How to convert Base64 string to pdf file using prawn gem - ruby-on-rails

Question

I want to generate pdf file from DB record. Encode it to Base64 string and store it to DB. Which works fine. Now I want reverse action, How can I decode Base64 string and generate pdf file again?
here is what I tried so far.
def data_pdf_base64
begin
# Create Prawn Object
my_pdf = Prawn::Document.new
# write text to pdf
my_pdf.text("Hello Gagan, How are you?")
# Save at tmp folder as pdf file
my_pdf.render_file("#{Rails.root}/tmp/pdf/gagan.pdf")
# Read pdf file and encode to Base64
encoded_string = Base64.encode64(File.open("#{Rails.root}/tmp/pdf/gagan.pdf"){|i| i.read})
# Delete generated pdf file from tmp folder
File.delete("#{Rails.root}/tmp/pdf/gagan.pdf") if File.exist?("#{Rails.root}/tmp/pdf/gagan.pdf")
# Now converting Base64 to pdf again
pdf = Prawn::Document.new
# I have used ttf font because it was giving me below error
# Your document includes text that's not compatible with the Windows-1252 character set. If you need full UTF-8 support, use TTF fonts instead of PDF's built-in fonts.
pdf.font Rails.root.join("app/assets/fonts/fontawesome-webfont.ttf")
pdf.text Base64.decode64 encoded_string
pdf.render_file("#{Rails.root}/tmp/pdf/gagan2.pdf")
rescue => e
return render :text => "Error: #{e}"
end
end
Now I am getting below error:
Encoding ASCII-8BIT can not be transparently converted to UTF-8.
Please ensure the encoding of the string you are attempting to use is
set correctly
I have tried How to convert base64 string to PNG using Prawn without saving on server in Rails but it gives me error:
"\xFF" from ASCII-8BIT to UTF-8
Can anyone point me what I am missing?

Answer 1

The answer is to decode the Base64 encoded string and either send it directly or save it directly to disk (naming it as a PDF file, but without using prawn).
The decoded string is a binary representation of the PDF file data, so there's no need to use Prawn or to re-calculate the content of the PDF data.
i.e.
raw_pdf_str = Base64.decode64 encoded_string
render :text, raw_pdf_str # <= this isn't the correct rendering pattern, but it's good enough as an example.
EDIT
To clarify some of the information given in the comments:
It's possible to send the string as an attachment without saving it to disk, either using render text: raw_pdf_str or the #send_data method (these are 4.x API versions, I don't remember the 5.x API style).
It's possible to encode the string (from the Prawn object) without saving the rendered PDF data to a file (save it to a String object instead). i.e.:
encoded_string = Base64.encode64(my_pdf.render)
The String data could be used directly as an email attachment, similarly to the pattern provided here only using the String directly instead of reading any data from a file. i.e.:
# inside a method in the Mailer class
attachments['my_pdf.pdf'] = { :mime_type => 'application/pdf',
:content => raw_pdf_str }