icecastLastPlayedSongs was replaced by icecastCurrentSong that fetch only one song at the very end of a playlist.log. Also added a benchmark for this func.

internal/radio/icecast.go

@@ -19,7 +19,9 @@ const (
 	IcecastPlaylistDateFormat = "02/Jan/2006:15:04:05 -0700"
 	SongTimeFormat            = "2006 15:04-0700"
 
-	bufferSizePerLine = 320
+	bufferSizePerLine = 512
+	separatorOne      = 26
+	separatorTwo      = 38 + 1
 )
 
 var (
@@ -96,61 +98,46 @@ func IcecastLastSong(playlistPath string) *Song {
 	return nil
 }
 
-func icecastLastPlayedSongs(playlistPath string, n int) ([]Song, error) {
-	var buf []byte
-	var offset int64 = 0
-	var bufferSize int64 = int64(n) * bufferSizePerLine
-
-	playlist, err := os.Open(playlistPath)
+func icecastCurrentSong(playlistPath string) (*Song, error) {
+	fd, err := os.Open(playlistPath)
 	if err != nil {
 		return nil, err
 	}
-	defer playlist.Close()
+	defer fd.Close()
 
-	playlist_stat, _ := playlist.Stat()
-
-	if playlist_stat.Size() == 0 {
+	fdSize, _ := fd.Seek(0, io.SeekEnd)
+	if fdSize == 0 {
 		return nil, nil
 	}
 
-	if playlist_stat.Size() < bufferSize {
-		buf = make([]byte, playlist_stat.Size())
-	} else {
-		buf = make([]byte, bufferSize)
-		offset = playlist_stat.Size() - bufferSize
+	var bufSize int64 = bufferSizePerLine
+	if fdSize < bufferSizePerLine {
+		bufSize = fdSize
 	}
 
-	_, err = playlist.ReadAt(buf, offset)
-	if err != nil && err != io.EOF {
+	_, err = fd.Seek(-bufSize, io.SeekEnd)
+	if err != nil {
 		return nil, err
 	}
 
-	lines := bytes.Split(buf, []byte("\n"))
+	buf := make([]byte, bufSize)
 
-	if len(lines) < 2 {
-		return nil, nil
+	_, err = fd.Read(buf)
+	if err != nil {
+		return nil, err
 	}
 
-	lines = lines[:len(lines)-1]
+	curSongEnd := bytes.LastIndexByte(buf, '\n')
+	line := buf[bytes.LastIndexByte(buf[:curSongEnd], '\n')+1 : curSongEnd]
 
-	if len(lines) > n {
-		lines = lines[len(lines)-n:]
-	}
+	songTime, _ := time.Parse(IcecastPlaylistDateFormat, string(line[:separatorOne]))
 
-	songs := make([]Song, 0, len(lines))
+	separatorThree := bytes.LastIndexByte(line, '|')
 
-	for _, line := range lines {
-		fields := bytes.Split(line, []byte("|"))
-
-		tim, _ := time.Parse(IcecastPlaylistDateFormat, string(fields[0]))
-
-		songs = append(songs, Song{
-			Time:      tim.Format(SongTimeFormat),
-			Listeners: string(fields[2]),
-			Song:      string(fields[3])})
-	}
-
-	return songs, nil
+	return &Song{
+		Time:      songTime.Format(SongTimeFormat),
+		Listeners: string(line[separatorTwo:separatorThree]),
+		Song:      string(line[separatorThree+1:])}, nil
 }
 
 type PlaylistLogWatcher struct {
@@ -180,13 +167,14 @@ func (pw *PlaylistLogWatcher) Watch(playlistPath string, n int) (err error) {
 	pw.watcher.WatchForMask(pw.changed, watcher.ModIgnMask)
 
 	if lastPlayedCache == nil {
-		lastPlayedCache = make([]Song, n)
-		songs, err := icecastLastPlayedSongs(playlistPath, n)
-		if err == nil && len(songs) > 0 {
-			copy(lastPlayedCache, songs)
-		} else if err != nil {
-			log.Fatalln("failed to retrieve last songs:", err)
+		lastPlayedCache = make([]Song, 0, n)
 	}
+
+	cur, err := icecastCurrentSong(playlistPath)
+	if err != nil {
+		log.Println("failed to fetch current song:", err)
+	} else if cur != nil && currentlyPlaying.Time != "" {
+		currentlyPlaying = *cur
 	}
 
 	go func() {
@@ -195,19 +183,19 @@ func (pw *PlaylistLogWatcher) Watch(playlistPath string, n int) (err error) {
 
 			if mask&syscall.IN_MODIFY > 0 {
 				lastPlayedCacheMutex.Lock()
-				songs, err := icecastLastPlayedSongs(playlistPath, 1)
-				if err == nil && len(songs) > 0 {
+				song, err := icecastCurrentSong(playlistPath)
+				if err == nil && song != nil {
 					CheckAndUpdateMostListenedSong(song, &currentlyPlaying)
 					if currentlyPlaying.Time == "" {
-						currentlyPlaying = songs[0]
+						currentlyPlaying = *song
 					} else {
-						currentlyPlaying.Listeners = songs[0].Listeners
+						currentlyPlaying.Listeners = song.Listeners
 						if len(lastPlayedCache) == n {
 							lastPlayedCache = append(lastPlayedCache[1:], currentlyPlaying)
 						} else {
 							lastPlayedCache = append(lastPlayedCache, currentlyPlaying)
 						}
-						currentlyPlaying = songs[0]
+						currentlyPlaying = *song
 					}
 				} else if err != nil {
 					log.Println("failed to retrieve last songs:", err)

internal/radio/icecast_test.go

@@ -0,0 +1,12 @@
+package radio
+
+import "testing"
+
+const playlistPath = "../../p.log"
+
+func BenchmarkIcecastCurrentSong(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		s, err := icecastCurrentSong(playlistPath)
+		b.Log(s, err)
+	}
+}