Controlling Information Access with the Rails Action Controller

Problem

You want to send e-book contents directly from your database to the browser as text and give the user the option to download a compressed version of each book.

Solution

You have a table that stores plain text e-books:

db/schema.rb:

  ActiveRecord::Schema.define(:version => 3) do

    create_table "ebooks", :force
=> true do |t|
      t.column "title", :string
      t.column "text", :text
    end
  end

In the DocumentController, define a view that calls send_data if the :download parameter is present, and render if it is not:

app/controllers/document_controller.rb:

  require 'zlib'
  require 'stringio' 

  class DocumentController
< ApplicationController

    def view
      @document = Ebook.find(params[:id])
      if (params[:download])
        send_data compress(@document.text),
                  :content_type =>
"application/x�gzip",
                  :filename =>
@document.title.gsub(' ','_') + ".gz"
      else
        render :text => @document.text
      end
    end

    protected
      def compress(text)
        gz = Zlib::GzipWriter.new(out = StringIO.new)
        gz.write(text)
        gz.close
        return out.string 
      end
   end

Discussion

If the view action of the DocumentController is invoked with the URL http://railsurl.com/document/ view/1, the e-book with an ID of 1 is rendered to the browser as plain text.

Adding the download parameter to the URL, which yields http://railsurl.com/document/view/1?download=1, requests that the contents of the e-book be compressed and sent to the browser as a binary file. The browser should download it, rather than trying to render it.

There are several different ways to render output in Rails. The most common are action renderers that process ERb templates, but it’s also customary to send binary image data to the browser.

See Also

• Recipe 15.3, “Serving Images Directly from a Database”