✨ [placeholder-pdf-lib]

* Use pdf-lib 1.17 types;
* Use the newly introduced FLAG enums;
* Reuse existing AcroForm (refs #198);
* Reuse existing Annots (refs #198);
* Fix mistaken signature length;

packages/placeholder-pdf-lib/src/pdflibAddPlaceholder.js

@@ -1,30 +1,40 @@
-import {DEFAULT_BYTE_RANGE_PLACEHOLDER, DEFAULT_SIGNATURE_LENGTH, SUBFILTER_ADOBE_PKCS7_DETACHED} from '@signpdf/utils';
 import {
-    PDFArray, PDFHexString, PDFName, PDFNumber, PDFString, toHexStringOfMinLength,
+    ANNOTATION_FLAGS,
+    DEFAULT_BYTE_RANGE_PLACEHOLDER,
+    DEFAULT_SIGNATURE_LENGTH,
+    SIG_FLAGS,
+    SUBFILTER_ADOBE_PKCS7_DETACHED,
+} from '@signpdf/utils';
+import {
+    PDFArray, PDFDict, PDFHexString, PDFName, PDFNumber, PDFString,
 } from 'pdf-lib';
 
 /**
- * @typedef {import('pdf-lib').PDFDocumentFactory} PDFDocumentFactory
+ * @typedef {import('pdf-lib').PDFDocument} PDFDocument
  */
 
 /**
 * @typedef {object} InputType
-* @property {PDFDocumentFactory} pdfDoc
+* @property {PDFDocument} pdfDoc
 * @property {string} reason
 * @property {string} contactInfo
 * @property {string} name
 * @property {string} location
 * @property {number} [signatureLength]
 * @property {string} [byteRangePlaceholder]
-* @property {string} [subFilter] One of SUBFILTER_* from @signpdf/utils
+* @property {string} [subFilter] One of SUBFILTER_* from \@signpdf/utils
 * @property {number[]} [widgetRect] [x1, y1, x2, y2] widget rectangle
 */
 
 /**
+ * Adds a signature placeholder to a PDF-LIB PDFDocument.
+ *
+ * Alters the passed pdfDoc and returns void.
+ *
  * @param {InputType}
- * @returns {Buffer}
+ * @returns {void}
  */
-export const pdflibAddPlaceholder = async ({
+export const pdflibAddPlaceholder = ({
     pdfDoc,
     reason,
     contactInfo,
@@ -35,17 +45,20 @@ export const pdflibAddPlaceholder = async ({
     subFilter = SUBFILTER_ADOBE_PKCS7_DETACHED,
     widgetRect = [0, 0, 0, 0],
 }) => {
-    const pages = pdfDoc.getPages();
+    const page = pdfDoc.getPage(0);
 
+    // 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(PDFString.of(byteRangePlaceholder));
-    byteRange.push(PDFString.of(byteRangePlaceholder));
-    byteRange.push(PDFString.of(byteRangePlaceholder));
+    byteRange.push(PDFName.of(byteRangePlaceholder));
+    byteRange.push(PDFName.of(byteRangePlaceholder));
+    byteRange.push(PDFName.of(byteRangePlaceholder));
 
-    const hexNull = toHexStringOfMinLength(0, 4);
-    const placeholder = PDFHexString.of(hexNull.repeat(signatureLength));
+    // Fill the contents of the placeholder with 00s.
+    const placeholder = PDFHexString.of(String.fromCharCode(0).repeat(signatureLength));
 
+    // Create a signature dictionary to be referenced in the signature widget.
     const signatureDict = pdfDoc.context.obj({
         Type: 'Sig',
         Filter: 'Adobe.PPKLite',
@@ -58,34 +71,55 @@ export const pdflibAddPlaceholder = async ({
         Name: PDFString.of(name),
         Location: PDFString.of(location),
     }, pdfDoc.index);
+    const signatureDictRef = pdfDoc.context.register(signatureDict);
 
+    // Create the signature widget
     const rect = PDFArray.withContext(pdfDoc.context);
     widgetRect.forEach((c) => rect.push(PDFNumber.of(c)));
     const widgetDict = pdfDoc.context.obj({
         Type: 'Annot',
         Subtype: 'Widget',
         FT: 'Sig',
         Rect: rect,
-        V: signatureDict,
+        V: signatureDictRef,
         T: PDFString.of('Signature1'),
-        F: 4,
-        P: pages[0].ref,
+        F: ANNOTATION_FLAGS.PRINT,
+        P: page.ref,
     }, pdfDoc.index);
     const widgetDictRef = pdfDoc.context.register(widgetDict);
 
-    pages[0].node.set(
-        PDFName.of('Annots'),
-        pdfDoc.context.obj([widgetDictRef]),
-    );
+    // Annotate the widget on the first 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);
 
-    pdfDoc.catalog.set(
-        PDFName.of('AcroForm'),
-        pdfDoc.context.obj({
-            SigFlags: 3,
-            Fields: [widgetDictRef],
-        }),
-    );
+    // Add an AcroForm or update the existing one
+    let acroForm = pdfDoc.catalog.lookupMaybe(PDFName.of('AcroForm'), PDFDict);
+    if (typeof acroForm === 'undefined') {
+        // Need to create a new AcroForm
+        acroForm = pdfDoc.context.obj({Fields: []});
+        const acroFormRef = pdfDoc.context.register(acroForm);
+        pdfDoc.catalog.set(PDFName.of('AcroForm'), acroFormRef);
+    }
 
-    const pdfBytes = await pdfDoc.save({useObjectStreams: false});
-    return Buffer.from(pdfBytes);
+    /**
+     * @type {PDFNumber}
+     */
+    let sigFlags;
+    if (acroForm.has(PDFName.of('SigFlags'))) {
+        // Already has some flags, will merge
+        sigFlags = acroForm.get(PDFName.of('SigFlags'));
+    } else {
+        // Create blank flags
+        sigFlags = PDFNumber.of(0);
+    }
+    const updatedFlags = PDFNumber.of(
+        sigFlags.asNumber() | SIG_FLAGS.SIGNATURES_EXIST | SIG_FLAGS.APPEND_ONLY,
+    );
+    acroForm.set(PDFName.of('SigFlags'), updatedFlags);
+    const fields = acroForm.get(PDFName.of('Fields'));
+    fields.push(widgetDictRef);
 };