tar_util.go

/*
Copyright 2018 Google LLC

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package util

import (
	"archive/tar"
	"compress/bzip2"
	"compress/gzip"
	"io"
	"io/ioutil"
	"os"
	"path/filepath"
	"syscall"

	"github.com/docker/docker/pkg/archive"
	"github.com/pkg/errors"
	"github.com/sirupsen/logrus"
)

// AddToTar adds the file i to tar w at path p
func AddToTar(p string, i os.FileInfo, hardlinks map[uint64]string, w *tar.Writer) error {
	linkDst := ""
	if i.Mode()&os.ModeSymlink != 0 {
		var err error
		linkDst, err = os.Readlink(p)
		if err != nil {
			return err
		}
	}
	hdr, err := tar.FileInfoHeader(i, linkDst)
	if err != nil {
		return err
	}
	hdr.Name = p

	hardlink, linkDst := checkHardlink(p, hardlinks, i)
	if hardlink {
		hdr.Linkname = linkDst
		hdr.Typeflag = tar.TypeLink
		hdr.Size = 0
	}
	if err := w.WriteHeader(hdr); err != nil {
		return err
	}
	if !(i.Mode().IsRegular()) || hardlink {
		return nil
	}
	r, err := os.Open(p)
	if err != nil {
		return err
	}
	defer r.Close()
	if _, err := io.Copy(w, r); err != nil {
		return err
	}
	return nil
}

func Whiteout(p string, w *tar.Writer) error {
	dir := filepath.Dir(p)
	name := ".wh." + filepath.Base(p)

	th := &tar.Header{
		Name: filepath.Join(dir, name),
		Size: 0,
	}
	if err := w.WriteHeader(th); err != nil {
		return err
	}

	return nil
}

// Returns true if path is hardlink, and the link destination
func checkHardlink(p string, hardlinks map[uint64]string, i os.FileInfo) (bool, string) {
	hardlink := false
	linkDst := ""
	if sys := i.Sys(); sys != nil {
		if stat, ok := sys.(*syscall.Stat_t); ok {
			nlinks := stat.Nlink
			if nlinks > 1 {
				inode := stat.Ino
				if original, exists := hardlinks[inode]; exists && original != p {
					hardlink = true
					logrus.Debugf("%s inode exists in hardlinks map, linking to %s", p, original)
					linkDst = original
				} else {
					hardlinks[inode] = p
				}
			}
		}
	}
	return hardlink, linkDst
}

// UnpackLocalTarArchive unpacks the tar archive at path to the directory dest
// Returns true if the path was actually unpacked
func UnpackLocalTarArchive(path, dest string) error {
	// First, we need to check if the path is a local tar archive
	if compressed, compressionLevel := fileIsCompressedTar(path); compressed {
		file, err := os.Open(path)
		if err != nil {
			return err
		}
		defer file.Close()
		if compressionLevel == archive.Gzip {
			return UnpackCompressedTar(path, dest)
		} else if compressionLevel == archive.Bzip2 {
			bzr := bzip2.NewReader(file)
			return unTar(bzr, dest)
		}
	}
	if fileIsUncompressedTar(path) {
		file, err := os.Open(path)
		if err != nil {
			return err
		}
		defer file.Close()
		return unTar(file, dest)
	}
	return errors.New("path does not lead to local tar archive")
}

//IsFileLocalTarArchive returns true if the file is a local tar archive
func IsFileLocalTarArchive(src string) bool {
	compressed, _ := fileIsCompressedTar(src)
	uncompressed := fileIsUncompressedTar(src)
	return compressed || uncompressed
}

func fileIsCompressedTar(src string) (bool, archive.Compression) {
	r, err := os.Open(src)
	if err != nil {
		return false, -1
	}
	defer r.Close()
	buf, err := ioutil.ReadAll(r)
	if err != nil {
		return false, -1
	}
	compressionLevel := archive.DetectCompression(buf)
	return (compressionLevel > 0), compressionLevel
}

func fileIsUncompressedTar(src string) bool {
	r, err := os.Open(src)
	defer r.Close()
	if err != nil {
		return false
	}
	fi, err := os.Lstat(src)
	if err != nil {
		return false
	}
	if fi.Size() == 0 {
		return false
	}
	tr := tar.NewReader(r)
	if tr == nil {
		return false
	}
	for {
		_, err := tr.Next()
		if err != nil {
			return false
		}
		return true
	}
}

// UnpackCompressedTar unpacks the compressed tar at path to dir
func UnpackCompressedTar(path, dir string) error {
	file, err := os.Open(path)
	if err != nil {
		return err
	}
	defer file.Close()
	gzr, err := gzip.NewReader(file)
	if err != nil {
		return err
	}
	defer gzr.Close()
	return unTar(gzr, dir)
}