fix tar PAX handling on Windows

pkg/v1/mutate/mutate.go

@@ -23,6 +23,7 @@ import (
 	"io"
 	"io/ioutil"
 	"path/filepath"
+	"runtime"
 	"strings"
 	"time"
 
@@ -244,6 +245,8 @@ func extract(img v1.Image, w io.Writer) error {
 	if err != nil {
 		return fmt.Errorf("retrieving image layers: %w", err)
 	}
+
+	isWin := runtime.GOOS == "windows"
 	// 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.
@@ -268,6 +271,14 @@ func extract(img v1.Image, w io.Writer) error {
 			// name, we may have duplicate entries, which angers tar-split.
 			header.Name = filepath.Clean(header.Name)
 
+			// tar.Next() sometimes mistakenly guesses format as USTAR, which creates a problem:
+			// if the header.Name is > 100 characters long, WriteHeader() returns an error like
+			// "archive/tar: cannot encode header: Format specifies USTAR; and USTAR cannot encode Name=...".
+			// To fix, change format from USTAR to PAX on Windows
+			if isWin && header.Format == tar.FormatUSTAR {
+				header.Format = tar.FormatPAX
+			}
+
 			basename := filepath.Base(header.Name)
 			dirname := filepath.Dir(header.Name)
 			tombstone := strings.HasPrefix(basename, whiteoutPrefix)
@@ -297,7 +308,9 @@ func extract(img v1.Image, w io.Writer) error {
 			// any entries with a matching (or child) name
 			fileMap[name] = tombstone || !(header.Typeflag == tar.TypeDir)
 			if !tombstone {
-				tarWriter.WriteHeader(header)
+				if err := tarWriter.WriteHeader(header); err != nil {
+					return err
+				}
 				if header.Size > 0 {
 					if _, err := io.CopyN(tarWriter, tarReader, header.Size); err != nil {
 						return err