Skip IPv6 addresses in cname_lookup middleware.

It already skips IPv4 addresses, and since IPv6 is the future of the
Internet*, we should probably do the right thing with those too.

* IPv6: Just two years away for over fifteen years!

Change-Id: I54f1db4e936fd38d05ac8b5c709efba76525b9d2

swift/common/middleware/cname_lookup.py

@@ -62,10 +62,14 @@ def lookup_cname(domain):  # pragma: no cover
 
 def is_ip(domain):
     try:
-        socket.inet_aton(domain)
+        socket.inet_pton(socket.AF_INET, domain)
         return True
     except socket.error:
-        return False
+        try:
+            socket.inet_pton(socket.AF_INET6, domain)
+            return True
+        except socket.error:
+            return False
 
 
 class CNAMELookupMiddleware(object):

test/unit/common/middleware/test_cname_lookup.py

@@ -47,7 +47,6 @@ class TestCNAMELookup(unittest.TestCase):
                                                       {'lookup_depth': 2})
 
     def test_pass_ip_addresses(self):
-
         cname_lookup.lookup_cname = original_lookup
 
         req = Request.blank('/', environ={'REQUEST_METHOD': 'GET'},
@@ -55,6 +54,11 @@ class TestCNAMELookup(unittest.TestCase):
         resp = self.app(req.environ, start_response)
         self.assertEquals(resp, 'FAKE APP')
 
+        req = Request.blank('/', environ={'REQUEST_METHOD': 'GET'},
+                            headers={'Host': 'fc00:7ea1:f155::6321:8841'})
+        resp = self.app(req.environ, start_response)
+        self.assertEquals(resp, 'FAKE APP')
+
     def test_passthrough(self):
 
         def my_lookup(d):