moby/daemon/export.go

package daemon

import (
	"fmt"
	"io"
	"runtime"

	"github.com/docker/docker/container"
	"github.com/docker/docker/pkg/archive"
	"github.com/docker/docker/pkg/ioutils"
)

// ContainerExport writes the contents of the container to the given
// writer. An error is returned if the container cannot be found.
func (daemon *Daemon) ContainerExport(name string, out io.Writer) error {
	container, err := daemon.GetContainer(name)
	if err != nil {
		return err
	}

	if runtime.GOOS == "windows" && container.Platform == "windows" {
		return fmt.Errorf("the daemon on this platform does not support exporting Windows containers")
	}

	if container.IsDead() {
		err := fmt.Errorf("You cannot export container %s which is Dead", container.ID)
		return stateConflictError{err}
	}

	if container.IsRemovalInProgress() {
		err := fmt.Errorf("You cannot export container %s which is being removed", container.ID)
		return stateConflictError{err}
	}

	data, err := daemon.containerExport(container)
	if err != nil {
		return fmt.Errorf("Error exporting container %s: %v", name, err)
	}
	defer data.Close()

	// Stream the entire contents of the container (basically a volatile snapshot)
	if _, err := io.Copy(out, data); err != nil {
		return fmt.Errorf("Error exporting container %s: %v", name, err)
	}
	return nil
}

func (daemon *Daemon) containerExport(container *container.Container) (arch io.ReadCloser, err error) {
	rwlayer, err := daemon.stores[container.Platform].layerStore.GetRWLayer(container.ID)
	if err != nil {
		return nil, err
	}
	defer func() {
		if err != nil {
			daemon.stores[container.Platform].layerStore.ReleaseRWLayer(rwlayer)
		}
	}()

	_, err = rwlayer.Mount(container.GetMountLabel())
	if err != nil {
		return nil, err
	}

	archive, err := archivePath(container.BaseFS, container.BaseFS.Path(), &archive.TarOptions{
		Compression: archive.Uncompressed,
		UIDMaps:     daemon.idMappings.UIDs(),
		GIDMaps:     daemon.idMappings.GIDs(),
	})
	if err != nil {
		rwlayer.Unmount()
		return nil, err
	}
	arch = ioutils.NewReadCloserWrapper(archive, func() error {
		err := archive.Close()
		rwlayer.Unmount()
		daemon.stores[container.Platform].layerStore.ReleaseRWLayer(rwlayer)
		return err
	})
	daemon.LogContainerEvent(container, "export")
	return arch, err
}