[Layer Scanning] Preserve the file permissions of files written to di…

…sk when extracting from a tar file. Currently, all files had `0600` permissions, which breaks go binary extraction.

PiperOrigin-RevId: 715374364

artifact/image/layerscanning/image/file_node.go

@@ -19,10 +19,10 @@ import (
 	"os"
 	"path"
 	"path/filepath"
+	"time"
 )
 
 const (
-
 	// filePermission represents the permission bits for a file, which are minimal since files in the
 	// layer scanning use case are read-only.
 	filePermission = 0600
@@ -31,28 +31,39 @@ const (
 	dirPermission = 0700
 )
 
-// FileNode represents a file in a virtual filesystem.
+// fileNode represents a file in a virtual filesystem.
 type fileNode struct {
+	// extractDir and originLayerID are used to construct the real file path of the fileNode.
 	extractDir    string
 	originLayerID string
-	isWhiteout    bool
-	virtualPath   string
-	targetPath    string
-	mode          fs.FileMode
-	file          *os.File
+
+	// isWhiteout is true if the fileNode represents a whiteout file
+	isWhiteout bool
+
+	// virtualPath is the path of the fileNode in the virtual filesystem.
+	virtualPath string
+	// targetPath is reserved for symlinks. It is the path that the symlink points to.
+	targetPath string
+
+	// size, mode, and modTime are used to implement the fs.FileInfo interface.
+	size    int64
+	mode    fs.FileMode
+	modTime time.Time
+
+	// file is the file object for the real file referred to by the fileNode.
+	file *os.File
 }
 
 // ========================================================
 // fs.File METHODS
 // ========================================================
 
 // Stat returns the file info of real file referred by the fileNode.
-// TODO: b/378130598 - Need to replace the os stat permission with the permissions on the filenode.
 func (f *fileNode) Stat() (fs.FileInfo, error) {
 	if f.isWhiteout {
 		return nil, fs.ErrNotExist
 	}
-	return os.Stat(f.RealFilePath())
+	return f, nil
 }
 
 // Read reads the real file referred to by the fileNode.
@@ -103,13 +114,14 @@ func (f *fileNode) RealFilePath() string {
 // fs.DirEntry METHODS
 // ========================================================
 
-// Name returns the name of the fileNode.
+// Name returns the name of the fileNode. Name is also used to implement the fs.FileInfo interface.
 func (f *fileNode) Name() string {
 	_, filename := path.Split(f.virtualPath)
 	return filename
 }
 
-// IsDir returns whether the fileNode represents a directory.
+// IsDir returns whether the fileNode represents a directory. IsDir is also used to implement the
+// fs.FileInfo interface.
 func (f *fileNode) IsDir() bool {
 	return f.Type().IsDir()
 }
@@ -123,3 +135,22 @@ func (f *fileNode) Type() fs.FileMode {
 func (f *fileNode) Info() (fs.FileInfo, error) {
 	return f.Stat()
 }
+
+// ========================================================
+// fs.FileInfo METHODS
+// ========================================================
+func (f *fileNode) Size() int64 {
+	return f.size
+}
+
+func (f *fileNode) Mode() fs.FileMode {
+	return f.mode
+}
+
+func (f *fileNode) ModTime() time.Time {
+	return f.modTime
+}
+
+func (f *fileNode) Sys() any {
+	return nil
+}

artifact/image/layerscanning/image/file_node_test.go

@@ -21,6 +21,7 @@ import (
 	"path"
 	"path/filepath"
 	"testing"
+	"time"
 
 	"github.com/google/go-cmp/cmp"
 	"github.com/google/go-cmp/cmp/cmpopts"
@@ -59,7 +60,94 @@ var (
 
