Skip cname_lookup when host is an IP address

cname_lookup cannot resolve IP addresses as CNAME records, and therefore
should not attempt to resolve the host in that case. The middleware is
skipped when the host is an IP address.

Change-Id: I6961ec205e771116ace1ebcb8c088f3116eb38f0
Fixes: bug #1172289

swift/common/middleware/cname_lookup.py

@@ -27,6 +27,8 @@ maximum lookup depth. If a match is found, the environment's Host header is
 rewritten and the request is passed further down the WSGI chain.
 """
 
+import socket
+
 try:
     import dns.resolver
     from dns.exception import DNSException
@@ -58,6 +60,14 @@ def lookup_cname(domain):  # pragma: no cover
         return 0, None
 
 
+def is_ip(domain):
+    try:
+        socket.inet_aton(domain)
+        return True
+    except socket.error:
+        return False
+
+
 class CNAMELookupMiddleware(object):
     """
     CNAME Lookup Middleware
@@ -93,6 +103,8 @@ class CNAMELookupMiddleware(object):
             given_domain, port = given_domain.rsplit(':', 1)
         if given_domain == self.storage_domain[1:]:  # strip initial '.'
             return self.app(env, start_response)
+        if is_ip(given_domain):
+            return self.app(env, start_response)
         a_domain = given_domain
         if not a_domain.endswith(self.storage_domain):
             if self.memcache is None:

test/unit/common/middleware/test_cname_lookup.py

@@ -36,6 +36,8 @@ def start_response(*args):
     pass
 
 
+original_lookup = cname_lookup.lookup_cname
+
 class TestCNAMELookup(unittest.TestCase):
 
     def setUp(self):
@@ -44,6 +46,15 @@ class TestCNAMELookup(unittest.TestCase):
         self.app = cname_lookup.CNAMELookupMiddleware(FakeApp(),
                                                       {'lookup_depth': 2})
 
+    def test_pass_ip_addresses(self):
+
+        cname_lookup.lookup_cname = original_lookup
+
+        req = Request.blank('/', environ={'REQUEST_METHOD': 'GET'},
+                            headers={'Host': '10.134.23.198'})
+        resp = self.app(req.environ, start_response)
+        self.assertEquals(resp, 'FAKE APP')
+
     def test_passthrough(self):
 
         def my_lookup(d):

tools/pip-requires

@@ -1,3 +1,4 @@
+dnspython>=1.10.0
 eventlet>=0.9.15
 greenlet>=0.3.1
 netifaces>=0.5