Instantiate image in rails 3.1 app then upload to S3 with paperclip

I'm creating a barcode .png in a callback using the Barby gem:

Isbn.rb:

before_save :barcode

def barcode
   barcode = Barby::Bookland.new(self.productidentifier_idvalue)
   my_bc = Barcodeimg.new(:isbn_id => self.id)
   my_bc.image = File.open("#{self.productidentifier_idvalue}-barcode.png", 'w')  do |f|
    f.write barcode.to_png
  end
   my_bc.save!
end

Then I'm hoping to upload it directly to S3 via paperclip: here's the Barcodeimg.rb model:

  require 'open-uri'
  require "aws/s3"
class Barcodeimg < ActiveRecord::Base

     has_attached_file :image,

                 :storage => :s3,
                 :s3_credentials => "#{Rails.root}/config/s3.yml",
                 :s3_protocol => "https",
                 :path => ":class/:id/:basename_:style.:extension",
                 :bucket => "bucketname",
                 :url  => ":s3_eu_url"
end

I know the credentials work as I'm using the exact same settings in another model. Any idea what I'm doing wrong? A new Barcodeimg instance is being saved, but without the attachment. There are no error messages - just no image appearing on S3! From the stack trace:

  SQL (1.8ms)  INSERT INTO "barcodei开发者_运维百科mgs" ( "created_at", "image_content_type", "image_file_name", "image_file_size", "image_remote_url", "isbn_id", "updated_at", "user_id") VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?) ["created_at", Tue, 30 Aug 2011 20:26:20 UTC +00:00], ["image_content_type", nil], ["image_file_name", nil], ["image_file_size", nil], ["image_remote_url", nil], ["isbn_id", 7128], ["updated_at", Tue, 30 Aug 2011 20:26:20 UTC +00:00], ["user_id", nil]]
[paperclip] Saving attachments.

File.open will return the result of the block. Which means you're writing the length of the file to your attachment.

I would replace the block with:

f = File.open("#{self.productidentifier_idvalue}-barcode.png", 'w+')
f.write barcode.to_png
my_bc.image = f

Another problem could be the permissions of the current directory. Do you have the rights to write there?