Add sign functionality

sign/pdfbyterange.go

@@ -0,0 +1,45 @@
+package sign
+
+import (
+	"fmt"
+	"strings"
+)
+
+func (context *SignContext) updateByteRange() error {
+	// Get current filesize. Easier than what should be the current size.
+	// @todo: find out of this is safe.
+	output_file_stat, _ := context.OutputFile.Stat()
+
+	// Don't count last newline as file length.
+	output_file_size := output_file_stat.Size() - 1
+
+	// Calculate ByteRange values to replace them.
+	context.ByteRangeValues = make([]int64, 4)
+
+	// Signature ByteRange part 1 start byte is always byte 0.
+	context.ByteRangeValues[0] = int64(0)
+
+	// Signature ByteRange part 1 length always stops at the actual signature start byte.
+	context.ByteRangeValues[1] = context.SignatureContentsStartByte
+
+	// Signature ByteRange part 2 start byte directly starts after the actual signature.
+	context.ByteRangeValues[2] = context.ByteRangeValues[1] + int64(signatureMaxLength)
+
+	// Signature ByteRange part 2 length is everything else of the file.
+	context.ByteRangeValues[3] = output_file_size - context.ByteRangeValues[2]
+
+	new_byte_range := fmt.Sprintf("/ByteRange[%d %d %d %d]", context.ByteRangeValues[0], context.ByteRangeValues[1], context.ByteRangeValues[2], context.ByteRangeValues[3])
+
+	// Make sure our ByteRange string didn't shrink in length.
+	new_byte_range += strings.Repeat(" ", len(signatureByteRangePlaceholder)-len(new_byte_range))
+
+	// Seek to ByteRange position in file.
+	context.OutputFile.Seek(context.ByteRangeStartByte, 0)
+
+	// Write new ByteRange.
+	if _, err := context.OutputFile.Write([]byte(new_byte_range)); err != nil {
+		return err
+	}
+
+	return nil
+}