Be more eager validating return value schema.

Ensure index is non-negative integer.

nucypher/policy/conditions/lingo.py

@@ -17,6 +17,7 @@ from marshmallow import (
     validates,
     validates_schema,
 )
+from marshmallow.validate import OneOf, Range
 from packaging.version import parse as parse_version
 
 from nucypher.policy.conditions.base import AccessControlCondition, _Serializable
@@ -197,27 +198,29 @@ class NotCompoundCondition(CompoundAccessControlCondition):
         super().__init__(operator=self.NOT_OPERATOR, operands=[operand])
 
 
+_COMPARATOR_FUNCTIONS = {
+    "==": pyoperator.eq,
+    "!=": pyoperator.ne,
+    ">": pyoperator.gt,
+    "<": pyoperator.lt,
+    "<=": pyoperator.le,
+    ">=": pyoperator.ge,
+}
+
+
 class ReturnValueTest:
     class InvalidExpression(ValueError):
         pass
 
-    _COMPARATOR_FUNCTIONS = {
-        "==": pyoperator.eq,
-        "!=": pyoperator.ne,
-        ">": pyoperator.gt,
-        "<": pyoperator.lt,
-        "<=": pyoperator.le,
-        ">=": pyoperator.ge,
-    }
     COMPARATORS = tuple(_COMPARATOR_FUNCTIONS)
 
     class ReturnValueTestSchema(CamelCaseSchema):
         SKIP_VALUES = (None,)
-        comparator = fields.Str(required=True)
+        comparator = fields.Str(required=True, validate=OneOf(_COMPARATOR_FUNCTIONS))
         value = fields.Raw(
             allow_none=False, required=True
         )  # any valid type (excludes None)
-        index = fields.Raw(allow_none=True)
+        index = fields.Int(strict=True, required=False, validate=Range(min=0))
 
         @post_load
         def make(self, data, **kwargs):
@@ -229,9 +232,9 @@ class ReturnValueTest:
                 f'"{comparator}" is not a permitted comparator.'
             )
 
-        if index is not None and not isinstance(index, int):
+        if index is not None and (not isinstance(index, int) or index < 0):
             raise self.InvalidExpression(
-                f'"{index}" is not a permitted index. Must be a an integer.'
+                f'"{index}" is not a permitted index. Must be a an non-negative integer.'
             )
 
         if not is_context_variable(value):
@@ -309,7 +312,7 @@ class ReturnValueTest:
         processed_data = self._process_data(data, self.index)
         left_operand = self._sanitize_value(processed_data)
         right_operand = self._sanitize_value(self.value)
-        result = self._COMPARATOR_FUNCTIONS[self.comparator](left_operand, right_operand)
+        result = _COMPARATOR_FUNCTIONS[self.comparator](left_operand, right_operand)
         return result
 
 

tests/unit/conditions/test_return_value.py

@@ -26,6 +26,12 @@ def test_return_value_test_schema():
     errors = schema.validate(data=test_dict)
     assert errors, f"{errors}"
 
+    # invalid comparator should cause error
+    test_dict = schema.dump(return_value_test)
+    test_dict["comparator"] = "<>"
+    errors = schema.validate(data=test_dict)
+    assert errors, f"{errors}"
+
     # missing value should cause error
     test_dict = schema.dump(return_value_test)
     del test_dict["value"]
@@ -38,10 +44,30 @@ def test_return_value_test_schema():
     errors = schema.validate(data=test_dict)
     assert not errors, f"{errors}"
 
+    # negative index should cause error
+    test_dict = schema.dump(return_value_test)
+    test_dict["index"] = -3
+    errors = schema.validate(data=test_dict)
+    assert errors, f"{errors}"
+
+    # non-integer index should cause error
+    test_dict = schema.dump(return_value_test)
+    test_dict["index"] = "25"
+    errors = schema.validate(data=test_dict)
+    assert errors, f"{errors}"
+
 
 def test_return_value_index_invalid():
     with pytest.raises(ReturnValueTest.InvalidExpression):
-        _ = ReturnValueTest(comparator=">", value="0", index="james")
+        _ = ReturnValueTest(comparator=">", value=0, index="james")
+
+    with pytest.raises(ReturnValueTest.InvalidExpression):
+        _ = ReturnValueTest(comparator=">", value=0, index=-1)
+
+    with pytest.raises(ReturnValueTest.InvalidExpression):
+        _ = ReturnValueTest(
+            comparator=">", value=0, index="10"
+        )  # should not be a string
 
 
 def test_return_value_index():