pdfkit无法从cdn rails 4.2 pdfkit渲染图像

我正在尝试使用pdfkit将显示图像从facebook cdn转换为pdf的html页面 . 我使用rails 4.2，pdfkit 0.6.2和wkhtmltopdf-binary 0.9.9.3 .

# Gemfile
gem 'pdfkit'
gem 'wkhtmltopdf-binary'

# controller
def generate_pdf
  @booklet = Booklet.find params[:id]
  @cover = Image.last
  @images = @booklet.images.sort_by(&:uploaded_at)
  respond_to do |format|
    format.html
    format.pdf do
      html = render_to_string(layout: true , action: "generate_pdf.html.haml")
      kit = PDFKit.new(html, page_size: 'A4', print_media_type: true)
      kit.stylesheets << "#{Rails.root}/app/assets/stylesheets/application.scss"
      pdf = kit.to_pdf
      send_data pdf, filename: 'booklet.pdf', type: 'application/pdf', disposition: 'inline'
    end
  end
end

# application.scss
@import 'bootstrap';                                                                                                                                           
@import 'custom';
@import 'jquery.booklet';
@import 'bootstrap-datepicker3';

# haml
= link_to 'Download Booklet', generate_pdf_booklet_path(@booklet, format: 'pdf'), class: 'btn btn-primary'

# config/application.rb
require 'pdfkit'
config.middleware.use PDFKit::Middleware

# config/initializers/mime_types.rb
Mime::Type.register "application/pdf", :pdf unless Mime::Type.lookup_by_extension(:pdf)

示例facebook cdn image urls是https://scontent.xx.fbcdn.net/hphotos-prn2/v/t1.0-9/s720x720/560041_10200752471482799_613254552_n.jpg?oh=900fe52ecc9b93e044cae4917f538626&oe=559F41E9和https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-xap1/t31.0-8/s720x720/906468_10201023370815113_668460846_o.jpg

当我发送pdf请求时，我在服务器日志上得到以下输出

Rendered booklets/generate_pdf.html.haml within layouts/application   (671.3ms)
QSslSocket: cannot resolve SSLv2_client_method
QSslSocket: cannot resolve SSLv2_server_method
QAbstractSocket::connectToHost() called when already looking up or connecting/connected to "fbcdn-sphotos-e-a.akamaihd.net"
QAbstractSocket::connectToHost() called when already looking up or connecting/connected to "fbcdn-sphotos-e-a.akamaihd.net"
QSslSocket::connectToHostEncrypted() called when already  connecting/connected
QSslSocket::connectToHostEncrypted() called when already connecting/connected
QAbstractSocket::connectToHost() called when already looking up or connecting/connected to "fbcdn-sphotos-b-a.akamaihd.net"
QAbstractSocket::connectToHost() called when already looking up or connecting/connected to "fbcdn-sphotos-b-a.akamaihd.net"
QSslSocket::connectToHostEncrypted() called when already connecting/connected
QAbstractSocket::connectToHost() called when already looking up or connecting/connected to "fbcdn-sphotos-f-a.akamaihd.net"
QAbstractSocket::connectToHost() called when already looking up or connecting/connected to "fbcdn-sphotos-c-a.akamaihd.net"
Rendered text template (0.0ms)
Sent data booklet.pdf (1.4ms)

pdf正在生成，但本 Map 像（app / assets / images）和cdn图像不会在pdf中呈现 . 此外，样式表不适用于pdf . 我错过了什么？

为上述问题创建了一个示例存储库 . 这里：https://github.com/prasadsurase/topdf