Add sign functionality

sign/pdftrailer.go

@@ -0,0 +1,44 @@
+package sign
+
+import (
+	"strconv"
+	"strings"
+)
+
+func (context *SignContext) writeTrailer() error {
+	trailer_length := context.PDFReader.XrefInformation.IncludingTrailerEndPos - context.PDFReader.XrefInformation.EndPos
+
+	// Read the trailer so we can replace the size.
+	context.InputFile.Seek(context.PDFReader.XrefInformation.EndPos+1, 0)
+	trailer_buf := make([]byte, trailer_length)
+	if _, err := context.InputFile.Read(trailer_buf); err != nil {
+		return err
+	}
+
+	root_string := "Root " + context.CatalogData.RootString
+	new_root := "Root " + strconv.FormatInt(int64(context.CatalogData.ObjectId), 10) + " 0 R"
+
+	size_string := "Size " + strconv.FormatInt(context.PDFReader.XrefInformation.ItemCount, 10)
+	new_size := "Size " + strconv.FormatInt(context.PDFReader.XrefInformation.ItemCount+2, 10)
+
+	trailer_string := string(trailer_buf)
+	trailer_string = strings.Replace(trailer_string, root_string, new_root, -1)
+	trailer_string = strings.Replace(trailer_string, size_string, new_size, -1)
+
+	// Write the new trailer.
+	if _, err := context.OutputFile.Write([]byte(trailer_string)); err != nil {
+		return err
+	}
+
+	// Write the new xref start position.
+	if _, err := context.OutputFile.Write([]byte(strconv.FormatInt(context.NewXrefStart, 10) + "\n")); err != nil {
+		return err
+	}
+
+	// Write PDF ending.
+	if _, err := context.OutputFile.Write([]byte("%%EOF\n")); err != nil {
+		return err
+	}
+
+	return nil
+}