ActionMailer - How to Add an attachment?

Seems simple enough but I haven't been able to get it to work. The files work fine from S3 on the web app, but when I email them out via the code below, the files are corrupt.

App Stack: rails 3, heroku, paperclip + s3

Here's the code:

class UserMailer < ActionMailer::Base
# Add Attachments if any
if @comment.attachments.count > 0
  @comment.attachments.each do |a|
    require 'open-uri'
    open("#{Rails.root.to_s}/tmp/#{a.attachment_file_name}", "wb") do |file|
      file << open(a.authenticated_开发者_Go百科url()).read
      attachments[a.attachment_file_name] = File.read("#{Rails.root.to_s}/tmp/#{a.attachment_file_name}")
    end
  end
end

mail( :to => "#{XXXX}", 
      :reply_to => "XXXXX>", 
      :subject => "XXXXXX"
      )

a.authenticated_url() just gives me a URL to s3 to get the file (of any type), I checked this, works fine. Something to do with the way I'm saving the tempfile must be breaking the ActionMailer Attachment.

Any ideas?

This might work better because it doesn't touch the filesystem (which is often problematic on Heroku):

require 'net/http'
require 'net/https' # You can remove this if you don't need HTTPS
require 'uri'

class UserMailer < ActionMailer::Base
  # Add Attachments if any
  if @comment.attachments.count > 0
    @comment.attachments.each do |a|
      # Parse the S3 URL into its constituent parts
      uri = URI.parse a.authenticated_url
      # Use Ruby's built-in Net::HTTP to read the attachment into memory
      response = Net::HTTP.start(uri.host, uri.port) { |http| http.get uri.path }
      # Attach it to your outgoing ActionMailer email
      attachments[a.attachment_file_name] = response.body
    end
  end
end

I don't think this will cause any extra memory issues because in any case you have to load the file's data into memory on the attachments[a.attachment_file_name] line.