Reimplement cache support for blobs in the registry data model

data/registry_model/registry_pre_oci_model.py

@@ -8,8 +8,10 @@ from peewee import IntegrityError
 
 from data import database
 from data import model
+from data.cache import cache_key
 from data.database import db_transaction
 from data.registry_model.interface import RegistryDataInterface
+from data.registry_model.datatype import FromDictionaryException
 from data.registry_model.datatypes import (Tag, RepositoryReference, Manifest, LegacyImage, Label,
                                            SecurityScanStatus, ManifestLayer, Blob, DerivedImage,
                                            TorrentInfo, BlobUpload)
@@ -685,6 +687,36 @@ class PreOCIModel(RegistryDataInterface):
     torrent_info = model.storage.save_torrent_info(image_storage, piece_length, pieces)
     return TorrentInfo.for_torrent_info(torrent_info)
 
+  def get_cached_repo_blob(self, model_cache, namespace_name, repo_name, blob_digest):
+    """
+    Returns the blob in the repository with the given digest if any or None if none.
+    Caches the result in the caching system.
+    """
+    def load_blob():
+      repository_ref = self.lookup_repository(namespace_name, repo_name)
+      if repository_ref is None:
+        return None
+
+      blob_found = self.get_repo_blob_by_digest(repository_ref, blob_digest,
+                                                include_placements=True)
+      if blob_found is None:
+        return None
+
+      return blob_found.asdict()
+
+    blob_cache_key = cache_key.for_repository_blob(namespace_name, repo_name, blob_digest)
+    blob_dict = model_cache.retrieve(blob_cache_key, load_blob)
+    
+    try:
+      return Blob.from_dict(blob_dict) if blob_dict is not None else None
+    except FromDictionaryException:
+      # The data was stale in some way. Simply reload.
+      repository_ref = self.lookup_repository(namespace_name, repo_name)
+      if repository_ref is None:
+        return None
+
+      return self.get_repo_blob_by_digest(repository_ref, blob_digest, include_placements=True)
+
   def get_repo_blob_by_digest(self, repository_ref, blob_digest, include_placements=False):
     """
     Returns the blob in the repository with the given digest, if any or None if none. Note that