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/libreoffice/routes.go

@@ -1,6 +1,7 @@
 package libreoffice
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
 	"net/http"
@@ -27,22 +28,33 @@ func convertRoute(libreOffice libreofficeapi.Uno, engine gotenberg.PdfEngine) ap
 				inputPaths       []string
 				landscape        bool
 				nativePageRanges string
+				exportFormFields bool
 				pdfa             string
 				pdfua            bool
 				nativePdfFormats bool
 				merge            bool
-				exportFormFields bool
+				metadata         map[string]interface{}
 			)
 
 			err := ctx.FormData().
 				MandatoryPaths(libreOffice.Extensions(), &inputPaths).
 				Bool("landscape", &landscape, false).
 				String("nativePageRanges", &nativePageRanges, "").
+				Bool("exportFormFields", &exportFormFields, true).
 				String("pdfa", &pdfa, "").
 				Bool("pdfua", &pdfua, false).
 				Bool("nativePdfFormats", &nativePdfFormats, true).
 				Bool("merge", &merge, false).
-				Bool("exportFormFields", &exportFormFields, true).
+				Custom("metadata", func(value string) error {
+					metadata = map[string]interface{}{}
+					if len(value) > 0 {
+						err := json.Unmarshal([]byte(value), &metadata)
+						if err != nil {
+							return err
+						}
+					}
+					return nil
+				}).
 				Validate()
 			if err != nil {
 				return fmt.Errorf("validate form data: %w", err)
@@ -116,6 +128,14 @@ func convertRoute(libreOffice libreofficeapi.Uno, engine gotenberg.PdfEngine) ap
 					outputPath = convertOutputPath
 				}
 
+				// Writes and potentially overrides metadata entries, if any.
+				if len(metadata) > 0 {
+					err = engine.WriteMetadata(ctx, ctx.Log(), outputPath, metadata)
+					if err != nil {
+						return fmt.Errorf("write metadata failure: %w", err)
+					}
+				}
+
 				// Last but not least, add the output path to the context so that
 				// the API is able to send it as a response to the client.
 				err = ctx.AddOutputPaths(outputPath)
@@ -160,6 +180,16 @@ func convertRoute(libreOffice libreofficeapi.Uno, engine gotenberg.PdfEngine) ap
 				}
 			}
 
+			// Writes and potentially overrides metadata entries, if any.
+			if len(metadata) > 0 {
+				for _, outputPath := range outputPaths {
+					err = engine.WriteMetadata(ctx, ctx.Log(), outputPath, metadata)
+					if err != nil {
+						return fmt.Errorf("write metadata: %w", err)
+					}
+				}
+			}
+
 			// Last but not least, add the output paths to the context so that
 			// the API is able to send them as a response to the client.
 			err = ctx.AddOutputPaths(outputPaths...)