restpdf.rb

require 'json'  
require 'base64'
require 'tempfile'
require 'sinatra'
require 'pdfkit'

# HTTP Status Codes
OK, BAD_REQUEST, UNAUTHORIZED, INTERNAL_SERVER_ERROR = 200, 400, 401, 500

# service is up and running
get '/' do
  status OK
end

# accpets json html and parameters, returns pdf
post '/' do  
  begin
    # parse json contents into variables
    body = JSON.parse(request.body.read)
    html, footer, token, options = body['content'], body['footer'], body['token'], body['options']
    html = html.nil? ? raise(ArgumentError, 'content missing') : Base64.strict_decode64(html)
    footer = footer.nil? ? false : Base64.strict_decode64(footer)

    # authentication via token
    unless token.nil? ? raise(ArgumentError, 'token missing') : token == ENV['TOKEN']
      halt UNAUTHORIZED, { error: "invalid token" }.to_json # answer client
    end

    # error handling and logging
  rescue ArgumentError, JSON::ParserError => e # empty content, invalid json or base64
    puts e.inspect # log message
    halt BAD_REQUEST, { error: "#{e.message}" }.to_json 

  rescue => e # something else happened
    puts e.inspect, e.backtrace 
    halt INTERNAL_SERVER_ERROR 
  end

  options = options.nil? ? {} : options

  if footer # wktohtml accepts footer only as file
    tmp = Tempfile.new(['footer', '.html'])
    tmp << footer; tmp.rewind; tmp.close
    options['footer-html'] = tmp.path
  end

  status OK
  PDFKit.new(html, options).to_pdf
end