Statement PDFs in Express

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 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/statements.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("/statements/:id.pdf", async (req, res, next) => {
  try {
    const statement = await db.statements.find(req.params.id);
    const html = await renderView("statement_pdf", { statement });

    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="statement-${req.params.id}.pdf"`);
    await pipeline(Readable.fromWeb(upstream.body), res);
  } catch (err) {
    next(err);
  }
});

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 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 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 Express documents, and the same statement in other stacks.