Easy zip generating with Rails, Nginx & Paperclip

Tonight I decided to try making NGINX handle my zip generating, to save the server some work, and the user of some frustration waiting for background jobs to finish. Here’s what I came up with.

First of all, I re-compiled Nginx with two modules; mod_zip, and passenger module. You may drop the Passenger module if you are using some other server, this solution works with anything that can print out some text :)

Roughly, these are the required steps:

gem install passenger
cd nginx-folder/
.configure --add-module=/path/to/passenger/gem/ext/nginx --add-module=/path/to/mod_zip-1.x
sudo make && sudo make install

If you wonder where your passenger is, you can easily find the root of passenger by running

passenger-config --root

So on to the fun part! I started by adding a member method to my galleries route called zip:

ActionController::Routing::Routes.draw do |map|
  map.resources :galleries, :member => {:zip => :get}
end

And In my controller I added these two methods (it can probably be done cleaner, but hey, it’s working :) Suggestions for other ways of writing these are welcome!

class GalleriesController < ApplicationController
  def zip
    @gallery = Gallery.find(params[:id])
    paperzip(@gallery.images.collect(&:data), @gallery.name)
  end
  
  private 
    def paperzip( attachments= [], name= 'file', style= :original )
      # set headers
      response.headers["Content-Disposition"] = "attachment; filename=#{name}.zip"
      response.headers["X-Archive-Files"] = "zip"
  
      # Generate file list
      render :text => attachments.collect{|a| 
        ['-', File.size(a.path(style)), a.url(style,false), a.original_filename.gsub(/ /,'_')].join(' ')
      }.join("\r\n")+"\r\n"
    end
end

Whoa! Let me break that down for you a little bit. Firstly the member method zip, which now has the named route “zip_gallery_path(@gallery)” in you views btw:

def zip
  @gallery = Gallery.find(params[:id])
  paperzip(@gallery.images.collect(&:data), @gallery.name)
end

This basically finds our gallery from the :id param, and calls on this method we’re defining as private for this controller, called paperzip() (I know, catchy). paperzip() takes a collection of Images (which has_attached_file :data), a string containing a name for the zip file about to be made, and a symbol which you can use to zip down the style you want. I’m running with :original here.

Let’s move on to the next couple of lines:

response.headers["Content-Disposition"] = "attachment; filename=#{name}.zip"
response.headers["X-Archive-Files"] = "zip"

What we do here is setting some custom headers for our response back to the client, and Nginx. The content-disposition tells it we want the user to be prompted to download a file, called something.zip. The X-Archive-Files header is the one that makes mod_zip trigger, and eagerly await a list of files to zip down and send. Mod_zip requires a list of files that looks something like this:

md5 bytes /relative/path filename<linebreak>

Note that the linebreak needs to be a \r\n, and be on every line, even the last one. So, in order to construct this list, I added the following lines to the method, returning it using “render :text”

render :text => attachments.collect{|a| 
    ['-', File.size(a.path(style)), a.url(style,false), a.original_filename.gsub(/ /,'_')].join(' ')
  }.join("\r\n")+"\r\n" 

And voila! Calling this action with a get request, will now trigger mod_zip and create us a fully working zip file. The good thing about using this over some other method, is that Nginx only uses a couple of kilobytes of that precious memory of yours while doing this, and does the job way quicker than any other method I’ve tried.