Add initial support for signature appearance

sign/appearance.go

@@ -0,0 +1,62 @@
+package sign
+
+import (
+	"bytes"
+	"fmt"
+)
+
+func (context *SignContext) createAppearance(rect [4]float64) ([]byte, error) {
+	text := context.SignData.Signature.Info.Name
+
+	rectWidth := rect[2] - rect[0]
+	rectHeight := rect[3] - rect[1]
+
+	if rectWidth < 1 || rectHeight < 1 {
+		return nil, fmt.Errorf("invalid rectangle dimensions: width %.2f and height %.2f must be greater than 0", rectWidth, rectHeight)
+	}
+
+	// Calculate font size
+	fontSize := rectHeight * 0.8                     // Initial font size
+	textWidth := float64(len(text)) * fontSize * 0.5 // Approximate text width
+	if textWidth > rectWidth {
+		fontSize = rectWidth / (float64(len(text)) * 0.5) // Adjust font size to fit text within rect width
+	}
+
+	var appearance_stream_buffer bytes.Buffer
+	appearance_stream_buffer.WriteString("q\n")                                           // Save graphics state
+	appearance_stream_buffer.WriteString("BT\n")                                          // Begin text
+	appearance_stream_buffer.WriteString(fmt.Sprintf("/F1 %.2f Tf\n", fontSize))          // Font and size
+	appearance_stream_buffer.WriteString(fmt.Sprintf("0 %.2f Td\n", rectHeight-fontSize)) // Position in unit square
+	appearance_stream_buffer.WriteString("0.2 0.2 0.6 rg\n")                              // Set font color to ballpoint-like color (RGB)
+	appearance_stream_buffer.WriteString(fmt.Sprintf("%s Tj\n", pdfString(text)))         // Show text
+	appearance_stream_buffer.WriteString("ET\n")                                          // End text
+	appearance_stream_buffer.WriteString("Q\n")                                           // Restore graphics state
+
+	var appearance_buffer bytes.Buffer
+	appearance_buffer.WriteString("<<\n")
+	appearance_buffer.WriteString("  /Type /XObject\n")
+	appearance_buffer.WriteString("  /Subtype /Form\n")
+	appearance_buffer.WriteString(fmt.Sprintf("  /BBox [0 0 %f %f]\n", rectWidth, rectHeight))
+	appearance_buffer.WriteString("  /Matrix [1 0 0 1 0 0]\n") // No scaling or translation
+
+	// Resources dictionary
+	appearance_buffer.WriteString("  /Resources <<\n")
+	appearance_buffer.WriteString("   /Font <<\n")
+	appearance_buffer.WriteString("     /F1 <<\n")
+	appearance_buffer.WriteString("       /Type /Font\n")
+	appearance_buffer.WriteString("       /Subtype /Type1\n")
+	appearance_buffer.WriteString("       /BaseFont /Times-Roman\n")
+	appearance_buffer.WriteString("     >>\n")
+	appearance_buffer.WriteString("   >>\n")
+	appearance_buffer.WriteString("  >>\n")
+
+	appearance_buffer.WriteString("  /FormType 1\n")
+	appearance_buffer.WriteString(fmt.Sprintf("  /Length %d\n", appearance_stream_buffer.Len()))
+	appearance_buffer.WriteString(">>\n")
+
+	appearance_buffer.WriteString("stream\n")
+	appearance_buffer.Write(appearance_stream_buffer.Bytes())
+	appearance_buffer.WriteString("endstream\n")
+
+	return appearance_buffer.Bytes(), nil
+}

sign/pdfcatalog.go

@@ -10,7 +10,7 @@ func (context *SignContext) createCatalog() ([]byte, error) {
 
 	// Start the catalog object
 	catalog_buffer.WriteString("<<\n")
-	catalog_buffer.WriteString("  /Type /Catalog")
+	catalog_buffer.WriteString("  /Type /Catalog\n")
 
