webhook: resulting file was deleted because of defer outside of goroutine

internal/app/api/merge.go

@@ -1,6 +1,7 @@
 package api
 
 import (
+	"errors"
 	"fmt"
 	"net/http"
 	"os"
@@ -13,20 +14,23 @@ import (
 func merge(c echo.Context) error {
 	r, err := newResource(c)
 	if err != nil {
-		return err
+		return hijackErr(err, r)
 	}
-	defer r.removeAll()
 	fpaths, err := r.filePaths([]string{".pdf"})
 	if err != nil {
-		return err
+		return hijackErr(err, r)
+	}
+	if len(fpaths) == 0 {
+		return hijackErr(errors.New("no suitable PDF files to merge"), r)
 	}
 	baseFilename, err := rand.Get()
 	if err != nil {
-		return fmt.Errorf("getting result file name: %v", err)
+		return hijackErr(fmt.Errorf("getting result file name: %v", err), r)
 	}
 	filename := fmt.Sprintf("%s.pdf", baseFilename)
 	fpath := fmt.Sprintf("%s/%s", r.dirPath, filename)
 	if r.webhookURL() == "" {
+		defer r.removeAll()
 		// if no webhook URL given, run merge
 		// and directly return the resulting PDF file
 		// or an error.
@@ -39,6 +43,7 @@ func merge(c echo.Context) error {
 	// run the following lines in a goroutine so that
 	// it doesn't block.
 	go func() {
+		defer r.removeAll()
 		if err := printer.Merge(fpaths, fpath); err != nil {
 			c.Logger().Errorf("%v", err)
 			return