 // TODO: b/377551664 - Add tests for the Stat method for the fileNode type.
 func TestStat(t *testing.T) {
-	return
+	baseTime := time.Now()
+	regularFileNode := &fileNode{
+		extractDir:    "tempDir",
+		originLayerID: "",
+		virtualPath:   "/bar",
+		isWhiteout:    false,
+		mode:          filePermission,
+		size:          1,
+		modTime:       baseTime,
+	}
+	symlinkFileNode := &fileNode{
+		extractDir:    "tempDir",
+		originLayerID: "",
+		virtualPath:   "/symlink-to-bar",
+		targetPath:    "/bar",
+		isWhiteout:    false,
+		mode:          fs.ModeSymlink | filePermission,
+		size:          1,
+		modTime:       baseTime,
+	}
+	whiteoutFileNode := &fileNode{
+		extractDir:    "tempDir",
+		originLayerID: "",
+		virtualPath:   "/bar",
+		isWhiteout:    true,
+		mode:          filePermission,
+	}
+
+	type info struct {
+		name    string
+		size    int64
+		mode    fs.FileMode
+		modTime time.Time
+	}
+
+	tests := []struct {
+		name     string
+		node     *fileNode
+		wantInfo info
+		wantErr  error
+	}{
+		{
+			name: "regular file",
+			node: regularFileNode,
+			wantInfo: info{
+				name:    "bar",
+				size:    1,
+				mode:    filePermission,
+				modTime: baseTime,
+			},
+		},
+		{
+			name: "symlink",
+			node: symlinkFileNode,
+			wantInfo: info{
+				name:    "symlink-to-bar",
+				size:    1,
+				mode:    fs.ModeSymlink | filePermission,
+				modTime: baseTime,
+			},
+		},
+		{
+			name:    "whiteout file",
+			node:    whiteoutFileNode,
+			wantErr: fs.ErrNotExist,
+		},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			gotFileNode, gotErr := tc.node.Stat()
+			if tc.wantErr != nil {
+				if diff := cmp.Diff(tc.wantErr, gotErr, cmpopts.EquateErrors()); diff != "" {
+					t.Errorf("Stat(%v) returned unexpected error (-want +got): %v", tc.node, diff)
+				}
+				return
+			}
+
+			gotInfo := info{
+				name:    gotFileNode.Name(),
+				size:    gotFileNode.Size(),
+				mode:    gotFileNode.Mode(),
+				modTime: gotFileNode.ModTime(),
+			}
+			if diff := cmp.Diff(tc.wantInfo, gotInfo, cmp.AllowUnexported(info{})); diff != "" {
+				t.Errorf("Stat(%v) returned unexpected fileNode (-want +got): %v", tc.node, diff)
+			}
+		})
+	}
 }
 
 func TestRead(t *testing.T) {

artifact/image/layerscanning/image/image.go

@@ -385,12 +385,17 @@ func (img *Image) handleDir(realFilePath, virtualPath, originLayerID string, tar
 			return nil, fmt.Errorf("failed to create directory with realFilePath %s: %w", realFilePath, err)
 		}
 	}
+
+	fileInfo := header.FileInfo()
+
 	return &fileNode{
 		extractDir:    img.ExtractDir,
 		originLayerID: originLayerID,
 		virtualPath:   virtualPath,
 		isWhiteout:    isWhiteout,
-		mode:          fs.FileMode(header.Mode) | fs.ModeDir,
+		mode:          fileInfo.Mode() | fs.ModeDir,
+		size:          fileInfo.Size(),
+		modTime:       fileInfo.ModTime(),
 	}, nil
 }
 
@@ -415,12 +420,16 @@ func (img *Image) handleFile(realFilePath, virtualPath, originLayerID string, ta
 		return nil, fmt.Errorf("unable to copy file: %w", err)
 	}
 
+	fileInfo := header.FileInfo()
+
 	return &fileNode{
 		extractDir:    img.ExtractDir,
 		originLayerID: originLayerID,
 		virtualPath:   virtualPath,
 		isWhiteout:    isWhiteout,
-		mode:          fs.FileMode(header.Mode),
+		mode:          fileInfo.Mode(),
+		size:          fileInfo.Size(),
+		modTime:       fileInfo.ModTime(),
 	}, nil
 }