DockerSource: Add support for Manifest version 1

Handle differences between version 1 and 2 of the Manifest file for
Docker registry.

Layers' blob sums in v1 are stored in a list "fsLayers" and the digest
is stored in following filed with name "blobSum". [1]

In v2 the layer list is stored in field with name "layers" and
ordered starting from the base image (opposite order of v1). The digest
is stored under a following field with name "digest". The size in bytes
is included in a field with name "size". [2]

[1] https://docs.docker.com/registry/spec/manifest-v2-1/#manifest-field-descriptions
[2] https://docs.docker.com/registry/spec/manifest-v2-2/#image-manifest-field-descriptions

2 files changed, 20 insertions, 5 deletions

diff --git a/src/virtBootstrap/sources.py b/src/virtBootstrap/sources.py
index 4f1b104..8800d72 100644
--- a/src/virtBootstrap/sources.py
+++ b/src/virtBootstrap/sources.py
@@ -128,10 +128,22 @@ class DockerSource(object):
                                                 username=self.username,
                                                 password=self.password)
 
-        for layer in self.manifest['layers']:
-            sum_type, layer_sum = layer['digest'].split(':')
+        if self.manifest['schemaVersion'] == 1:
+            layers_list = self.manifest['fsLayers'][::-1]
+            digest_field = 'blobSum'
+        elif self.manifest['schemaVersion'] == 2:
+            layers_list = self.manifest['layers']
+            digest_field = 'digest'
+        else:
+            raise ValueError('Unsupported manifest schema.')
+
+        for layer in layers_list:
+            layer_digest = layer[digest_field]
+            layer_size = layer['size'] if 'size' in layer else None
+
+            sum_type, layer_sum = layer_digest.split(':')
             file_path = os.path.join(self.images_dir, layer_sum + '.tar')
-            self.layers.append([sum_type, layer_sum, file_path, layer['size']])
+            self.layers.append([sum_type, layer_sum, file_path, layer_size])
 
     def gen_valid_uri(self, uri):
         """
diff --git a/src/virtBootstrap/utils.py b/src/virtBootstrap/utils.py
index daabd26..a65d3f5 100644
--- a/src/virtBootstrap/utils.py
+++ b/src/virtBootstrap/utils.py
@@ -138,8 +138,11 @@ def log_layer_extract(layer, current, total, progress):
     Create log message on layer extract.
     """
     sum_type, sum_value, layer_file, layer_size = layer
-    progress("Extracting layer (%s/%s) with size: %s"
-             % (current, total, bytes_to_size(layer_size)), logger=logger)
+    msg = 'Extracting layer (%s/%s)' % (current, total)
+
+    if layer_size:
+        msg += " with size: %s" % bytes_to_size(layer_size)
+    progress(msg, logger=logger)
     logger.debug('Untar layer: (%s:%s) %s', sum_type, sum_value, layer_file)