Parse extension ID from history so that we can output a useful log me…

…ssage

Signed-off-by: Natalie Arellano <narellano@vmware.com>

exporter.go

@@ -320,7 +320,7 @@ func (e *Exporter) addExtensionLayers(opts ExportOptions, meta *platform.LayersM
 			layerPath = filepath.Join(artifactsDir, calculatedDiffID)
 		}
 		layer := layers.Layer{
-			ID:      "from extensions",
+			ID:      parseExtensionIDFromHistory(history[idx]),
 			TarPath: layerPath,
 			Digest:  layerHex.String(),
 			History: history[idx],
@@ -332,6 +332,18 @@ func (e *Exporter) addExtensionLayers(opts ExportOptions, meta *platform.LayersM
 	return nil
 }
 
+func parseExtensionIDFromHistory(history v1.History) string {
+	r := strings.NewReader(history.CreatedBy)
+	var (
+		layerName, extensionID string
+	)
+	n, err := fmt.Fscanf(r, layers.ExtensionLayerName, &layerName, &extensionID)
+	if err != nil || n != 2 {
+		return "from extensions"
+	}
+	return strings.ReplaceAll(extensionID, "@", ":") // matches buildpacks
+}
+
 func isLocalImage(workingImage imgutil.Image) bool {
 	if _, ok := workingImage.(*local.Image); ok {
 		return true