 	// (Optional; PDF 1.4) The version of the PDF specification to which
 	// the document conforms (for example, 1.4) if later than the version
@@ -49,33 +49,45 @@ func (context *SignContext) createCatalog() ([]byte, error) {
 	// Add Pages and Names references if they exist
 	if foundPages {
 		pages := root.Key("Pages").GetPtr()
-		catalog_buffer.WriteString(" /Pages " + strconv.Itoa(int(pages.GetID())) + " " + strconv.Itoa(int(pages.GetGen())) + " R")
+		catalog_buffer.WriteString("  /Pages " + strconv.Itoa(int(pages.GetID())) + " " + strconv.Itoa(int(pages.GetGen())) + " R\n")
 	}
 	if foundNames {
 		names := root.Key("Names").GetPtr()
-		catalog_buffer.WriteString(" /Names " + strconv.Itoa(int(names.GetID())) + " " + strconv.Itoa(int(names.GetGen())) + " R")
+		catalog_buffer.WriteString("  /Names " + strconv.Itoa(int(names.GetID())) + " " + strconv.Itoa(int(names.GetGen())) + " R\n")
 	}
 
 	// Start the AcroForm dictionary with /NeedAppearances
-	catalog_buffer.WriteString(" /AcroForm << /Fields [")
+	catalog_buffer.WriteString("  /AcroForm <<\n")
+	catalog_buffer.WriteString("    /Fields [")
 
 	// Add existing signatures to the AcroForm dictionary
-	for i, sig := range context.SignData.ExistingSignatures {
+	for i, sig := range context.existingSignatures {
 		if i > 0 {
 			catalog_buffer.WriteString(" ")
 		}
-		catalog_buffer.WriteString(strconv.Itoa(int(sig.ObjectId)) + " 0 R")
+		catalog_buffer.WriteString(strconv.Itoa(int(sig.objectId)) + " 0 R")
 	}
 
 	// Add the visual signature field to the AcroForm dictionary
-	if len(context.SignData.ExistingSignatures) > 0 {
+	if len(context.existingSignatures) > 0 {
 		catalog_buffer.WriteString(" ")
 	}
-	catalog_buffer.WriteString(strconv.Itoa(int(context.VisualSignData.ObjectId)) + " 0 R")
+	catalog_buffer.WriteString(strconv.Itoa(int(context.VisualSignData.objectId)) + " 0 R")
 
-	catalog_buffer.WriteString("]") // close Fields array
+	catalog_buffer.WriteString("]\n") // close Fields array
 
-	catalog_buffer.WriteString(" /NeedAppearances false")
+	// (Optional; deprecated in PDF 2.0) A flag specifying whether
+	// to construct appearance streams and appearance
+	// dictionaries for all widget annotations in the document (see
+	// 12.7.4.3, "Variable text"). Default value: false. A PDF writer
+	// shall include this key, with a value of true, if it has not
+	// provided appearance streams for all visible widget
+	// annotations present in the document.
+	// if context.SignData.Visible {
+	// 	catalog_buffer.WriteString(" /NeedAppearances true")
+	// } else {
+	// 	catalog_buffer.WriteString(" /NeedAppearances false")
+	// }
 
 	// Signature flags (Table 225)
 	//
@@ -100,14 +112,14 @@ func (context *SignContext) createCatalog() ([]byte, error) {
 	// Set SigFlags and Permissions based on Signature Type
 	switch context.SignData.Signature.CertType {
 	case CertificationSignature, ApprovalSignature, TimeStampSignature:
-		catalog_buffer.WriteString(" /SigFlags 3")
+		catalog_buffer.WriteString("    /SigFlags 3\n")
 	case UsageRightsSignature:
-		catalog_buffer.WriteString(" /SigFlags 1")
+		catalog_buffer.WriteString("    /SigFlags 1\n")
 	}
 
 	// Finalize the AcroForm and Catalog object
-	catalog_buffer.WriteString(" >>\n") // Close AcroForm
-	catalog_buffer.WriteString(">>\n")  // Close Catalog
+	catalog_buffer.WriteString("  >>\n") // Close AcroForm
+	catalog_buffer.WriteString(">>\n")   // Close Catalog
 
