feat: add ban_tags_enabled/ban_tags to docker remotes to block named tags (#43)

Adds two per-remote config keys for docker remotes:

  ban_tags_enabled: false   # opt-in, default off
  ban_tags:
    - latest
    - edge

When ban_tags_enabled is true and a manifest request arrives for a named
tag in ban_tags, the proxy returns 403. sha256-addressed pulls are never
blocked, so images already pulled can still be referenced by digest.
Blob requests are unaffected.

Reviewed-on: #43

tests/conftest.py

@@ -41,6 +41,13 @@ TEST_REMOTES = {
             "immutable_patterns": ["^library/nginx"],
             "cache": {"immutable_ttl": 0, "mutable_ttl": 300},
         },
+        "docker-bantags-test": {
+            "base_url": "https://registry.example.com",
+            "package": "docker",
+            "ban_tags_enabled": True,
+            "ban_tags": ["latest", "edge"],
+            "cache": {"immutable_ttl": 0, "mutable_ttl": 300},
+        },
         "generic-test": {
             "base_url": "https://releases.example.com",
             "package": "generic",

tests/test_routes.py

@@ -388,6 +388,84 @@ class TestDockerProxy:
         assert response.status_code == 200
 
 
+# ---------------------------------------------------------------------------
+# Docker ban_tags feature
+# ---------------------------------------------------------------------------
+
+
+class TestDockerBanTags:
+    def test_banned_tag_returns_403(self, client, patched_deps):
+        response = client.get("/v2/docker-bantags-test/library/nginx/manifests/latest")
+        assert response.status_code == 403
+        assert "latest" in response.json()["detail"]
+
+    def test_second_banned_tag_returns_403(self, client, patched_deps):
+        response = client.get("/v2/docker-bantags-test/library/nginx/manifests/edge")
+        assert response.status_code == 403
+        assert "edge" in response.json()["detail"]
+
+    def test_allowed_tag_proceeds(self, client, patched_deps):
+        deps = patched_deps
+        manifest = json.dumps({"mediaType": "application/vnd.oci.image.manifest.v1+json", "layers": []}).encode()
+        deps["storage"].exists.return_value = True
+        deps["storage"].download_object.return_value = manifest
+        deps["cache"].is_mutable_file.return_value = True
+        deps["cache"].is_index_valid.return_value = True
+
+        response = client.get("/v2/docker-bantags-test/library/nginx/manifests/1.25.3")
+        assert response.status_code == 200
+
+    def test_digest_pull_bypasses_ban(self, client, patched_deps):
+        # sha256-addressed pulls must never be blocked by the tag ban list
+        deps = patched_deps
+        manifest = json.dumps({"mediaType": "application/vnd.oci.image.manifest.v1+json", "layers": []}).encode()
+        deps["storage"].exists.return_value = True
+        deps["storage"].download_object.return_value = manifest
+        deps["cache"].is_mutable_file.return_value = False
+
+        digest = "sha256:" + "a" * 64
+        with patch("artifactapi.artifact.proxy._fetch_last_modified", new_callable=AsyncMock, return_value=None):
+            response = client.get(f"/v2/docker-bantags-test/library/nginx/manifests/{digest}")
+        assert response.status_code == 200
+
+    def test_ban_tags_disabled_by_default(self, client, patched_deps):
+        # docker-test has no ban_tags_enabled — "latest" must pass through
+        deps = patched_deps
+        manifest = json.dumps({"mediaType": "application/vnd.oci.image.manifest.v1+json", "layers": []}).encode()
+        deps["storage"].exists.return_value = True
+        deps["storage"].download_object.return_value = manifest
+        deps["cache"].is_mutable_file.return_value = True
+        deps["cache"].is_index_valid.return_value = True
+
+        response = client.get("/v2/docker-test/library/nginx/manifests/latest")
+        assert response.status_code == 200
+
+    def test_ban_tags_enabled_but_empty_list_allows_all(self, client, patched_deps):
+        # If ban_tags_enabled is true but ban_tags is empty nothing should be blocked.
+        # docker-test doesn't have ban_tags_enabled, but we can verify via the
+        # docker-bantags-test remote with an unlisted tag.
+        deps = patched_deps
+        manifest = json.dumps({"mediaType": "application/vnd.oci.image.manifest.v1+json", "layers": []}).encode()
+        deps["storage"].exists.return_value = True
+        deps["storage"].download_object.return_value = manifest
+        deps["cache"].is_mutable_file.return_value = True
+        deps["cache"].is_index_valid.return_value = True
+
+        response = client.get("/v2/docker-bantags-test/library/nginx/manifests/stable")
+        assert response.status_code == 200
+
+    def test_ban_check_does_not_apply_to_blobs(self, client, patched_deps):
+        # Blob paths don't contain /manifests/ — the ban check must not interfere
+        deps = patched_deps
+        deps["storage"].exists.return_value = True
+        deps["storage"].download_object.return_value = b"\x00" * 100
+        deps["cache"].is_mutable_file.return_value = False
+
+        with patch("artifactapi.artifact.proxy._fetch_last_modified", new_callable=AsyncMock, return_value=None):
+            response = client.get("/v2/docker-bantags-test/library/nginx/blobs/sha256:" + "b" * 64)
+        assert response.status_code == 200
+
+
 # ---------------------------------------------------------------------------
 # Generic artifact route  /api/v1/remote/{remote}/{path}
 # ---------------------------------------------------------------------------