Refactor the util directory to use subpackages.

util/registry/tarlayerformat.py

@@ -0,0 +1,94 @@
+import os
+import tarfile
+import copy
+
+class TarLayerReadException(Exception):
+  """ Exception raised when reading a layer has failed. """
+  pass
+
+
+class TarLayerFormat(object):
+  """ Class which creates a generator of the combined TAR data. """
+  def __init__(self, tar_iterator, path_prefix=None):
+    self.tar_iterator = tar_iterator
+    self.path_prefix = path_prefix
+
+  def get_generator(self):
+    for current_tar in self.tar_iterator():
+      # Read the current TAR. If it is empty, we just continue
+      # to the next one.
+      tar_file = None
+      try:
+        tar_file = tarfile.open(mode='r|*', fileobj=current_tar)
+      except tarfile.ReadError as re:
+        if re.message != 'empty file':
+          raise TarLayerReadException('Could not read layer')
+
+      if not tar_file:
+        continue
+
+      # For each of the tar entries, yield them IF and ONLY IF we have not
+      # encountered the path before.
+
+      # 9MB (+ padding below) so that it matches the 10MB expected by Gzip.
+      chunk_size = 1024 * 1024 * 9
+
+      for tar_info in tar_file:
+        if not self.check_tar_info(tar_info):
+          continue
+
+        # Yield the tar header.
+        if self.path_prefix:
+          # Note: We use a copy here because we need to make sure we copy over all the internal
+          # data of the tar header. We cannot use frombuf(tobuf()), however, because it doesn't
+          # properly handle large filenames.
+          clone = copy.deepcopy(tar_info)
+          clone.name = os.path.join(self.path_prefix, clone.name)
+
+          # If the entry is a *hard* link, then prefix it as well. Soft links are relative.
+          if clone.linkname and clone.type == tarfile.LNKTYPE:
+            clone.linkname = os.path.join(self.path_prefix, clone.linkname)
+
+          yield clone.tobuf()
+        else:
+          yield tar_info.tobuf()
+
+        # Try to extract any file contents for the tar. If found, we yield them as well.
+        if tar_info.isreg():
+          file_stream = tar_file.extractfile(tar_info)
+          if file_stream is not None:
+            length = 0
+            while True:
+              current_block = file_stream.read(chunk_size)
+              if not len(current_block):
+                break
+
+              yield current_block
+              length += len(current_block)
+
+            file_stream.close()
+
+            # Files must be padding to 512 byte multiples.
+            if length % 512 != 0:
+              yield '\0' * (512 - (length % 512))
+
+      # Close the layer stream now that we're done with it.
+      tar_file.close()
+
+      # Conduct any post-tar work.
+      self.after_tar_layer(current_tar)
+
+    # Last two records are empty in TAR spec.
+    yield '\0' * 512
+    yield '\0' * 512
+
+
+  def check_tar_info(self, tar_info):
+    """ Returns true if the current tar_info should be added to the combined tar. False
+        otherwise.
+    """
+    raise NotImplementedError()
+
+  def after_tar_layer(self, current_tar):
+    """ Invoked after a TAR layer is added, to do any post-add work. """
+    raise NotImplementedError()