windows yaml.safe_load returns None on unreadable files..

src/allmydata/client.py

@@ -1,7 +1,7 @@
 import os, stat, time, weakref
 from base64 import urlsafe_b64encode
 from functools import partial
-from errno import ENOENT
+from errno import ENOENT, EPERM
 
 from zope.interface import implementer
 from twisted.internet import reactor, defer
@@ -297,7 +297,11 @@ def create_introducer_clients(config, main_tub):
         with introducers_filepath.open() as f:
             introducers_yaml = yamlutil.safe_load(f)
             if introducers_yaml is None:
-                introducers_yaml = {}
+                raise EnvironmentError(
+                    EPERM,
+                    "Can't read '{}'".format(introducers_yaml_filename),
+                    introducers_yaml_filename,
+                )
             introducers = introducers_yaml.get("introducers", {})
             log.msg(
                 "found {} introducers in private/introducers.yaml".format(

src/allmydata/test/test_introducer.py

@@ -59,13 +59,18 @@ class Node(testutil.SignalMixin, testutil.ReallyEqualMixin, unittest.TestCase):
 
     def test_introducer_clients_unloadable(self):
         """
-        If introducers.yaml exists but we can't read it for some reason
-        we'll ignore it.
+        Error if introducers.yaml exists but we can't read it
         """
-        basedir = "introducer.IntroducerNode.test_introducer_clients_unloadable"
+        basedir = u"introducer.IntroducerNode.test_introducer_clients_unloadable"
         os.mkdir(basedir)
+        os.mkdir(os.path.join(basedir, u"private"))
+        yaml_fname = os.path.join(basedir, u"private", u"introducers.yaml")
+        with open(yaml_fname, 'w') as f:
+            f.write(u'---\n')
+        os.chmod(yaml_fname, 0o000)
+        self.addCleanup(lambda: os.chmod(yaml_fname, 0o700))
         # just mocking the yaml failure, as "yamlutil.safe_load" only
-        # returns None on some platforms
+        # returns None on some platforms for unreadable files
 
         with patch("allmydata.client.yamlutil") as p:
             p.safe_load = Mock(return_value=None)
@@ -73,8 +78,8 @@ class Node(testutil.SignalMixin, testutil.ReallyEqualMixin, unittest.TestCase):
             fake_tub = Mock()
             config = read_config(basedir, "portnum")
 
-            ic = create_introducer_clients(config, fake_tub)
-        self.assertEqual([], ic)
+            with self.assertRaises(EnvironmentError) as ctx:
+                create_introducer_clients(config, fake_tub)
 
     @defer.inlineCallbacks
     def test_furl(self):