Fix is_connected property when not using loop_forever

ChangeLog.txt

@@ -5,6 +5,9 @@ v2.0.0 - 2023-xx-xx
   Minimum tested version is Python 3.7
 - Add on_pre_connect() callback, which is called immediately before a
   connection attempt is made.
+- Fix is_connected property to correctly return False when connection is lost
+  and loop_start/loop_forever isn't used. Closes #525.
+
 
 
 v1.6.1 - 2021-10-21

src/paho/mqtt/client.py

@@ -118,6 +118,7 @@
 mqtt_cs_connected = 1
 mqtt_cs_disconnecting = 2
 mqtt_cs_connect_async = 3
+mqtt_cs_connection_lost = 4
 
 # Message state
 mqtt_ms_invalid = 0
@@ -600,7 +601,8 @@ def __init__(self, client_id="", clean_session=None, userdata=None,
         self._ssl_context = None
         # Only used when SSL context does not have check_hostname attribute
         self._tls_insecure = False
-        self._logger = None
+        logging.basicConfig(level=logging.DEBUG)
+        self._logger = logging.getLogger("plop")
         self._registered_write = False
         # No default callbacks
         self._on_log = None
@@ -1153,10 +1155,19 @@ def _loop(self, timeout=1.0):
             socklist = select.select(rlist, wlist, [], timeout)
         except TypeError:
             # Socket isn't correct type, in likelihood connection is lost
+            # ... or we called disconnect(). In that case the socket will
+            # be closed but some loop (like loop_forever) will continue to
+            # call _loop(). We still want to break that loop by returning an
+            # rc != MQTT_ERR_SUCCESS and we don't want state to change from
+            # mqtt_cs_disconnecting.
+            if self._state != mqtt_cs_disconnecting:
+                self._state = mqtt_cs_connection_lost
             return MQTT_ERR_CONN_LOST
         except ValueError:
             # Can occur if we just reconnected but rlist/wlist contain a -1 for
             # some reason.
+            if self._state != mqtt_cs_disconnecting:
+                self._state = mqtt_cs_connection_lost
             return MQTT_ERR_CONN_LOST
         except Exception:
             # Note that KeyboardInterrupt, etc. can still terminate since they
@@ -1620,6 +1631,8 @@ def loop_misc(self):
             if self._state == mqtt_cs_disconnecting:
                 rc = MQTT_ERR_SUCCESS
             else:
+                self._state = mqtt_cs_connection_lost
+                self._easy_log(MQTT_LOG_DEBUG, "... 2")
                 rc = MQTT_ERR_KEEPALIVE
 
             self._do_on_disconnect(rc)
@@ -2389,6 +2402,10 @@ def _loop_rc_handle(self, rc, properties=None):
 
             self._do_on_disconnect(rc, properties)
 
+        if rc == MQTT_ERR_CONN_LOST:
+            self._easy_log(MQTT_LOG_DEBUG, "... 3")
+            self._state = mqtt_cs_connection_lost
+
         return rc
 
     def _packet_read(self):