Contract PDFs in Ruby on Rails

Why contracts become PDFs

A contract has to be fixed at signature. Both parties need to be certain they are looking at identical words, which a rendered page cannot guarantee. That is the difference between a document and a view of a database, and it is why legal and sales operations keep asking for this.

What a contract has to carry

Before any of the code below matters, the template has to produce a document that is actually a contract. These are the fields that make it one, and the ones a reader or an auditor will look for first.

• the parties, by legal entity name and registered number
• the effective date and the term
• numbered clauses with stable numbering, since amendments reference them
• the commercial schedule, usually as an annexe rather than in the body
• signature blocks with name, title and date for each party

Turning your ERB template into a document

You already have the markup. Render_to_string(template: "invoices/pdf", layout: false) gives you it as a string, which is the only input the render needs. stylesheet_link_tag emits a digested path like /assets/application-9a2f.css, which only exists on your host. For a renderer that does not share your origin, either inline the stylesheet with Rails.application.assets or point at an absolute URL on a public CDN.

The Ruby on Rails implementation

Net::HTTP ships with the runtime, so this adds no dependency. The render happens in a controller action using send_data, and you send_data with type: "application/pdf".

# app/controllers/contracts_controller.rb
require "net/http"

class ContractsController < ApplicationController
  def pdf
    contract = Contract.find(params[:id])

    # layout: false is not optional. Without it the application layout wraps the
    # document and your site navigation prints across the top of page one.
    html = render_to_string(
      template: "contracts/pdf",
      layout: false,
      assigns: { contract: contract },
    )

    uri = URI("https://api.pdfpipe.xyz/v1/pdf")
    request = Net::HTTP::Post.new(uri)
    request["Authorization"] = "Bearer #{Rails.application.credentials.pdfpipe_key}"
    request["Content-Type"] = "application/json"
    request.body = {
      html: html,
      options: { format: "A4", printBackground: true },
    }.to_json

    upstream = Net::HTTP.start(uri.host, uri.port, use_ssl: true, read_timeout: 60) do |http|
      http.request(request)
    end

    # ASCII-8BIT, and it must stay that way. Anything that assumes UTF-8 here
    # corrupts the file with no error to explain it.
    send_data upstream.body,
              filename: "contract-#{contract.reference}.pdf",
              type: "application/pdf",
              disposition: "attachment"
  end
end

The CSS that makes a contract page correctly

The layout problem specific to this document is that numbered clauses with cross-references, where a page break in the wrong place separates a clause from the term it defines. These rules handle it.

/* A clause must not be separated from the term it defines, and a
   signature block alone on a final page invites a dispute. */
.clause     { break-inside: avoid; }
.signatures { break-inside: avoid; break-before: avoid; }

p { orphans: 3; widows: 3; }

@page { size: A4; margin: 25mm 20mm; }

What goes wrong in Ruby on Rails

Forgetting layout: false is the single most common mistake here. Without it the application layout wraps the document, and the PDF arrives with your site navigation printed across the top of page one.

What people try first

Most Ruby on Rails projects reach for wicked_pdf, which shells out to wkhtmltopdf, or Prawn, which is excellent but means describing the document in Ruby drawing calls rather than in HTML you already have. That works until it is running on more than one machine, at which point the browser becomes the thing you operate rather than the thing you use.

Where the contract lives afterwards

Rendering is the short part. A contract is retained for the term plus the limitation period, which typically means well over a decade. Immutability matters more here than anywhere else on this list: both parties must be able to prove the words have not moved.

Getting the document right

• Check the parties and the effective date, which is what every later dispute turns on.
• Generation is triggered by agreement being reached, often with a signature workflow following, so size the timeout for that path rather than for a health check.
• These are produced one at a time by a person who is waiting, so latency is felt directly.
• Backgrounds are painted by default here, so a design that uses colour needs nothing set. Only an explicit print_background of false turns them off.

Frequently asked

Related

Other Ruby on Rails documents, and the same contract in other stacks.