Packing slip PDFs in Express

Why packing slips become PDFs

A packing slip is printed and physically placed in a box. It exists to be paper. That is the difference between a document and a view of a database, and it is why warehouse and fulfilment teams keep asking for this.

What a packing slip has to carry

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

• the order reference, which the picker checks against the pick list
• each line with SKU, description and quantity shipped
• backordered lines shown explicitly rather than omitted
• the ship-to address as it will appear on the carton
• the carrier reference or tracking number where it exists

Turning your whichever view engine you configured, commonly EJS or Handlebars template into a document

You already have the markup. App.render("invoice", data, (err, html) => ...) gives you it as a string, which is the only input the render needs. app.render gives you the HTML string rather than writing it to a response, which is exactly what you want here. Note it is callback-based; promisify it once rather than nesting.

The Express implementation

fetch ships with the runtime, so this adds no dependency. The render happens in a route handler that pipes the response, and you pipe the upstream body into res.

// routes/packing-slips.js
import { pipeline } from "node:stream/promises";
import { Readable } from "node:stream";
import { promisify } from "node:util";

const renderView = promisify(app.render.bind(app));

app.get("/packing-slips/:id.pdf", async (req, res, next) => {
  try {
    const packingSlip = await db.packingSlips.find(req.params.id);
    const html = await renderView("packing_slip_pdf", { packingSlip });

    const upstream = await fetch("https://api.pdfpipe.xyz/v1/pdf", {
      method: "POST",
      headers: {
        Authorization: `Bearer ${process.env.PDFPIPE_KEY}`,
        "Content-Type": "application/json",
      },
      body: JSON.stringify({
        html,
        options: { format: "A4", printBackground: true },
      }),
    });

    if (!upstream.ok) throw new Error(`render failed: ${upstream.status}`);

    // Header first, then pipe. res.send would buffer the whole document.
    res.setHeader("Content-Type", "application/pdf");
    res.setHeader("Content-Disposition", `attachment; filename="packing-slip-${req.params.id}.pdf"`);
    await pipeline(Readable.fromWeb(upstream.body), res);
  } catch (err) {
    next(err);
  }
});

The CSS that makes a packing slip page correctly

The layout problem specific to this document is that it must print correctly on the label and A5 stock warehouses actually use, not just on A4. These rules handle it.

/* Warehouses print on A5 and label stock, not A4. */
@page {
  size: A5;
  margin: 8mm;
}

.signature {
  break-inside: avoid;
  margin-top: auto;
}

What goes wrong in Express

res.send on a Buffer sets Content-Length correctly but has already read the whole document into memory. res.end with no Content-Type makes the browser render the PDF bytes as text. Set the header, then pipe.

What people try first

Most Express projects reach for puppeteer, launched per request. That downloads roughly 300 MB of Chromium into your image and holds a browser process per concurrent render. 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 packing slip lives afterwards

Rendering is the short part. The packing slip is thrown away when the box is opened. It has essentially no retention requirement, which is unusual on this list and worth knowing: the document does not need to be stored, only printed correctly the first time.

Getting the document right

• Check the order reference and quantities, which a picker checks against the physical goods.
• Generation is triggered by an order moving to fulfilment, 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 Express documents, and the same packing slip in other stacks.