Payslip PDFs in Ruby

Why payslips become PDFs

A payslip is a personal financial record an employee keeps, uses to apply for credit, and expects to be able to open years later. That is the difference between a document and a view of a database, and it is why HR and payroll teams keep asking for this.

What a payslip has to carry

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

• gross pay, itemised by basic, overtime and any allowances
• each deduction named separately with its own amount
• net pay, which is the number the employee checks first
• year-to-date totals for gross, tax and net
• the pay period and the payment date, which are not the same day
• the employee identifier and tax reference

The Ruby 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 the right type and disposition.

require "net/http"
require "json"

class PayslipsController < ApplicationController
  def show
    html = render_to_string(template: "payslips/show", layout: "pdf")

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

    response = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) do |http|
      http.request(request)
    end

    # Net::HTTP hands back ASCII-8BIT. Do not re-encode it.
    send_data response.body,
              type: "application/pdf",
              disposition: "inline",
              filename: "#{params[:id]}.pdf"
  end
end

The CSS that makes a payslip page correctly

The layout problem specific to this document is that gross, deductions and net must be visible together without scrolling or breaking, on one page, every time. These rules handle it.

/* Gross, deductions and net have to be visible together. One page,
   every time, regardless of how many deduction lines there are. */
.payslip { break-inside: avoid; }
.summary { break-inside: avoid; }

@page { size: A4; margin: 15mm; }

What goes wrong in Ruby

Net::HTTP returns a String with ASCII-8BIT encoding. Do not run it through anything that assumes UTF-8, or the PDF arrives corrupted with no error anywhere to explain it.

What people try first

Most Ruby projects reach for wkhtmltopdf via wicked_pdf, which needs a system binary on every machine and is built on a Qt WebKit fork that stopped tracking the web years ago. 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 payslip lives afterwards

Rendering is the short part. Payslips are personal financial records the employee will need for credit applications and tax filings for years. Employers commonly retain them for six years, and employees expect to be able to download an old one long after they have left.

Getting the document right

• Check net pay and the deduction breakdown, which is what an employee checks first and complains about immediately.
• Generation is triggered by a payroll run, producing every employee's document at once, so size the timeout for that path rather than for a health check.
• This is a batch shape: render the run through the batch endpoint rather than firing thousands of individual requests.
• 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 documents, and the same payslip in other stacks.