Rails: Received string from web service should be converted to a pdf image to be displayed

Question

When using a web service I receive a string that looks like this:

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

Sorry for that.

Anyway, this should be a pdf because that was one of the request parameters. (I could also have chosen for .gif, or .jpg in different qualities.)

I tried reading the content, like this:

@label_binary = @response_label[:generate_label_response][:response_shipments][:response_shipment][:labels][:label][:content]

binary_data = Base64.decode64(@label_binary)
@label = File.open('file_name.pdf', 'wb') {|f| f.write(Base64.decode64(binary_data))}

But what this prints then as @label is just a number (three of four digits). Same when I use urlsafe_decode64.

Not very helpful.

Preferred end-result would be a pdf image file that I can immediately display (in this case a barcode on top of an invoice for sending a package). Could I for this purpose save the file temporarily? Meaning: every time I need to display I rebuild this image. I think that would be best.

EDIT

I am making the call now directly to a 600dpi .jpg image and then:

base_64_binary_data = @response_label[:generate_label_response][:response_shipments][:response_shipment][:labels][:label][:content]

@jpg_file = File.open('label.jpg', 'wb') do |file|
  content = Base64.decode64 base_64_binary_data
  file << content
end

This file shows up at my_apps_name/label.jpg. In my filesystem I can see the picture crystal clear.

In my view I then put:

<%= image_tag @jpg_file.path %>

When I inspect my html in the browser I see:

<img src="/images/label.jpg" alt="Label">

I suppose this is easily fixed, suggestions are still welcome of course, but...

..more importantly: What if this call is made several times at once. Will rails manage? Should I maybe save these images (to my S3) or build some kind of chronejob to manage it?

(I am not sure of the added value of mini_magic anymore, since I can see the .jpg being already there.)

Then on a complete side note, maybe better left for a separate question: what if the API on the other side fails?

Answer 1

Step one

decode http response

require "base64"

BASE_64_BINARY_DATA = "PASTE YOUR BIG STRING HERE"

pdf_file = File.open('your_pdf.pdf', 'wb') do |file|
  content = Base64.decode64 BASE_64_BINARY_DATA
  file << content
end

Step two

convert pdf file to an image

1. add to gemfile 'gem 'mini_magick' and use 'bundle install' command

2. put somewhere in your code

   require 'mini_magick'
   pdf = MiniMagick::Image.new(pdf_file.path)
   pdf.pages.first.write("preview.png")

image saved as preview.png

To display pdf image put in the view

<%= image_tag ("path_to_image/preview.jpg")%>