Split xref table and stream code and tests

sign/pdfxref_table.go

@@ -0,0 +1,42 @@
+package sign
+
+import (
+	"fmt"
+)
+
+// writeIncrXrefTable writes the incremental cross-reference table to the output buffer.
+func (context *SignContext) writeIncrXrefTable() error {
+	// Write xref header
+	if _, err := context.OutputBuffer.Write([]byte("xref\n")); err != nil {
+		return fmt.Errorf("failed to write incremental xref header: %w", err)
+	}
+
+	// Write updated entries
+	for _, entry := range context.updatedXrefEntries {
+		pageXrefObj := fmt.Sprintf("%d %d\n", entry.ID, 1)
+		if _, err := context.OutputBuffer.Write([]byte(pageXrefObj)); err != nil {
+			return fmt.Errorf("failed to write updated xref object: %w", err)
+		}
+
+		xrefLine := fmt.Sprintf("%010d 00000 n\r\n", entry.Offset)
+		if _, err := context.OutputBuffer.Write([]byte(xrefLine)); err != nil {
+			return fmt.Errorf("failed to write updated incremental xref entry: %w", err)
+		}
+	}
+
+	// Write xref subsection header
+	startXrefObj := fmt.Sprintf("%d %d\n", context.lastXrefID+1, len(context.newXrefEntries))
+	if _, err := context.OutputBuffer.Write([]byte(startXrefObj)); err != nil {
+		return fmt.Errorf("failed to write starting xref object: %w", err)
+	}
+
+	// Write new entries
+	for _, entry := range context.newXrefEntries {
+		xrefLine := fmt.Sprintf("%010d 00000 n\r\n", entry.Offset)
+		if _, err := context.OutputBuffer.Write([]byte(xrefLine)); err != nil {
+			return fmt.Errorf("failed to write incremental xref entry: %w", err)
+		}
+	}
+
+	return nil
+}