Asserts replacer (#223)

* Add a condition checker function

raising a configurable exception to replace bare asserts throughout
python code

* Replace assert with check_condition()

* Rename "check_condition" to "ensure"

* Test for a CustomError exception

* Correct typo.

src/nacl/bindings/crypto_shorthash.py

@@ -14,6 +14,8 @@
 
 from __future__ import absolute_import, division, print_function
 
+import nacl.exceptions as exc
+from nacl import utils
 from nacl._sodium import ffi, lib
 
 BYTES = lib.crypto_shorthash_siphash24_bytes()
@@ -34,5 +36,5 @@ def crypto_shorthash_siphash24(data, key):
     digest = ffi.new("unsigned char[]", BYTES)
     rc = lib.crypto_shorthash_siphash24(digest, data, len(data), key)
 
-    assert rc == 0
+    utils.ensure(rc == 0, raising=exc.RuntimeError)
     return ffi.buffer(digest, BYTES)[:]

src/nacl/exceptions.py

@@ -25,3 +25,11 @@ class BadSignatureError(CryptoError):
     """
     Raised when the signature was forged or otherwise corrupt.
     """
+
+
+class RuntimeError(CryptoError, RuntimeError):
+    pass
+
+
+class AssertionError(CryptoError, AssertionError):
+    pass

src/nacl/utils.py

@@ -17,6 +17,7 @@
 import six
 
 import nacl.bindings
+from nacl import exceptions as exc
 
 
 class EncryptedMessage(six.binary_type):
@@ -58,3 +59,24 @@ def __str__(self):
 
 def random(size=32):
     return nacl.bindings.randombytes(size)
+
+
+def ensure(cond, *args, **kwds):
+    """
+    Return if a condition is true, otherwise raise a caller-configurable
+    :py:class:`Exception`
+    :param bool cond: the condition to be checked
+    :param sequence args: the arguments to be passed to the exception's
+                          constructor
+    The only accepted named parameter is `raising` used to configure the
+    exception to be raised if `cond` is not `True`
+    """
+    _CHK_UNEXP = 'check_condition() got an unexpected keyword argument {0}'
+
+    raising = kwds.pop('raising', exc.AssertionError)
+    if kwds:
+        raise TypeError(_CHK_UNEXP.format(repr(kwds.popitem[0])))
+
+    if cond is True:
+        return
+    raise raising(*args)

tests/test_utils.py

@@ -14,7 +14,14 @@
 
 from __future__ import absolute_import, division, print_function
 
+import pytest
+
 import nacl.utils
+from nacl import exceptions as exc
+
+
+class CustomError(exc.CryptoError):
+    pass
 
 
 def test_random_bytes_produces():
@@ -23,3 +30,23 @@ def test_random_bytes_produces():
 
 def test_random_bytes_produces_different_bytes():
     assert nacl.utils.random(16) != nacl.utils.random(16)
+
+
+def test_util_ensure_with_true_condition():
+    nacl.utils.ensure(1 == 1, 'one equals one')
+
+
+def test_util_ensure_with_false_condition():
+    with pytest.raises(AssertionError):
+        nacl.utils.ensure(1 == 0, 'one is not zero',
+                          raising=exc.AssertionError)
+
+
+def test_util_ensure_with_unwanted_kwarg():
+    with pytest.raises(TypeError):
+        nacl.utils.ensure(1 == 1, unexpected='unexpected')
+
+
+def test_util_ensure_custom_exception():
+    with pytest.raises(CustomError):
+        nacl.utils.ensure(1 == 0, 'Raising a CustomError', raising=CustomError)