这是一个工作帮助

Question

我想将网页呈现为PDF格式。它使用单个图像，我已经读过你需要提供PDFkit的绝对URL才能使用图像，所以我的代码是：

= image_tag image_url(user.avatar)

这在以HTML格式查看时有效，并且PDFkit能够在删除图像的情况下生成PDF。但是，在使用图像时，它会挂起，直到我杀死服务器。我怎样才能让它发挥作用？

这是杀死服务器时的完整输出：

2013-12-04 13:53:36.576 wkhtmltopdf[27410:507] CoreText performance note: Client called CTFontCreateWithName() using name "Arial" and got font with PostScript name "ArialMT". For best performance, only use PostScript names when calling this API.
2013-12-04 13:53:36.577 wkhtmltopdf[27410:507] CoreText performance note: Set a breakpoint on CTFontLogSuboptimalRequest to debug.
2013-12-04 13:53:36.582 wkhtmltopdf[27410:507] CoreText performance note: Client called CTFontCreateWithName() using name "Arial" and got font with PostScript name "ArialMT". For best performance, only use PostScript names when calling this API.
2013-12-04 13:53:36.584 wkhtmltopdf[27410:507] CoreText performance note: Client called CTFontCreateWithName() using name "Arial" and got font with PostScript name "ArialMT". For best performance, only use PostScript names when calling this API.
^C
RuntimeError - command failed: /usr/local/bin/wkhtmltopdf --page-size Legal --print-media-type --quiet - -:
  pdfkit (0.5.4) lib/pdfkit/pdfkit.rb:73:in `to_pdf'
  pdfkit (0.5.4) lib/pdfkit/middleware.rb:21:in `call'
  warden (1.2.3) lib/warden/manager.rb:35:in `block in call'
  warden (1.2.3) lib/warden/manager.rb:34:in `catch'
  warden (1.2.3) lib/warden/manager.rb:34:in `call'
  rack (1.5.2) lib/rack/etag.rb:23:in `call'
  rack (1.5.2) lib/rack/conditionalget.rb:25:in `call'
  rack (1.5.2) lib/rack/head.rb:11:in `call'
  actionpack (4.0.0) lib/action_dispatch/middleware/params_parser.rb:27:in `call'
  actionpack (4.0.0) lib/action_dispatch/middleware/flash.rb:241:in `call'
  rack (1.5.2) lib/rack/session/abstract/id.rb:225:in `context'
  rack (1.5.2) lib/rack/session/abstract/id.rb:220:in `call'
  actionpack (4.0.0) lib/action_dispatch/middleware/cookies.rb:486:in `call'
  activerecord (4.0.0) lib/active_record/query_cache.rb:36:in `call'
  activerecord (4.0.0) lib/active_record/connection_adapters/abstract/connection_pool.rb:626:in `call'
  activerecord (4.0.0) lib/active_record/migration.rb:369:in `call'
  actionpack (4.0.0) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
  activesupport (4.0.0) lib/active_support/callbacks.rb:373:in `_run__4124003592524659480__call__callbacks'
  activesupport (4.0.0) lib/active_support/callbacks.rb:80:in `run_callbacks'
  actionpack (4.0.0) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
  actionpack (4.0.0) lib/action_dispatch/middleware/reloader.rb:64:in `call'
  actionpack (4.0.0) lib/action_dispatch/middleware/remote_ip.rb:76:in `call'
  better_errors (1.0.1) lib/better_errors/middleware.rb:84:in `protected_app_call'
  better_errors (1.0.1) lib/better_errors/middleware.rb:79:in `better_errors_call'
  better_errors (1.0.1) lib/better_errors/middleware.rb:56:in `call'
  actionpack (4.0.0) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
  actionpack (4.0.0) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
  railties (4.0.0) lib/rails/rack/logger.rb:38:in `call_app'
  railties (4.0.0) lib/rails/rack/logger.rb:21:in `block in call'
  activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `block in tagged'
  activesupport (4.0.0) lib/active_support/tagged_logging.rb:25:in `tagged'
  activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `tagged'
  railties (4.0.0) lib/rails/rack/logger.rb:21:in `call'
  actionpack (4.0.0) lib/action_dispatch/middleware/request_id.rb:21:in `call'
  rack (1.5.2) lib/rack/methodoverride.rb:21:in `call'
  rack (1.5.2) lib/rack/runtime.rb:17:in `call'
  activesupport (4.0.0) lib/active_support/cache/strategy/local_cache.rb:83:in `call'
  rack (1.5.2) lib/rack/lock.rb:17:in `call'
  actionpack (4.0.0) lib/action_dispatch/middleware/static.rb:64:in `call'
  railties (4.0.0) lib/rails/engine.rb:511:in `call'
  railties (4.0.0) lib/rails/application.rb:97:in `call'
  rack (1.5.2) lib/rack/content_length.rb:14:in `call'
  thin (1.6.0) lib/thin/connection.rb:82:in `block in pre_process'
  thin (1.6.0) lib/thin/connection.rb:80:in `catch'
  thin (1.6.0) lib/thin/connection.rb:80:in `pre_process'
  thin (1.6.0) lib/thin/connection.rb:55:in `process'
  thin (1.6.0) lib/thin/connection.rb:41:in `receive_data'
  eventmachine (1.0.3) lib/eventmachine.rb:187:in `run_machine'
  eventmachine (1.0.3) lib/eventmachine.rb:187:in `run'
  thin (1.6.0) lib/thin/backends/base.rb:73:in `start'
  thin (1.6.0) lib/thin/server.rb:162:in `start'
  rack (1.5.2) lib/rack/handler/thin.rb:16:in `run'
  rack (1.5.2) lib/rack/server.rb:264:in `start'
  railties (4.0.0) lib/rails/commands/server.rb:84:in `start'
  railties (4.0.0) lib/rails/commands.rb:78:in `block in <top (required)>'
  railties (4.0.0) lib/rails/commands.rb:73:in `tap'
  railties (4.0.0) lib/rails/commands.rb:73:in `<top (required)>'
  bin/rails:4:in `require'
  bin/rails:4:in `<main>'

