machine: add sparse file writer

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

pkg/machine/compression/sparse_file_writer_test.go

@@ -0,0 +1,109 @@
+package compression
+
+import (
+	"bytes"
+	"errors"
+	"io"
+	"testing"
+)
+
+type memorySparseFile struct {
+	buffer bytes.Buffer
+	pos    int64
+}
+
+func (m *memorySparseFile) Seek(offset int64, whence int) (int64, error) {
+	var newPos int64
+	switch whence {
+	case io.SeekStart:
+		newPos = offset
+	case io.SeekCurrent:
+		newPos = m.pos + offset
+	case io.SeekEnd:
+		newPos = int64(m.buffer.Len()) + offset
+	default:
+		return 0, errors.New("unsupported seek whence")
+	}
+
+	if newPos < 0 {
+		return 0, errors.New("negative position is not allowed")
+	}
+
+	m.pos = newPos
+	return newPos, nil
+}
+
+func (m *memorySparseFile) Write(b []byte) (n int, err error) {
+	if int64(m.buffer.Len()) < m.pos {
+		padding := make([]byte, m.pos-int64(m.buffer.Len()))
+		_, err := m.buffer.Write(padding)
+		if err != nil {
+			return 0, err
+		}
+	}
+
+	m.buffer.Next(int(m.pos) - m.buffer.Len())
+
+	n, err = m.buffer.Write(b)
+	m.pos += int64(n)
+	return n, err
+}
+
+func (m *memorySparseFile) Close() error {
+	return nil
+}
+
+func testInputWithWriteLen(t *testing.T, input []byte, chunkSize int) {
+	m := &memorySparseFile{}
+	sparseWriter := NewSparseWriter(m)
+
+	for i := 0; i < len(input); i += chunkSize {
+		end := i + chunkSize
+		if end > len(input) {
+			end = len(input)
+		}
+		_, err := sparseWriter.Write(input[i:end])
+		if err != nil {
+			t.Fatalf("Expected no error, got %v", err)
+		}
+	}
+	err := sparseWriter.Close()
+	if err != nil {
+		t.Fatalf("Expected no error, got %v", err)
+	}
+	if !bytes.Equal(input, m.buffer.Bytes()) {
+		t.Fatalf("Incorrect output")
+	}
+}
+
+func testInput(t *testing.T, inputBytes []byte) {
+	currentLen := 1
+	for {
+		testInputWithWriteLen(t, inputBytes, currentLen)
+		currentLen <<= 1
+		if currentLen > len(inputBytes) {
+			break
+		}
+	}
+}
+
+func TestSparseWriter(t *testing.T) {
+	testInput(t, []byte("hello"))
+	testInput(t, append(make([]byte, 100), []byte("hello")...))
+	testInput(t, []byte(""))
+
+	// add "hello" at the beginning
+	largeInput := make([]byte, 1024*1024)
+	copy(largeInput, []byte("hello"))
+	testInput(t, largeInput)
+
+	// add "hello" at the end
+	largeInput = make([]byte, 1024*1024)
+	copy(largeInput[1024*1024-5:], []byte("hello"))
+	testInput(t, largeInput)
+
+	// add "hello" in the middle
+	largeInput = make([]byte, 1024*1024)
+	copy(largeInput[len(largeInput)/2:], []byte("hello"))
+	testInput(t, largeInput)
+}