 	return catalog_buffer.Bytes(), nil
 }

sign/pdfcatalog_test.go

@@ -15,25 +15,25 @@ var testFiles = []struct {
 	{
 		file: "../testfiles/testfile20.pdf",
 		expectedCatalogs: map[CertType]string{
-			CertificationSignature: "<<\n  /Type /Catalog /Pages 3 0 R /AcroForm << /Fields [10 0 R] /NeedAppearances false /SigFlags 3 >>\n>>\n",
-			UsageRightsSignature:   "<<\n  /Type /Catalog /Pages 3 0 R /AcroForm << /Fields [10 0 R] /NeedAppearances false /SigFlags 1 >>\n>>\n",
-			ApprovalSignature:      "<<\n  /Type /Catalog /Pages 3 0 R /AcroForm << /Fields [10 0 R] /NeedAppearances false /SigFlags 3 >>\n>>\n",
+			CertificationSignature: "<<\n  /Type /Catalog\n  /Pages 3 0 R\n  /AcroForm <<\n    /Fields [10 0 R]\n    /SigFlags 3\n  >>\n>>\n",
+			UsageRightsSignature:   "<<\n  /Type /Catalog\n  /Pages 3 0 R\n  /AcroForm <<\n    /Fields [10 0 R]\n    /SigFlags 1\n  >>\n>>\n",
+			ApprovalSignature:      "<<\n  /Type /Catalog\n  /Pages 3 0 R\n  /AcroForm <<\n    /Fields [10 0 R]\n    /SigFlags 3\n  >>\n>>\n",
 		},
 	},
 	{
 		file: "../testfiles/testfile21.pdf",
 		expectedCatalogs: map[CertType]string{
-			CertificationSignature: "<<\n  /Type /Catalog /Pages 9 0 R /Names 6 0 R /AcroForm << /Fields [16 0 R] /NeedAppearances false /SigFlags 3 >>\n>>\n",
-			UsageRightsSignature:   "<<\n  /Type /Catalog /Pages 9 0 R /Names 6 0 R /AcroForm << /Fields [16 0 R] /NeedAppearances false /SigFlags 1 >>\n>>\n",
-			ApprovalSignature:      "<<\n  /Type /Catalog /Pages 9 0 R /Names 6 0 R /AcroForm << /Fields [16 0 R] /NeedAppearances false /SigFlags 3 >>\n>>\n",
+			CertificationSignature: "<<\n  /Type /Catalog\n  /Pages 9 0 R\n  /Names 6 0 R\n  /AcroForm <<\n    /Fields [16 0 R]\n    /SigFlags 3\n  >>\n>>\n",
+			UsageRightsSignature:   "<<\n  /Type /Catalog\n  /Pages 9 0 R\n  /Names 6 0 R\n  /AcroForm <<\n    /Fields [16 0 R]\n    /SigFlags 1\n  >>\n>>\n",
+			ApprovalSignature:      "<<\n  /Type /Catalog\n  /Pages 9 0 R\n  /Names 6 0 R\n  /AcroForm <<\n    /Fields [16 0 R]\n    /SigFlags 3\n  >>\n>>\n",
 		},
 	},
 }
 
 func TestCreateCatalog(t *testing.T) {
 	for _, testFile := range testFiles {
 		for certType, expectedCatalog := range testFile.expectedCatalogs {
-			t.Run(fmt.Sprintf("%s_certType-%d", testFile.file, certType), func(st *testing.T) {
+			t.Run(fmt.Sprintf("%s_%s", testFile.file, certType.String()), func(st *testing.T) {
 				inputFile, err := os.Open(testFile.file)
 				if err != nil {
 					st.Errorf("Failed to load test PDF")
@@ -57,13 +57,7 @@ func TestCreateCatalog(t *testing.T) {
 					PDFReader: rdr,
 					InputFile: inputFile,
 					VisualSignData: VisualSignData{
-						ObjectId: uint32(rdr.XrefInformation.ItemCount),
-					},
-					CatalogData: CatalogData{
-						ObjectId: uint32(rdr.XrefInformation.ItemCount) + 1,
-					},
-					InfoData: InfoData{
-						ObjectId: uint32(rdr.XrefInformation.ItemCount) + 2,
+						objectId: uint32(rdr.XrefInformation.ItemCount),
 					},
 					SignData: SignData{
 						Signature: SignDataSignature{
@@ -80,7 +74,7 @@ func TestCreateCatalog(t *testing.T) {
 				}
 
 				if string(catalog) != expectedCatalog {
-					st.Errorf("Catalog mismatch, expected\n%s\nbut got\n%s", expectedCatalog, catalog)
+					st.Errorf("Catalog mismatch, expected\n%q\nbut got\n%q", expectedCatalog, catalog)
 				}
 			})
 		}

