Receipt PDFs in Django

Why receipts become PDFs

A receipt is proof a payment happened, and customers attach it to expense claims. It has to survive being forwarded, printed and filed by someone who never had an account with you. That is the difference between a document and a view of a database, and it is why ecommerce and point-of-sale teams keep asking for this.

What a receipt has to carry

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

• the payment reference from the processor, which is what a dispute is traced by
• the amount actually captured, which is not always the amount ordered
• the payment method, usually the card brand and last four digits
• the timestamp with a timezone, since expense systems reconcile by date
• the merchant legal name, which may differ from the brand on the site

Turning your the Django template language template into a document

You already have the markup. Render_to_string("invoices/detail.html", context) gives you it as a string, which is the only input the render needs. Django resolves {% static %} to a path relative to STATIC_URL, which means the stylesheet URL in your rendered HTML is only meaningful to a browser that already has a session on your host. A renderer fetching it from outside gets a 404 and produces an unstyled document. Inline the CSS into the string you send, or make STATIC_URL absolute for this one code path.

The Django implementation

httpx is the client most projects here already have. The render happens in a view that returns FileResponse, and you hand the bytes back as a FileResponse with an explicit content type.

# views.py
import httpx
from django.conf import settings
from django.http import FileResponse
from django.shortcuts import get_object_or_404
from django.template.loader import render_to_string

from .models import Receipt


def receipt_pdf(request, pk):
    receipt = get_object_or_404(Receipt, pk=pk)

    # A template that extends nothing. The on-screen template carries base.html,
    # the nav and the messages block, none of which belong in a receipt.
    html = render_to_string("receipts/pdf.html", {"receipt": receipt})

    upstream = httpx.stream(
        "POST",
        "https://api.pdfpipe.xyz/v1/pdf",
        headers={"Authorization": f"Bearer {settings.PDFPIPE_KEY}"},
        json={"html": html, "options": {"format": "A4", "printBackground": True}},
        timeout=60.0,
    )

    response = upstream.__enter__()
    response.raise_for_status()

    return FileResponse(
        response.iter_bytes(),
        content_type="application/pdf",
        filename=f"receipt-{receipt.reference}.pdf",
    )

The CSS that makes a receipt page correctly

The layout problem specific to this document is that receipts are short and usually want a narrow page, so the default A4 canvas leaves an expanse of white unless the page size is set deliberately. These rules handle it.

/* A receipt on A4 is mostly white space. Set the page to the
   content, and let it grow only as far as the items require. */
@page {
  size: 80mm 200mm;
  margin: 6mm;
}

body { font-size: 11px; }

What goes wrong in Django

The template that renders your on-screen view is almost always the wrong one to send. It carries the base layout, the nav, and the messages framework, all of which land in the PDF. Render a template that extends nothing, and keep it beside the view template so the two do not drift.

What people try first

Most Django projects reach for WeasyPrint or xhtml2pdf, both of which put layout in your Python process. WeasyPrint needs Cairo and Pango in the image; xhtml2pdf supports a subset of CSS that stopped growing 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 receipt lives afterwards

Rendering is the short part. The customer keeps it, not you, and they submit it to an expense system months later. It has to be readable by software that never saw your site, which is why the amount and reference belong in selectable text rather than inside an image.

Getting the document right

• Check the amount paid and the payment reference, which is what an expense system matches against.
• Generation is triggered by a successful payment webhook, so size the timeout for that path rather than for a health check.
• Volume arrives in bursts, so queue the render rather than doing it inside the request that triggered it.
• 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 Django documents, and the same receipt in other stacks.