Today I Learned

A JetRockets project

2 posts about #rails

Usage image files from S3 in WickedPdf

If you need to use image files from S3 in your generated pdf file using WickedPdf, then you need to first upload the image. You can create method that does this and add it to the helper.

require 'open-uri'

module PdfHelper
  def embed_remote_image(url, content_type)
    asset = open(url, "r:UTF-8", &:read)
    base64 = Base64.encode64(asset.to_s).gsub(/\s+/, "")
    "data:#{content_type};base64,#{Rack::Utils.escape(base64)}"
  end
end

And use image_tag instead of wicked_pdf_image_tag

= image_tag embed_remote_image(file.logo_url, 'image/jpeg')

How to implement inheritance in Grape resources?

Grape uses specific DSL to define endpoints in API, that’s why you can’t use base class’ instance methods in descendant resources. But there’s one trick:

There’s an #inherited class method in Ruby which is triggered every time some class inherits from ancestor class. It passes one argument - descendant class. Calling descendant’s #instance_eval method we can place any useful stuff inside a block: methods, helpers, before-do’s, etc, in this way evaluating it in context of subclass.

class Base < Grape::API
  def self.inherited(subclass)
    super

    subclass.instance_eval do
      helpers do
        def current_user
          @current_user ||= User.find(params[:user_id])
        end
      end
      # ...
    end 
  end
end

class DocumentsResource < Base
  post '/documents' do
    @document = current_user.documents.build
    # ...
  end
end

Note that it’s not real inheritance because Base class has not methods defined inside subclass#instance_eval block.