github.com/rsampaio/docker@v0.7.2-0.20150827203920-fdc73cc3fc31/pkg/chrootarchive/diff_unix.go (about)

     1  //+build !windows
     2  
     3  package chrootarchive
     4  
     5  import (
     6  	"bytes"
     7  	"encoding/json"
     8  	"flag"
     9  	"fmt"
    10  	"io/ioutil"
    11  	"os"
    12  	"path/filepath"
    13  	"runtime"
    14  
    15  	"github.com/docker/docker/pkg/archive"
    16  	"github.com/docker/docker/pkg/reexec"
    17  	"github.com/docker/docker/pkg/system"
    18  )
    19  
    20  type applyLayerResponse struct {
    21  	LayerSize int64 `json:"layerSize"`
    22  }
    23  
    24  // applyLayer is the entry-point for docker-applylayer on re-exec. This is not
    25  // used on Windows as it does not support chroot, hence no point sandboxing
    26  // through chroot and rexec.
    27  func applyLayer() {
    28  
    29  	var (
    30  		tmpDir = ""
    31  		err    error
    32  	)
    33  	runtime.LockOSThread()
    34  	flag.Parse()
    35  
    36  	if err := chroot(flag.Arg(0)); err != nil {
    37  		fatal(err)
    38  	}
    39  
    40  	// We need to be able to set any perms
    41  	oldmask, err := system.Umask(0)
    42  	defer system.Umask(oldmask)
    43  	if err != nil {
    44  		fatal(err)
    45  	}
    46  
    47  	if tmpDir, err = ioutil.TempDir("/", "temp-docker-extract"); err != nil {
    48  		fatal(err)
    49  	}
    50  
    51  	os.Setenv("TMPDIR", tmpDir)
    52  	size, err := archive.UnpackLayer("/", os.Stdin)
    53  	os.RemoveAll(tmpDir)
    54  	if err != nil {
    55  		fatal(err)
    56  	}
    57  
    58  	encoder := json.NewEncoder(os.Stdout)
    59  	if err := encoder.Encode(applyLayerResponse{size}); err != nil {
    60  		fatal(fmt.Errorf("unable to encode layerSize JSON: %s", err))
    61  	}
    62  
    63  	flush(os.Stdout)
    64  	flush(os.Stdin)
    65  	os.Exit(0)
    66  }
    67  
    68  // applyLayerHandler parses a diff in the standard layer format from `layer`, and
    69  // applies it to the directory `dest`. Returns the size in bytes of the
    70  // contents of the layer.
    71  func applyLayerHandler(dest string, layer archive.Reader, decompress bool) (size int64, err error) {
    72  	dest = filepath.Clean(dest)
    73  	if decompress {
    74  		decompressed, err := archive.DecompressStream(layer)
    75  		if err != nil {
    76  			return 0, err
    77  		}
    78  		defer decompressed.Close()
    79  
    80  		layer = decompressed
    81  	}
    82  
    83  	cmd := reexec.Command("docker-applyLayer", dest)
    84  	cmd.Stdin = layer
    85  
    86  	outBuf, errBuf := new(bytes.Buffer), new(bytes.Buffer)
    87  	cmd.Stdout, cmd.Stderr = outBuf, errBuf
    88  
    89  	if err = cmd.Run(); err != nil {
    90  		return 0, fmt.Errorf("ApplyLayer %s stdout: %s stderr: %s", err, outBuf, errBuf)
    91  	}
    92  
    93  	// Stdout should be a valid JSON struct representing an applyLayerResponse.
    94  	response := applyLayerResponse{}
    95  	decoder := json.NewDecoder(outBuf)
    96  	if err = decoder.Decode(&response); err != nil {
    97  		return 0, fmt.Errorf("unable to decode ApplyLayer JSON response: %s", err)
    98  	}
    99  
   100  	return response.LayerSize, nil
   101  }