Grover

A Ruby gem to transform HTML into PDFs using Google Puppeteer and Chromium.

Installation

Add this line to your application's Gemfile:

gem 'grover'

Google Puppeteer

npm install puppeteer

Usage

# Grover.new accepts a URL or inline HTML and optional parameters for Puppeteer
grover = Grover.new('https://google.com', format: 'A4')

# Get an inline PDF
pdf = grover.to_pdf

# Options can be provided through meta tags
Grover.new('<html><head><meta name="grover-page_ranges" content="1-3"')
Grover.new('<html><head><meta name="grover-margin-top" content="10px"')

N.B.

options are underscore case, and sub-options separated with a dash
all options can be overwritten, including emulate_media and display_url

Relative paths

If calling Grover directly (not through middleware) you will need to either specify a display_url or modify your HTML by converting any relative paths to absolute paths before passing to Grover.

This can be achieved using the HTML pre-processor helper:

absolute_html = Grover::HTMLPreprocessor.process relative_html, 'http://my.server/', 'http'

This is important because Chromium will try and resolve any relative paths via the display url host. If not provided, the display URL defaults to http://example.com.

Why would you pre-process the HTML rather than just use the `display_url`

There are many scenarios where specifying a different host of relative paths would be preferred. For example, your server might be behind a NAT gateway and the display URL in front of it. The display URL might be shown in the header/footer, and as such shouldn't expose details of your private network.

If you run into trouble, take a look at the debugging section below which would allow you to inspect the page content and devtools.

Configuration

Grover can be configured to adjust the layout of the resulting PDF. For available options, see https://github.com/GoogleChrome/puppeteer/blob/v1.7.0/docs/api.md#pagepdfoptions

Also available are the emulate_media, cache and timeout options.

# config/initializers/grover.rb
Grover.configure do |config|
  config.options = {
    format: 'A4',
    margin: {
      top: '5px',
      bottom: '10cm'
    },
    prefer_css_page_size: true,
    emulate_media: 'screen',
    cache: false,
    timeout: 0 # Timeout in ms. A value of `0` means 'no timeout'
  }
end

Page URL for middleware requests (or passing through raw HTML)

If you want to have the header or footer display the page URL, Grover requires that this is passed through via the display_url option. This is because the page URL is not available in the raw HTML!

For Rack middleware conversions, the original request URL (without the .pdf extension) will be passed through and assigned to display_url for you. You can of course override this by using a meta tag in the downstream HTML response.

For raw HTML conversions, if the display_url is not provided http://example.com will be used as the default.

Header and footer templates

Should be valid HTML markup with following classes used to inject printing values into them:

date formatted print date
title document title
url document location
pageNumber current page number
totalPages total pages in the document

Middleware

Grover comes with a middleware that allows users to get a PDF view of any page on your site by appending .pdf to the URL.

Middleware Setup

Non-Rails Rack apps

# in config.ru
require 'grover'
use Grover::Middleware

Rails apps

# in application.rb
require 'grover'
config.middleware.use Grover::Middleware

Cover pages

Since the header/footer for Puppeteer is configured globally, displaying of front/back cover pages (with potentially different headers/footers etc) is not possible.

To get around this, Grover's middleware allows you to specify relative paths for the cover page contents via front_cover_path and back_cover_path either via the global configuration, or via meta tags. These paths (with query parameters) are then requested from the downstream app.

The cover pages are converted to PDF in isolation, and then combined together with the original PDF response, before being returned back up through the Rack stack.

N.B To simplify things, the same request method and body are used for the cover page requests.

# config/initializers/grover.rb
Grover.configure do |config|
  config.options = {
    front_cover_path: '/some/global/cover/page?foo=bar'
  }
end

Or via the meta tags in the original response:

<html>
  <head>
    <meta name="grover-back_cover_path" content="/back/cover/page?bar=baz" />
  </head>
  ...
</html>

Debugging

If you're having trouble with converting the HTML content, you can enable some debugging options to help. These can be enabled as global options via Grover.configure, by passing through to the Grover initializer, or using meta tag options.

debug: {
  headless: false,  # Default true. When set to false, the Chromium browser will be displayed
  devtools: true    # Default false. When set to true, the browser devtools will be displayed. 
}

N.B.

The headless option disabled is not compatible with exporting of the PDF.
If showing the devtools, the browser will halt resulting in a navigation timeout

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/Studiosity/grover.

Note that spec tests are appreciated to minimise regressions. Before submitting a PR, please ensure that:

$ rspec

and

$ rubocop

both succeed

Special mention

Thanks are given to the great work done in the PDFKit project. The middleware and HTML preprocessing components were used heavily in the implementation of Grover.

License

The gem is available as open source under the terms of the MIT License.

ss44/grover