minstrel/internal/library/vorbisgenre_test.go

package library

import (
	"bytes"
	"encoding/binary"
	"strings"
	"testing"

	"github.com/dhowden/tag"
)

// vorbisComment builds a comment block: vendor, count, then each "KEY=value".
func vorbisComment(fields ...string) []byte {
	var b bytes.Buffer
	vendor := "minstrel-test"
	_ = binary.Write(&b, binary.LittleEndian, uint32(len(vendor)))
	b.WriteString(vendor)
	_ = binary.Write(&b, binary.LittleEndian, uint32(len(fields)))
	for _, f := range fields {
		_ = binary.Write(&b, binary.LittleEndian, uint32(len(f)))
		b.WriteString(f)
	}
	return b.Bytes()
}

// buildFLAC assembles a STREAMINFO block and a comment block, optionally
// behind an ID3v2 tag the way some taggers write them.
func buildFLAC(withID3 bool, fields ...string) []byte {
	var b bytes.Buffer
	if withID3 {
		pad := make([]byte, 20)
		b.WriteString("ID3")
		b.Write([]byte{4, 0, 0})
		b.Write(synchsafeBytes(len(pad)))
		b.Write(pad)
	}
	b.WriteString("fLaC")
	b.Write([]byte{0x00, 0, 0, 34}) // STREAMINFO, not last
	b.Write(make([]byte, 34))
	vc := vorbisComment(fields...)
	b.Write([]byte{0x84, byte(len(vc) >> 16), byte(len(vc) >> 8), byte(len(vc))}) // last, type 4
	b.Write(vc)
	return b.Bytes()
}

// oggCRC is the Ogg page checksum: CRC-32, polynomial 0x04c11db7, no
// reflection, zero initial value. dhowden/tag verifies it, so the end-to-end
// tests need real pages.
func oggCRC(p []byte) uint32 {
	var crc uint32
	for _, c := range p {
		crc ^= uint32(c) << 24
		for i := 0; i < 8; i++ {
			if crc&0x80000000 != 0 {
				crc = crc<<1 ^ 0x04c11db7
			} else {
				crc <<= 1
			}
		}
	}
	return crc
}

// buildOgg lays packets out as Ogg pages for one logical stream, splitting a
// packet across pages when it needs more than 255 lacing values.
func buildOgg(serial uint32, packets ...[]byte) []byte {
	var out bytes.Buffer
	var seq uint32
	for _, p := range packets {
		var lacing []byte
		for n := len(p); ; n -= 255 {
			if n >= 255 {
				lacing = append(lacing, 255)
				continue
			}
			lacing = append(lacing, byte(n))
			break
		}
		continued := false
		for off := 0; len(lacing) > 0; {
			segs := lacing
			if len(segs) > 255 {
				segs = segs[:255]
			}
			lacing = lacing[len(segs):]
			n := 0
			for _, s := range segs {
				n += int(s)
			}
			var page bytes.Buffer
			page.WriteString("OggS")
			page.WriteByte(0)
			flags := byte(0)
			if continued {
				flags |= 0x01
			}
			if seq == 0 {
				flags |= 0x02
			}
			page.WriteByte(flags)
			page.Write(make([]byte, 8)) // granule position
			_ = binary.Write(&page, binary.LittleEndian, serial)
			_ = binary.Write(&page, binary.LittleEndian, seq)
			page.Write(make([]byte, 4)) // checksum, filled below
			page.WriteByte(byte(len(segs)))
			page.Write(segs)
			page.Write(p[off : off+n])
			raw := page.Bytes()
			binary.LittleEndian.PutUint32(raw[22:26], oggCRC(raw))
			out.Write(raw)
			off += n
			seq++
			continued = true
		}
	}
	return out.Bytes()
}

func vorbisIdent() []byte { return append([]byte("\x01vorbis"), make([]byte, 23)...) }

// mp4Box wraps children in an atom of the given kind.
func mp4Box(kind string, children ...[]byte) []byte {
	body := bytes.Join(children, nil)
	b := make([]byte, 8, 8+len(body))
	binary.BigEndian.PutUint32(b, uint32(8+len(body)))
	copy(b[4:], kind)
	return append(b, body...)
}

func mp4Text(value string) []byte {
	return mp4Box("data", []byte{0, 0, 0, 1, 0, 0, 0, 0}, []byte(value))
}

