feat(ExifTool): add capability to overwrite metadata of the PDF generated (#776)

* add new metadata functions to pdf engine interface

* add exiftool module with relevant test cases

* use exiftool to overwrite metadata in libreoffice

* use exiftool to overwrite metadata in chromium

* fix linter issues

* fix more linter issues

* more test cases for better coverage

* remove utils

* minor changes

* remove metadata from pdfoptions

* correct indentation

* read/write metadata one file at a time.

pkg/modules/pdftk/pdftk.go

@@ -75,6 +75,16 @@ func (engine *PdfTk) Convert(ctx context.Context, logger *zap.Logger, formats go
 	return fmt.Errorf("convert PDF to '%+v' with PDFtk: %w", formats, gotenberg.ErrPdfEngineMethodNotSupported)
 }
 
+// ReadMetadata is not available in this implementation.
+func (engine *PdfTk) ReadMetadata(ctx context.Context, logger *zap.Logger, inputPaths string, metadata map[string]interface{}) error {
+	return fmt.Errorf("read PDF metadata with PDFtk: %w", gotenberg.ErrPdfEngineMethodNotSupported)
+}
+
+// WriteMetadata is not available in this implementation.
+func (engine *PdfTk) WriteMetadata(ctx context.Context, logger *zap.Logger, inputPaths string, newMetadata map[string]interface{}) error {
+	return fmt.Errorf("write PDF metadata with PDFtk: %w", gotenberg.ErrPdfEngineMethodNotSupported)
+}
+
 // Interface guards.
 var (
 	_ gotenberg.Module      = (*PdfTk)(nil)

pkg/modules/pdftk/pdftk_test.go

@@ -148,3 +148,21 @@ func TestPdfTk_Convert(t *testing.T) {
 		t.Errorf("expected error %v, but got: %v", gotenberg.ErrPdfEngineMethodNotSupported, err)
 	}
 }
+
+func TestLibreOfficePdfEngine_ReadMetadata(t *testing.T) {
+	engine := new(PdfTk)
+	err := engine.ReadMetadata(context.Background(), zap.NewNop(), "", nil)
+
+	if !errors.Is(err, gotenberg.ErrPdfEngineMethodNotSupported) {
+		t.Errorf("expected error %v, but got: %v", gotenberg.ErrPdfEngineMethodNotSupported, err)
+	}
+}
+
+func TestLibreOfficePdfEngine_WriteMetadata(t *testing.T) {
+	engine := new(PdfTk)
+	err := engine.WriteMetadata(context.Background(), zap.NewNop(), "", nil)
+
+	if !errors.Is(err, gotenberg.ErrPdfEngineMethodNotSupported) {
+		t.Errorf("expected error %v, but got: %v", gotenberg.ErrPdfEngineMethodNotSupported, err)
+	}
+}