Add hash function which only considers mtime when snapshotting

executor/cmd/root.go

@@ -33,6 +33,7 @@ var (
 	dockerfilePath string
 	destination    string
 	srcContext     string
+	mtime          bool
 	logLevel       string
 )
 
@@ -40,6 +41,7 @@ func init() {
 	RootCmd.PersistentFlags().StringVarP(&dockerfilePath, "dockerfile", "f", "/workspace/Dockerfile", "Path to the dockerfile to be built.")
 	RootCmd.PersistentFlags().StringVarP(&srcContext, "context", "c", "", "Path to the dockerfile build context.")
 	RootCmd.PersistentFlags().StringVarP(&destination, "destination", "d", "", "Registry the final image should be pushed to (ex: gcr.io/test/example:latest)")
+	RootCmd.PersistentFlags().BoolVarP(&mtime, "mtime", "", false, "Only look at mtime of a file when snapshotting")
 	RootCmd.PersistentFlags().StringVarP(&logLevel, "verbosity", "v", constants.DefaultLogLevel, "Log level (debug, info, warn, error, fatal, panic")
 }
 
@@ -74,8 +76,12 @@ func execute() error {
 	if err := util.ExtractFileSystemFromImage(baseImage); err != nil {
 		return err
 	}
-
-	l := snapshot.NewLayeredMap(util.Hasher())
+	hasher := util.Hasher()
+	if mtime {
+		logrus.Info("Only file modification times will be considered when snapshotting.")
+		hasher = util.MtimeHasher()
+	}
+	l := snapshot.NewLayeredMap(hasher)
 	snapshotter := snapshot.NewSnapshotter(l, constants.RootDir)
 
 	// Take initial snapshot

integration_tests/integration_test_yaml.go

@@ -28,6 +28,7 @@ var fileTests = []struct {
 	configPath     string
 	context        string
 	repo           string
+	mtime          bool
 }{
 	{
 		description:    "test extract filesystem",
@@ -35,6 +36,7 @@ var fileTests = []struct {
 		configPath:     "/workspace/integration_tests/dockerfiles/config_test_extract_fs.json",
 		context:        "integration_tests/dockerfiles/",
 		repo:           "extract-filesystem",
+		mtime:          true,
 	},
 	{
 		description:    "test run",
@@ -49,6 +51,7 @@ var fileTests = []struct {
 		configPath:     "/workspace/integration_tests/dockerfiles/config_test_run_2.json",
 		context:        "integration_tests/dockerfiles/",
 		repo:           "test-run-2",
+		mtime:          true,
 	},
 	{
 		description:    "test copy",
@@ -56,6 +59,7 @@ var fileTests = []struct {
 		configPath:     "/workspace/integration_tests/dockerfiles/config_test_copy.json",
 		context:        "/workspace/integration_tests/",
 		repo:           "test-copy",
+		mtime:          true,
 	},
 }
 
@@ -139,9 +143,13 @@ func main() {
 
 		// Then, buld the image with kbuild
 		kbuildImage := testRepo + kbuildPrefix + test.repo
+		mtime := ""
+		if test.mtime {
+			mtime = "--mtime"
+		}
 		kbuild := step{
 			Name: executorImage,
-			Args: []string{executorCommand, "--destination", kbuildImage, "--dockerfile", test.dockerfilePath, "--context", test.context},
+			Args: []string{executorCommand, "--destination", kbuildImage, "--dockerfile", test.dockerfilePath, "--context", test.context, mtime},
 		}
 
 		// Pull the kbuild image

pkg/util/util.go

@@ -61,3 +61,17 @@ func Hasher() func(string) (string, error) {
 	}
 	return hasher
 }
+
+// Hasher returns a hash function, which only looks at mtime to determine if a file has changed
+func MtimeHasher() func(string) (string, error) {
+	hasher := func(p string) (string, error) {
+		h := md5.New()
+		fi, err := os.Lstat(p)
+		if err != nil {
+			return "", err
+		}
+		h.Write([]byte(fi.ModTime().String()))
+		return hex.EncodeToString(h.Sum(nil)), nil
+	}
+	return hasher
+}