image: avoid panic on nil fields when converting

The following error occurs when the create command is executed：

    panic: runtime error: invalid memory address or nil pointer dereference [recovered]
    panic: runtime error: invalid memory address or nil pointer dereference
    [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x48ef43]
    goroutine 19 [running]:
    panic(0x808060, 0xc420010130)
    /home/zhouhao/go/src/runtime/panic.go:500 +0x1ae
    testing.tRunner.func1(0xc4200932c0)
    /home/zhouhao/go/src/testing/testing.go:579 +0x474
    panic(0x808060, 0xc420010130)
    /home/zhouhao/go/src/runtime/panic.go:458 +0x271
    ...

Because there is no non-empty check on the optional fields in config.go.

Signed-off-by: zhouhao <zhouhao@cn.fujitsu.com>

Author: zhouhao

image/config.go

@@ -73,8 +73,11 @@ func (c *config) runtimeSpec(rootfs string) (*specs.Spec, error) {
 	var s specs.Spec
 	s.Version = specs.Version
 	// we should at least apply the default spec, otherwise this is totally useless
-	s.Process.Terminal = true
+	s.Root = &specs.Root{}
 	s.Root.Path = rootfs
+
+	s.Process = &spec.Process{}
+	s.Process.Terminal = true
 	s.Process.Cwd = "/"
 	if c.Config.WorkingDir != "" {
 		s.Process.Cwd = c.Config.WorkingDir

image/image_test.go

@@ -187,13 +187,37 @@ type imageLayout struct {
 	tarList   []tarContent
 }
 
-func TestValidateLayout(t *testing.T) {
+func TestImageLayout(t *testing.T) {
 	root, err := ioutil.TempDir("", "oci-test")
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer os.RemoveAll(root)
 
+	dest1, err := ioutil.TempDir("", "dest1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dest1)
+
+	dest2, err := ioutil.TempDir("", "dest2")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dest2)
+
+	dest3, err := ioutil.TempDir("", "dest3")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dest3)
+
+	dest4, err := ioutil.TempDir("", "dest4")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dest4)
+
 	il := imageLayout{
 		rootDir:   root,
 		layout:    layoutStr,
@@ -217,6 +241,23 @@ func TestValidateLayout(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
+
+	err = UnpackLayout(root, dest1, refTag[0], "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = UnpackLayout(root, dest2, refTag[1], "linux:amd64")
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = CreateRuntimeBundleLayout(root, dest3, refTag[0], "rootfs", "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = CreateRuntimeBundleLayout(root, dest4, refTag[1], "rootfs", "linux:amd64")
+	if err != nil {
+		t.Fatal(err)
+	}
 }
 
 func createImageLayoutBundle(il imageLayout) error {