sign/pdfsignature.go

@@ -176,7 +176,7 @@ func (context *SignContext) createSignaturePlaceholder() []byte {
 	//
 	// A timestamp can be embedded in a CMS binary data object (see 12.8.3.3, "CMS
 	// (PKCS #7) signatures").
-	if context.SignData.TSA.URL == "" {
+	if context.SignData.TSA.URL == "" && !context.SignData.Signature.Info.Date.IsZero() {
 		signature_buffer.WriteString(" /M ")
 		signature_buffer.WriteString(pdfDateTime(context.SignData.Signature.Info.Date))
 		signature_buffer.WriteString("\n")
@@ -499,7 +499,7 @@ func (context *SignContext) fetchExistingSignatures() ([]SignData, error) {
 		if field.Key("FT").Name() == "Sig" {
 			ptr := field.GetPtr()
 			sig := SignData{
-				ObjectId: uint32(ptr.GetID()),
+				objectId: uint32(ptr.GetID()),
 			}
 			signatures = append(signatures, sig)
 		}

sign/pdfsignature_test.go

@@ -63,21 +63,12 @@ func TestCreateSignaturePlaceholder(t *testing.T) {
 					},
 				}
 
-				sign_data.ObjectId = uint32(rdr.XrefInformation.ItemCount) + 3
+				sign_data.objectId = uint32(rdr.XrefInformation.ItemCount) + 3
 
 				context := SignContext{
 					PDFReader: rdr,
 					InputFile: inputFile,
-					VisualSignData: VisualSignData{
-						ObjectId: uint32(rdr.XrefInformation.ItemCount),
-					},
-					CatalogData: CatalogData{
-						ObjectId: uint32(rdr.XrefInformation.ItemCount) + 1,
-					},
-					InfoData: InfoData{
-						ObjectId: uint32(rdr.XrefInformation.ItemCount) + 2,
-					},
-					SignData: sign_data,
+					SignData:  sign_data,
 				}
 
 				signature := context.createSignaturePlaceholder()

sign/pdfvisualsignature.go

@@ -27,20 +27,37 @@ const (
 // pageNumber: the page number where the signature should be placed.
 // rect: the rectangle defining the position and size of the signature field.
 // Returns the visual signature string and an error if any.
-func (context *SignContext) createVisualSignature(visible bool, pageNumber int, rect [4]float64) ([]byte, error) {
+func (context *SignContext) createVisualSignature(visible bool, pageNumber uint32, rect [4]float64) ([]byte, error) {
 	var visual_signature bytes.Buffer
 
+	visual_signature.WriteString("<<\n")
+
 	// Define the object as an annotation.
-	visual_signature.WriteString("<< /Type /Annot")
+	visual_signature.WriteString("  /Type /Annot\n")
 	// Specify the annotation subtype as a widget.
-	visual_signature.WriteString(" /Subtype /Widget")
+	visual_signature.WriteString("  /Subtype /Widget\n")
 
 	if visible {
 		// Set the position and size of the signature field if visible.
-		visual_signature.WriteString(fmt.Sprintf(" /Rect [%f %f %f %f]", rect[0], rect[1], rect[2], rect[3]))
+		visual_signature.WriteString(fmt.Sprintf("  /Rect [%f %f %f %f]\n", rect[0], rect[1], rect[2], rect[3]))
+
+		appearance, err := context.createAppearance(rect)
+		if err != nil {
+			return nil, fmt.Errorf("failed to create appearance: %w", err)
+		}
+
+		appearanceObjectId, err := context.addObject(appearance)
+		if err != nil {
+			return nil, fmt.Errorf("failed to add appearance object: %w", err)
+		}
+
+		// An appearance dictionary specifying how the annotation
+		// shall be presented visually on the page (see 12.5.5, "Appearance streams").
+		visual_signature.WriteString(fmt.Sprintf("  /AP << /N %d 0 R >>\n", appearanceObjectId))
+
 	} else {
 		// Set the rectangle to zero if the signature is invisible.
-		visual_signature.WriteString(" /Rect [0 0 0 0]")
+		visual_signature.WriteString("  /Rect [0 0 0 0]\n")
 	}
 
 	// Retrieve the root object from the PDF trailer.
@@ -72,40 +89,72 @@ func (context *SignContext) createVisualSignature(visible bool, pageNumber int,
 		page_ptr := page.GetPtr()
 
 		// Store the page ID in the visual signature context so that we can add it to xref table later.
-		context.VisualSignData.PageId = page_ptr.GetID()
+		context.VisualSignData.pageObjectId = page_ptr.GetID()
 
 		// Add the page reference to the visual signature.
-		visual_signature.WriteString(" /P " + strconv.Itoa(int(page_ptr.GetID())) + " " + strconv.Itoa(int(page_ptr.GetGen())) + " R")
+		visual_signature.WriteString("  /P " + strconv.Itoa(int(page_ptr.GetID())) + " " + strconv.Itoa(int(page_ptr.GetGen())) + " R\n")
 	}
 
