refactor: reduce GC pressure by pre-allocating slices

Signed-off-by: Deluan <deluan@navidrome.org>

scanner/mapping.go

@@ -143,7 +143,7 @@ func (s MediaFileMapper) albumArtistID(md metadata.Tags) string {
 func (s MediaFileMapper) mapGenres(genres []string) (string, model.Genres) {
 	var result model.Genres
 	unique := map[string]struct{}{}
-	var all []string
+	all := make([]string, 0, len(genres)*2)
 	for i := range genres {
 		gs := strings.FieldsFunc(genres[i], func(r rune) bool {
 			return strings.ContainsRune(conf.Server.Scanner.GenreSeparators, r)

scanner/metadata/metadata.go

@@ -84,7 +84,7 @@ func NewTag(filePath string, fileInfo os.FileInfo, tags ParsedTags) Tags {
 func removeDuplicatesAndEmpty(values []string) []string {
 	encountered := map[string]struct{}{}
 	empty := true
-	var result []string
+	result := make([]string, 0, len(values))
 	for _, v := range values {
 		if _, ok := encountered[v]; ok {
 			continue
@@ -300,7 +300,7 @@ func (t Tags) getFirstTagValue(tagNames ...string) string {
 }
 
 func (t Tags) getAllTagValues(tagNames ...string) []string {
-	var values []string
+	values := make([]string, 0, len(tagNames)*2)
 	for _, tag := range tagNames {
 		if v, ok := t.Tags[tag]; ok {
 			values = append(values, v...)
@@ -311,7 +311,8 @@ func (t Tags) getAllTagValues(tagNames ...string) []string {
 
 func (t Tags) getSortTag(originalTag string, tagNames ...string) string {
 	formats := []string{"sort%s", "sort_%s", "sort-%s", "%ssort", "%s_sort", "%s-sort"}
-	all := []string{originalTag}
+	all := make([]string, 1, len(tagNames)*len(formats)+1)
+	all[0] = originalTag
 	for _, tag := range tagNames {
 		for _, format := range formats {
 			name := fmt.Sprintf(format, tag)

scanner/tag_scanner.go

@@ -294,7 +294,7 @@ func (s *TagScanner) processChangedDir(ctx context.Context, refresher *refresher
 
 	// If track from folder is newer than the one in DB, select for update/insert in DB
 	log.Trace(ctx, "Processing changed folder", "dir", dir, "tracksInDB", len(currentTracks), "tracksInFolder", len(files))
-	var filesToUpdate []string
+	filesToUpdate := make([]string, 0, len(files))
 	for filePath, entry := range files {
 		c, inDB := currentTracks[filePath]
 		if !inDB || fullScan {

scanner/walk_dir_tree.go

@@ -64,7 +64,6 @@ func walkFolder(ctx context.Context, rootPath string, currentFolder string, resu
 }
 
 func loadDir(ctx context.Context, dirPath string) ([]string, *dirStats, error) {
-	var children []string
 	stats := &dirStats{}
 
 	dirInfo, err := os.Stat(dirPath)
@@ -77,11 +76,13 @@ func loadDir(ctx context.Context, dirPath string) ([]string, *dirStats, error) {
 	dir, err := os.Open(dirPath)
 	if err != nil {
 		log.Error(ctx, "Error in Opening directory", "path", dirPath, err)
-		return children, stats, err
+		return nil, stats, err
 	}
 	defer dir.Close()
 
-	for _, entry := range fullReadDir(ctx, dir) {
+	entries := fullReadDir(ctx, dir)
+	children := make([]string, 0, len(entries))
+	for _, entry := range entries {
 		isDir, err := isDirOrSymlinkToDir(dirPath, entry)
 		// Skip invalid symlinks
 		if err != nil {