Add more Writer functionality

kaitai/seekbuf.go

@@ -0,0 +1,77 @@
+package kaitai
+
+import (
+	"errors"
+	"io"
+)
+
+// SeekableBuffer is an in-memory buffer that implements io.ReadWriteSeeker.
+type SeekableBuffer struct {
+	data []byte
+	pos  int64
+}
+
+// NewSeekableBuffer creates a SeekableBuffer with the given initial data.
+func NewSeekableBuffer(data []byte) *SeekableBuffer {
+	return &SeekableBuffer{data: data}
+}
+
+// NewSeekableBufferSize creates a SeekableBuffer pre-allocated to size bytes.
+func NewSeekableBufferSize(size int) *SeekableBuffer {
+	return &SeekableBuffer{data: make([]byte, size)}
+}
+
+func (sb *SeekableBuffer) Read(p []byte) (n int, err error) {
+	if sb.pos >= int64(len(sb.data)) {
+		return 0, io.EOF
+	}
+	n = copy(p, sb.data[sb.pos:])
+	sb.pos += int64(n)
+	return n, nil
+}
+
+func (sb *SeekableBuffer) Write(p []byte) (n int, err error) {
+	end := sb.pos + int64(len(p))
+	if end > int64(len(sb.data)) {
+		// Grow buffer
+		if end > int64(cap(sb.data)) {
+			newData := make([]byte, end, end*2)
+			copy(newData, sb.data)
+			sb.data = newData
+		} else {
+			sb.data = sb.data[:end]
+		}
+	}
+	n = copy(sb.data[sb.pos:], p)
+	sb.pos += int64(n)
+	return n, nil
+}
+
+func (sb *SeekableBuffer) Seek(offset int64, whence int) (int64, error) {
+	var newPos int64
+	switch whence {
+	case io.SeekStart:
+		newPos = offset
+	case io.SeekCurrent:
+		newPos = sb.pos + offset
+	case io.SeekEnd:
+		newPos = int64(len(sb.data)) + offset
+	default:
+		return 0, errors.New("SeekableBuffer.Seek: invalid whence")
+	}
+	if newPos < 0 {
+		return 0, errors.New("SeekableBuffer.Seek: negative position")
+	}
+	sb.pos = newPos
+	return newPos, nil
+}
+
+// Bytes returns the buffer contents.
+func (sb *SeekableBuffer) Bytes() []byte {
+	return sb.data
+}
+
+// Len returns the current length of the buffer.
+func (sb *SeekableBuffer) Len() int {
+	return len(sb.data)
+}

