changed test to itest because we're opening files (well, devices ...) using /dev/urandom if available else stdlib random, testing failure scenarios

itest_onetimepad.py

@@ -23,6 +23,17 @@ class TestOneTimePad(unittest.TestCase):
                              '{1}, actual={2}'.format(self._padsize,
                                                       width, actual))
 
+    def test_get_randint_on_nonexistent_randomness_file_fails_ioerror(self):
+        OT._DEV_RANDOM['fp'] = None
+        self.assertRaises(IOError, OT._get_randint,
+                          randomness_file='/foo/bar/busted/borken',
+                          fallback_to_fake=False)
+
+    def test_get_randint_on_nonexistent_randomness_file_uses_fake(self):
+        OT._DEV_RANDOM['fp'] = None
+        random_int = OT._get_randint(randomness_file='/broke/as/joke')
+        self.assertTrue(random_int in range(0, 255))
+
     def test_is_padline(self):
         for lineno in PADLINES:
             self.assertTrue(OT._is_padline(lineno),

onetimepad.py

@@ -1,4 +1,3 @@
-import random
 from itertools import izip
 
 PAD_MODULO = 3
@@ -46,7 +45,7 @@ def create_pad_lines(length, width=DEFAULT_PAD_WIDTH):
 def _create_chars_for_pad(length):
     chars = []
     for char in range(length):
-        chars.append(_AS_ALPHA[random.randint(CIPHER_FLOOR, CIPHER_CEIL)])
+        chars.append(_AS_ALPHA[_get_randint()])
     return ''.join(chars)
 
 
@@ -155,6 +154,34 @@ def _is_cipherline(lineno):
     return not lineno % PAD_MODULO
 
 
+def _get_randint(randomness_file='/dev/urandom', fallback_to_fake=True):
+    if not _DEV_RANDOM.get('fp'):
+        _get_urandom_fp(randomness_file=randomness_file,
+                        fallback_to_fake=fallback_to_fake)
+    ret = ord(_DEV_RANDOM['fp'].read(1)) % CIPHER_CEIL
+    return ret if ret != 0 else _get_randint()
+
+
+class _FakeDevUrandom(object):
+
+    def read(self, nchars):
+        import random
+        return ''.join([chr(random.randint(0, 255)) for i in range(0, nchars)])
+
+
+def _get_urandom_fp(randomness_file='/dev/urandom', fallback_to_fake=True):
+    try:
+        _DEV_RANDOM['fp'] = open(randomness_file)
+    except (OSError, IOError):
+        if fallback_to_fake:
+            _DEV_RANDOM['fp'] = _FakeDevUrandom()
+        else:
+            raise
+
+
+_DEV_RANDOM = {}
+
+
 def _mk_as_alpha_as_nums():
     as_alpha = {}
     as_nums = {}