musherator.rb

#!/usr/bin/env ruby

require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'
  gem 'premailer'
  gem 'nokogiri'
  gem 'base64'
  gem 'mail'
end

# Inline styles
premailer = Premailer.new($stdin, warn_level: Premailer::Warnings::SAFE)

Mail.defaults do
  delivery_method :smtp,
    address: "smtp.gmail.com",
    port: 587,
    user_name: "[email protected]",
    authentication: "plain",
    password: "right there"
end

def ingest_and_rewrite_images(html_string, into_mail_mime_part)
  # Add an attachment as a multipart part, under the /related multipart part.
  # Since it is related, these attachments will not show as downloadable attachments
  # - but they will be usable within the same part!
  # Once an image is attached to the part, we can get its URL (which uses a generated cid:)
  # and replace the src in the HTML with that.
  # https://stackoverflow.com/a/46468212/153886
  noko_doc = Nokogiri::HTML(html_string)
  noko_doc.css("img").map do |image_node|
    image_relative_path = image_node["src"]
    raise "Referenced image #{image_relative_path.inspect} not found" unless File.exist?(image_relative_path)

    fn = File.basename(image_relative_path)
    into_mail_mime_part.attachments[fn] = {filename: image_relative_path}
    cid_url = into_mail_mime_part.attachments[fn].url
    image_node["src"] = cid_url
  end
  noko_doc.to_html
end

mail = Mail.new
mail.part :content_type => "multipart/mixed" do |p1|
  p1.part :content_type => "multipart/related" do |p2|
    html_with_cids = ingest_and_rewrite_images(premailer.to_inline_css, p2)
    p2.part :content_type => "multipart/alternative", :content_disposition => "inline" do |p3|
      p3.part :content_type => "text/plain; charset=utf-8", :body => premailer.to_plain_text
      p3.part :content_type => "text/html; charset=utf-8", :body => html_with_cids
    end
  end
end
mail.from "Julik <[email protected]>"
mail.to "[email protected]"
mail.subject "Musherator HTML test #{Time.now.strftime("%Y-%m-%d %H:%M")}"

test_email_filename = "test.eml"
File.open(test_email_filename, "wb") { |fo| fo.write(mail.to_s) }
`open #{test_email_filename}` # Mail.app opens .emls

#mail.deliver!