backport hmac.compare_digest to partially implement PEP 466 (closes #21306)

Backport from Alex Gaynor.

2 files changed, 114 insertions, 1 deletions

diff --git a/Lib/hmac.py b/Lib/hmac.py
index 5388106..9cd1a9f 100644
--- a/Lib/hmac.py
+++ b/Lib/hmac.py
@@ -5,6 +5,9 @@ Implements the HMAC algorithm as described by RFC 2104.
 
 import warnings as _warnings
 
+from operator import _compare_digest as compare_digest
+
+
 trans_5C = "".join ([chr (x ^ 0x5C) for x in xrange(256)])
 trans_36 = "".join ([chr (x ^ 0x36) for x in xrange(256)])
 
diff --git a/Lib/test/test_hmac.py b/Lib/test/test_hmac.py
index cd148e9..3f6f756 100644
--- a/Lib/test/test_hmac.py
+++ b/Lib/test/test_hmac.py
@@ -302,12 +302,122 @@ class CopyTestCase(unittest.TestCase):
         self.assertTrue(h1.hexdigest() == h2.hexdigest(),
             "Hexdigest of copy doesn't match original hexdigest.")
 
+
+class CompareDigestTestCase(unittest.TestCase):
+
+    def test_compare_digest(self):
+        # Testing input type exception handling
+        a, b = 100, 200
+        self.assertRaises(TypeError, hmac.compare_digest, a, b)
+        a, b = 100, b"foobar"
+        self.assertRaises(TypeError, hmac.compare_digest, a, b)
+        a, b = b"foobar", 200
+        self.assertRaises(TypeError, hmac.compare_digest, a, b)
+        a, b = u"foobar", b"foobar"
+        self.assertRaises(TypeError, hmac.compare_digest, a, b)
+        a, b = b"foobar", u"foobar"
+        self.assertRaises(TypeError, hmac.compare_digest, a, b)
+
+        # Testing bytes of different lengths
+        a, b = b"foobar", b"foo"
+        self.assertFalse(hmac.compare_digest(a, b))
+        a, b = b"\xde\xad\xbe\xef", b"\xde\xad"
+        self.assertFalse(hmac.compare_digest(a, b))
+
+        # Testing bytes of same lengths, different values
+        a, b = b"foobar", b"foobaz"
+        self.assertFalse(hmac.compare_digest(a, b))
+        a, b = b"\xde\xad\xbe\xef", b"\xab\xad\x1d\xea"
+        self.assertFalse(hmac.compare_digest(a, b))
+
+        # Testing bytes of same lengths, same values
+        a, b = b"foobar", b"foobar"
+        self.assertTrue(hmac.compare_digest(a, b))
+        a, b = b"\xde\xad\xbe\xef", b"\xde\xad\xbe\xef"
+        self.assertTrue(hmac.compare_digest(a, b))
+
+        # Testing bytearrays of same lengths, same values
+        a, b = bytearray(b"foobar"), bytearray(b"foobar")
+        self.assertTrue(hmac.compare_digest(a, b))
+
+        # Testing bytearrays of diffeent lengths
+        a, b = bytearray(b"foobar"), bytearray(b"foo")
+        self.assertFalse(hmac.compare_digest(a, b))
+
+        # Testing bytearrays of same lengths, different values
+        a, b = bytearray(b"foobar"), bytearray(b"foobaz")
+        self.assertFalse(hmac.compare_digest(a, b))
+
+        # Testing byte and bytearray of same lengths, same values
+        a, b = bytearray(b"foobar"), b"foobar"
+        self.assertTrue(hmac.compare_digest(a, b))
+        self.assertTrue(hmac.compare_digest(b, a))
+
+        # Testing byte bytearray of diffeent lengths
+        a, b = bytearray(b"foobar"), b"foo"
+        self.assertFalse(hmac.compare_digest(a, b))
+        self.assertFalse(hmac.compare_digest(b, a))
+
+        # Testing byte and bytearray of same lengths, different values
+        a, b = bytearray(b"foobar"), b"foobaz"
+        self.assertFalse(hmac.compare_digest(a, b))
+        self.assertFalse(hmac.compare_digest(b, a))
+
+        # Testing str of same lengths
+        a, b = "foobar", "foobar"
+        self.assertTrue(hmac.compare_digest(a, b))
+
+        # Testing str of diffeent lengths
+        a, b = "foo", "foobar"
+        self.assertFalse(hmac.compare_digest(a, b))
+
+        # Testing bytes of same lengths, different values
+        a, b = "foobar", "foobaz"
+        self.assertFalse(hmac.compare_digest(a, b))
+
+        # Testing error cases
+        a, b = u"foobar", b"foobar"
+        self.assertRaises(TypeError, hmac.compare_digest, a, b)
+        a, b = b"foobar", u"foobar"
+        self.assertRaises(TypeError, hmac.compare_digest, a, b)
+        a, b = b"foobar", 1
+        self.assertRaises(TypeError, hmac.compare_digest, a, b)
+        a, b = 100, 200
+        self.assertRaises(TypeError, hmac.compare_digest, a, b)
+        a, b = "fooä", "fooä"
+        self.assertTrue(hmac.compare_digest(a, b))
+
+        # subclasses are supported by ignore __eq__
+        class mystr(str):
+            def __eq__(self, other):
+                return False
+
+        a, b = mystr("foobar"), mystr("foobar")
+        self.assertTrue(hmac.compare_digest(a, b))
+        a, b = mystr("foobar"), "foobar"
+        self.assertTrue(hmac.compare_digest(a, b))
+        a, b = mystr("foobar"), mystr("foobaz")
+        self.assertFalse(hmac.compare_digest(a, b))
+
+        class mybytes(bytes):
+            def __eq__(self, other):
+                return False
+
+        a, b = mybytes(b"foobar"), mybytes(b"foobar")
+        self.assertTrue(hmac.compare_digest(a, b))
+        a, b = mybytes(b"foobar"), b"foobar"
+        self.assertTrue(hmac.compare_digest(a, b))
+        a, b = mybytes(b"foobar"), mybytes(b"foobaz")
+        self.assertFalse(hmac.compare_digest(a, b))
+
+
 def test_main():
     test_support.run_unittest(
         TestVectorsTestCase,
         ConstructorTestCase,
         SanityTestCase,
-        CopyTestCase
+        CopyTestCase,
+        CompareDigestTestCase,
     )
 
 if __name__ == "__main__":