kaitai/seekbuf_test.go

@@ -0,0 +1,168 @@
+package kaitai
+
+import (
+	"bytes"
+	"errors"
+	"io"
+	"testing"
+)
+
+func TestNewSeekableBuffer(t *testing.T) {
+	data := []byte{0x01, 0x02, 0x03}
+	sb := NewSeekableBuffer(data)
+	if !bytes.Equal(sb.Bytes(), data) {
+		t.Errorf("Bytes() = %v, want %v", sb.Bytes(), data)
+	}
+	if sb.Len() != len(data) {
+		t.Errorf("Len() = %d, want %d", sb.Len(), len(data))
+	}
+	pos, err := sb.Seek(0, io.SeekCurrent)
+	if err != nil {
+		t.Fatalf("Seek returned error: %v", err)
+	}
+	if pos != 0 {
+		t.Errorf("initial position = %d, want 0", pos)
+	}
+}
+
+func TestNewSeekableBufferSize(t *testing.T) {
+	sb := NewSeekableBufferSize(16)
+	if sb.Len() != 16 {
+		t.Errorf("Len() = %d, want 16", sb.Len())
+	}
+	for i, b := range sb.Bytes() {
+		if b != 0 {
+			t.Errorf("Bytes()[%d] = %#x, want 0", i, b)
+		}
+	}
+}
+
+func TestSeekableBuffer_Read(t *testing.T) {
+	sb := NewSeekableBuffer([]byte{0x10, 0x20, 0x30, 0x40})
+
+	out := make([]byte, 2)
+	n, err := sb.Read(out)
+	if err != nil {
+		t.Fatalf("Read error: %v", err)
+	}
+	if n != 2 || !bytes.Equal(out, []byte{0x10, 0x20}) {
+		t.Errorf("first Read = (%d, %v), want (2, [10 20])", n, out)
+	}
+
+	out = make([]byte, 8)
+	n, err = sb.Read(out)
+	if err != nil {
+		t.Fatalf("second Read error: %v", err)
+	}
+	if n != 2 || !bytes.Equal(out[:n], []byte{0x30, 0x40}) {
+		t.Errorf("second Read = (%d, %v), want (2, [30 40])", n, out[:n])
+	}
+
+	n, err = sb.Read(out)
+	if !errors.Is(err, io.EOF) {
+		t.Errorf("expected io.EOF at end, got n=%d err=%v", n, err)
+	}
+}
+
+func TestSeekableBuffer_Write(t *testing.T) {
+	sb := NewSeekableBuffer(nil)
+	n, err := sb.Write([]byte{0xAA, 0xBB})
+	if err != nil {
+		t.Fatalf("Write error: %v", err)
+	}
+	if n != 2 {
+		t.Errorf("Write n = %d, want 2", n)
+	}
+	if !bytes.Equal(sb.Bytes(), []byte{0xAA, 0xBB}) {
+		t.Errorf("Bytes() = %v, want [AA BB]", sb.Bytes())
+	}
+
+	_, err = sb.Write([]byte{0xCC, 0xDD, 0xEE})
+	if err != nil {
+		t.Fatalf("Write error: %v", err)
+	}
+	if !bytes.Equal(sb.Bytes(), []byte{0xAA, 0xBB, 0xCC, 0xDD, 0xEE}) {
+		t.Errorf("Bytes() = %v, want [AA BB CC DD EE]", sb.Bytes())
+	}
+}
+
+func TestSeekableBuffer_WriteOverwrite(t *testing.T) {
+	sb := NewSeekableBuffer([]byte{0x01, 0x02, 0x03, 0x04})
+	_, err := sb.Seek(1, io.SeekStart)
+	if err != nil {
+		t.Fatalf("Seek error: %v", err)
+	}
+	_, err = sb.Write([]byte{0xFE, 0xFF})
+	if err != nil {
+		t.Fatalf("Write error: %v", err)
+	}
+	want := []byte{0x01, 0xFE, 0xFF, 0x04}
+	if !bytes.Equal(sb.Bytes(), want) {
+		t.Errorf("Bytes() = %v, want %v", sb.Bytes(), want)
+	}
+}
+
+func TestSeekableBuffer_WriteGrowAfterSeek(t *testing.T) {
+	sb := NewSeekableBuffer([]byte{0x01, 0x02})
+	_, err := sb.Seek(1, io.SeekStart)
+	if err != nil {
+		t.Fatalf("Seek error: %v", err)
+	}
+	_, err = sb.Write([]byte{0xAA, 0xBB, 0xCC})
+	if err != nil {
+		t.Fatalf("Write error: %v", err)
+	}
+	want := []byte{0x01, 0xAA, 0xBB, 0xCC}
+	if !bytes.Equal(sb.Bytes(), want) {
+		t.Errorf("Bytes() = %v, want %v", sb.Bytes(), want)
+	}
+}
+
+func TestSeekableBuffer_Seek(t *testing.T) {
+	tests := []struct {
+		name    string
+		offset  int64
+		whence  int
+		wantPos int64
+		wantErr bool
+	}{
+		{"SeekStart", 2, io.SeekStart, 2, false},
+		{"SeekCurrent forward", 1, io.SeekCurrent, 1, false},
+		{"SeekEnd zero offset", 0, io.SeekEnd, 4, false},
+		{"SeekStart zero", 0, io.SeekStart, 0, false},
+		{"SeekStart negative", -1, io.SeekStart, 0, true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			sb := NewSeekableBuffer([]byte{0x01, 0x02, 0x03, 0x04})
+			got, err := sb.Seek(tt.offset, tt.whence)
+			if (err != nil) != tt.wantErr {
+				t.Fatalf("Seek error = %v, wantErr %v", err, tt.wantErr)
+			}
+			if err == nil && got != tt.wantPos {
+				t.Errorf("Seek returned %d, want %d", got, tt.wantPos)
+			}
+		})
+	}
+}
+
+func TestSeekableBuffer_RoundTrip(t *testing.T) {
+	sb := NewSeekableBuffer(nil)
+	want := []byte{0xDE, 0xAD, 0xBE, 0xEF}
+	_, err := sb.Write(want)
+	if err != nil {
+		t.Fatalf("Write error: %v", err)
+	}
+	_, err = sb.Seek(0, io.SeekStart)
+	if err != nil {
+		t.Fatalf("Seek error: %v", err)
+	}
+	got := make([]byte, len(want))
+	_, err = io.ReadFull(sb, got)
+	if err != nil {
+		t.Fatalf("ReadFull error: %v", err)
+	}
+	if !bytes.Equal(got, want) {
+		t.Errorf("round-tripped bytes = %v, want %v", got, want)
+	}
+}

kaitai/util.go

@@ -54,6 +54,21 @@ func ProcessZlib(in []byte) ([]byte, error) {
 	return res, nil
 }
 
+// UnprocessZlib compresses data using zlib.
+func UnprocessZlib(in []byte) ([]byte, error) {
+	var buf bytes.Buffer
+	w := zlib.NewWriter(&buf)
+	_, err := w.Write(in)
+	if err != nil {
+		return nil, fmt.Errorf("UnprocessZlib: error writing zlib data: %w", err)
+	}
+	err = w.Close()
+	if err != nil {
+		return nil, fmt.Errorf("UnprocessZlib: error flushing zlib stream: %w", err)
+	}
+	return buf.Bytes(), nil
+}
+
 // BytesToStr returns a string decoded by the given decoder.
 func BytesToStr(in []byte, decoder *encoding.Decoder) (string, error) {
 	i := bytes.NewReader(in)

kaitai/util_test.go

@@ -101,6 +101,33 @@ func TestProcessZlib(t *testing.T) {
 	}
 }
 
+func TestUnprocessZlib(t *testing.T) {
+	tests := []struct {
+		name string
+		in   []byte
+	}{
+		{"Empty", []byte{}},
+		{"Short string", []byte("goodbye, world")},
+		{"Binary data", []byte{0x00, 0x01, 0x02, 0xff, 0xfe, 0xfd, 0x00, 0x00, 0x00}},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			compressed, err := UnprocessZlib(tt.in)
+			if err != nil {
+				t.Fatalf("UnprocessZlib() error = %v", err)
+			}
+			// Round-trip through ProcessZlib to verify validity.
+			got, err := ProcessZlib(compressed)
+			if err != nil {
+				t.Fatalf("ProcessZlib() after compress error = %v", err)
+			}
+			if !reflect.DeepEqual(got, tt.in) && !(len(got) == 0 && len(tt.in) == 0) {
+				t.Errorf("round-trip mismatch: got %v, want %v", got, tt.in)
+			}
+		})
+	}
+}
+
 func TestBytesToStr(t *testing.T) {
 	utf16 := unicode.UTF16(unicode.BigEndian, unicode.ExpectBOM)
 	type args struct {