 	// Define the annotation flags for the signature field (132)
-	// annotationFlags := AnnotationFlagPrint | AnnotationFlagNoZoom | AnnotationFlagNoRotate | AnnotationFlagReadOnly | AnnotationFlagLockedContents
-	visual_signature.WriteString(fmt.Sprintf(" /F %d", 132))
+	annotationFlags := AnnotationFlagPrint | AnnotationFlagLocked
+	visual_signature.WriteString(fmt.Sprintf("  /F %d\n", annotationFlags))
+
 	// Define the field type as a signature.
-	visual_signature.WriteString(" /FT /Sig")
+	visual_signature.WriteString("  /FT /Sig\n")
 	// Set a unique title for the signature field.
-	visual_signature.WriteString(" /T " + pdfString("Signature "+strconv.Itoa(len(context.SignData.ExistingSignatures)+1)))
-
-	// (Optional) A set of bit flags specifying the interpretation of specific entries
-	// in this dictionary. A value of 1 for the flag indicates that the associated entry
-	// is a required constraint. A value of 0 indicates that the associated entry is
-	// an optional constraint. Bit positions are 1 (Filter); 2 (SubFilter); 3 (V); 4
-	// (Reasons); 5 (LegalAttestation); 6 (AddRevInfo); and 7 (DigestMethod).
-	// For PDF 2.0 the following bit flags are added: 8 (Lockdocument); and 9
-	// (AppearanceFilter). Default value: 0.
-	visual_signature.WriteString(" /Ff 0")
+	visual_signature.WriteString(fmt.Sprintf("  /T %s\n", pdfString("Signature "+strconv.Itoa(len(context.existingSignatures)+1))))
 
 	// Reference the signature dictionary.
-	visual_signature.WriteString(" /V " + strconv.Itoa(int(context.SignData.ObjectId)) + " 0 R")
+	visual_signature.WriteString(fmt.Sprintf("  /V %d 0 R\n", context.SignData.objectId))
 
 	// Close the dictionary and end the object.
-	visual_signature.WriteString(" >>\n")
+	visual_signature.WriteString(">>\n")
 
 	return visual_signature.Bytes(), nil
 }
 
+func (context *SignContext) createIncPageUpdate(pageNumber, annot uint32) ([]byte, error) {
+	var page_buffer bytes.Buffer
+
+	// Retrieve the root object from the PDF trailer.
+	root := context.PDFReader.Trailer().Key("Root")
+	page, err := findPageByNumber(root.Key("Pages"), pageNumber)
+	if err != nil {
+		return nil, err
+	}
+
+	page_buffer.WriteString("<<\n")
+
+	// TODO: Update digitorus/pdf to get raw values without resolving pointers
+	for _, key := range page.Keys() {
+		switch key {
+		case "Contents", "Parent":
+			ptr := page.Key(key).GetPtr()
+			page_buffer.WriteString(fmt.Sprintf("  /%s %d 0 R\n", key, ptr.GetID()))
+		case "Annots":
+			page_buffer.WriteString("  /Annots [\n")
+			for i := 0; i < page.Key("Annots").Len(); i++ {
+				ptr := page.Key(key).Index(i).GetPtr()
+				page_buffer.WriteString(fmt.Sprintf("    %d 0 R\n", ptr.GetID()))
+			}
+			page_buffer.WriteString(fmt.Sprintf("    %d 0 R\n", annot))
+			page_buffer.WriteString("  ]\n")
+		default:
+			page_buffer.WriteString(fmt.Sprintf("  /%s %s\n", key, page.Key(key).String()))
+		}
+	}
+
+	if page.Key("Annots").IsNull() {
+		page_buffer.WriteString(fmt.Sprintf("  /Annots [%d 0 R]\n", annot))
+	}
+
+	page_buffer.WriteString(">>\n")
+
+	return page_buffer.Bytes(), nil
+}
+
 // Helper function to find a page by its number.
-func findPageByNumber(pages pdf.Value, pageNumber int) (pdf.Value, error) {
+func findPageByNumber(pages pdf.Value, pageNumber uint32) (pdf.Value, error) {
 	if pages.Key("Type").Name() == "Pages" {
 		kids := pages.Key("Kids")
 		for i := 0; i < kids.Len(); i++ {