docker/archive/diff.go

package archive

import (
	"bufio"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"path/filepath"
	"strings"
	"syscall"

	"github.com/docker/docker/vendor/src/code.google.com/p/go/src/pkg/archive/tar"
)

// 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))
}

// ApplyLayer parses a diff in the standard layer format from `layer`, and
// applies it to the directory `dest`.
func ApplyLayer(dest string, layer ArchiveReader) 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)
	trBuf := bufio.NewReaderSize(nil, trBufSize)

	var dirs []*tar.Header

	aufsTempdir := ""
	aufsHardlinks := make(map[string]*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, 0600)
				if err != nil {
					return err
				}
			}
		}

		// Skip AUFS metadata dirs
		if strings.HasPrefix(hdr.Name, ".wh..wh.") {
			// Regular files inside /.wh..wh.plnk can be used as hardlink targets
			// We don't want this directory, but we need the files in them so that
			// such hardlinks can be resolved.
			if strings.HasPrefix(hdr.Name, ".wh..wh.plnk") && hdr.Typeflag == tar.TypeReg {
				basename := filepath.Base(hdr.Name)
				aufsHardlinks[basename] = hdr
				if aufsTempdir == "" {
					if aufsTempdir, err = ioutil.TempDir("", "dockerplnk"); err != nil {
						return err
					}
					defer os.RemoveAll(aufsTempdir)
				}
				if err := createTarFile(filepath.Join(aufsTempdir, basename), dest, hdr, tr, true); err != nil {
					return err
				}
			}
			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
					}
				}
			}

			trBuf.Reset(tr)
			srcData := io.Reader(trBuf)
			srcHdr := hdr

			// Hard links into /.wh..wh.plnk don't work, as we don't extract that directory, so
			// we manually retarget these into the temporary files we extracted them into
			if hdr.Typeflag == tar.TypeLink && strings.HasPrefix(filepath.Clean(hdr.Linkname), ".wh..wh.plnk") {
				linkBasename := filepath.Base(hdr.Linkname)
				srcHdr = aufsHardlinks[linkBasename]
				if srcHdr == nil {
					return fmt.Errorf("Invalid aufs hardlink")
				}
				tmpFile, err := os.Open(filepath.Join(aufsTempdir, linkBasename))
				if err != nil {
					return err
				}
				defer tmpFile.Close()
				srcData = tmpFile
			}

			if err := createTarFile(path, dest, srcHdr, srcData, true); 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
}