Merge lp:~jtv/maas/resolve_hostname into lp:~maas-committers/maas/trunk

[Jeroen T. Vermeulen]

New networking helper: resolve_hostname.

This is preparation for an IPv6 branch that is about to go up for separate review. In order to support sending DNS server addresses to DHCPv6 clients I had to pry apart the implementation of get_maas_facing_server_address. The separation of concerns also simplifies the testing a bit — there are a lot fewer combinations to go through.

Is it time to introduce an enum for IPv4/IPv6? It'd have to go into provisioningserver.enum, which does not currently exist, so I've been reluctant. Or should I pass AF_INET/AF_INET6? I didn't want to expose that level of implementation detail in an otherwise nicely abstract API.

Jeroen

[Julian Edwards (julian-edwards)]

> provisioningserver.enum

I know I keep saying it, but a common third library would be awesome :/

AF_INET[6] sounds fine enough for me though, it's pretty generic.

review: Approve

[Jeroen T. Vermeulen (jtv)]

Yes, we absolutely want a common package! I've been splitting utility functions out of __init__.py modules, and I'm sure some of the resulting modules could simply move into a common section. Easier to see now what the dependencies are, too.

=== modified file 'src/provisioningserver/utils/network.py'
--- src/provisioningserver/utils/network.py	2014-08-13 21:49:35 +0000
+++ src/provisioningserver/utils/network.py	2014-08-28 06:29:58 +0000
@@ -19,9 +19,19 @@
     'get_all_addresses_for_interface',
     'get_all_interface_addresses',
     'make_network',
+    'resolve_hostname',
     ]
 
 
+from socket import (
+    AF_INET,
+    AF_INET6,
+    EAI_NODATA,
+    EAI_NONAME,
+    gaierror,
+    getaddrinfo,
+    )
+
 from netaddr import (
     IPAddress,
     IPNetwork,
@@ -152,3 +162,37 @@
     for interface in netifaces.interfaces():
         for address in get_all_addresses_for_interface(interface):
             yield address
+
+
+def resolve_hostname(hostname, ip_version=4):
+    """Wrapper around `getaddrinfo`: return addresses for `hostname`.
+
+    :param hostname: Host name (or IP address).
+    :param ip_version: Look for addresses of this IP version only: 4 for IPv4,
+        or 6 for IPv6.
+    :return: A set of `IPAddress`.  Empty if `hostname` does not resolve for
+        the requested IP version.
+    """
+    addr_families = {
+        4: AF_INET,
+        6: AF_INET6,
+        }
+    assert ip_version in addr_families
+    # Arbitrary non-privileged port, on which we can call getaddrinfo.
+    port = 33360
+    try:
+        address_info = getaddrinfo(hostname, port, addr_families[ip_version])
+    except gaierror as e:
+        if e.errno in (EAI_NONAME, EAI_NODATA):
+            # Name does not resolve.
+            address_info = []
+        else:
+            raise
+
+    # The contents of sockaddr differ for IPv6 and IPv4, but the
+    # first element is always the address, and that's all we care
+    # about.
+    return {
+        IPAddress(sockaddr[0])
+        for family, socktype, proto, canonname, sockaddr in address_info
+        }

=== modified file 'src/provisioningserver/utils/tests/test_network.py'
--- src/provisioningserver/utils/tests/test_network.py	2014-08-13 21:49:35 +0000
+++ src/provisioningserver/utils/tests/test_network.py	2014-08-28 06:29:58 +0000
@@ -14,11 +14,21 @@
 __metaclass__ = type
 __all__ = []
 
+from socket import (
+    EAI_BADFLAGS,
+    EAI_NODATA,
+    EAI_NONAME,
+    gaierror,
+    )
+
 from maastesting.factory import factory
 from maastesting.matchers import MockCalledOnceWith
 from maastesting.testcase import MAASTestCase
 import mock
-from netaddr import IPNetwork
+from netaddr import (
+    IPAddress,
+    IPNetwork,
+    )
 import netifaces
 from netifaces import (
     AF_LINK,
@@ -34,6 +44,7 @@
     get_all_addresses_for_interface,
     get_all_interface_addresses,
     make_network,
+    resolve_hostname,
     )
 
 
@@ -345,3 +356,72 @@
         self.assertEqual(
             ip,
             clean_up_netifaces_address('%s%%%s' % (ip, interface), interface))
+
+
+class TestResolveHostname(MAASTestCase):
+    """Tests for `resolve_hostname`."""
+
+    def patch_getaddrinfo(self, *addrs):
+        fake = self.patch(network_module, 'getaddrinfo')
+        fake.return_value = [
+            (None, None, None, None, (unicode(address), None))
+            for address in addrs
+            ]
+        return fake
+
+    def patch_getaddrinfo_fail(self, exception):
+        fake = self.patch(network_module, 'getaddrinfo')
+        fake.side_effect = exception
+        return fake
+
+    def test__rejects_weird_IP_version(self):
+        self.assertRaises(
+            AssertionError,
+            resolve_hostname, factory.make_hostname(), ip_version=5)
+
+    def test__integrates_with_getaddrinfo(self):
+        result = resolve_hostname('localhost', 4)
+        self.assertIsInstance(result, set)
+        [localhost] = result
+        self.assertIsInstance(localhost, IPAddress)
+        self.assertIn(localhost, IPNetwork('127.0.0.0/8'))
+
+    def test__resolves_IPv4_address(self):
+        ip = factory.getRandomIPAddress()
+        fake = self.patch_getaddrinfo(ip)
+        hostname = factory.make_hostname()
+        result = resolve_hostname(hostname, 4)
+        self.assertIsInstance(result, set)
+        self.assertEqual({IPAddress(ip)}, result)
+        self.assertThat(fake, MockCalledOnceWith(hostname, mock.ANY, AF_INET))
+
+    def test__resolves_IPv6_address(self):
+        ip = factory.make_ipv6_address()
+        fake = self.patch_getaddrinfo(ip)
+        hostname = factory.make_hostname()
+        result = resolve_hostname(hostname, 6)
+        self.assertIsInstance(result, set)
+        self.assertEqual({IPAddress(ip)}, result)
+        self.assertThat(fake, MockCalledOnceWith(hostname, mock.ANY, AF_INET6))
+
+    def test__returns_empty_if_address_does_not_resolve(self):
+        self.patch_getaddrinfo_fail(
+            gaierror(EAI_NONAME, "Name or service not known"))
+        self.assertEqual(set(), resolve_hostname(factory.make_hostname(), 4))
+
+    def test__returns_empty_if_address_resolves_to_no_data(self):
+        self.patch_getaddrinfo_fail(
+            gaierror(EAI_NODATA, "No data returned"))
+        self.assertEqual(set(), resolve_hostname(factory.make_hostname(), 4))
+
+    def test__propagates_other_gaierrors(self):
+        self.patch_getaddrinfo_fail(gaierror(EAI_BADFLAGS, "Bad parameters"))
+        self.assertRaises(
+            gaierror,
+            resolve_hostname, factory.make_hostname(), 4)
+
+    def test__propagates_unexpected_errors(self):
+        self.patch_getaddrinfo_fail(KeyError("Huh what?"))
+        self.assertRaises(
+            KeyError,
+            resolve_hostname, factory.make_hostname(), 4)