Add an additional short circuit to avoid parsing the manifest when not necessary for older Docker clients

We also add tests for this case

endpoints/v2/manifest.py

@@ -15,7 +15,7 @@ from endpoints.v2 import v2_bp, require_repo_read, require_repo_write
 from endpoints.v2.errors import (ManifestInvalid, ManifestUnknown, NameInvalid, TagExpired,
                                  NameUnknown)
 from image.docker import ManifestException
-from image.docker.schema1 import DOCKER_SCHEMA1_MANIFEST_CONTENT_TYPE
+from image.docker.schema1 import DOCKER_SCHEMA1_MANIFEST_CONTENT_TYPE, DOCKER_SCHEMA1_CONTENT_TYPES
 from image.docker.schema2 import DOCKER_SCHEMA2_CONTENT_TYPES, OCI_CONTENT_TYPES
 from image.docker.schemas import parse_manifest_from_bytes
 from notifications import spawn_notification
@@ -113,6 +113,12 @@ def _rewrite_schema_if_necessary(namespace_name, repo_name, tag_name, manifest):
   if manifest.media_type in mimetypes:
     return manifest.internal_manifest_bytes, manifest.digest, manifest.media_type
 
+  # Short-circuit check: If the mimetypes is empty or just `application/json`, verify we have
+  # a schema 1 manifest and return it.
+  if not mimetypes or mimetypes == ['application/json']:
+    if manifest.media_type in DOCKER_SCHEMA1_CONTENT_TYPES:
+      return manifest.internal_manifest_bytes, manifest.digest, manifest.media_type
+
   logger.debug('Manifest `%s` not compatible against %s; checking for conversion', manifest.digest,
                request.accept_mimetypes)
   converted = registry_model.convert_manifest(manifest, namespace_name, repo_name, tag_name,

test/registry/protocol_v2.py

@@ -208,7 +208,7 @@ class V2Protocol(RegistryProtocol):
 
     headers = {
       'Authorization': 'Bearer ' + token,
-      'Accept': ','.join(options.accept_mimetypes) if options.accept_mimetypes else '*/*',
+      'Accept': ','.join(options.accept_mimetypes) if options.accept_mimetypes is not None else '*/*',
     }
 
     # Push all blobs.
@@ -340,7 +340,7 @@ class V2Protocol(RegistryProtocol):
 
     headers = {
       'Authorization': 'Bearer ' + token,
-      'Accept': ','.join(options.accept_mimetypes) if options.accept_mimetypes else '*/*',
+      'Accept': ','.join(options.accept_mimetypes) if options.accept_mimetypes is not None else '*/*',
     }
 
     # Build fake manifests.
@@ -530,7 +530,9 @@ class V2Protocol(RegistryProtocol):
     }
 
     if self.schema2:
-      headers['Accept'] = ','.join(options.accept_mimetypes or DOCKER_SCHEMA2_CONTENT_TYPES)
+      headers['Accept'] = ','.join(options.accept_mimetypes
+                                   if options.accept_mimetypes is not None
+                                   else DOCKER_SCHEMA2_CONTENT_TYPES)
 
     manifests = {}
     image_ids = {}

test/registry/registry_tests.py

@@ -1854,3 +1854,27 @@ def test_push_pull_emoji_unicode_direct(pusher, puller, unicode_emoji_images, li
   # Pull the repository to verify.
   puller.pull(liveserver_session, 'devtable', 'newrepo', 'latest', unicode_emoji_images,
               credentials=credentials, options=options)
+
+
+@pytest.mark.parametrize('accepted_mimetypes', [
+  [],
+  ['application/json'],
+])
+def test_push_pull_older_mimetype(pusher, puller, basic_images, liveserver_session, app_reloader,
+                                  accepted_mimetypes):
+  """ Test: Push and pull an image, but override the accepted mimetypes to that sent by older
+            Docker clients.
+  """
+  credentials = ('devtable', 'password')
+
+  # Push a new repository.
+  pusher.push(liveserver_session, 'devtable', 'newrepo', 'latest', basic_images,
+              credentials=credentials)
+
+  # Turn off automatic unicode encoding when building the manifests.
+  options = ProtocolOptions()
+  options.accept_mimetypes = accepted_mimetypes
+
+  # Pull the repository to verify.
+  puller.pull(liveserver_session, 'devtable', 'newrepo', 'latest', basic_images,
+              credentials=credentials, options=options)