Dns test love (#908)

* Resolve the DNS test differences.

Also document some of the known ways that c-ares is different as a
result of these test fixes.

Fixes #774.

* spurious assert statement.

* disable the ipv6 dual stack test even without ares, it has the same issue on travis ci. must have a different resolver configuration than I do.

* more dns tweaks for travis

* One small failure on travis.

changelog.rst

@@ -7,7 +7,9 @@
 1.2b1 (unreleased)
 ==================
 
-- TBD
+- The c-ares DNS resolver ignores bad flags to getnameinfo, like the
+  system resolver does. Discovered when cleaning up the DNS resolver
+  tests to produce more reliable results. See :issue:`774`.
 
 1.2a2 (Dec 9, 2017)
 ===================

src/gevent/ares.pyx

@@ -446,4 +446,9 @@ cdef public class channel [object PyGeventAresChannelObject, type PyGeventAresCh
         cares.ares_getnameinfo(self.channel, x, length, flags, <void*>gevent_ares_nameinfo_callback, <void*>arg)
 
     def getnameinfo(self, object callback, tuple sockaddr, int flags):
-        return self._getnameinfo(callback, sockaddr, _convert_cares_flags(flags))
+        try:
+            flags = _convert_cares_flags(flags)
+        except gaierror:
+            # The stdlib just ignores bad flags
+            flags = 0
+        return self._getnameinfo(callback, sockaddr, flags)

src/gevent/resolver_ares.py

@@ -31,6 +31,25 @@ class Resolver(object):
     the threaded resolver). However, because it does not use threads,
     it may scale better for applications that make many lookups.
 
+    There are some known differences from the system resolver:
+
+    - ``gethostbyname_ex`` and ``gethostbyaddr`` may return different
+      for the ``aliaslist`` tuple member. (Sometimes the same,
+      sometimes in a different order, sometimes a different alias
+      altogether.)
+    - ``gethostbyname_ex`` may return the ``ipaddrlist`` in a different order.
+    - ``getaddrinfo`` does not return ``SOCK_RAW`` results.
+    - ``getaddrinfo`` may return results in a different order.
+    - Handling of ``.local`` (mDNS) names may be different, even if they are listed in
+      the hosts file.
+    - c-ares will not resolve ``broadcasthost``, even if listed in the hosts file.
+    - This implementation may raise ``gaierror(4)`` where the system implementation would raise
+      ``herror(1)``.
+    - The results for ``localhost`` may be different. In particular, some system
+      resolvers will return more results from ``getaddrinfo`` than c-ares does,
+      such as SOCK_DGRAM results, and c-ares may report more ips on a multi-homed
+      host.
+
     .. caution:: This module is considered extremely experimental on PyPy, and
        due to its implementation in cython, it may be slower. It may also lead to
        interpreter crashes.

src/greentest/known_failures.py

@@ -36,22 +36,6 @@ FAILING_TESTS = [
 ]
 
 
-if os.environ.get('GEVENT_RESOLVER') == 'ares' or LEAKTEST:
-    # XXX fix this
-    FAILING_TESTS += [
-        'FLAKY test__socket_dns.py',
-        'FLAKY test__socket_dns6.py',
-    ]
-else:
-    FAILING_TESTS += [
-        # A number of the host names hardcoded have multiple, load
-        # balanced DNS entries. Therefore, multiple sequential calls
-        # of the resolution function, whether gevent or stdlib, can
-        # return non-equal results, possibly dependent on the host
-        # dns configuration
-        'FLAKY test__socket_dns6.py',
-    ]
-
 if sys.platform == 'win32':
     # other Windows-related issues (need investigating)
     FAILING_TESTS += [

src/greentest/test__socket_dns6.py

@@ -2,7 +2,7 @@
 # -*- coding: utf-8 -*-
 import greentest
 import socket
-from test__socket_dns import TestCase, add
+from test__socket_dns import TestCase, add, RESOLVER_IS_ARES
 
 
 class Test6(TestCase):
@@ -26,15 +26,34 @@ class Test6(TestCase):
 class Test6_google(Test6):
     host = 'ipv6.google.com'
 
+    def _normalize_result_getnameinfo(self, result):
+        if greentest.RUNNING_ON_CI and RESOLVER_IS_ARES:
+            # Disabled, there are multiple possibilities
+            # and we can get different ones, rarely.
+            return ()
+        return result
 
-class Test6_ds(Test6):
+add(Test6, Test6.host)
+add(Test6_google, Test6_google.host)
+
+
+if not greentest.RUNNING_ON_CI:
+    # We can't control the DNS servers we use there
+    # for the system. This works best with the google DNS servers
+    # The getnameinfo test can fail on CI
+    class Test6_ds(Test6):
         # host that has both A and AAAA records
         host = 'ds.test-ipv6.com'
 
+        def _normalize_result_gethostbyaddr(self, result):
+            # This test is effectively disabled. There are multiple address
+            # that resolve and which ones you get depend on the settings
+            # of the system and ares. They don't match exactly.
+            return ()
 
-add(Test6, Test6.host)
-add(Test6_google, Test6_google.host)
-add(Test6_ds, Test6_ds.host)
+        _normalize_result_gethostbyname = _normalize_result_gethostbyaddr
+
+    add(Test6_ds, Test6_ds.host)
 
 
 if __name__ == '__main__':