Fix regression introduced in #595. (#597)

Whenever the connecting to the remote server fails, query DNS and cache the result. This
should reduce the number of DNS requests the internet predicate
generates without changing the behaviour.

i3pystatus/core/util.py

@@ -359,9 +359,9 @@ class internet:
     """
     Checks for internet connection by connecting to a server.
 
-    Used server can be configured via the `address` class variable which expects a tuple in the form
-    (hostname/IP, port). The rate at which the connection status is checked
-    can be configured via the `check_frequency` class variable (in seconds).
+    This class exposes two configuration variables:
+        * address - a tuple containing (host,port) of the server to connect to
+        * check_frequency - the frequency in seconds for checking the connection
 
     :rtype: bool
 
@@ -370,27 +370,57 @@ class internet:
         :py:func:`require`
 
     """
-    address = ("8.8.8.8", 53)
-
+    address = ("google-public-dns-a.google.com", 53)
     check_frequency = 1
+
+    dns_cache = []
     last_checked = time.perf_counter() - check_frequency
-    status = False
+
+    connected = False
 
     def __new__(cls):
+        if not internet.connected:
+            internet.dns_cache = internet.resolve()
+
         now = time.perf_counter()
         elapsed = now - internet.last_checked
-        if elapsed > internet.check_frequency:
+        if not internet.connected or elapsed > internet.check_frequency:
             internet.last_checked = now
-            internet.status = internet.check()
-        return internet.status
+            internet.connected = internet.check_connection()
+        return internet.connected
 
     @staticmethod
-    def check():
+    def check_connection():
+        for res in internet.dns_cache:
+            try:
+                if internet.check(res):
+                    return True
+            except OSError:
+                pass
+        return False
+
+    @staticmethod
+    def check(res):
+        af, socktype, proto, canonname, sa = res
+        sock = None
         try:
-            socket.create_connection(internet.address, 1).close()
+            sock = socket.socket(af, socktype, proto)
+            sock.settimeout(1)
+            sock.connect(sa)
+            sock.close()
             return True
-        except (OSError, socket.gaierror):
-            return False
+        except socket.error:
+            if sock is not None:
+                sock.close()
+            raise
+
+    @staticmethod
+    def resolve():
+        host, port = internet.address
+        try:
+            return socket.getaddrinfo(host, port, 0, socket.SOCK_STREAM)
+        except socket.gaierror:
+            return []
 
 
 def make_graph(values, lower_limit=0.0, upper_limit=100.0, style="blocks"):