feat(order_utils.py): schema resolver cache (#1317)

* Implemented basic functionality for using cache layer of LocalRefResolver

* Use `importlib` instead of `imp`, since it's been deprecated. Legacy `load_module()` reloads modules even if they are already imported, causing tests to fail when run in non-deterministic ordering, so we replace it with `import_module()`

4 files changed, 81 insertions, 38 deletions

diff --git a/python-packages/order_utils/src/zero_ex/json_schemas/__init__.py b/python-packages/order_utils/src/zero_ex/json_schemas/__init__.py
index 2a1728b8a..a76a2fa3b 100644
--- a/python-packages/order_utils/src/zero_ex/json_schemas/__init__.py
+++ b/python-packages/order_utils/src/zero_ex/json_schemas/__init__.py
@@ -8,6 +8,51 @@ from pkg_resources import resource_string
 import jsonschema
 
 
+class _LocalRefResolver(jsonschema.RefResolver):
+    """Resolve package-local JSON schema id's."""
+
+    def __init__(self):
+        """Initialize a new instance."""
+        self.ref_to_file = {
+            "/addressSchema": "address_schema.json",
+            "/hexSchema": "hex_schema.json",
+            "/orderSchema": "order_schema.json",
+            "/wholeNumberSchema": "whole_number_schema.json",
+            "/ECSignature": "ec_signature_schema.json",
+            "/signedOrderSchema": "signed_order_schema.json",
+            "/ecSignatureParameterSchema": (
+                "ec_signature_parameter_schema.json" + ""
+            ),
+        }
+        jsonschema.RefResolver.__init__(self, "", "")
+
+    def resolve_from_url(self, url: str) -> str:
+        """Resolve the given URL.
+
+        :param url: a string representing the URL of the JSON schema to fetch.
+        :returns: a string representing the deserialized JSON schema
+        :raises jsonschema.ValidationError: when the resource associated with
+                   `url` does not exist.
+        """
+        ref = url.replace("file://", "")
+        if ref in self.ref_to_file:
+            return json.loads(
+                resource_string(
+                    "zero_ex.json_schemas", f"schemas/{self.ref_to_file[ref]}"
+                )
+            )
+        raise jsonschema.ValidationError(
+            f"Unknown ref '{ref}'. "
+            + f"Known refs: {list(self.ref_to_file.keys())}."
+        )
+
+
+# Instantiate the `_LocalRefResolver()` only once so that `assert_valid()` can
+# perform multiple schema validations without reading from disk the schema
+# every time.
+_LOCAL_RESOLVER = _LocalRefResolver()
+
+
 def assert_valid(data: Mapping, schema_id: str) -> None:
     """Validate the given `data` against the specified `schema`.
 
@@ -24,38 +69,6 @@ def assert_valid(data: Mapping, schema_id: str) -> None:
     ... )
     """
     # noqa
-    class LocalRefResolver(jsonschema.RefResolver):
-        """Resolve package-local JSON schema id's."""
-
-        def __init__(self):
-            self.ref_to_file = {
-                "/addressSchema": "address_schema.json",
-                "/hexSchema": "hex_schema.json",
-                "/orderSchema": "order_schema.json",
-                "/wholeNumberSchema": "whole_number_schema.json",
-                "/ECSignature": "ec_signature_schema.json",
-                "/ecSignatureParameterSchema": (
-                    "ec_signature_parameter_schema.json" + ""
-                ),
-            }
-            jsonschema.RefResolver.__init__(self, "", "")
-
-        def resolve_from_url(self, url):
-            """Resolve the given URL."""
-            ref = url.replace("file://", "")
-            if ref in self.ref_to_file:
-                return json.loads(
-                    resource_string(
-                        "zero_ex.json_schemas",
-                        f"schemas/{self.ref_to_file[ref]}",
-                    )
-                )
-            raise jsonschema.ValidationError(
-                f"Unknown ref '{ref}'. "
-                + f"Known refs: {list(self.ref_to_file.keys())}."
-            )
 
-    resolver = LocalRefResolver()
-    jsonschema.validate(
-        data, resolver.resolve_from_url(schema_id), resolver=resolver
-    )
+    _, schema = _LOCAL_RESOLVER.resolve(schema_id)
+    jsonschema.validate(data, schema, resolver=_LOCAL_RESOLVER)
diff --git a/python-packages/order_utils/stubs/jsonschema/__init__.pyi b/python-packages/order_utils/stubs/jsonschema/__init__.pyi
index 762b58b22..442e2f65e 100644
--- a/python-packages/order_utils/stubs/jsonschema/__init__.pyi
+++ b/python-packages/order_utils/stubs/jsonschema/__init__.pyi
@@ -1,5 +1,11 @@
-from typing import Any, Dict
+from typing import Any, Dict, Tuple
 
-class RefResolver: pass
+
+class RefResolver:
+    def resolve(self, url: str) -> Tuple[str, Dict]:
+        ...
+
+
+class ValidationError(Exception): pass
 
 def validate(instance: Any, schema: Dict, cls=None, *args, **kwargs) -> None: pass
diff --git a/python-packages/order_utils/test/test_doctest.py b/python-packages/order_utils/test/test_doctest.py
index f692b3b6c..297f75e75 100644
--- a/python-packages/order_utils/test/test_doctest.py
+++ b/python-packages/order_utils/test/test_doctest.py
@@ -2,16 +2,17 @@
 
 from doctest import testmod
 import pkgutil
+import importlib
 
 import zero_ex
 
 
 def test_all_doctests():
     """Gather zero_ex.* modules and doctest them."""
-    for (importer, modname, _) in pkgutil.walk_packages(
+    for (_, modname, _) in pkgutil.walk_packages(
         path=zero_ex.__path__, prefix="zero_ex."
     ):
-        module = importer.find_module(modname).load_module(modname)
+        module = importlib.import_module(modname)
         print(module)
         (failure_count, _) = testmod(module)
         assert failure_count == 0
diff --git a/python-packages/order_utils/test/test_json_schemas.py b/python-packages/order_utils/test/test_json_schemas.py
new file mode 100644
index 000000000..51cecbd4f
--- /dev/null
+++ b/python-packages/order_utils/test/test_json_schemas.py
@@ -0,0 +1,23 @@
+"""Tests of zero_ex.json_schemas"""
+
+
+from zero_ex.order_utils import make_empty_order
+from zero_ex.json_schemas import _LOCAL_RESOLVER, assert_valid
+
+
+def test_assert_valid_caches_resources():
+    """Test that the JSON ref resolver in `assert_valid()` caches resources
+
+    In order to test the cache we much access the private class of
+    `json_schemas` and reset the LRU cache on `_LocalRefResolver`.
+    For this to happen, we need to disable errror `W0212`
+    on _LOCAL_RESOLVER
+    """
+    _LOCAL_RESOLVER._remote_cache.cache_clear()  # pylint: disable=W0212
+
+    assert_valid(make_empty_order(), "/orderSchema")
+    cache_info = (
+        _LOCAL_RESOLVER._remote_cache.cache_info()  # pylint: disable=W0212
+    )
+    assert cache_info.currsize == 4
+    assert cache_info.hits == 10