inline.rb

#!/usr/bin/env ruby

require 'base64'
require 'nokogiri'
require 'uri'

def main
  html = Nokogiri::HTML($stdin.read)
  inline_all_images(html)
  inline_all_css(html)
  $stdout.write(html.to_s)
end

def inline_all_images(html)
  html.css("img").each do |img|
    img['src'] = base64_image_src(img['src'])
  end
end

def inline_all_css(html)
  html.css(%{link[rel="stylesheet"]}).each do |link|
    unless is_remote_path?(link['href'])
      inline_css_node(link)
    end
  end
end

def inline_css_node(link)
  style_node = Nokogiri::XML::Node.new("style", link.parent)
  style_node.content = File.read(path_to_local_path(link['href']))
  link.add_next_sibling(style_node)
  link.remove
end

def base64_image_src(path)
  content_type = {
    ".svg" => "image/svg+xml",
    ".jpg" => "image/jpeg",
  }.fetch(File.extname(path))
  base64ed_data = Base64.encode64(File.read(path))
  "data:#{content_type};base64,#{base64ed_data}"
end

def is_remote_path?(path)
  uri = URI.parse(path)
  uri.scheme != nil || path.start_with?("//")
end

def path_to_local_path(path)
  # We treat the current working directory as the root of the "server", so any
  # absolute path in the markup becomes a path relative to the current
  # directory.
  path.sub(/^\//, "")
end

main