docker/archive/diff.go

package archive

import (
	"archive/tar"
	"io"
	"os"
	"path/filepath"
	"strings"
	"syscall"
	"time"
)

// Linux device nodes are a bit weird due to backwards compat with 16 bit device nodes.
// They are, from low to high: the lower 8 bits of the minor, then 12 bits of the major,
// then the top 12 bits of the minor
func mkdev(major int64, minor int64) uint32 {
	return uint32(((minor & 0xfff00) << 12) | ((major & 0xfff) << 8) | (minor & 0xff))
}
func timeToTimespec(time time.Time) (ts syscall.Timespec) {
	if time.IsZero() {
		// Return UTIME_OMIT special value
		ts.Sec = 0
		ts.Nsec = ((1 << 30) - 2)
		return
	}
	return syscall.NsecToTimespec(time.UnixNano())
}

// ApplyLayer parses a diff in the standard layer format from `layer`, and
// applies it to the directory `dest`.
func ApplyLayer(dest string, layer Archive) error {
	// We need to be able to set any perms
	oldmask := syscall.Umask(0)
	defer syscall.Umask(oldmask)

	layer, err := DecompressStream(layer)
	if err != nil {
		return err
	}

	tr := tar.NewReader(layer)

	var dirs []*tar.Header

	// Iterate through the files in the archive.
	for {
		hdr, err := tr.Next()
		if err == io.EOF {
			// end of tar archive
			break
		}
		if err != nil {
			return err
		}

		// Normalize name, for safety and for a simple is-root check
		hdr.Name = filepath.Clean(hdr.Name)

		if !strings.HasSuffix(hdr.Name, "/") {
			// Not the root directory, ensure that the parent directory exists.
			// This happened in some tests where an image had a tarfile without any
			// parent directories.
			parent := filepath.Dir(hdr.Name)
			parentPath := filepath.Join(dest, parent)
			if _, err := os.Lstat(parentPath); err != nil && os.IsNotExist(err) {
				err = os.MkdirAll(parentPath, 600)
				if err != nil {
					return err
				}
			}
		}

		// Skip AUFS metadata dirs
		if strings.HasPrefix(hdr.Name, ".wh..wh.") {
			continue
		}

		path := filepath.Join(dest, hdr.Name)
		base := filepath.Base(path)
		if strings.HasPrefix(base, ".wh.") {
			originalBase := base[len(".wh."):]
			originalPath := filepath.Join(filepath.Dir(path), originalBase)
			if err := os.RemoveAll(originalPath); err != nil {
				return err
			}
		} else {
			// If path exits we almost always just want to remove and replace it.
			// The only exception is when it is a directory *and* the file from
			// the layer is also a directory. Then we want to merge them (i.e.
			// just apply the metadata from the layer).
			if fi, err := os.Lstat(path); err == nil {
				if !(fi.IsDir() && hdr.Typeflag == tar.TypeDir) {
					if err := os.RemoveAll(path); err != nil {
						return err
					}
				}
			}

			if err := createTarFile(path, dest, hdr, tr); err != nil {
				return err
			}

			// Directory mtimes must be handled at the end to avoid further
			// file creation in them to modify the directory mtime
			if hdr.Typeflag == tar.TypeDir {
				dirs = append(dirs, hdr)
			}
		}
	}

	for _, hdr := range dirs {
		path := filepath.Join(dest, hdr.Name)
		ts := []syscall.Timespec{timeToTimespec(hdr.AccessTime), timeToTimespec(hdr.ModTime)}
		if err := syscall.UtimesNano(path, ts); err != nil {
			return err
		}
	}

	return nil
}