cache DNS results in UDPRelay

shadowsocks/udprelay.py

@@ -103,6 +103,7 @@ class UDPRelay(object):
                                          close_callback=self._close_client)
         self._client_fd_to_server_addr = \
             lru_cache.LRUCache(timeout=config['timeout'])
+        self._dns_cache = lru_cache.LRUCache(timeout=300)
         self._eventloop = None
         self._closed = False
         self._last_time = time.time()
@@ -170,11 +171,15 @@ class UDPRelay(object):
         else:
             server_addr, server_port = dest_addr, dest_port
 
+        addrs = self._dns_cache.get(server_addr, None)
+        if addrs is None:
             addrs = socket.getaddrinfo(server_addr, server_port, 0,
                                        socket.SOCK_DGRAM, socket.SOL_UDP)
             if not addrs:
                 # drop
                 return
+            else:
+                self._dns_cache[server_addr] = addrs
 
         af, socktype, proto, canonname, sa = addrs[0]
         key = client_key(r_addr, af)