From 5fdeda2ede202eac8ec70f735dafbc524ad82caf Mon Sep 17 00:00:00 2001
From: DiheChen <michikawachin@outlook.com>
Date: Thu, 5 Nov 2026 12:13:19 +0800
Subject: [PATCH] fix: measure FLAC files that have data after the audio

---
 internal/lib/wav/decode.go      |  6 ++++++
 internal/lib/wav/decode_test.go | 36 +++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/internal/lib/wav/decode.go b/internal/lib/wav/decode.go
index 9aee283..601e91f 100644
--- a/internal/lib/wav/decode.go
+++ b/internal/lib/wav/decode.go
@@ -318,8 +318,13 @@ func newFLACDecoder(r io.Reader) (Decoder, error) {
 	info := stream.Info
 	divisor := float64(int64(1) << (info.BitsPerSample - 1))
 	d := &streamDecoder{rate: int(info.SampleRate), ch: int(info.NChannels)}
+	var decoded uint64
 	d.fill = func() error {
 		for {
+			// QQ 音乐的 FLAC 在音频之后还有数据：继续读会被当成音频帧报错，整首的分析结果都会作废。NSamples 为 0 表示文件没有声明总数。
+			if info.NSamples > 0 && decoded >= info.NSamples {
+				return io.EOF
+			}
 			frame, err := stream.ParseNext()
 			if err != nil {
 				return err // 含 io.EOF
@@ -328,6 +333,7 @@ func newFLACDecoder(r io.Reader) (Decoder, error) {
 				continue
 			}
 			n := frame.Subframes[0].NSamples
+			decoded += uint64(n)
 			ch := len(frame.Subframes)
 			out := d.q.buf[d.q.grow(n*ch):]
 			for c, sub := range frame.Subframes {
diff --git a/internal/lib/wav/decode_test.go b/internal/lib/wav/decode_test.go
index 25bcf98..86bddcf 100644
--- a/internal/lib/wav/decode_test.go
+++ b/internal/lib/wav/decode_test.go
@@ -271,6 +271,42 @@ func TestDecodeRejectsUndecodableMP3(t *testing.T) {
 	}
 }
 
+func TestDecodeFLACStopsAtDeclaredSamples(t *testing.T) {
+	file, err := os.ReadFile("testdata/sine.flac")
+	if err != nil {
+		t.Fatal(err)
+	}
+	want, err := Decode(bytes.NewReader(file))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	withTrailer := append(slices.Clone(file), 0x00, 0x01, 0x02, 0x03)
+	got, err := Decode(bytes.NewReader(withTrailer))
+	if err != nil {
+		t.Fatalf("音频之后有多余数据：%v", err)
+	}
+	if got.Frames() != want.Frames() {
+		t.Errorf("采样帧 = %d，期望 %d", got.Frames(), want.Frames())
+	}
+
+	// STREAMINFO 的总采样数占第 21 字节的低 4 位和之后的 4 个字节，全 0 表示未知。
+	undeclared := slices.Clone(file)
+	undeclared[21] &= 0xF0
+	clear(undeclared[22:26])
+	got, err = Decode(bytes.NewReader(undeclared))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got.Frames() != want.Frames() {
+		t.Errorf("未声明总采样数时采样帧 = %d，期望读到文件结束的 %d", got.Frames(), want.Frames())
+	}
+
+	if _, err := Decode(bytes.NewReader(file[:len(file)-200])); err == nil {
+		t.Error("音频比声明的少时应该报错")
+	}
+}
+
 func TestDamageReportsSkippedMP3Data(t *testing.T) {
 	decode := func(t *testing.T, file []byte) Decoder {
 		t.Helper()