moby/builder/dockerfile/copy_unix.go

package dockerfile

import (
	"os"
	"path/filepath"

	"github.com/docker/docker/pkg/idtools"
)

func pathExists(path string) (bool, error) {
	_, err := os.Stat(path)
	switch {
	case err == nil:
		return true, nil
	case os.IsNotExist(err):
		return false, nil
	}
	return false, err
}

// TODO: review this
func fixPermissions(source, destination string, rootIDs idtools.IDPair) error {
	doChownDestination, err := chownDestinationRoot(destination)
	if err != nil {
		return err
	}

	// We Walk on the source rather than on the destination because we don't
	// want to change permissions on things we haven't created or modified.
	return filepath.Walk(source, func(fullpath string, info os.FileInfo, err error) error {
		// Do not alter the walk root iff. it existed before, as it doesn't fall under
		// the domain of "things we should chown".
		if !doChownDestination && (source == fullpath) {
			return nil
		}

		// Path is prefixed by source: substitute with destination instead.
		cleaned, err := filepath.Rel(source, fullpath)
		if err != nil {
			return err
		}

		fullpath = filepath.Join(destination, cleaned)
		return os.Lchown(fullpath, rootIDs.UID, rootIDs.GID)
	})
}

// If the destination didn't already exist, or the destination isn't a
// directory, then we should Lchown the destination. Otherwise, we shouldn't
// Lchown the destination.
func chownDestinationRoot(destination string) (bool, error) {
	destExists, err := pathExists(destination)
	if err != nil {
		return false, err
	}
	destStat, err := os.Stat(destination)
	if err != nil {
		// This should *never* be reached, because the destination must've already
		// been created while untar-ing the context.
		return false, err
	}

	return !destExists || !destStat.IsDir(), nil
}