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moby--moby/pkg/chrootarchive/diff.go

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package chrootarchive
import (
"bytes"
"encoding/json"
"flag"
"fmt"
"io/ioutil"
"os"
"path/filepath"
"runtime"
"syscall"
"github.com/docker/docker/pkg/archive"
"github.com/docker/docker/pkg/reexec"
)
type applyLayerResponse struct {
LayerSize int64 `json:"layerSize"`
}
func applyLayer() {
runtime.LockOSThread()
flag.Parse()
if err := chroot(flag.Arg(0)); err != nil {
fatal(err)
}
// We need to be able to set any perms
oldmask := syscall.Umask(0)
defer syscall.Umask(oldmask)
tmpDir, err := ioutil.TempDir("/", "temp-docker-extract")
if err != nil {
fatal(err)
}
os.Setenv("TMPDIR", tmpDir)
size, err := archive.UnpackLayer("/", os.Stdin)
os.RemoveAll(tmpDir)
if err != nil {
fatal(err)
}
encoder := json.NewEncoder(os.Stdout)
if err := encoder.Encode(applyLayerResponse{size}); err != nil {
fatal(fmt.Errorf("unable to encode layerSize JSON: %s", err))
}
flush(os.Stdout)
flush(os.Stdin)
os.Exit(0)
}
func ApplyLayer(dest string, layer archive.ArchiveReader) (size int64, err error) {
dest = filepath.Clean(dest)
decompressed, err := archive.DecompressStream(layer)
if err != nil {
return 0, err
}
defer decompressed.Close()
cmd := reexec.Command("docker-applyLayer", dest)
cmd.Stdin = decompressed
outBuf, errBuf := new(bytes.Buffer), new(bytes.Buffer)
cmd.Stdout, cmd.Stderr = outBuf, errBuf
if err = cmd.Run(); err != nil {
return 0, fmt.Errorf("ApplyLayer %s stdout: %s stderr: %s", err, outBuf, errBuf)
}
// Stdout should be a valid JSON struct representing an applyLayerResponse.
response := applyLayerResponse{}
decoder := json.NewDecoder(outBuf)
if err = decoder.Decode(&response); err != nil {
return 0, fmt.Errorf("unable to decode ApplyLayer JSON response: %s", err)
}
return response.LayerSize, nil
}