// buildMP4 places the ©gen atoms under moov/udta/meta/ilst. isoMeta adds the
// four version/flags bytes ISO files carry before meta's children.
func buildMP4(isoMeta bool, genAtoms ...[]byte) []byte {
	ilst := mp4Box("ilst", append([][]byte{mp4Box("\xa9nam", mp4Text("A Song"))}, genAtoms...)...)
	hdlr := mp4Box("hdlr", make([]byte, 25))
	var meta []byte
	if isoMeta {
		meta = mp4Box("meta", []byte{0, 0, 0, 0}, hdlr, ilst)
	} else {
		meta = mp4Box("meta", hdlr, ilst)
	}
	ftyp := mp4Box("ftyp", []byte("M4A \x00\x00\x00\x00M4A mp42isom"))
	mdat := mp4Box("mdat", make([]byte, 64))
	// moov after mdat, as many encoders write it.
	return bytes.Join([][]byte{ftyp, mdat, mp4Box("moov", mp4Box("udta", meta))}, nil)
}

var lifeForms = []string{
	"Boom Bap", "Downtempo", "Hip Hop", "Instrumental",
	"Lo-Fi", "Lo-Fi Hip Hop", "Chillwave", "Instrumental Hip Hop",
}

func genreFields(values ...string) []string {
	out := make([]string, len(values))
	for i, v := range values {
		out[i] = "GENRE=" + v
	}
	return out
}

// Shaped like a real multi-genre FLAC:
// eight GENRE fields, of which dhowden/tag keeps the last.
func TestExtractGenres_FLACRepeatedFields(t *testing.T) {
	data := buildFLAC(false, append([]string{"TITLE=Eons"}, genreFields(lifeForms...)...)...)
	rs := bytes.NewReader(data)
	meta, err := tag.ReadFrom(rs)
	if err != nil {
		t.Fatalf("tag.ReadFrom: %v", err)
	}
	// Confirm the upstream behaviour this reader works around is still present.
	if got := meta.Genre(); got != "Instrumental Hip Hop" {
		t.Logf("note: dhowden/tag no longer keeps only the last GENRE (got %q)", got)
	}
	genres, fellBack := extractGenres(meta, rs)
	if fellBack {
		t.Error("fellBack = true, want false")
	}
	if !equalStrings(genres, lifeForms) {
		t.Errorf("genres = %q, want %q", genres, lifeForms)
	}
}

func TestReadFLACGenreValues(t *testing.T) {
	tests := []struct {
		name string
		data []byte
		want []string
		err  bool
	}{
		{"field names are case-insensitive", buildFLAC(false, "genre=Shoegaze", "Genre=Dream Pop"), []string{"Shoegaze", "Dream Pop"}, false},
		{"behind an ID3v2 tag", buildFLAC(true, "GENRE=Jazz", "GENRE=Bop"), []string{"Jazz", "Bop"}, false},
		{"no genre is not an error", buildFLAC(false, "TITLE=x"), nil, false},
		{"empty values dropped", buildFLAC(false, "GENRE= ", "GENRE=Rock"), []string{"Rock"}, false},
		{"a key that only starts with GENRE", buildFLAC(false, "GENRES=Rock", "GENRE=Jazz"), []string{"Jazz"}, false},
		{"not a FLAC", []byte("RIFF....WAVEfmt "), nil, true},
	}
	for _, tc := range tests {
		t.Run(tc.name, func(t *testing.T) {
			got, err := readFLACGenreValues(bytes.NewReader(tc.data))
			if (err != nil) != tc.err {
				t.Fatalf("err = %v, want error: %v", err, tc.err)
			}
			if !equalStrings(got, tc.want) {
				t.Errorf("got %q, want %q", got, tc.want)
			}
		})
	}
}

