Fix support for services connected via IPv6 (#1141)

* Fix support for services connected via IPv6

Use the correct address family when connecting to the various RPC services.

The solution is basically the same suggested here:
https://github.com/cms-dev/cms/issues/157#issuecomment-463427954

This work is the result of the work of @edomora97, @mark03 and @Dariost.

* Mock getaddrinfo in test_background_connect

Calling getaddrinfo somehow breaks the mocking interface of socket,
replacing the MagicMock with the original function. This would break the
assert and the test in general.
To prevent so getaddrinfo is mocked as well, making it return just an
address without side effects.

* Try all the resolved addresses

- Try to resolve only with the SOCK_STREAM type
- Try to connect to all the resolved IP addresses, sometimes the first
  in the list is not the correct one (e.g. IPv4/v6)
- Remove redundant getaddrinfo in _connection_handler

* Stop after the first connection

* Pass family, type and proto to socket.socket()

As suggested in https://docs.python.org/3/library/socket.html#socket.getaddrinfo

* Fix tests

cms/io/rpc.py

@@ -5,6 +5,7 @@
 # Copyright © 2010-2018 Stefano Maggiolo <s.maggiolo@gmail.com>
 # Copyright © 2010-2012 Matteo Boscariol <boscarim@hotmail.com>
 # Copyright © 2013-2017 Luca Wehrstedt <luca.wehrstedt@gmail.com>
+# Copyright © 2019 Edoardo Morassutto <edoardo.morassutto@gmail.com>
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU Affero General Public License as
@@ -478,13 +479,28 @@ class RemoteServiceClient(RemoteServiceBase):
 
         """
         try:
-            sock = gevent.socket.socket(socket.AF_INET, socket.SOCK_STREAM)
-            sock.connect(self.remote_address)
+            # Try to resolve the address, this can lead to many possible
+            # addresses, we'll try all of them.
+            addresses = gevent.socket.getaddrinfo(
+                self.remote_address.ip,
+                self.remote_address.port,
+                type=socket.SOCK_STREAM)
+        except socket.gaierror:
+            logger.warning("Cannot resolve %s.", self.remote_address)
+            raise
+
+        for family, type, proto, _canonname, sockaddr in addresses:
+            try:
+                host, port, *rest = sockaddr
+                logger.debug("Trying to connect to %s at port %d.", host, port)
+                sock = gevent.socket.socket(family, type, proto)
+                sock.connect(sockaddr)
             except OSError as error:
-            logger.debug("Couldn't connect to %s: %s.",
-                         self._repr_remote(), error)
+                logger.debug("Couldn't connect to %s at %s port %d: %s.",
+                             self._repr_remote(), host, port, error)
             else:
                 self.initialize(sock, self.remote_service_coord)
+                break
 
     def _run(self):
         """Maintain the connection up, if required.

cms/io/service.py

@@ -5,6 +5,7 @@
 # Copyright © 2010-2016 Stefano Maggiolo <s.maggiolo@gmail.com>
 # Copyright © 2010-2012 Matteo Boscariol <boscarim@hotmail.com>
 # Copyright © 2013 Luca Wehrstedt <luca.wehrstedt@gmail.com>
+# Copyright © 2019 Edoardo Morassutto <edoardo.morassutto@gmail.com>
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU Affero General Public License as
@@ -156,13 +157,7 @@ class Service:
         connection.
 
         """
-        try:
-            ipaddr, port = address
-            ipaddr = gevent.socket.gethostbyname(ipaddr)
-            address = Address(ipaddr, port)
-        except OSError:
-            logger.warning("Unexpected error.", exc_info=True)
-            return
+        address = Address(address[0], address[1])
         remote_service = RemoteServiceServer(self, address)
         remote_service.handle(sock)
 

cmstestsuite/unit_tests/io/rpc_test.py

@@ -3,6 +3,7 @@
 # Contest Management System - http://cms-dev.github.io/
 # Copyright © 2014-2017 Luca Wehrstedt <luca.wehrstedt@gmail.com>
 # Copyright © 2015 Stefano Maggiolo <s.maggiolo@gmail.com>
+# Copyright © 2019 Edoardo Morassutto <edoardo.morassutto@gmail.com>
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU Affero General Public License as
@@ -21,6 +22,7 @@
 
 """
 
+import socket
 import unittest
 from unittest.mock import Mock, patch
 
@@ -231,7 +233,14 @@ class TestRPC(unittest.TestCase):
         self.assertEqual(result.value, ["Hello", 42, "World"])
 
     @patch("cms.io.rpc.gevent.socket.socket")
-    def test_background_connect(self, socket_mock):
+    @patch("cms.io.rpc.gevent.socket.getaddrinfo")
+    def test_background_connect(self, getaddrinfo_mock, socket_mock):
+        # Calling getaddrinfo breaks the mocking of the socket, so it is mocked
+        # as well. It returns the addresses associated with the service, in
+        # this case just one.
+        getaddrinfo_mock.return_value = [
+            (gevent.socket.AF_INET, gevent.socket.SOCK_STREAM, 6, "",
+                (self.host, self.port))]
         # Patch the connect method of sockets so that it blocks until
         # we set the done_event (we will do so at the end of the test).
         connect_mock = socket_mock.return_value.connect
@@ -255,7 +264,9 @@ class TestRPC(unittest.TestCase):
         # event triggered.
         done_event.set()
         gevent.sleep()
-        connect_mock.assert_called_once_with(Address(self.host, self.port))
+        getaddrinfo_mock.assert_called_once_with(self.host, self.port,
+                                                 type=socket.SOCK_STREAM)
+        connect_mock.assert_called_once_with((self.host, self.port))
 
     def test_autoreconnect1(self):
         client = self.get_client(ServiceCoord("Foo", 0), auto_retry=0.002)