add validated audio interleaving

internal/output/audio.go

@@ -0,0 +1,65 @@
+package output
+
+import (
+	"errors"
+
+	"mxl-player/internal/playback"
+)
+
+var (
+	ErrInvalidAudioFrame    = errors.New("invalid audio frame")
+	ErrAudioPayloadTooSmall = errors.New("audio channel payload is too small")
+)
+
+func InterleaveF32(frame playback.AudioFrame) ([]byte, error) {
+	if frame.Channels == 0 ||
+		frame.SampleCount == 0 ||
+		frame.SampleRateNumerator <= 0 ||
+		frame.SampleRateDenominator <= 0 {
+		return nil, ErrInvalidAudioFrame
+	}
+
+	if uint64(len(frame.Samples)) != frame.Channels {
+		return nil, ErrInvalidAudioFrame
+	}
+
+	if frame.SampleCount > ^uint64(0)/4 {
+		return nil, ErrInvalidAudioFrame
+	}
+	bytesPerChannel := frame.SampleCount * 4
+
+	if frame.Channels > ^uint64(0)/bytesPerChannel {
+		return nil, ErrInvalidAudioFrame
+	}
+	totalBytes := frame.Channels * bytesPerChannel
+
+	maxInt := uint64(^uint(0) >> 1)
+	if totalBytes > maxInt {
+		return nil, ErrInvalidAudioFrame
+	}
+
+	for _, samples := range frame.Samples {
+		if bytesPerChannel > uint64(len(samples)) {
+			return nil, ErrAudioPayloadTooSmall
+		}
+	}
+
+	result := make([]byte, int(totalBytes))
+
+	for sample := uint64(0); sample < frame.SampleCount; sample++ {
+		for channel := uint64(0); channel < frame.Channels; channel++ {
+			sourceOffset := sample * 4
+			destinationOffset := (sample*frame.Channels + channel) * 4
+
+			sourceStart := int(sourceOffset)
+			destinationStart := int(destinationOffset)
+
+			copy(
+				result[destinationStart:destinationStart+4],
+				frame.Samples[channel][sourceStart:sourceStart+4],
+			)
+		}
+	}
+
+	return result, nil
+}

internal/output/audio_test.go

@@ -0,0 +1,116 @@
+package output
+
+import (
+	"bytes"
+	"errors"
+	"testing"
+
+	"mxl-player/internal/playback"
+)
+
+func validAudioFrame() playback.AudioFrame {
+	return playback.AudioFrame{
+		Index:                 42,
+		SampleCount:           2,
+		Channels:              2,
+		SampleRateNumerator:   48000,
+		SampleRateDenominator: 1,
+		Samples: [][]byte{
+			{1, 2, 3, 4, 5, 6, 7, 8},
+			{9, 10, 11, 12, 13, 14, 15, 16},
+		},
+	}
+}
+
+func TestInterleaveF32OrdersSamplesByFrameThenChannel(t *testing.T) {
+	frame := validAudioFrame()
+	want := []byte{
+		1, 2, 3, 4,
+		9, 10, 11, 12,
+		5, 6, 7, 8,
+		13, 14, 15, 16,
+	}
+
+	got, err := InterleaveF32(frame)
+	if err != nil {
+		t.Fatalf("InterleaveF32() error = %v", err)
+	}
+	if !bytes.Equal(got, want) {
+		t.Fatalf("InterleaveF32() = %v, want %v", got, want)
+	}
+}
+
+func TestInterleaveF32IgnoresBytesAfterSampleCount(t *testing.T) {
+	frame := validAudioFrame()
+	frame.SampleCount = 1
+
+	got, err := InterleaveF32(frame)
+	if err != nil {
+		t.Fatalf("InterleaveF32() error = %v", err)
+	}
+	want := []byte{1, 2, 3, 4, 9, 10, 11, 12}
+	if !bytes.Equal(got, want) {
+		t.Fatalf("InterleaveF32() = %v, want %v", got, want)
+	}
+}
+
+func TestInterleaveF32RejectsInvalidMetadata(t *testing.T) {
+	tests := []struct {
+		name   string
+		mutate func(*playback.AudioFrame)
+	}{
+		{name: "zero samples", mutate: func(f *playback.AudioFrame) { f.SampleCount = 0 }},
+		{name: "zero channels", mutate: func(f *playback.AudioFrame) { f.Channels = 0 }},
+		{name: "zero rate numerator", mutate: func(f *playback.AudioFrame) { f.SampleRateNumerator = 0 }},
+		{name: "negative rate numerator", mutate: func(f *playback.AudioFrame) { f.SampleRateNumerator = -1 }},
+		{name: "zero rate denominator", mutate: func(f *playback.AudioFrame) { f.SampleRateDenominator = 0 }},
+		{name: "wrong channel count", mutate: func(f *playback.AudioFrame) { f.Channels = 3 }},
+		{name: "sample size overflow", mutate: func(f *playback.AudioFrame) { f.SampleCount = ^uint64(0) }},
+		{
+			name: "allocation size overflow",
+			mutate: func(f *playback.AudioFrame) {
+				f.SampleCount = uint64(^uint(0)>>1) / 4
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			frame := validAudioFrame()
+			tt.mutate(&frame)
+			result, err := InterleaveF32(frame)
+			if result != nil {
+				t.Fatalf("InterleaveF32() result = %v, want nil", result)
+			}
+			if !errors.Is(err, ErrInvalidAudioFrame) {
+				t.Fatalf("InterleaveF32() error = %v, want %v", err, ErrInvalidAudioFrame)
+			}
+		})
+	}
+}
+
+func TestInterleaveF32RejectsShortChannel(t *testing.T) {
+	frame := validAudioFrame()
+	frame.Samples[1] = frame.Samples[1][:7]
+
+	result, err := InterleaveF32(frame)
+	if result != nil {
+		t.Fatalf("InterleaveF32() result = %v, want nil", result)
+	}
+	if !errors.Is(err, ErrAudioPayloadTooSmall) {
+		t.Fatalf("InterleaveF32() error = %v, want %v", err, ErrAudioPayloadTooSmall)
+	}
+}
+
+func TestInterleaveF32ReturnsIndependentOutput(t *testing.T) {
+	frame := validAudioFrame()
+	result, err := InterleaveF32(frame)
+	if err != nil {
+		t.Fatalf("InterleaveF32() error = %v", err)
+	}
+
+	frame.Samples[0][0] = 99
+	if result[0] != 1 {
+		t.Fatalf("output changed with borrowed input: first byte = %d, want 1", result[0])
+	}
+}