test20.ts

import { Assets } from '../index.ts';
// @deno-types="../dummy.d.ts"
import {
  PDFArray,
  PDFDocument,
  PDFHexString,
  PDFInvalidObject,
  PDFName,
  PDFNumber,
  PDFString,
  rgb,
  StandardFonts,
} from '../../../dist/pdf-lib.esm.js';

/**
 * This test modifies the pdf adding a page and a placeholder for an electronic signature.
 * It also deletes the first page of the PDF.
 * The file should have an incremental update at the end, and the start of the file be exactly the original file.
 */
export default async (assets: Assets) => {
  const pdfDoc = await PDFDocument.load(assets.pdfs.simple, {
    forIncrementalUpdate: true,
  });
  // add a page (small one), with the visual representation of the digital signature, as a
  // square box with text centered in it.
  const page = pdfDoc.addPage([500, 200]);
  // remove a page from de PDF
  pdfDoc.removePage(0);
  // embed fonts for the visual representation of the signature
  const font = pdfDoc.embedStandardFont(StandardFonts.Helvetica);
  const fontBold = pdfDoc.embedStandardFont(StandardFonts.HelveticaBoldOblique);
  // couple of warning lines, about the signature and the visual representation
  const signatureWarning =
    '-- This is not the real signature of the document, just a a visual representation --';
  const useLibreOffice =
    '-- If your PDF viewer does not shows digital signatures, you can use "LibreOffice Draw" --';
  const fontSize = 14;
  const warningFontSize = 10;
  // text in the visual representation maximun width
  const textWidth = Math.max(
    font.widthOfTextAtSize('Electronic Signature Test #20', fontSize),
    fontBold.widthOfTextAtSize(useLibreOffice, warningFontSize),
  );
  // text line in the visual representation maximun height
  const textHeight =
    Math.max(
      font.heightAtSize(fontSize),
      fontBold.heightAtSize(warningFontSize),
    ) + 2;
  // X position where the visual representation square starts
  const startXpos = Math.trunc((page.getWidth() - textWidth) / 2);
  // total vertical size of the visual representation
  const visualRepHeight = textHeight * 4 + 20;
  // rectangle containing the text
  page.drawRectangle({
    x: startXpos - 10,
    y: page.getHeight() - visualRepHeight - 50,
    width: textWidth + 20,
    height: visualRepHeight,
    borderWidth: 2,
    borderColor: rgb(0.45, 0.45, 0.45),
  });
  let lineWidth = font.widthOfTextAtSize(
    'Electronic Signature Test #20',
    fontSize,
  );
  // vertial position where the text line will be outputted
  let currentYPos = page.getHeight() - textHeight - 60;
  // line #1
  page.drawText('Electronic Signature Test #20', {
    x: startXpos + Math.round((textWidth - lineWidth) / 2),
    y: currentYPos,
    size: fontSize,
    font,
  });
  // timestamp of the signature, line #2
  const signatureTimestamp = new Date().toISOString();
  lineWidth = font.widthOfTextAtSize(signatureTimestamp, fontSize);
  currentYPos -= textHeight;
  page.drawText(signatureTimestamp, {
    x: startXpos + Math.round((textWidth - lineWidth) / 2),
    y: currentYPos,
    size: fontSize,
    font,
  });
  // first warning, line #3
  lineWidth = fontBold.widthOfTextAtSize(signatureWarning, warningFontSize);
  currentYPos -= textHeight;
  page.drawText(signatureWarning, {
    x: startXpos + Math.round((textWidth - lineWidth) / 2),
    y: currentYPos,
    size: warningFontSize,
    font: fontBold,
  });
  // second warning, line #4
  lineWidth = fontBold.widthOfTextAtSize(useLibreOffice, warningFontSize);
  currentYPos -= textHeight;
  page.drawText(useLibreOffice, {
    x: startXpos + Math.round((textWidth - lineWidth) / 2),
    y: currentYPos,
    size: warningFontSize,
    font: fontBold,
  });

