Removed large whitespace in signature dictionary to get valid signatures.

Whitespace was causing ByteRange to not cover the entire document.  Ideally should be everything outside the < > in the signature Contents field.

pdf/model/appender.go

@@ -19,7 +19,7 @@ import (
 	"github.com/unidoc/unidoc/pdf/core"
 )
 
-// PdfAppender appends a new Pdf content to an existing Pdf document.
+// PdfAppender appends new PDF content to an existing PDF document via incremental updates.
 type PdfAppender struct {
 	rs       io.ReadSeeker
 	parser   *core.PdfParser
@@ -416,7 +416,6 @@ func (a *PdfAppender) Sign(pageNum int, handler SignatureHandler) (acroForm *Pdf
 	appearance.V = sig.ToPdfObject()
 	appearance.FT = core.MakeName("Sig")
 	appearance.V = sig.ToPdfObject()
-	//appearance.Ff = core.MakeInteger(0)
 	appearance.T = core.MakeString("Signature1")
 	appearance.F = core.MakeInteger(132)
 	appearance.P = page.ToPdfObject()
@@ -424,9 +423,14 @@ func (a *PdfAppender) Sign(pageNum int, handler SignatureHandler) (acroForm *Pdf
 		core.MakeInteger(0))
 	appearance.Signature = sig
 
+	// Add the signature appearance to the page annotations.
+	page.Annotations = append(page.Annotations, appearance.PdfAnnotationWidget.PdfAnnotation)
+
 	a.pages[pageIndex] = page
 
+	// Update acroform.
 	a.ReplaceAcroForm(acroForm)
+
 	return acroForm, appearance, nil
 }
 
@@ -437,7 +441,6 @@ func (a *PdfAppender) ReplaceAcroForm(acroForm *PdfAcroForm) {
 
 // Write writes the Appender output to io.Writer.
 func (a *PdfAppender) Write(w io.Writer) error {
-
 	writer := NewPdfWriter()
 
 	pagesDict, ok := core.GetDict(writer.pages)
@@ -499,7 +502,7 @@ func (a *PdfAppender) Write(w io.Writer) error {
 				common.Log.Trace("Page Parent: %T", parent)
 				parentDict, ok := parent.PdfObject.(*core.PdfObjectDictionary)
 				if !ok {
-					return errors.New("Invalid Parent object")
+					return errors.New("invalid Parent object")
 				}
 				for _, field := range inheritedFields {
 					common.Log.Trace("Field %s", field)
@@ -593,10 +596,13 @@ func (a *PdfAppender) Write(w io.Writer) error {
 		writerW = bytes.NewBuffer(nil)
 	}
 
+	// Do a mock write to get offsets.
+	// TODO(gunnsth): Only needed when dealing with signatures?
 	if err := writer.Write(writerW); err != nil {
 		return err
 	}
 
+	// TODO(gunnsth): Consider whether the dynamic content can be handled with generic write hooks?
 	if hasSigDict {
 		bufferData := writerW.(*bytes.Buffer).Bytes()
 		byteRange := core.MakeArray()

pdf/model/signature.go

@@ -12,7 +12,8 @@ import (
 	"github.com/unidoc/unidoc/pdf/core"
 )
 
-// pdfSignDictionary is needed because of the digital checksum calculates after a new file creation and writes as a value into PdfDictionary in the existing file.
+// pdfSignDictionary is used as a wrapper around PdfSignature for digital checksum calculation
+// and population of /Contents and /ByteRange.
 type pdfSignDictionary struct {
 	*core.PdfObjectDictionary
 	handler              *SignatureHandler
@@ -53,14 +54,14 @@ func (d *pdfSignDictionary) WriteString() string {
 			d.byteRangeOffsetStart = out.Len()
 			out.WriteString(v.WriteString())
 			out.WriteString(" ")
-			d.byteRangeOffsetEnd = out.Len()
+			d.byteRangeOffsetEnd = out.Len() - 1
 		case "Contents":
 			out.WriteString(k.WriteString())
 			out.WriteString(" ")
 			d.contentsOffsetStart = out.Len()
 			out.WriteString(v.WriteString())
 			out.WriteString(" ")
-			d.contentsOffsetEnd = out.Len()
+			d.contentsOffsetEnd = out.Len() - 1
 		default:
 			out.WriteString(k.WriteString())
 			out.WriteString(" ")
@@ -100,7 +101,11 @@ type PdfSignature struct {
 // NewPdfSignature creates a new PdfSignature object.
 func NewPdfSignature() *PdfSignature {
 	sig := &PdfSignature{}
-	sigDict := &pdfSignDictionary{PdfObjectDictionary: core.MakeDict(), handler: &sig.Handler, signature: sig}
+	sigDict := &pdfSignDictionary{
+		PdfObjectDictionary: core.MakeDict(),
+		handler:             &sig.Handler,
+		signature:           sig,
+	}
 	sig.container = core.MakeIndirectObject(sigDict)
 	return sig
 }
@@ -172,7 +177,9 @@ func (sig *PdfSignature) ToPdfObject() core.PdfObject {
 	if sig.Contents != nil {
 		dict.Set("Contents", sig.Contents)
 	}
-	// FIXME: ByteRange and Contents need to be updated dynamically.
+	// NOTE: ByteRange and Contents need to be updated dynamically.
+	// TODO: Currently dynamic update is only in the appender, need to support in the PdfWriter
+	// too for the initial signature on document creation.
 	return container
 }
 
@@ -252,10 +259,8 @@ type PdfSignatureField struct {
 	container *core.PdfIndirectObject
 
 	V    *PdfSignature
-	// Type: /Sig
+	Lock *core.PdfIndirectObject
-	// V: *PdfSignature...
+	SV   *core.PdfIndirectObject
-	Lock *core.PdfIndirectObject // Shall be an indirect reference.
-	SV   *core.PdfIndirectObject // Shall be an indirect reference.
 	Kids *core.PdfObjectArray
 }
 
@@ -304,7 +309,7 @@ type PdfSignatureFieldLock struct {
 // (Table 234 - p. 455 in PDF32000_2008).
 type PdfSignatureFieldSeed struct {
 	container *core.PdfIndirectObject
-	// Type
+
 	Ff               *core.PdfObjectInteger
 	Filter           *core.PdfObjectName
 	SubFilter        *core.PdfObjectArray