github.com/pritambaral/docker@v1.4.2-0.20150120174542-b2fe1b3dd952/pkg/chrootarchive/diff.go (about)

     1  package chrootarchive
     2  
     3  import (
     4  	"bytes"
     5  	"encoding/json"
     6  	"flag"
     7  	"fmt"
     8  	"io"
     9  	"io/ioutil"
    10  	"os"
    11  	"path/filepath"
    12  	"runtime"
    13  	"syscall"
    14  
    15  	"github.com/docker/docker/pkg/archive"
    16  	"github.com/docker/docker/pkg/reexec"
    17  )
    18  
    19  type applyLayerResponse struct {
    20  	LayerSize int64 `json:"layerSize"`
    21  }
    22  
    23  func applyLayer() {
    24  	runtime.LockOSThread()
    25  	flag.Parse()
    26  
    27  	if err := chroot(flag.Arg(0)); err != nil {
    28  		fatal(err)
    29  	}
    30  
    31  	// We need to be able to set any perms
    32  	oldmask := syscall.Umask(0)
    33  	defer syscall.Umask(oldmask)
    34  	tmpDir, err := ioutil.TempDir("/", "temp-docker-extract")
    35  	if err != nil {
    36  		fatal(err)
    37  	}
    38  
    39  	os.Setenv("TMPDIR", tmpDir)
    40  	size, err := archive.UnpackLayer("/", os.Stdin)
    41  	os.RemoveAll(tmpDir)
    42  	if err != nil {
    43  		fatal(err)
    44  	}
    45  
    46  	encoder := json.NewEncoder(os.Stdout)
    47  	if err := encoder.Encode(applyLayerResponse{size}); err != nil {
    48  		fatal(fmt.Errorf("unable to encode layerSize JSON: %s", err))
    49  	}
    50  
    51  	flush(os.Stdout)
    52  	flush(os.Stdin)
    53  	os.Exit(0)
    54  }
    55  
    56  func ApplyLayer(dest string, layer archive.ArchiveReader) (size int64, err error) {
    57  	dest = filepath.Clean(dest)
    58  	decompressed, err := archive.DecompressStream(layer)
    59  	if err != nil {
    60  		return 0, err
    61  	}
    62  
    63  	defer func() {
    64  		if c, ok := decompressed.(io.Closer); ok {
    65  			c.Close()
    66  		}
    67  	}()
    68  
    69  	cmd := reexec.Command("docker-applyLayer", dest)
    70  	cmd.Stdin = decompressed
    71  
    72  	outBuf, errBuf := new(bytes.Buffer), new(bytes.Buffer)
    73  	cmd.Stdout, cmd.Stderr = outBuf, errBuf
    74  
    75  	if err = cmd.Run(); err != nil {
    76  		return 0, fmt.Errorf("ApplyLayer %s stdout: %s stderr: %s", err, outBuf, errBuf)
    77  	}
    78  
    79  	// Stdout should be a valid JSON struct representing an applyLayerResponse.
    80  	response := applyLayerResponse{}
    81  	decoder := json.NewDecoder(outBuf)
    82  	if err = decoder.Decode(&response); err != nil {
    83  		return 0, fmt.Errorf("unable to decode ApplyLayer JSON response: %s", err)
    84  	}
    85  
    86  	return response.LayerSize, nil
    87  }