networks: Implement diagnostics

- Since DNS server is started now by setting ipv4 'shared' method on a
  network connection, DNS tests are done here.

plinth/modules/networks/__init__.py

@@ -19,9 +19,90 @@
 Plinth module to interface with network-manager
 """
 
+from gettext import gettext as _
+from logging import Logger
+import subprocess
+
 from . import networks
 from .networks import init
+from plinth import action_utils
+from plinth import network
+
 
 __all__ = ['networks', 'init']
 
 depends = ['plinth.modules.system']
+
+logger = Logger(__name__)
+
+
+def diagnose():
+    """Run diagnostics and return the results."""
+    results = []
+
+    interfaces = _get_shared_interfaces()
+    addresses = _get_interface_addresses(interfaces)
+
+    for address in addresses:
+        results.append(action_utils.diagnose_port_listening(53, 'tcp', address))
+        results.append(action_utils.diagnose_port_listening(53, 'udp', address))
+
+    results.append(_diagnose_dnssec('4'))
+    results.append(_diagnose_dnssec('6'))
+
+    return results
+
+
+def _get_shared_interfaces():
+    """Get active network interfaces in shared mode."""
+    shared_interfaces = []
+    for connection in network.get_connection_list():
+        if not connection['is_active']:
+            continue
+
+        connection_uuid = connection['uuid']
+        connection = network.get_connection(connection_uuid)
+
+        settings_ipv4 = connection.get_setting_ip4_config()
+        if settings_ipv4.get_method() == 'shared':
+            settings_connection = connection.get_setting_connection()
+            interface = settings_connection.get_interface_name()
+            if interface:
+                shared_interfaces.append(interface)
+
+    return shared_interfaces
+
+
+def _get_interface_addresses(interfaces):
+    """Get the IPv4 addresses for the given interfaces."""
+    output = subprocess.check_output(['ip', '-o', 'addr'])
+    lines = output.decode().splitlines()
+
+    addresses = []
+    for line in lines:
+        parts = line.split()
+        if parts[1] in interfaces and parts[2] == 'inet':
+            addresses.append(parts[3].split('/')[0])
+
+    return addresses
+
+
+def _diagnose_dnssec(kind='4'):
+    """Perform diagnostic on whether the system is using DNSSEC.
+
+    Kind is either '4' or '6' for IPv4 and IPv6 respectively.
+    """
+    kind_option = {'4': '-4', '6': '-6'}[kind]
+
+    result = 'failed'
+    try:
+        output = subprocess.check_output(
+            ['dig', kind_option, '+time=2', '+tries=1',
+             'test.dnssec-or-not.net', 'TXT'])
+
+        if 'Yes, you are using DNSSEC' in output.decode():
+            result = 'passed'
+    except subprocess.CalledProcessError:
+        pass
+
+    return [_('Using DNSSEC on IPv{kind}').format(kind=kind), result]

plinth/modules/networks/templates/connections_list.html

@@ -93,6 +93,8 @@
           </div>
         {% endfor %}
       </div>
+
+      {% include "diagnostics_button.html" with module="networks" %}
     </div>
   </div>