Add input type validation to max_len and min_len validators to preven…

src/attr/_compat.py

@@ -5,7 +5,7 @@
 import sys
 import threading
 
-from collections.abc import Mapping, Sequence  # noqa: F401
+from collections.abc import Mapping, Sequence, Sized  # noqa: F401
 from typing import _GenericAlias
 
 

src/attr/validators.py

@@ -10,6 +10,7 @@
 from contextlib import contextmanager
 from re import Pattern
 
+from ._compat import Mapping, Sized
 from ._config import get_run_validators, set_run_validators
 from ._make import _AndValidator, and_, attrib, attrs
 from .converters import default_if_none
@@ -397,6 +398,15 @@ def __call__(self, inst, attr, value):
         if self.mapping_validator is not None:
             self.mapping_validator(inst, attr, value)
 
+        if not isinstance(value, Mapping):
+            msg = f"'{attr.name}' must be a mapping (got {value!r} that is a {value.__class__!r})."
+            raise TypeError(
+                msg,
+                attr,
+                Mapping,
+                value,
+            )
+
         for key in value:
             if self.key_validator is not None:
                 self.key_validator(inst, attr, key)
@@ -543,6 +553,9 @@ def __call__(self, inst, attr, value):
         """
         We use a callable class to be able to change the ``__repr__``.
         """
+        if not isinstance(value, Sized):
+            msg = f"'{attr.name}' must be a sized object (got {value!r} that is a {value.__class__!r})."
+            raise TypeError(msg)
         if len(value) > self.max_length:
             msg = f"Length of '{attr.name}' must be <= {self.max_length}: {len(value)}"
             raise ValueError(msg)
@@ -572,6 +585,9 @@ def __call__(self, inst, attr, value):
         """
         We use a callable class to be able to change the ``__repr__``.
         """
+        if not isinstance(value, Sized):
+            msg = f"'{attr.name}' must be a sized object (got {value!r} that is a {value.__class__!r})."
+            raise TypeError(msg)
         if len(value) < self.min_length:
             msg = f"Length of '{attr.name}' must be >= {self.min_length}: {len(value)}"
             raise ValueError(msg)

tests/test_validators.py

@@ -807,6 +807,22 @@ def test_validators_iterables(self, conv):
         assert and_(*value_validator) == v.value_validator
         assert and_(*mapping_validator) == v.mapping_validator
 
+    def test_fail_non_mapping(self):
+        """
+        Raise TypeError if value is not a mapping.
+        """
+        key_validator = instance_of(str)
+        value_validator = instance_of(int)
+        v = deep_mapping(key_validator, value_validator)
+        a = simple_attr("test")
+        with pytest.raises(TypeError) as e:
+            v(None, a, [1, 2, 3])
+
+        msg = (
+            f"'{a.name}' must be a mapping (got [1, 2, 3] that is a {list!r})."
+        )
+        assert msg in str(e.value)
+
 
 class TestIsCallable:
     """
@@ -1023,6 +1039,20 @@ def test_repr(self):
         """
         assert repr(max_len(23)) == "<max_len validator for 23>"
 
+    def test_fail_non_sized(self):
+        """
+        Raise TypeError if value is not a sized object (e.g., generator).
+        """
+
+        @attr.s
+        class Tester:
+            value = attr.ib(validator=max_len(self.MAX_LENGTH))
+
+        with pytest.raises(TypeError) as e:
+            Tester(x for x in range(2))
+
+        assert "must be a sized object" in str(e.value)
+
 
 class TestMinLen:
     """
@@ -1094,6 +1124,20 @@ def test_repr(self):
         """
         assert repr(min_len(23)) == "<min_len validator for 23>"
 
+    def test_fail_non_sized(self):
+        """
+        Raise TypeError if value is not a sized object (e.g., generator).
+        """
+
+        @attr.s
+        class Tester:
+            value = attr.ib(validator=min_len(self.MIN_LENGTH))
+
+        with pytest.raises(TypeError) as e:
+            Tester(x for x in range(2))
+
+        assert "must be a sized object" in str(e.value)
+
 
 class TestSubclassOf:
     """