firewall: put DNS resolving into its own function

qubesagent/firewall.py

@@ -127,6 +127,26 @@ class FirewallWorker(object):
         rules.append({'action': policy})
         return rules
 
+    def resolve_dns(self, fqdn, family):
+        """
+        Resolve the given FQDN via DNS.
+        :param fqdn: FQDN
+        :param family: 4 or 6 for IPv4 or IPv6
+        :return: see socket.getaddrinfo()
+        :raises: RuleParseError
+        """
+        try:
+            addrinfo = socket.getaddrinfo(fqdn, None,
+                (socket.AF_INET6 if family == 6 else socket.AF_INET))
+        except socket.gaierror as e:
+            raise RuleParseError('Failed to resolve {}: {}'.format(
+                fqdn, str(e)))
+        except UnicodeError as e:
+            raise RuleParseError('Invalid destination {}: {}'.format(
+                fqdn, str(e)))
+        return addrinfo
+
+
     def update_dns_info(self, source, dns):
         """
         Write resolved DNS addresses back to QubesDB. This can be useful
@@ -339,12 +359,7 @@ class IptablesWorker(FirewallWorker):
             elif 'dst6' in rule:
                 dsthosts = [rule['dst6']]
             elif 'dsthost' in rule:
-                try:
-                    addrinfo = socket.getaddrinfo(rule['dsthost'], None,
-                        (socket.AF_INET6 if family == 6 else socket.AF_INET))
-                except socket.gaierror as e:
-                    raise RuleParseError('Failed to resolve {}: {}'.format(
-                        rule['dsthost'], str(e)))
+                addrinfo = self.resolve_dns(rule['dsthost'], family)
                 dsthosts = set(item[4][0] + fullmask for item in addrinfo)
                 ret_dns[rule['dsthost']] = dsthosts
             else:
@@ -652,15 +667,7 @@ class NftablesWorker(FirewallWorker):
             elif 'dst6' in rule:
                 nft_rule += ' ip6 daddr {}'.format(rule['dst6'])
             elif 'dsthost' in rule:
-                try:
-                    addrinfo = socket.getaddrinfo(rule['dsthost'], None,
-                        (socket.AF_INET6 if family == 6 else socket.AF_INET))
-                except socket.gaierror as e:
-                    raise RuleParseError('Failed to resolve {}: {}'.format(
-                        rule['dsthost'], str(e)))
-                except UnicodeError as e:
-                    raise RuleParseError('Invalid destination {}: {}'.format(
-                        rule['dsthost'], str(e)))
+                addrinfo = self.resolve_dns(rule['dsthost'], family)
                 dsthosts = set(item[4][0] + fullmask for item in addrinfo)
                 nft_rule += ' {} daddr {{ {} }}'.format(ip_match,
                     ', '.join(dsthosts))