workaround (too?) strict validation in artifactory

Kaniko will in some cases create cfg-blobs where the amount of entries
in the `history` attr is smaller than the amount of fs-layer-blobs.

This leads to artifactory rejecting the manifest with an error message
like so:

```
{"errors":[{"code":"MANIFEST_INVALID","message":"manifest
invalid","detail":{"description":"Circuit Breaker Threshold Reached,
Breaking Operation. see log output for manifest details."}}]}
```

There are some bugs reports to be found on that behaviour, e.g.:

GoogleContainerTools/jib#875

As a workaround, cp the last history-entry in case the amount of layers
exceeds the history-entries to prevent this behaviour from happening.

oci/kaniko.py

@@ -126,13 +126,52 @@ def _read_chunk(self, offset: int, length: int):
  def cfg_blob(self):
  cfg_info = self.tarfile.getmember(name=self.kaniko_manifest.Config)
 
- return _KanikoBlob(
+ # HACK: unfortunately, we need to patch the cfg-blob in case there are
+ # less history-entries than layer-blobs
+ def _mk_wrapper():
+ return _KanikoBlob(
+ read_chunk=self._read_chunk,
+ offset=cfg_info.offset_data,
+ name=cfg_info.name,
+ size=cfg_info.size,
+ hash_algorithm=cfg_info.name.split(':')[0],
+ )
+
+ cfg_blob_bytes = _mk_wrapper().read()
+ cfg_blob_dict = json.loads(cfg_blob_bytes)
+
+ layers_count = len(tuple(self.layer_blobs()))
+
+ if layers_count <= (history_leng := len((history := cfg_blob_dict['history']))):
+ # no patching needed
+ print('no patching required')
+ return _mk_wrapper()
+
+ missing_history_count = layers_count - history_leng
+ last_history_entry = history[-1] # hackily cp last entry
+ for _ in range(missing_history_count):
+ history.append(last_history_entry)
+
+ cfg_blob_dict['history'] = history
+ cfg_blob_bytes = json.dumps(cfg_blob_dict).encode('utf-8')
+
+ import hashlib
+ cfg_hash = hashlib.sha256(cfg_blob_bytes).hexdigest()
+
+ cfg_blob_buf = io.BytesIO(cfg_blob_bytes)
+ cfg_blob_buf.seek(0)
+
+ # now we need to fake a kaniko-blob-wrapper
+ cfg_blob_wrapper = _KanikoBlob(
  read_chunk=self._read_chunk,
  offset=cfg_info.offset_data,
- name=cfg_info.name,
- size=cfg_info.size,
+ name=f'sha256:{cfg_hash}', # XXX name is parsed again for digest_str()
+ size=len(cfg_blob_bytes),
  hash_algorithm=cfg_info.name.split(':')[0],
  )
+ cfg_blob_wrapper.read = cfg_blob_buf.read
+
+ return cfg_blob_wrapper
 
  def layer_blobs(self):
  for layer_name in self.kaniko_manifest.Layers: