Add support for scratch images, and integration test

pkg/constants/constants.go

@@ -39,4 +39,7 @@ const (
 	// BuildContextDir is the directory a build context will be unpacked into,
 	// for example, a tarball from a GCS bucket will be unpacked here
 	BuildContextDir = "/kaniko/buildcontext/"
+
+	// NoBaseImage is the scratch image
+	NoBaseImage = "scratch"
 )

pkg/image/image.go

@@ -18,6 +18,7 @@ package image
 
 import (
 	img "github.com/GoogleCloudPlatform/container-diff/pkg/image"
+	"github.com/GoogleCloudPlatform/k8s-container-builder/pkg/constants"
 	"github.com/containers/image/copy"
 	"github.com/containers/image/docker"
 	"github.com/containers/image/signature"
@@ -30,6 +31,9 @@ import (
 
 // InitializeSourceImage initializes the source image with the base image
 func NewSourceImage(srcImg string) (*img.MutableSource, error) {
+	if srcImg == constants.NoBaseImage {
+		return img.NewMutableSource(nil)
+	}
 	logrus.Infof("Initializing source image %s", srcImg)
 	ref, err := docker.ParseReference("//" + srcImg)
 	if err != nil {

pkg/util/fs_util.go

@@ -35,6 +35,15 @@ var volumeWhitelist = []string{}
 
 // ExtractFileSystemFromImage pulls an image and unpacks it to a file system at root
 func ExtractFileSystemFromImage(img string) error {
+	whitelist, err := fileSystemWhitelist(constants.WhitelistPath)
+	if err != nil {
+		return err
+	}
+	logrus.Infof("Whitelisted directories are %s", whitelist)
+	if img == constants.NoBaseImage {
+		logrus.Info("No base image, nothing to extract")
+		return nil
+	}
 	ref, err := docker.ParseReference("//" + img)
 	if err != nil {
 		return err
@@ -43,11 +52,6 @@ func ExtractFileSystemFromImage(img string) error {
 	if err != nil {
 		return err
 	}
-	whitelist, err := fileSystemWhitelist(constants.WhitelistPath)
-	if err != nil {
-		return err
-	}
-	logrus.Infof("Whitelisted directories are %s", whitelist)
 	return pkgutil.GetFileSystemFromReference(ref, imgSrc, constants.RootDir, whitelist)
 }