Generating a PDF With Images from Base64 with Prawn - ruby-on-rails

Question

I am trying to save multiple pngs in one pdf. I'm receiving the PNGs from an API Call to the Endicia Label Server, which is giving me a Base64 Encoded Image as response.
Based on this Question:
How to convert base64 string to PNG using Prawn without saving on server in Rails
def batch_order_labels
#orders = Spree::Order.ready_to_ship.limit(1)
dt = Date.current.strftime("%d %b %Y ")
title = "Labels - #{dt} - #{#orders.count} Orders"
Prawn::Document.generate("#{title}.pdf") do |pdf|
#orders.each do |order|
label = order.generate_label
if order.international?
#image = label.response_body.scan(/<Image PartNumber=\"1\">([^<>]*)<\/Image>/imu).flatten.last
else
#image = label.image
end
file = Tempfile.new('labelimg', :encoding => 'utf-8')
file.write Base64.decode64(#image)
file.close
pdf.image file
pdf.start_new_page
end
end
send_data("#{title}.pdf")
end
But I'm receiving following error:
"\x89" from ASCII-8BIT to UTF-8
Any Idea?

Answer 1

There's no need to write the image data to a tempfile, Prawn::Document#image can accept a StringIO.
Try replacing this:
file = Tempfile.new('labelimg', :encoding => 'utf-8')
file.write Base64.decode64(#image)
file.close
pdf.image file
With this:
require 'stringio'
.....
image_data = StringIO.new( Base64.decode64(#image) )
pdf.image(image_data)

Answer 2

The Problem is, that the Api is returning this thing in UTF-8 - So I dont have a great choice.
Anyhow, I found this solution to be working
file = Tempfile.new('labelimg', :encoding => 'utf-8')
File.open(file, 'wb') do |f|
f.write Base64.decode64(#image)
end

Answer 3

you can't convert the Base64 to UTF-8.
Leave it as plain ASCII:
file = Tempfile.new('labelimg', :encoding => 'ascii-8bit')
file.write Base64.decode64(#image)
file.close
or even better - leave it as binary:
file = Tempfile.new('labelimg')
file.write Base64.decode64(#image)
file.close
UTF-8 is multibite format and it's not usable for transferring binary data such as pics.