Added checking of localhost for another DNS service on *:53

Author: stamparm

lib/request/dns.py

@@ -59,6 +59,7 @@ def response(self, resolution):
 
 class DNSServer(object):
     def __init__(self):
+        self._check_localhost()
         self._requests = []
         self._lock = threading.Lock()
         self._socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
@@ -67,6 +68,19 @@ def __init__(self):
         self._running = False
         self._initialized = False
 
+    def _check_localhost(self):
+        response = ""
+        try:
+            s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+            s.connect(("", 53))
+            s.send("6509012000010000000000010377777706676f6f676c6503636f6d00000100010000291000000000000000".decode("hex"))  # A www.google.com
+            response = s.recv(512)
+        except:
+            pass
+        finally:
+            if response and "google" in response:
+                raise socket.error("another DNS service already running on *:53")
+
     def pop(self, prefix=None, suffix=None):
         """
         Returns received DNS resolution request (if any) that has given