Initial

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

vendor/github.com/Microsoft/hcsshim/internal/wclayer/exportlayer.go

@@ -0,0 +1,76 @@
+package wclayer
+
+import (
+	"io/ioutil"
+	"os"
+
+	"github.com/Microsoft/go-winio"
+	"github.com/Microsoft/hcsshim/internal/hcserror"
+	"github.com/sirupsen/logrus"
+)
+
+// ExportLayer will create a folder at exportFolderPath and fill that folder with
+// the transport format version of the layer identified by layerId. This transport
+// format includes any metadata required for later importing the layer (using
+// ImportLayer), and requires the full list of parent layer paths in order to
+// perform the export.
+func ExportLayer(path string, exportFolderPath string, parentLayerPaths []string) (err error) {
+	title := "hcsshim::ExportLayer"
+	fields := logrus.Fields{
+		"path":             path,
+		"exportFolderPath": exportFolderPath,
+	}
+	logrus.WithFields(fields).Debug(title)
+	defer func() {
+		if err != nil {
+			fields[logrus.ErrorKey] = err
+			logrus.WithFields(fields).Error(err)
+		} else {
+			logrus.WithFields(fields).Debug(title + " - succeeded")
+		}
+	}()
+
+	// Generate layer descriptors
+	layers, err := layerPathsToDescriptors(parentLayerPaths)
+	if err != nil {
+		return err
+	}
+
+	err = exportLayer(&stdDriverInfo, path, exportFolderPath, layers)
+	if err != nil {
+		return hcserror.New(err, title+" - failed", "")
+	}
+	return nil
+}
+
+type LayerReader interface {
+	Next() (string, int64, *winio.FileBasicInfo, error)
+	Read(b []byte) (int, error)
+	Close() error
+}
+
+// NewLayerReader returns a new layer reader for reading the contents of an on-disk layer.
+// The caller must have taken the SeBackupPrivilege privilege
+// to call this and any methods on the resulting LayerReader.
+func NewLayerReader(path string, parentLayerPaths []string) (LayerReader, error) {
+	exportPath, err := ioutil.TempDir("", "hcs")
+	if err != nil {
+		return nil, err
+	}
+	err = ExportLayer(path, exportPath, parentLayerPaths)
+	if err != nil {
+		os.RemoveAll(exportPath)
+		return nil, err
+	}
+	return &legacyLayerReaderWrapper{newLegacyLayerReader(exportPath)}, nil
+}
+
+type legacyLayerReaderWrapper struct {
+	*legacyLayerReader
+}
+
+func (r *legacyLayerReaderWrapper) Close() error {
+	err := r.legacyLayerReader.Close()
+	os.RemoveAll(r.root)
+	return err
+}