Contents.push is not a function

[mrfolkblues]

I have a script that writes a timestamp string to the top of each page of a PDF that comes in as a base64 encoded string from a file upload UI. It looks basically like this:

'use strict'

const moment = require('moment-timezone')
const { PDFDocument, StandardFonts } = require('pdf-lib')

const getTimeStamp = (prefix = '') => {
  const retrDate = moment().tz('America/Chicago').format(prefix === '' ? 'MM/DD/YYYY hh:mm:ss A [CT]' : `[${prefix}] MM/DD/YYYY hh:mm:ss A [CT]`)
  return retrDate
}

const addTimestamp = async (pdfDataBuffer) => {
  // load the PDF document from the Buffer
  const pdfDoc = await PDFDocument.load(pdfDataBuffer)

  // embed the font to use
  const courierFont = await pdfDoc.embedFont(StandardFonts.CourierBold)

  // pre-calculate the timestamp text width
  const timeStamp = getTimeStamp()
  const textWidth = courierFont.widthOfTextAtSize(timeStamp, 10)

  // get an array of the document's pages
  const pages = pdfDoc.getPages()

  pages.forEach((page, index) => {
    // get the page dimensions
    const { width, height } = page.getSize()

    // set height a little taller for timestamp space
    page.setHeight(height + 15)

    // write the timestamp to the page
    page.drawText(timeStamp, {
      x: (width - textWidth) / 2,
      y: height + 5,
      size: 10,
      font: courierFont
    })
  })

  // serialize the PDFDocument to bytes (a Uint8Array)
  return pdfDoc.save()
}

module.exports = { getTimeStamp, addTimestamp }

Most documents are processed successfully. I have had one failure so far though. The error message & stack were:

TypeError: Contents.push is not a function
at PDFPageLeaf.addContentStream (/Users/mrfolkblues/.../myproject/node_modules/pdf-lib/cjs/core/structures/PDFPageLeaf.js:75:18)
at PDFPage.getContentStream (/Users/mrfolkblues/.../myproject/node_modules/pdf-lib/cjs/api/PDFPage.js:1365:19)
at PDFPage.drawText (/Users/mrfolkblues/.../myproject/node_modules/pdf-lib/cjs/api/PDFPage.js:864:34)
at /Users/mrfolkblues/.../myproject/utils/timestampUtil.js:57:10
at Array.forEach (<anonymous>)
at addTimestamp (/Users/mrfolkblues/.../myproject/utils/timestampUtil.js:45:9)
...

This will, unfortunately, be difficult or impossible to reproduce without the document in question, which I cannot share for privacy reasons. However, I can share a little information.

The drawText() method failed on the final page of the document. I logged page.node.normalizedEntries().Contents using a safeStringify function I found to handle circular references. The output of page.node.normalizedEntries().Contents for the next to last page looked like this:

{
  "array": [
    {
      "objectNumber": 32,
      "generationNumber": 0,
      "tag": "32 0 R"
    },
    {
      "objectNumber": 22,
      "generationNumber": 0,
      "tag": "22 0 R"
    },
    {
      "objectNumber": 33,
      "generationNumber": 0,
      "tag": "33 0 R"
    }
  ],
  "context": {
    "largestObjectNumber": 36,
    "header": {
...

While the output of the last page looked like this:

{
  "data": {
    "type": "Buffer",
    "data": [
      60,
      60,
      47,
      76,
      101,
...

I'm hoping this means something to someone. I'd make a proper issue if I felt like this could be reproduced reliably. Please reply if you have any insight into this problem.