Answer 1

这是一个臭名昭着的问题，你正在遇到它，因为你的HTML中可能有相对链接的资产（即图像，CSS，JS，字体等），而你的网络服务器只能处理一个请求/一次线程（如WEBrick）。

那会发生什么？当您请求其URL时，服务器开始生成PDF。 PDFkit查找链接的资产，因此它尝试从服务器加载此资产，该服务器恰好与运行PDFkit的服务器相同。但是，服务器的单线程已经忙于运行PDFkit，因此它无法“释放”来提供所请求的资产。总而言之，这是一个僵局--PDFkit正在等待等待PDFkit完成处理的同一台服务器上的资产，以便它可以将资产提供给PDFkit ......

解决方案：Base64-embed your assets in the HTML，以便PDFkit不需要提出任何其他请求（我个人首选的解决方案），或暂时将资产卸载到另一台服务器（例如临时AWS）桶）。您也可以尝试使用启用了多线程的unicorn或Thin网络服务器，或在config.threadsafe!中添加in application.rb，但无法保证这些方法可以正常使用。< / p>

当然，这些黑客攻击（嵌入资源或托管其他地方）只应该在开发环境中使用 - 你不应该在生产中遇到这些问题，因为实时服务器应该（希望）能够处理多个GET请求。

Answer 2

您可以在开发中使用unicorn，一次提供多个请求。并且易于设置。参考 http://dave.is/unicorn.html和 https://devcenter.heroku.com/articles/rails-unicorn

它解决了我在开发中的问题。

Answer 3

这是一个工作帮助

阿尔曼的回答给了我很多帮助。这是我提出的一个实现。

module PdfHelper

  def pdf_image_tag(image_name)
    if Rails.env.development? || Rails.env.test?
      # Unless running a web server that can process 2 requests at the same
      # time, trying to insert an image in a PDF creates a deadlock: the server
      # can't finish processing the PDF request until it gets the image, but it
      # can't start processing the image request until it has finished
      # processing the PDF request.
      # This will not be a problem in production, but in dev, a workaround is
      # to base64 the image and insert its contents into the HTML
      image_data = Rails.application.assets[image_name].to_s
      image_tag "data:image/png;base64,#{::Base64.encode64(image_data)}"
    else
      image_tag image_name
    end
  end

end

Answer 4

您收到此错误是因为默认情况下WEBrick是一个单线程服务器，并且能够一次完成一个请求（因为单个工作线程）。要在Rails 4.0中使WEBrick完全多线程化，只需将其添加到config/initializers/multithreaded_webrick.rb：

# Remove Rack::Lock so WEBrick can be fully multi-threaded.
require 'rails/commands/server'

class Rails::Server
  def middleware
    middlewares = []
    middlewares << [Rails::Rack::Debugger] if options[:debugger]
    middlewares << [::Rack::ContentLength]

    Hash.new middlewares
  end
end

在您的application.rb

中添加config.middleware.delete 'Rack::Lock'

生成带有图像的pdf时，PDFkit会挂起

4 个答案:

这是一个工作帮助