tests(nano): add missing tests for rng immutability

hathor/nanocontracts/rng.py

@@ -16,7 +16,7 @@
 
 from typing import Any, Sequence, TypeVar
 
-from cryptography.hazmat.primitives.ciphers import Cipher, algorithms
+from cryptography.hazmat.primitives.ciphers import Cipher, CipherContext, algorithms
 
 from hathor.difficulty import Hash
 
@@ -36,19 +36,20 @@ class NanoRNG(metaclass=NoMethodOverrideMeta):
     This implementation uses the ChaCha20 encryption as RNG.
     """
 
-    __slots__ = ('__seed', '__encryptor', '__frozen')
+    __slots__ = ('__seed', '__encryptor')
 
     def __init__(self, seed: bytes) -> None:
-        self.__seed = Hash(seed)
+        self.__seed: Hash
+        object.__setattr__(self, '_NanoRNG__seed', Hash(seed))
 
         key = self.__seed
         nonce = self.__seed[:16]
 
         algorithm = algorithms.ChaCha20(key, nonce)
         cipher = Cipher(algorithm, mode=None)
-        self.__encryptor = cipher.encryptor()
 
-        self.__frozen = True
+        self.__encryptor: CipherContext
+        object.__setattr__(self, '_NanoRNG__encryptor', cipher.encryptor())
 
     @classmethod
     def create_with_shell(cls, seed: bytes) -> NanoRNG:
@@ -63,9 +64,7 @@ class ShellNanoRNG(NanoRNG):
         return ShellNanoRNG(seed=seed)
 
     def __setattr__(self, name: str, value: Any) -> None:
-        if getattr(self, '_NanoRNG__frozen', False):
-            raise AttributeError("Cannot assign methods to this object.")
-        super().__setattr__(name, value)
+        raise AttributeError("Cannot assign methods to this object.")
 
     @property
     def seed(self) -> Hash:

tests/nanocontracts/test_rng.py

@@ -73,37 +73,107 @@ def test_rng_override(self) -> None:
         seed = b'0' * 32
         rng = NanoRNG(seed=seed)
 
+        #
+        # Existing attribute on instance
+        #
+
+        # protected by overridden __setattr__
+        with pytest.raises(AttributeError, match='Cannot assign methods to this object.'):
+            rng._NanoRNG__seed = b'1' * 32
+
+        # protected by overridden __setattr__
+        with pytest.raises(AttributeError, match='Cannot assign methods to this object.'):
+            setattr(rng, '_NanoRNG__seed', b'1' * 32)
+
+        # it doesn't protect against this case
+        object.__setattr__(rng, '_NanoRNG__seed', b'changed')
+        assert getattr(rng, '_NanoRNG__seed') == b'changed'
+
+        #
+        # New attribute on instance
+        #
+
+        # protected by overridden NanoRNG.__setattr__
+        with pytest.raises(AttributeError, match='Cannot assign methods to this object.'):
+            rng.new_attr = 123
+
+        # protected by overridden NanoRNG.__setattr__
+        with pytest.raises(AttributeError, match='Cannot assign methods to this object.'):
+            setattr(rng, 'new_attr', 123)
+
+        # protected by __slots__
+        with pytest.raises(AttributeError, match="'NanoRNG' object has no attribute 'new_attr'"):
+            object.__setattr__(rng, 'new_attr', 123)
+
+        #
+        # Existing method on instance
+        #
+
+        # protected by overridden NanoRNG.__setattr__
         with pytest.raises(AttributeError, match='Cannot assign methods to this object.'):
             rng.random = lambda self: 2  # type: ignore[method-assign, misc, assignment]
 
+        # protected by overridden NanoRNG.__setattr__
         with pytest.raises(AttributeError, match='Cannot assign methods to this object.'):
             setattr(rng, 'random', lambda self: 2)
 
+        # protected by overridden NanoRNG.__setattr__
         with pytest.raises(AttributeError, match='Cannot assign methods to this object.'):
             from types import MethodType
             rng.random = MethodType(lambda self: 2, rng)  # type: ignore[method-assign]
 
+        # protected by __slots__
         with pytest.raises(AttributeError, match='\'NanoRNG\' object attribute \'random\' is read-only'):
             object.__setattr__(rng, 'random', lambda self: 2)
 
+        #
+        # Existing method on class
+        #
+
+        # protected by overridden NoMethodOverrideMeta.__setattr__
         with pytest.raises(AttributeError, match='Cannot override method `random`'):
             NanoRNG.random = lambda self: 2  # type: ignore[method-assign]
 
+        # protected by overridden NoMethodOverrideMeta.__setattr__
         with pytest.raises(AttributeError, match='Cannot override method `random`'):
             setattr(NanoRNG, 'random', lambda self: 2)
 
+        # protected by Python itself
         with pytest.raises(TypeError, match='can\'t apply this __setattr__ to NoMethodOverrideMeta object'):
             object.__setattr__(NanoRNG, 'random', lambda self: 2)
 
+        #
+        # Existing method on __class__
+        #
+
+        # protected by overridden NoMethodOverrideMeta.__setattr__
         with pytest.raises(AttributeError, match='Cannot override method `random`'):
             rng.__class__.random = lambda self: 2  # type: ignore[method-assign]
 
+        # protected by overridden NoMethodOverrideMeta.__setattr__
         with pytest.raises(AttributeError, match='Cannot override method `random`'):
             setattr(rng.__class__, 'random', lambda self: 2)
 
+        # protected by Python itself
         with pytest.raises(TypeError, match='can\'t apply this __setattr__ to NoMethodOverrideMeta object'):
             object.__setattr__(rng.__class__, 'random', lambda self: 2)
 
+        #
+        # New attribute on class
+        #
+
+        # protected by overridden NoMethodOverrideMeta.__setattr__
+        with pytest.raises(AttributeError, match='Cannot override method `new_attr`'):
+            NanoRNG.new_attr = 123
+
+        # protected by overridden NoMethodOverrideMeta.__setattr__
+        with pytest.raises(AttributeError, match='Cannot override method `new_attr`'):
+            setattr(NanoRNG, 'new_attr', 123)
+
+        # protected by Python itself
+        with pytest.raises(TypeError, match='can\'t apply this __setattr__ to NoMethodOverrideMeta object'):
+            object.__setattr__(NanoRNG, 'new_attr', 123)
+
         assert rng.random() < 1
 
     def test_rng_shell_class(self) -> None: