Statement PDFs in Ruby on Rails

Why statements become PDFs

A statement summarises a period that is now closed. Regenerating it later from live data would produce a different document, which defeats the point. That is the difference between a document and a view of a database, and it is why finance and account management keep asking for this.

What a statement has to carry

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

• the opening balance and the closing balance
• every transaction in the period with date, description and signed amount
• a running balance column, so a reader can find where a discrepancy starts
• the account identifier, usually masked
• the statement period, which must not overlap the previous one

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/statements_controller.rb
require "net/http"

class StatementsController < ApplicationController
  def pdf
    statement = Statement.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: "statements/pdf",
      layout: false,
      assigns: { statement: statement },
    )

    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: "statement-#{statement.reference}.pdf",
              type: "application/pdf",
              disposition: "attachment"
  end
end

The CSS that makes a statement page correctly

The layout problem specific to this document is that a long transaction table spanning many pages, needing repeated headers and a running balance that stays legible after a break. These rules handle it.

/* Line items run past one page. Repeat the header, keep the
   totals block whole, and never strand a single row. */
thead { display: table-header-group; }
tfoot { display: table-footer-group; }
tr    { break-inside: avoid; }

.totals {
  break-inside: avoid;
  break-before: auto;
}

@page {
  size: A4;
  margin: 18mm 16mm 22mm;
}

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 statement lives afterwards

Rendering is the short part. Statements are the document most often requested again years later, usually for a loan application or an audit. Regenerating one from current data would produce different figures, so the rendered file is the record and has to be stored as issued.

Getting the document right

• Check the closing balance, which has to reconcile with the transactions listed above it.
• Generation is triggered by the end of a billing or accounting period, 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 on Rails documents, and the same statement in other stacks.