Improve cursor behavior on closed connections

- Added internal attribute cursor._thread_id to detect
  automatic reconnect.
- If a reconnect occurred, only buffered resultsets using
  the text protocol can be accessed. (The same applies
  if a connection was closed).
- If connection reconnected, _thread_id attribute will be updated
  when using execute() or executemany() method.

testing/test/integration/test_cursor.py

@@ -8,6 +8,7 @@ import decimal
 import json
 from decimal import Decimal
 import array
+import time
 
 import mariadb
 from mariadb.constants import FIELD_TYPE, EXT_FIELD_TYPE, ERR, CURSOR, INDICATOR, CLIENT
@@ -41,6 +42,51 @@ class TestCursor(unittest.TestCase):
         cursor.close()
         del cursor
 
+    def test_cursor_reconnect(self):
+        conn= create_connection({'reconnect' : True})
+        self.assertEqual(conn.auto_reconnect, True)
+        cursor= conn.cursor(binary=True)
+        cursor.execute("SET session wait_timeout=3")
+
+        # binary protocol should fail
+        cursor.execute("SELECT 1 UNION SELECT 2 UNION SELECT 3")
+        time.sleep(5)
+        try:
+             cursor.fetchone()
+        except mariadb.ProgrammingError:
+             pass
+
+        cursor.close()
+
+        # Text protocol unbuffered should fail
+        cursor= conn.cursor(binary=False, buffered=False)
+        cursor.execute("SET session wait_timeout=3")
+
+        # text protocol unbuffered should fail
+        cursor.execute("SELECT 1 UNION SELECT 2 UNION SELECT 3")
+        time.sleep(5)
+        try:
+            cursor.fetchone()
+        except mariadb.ProgrammingError:
+            pass
+
+        # reeusing cursor should work
+        cursor= conn.cursor(binary=False, buffered=True)
+        cursor.execute("SET session wait_timeout=3")
+        time.sleep(5)
+        # reconnect
+        cursor.execute("SELECT 1 UNION SELECT 2 UNION SELECT 3")
+        self.assertNotEqual(cursor._thread_id, cursor.connection.thread_id)
+        row= cursor.fetchone()
+        self.assertEqual(row[0],1)
+        # execute should update cursor._thread_id
+        cursor.execute("SELECT 1 UNION SELECT 2 UNION SELECT 3")
+        self.assertEqual(cursor._thread_id, cursor.connection.thread_id)
+
+        cursor.close()
+        conn.close()
+
+
     def test_conpy283(self):
         conn= create_connection()
         cursor= conn.cursor(dictionary=True)