func TestReadFLACGenreValues_TruncatedCommentIsAnError(t *testing.T) {
	data := buildFLAC(false, "GENRE=Jazz", "GENRE=Bop")
	if _, err := readFLACGenreValues(bytes.NewReader(data[:len(data)-2])); err == nil {
		t.Error("err = nil for a cut-off comment block")
	}
}

func TestExtractGenres_OggVorbisRepeatedFields(t *testing.T) {
	comment := append([]byte("\x03vorbis"), vorbisComment(genreFields("Shoegaze", "Dream Pop")...)...)
	comment = append(comment, 1) // framing bit
	rs := bytes.NewReader(buildOgg(7, vorbisIdent(), comment))
	meta, err := tag.ReadFrom(rs)
	if err != nil {
		t.Fatalf("tag.ReadFrom: %v", err)
	}
	genres, fellBack := extractGenres(meta, rs)
	if fellBack || !equalStrings(genres, []string{"Shoegaze", "Dream Pop"}) {
		t.Errorf("genres = %q (fellBack %v), want [Shoegaze Dream Pop]", genres, fellBack)
	}
}

func TestReadOggGenreValues_Opus(t *testing.T) {
	head := append([]byte("OpusHead"), make([]byte, 11)...)
	tags := append([]byte("OpusTags"), vorbisComment(genreFields("Ambient", "Drone")...)...)
	got, err := readOggGenreValues(bytes.NewReader(buildOgg(3, head, tags)))
	if err != nil || !equalStrings(got, []string{"Ambient", "Drone"}) {
		t.Errorf("got %q, %v; want [Ambient Drone]", got, err)
	}
}

// Cover art makes the comment packet span pages. A reader that stopped at the
// first page boundary would read a truncated block.
func TestReadOggGenreValues_PacketSpansPages(t *testing.T) {
	fields := append([]string{"METADATA_BLOCK_PICTURE=" + strings.Repeat("A", 70000)}, genreFields("Jazz", "Bop")...)
	comment := append([]byte("\x03vorbis"), vorbisComment(fields...)...)
	got, err := readOggGenreValues(bytes.NewReader(buildOgg(9, vorbisIdent(), comment)))
	if err != nil || !equalStrings(got, []string{"Jazz", "Bop"}) {
		t.Errorf("got %q, %v; want [Jazz Bop]", got, err)
	}
}

func TestReadMP4GenreValues(t *testing.T) {
	tests := []struct {
		name string
		data []byte
		want []string
	}{
		{"several data atoms in one ©gen", buildMP4(true, mp4Box("\xa9gen", mp4Text("Hip Hop"), mp4Text("Lo-Fi"))), []string{"Hip Hop", "Lo-Fi"}},
		{"repeated ©gen atoms", buildMP4(true, mp4Box("\xa9gen", mp4Text("Hip Hop")), mp4Box("\xa9gen", mp4Text("Lo-Fi"))), []string{"Hip Hop", "Lo-Fi"}},
		{"QuickTime meta without version bytes", buildMP4(false, mp4Box("\xa9gen", mp4Text("Jazz"), mp4Text("Bop"))), []string{"Jazz", "Bop"}},
		{"no ©gen is not an error", buildMP4(true), nil},
	}
	for _, tc := range tests {
		t.Run(tc.name, func(t *testing.T) {
			got, err := readMP4GenreValues(bytes.NewReader(tc.data))
			if err != nil {
				t.Fatalf("err = %v", err)
			}
			if !equalStrings(got, tc.want) {
				t.Errorf("got %q, want %q", got, tc.want)
			}
		})
	}
}

func TestExtractGenres_MP4MultiValue(t *testing.T) {
	rs := bytes.NewReader(buildMP4(true, mp4Box("\xa9gen", mp4Text("Hip Hop"), mp4Text("Lo-Fi"))))
	meta, err := tag.ReadFrom(rs)
	if err != nil {
		t.Fatalf("tag.ReadFrom: %v", err)
	}
	genres, fellBack := extractGenres(meta, rs)
	if fellBack || !equalStrings(genres, []string{"Hip Hop", "Lo-Fi"}) {
		t.Errorf("genres = %q (fellBack %v), want [Hip Hop Lo-Fi]", genres, fellBack)
	}
}