fix copySparse for empty qcow2 disk

.github/workflows/test.yml

@@ -72,6 +72,10 @@ jobs:
         # For non-Homebrew we have to support an old release of Go
         go-version: ["1.21.x", "1.22.x"]
     steps:
+    - name: Install test dependencies
+      run: |
+        sudo apt-get update
+        sudo apt-get install -y --no-install-recommends qemu-utils
     - uses: actions/checkout@v4
       with:
         fetch-depth: 1

pkg/nativeimgutil/nativeimgutil.go

@@ -123,10 +123,13 @@ func convertRawToRaw(source, dest string, size *int64) error {
 }
 
 func copySparse(w *os.File, r io.Reader, bufSize int64) (int64, error) {
-	var n int64
+	var (
+		n              int64
+		eof, hasWrites bool
+	)
+
 	zeroBuf := make([]byte, bufSize)
 	buf := make([]byte, bufSize)
-	var eof bool
 	for !eof {
 		rN, rErr := r.Read(buf)
 		if rErr != nil {
@@ -143,6 +146,7 @@ func copySparse(w *os.File, r io.Reader, bufSize int64) (int64, error) {
 			// no need to ftruncate here
 			n += int64(rN)
 		} else {
+			hasWrites = true
 			wN, wErr := w.Write(buf)
 			if wN > 0 {
 				n += int64(wN)
@@ -155,6 +159,11 @@ func copySparse(w *os.File, r io.Reader, bufSize int64) (int64, error) {
 			}
 		}
 	}
+
+	// Ftruncate must be run if the file contains only zeros
+	if !hasWrites {
+		return n, MakeSparse(w, n)
+	}
 	return n, nil
 }
 

pkg/nativeimgutil/nativeimgutil_test.go

@@ -0,0 +1,85 @@
+package nativeimgutil
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"gotest.tools/v3/assert"
+)
+
+func createImg(name, format, size string) error {
+	return exec.Command("qemu-img", "create", name, "-f", format, size).Run()
+}
+
+func TestConvertToRaw(t *testing.T) {
+	_, err := exec.LookPath("qemu-img")
+	if err != nil {
+		t.Skipf("qemu-img does not seem installed: %v", err)
+	}
+	tmpDir := t.TempDir()
+
+	qcowImage, err := os.Create(filepath.Join(tmpDir, "qcow.img"))
+	assert.NilError(t, err)
+	defer qcowImage.Close()
+	err = createImg(qcowImage.Name(), "qcow2", "1M")
+	assert.NilError(t, err)
+
+	rawImage, err := os.Create(filepath.Join(tmpDir, "raw.img"))
+	assert.NilError(t, err)
+	defer rawImage.Close()
+	err = createImg(rawImage.Name(), "raw", "1M")
+	assert.NilError(t, err)
+
+	rawImageExtended, err := os.Create(filepath.Join(tmpDir, "raw_extended.img"))
+	assert.NilError(t, err)
+	defer rawImageExtended.Close()
+	err = createImg(rawImageExtended.Name(), "raw", "2M")
+	assert.NilError(t, err)
+
+	t.Run("qcow without backing file", func(t *testing.T) {
+		resultImage := filepath.Join(tmpDir, strings.ReplaceAll(t.Name(), string(os.PathSeparator), "_"))
+		assert.NilError(t, err)
+
+		err = ConvertToRaw(qcowImage.Name(), resultImage, nil, false)
+		assert.NilError(t, err)
+		assertFileEquals(t, rawImage.Name(), resultImage)
+	})
+
+	t.Run("qcow with backing file", func(t *testing.T) {
+		resultImage := filepath.Join(tmpDir, strings.ReplaceAll(t.Name(), string(os.PathSeparator), "_"))
+		assert.NilError(t, err)
+
+		err = ConvertToRaw(qcowImage.Name(), resultImage, nil, true)
+		assert.NilError(t, err)
+		assertFileEquals(t, rawImage.Name(), resultImage)
+	})
+
+	t.Run("qcow with extra size", func(t *testing.T) {
+		resultImage := filepath.Join(tmpDir, strings.ReplaceAll(t.Name(), string(os.PathSeparator), "_"))
+		assert.NilError(t, err)
+		size := int64(2_097_152) // 2mb
+		err = ConvertToRaw(qcowImage.Name(), resultImage, &size, false)
+		assert.NilError(t, err)
+		assertFileEquals(t, rawImageExtended.Name(), resultImage)
+	})
+
+	t.Run("raw", func(t *testing.T) {
+		resultImage := filepath.Join(tmpDir, strings.ReplaceAll(t.Name(), string(os.PathSeparator), "_"))
+		assert.NilError(t, err)
+
+		err = ConvertToRaw(rawImage.Name(), resultImage, nil, false)
+		assert.NilError(t, err)
+		assertFileEquals(t, rawImage.Name(), resultImage)
+	})
+}
+
+func assertFileEquals(t *testing.T, expected, actual string) {
+	expectedContent, err := os.ReadFile(expected)
+	assert.NilError(t, err)
+	actualContent, err := os.ReadFile(actual)
+	assert.NilError(t, err)
+	assert.DeepEqual(t, expectedContent, actualContent)
+}