feat(pdfengines): add support for flattening annotations (#1105)

* initial changes

* Add tests

* Fix edge case when we need to regenerate appearances

* Fix comments

* Add missing comment

* Add missing comment

* Add missing comment

* Add flatten option to the merge route

* Add flatten option to the libreoffice convert route

* Add flatten option to the chromium convert route

* Revert "Add flatten option to the chromium convert route"

This reverts commit cdab8b4e6b.

* Ignore lint false positives

* Add missing tests

* Add flatten route tests

* Replace input instead of creating a new file

* create copy before flatten in tests

---------

Co-authored-by: Peter Chakalov <peter.chakalov@abraxa.com>

pkg/modules/libreoffice/pdfengine/pdfengine.go

@@ -56,6 +56,11 @@ func (engine *LibreOfficePdfEngine) Split(ctx context.Context, logger *zap.Logge
 	return nil, fmt.Errorf("split PDF with LibreOffice: %w", gotenberg.ErrPdfEngineMethodNotSupported)
 }
 
+// Flatten is not available in this implementation.
+func (engine *LibreOfficePdfEngine) Flatten(ctx context.Context, logger *zap.Logger, inputPath string) error {
+	return fmt.Errorf("Flatten PDF with LibreOffice: %w", gotenberg.ErrPdfEngineMethodNotSupported)
+}
+
 // Convert converts the given PDF to a specific PDF format. Currently, only the
 // PDF/A-1b, PDF/A-2b, PDF/A-3b and PDF/UA formats are available. If another
 // PDF format is requested, it returns a [gotenberg.ErrPdfFormatNotSupported]

pkg/modules/libreoffice/pdfengine/pdfengine_test.go

@@ -127,6 +127,15 @@ func TestLibreOfficePdfEngine_Split(t *testing.T) {
 	}
 }
 
+func TestLibreOfficePdfEngine_Flatten(t *testing.T) {
+	engine := new(LibreOfficePdfEngine)
+	err := engine.Flatten(context.Background(), zap.NewNop(), "")
+
+	if !errors.Is(err, gotenberg.ErrPdfEngineMethodNotSupported) {
+		t.Errorf("expected error %v, but got: %v", gotenberg.ErrPdfEngineMethodNotSupported, err)
+	}
+}
+
 func TestLibreOfficePdfEngine_Convert(t *testing.T) {
 	for _, tc := range []struct {
 		scenario      string

pkg/modules/libreoffice/routes.go

@@ -60,6 +60,7 @@ func convertRoute(libreOffice libreofficeapi.Uno, engine gotenberg.PdfEngine) ap
 				maxImageResolution              int
 				nativePdfFormats                bool
 				merge                           bool
+				flatten                         bool
 			)
 
 			err := form.
@@ -135,6 +136,7 @@ func convertRoute(libreOffice libreofficeapi.Uno, engine gotenberg.PdfEngine) ap
 					}
 					return nil
 				}).
+				Bool("flatten", &flatten, false).
 				Validate()
 			if err != nil {
 				return fmt.Errorf("validate form data: %w", err)
@@ -261,6 +263,13 @@ func convertRoute(libreOffice libreofficeapi.Uno, engine gotenberg.PdfEngine) ap
 				return fmt.Errorf("write metadata: %w", err)
 			}
 
+			if flatten {
+				err = pdfengines.FlattenStub(ctx, engine, outputPaths)
+				if err != nil {
+					return fmt.Errorf("flatten PDFs: %w", err)
+				}
+			}
+
 			if len(outputPaths) > 1 && splitMode == zeroValuedSplitMode {
 				// If .zip archive, document.docx -> document.docx.pdf.
 				for i, inputPath := range inputPaths {

pkg/modules/libreoffice/routes_test.go

@@ -402,6 +402,38 @@ func TestConvertRoute(t *testing.T) {
 			expectHttpError:        false,
 			expectOutputPathsCount: 0,
 		},
+		{
+			scenario: "PDF engine flatten error",
+			ctx: func() *api.ContextMock {
+				ctx := &api.ContextMock{Context: new(api.Context)}
+				ctx.SetFiles(map[string]string{
+					"document.docx": "/document.docx",
+				})
+				ctx.SetValues(map[string][]string{
+					"flatten": {
+						"true",
+					},
+				})
+				ctx.SetCancelled(true)
+				return ctx
+			}(),
+			libreOffice: &libreofficeapi.ApiMock{
+				PdfMock: func(ctx context.Context, logger *zap.Logger, inputPath, outputPath string, options libreofficeapi.Options) error {
+					return nil
+				},
+				ExtensionsMock: func() []string {
+					return []string{".docx"}
+				},
+			},
+			engine: &gotenberg.PdfEngineMock{
+				FlattenMock: func(ctx context.Context, logger *zap.Logger, inputPath string) error {
+					return errors.New("foo")
+				},
+			},
+			expectError:            true,
+			expectHttpError:        false,
+			expectOutputPathsCount: 0,
+		},
 		{
 			scenario: "cannot add output paths",
 			ctx: func() *api.ContextMock {
@@ -454,6 +486,9 @@ func TestConvertRoute(t *testing.T) {
 					"metadata": {
 						"{\"Creator\": \"foo\", \"Producer\": \"bar\" }",
 					},
+					"flatten": {
+						"true",
+					},
 				})
 				return ctx
 			}(),
@@ -475,6 +510,9 @@ func TestConvertRoute(t *testing.T) {
 				WriteMetadataMock: func(ctx context.Context, logger *zap.Logger, metadata map[string]interface{}, inputPath string) error {
 					return nil
 				},
+				FlattenMock: func(ctx context.Context, logger *zap.Logger, inputPath string) error {
+					return nil
+				},
 			},
 			expectError:            false,
 			expectHttpError:        false,
@@ -502,6 +540,9 @@ func TestConvertRoute(t *testing.T) {
 					"metadata": {
 						"{\"Creator\": \"foo\", \"Producer\": \"bar\" }",
 					},
+					"flatten": {
+						"true",
+					},
 				})
 				ctx.SetPathRename(&gotenberg.PathRenameMock{RenameMock: func(oldpath, newpath string) error {
 					return nil
@@ -526,6 +567,9 @@ func TestConvertRoute(t *testing.T) {
 				WriteMetadataMock: func(ctx context.Context, logger *zap.Logger, metadata map[string]interface{}, inputPath string) error {
 					return nil
 				},
+				FlattenMock: func(ctx context.Context, logger *zap.Logger, inputPath string) error {
+					return nil
+				},
 			},
 			expectError:            false,
 			expectHttpError:        false,