feat: simplify how subjects are created from existing manifest

Signed-off-by: Tomas Coufal <[email protected]>

docs/getting_started/user-guide.md

@@ -489,6 +489,28 @@ def push(uri, root):
 
 </details>
 
+<details>
+
+<summary>Example of basic artifact attachment</summary>
+
+We are assuming an `derived-artifact.txt` in the present working directory and that there's already a `localhost:5000/dinosaur/artifact:v1` artifact present in the registry. Here is an example of how to [attach](https://oras.land/docs/concepts/reftypes/) a derived artifact to the existing artifact.
+
+```python
+import oras.client
+import oras.oci
+
+client = oras.client.OrasClient(insecure=True)
+
+manifest = client.remote.get_manifest("localhost:5000/dinosaur/artifact:v1")
+subject = oras.oci.Subject.from_manifest(manifest)
+
+client.push(files=["derived-artifact.txt"], target="localhost:5000/dinosaur/artifact:v1-derived", subject=subject)
+Successfully pushed localhost:5000/dinosaur/artifact:v1-derived
+Out[4]: <Response [201]>
+```
+
+</details>
+
 The above examples are just a start! See our [examples](https://github.com/oras-project/oras-py/tree/main/examples)
 folder alongside the repository for more code examples and clients. If you would like help
 for an example, or to contribute an example, [you know what to do](https://github.com/oras-project/oras-py/issues)!

oras/oci.py

@@ -3,7 +3,10 @@
 __license__ = "Apache-2.0"
 
 import copy
+import hashlib
+import json
 import os
+from dataclasses import dataclass
 from typing import Dict, Optional, Tuple
 
 import jsonschema
@@ -151,3 +154,26 @@ def NewManifest() -> dict:
     Get an empty manifest config.
     """
     return copy.deepcopy(EmptyManifest)
+
+@dataclass
+class Subject:
+    mediaType: str
+    digest: str
+    size: int
+
+    @classmethod
+    def from_manifest(cls, manifest: dict) -> "Subject":
+        """
+        Create a new Subject from a Manifest
+
+        :param manifest: manifest to convert to subject
+        """
+        manifest_string = json.dumps(manifest).encode("utf-8")
+        digest = "sha256:" + hashlib.sha256(manifest_string).hexdigest()
+        size = len(manifest_string)
+
+        return cls(
+            manifest["mediaType"] or oras.defaults.default_manifest_media_type,
+            digest,
+            size,
+        )

oras/provider.py

@@ -6,7 +6,7 @@
 import os
 import urllib
 from contextlib import contextmanager, nullcontext
-from dataclasses import asdict, dataclass
+from dataclasses import asdict
 from http.cookiejar import DefaultCookiePolicy
 from tempfile import TemporaryDirectory
 from typing import Callable, Generator, List, Optional, Tuple, Union
@@ -35,11 +35,6 @@ def temporary_empty_config() -> Generator[str, None, None]:
         yield config_file
 
 
-@dataclass
-class Subject:
-    mediaType: str
-    digest: str
-    size: int
 
 
 class Registry:
@@ -697,7 +692,7 @@ def push(self, *args, **kwargs) -> requests.Response:
         :param refresh_headers: if true or None, headers are refreshed
         :type refresh_headers: bool
         :param subject: optional subject reference
-        :type subject: Subject
+        :type subject: oras.oci.Subject
         """
         container = self.get_container(kwargs["target"])
         self.load_configs(container, configs=kwargs.get("config_path"))

oras/tests/test_oci.py

@@ -0,0 +1,19 @@
+import pytest
+
+import oras.defaults
+import oras.oci
+
+@pytest.mark.with_auth(False)
+def test_create_subject_from_manifest():
+    """
+    Basic tests for oras Subject creation from empty manifest
+    """
+    manifest = oras.oci.NewManifest()
+    subject = oras.oci.Subject.from_manifest(manifest)
+
+    assert subject.mediaType == oras.defaults.default_manifest_media_type
+    assert (
+        subject.digest
+        == "sha256:7a6f84d8c73a71bf9417c13f721ed102f74afac9e481f89e5a72d28954e7d0c5"
+    )
+    assert subject.size == 126

oras/tests/test_provider.py

@@ -9,6 +9,7 @@
 
 import oras.client
 import oras.defaults
+import oras.oci
 import oras.provider
 import oras.utils