SVG-to-PNG Converter using Ruby-GNOME2/RSVG on Sinatra

app.rb

# coding: utf-8
require 'sinatra'
require 'rsvg2'
require 'haml'

get '/' do
  haml :index
end

post '/result' do
  if params[:file]
    svg_data = params[:file][:tempfile].read
    png_data = ImageConvert.svg_to_png(svg_data, params[:width].to_i, params[:height].to_i)
  else
  end
  content_type 'png'
  png_data
end

class ImageConvert
  def self.svg_to_png(svg, width, height)
    svg = RSVG::Handle.new_from_data(svg)
    width   = width  ||=500
    height  = height ||=500
    surface = Cairo::ImageSurface.new(Cairo::FORMAT_ARGB32, width, height)
    context = Cairo::Context.new(surface)
    context.render_rsvg_handle(svg)
    b = StringIO.new
    surface.write_to_png(b)
    return b.string
  end
end

Gemfile

source "https://rubygems.org"

gem "sinatra"
gem "haml"
gem "rsvg2"

index.haml

!!!html5
%html
  %head
    %meta{:charset => "UTF-8"}
    %title SVG to PNG
  %body
    %h1 SVG to PNG
    %form{:action => "./result", :method => "post", :enctype => "multipart/form-data"}
      %ul
        %li
          %input{:type => "file", :name => "file"}
        %li
          %input{:type => "number", :name => "width", :value => "500"}
        %li
          %input{:type => "number", :name => "height", :value => "500"}
      %input{:type => "submit", :name => "submit"}