Bjørn Forsberg forsbergplustwo

Generating PDFs in Ruby, using Ferrum gem on Heroku

by Bjorn Forsberg

Ferrum is a pure Ruby gem, providing a high-level API to control Chrome, which runs headless by default. Ferrum is a great alternative to Node's Puppeteer library, which is a pain to use with Ruby and Heroku.

Ferrum can be used for any browser scripting work, as well as for generating screenshots and PDFs. We use it mainly for PDF generation, hosted on Heroku, and the setup flow goes like this:

Add Chromium locally if not already done: brew install chromium

Installing a Gem on Heroku from a Private GitHub Repo

Sometimes you want to use a gem on Heroku that is in a private repository on GitHub.

Using git over http you can authenticate to GitHub using basic authentication. However, we don't want to embed usernames and passwords in Gemfiles. Instead, we can use authentication tokens.

This method does not add your OAuth token to Gemfile.lock. It uses bundle config to store your credentials, and allows you to configure Heroku to use environment variables when deploying.

Generate an OAuth token from GitHub

	# # USAGE
	#
	# # Include the concern in the class
	# class Settings::CreateSetting
	# include SimpleServiceObject
	#
	# # optional: include validation
	# validates :shop, presence: true
	#
	# # mandatory: initialize the command with keyword arguments

	require 'json'

	class GraphqlResponseRubyfier
	def initialize(response)
	@response = JSON.parse(response)
	end

	def rubyfy
	rubyfied_response = to_o(@response)
	puts(rubyfied_response)

	require "ruby-boolean"
	class TypeValidator < ActiveModel::EachValidator
	def validate_each(record, attribute, value)
	value_to_test = type_before_coercion(record, attribute, value)
	expected_type = type_class(options[:with])

	record.errors.add attribute, (options[:message] \|\| "argument of #{record.class} is not of class: #{options[:with].to_s.camelize}. It is class: #{value.class} with value of #{value}") unless value_to_test.is_a?(expected_type)
	end

	private

	CollectionsQuery = <<~GRAPHQL
	{
	shop {
	name
	}
	collections(first: 15, sortKey: UPDATED_AT, reverse: true) {
	edges {
	node {
	id
	title

	!function() {
	var e = function(e) {
	var t = {
	exports: {}
	};
	return e.call(t.exports, t, t.exports),
	t.exports
	};
	e(function() {
	"use strict";

	# my_engine/my_engine.gemspec

	spec.add_dependency "importmap-rails", "~> 0.7.6"

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