  // Add an AcroForm or update the existing one
  const acroForm = pdfDoc.catalog.getOrCreateAcroForm();

  // Create a placeholder where the the last 3 parameters of the
  // actual range will be replaced when signing is done.
  const byteRange = PDFArray.withContext(pdfDoc.context);
  byteRange.push(PDFNumber.of(0));
  byteRange.push(PDFName.of('*********'));
  byteRange.push(PDFName.of('*********'));
  byteRange.push(PDFName.of('*********'));

  // Fill the contents of the placeholder with 00s.
  const placeholder = PDFHexString.of(String.fromCharCode(0).repeat(8096));

  // Create a signature dictionary to be referenced in the signature widget.
  const appBuild = { App: { Name: 'Test #20' } };
  const signatureDict = pdfDoc.context.obj({
    Type: 'Sig',
    Filter: 'Adobe.PPKLite',
    SubFilter: 'adbe.pkcs7.detached',
    ByteRange: byteRange,
    Contents: placeholder,
    Reason: PDFString.of('Test #20'),
    M: PDFString.fromDate(new Date()),
    ContactInfo: PDFString.of('dabdala@adnsistemas.com.ar'),
    Name: PDFString.of('David Abdala'),
    Location: PDFString.of('Mendoza, Argentina'),
    Prop_Build: {
      Filter: { Name: 'Adobe.PPKLite' },
      ...appBuild,
    },
  });
  // Register signatureDict as a PDFInvalidObject to prevent PDFLib from serializing it
  // in an object stream.
  const signatureBuffer = new Uint8Array(signatureDict.sizeInBytes());
  signatureDict.copyBytesInto(signatureBuffer, 0);
  const signatureObj = PDFInvalidObject.of(signatureBuffer);
  const signatureDictRef = pdfDoc.context.register(signatureObj);

  // Create the signature widget
  const widgetRect = [0, 0, 0, 0];
  const rect = PDFArray.withContext(pdfDoc.context);
  widgetRect.forEach((c) => rect.push(PDFNumber.of(c)));
  const apStream = pdfDoc.context.formXObject([], {
    BBox: widgetRect,
    Resources: {}, // Necessary to avoid Acrobat bug (see https://stackoverflow.com/a/73011571)
  });
  const widgetDict = pdfDoc.context.obj({
    Type: 'Annot',
    Subtype: 'Widget',
    FT: 'Sig',
    Rect: rect,
    V: signatureDictRef,
    T: PDFString.of('TestSig'),
    TU: PDFString.of('Electronic Signature Test #20'),
    F: 2,
    P: page.ref,
    AP: { N: pdfDoc.context.register(apStream) }, // Required for PDF/A compliance
  });
  const widgetDictRef = pdfDoc.context.register(widgetDict);

  // Annotate the widget on the given page
  let annotations = page.node.lookupMaybe(PDFName.of('Annots'), PDFArray);
  if (typeof annotations === 'undefined') {
    annotations = pdfDoc.context.obj([]);
  }
  annotations.push(widgetDictRef);
  page.node.set(PDFName.of('Annots'), annotations);

  let sigFlags: PDFNumber;
  if (acroForm.dict.has(PDFName.of('SigFlags'))) {
    // Already has some flags, will merge
    sigFlags = acroForm.dict.get(PDFName.of('SigFlags')) as PDFNumber;
  } else {
    // Create blank flags
    sigFlags = PDFNumber.of(0);
  }
  const updatedFlags = PDFNumber.of(sigFlags!.asNumber() | 1 | 2);
  acroForm.dict.set(PDFName.of('SigFlags'), updatedFlags);
  let fields = acroForm.dict.get(PDFName.of('Fields'));
  if (!(fields instanceof PDFArray)) {
    fields = pdfDoc.context.obj([]);
    acroForm.dict.set(PDFName.of('Fields'), fields);
  }
  (fields as PDFArray).push(widgetDictRef);
  return await pdfDoc.save({ useObjectStreams: false });
};