PDF Generation Hangs Using PDFkit and Wkhtmotopdf

PDF Generation hangs using PDFKit and wkhtmotopdf

Turns out it had nothing to do with the cli and it was actually due to Jammit running in development. Disabling Jammit fixes the PDFkit hanging issue.

generating pdf hangs on rails 4 using PDFkit gem

The issue was due to stylesheet_link_tag and javascript_include_tag using relative URLs, which often causes wkhtmltopdf to hang when loading assets from the same server that wkhtmltopdf is running on.

Using absolute URLs for assets solved the problem.

Set asset_host in Rails' config, which also affects stylesheet_link_tag and javascript_include_tag:

# Modify asset host config setting in `config/application.rb`
# Or create a new initializer: `config/initializers/wkhtmltopdf.rb`
config.action_controller.asset_host = "http://mysite.com"

# Or you can have different hosts for development (local) and production (CDN):
# In `config/environments/development.rb`
config.action_controller.asset_host = "http://localhost"
# In `config/environments/production.rb`
config.action_controller.asset_host = "http://d111111abcdef8.cloudfront.net"

PDFKIT hangs while generating PDF in controller but not in console

Check https://github.com/pdfkit/pdfkit#troubleshooting

If you have some assets in that template that should be served by your local server, then in development in may hang depending on your server configuration. Your current request to render PDF "blocks" the server and it cannot respond to subsequent requests for assets (images, css, js). If possible, serve them from CDN, use multi-process server config in development etc.

PDFkit hangs when generating a pdf with an image

This is a notorious issue, and you're running into it because your probably have relatively linked assets in your HTML (i.e. images, CSS, JS, fonts, etc), and your web server is only capable of handling one request/thread at a time (like WEBrick).

So what happens? The server begins generating the PDF when you request its URL. PDFkit finds a linked asset, so it tries to load this asset from the server, which happens to be the same server that PDFkit is running on. However, the server's single thread is already busy running PDFkit, so it cannot "free up" to serve the requested asset. In conclusion, it's a deadlock -- PDFkit is awaiting on an asset on the same server that is waiting for PDFkit to finish up processing, so that it can serve the asset to PDFkit...

Solution: either Base64-embed your assets in the HTML so that PDFkit doesn't need to make any additional requests (my personally preferred solution), or temporarily offload the assets to another server (e.g. a temporary AWS bucket). You can also try using the unicorn or Thin webserver with multi-threading enabled, or adding config.threadsafe! in in application.rb, but there is no guarantee that these methods will work.

Of course, these hacks (embedding assets or hosting elsewhere) should only be used in the dev environment -- you shouldn't be running into these kinds of issues in production, as the live server should (hopefully) be able to handle multiple GET requests.

Why does PDFKit/wkhtmltopdf hang but renders PDF as expected when Rails app is killed?

The problem is with wkhtmltopdf itself, specifically, any version after 0.9.9. wkhtmltopdf hangs when run directly from the command-line.

Steps to correct:

brew uninstall wkhtmltopdf
cd /usr/local/Library/Formula/
git checkout 6e2d550 /usr/local/Library/Formula/wkhtmltopdf.rb
brew install wkhtmltopdf

Then verify the correct version is installed wkhtmltopdf --version which should yield wkhtmltopdf 0.9.9

Citations:

1. https://github.com/mileszs/wicked_pdf/issues/110
2. http://wearepandr.com/blog/article/homebrew-and-installing-old-package-versions#blog_nav

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