Add sign functionality

sign/pdfxref.go

@@ -0,0 +1,55 @@
+package sign
+
+import (
+	"errors"
+	"strconv"
+)
+
+func (context *SignContext) writeXref() error {
+
+	// @todo: support stream xref.
+
+	if context.PDFReader.XrefInformation.Type == "table" {
+		if err := context.writeXrefTable(); err != nil {
+			return err
+		}
+	} else {
+		return errors.New("Unkwn xref type: " + context.PDFReader.XrefInformation.Type)
+	}
+
+	return nil
+}
+
+func (context *SignContext) writeXrefTable() error {
+	xref_size := "xref\n0 " + strconv.FormatInt(context.PDFReader.XrefInformation.ItemCount, 10)
+	new_xref_size := "xref\n0 " + strconv.FormatInt(context.PDFReader.XrefInformation.ItemCount+2, 10)
+
+	if _, err := context.OutputFile.Write([]byte(new_xref_size)); err != nil {
+		return err
+	}
+
+	// Write the old xref table to the output pdf.
+	if err := writePartFromSourceFileToTargetFile(context.InputFile, context.OutputFile, context.PDFReader.XrefInformation.StartPos+int64(len(xref_size)), context.PDFReader.XrefInformation.Length-int64(len(xref_size))); err != nil {
+		return err
+	}
+
+	// Create the new catalog xref line.
+	catalog_object_start_position := strconv.FormatInt(context.PDFReader.XrefInformation.StartPos, 10)
+	catalog_xref_line := leftPad(catalog_object_start_position, "0", 10-len(catalog_object_start_position)) + " 00000 n\n"
+
+	// Write the new catalog xref line.
+	if _, err := context.OutputFile.Write([]byte(catalog_xref_line)); err != nil {
+		return err
+	}
+
+	// Create the new signature xref line.
+	signature_object_start_position := strconv.FormatInt(context.PDFReader.XrefInformation.StartPos+context.CatalogData.Length, 10)
+	signature_xref_line := leftPad(signature_object_start_position, "0", 10-len(signature_object_start_position)) + " 00000 n\n"
+
+	// Write the new signature xref line.
+	if _, err := context.OutputFile.Write([]byte(signature_xref_line)); err != nil {
+		return err
+	}
+
+	return nil
+}