. I wrote an extension that accomplishes this and included it in PaperclipExtended. All you need to do is download both Paperclip and PaperclipExtended and change your model definition.

class User < ActiveRecord::Base
    has_attached_file :avatar,
                      :storage => :s3,
                      :s3_credentials => "#{RAILS_ROOT}/config/s3.yml",
                      :path => "avatars/:id/:style_:extension",
                      :bucket => lambda do |attachment|
                        i = attachment.instance.id % 4
                        "bucket_#{i}"
                      end
end

This will place each avatar in one of four buckets: bucket_0, bucket_1, bucket_2 or bucket_3. The exact bucket is chosen at runtime and in this case it’s based on models id.

Getting attachment’s url:

puts User.find(1).avatar.url(:original)
# => http://bucket_1.s3.amazonaws.com/avatars/1/original.jpg

If you have a page on your website that displays many uploaded photos, placing them in different buckets should make noticeable difference to user - they will load faster.

Paperclip is a great plugin for Ruby on Rails which eases the pain of image upload and resize process. The usage is very simple, results are what you want in most cases. Not in all cases though.

Your role is only to define the sizes of thumbnails that will be generated from original image. Thumnailing in is fact done by calling ImageMagick’s convert command with -scale argument, for example convert -scale ‘640×480>’.

You can alter how exactly the image is scaled by appending modifiers to desired thumbnail size, like ‘>’ in ‘640×480>, however it won’t give you unlimited power over thumbnailing process.

Consider following example. I have a small image (120×120).

Scaling it to smaller size gives me the result I want. But when the result image needs to be bigger than original, the original image is enlarged in a way that you’ll see single pixels.

What I want to achieve is the enlargment done not by scaling the original image, but by adding a border around it.

This cannot be achieved by adding any of modifiers to desired thumbnail size, so why not to pass additional arguments to convert command? Yes, that would be a solution.

And here’s my solution - PaperclipExtended. It’s a plugin that modifies original Paperclip, so that now it accepts additional (optional) parameter :commands when defining the thumbnails sizes.

class User < ActiveRecord::Base
  has_attached_file :avatar, :styles => { :medium => "300x300>", :small => "100x100>" },
    :commands => { :medium => "-background white -gravity center -extent 300x300 +repage" }
end

During thumbnail generation Paperclip will now append given commands to convert command. Convert command for medium style will be now:
convert -scale ‘300×300>’ -background white -gravity center -extent 300×300 +repage
Convert command for small style will remain unchanged.

Passing such commands will help me with the enlargment I mentioned above. For what else could be done check the documentation of ImageMagick’s command line options.

PaperclipExtended is not a replacement for Paperclip, just an extension. It works with version 2.1.2 of Paperclip plugin (the current one and the only one I tested). Compatibility with future version is not guaranteed.

I put a plugin on GitHub.
http://github.com/netguru/paperclip-extended

How to install:

script/plugin install git://github.com/netguru/paperclip-extended.git

Configuration is the same as of original Paperclip plugin, but you can now add an optional :commands parameter.

Hope it’ll be helpful!

If you have any questions, post them in comments to this post.