Fix flac.Seek()

flac/decode.go

@@ -157,7 +157,19 @@ func (d *decoder) Seek(p int) error {
 	}
 
 	pos, err := d.stream.Seek(uint64(p))
-	d.pos = int(pos)
+	if err != nil {
+		return errors.Wrap(err, "flac")
+	}
+
+	toDiscard := p - int(pos)
+	err = d.refill()
+	if err != nil {
+		return err
+	}
+	d.buf = d.buf[toDiscard:]
+
+	d.pos = p
+
 	return err
 }
 

flac/decode_test.go

@@ -16,7 +16,7 @@ import (
 )
 
 func TestDecoder_ReturnBehaviour(t *testing.T) {
-	f, err := os.Open(testtools.TestFilePath("valid_44100hz_22050_samples.flac"))
+	f, err := os.Open(testtools.TestFilePath("valid_44100hz_22050_samples_ffmpeg.flac"))
 	assert.NoError(t, err)
 	defer f.Close()
 
@@ -27,12 +27,38 @@ func TestDecoder_ReturnBehaviour(t *testing.T) {
 	testtools.AssertStreamerHasCorrectReturnBehaviour(t, s, s.Len())
 }
 
+func TestDecoder_Stream(t *testing.T) {
+	flacFile, err := os.Open(testtools.TestFilePath("valid_44100hz_22050_samples_ffmpeg.flac"))
+	assert.NoError(t, err)
+	defer flacFile.Close()
+
+	// Use WAV file as reference. Since both FLAC and WAV are lossless, comparing
+	// the samples should be possible (allowing for some floating point errors).
+	wavFile, err := os.Open(testtools.TestFilePath("valid_44100hz_22050_samples.wav"))
+	assert.NoError(t, err)
+	defer wavFile.Close()
+
+	flacStream, _, err := flac.Decode(flacFile)
+	assert.NoError(t, err)
+
+	wavStream, _, err := wav.Decode(wavFile)
+	assert.NoError(t, err)
+
+	assert.Equal(t, wavStream.Len(), flacStream.Len())
+
+	wavSamples := testtools.Collect(wavStream)
+	flacSamples := testtools.Collect(flacStream)
+
+	testtools.AssertSamplesEqual(t, wavSamples, flacSamples)
+}
+
 func TestDecoder_Seek(t *testing.T) {
-	flacFile, err := os.Open(testtools.TestFilePath("valid_44100hz_22050_samples.flac"))
+	flacFile, err := os.Open(testtools.TestFilePath("valid_44100hz_22050_samples_ffmpeg.flac"))
 	assert.NoError(t, err)
 	defer flacFile.Close()
 
-	// Use WAV file as reference
+	// Use WAV file as reference. Since both FLAC and WAV are lossless, comparing
+	// the samples should be possible (allowing for some floating point errors).
 	wavFile, err := os.Open(testtools.TestFilePath("valid_44100hz_22050_samples.wav"))
 	assert.NoError(t, err)
 	defer wavFile.Close()
@@ -63,7 +89,7 @@ func TestDecoder_Seek(t *testing.T) {
 
 	wavSamples := testtools.CollectNum(100, wavStream)
 	flacSamples := testtools.CollectNum(100, flacStream)
-	assert.Equal(t, wavSamples, flacSamples)
+	testtools.AssertSamplesEqual(t, wavSamples, flacSamples)
 
 	// Test middle of 2nd frame
 	seekPos = (int(frameStarts[1]) + int(frameStarts[2])) / 2
@@ -76,7 +102,7 @@ func TestDecoder_Seek(t *testing.T) {
 
 	wavSamples = testtools.CollectNum(100, wavStream)
 	flacSamples = testtools.CollectNum(100, flacStream)
-	assert.Equal(t, wavSamples, flacSamples)
+	testtools.AssertSamplesEqual(t, wavSamples, flacSamples)
 
 	// Test end of 2nd frame
 	seekPos = int(frameStarts[2]) - 1
@@ -89,7 +115,7 @@ func TestDecoder_Seek(t *testing.T) {
 
 	wavSamples = testtools.CollectNum(100, wavStream)
 	flacSamples = testtools.CollectNum(100, flacStream)
-	assert.Equal(t, wavSamples, flacSamples)
+	testtools.AssertSamplesEqual(t, wavSamples, flacSamples)
 }
 
 func getFlacFrameStartPositions(r io.Reader) ([]uint64, error) {

internal/testtools/asserts.go

@@ -54,3 +54,25 @@ func AssertStreamerHasCorrectReturnBehaviour(t *testing.T, s beep.Streamer, expe
 	assert.Equal(t, 0, n)
 	assert.NoError(t, s.Err())
 }
+
+func AssertSamplesEqual(t *testing.T, expected, actual [][2]float64) {
+	t.Helper()
+
+	if len(expected) != len(actual) {
+		t.Errorf("expected sample data length to be %d, got %d", len(expected), len(actual))
+		return
+	}
+
+	const epsilon = 1e-9
+	equals := true
+	for i := range expected {
+		if actual[i][0] < expected[i][0]-epsilon || actual[i][0] > expected[i][0]+epsilon ||
+			actual[i][1] < expected[i][1]-epsilon || actual[i][1] > expected[i][1]+epsilon {
+			equals = false
+			break
+		}
+	}
+	if !equals {
+		t.Errorf("the sample data isn't equal to the expected data")
+	}
+}