fix: align transitive compatibility checks

Make so that the transitive compatibility checks that are done in the
schema creation endpoint are also done in the schema validation
endpoint.

In the creation endpoint (`/subjects/<subject-key>/versions`), if the
compatibility mode is transient then the new schema is checked against
all schemas.

In the validation endpoint (`/compatibility/subjects/<subject-key>/versions/<schema-version>`):
 - Before this fix, only the latest schema is checked against (even in
   case of transitive mode)
 - After this fix, in case of transitive mode then all schema are
   checked against.
   Note that in this case the version provided in the POST request
   (`<schema-version>`) is ignored.

[EC-289]

README.rst

@@ -149,6 +149,10 @@ Test the compatibility of a schema with the latest schema under subject "test-ke
     http://localhost:8081/compatibility/subjects/test-key/versions/latest
   {"is_compatible":true}
 
+NOTE: if the subject's compatibility mode is transitive (BACKWARD_TRANSITIVE, FORWARD_TRANSITIVE or FULL_TRANSITIVE) then the
+compatibility is checked not only against the latest schema, but also against all previous schemas, as it would be done
+when trying to register the new schema through the `subjects/<subject-key>/versions` endpoint.
+
 Get current global backwards compatibility setting value::
 
   $ curl -X GET http://localhost:8081/config

karapace/schema_registry_apis.py

@@ -10,8 +10,8 @@
 from http import HTTPStatus
 from karapace.auth import HTTPAuthorizer, Operation, User
 from karapace.compatibility import CompatibilityModes
-from karapace.compatibility.schema_compatibility import SchemaCompatibility
 from karapace.compatibility.jsonschema.checks import is_incompatible
+from karapace.compatibility.schema_compatibility import SchemaCompatibility
 from karapace.config import Config
 from karapace.errors import (
     IncompatibleSchema,
@@ -397,13 +397,14 @@ async def compatibility_check(
             )
 
         new_schema = self.get_new_schema(request.json, content_type)
-        old_schema = self.get_old_schema(subject, Versioner.V(version), content_type)
-
-        result = SchemaCompatibility.check_compatibility(
-            old_schema,
-            new_schema,
-            compatibility_mode
-        )
+        if compatibility_mode.is_transitive():
+            # Ignore the schema version provided in the rest api call (`version`)
+            # Instead check against all previous versions (including `version` if existing)
+            result = self.schema_registry.check_schema_compatibility(new_schema, subject)
+        else:
+            # Check against the schema version provided in the rest api call (`version`)
+            old_schema = self.get_old_schema(subject, Versioner.V(version), content_type)
+            result = SchemaCompatibility.check_compatibility(old_schema, new_schema, compatibility_mode)
 
         if is_incompatible(result):
             self.r({"is_compatible": False}, content_type)
@@ -1339,7 +1340,6 @@ def get_new_schema(self, body: JsonObject, content_type: str) -> ValidatedTypedS
                 status=HTTPStatus.UNPROCESSABLE_ENTITY,
             )
 
-
     def get_old_schema(self, subject: Subject, version: Version, content_type: str) -> ValidatedTypedSchema:
         try:
             old = self.schema_registry.subject_version_get(subject=subject, version=version)

tests/unit/test_schema_registry_api.py

@@ -71,6 +71,43 @@ async def test_forward_when_not_ready() -> None:
             )
 
 
+async def test_compatibility_check_in_transitive_mode() -> None:
+    # Given
+    config = set_config_defaults(DEFAULTS)
+    config["compatibility"] = "FULL_TRANSITIVE"
+    controller = KarapaceSchemaRegistryController(config=config)
+
+    result = Mock(spec=SchemaCompatibilityResult)
+    result.compatibility = SchemaCompatibilityType.compatible
+
+    controller.schema_registry = Mock(spec=KarapaceSchemaRegistry)
+    controller.schema_registry.get_compatibility_mode = Mock(return_value=CompatibilityModes.FULL_TRANSITIVE)
+    controller.schema_registry.check_schema_compatibility = Mock(return_value=result)
+
+    new_schema = ValidatedTypedSchema.parse(SchemaType.JSONSCHEMA, '{"type": "array"}')
+    controller.get_new_schema = Mock(return_value=new_schema)
+
+    request_mock = Mock(HTTPRequest)
+    request_mock.json = '{"schema": "{}", "schemaType": "JSON", "references": [], "metadata": {}, "ruleSet": {}}'
+
+    subject = Subject("subject1")
+
+    # When
+    with pytest.raises(HTTPResponse) as exc_info:
+        await controller.compatibility_check(
+            "application/json",
+            subject=subject,
+            version="1",
+            request=request_mock,
+        )
+
+    # Then run same checks as in schema registration
+    controller.schema_registry.check_schema_compatibility.assert_called_once_with(new_schema, subject)
+
+    assert exc_info.type is HTTPResponse
+    assert str(exc_info.value) == "HTTPResponse 200"
+
+
 async def test_compatibility_check_in_not_transitive_mode() -> None:
     # Given
     config = set_config_defaults(DEFAULTS)

website/source/quickstart.rst

@@ -60,6 +60,10 @@ Test the compatibility of a schema with the latest schema under subject "test-ke
     $KARAPACE_REGISTRY_URI/compatibility/subjects/test-key/versions/latest
   {"is_compatible":true}
 
+NOTE: if the subject's compatibility mode is transitive (BACKWARD_TRANSITIVE, FORWARD_TRANSITIVE or FULL_TRANSITIVE) then the
+compatibility is checked not only against the latest schema, but also against all previous schemas, as it would be done
+when trying to register the new schema through the `subjects/<subject-key>/versions` endpoint.
+
 Get current global backwards compatibility setting value::
 
   $ curl -X GET $KARAPACE_REGISTRY_URI/config