ファイル名の上限を拡大し、動画の配信・削除を os.Root に置き換え（エピソード ID は 64 バイト上限）

internal/media/path.go

@@ -1,23 +1,41 @@
 package media
 
 import (
+	"fmt"
 	"path/filepath"
 	"strings"
 	"unicode"
 )
 
-const maxComponentRunes = 80
-const maxComponentBytes = 60
+const (
+	maxSeriesBytes    = 90
+	maxEpisodeBytes   = 140
+	maxEpisodeIDBytes = 64
+	maxFilenameBytes  = 255
+)
 
 // RelativeVideoPath は worker と web が共有する保存先の相対パスを返す。
-func RelativeVideoPath(seriesTitle, episodeTitle, episodeID string) string {
-	series := sanitizeComponent(seriesTitle)
-	episode := sanitizeComponent(episodeTitle)
-	id := sanitizeComponent(episodeID)
-	return filepath.Join(series, series+" "+episode+" ["+id+"].mp4")
+func RelativeVideoPath(seriesTitle, episodeTitle, episodeID string) (string, error) {
+	series := sanitizeComponent(seriesTitle, maxSeriesBytes)
+	episode := sanitizeComponent(episodeTitle, maxEpisodeBytes)
+	id := sanitizeComponent(episodeID, -1)
+	if len(id) > maxEpisodeIDBytes {
+		return "", fmt.Errorf("エピソードIDはサニタイズ後%dバイト以下である必要があります: %dバイト", maxEpisodeIDBytes, len(id))
+	}
+
+	// A directory entry must fit within the NFS namlen limit. Keep the episode
+	// ID intact and use the remaining bytes for the episode title.
+	const separators = "  [].mp4"
+	seriesInFilename := series
+	titleBytes := maxFilenameBytes - len(seriesInFilename) - len(id) - len(separators)
+	if titleBytes < 0 {
+		titleBytes = 0
+	}
+	episode = truncateComponent(episode, titleBytes, false)
+	return filepath.Join(series, seriesInFilename+" "+episode+" ["+id+"].mp4"), nil
 }
 
-func sanitizeComponent(value string) string {
+func sanitizeComponent(value string, maxBytes int) string {
 	var result []rune
 	lastReplacement := false
 	for _, r := range value {
@@ -39,22 +57,25 @@ func sanitizeComponent(value string) string {
 	if clean == "" || clean == "." || clean == ".." {
 		return "名称未設定"
 	}
-	runes := []rune(clean)
-	if len(runes) > maxComponentRunes {
-		runes = runes[:maxComponentRunes]
+	return truncateComponent(clean, maxBytes, true)
+}
+
+func truncateComponent(value string, maxBytes int, fallback bool) string {
+	if maxBytes < 0 {
+		return value
 	}
 	var limited []rune
 	bytes := 0
-	for _, r := range runes {
+	for _, r := range value {
 		size := len(string(r))
-		if bytes+size > maxComponentBytes {
+		if bytes+size > maxBytes {
 			break
 		}
 		limited = append(limited, r)
 		bytes += size
 	}
-	clean = strings.Trim(string(limited), " .")
-	if clean == "" || clean == "." || clean == ".." {
+	clean := strings.Trim(string(limited), " .")
+	if fallback && (clean == "" || clean == "." || clean == "..") {
 		return "名称未設定"
 	}
 	return clean