Work in progress: Docker -> ACI conversion

formats/squashed.py

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+from app import app
+from util.gzipwrap import GZIP_BUFFER_SIZE
+from util.streamlayerformat import StreamLayerMerger
+from formats.tarimageformatter import TarImageFormatter
+
+import copy
+import json
+import tarfile
+
+class FileEstimationException(Exception):
+  """ Exception raised by build_docker_load_stream if the estimated size of the layer TAR
+      was lower than the actual size. This means the sent TAR header is wrong, and we have
+      to fail.
+  """
+  pass
+
+
+class SquashedDockerImage(TarImageFormatter):
+  """ Image formatter which produces a squashed image compatible with the `docker load`
+      command.
+  """
+
+  def stream_generator(self, namespace, repository, tag, synthetic_image_id,
+                       layer_json, get_image_iterator, get_layer_iterator):
+    # Docker import V1 Format (.tar):
+    #  repositories - JSON file containing a repo -> tag -> image map
+    #  {image ID folder}:
+    #     json - The layer JSON
+    #     layer.tar - The TARed contents of the layer
+    #     VERSION - The docker import version: '1.0'
+    layer_merger = StreamLayerMerger(get_layer_iterator)
+
+    # Yield the repositories file:
+    synthetic_layer_info = {}
+    synthetic_layer_info[tag + '.squash'] = synthetic_image_id
+
+    hostname = app.config['SERVER_HOSTNAME']
+    repositories = {}
+    repositories[hostname + '/' + namespace + '/' + repository] = synthetic_layer_info
+
+    yield self.tar_file('repositories', json.dumps(repositories))
+
+    # Yield the image ID folder.
+    yield self.tar_folder(synthetic_image_id)
+
+    # Yield the JSON layer data.
+    layer_json = self._build_layer_json(layer_json, synthetic_image_id)
+    yield self.tar_file(synthetic_image_id + '/json', json.dumps(layer_json))
+
+    # Yield the VERSION file.
+    yield self.tar_file(synthetic_image_id + '/VERSION', '1.0')
+
+    # Yield the merged layer data's header.
+    estimated_file_size = 0
+    for image in get_image_iterator():
+      estimated_file_size += image.storage.uncompressed_size
+
+    yield self.tar_file_header(synthetic_image_id + '/layer.tar', estimated_file_size)
+
+    # Yield the contents of the merged layer.
+    yielded_size = 0
+    for entry in layer_merger.get_generator():
+      yield entry
+      yielded_size += len(entry)
+
+    # If the yielded size is more than the estimated size (which is unlikely but possible), then
+    # raise an exception since the tar header will be wrong.
+    if yielded_size > estimated_file_size:
+      raise FileEstimationException()
+
+    # If the yielded size is less than the estimated size (which is likely), fill the rest with
+    # zeros.
+    if yielded_size < estimated_file_size:
+      to_yield = estimated_file_size - yielded_size
+      while to_yield > 0:
+        yielded = min(to_yield, GZIP_BUFFER_SIZE)
+        yield '\0' * yielded
+        to_yield -= yielded
+
+    # Yield any file padding to 512 bytes that is necessary.
+    yield self.tar_file_padding(estimated_file_size)
+
+    # Last two records are empty in TAR spec.
+    yield '\0' * 512
+    yield '\0' * 512
+
+
+  def _build_layer_json(self, layer_json, synthetic_image_id):
+    updated_json = copy.deepcopy(layer_json)
+    updated_json['id'] = synthetic_image_id
+
+    if 'parent' in updated_json:
+      del updated_json['parent']
+
+    if 'config' in updated_json and 'Image' in updated_json['config']:
+      updated_json['config']['Image'] = synthetic_image_id
+
+    if 'container_config' in updated_json and 'Image' in updated_json['container_config']:
+      updated_json['container_config']['Image'] = synthetic_image_id
+
+    return updated_json
+