Fix signature validation

pdf/annotator/form_field.go

@@ -249,21 +249,15 @@ func NewSignatureField(signature *model.PdfSignature, fields []*SignatureLine, o
 		return nil, errors.New("signature cannot be nil")
 	}
 
-	field := model.NewPdfFieldSignature(signature)
-	field.T = core.MakeString("")
-
 	apDict, err := genFieldSignatureAppearance(fields, opts)
 	if err != nil {
 		return nil, err
 	}
 
-	widget := model.NewPdfAnnotationWidget()
-	widget.Rect = core.MakeArrayFromFloats(opts.Rect)
-	widget.F = core.MakeInteger(4)
-	widget.Parent = field.ToPdfObject()
-	widget.AP = apDict
-
-	field.Annotations = append(field.Annotations, widget)
+	field := model.NewPdfFieldSignature(signature)
+	field.Rect = core.MakeArrayFromFloats(opts.Rect)
+	field.F = core.MakeInteger(132)
+	field.AP = apDict
 	return field, nil
 }
 
@@ -380,10 +374,13 @@ func genFieldSignatureAppearance(fields []*SignatureLine, opts *SignatureFieldOp
 		opts.FillColor = model.NewPdfColorDeviceGray(1)
 	}
 
-	cc.Add_q().Add_re(rect[0], rect[1], rectWidth, rectHeight).
-		Add_w(opts.BorderSize).SetStrokingColor(opts.BorderColor).
+	cc.Add_q().
+		Add_re(rect[0], rect[1], rectWidth, rectHeight).
+		Add_w(opts.BorderSize).
+		SetStrokingColor(opts.BorderColor).
 		SetNonStrokingColor(opts.FillColor).
-		Add_B().Add_Q()
+		Add_B().
+		Add_Q()
 
 	// Draw signature.
 	cc.Add_q()

pdf/model/appender.go

@@ -394,6 +394,7 @@ func (a *PdfAppender) Sign(pageNum int, field *PdfFieldSignature) error {
 	if signature == nil {
 		return errors.New("signature dictionary cannot be nil")
 	}
+	a.addNewObjects(signature.container)
 
 	// Get a copy of the selected page.
 	pageIndex := pageNum - 1
@@ -402,17 +403,9 @@ func (a *PdfAppender) Sign(pageNum int, field *PdfFieldSignature) error {
 	}
 	page := a.pages[pageIndex].Duplicate()
 
-	// Initialize signature.
-	if err := signature.Initialize(); err != nil {
-		return err
-	}
-	a.addNewObjects(signature.container)
-
 	// Add signature field annotations to the page annotations.
-	for _, annotation := range field.Annotations {
-		annotation.P = page.ToPdfObject()
-		page.Annotations = append(page.Annotations, annotation.PdfAnnotation)
-	}
+	field.P = page.ToPdfObject()
+	page.Annotations = append(page.Annotations, field.PdfAnnotationWidget.PdfAnnotation)
 
 	// Add signature field to the form.
 	acroForm := a.Reader.AcroForm

pdf/model/appender_test.go

@@ -457,6 +457,10 @@ func TestAppenderSignPage4(t *testing.T) {
 	signature.SetReason("TestAppenderSignPage4")
 	signature.SetDate(time.Now(), "")
 
+	if err := signature.Initialize(); err != nil {
+		return
+	}
+
 	sigField := model.NewPdfFieldSignature(signature)
 	sigField.T = core.MakeString("Signature1")
 
@@ -541,6 +545,10 @@ func TestAppenderSignMultiple(t *testing.T) {
 		signature.SetReason("TestAppenderSignPage4")
 		signature.SetDate(time.Now(), "")
 
+		if err := signature.Initialize(); err != nil {
+			return
+		}
+
 		sigField := model.NewPdfFieldSignature(signature)
 		sigField.T = core.MakeString("Signature1")
 
@@ -619,6 +627,10 @@ func TestSignatureAppearance(t *testing.T) {
 	signature.SetReason("TestSignatureAppearance Reason")
 	signature.SetDate(time.Now(), "")
 
+	if err := signature.Initialize(); err != nil {
+		return
+	}
+
 	numPages, err := pdfReader.GetNumPages()
 	if err != nil {
 		t.Errorf("Fail: %v\n", err)
@@ -644,6 +656,8 @@ func TestSignatureAppearance(t *testing.T) {
 			},
 			opts,
 		)
+		sigField.T = core.MakeString(fmt.Sprintf("Signature %d", pageNum))
+		sigField.F = core.MakeInteger(132)
 
 		if err = appender.Sign(pageNum, sigField); err != nil {
 			t.Errorf("Fail: %v\n", err)
@@ -667,6 +681,8 @@ func TestSignatureAppearance(t *testing.T) {
 			},
 			opts,
 		)
+		sigField.T = core.MakeString(fmt.Sprintf("Signature2 %d", pageNum))
+		sigField.F = core.MakeInteger(132)
 
 		if err = appender.Sign(pageNum, sigField); err != nil {
 			log.Fatalf("Fail: %v\n", err)
@@ -691,6 +707,8 @@ func TestSignatureAppearance(t *testing.T) {
 			},
 			opts,
 		)
+		sigField.T = core.MakeString(fmt.Sprintf("Signature3 %d", pageNum))
+		sigField.F = core.MakeInteger(132)
 
 		if err = appender.Sign(pageNum, sigField); err != nil {
 			log.Fatalf("Fail: %v\n", err)

pdf/model/fields.go

@@ -433,6 +433,7 @@ func (ch *PdfFieldChoice) ToPdfObject() core.PdfObject {
 // the name of the signer and verifying document contents.
 type PdfFieldSignature struct {
 	*PdfField
+	*PdfAnnotationWidget
 
 	V    *PdfSignature
 	Lock *core.PdfIndirectObject
@@ -441,22 +442,28 @@ type PdfFieldSignature struct {
 
 // NewPdfFieldSignature returns an initialized signature field.
 func NewPdfFieldSignature(signature *PdfSignature) *PdfFieldSignature {
-	field := &PdfFieldSignature{
-		PdfField: NewPdfField(),
-		V:        signature,
-	}
+	field := &PdfFieldSignature{}
+	field.PdfField = NewPdfField()
 	field.PdfField.SetContext(field)
-	field.FT = core.MakeName("Sig")
 
+	field.PdfAnnotationWidget = NewPdfAnnotationWidget()
+	field.PdfAnnotationWidget.SetContext(field)
+	field.PdfAnnotationWidget.container = field.PdfField.container
+
+	field.T = core.MakeString("")
+	field.V = signature
 	return field
 }
 
 // ToPdfObject returns an indirect object containing the signature field dictionary.
 func (sig *PdfFieldSignature) ToPdfObject() core.PdfObject {
-	// Set general field attributes
+	// Set general field attributes.
+	if sig.PdfAnnotationWidget != nil {
+		sig.PdfAnnotationWidget.ToPdfObject()
+	}
 	sig.PdfField.ToPdfObject()
 
-	// Handle signature field specific attributes
+	// Handle signature field specific attributes.
 	container := sig.container
 
 	d := container.PdfObject.(*core.PdfObjectDictionary)