add daemon method to DynamicResolver

Keeps main process up indefinitely as long as DynamicResolver UDP
socketserver is up

onedns/resolver.py

@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 from __future__ import print_function
+import time
 
 import dnslib
 from dnslib import server
@@ -100,3 +101,12 @@ class DynamicResolver(server.BaseResolver):
             if srv:
                 srv.stop()
                 srv.server.socket.close()
+
+    def daemon(self, *args, **kwargs):
+        testing = kwargs.pop('testing', False)
+        if self._udp_server is None or not self._udp_server.isAlive():
+            self.start(*args, **kwargs)
+        while self._udp_server.isAlive():
+            time.sleep(1)
+            if testing:
+                break

onedns/tests/test_dynamicresolver.py

@@ -49,3 +49,9 @@ def test_get_fqdn(dns, name, ip):
     dns.add_host(name, ip)
     assert dns.zone[0][0].label[0] == name.split('.')[0]
     assert '.'.join(dns.zone[0][0].label[1:]) == conftest.DOMAIN
+
+
+def test_daemon(dns):
+    dns.close()
+    dns.daemon(dns_address=conftest.INTERFACE, dns_port=conftest.PORT,
+               tcp=True, testing=True)