From 5452eb3c4a87ac0d368fd09e8d92e094d759d9a9 Mon Sep 17 00:00:00 2001
From: Joao Pereira <joaod@vmware.com>
Date: Mon, 8 Jan 2024 16:59:38 -0600
Subject: [PATCH] Reverse the order of extraction of layers

Signed-off-by: Joao Pereira <joaod@vmware.com>
---
 pkg/imgpkg/image/dir_image.go | 47 ++++++++++++++++++++++++++++-------
 1 file changed, 38 insertions(+), 9 deletions(-)

diff --git a/pkg/imgpkg/image/dir_image.go b/pkg/imgpkg/image/dir_image.go
index 51435066..58f17a7f 100644
--- a/pkg/imgpkg/image/dir_image.go
+++ b/pkg/imgpkg/image/dir_image.go
@@ -50,13 +50,19 @@ func (i *DirImage) AsDirectory() error {
 		return err
 	}
 
-	for idx, imgLayer := range layers {
+	fileMap := map[string]bool{}
+
+	// we iterate through the layers in reverse order because it makes handling
+	// whiteout layers more efficient, since we can just keep track of the removed
+	// files as we see .wh. layers and ignore those in previous layers.
+	for idx := len(layers) - 1; idx >= 0; idx-- {
+		imgLayer := layers[idx]
 		digest, err := imgLayer.Digest()
 		if err != nil {
 			return err
 		}
 
-		i.logger.Logf("Extracting layer '%s' (%d/%d)\n", digest, idx+1, len(layers))
+		i.logger.Logf("Extracting layer '%s' (%d/%d)\n", digest, len(layers)-idx, len(layers))
 
 		layerStream, err := imgLayer.Uncompressed()
 		if err != nil {
@@ -65,7 +71,7 @@ func (i *DirImage) AsDirectory() error {
 
 		defer layerStream.Close()
 
-		err = i.writeLayer(layerStream)
+		err = i.writeLayer(fileMap, layerStream)
 		if err != nil {
 			return err
 		}
@@ -76,7 +82,7 @@ func (i *DirImage) AsDirectory() error {
 
 // Taken from https://github.com/concourse/registry-image-resource/blob/b5481130ad61bc74e0a74f9b00b287b3a24bab88/cmd/in/unpack.go
 
-func (i *DirImage) writeLayer(stream io.Reader) error {
+func (i *DirImage) writeLayer(fileMap map[string]bool, stream io.Reader) error {
 	tarReader := tar.NewReader(stream)
 
 	for {
@@ -102,6 +108,12 @@ func (i *DirImage) writeLayer(stream io.Reader) error {
 			if err != nil {
 				return nil
 			}
+			fileMap[base] = true
+			continue
+		}
+
+		// check for a whited out parent directory
+		if inWhiteoutDir(fileMap, path) {
 			continue
 		}
 
@@ -116,6 +128,7 @@ func (i *DirImage) writeLayer(stream io.Reader) error {
 			}
 		}
 
+		fileMap[hdr.Name] = true
 		err = i.extractTarEntry(hdr, tarReader)
 		if err != nil {
 			return err
@@ -125,6 +138,23 @@ func (i *DirImage) writeLayer(stream io.Reader) error {
 	return nil
 }
 
+func inWhiteoutDir(fileMap map[string]bool, file string) bool {
+	for {
+		if file == "" {
+			break
+		}
+		dirname := filepath.Dir(file)
+		if file == dirname {
+			break
+		}
+		if val, ok := fileMap[dirname]; ok && val {
+			return true
+		}
+		file = dirname
+	}
+	return false
+}
+
 // Taken from https://github.com/concourse/go-archive/blob/f26802964d15194bddb07bf116ea567c56af973f/tarfs/extract.go
 
 func (i *DirImage) extractTarEntry(header *tar.Header, input io.Reader) error {
@@ -150,10 +180,7 @@ func (i *DirImage) extractTarEntry(header *tar.Header, input io.Reader) error {
 
 	switch header.Typeflag {
 	case tar.TypeDir:
-		err := os.MkdirAll(path, permMode)
-		if err != nil {
-			return err
-		}
+		return nil
 
 	case tar.TypeReg, tar.TypeRegA:
 		file, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE|os.O_TRUNC, permMode)
@@ -175,7 +202,9 @@ func (i *DirImage) extractTarEntry(header *tar.Header, input io.Reader) error {
 	case tar.TypeLink, tar.TypeSymlink:
 		// skipping symlinks as a security feature
 		return nil
-
+	case tar.TypeChar, tar.TypeBlock:
+		// skipping devices
+		return nil
 	default:
 		return fmt.Errorf("Unsupported tar entry type '%c' for file '%s'", header.Typeflag, header.Name)
 	}