Merge pull request #1424 from alex/verify-interfaces

Fixes #1024 -- a utility function for checking an implementor against an ABC

1 files changed, 27 insertions, 0 deletions

diff --git a/cryptography/utils.py b/cryptography/utils.py
index 1deb3d1d..03c8c0e8 100644
--- a/cryptography/utils.py
+++ b/cryptography/utils.py
@@ -13,6 +13,8 @@
 
 from __future__ import absolute_import, division, print_function
 
+import abc
+import inspect
 import sys
 
 
@@ -21,6 +23,7 @@ DeprecatedIn06 = DeprecationWarning
 
 def register_interface(iface):
     def register_decorator(klass):
+        verify_interface(iface, klass)
         iface.register(klass)
         return klass
     return register_decorator
@@ -30,6 +33,30 @@ def read_only_property(name):
     return property(lambda self: getattr(self, name))
 
 
+class InterfaceNotImplemented(Exception):
+    pass
+
+
+def verify_interface(iface, klass):
+    for method in iface.__abstractmethods__:
+        if not hasattr(klass, method):
+            raise InterfaceNotImplemented(
+                "{0} is missing a {1!r} method".format(klass, method)
+            )
+        if isinstance(getattr(iface, method), abc.abstractproperty):
+            # Can't properly verify these yet.
+            continue
+        spec = inspect.getargspec(getattr(iface, method))
+        actual = inspect.getargspec(getattr(klass, method))
+        if spec != actual:
+            raise InterfaceNotImplemented(
+                "{0}.{1}'s signature differs from the expected. Expected: "
+                "{2!r}. Received: {3!r}".format(
+                    klass, method, spec, actual
+                )
+            )
+
+
 def bit_length(x):
     if sys.version_info >= (2, 7):
         return x.bit_length()