Rendering .xslx from Rails 3 made easy

Update:

I've released a gem for rendering .xls and .xslx from Ruby on Rails

A while ago I was looking for something that allows generating simple xlsx files from Ruby.
I soon found simple_xlsx. Unlike other gems that let you generate Excel files, this one does not have any Windows dependencies, so the choice was easy.

Generating xlsx file procedurally worked out of the box, but I wanted the xlsx to become part of the view.

After reading Yehuda's post on custom renderers I decided to write one that converts HTML to XLSX.

The goal is to be able to render both xlsx and html with something like this:

class ContactsController < ApplicationController
  respond_to :xlsx, :html

  def index
    @contacts = current_user.contacts
    
    # render either xlsx or html depending on request.format:
    respond_with(@contacts) 
  end
end

Moreover, it would be nice to be able to generate them from the same partial, e.g. like the one below:

-# _contacts.haml
%table
  %caption My contacts
  %thead
    %tr
      %th Email
      %th Phone
  %tbody
  - contacts.each do |contact| 
      %tr
        %td= contact.email
        %td= contact.phone_number

In contacts/index.html.haml you would have something like:

= render 'menu'
= render '_contacts', :contacts => @contacts

And in contacts/index.xlsx.haml same, but without the navigation stuff:

= render '_contacts', :contacts => @contacts

Turned out, it is easy to do in Rails 3. After some hours and help from SO, I finished a simple implementation: Add the mime type to config/initializers/mime_types.rb:

Mime::Type.register "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet", :xlsx

Add the renderer, and register a responder:

require 'action_controller/metal/renderers'
require 'action_controller/metal/responder'

# This will let us do thing like `render :xlsx => 'index'`
# This is also how Rails internally implements its :json and :xml renderers
# Rarely used, nevertheless public API
ActionController::Renderers.add :xlsx do |template, options|
  output = Tempfile.new("#{template}.xslx")
  html   = render_to_string(template, options)
  SimpleXlsx::Serializer.new(output) do |xlsx_doc|
    Nokogiri::XML::Document.parse(html).xpath('/table').each do |xml_table|
      xlsx_doc.add_sheet(xml_table.css('caption').inner_text) do |sheet|
        xml_table.css('tr').each do |row|
          sheet.add_row(row.css('th,td').map(&:inner_text))
        end
      end
    end
  end
  send_data File.open(output.path, 'rb', &:read), :type => :xlsx
end

# This sets up a default render call for when you do 
# respond_to do |format|
#   format.xlsx
# end
class ActionController::Responder
  def to_xlsx
    controller.render :xlsx => controller.action_name
  end
end