Using Rails Paperclip gem to preprocess file before saving - ruby-on-rails

Question

I'm using the Paperclip gem on a Rails 3.2 app where users can upload a specialized file type that contains an image and other information (let's call it a ".elf" file).
I've written all the code needed to extract an image from an elf file via a class called ElfObject, and this works well when tested in the app's console. What I want to do is extract the image and other data from the .elf file before Paperclip saves it to AWS S3, store the other data in the model, and then save just the image object as the Paperclip attachment on S3. Here's the relevant code in the model:
class Photo < ActiveRecord::Base
validates_attachment :attachment,
:presence => true
has_attached_file :attachment,
:storage => :s3,
[[S3 credentials removed]]
before_attachment_post_process :import_photo
attr_accessible :name, :attachment, :properties
def import_photo
if attachment_file_name =~ %r{^*\.elf$}
origfile = attachment.queued_for_write
elf = ElfObject.read(origfile)
properties = elf.get_properties
attachment = elf.image.write "image_for_#{attachment_file_name}.png"
save!
end
end
When I try to upload this way on the app, it raises the error ArgumentError (Invalid argument 'file'. Expected String, got Hash.) from the line elf = ElfObject.read(origfile). If I try something like elf = ElfObject.read(origfile.path), I get NoMethodError (undefined method `path' for #).
Clearly, I'm not fully understanding how to access the file from Paperclip prior to it being posted--any ideas on where I'm going wrong and how to fix it?

Answer 1

It seems like the problem is exactly what the error is saying... that origfile is a Hash, rather than a String.
If that is the case then attachment.queued_for_write returns a Hash, which means you need to find the key that holds the file path string.
origfile = attachment.queued_for_write
p origfile.inspect #print it out so you can figure out what key holds the path
Edited answer try this:
def import_photo
if attachment_file_name =~ %r{^*\.elf$}
origfile = attachment.queued_for_write[:original]
elf = ElfObject.read(origfile.path)
properties = elf.get_properties
attachment = elf.image.write "image_for_#{attachment_file_name}.png"
save!
end
end