Uploading PDF with Prawn and Carrierwave without saving the file on disk

I generate a PDF file for an invoice in a background job and I want to attach it to the invoice. I use Carrierwave for file uploads but here I do not upload it from the UI. I would like to be able to attach the file without saving it on disk.

invoice.rb

mount_uploader :file, InvoiceFileUploader

background job

class GeneratePdfJob < ApplicationJob
  queue_as :default

  def perform(invoice)
    pdf = InvoiceServices::PdfGenerator.new(invoice)
    file_name = [invoice.number.gsub('/','-'), invoice.due_date.to_s, SecureRandom.urlsafe_base64].join('-') + '.pdf'
    pdf.render_file(file_name)
    file = File.new(file_name)
    invoice.file = file
    File.delete(file_name)
  end
end

So right now I call render_file method to actually create the file but this file gets saved in the root folder of my application so I need to delete it afterwards. Is there a better way? Is there a way to attach the file without actually saving it on disk?

Solution

what you are trying to archive is really impressive. Thanks for the idea. this will reduce lots of disk IO-related issues in PDF generation.

1st: Renders the PDF document to a string

instead of render_file method use Prawn::Document#rendermethod which returns string representation of the PDF.

2nd: use that string to upload to carrier wave without any tempory file.

# define class that extends IO with methods that are required by carrierwave
class CarrierStringIO < StringIO
  def original_filename
    "invoice.pdf"
  end

  def content_type
    "application/pdf"
  end
end

class InvoiceFileUploader < CarrierWave::Uploader::Base
  def filename
    [model.number.gsub('/','-'), model.due_date.to_s, SecureRandom.urlsafe_base64].join('-') + '.pdf'
  end
end

class Invoice
  mount_uploader :file, InvoiceFileUploader

  def pdf_data=(data)
    self.file = CarrierStringIO.new(data)
  end
end

class GeneratePdfJob < ApplicationJob
  queue_as :default

  def perform(invoice)
    pdf = InvoiceServices::PdfGenerator.new(invoice)        
    invoice.pdf_data = pdf.render
  end
end