Move is_ip from asyncdns to common

Since implement CIDR forbidden need this function,
move it to common file seems to be a better choice.

shadowsocks/asyncdns.py

@@ -233,18 +233,6 @@ def parse_response(data):
         return None
 
 
-def is_ip(address):
-    for family in (socket.AF_INET, socket.AF_INET6):
-        try:
-            if type(address) != str:
-                address = address.decode('utf8')
-            socket.inet_pton(family, address)
-            return family
-        except (TypeError, ValueError, OSError, IOError):
-            pass
-    return False
-
-
 def is_valid_hostname(hostname):
     if len(hostname) > 255:
         return False
@@ -296,7 +284,7 @@ class DNSResolver(object):
                             parts = line.split()
                             if len(parts) >= 2:
                                 server = parts[1]
-                                if is_ip(server) == socket.AF_INET:
+                                if common.is_ip(server) == socket.AF_INET:
                                     if type(server) != str:
                                         server = server.decode('utf8')
                                     self._servers.append(server)
@@ -316,7 +304,7 @@ class DNSResolver(object):
                     parts = line.split()
                     if len(parts) >= 2:
                         ip = parts[0]
-                        if is_ip(ip):
+                        if common.is_ip(ip):
                             for i in range(1, len(parts)):
                                 hostname = parts[i]
                                 if hostname:
@@ -423,7 +411,7 @@ class DNSResolver(object):
             hostname = hostname.encode('utf8')
         if not hostname:
             callback(None, Exception('empty hostname'))
-        elif is_ip(hostname):
+        elif common.is_ip(hostname):
             callback((hostname, hostname), None)
         elif hostname in self._hosts:
             logging.debug('hit hosts: %s', hostname)

shadowsocks/common.py

@@ -101,6 +101,18 @@ def inet_pton(family, addr):
         raise RuntimeError("What family?")
 
 
+def is_ip(address):
+    for family in (socket.AF_INET, socket.AF_INET6):
+        try:
+            if type(address) != str:
+                address = address.decode('utf8')
+            inet_pton(family, address)
+            return family
+        except (TypeError, ValueError, OSError, IOError):
+            pass
+    return False
+
+
 def patch_socket():
     if not hasattr(socket, 'inet_pton'):
         socket.inet_pton = inet_pton