Parse NULL-bitmask in table map event (#361)

[Fields in table map event](https://dev.mysql.com/doc/internals/en/table-map-event.html)

[buffer layout for table map
event](https://github.com/mysql/mysql-server/blob/beb865a960b9a8a16cf999c323e46c5b0c67f21f/libbinlogevents/include/rows_event.h#L633-L639)
[null bitmask in mysql-server](https://github.com/mysql/mysql-server/blob/beb865a960b9a8a16cf999c323e46c5b0c67f21f/libbinlogevents/src/rows_event.cpp#L93)

pymysqlreplication/row_event.py

@@ -648,8 +648,9 @@ def __init__(self, from_packet, event_size, table_map, ctl_connection, **kwargs)
         self.table_obj = Table(self.column_schemas, self.table_id, self.schema,
                                self.table, self.columns)
 
-        # TODO: get this information instead of trashing data
-        # n              NULL-bitmask, length: (column-length * 8) / 7
+        # ith column is nullable if (i - 1)th bit is set to True, not nullable otherwise
+        ## Refer to definition of and call to row.event.__is_null() to interpret bitmap corresponding to columns
+        self.null_bitmask = self.packet.read((self.column_count + 7) / 8)
 
     def get_table(self):
         return self.table_obj

pymysqlreplication/tests/test_data_type.py

@@ -77,6 +77,30 @@ def create_table(self, create_query):
 
         return event
 
+    def create_and_get_tablemap_event(self, bit):
+        """Create table and return tablemap event
+
+        Returns:
+            Table map event
+        """
+        self.execute(create_query)
+        self.execute(insert_query)
+        self.execute("COMMIT")
+
+        self.assertIsInstance(self.stream.fetchone(), RotateEvent)
+        self.assertIsInstance(self.stream.fetchone(), FormatDescriptionEvent)
+        #QueryEvent for the Create Table
+        self.assertIsInstance(self.stream.fetchone(), QueryEvent)
+
+        #QueryEvent for the BEGIN
+        self.assertIsInstance(self.stream.fetchone(), QueryEvent)
+
+        event = self.stream.fetchone()
+
+        self.assertEqual(event.event_type, TABLE_MAP_EVENT)
+
+        return event
+
     def test_decimal(self):
         create_query = "CREATE TABLE test (test DECIMAL(2,1))"
         insert_query = "INSERT INTO test VALUES(4.2)"
@@ -669,16 +693,75 @@ def test_status_vars(self):
         Note that if you change default db name 'pymysqlreplication_test',
         event.mts_accessed_db_names MUST be asserted against the changed db name.
 
-        Returns:
-            binary string parsed from __data_buffer
-
         Raises:
-            AssertionError: if no 
+            AssertionError: if status variables not set correctly
         """
         create_query = "CREATE TABLE test (id INTEGER)"
         event = self.create_table(create_query)
         self.assertEqual(event.catalog_nz_code, b'std')
         self.assertEqual(event.mts_accessed_db_names, [b'pymysqlreplication_test'])
 
+    def test_null_bitmask(self)
+        """Test parse of null-bitmask in table map events
+
+        Create table with 16 columns with nullability specified by 'bit_mask' variable
+        'bit_mask' variable is asserted against null_bitmask attribute in table map event.
+
+        Raises:
+            AssertionError: if null_bitmask isn't set as specified in 'bit_mask' variable
+        """ 
+
+        # any 2-byte bitmask in little-endian hex bytes format (b'a\x03')
+        ## b'a\x03' = 1101100001(2)
+        bit_mask = b'a\x03'
+
+        # Prepare create_query
+        create_query = "CREATE TABLE test"
+
+        columns = []
+        for i in range(16):
+            # column_definition consists of...
+            ## column name, column type, nullability
+            column_definition = []
+
+            column_name = chr(ord('a') + i)
+            column_definition.append(column_name)
+
+            column_type = "INT"
+            column_definition.append(column_type)
+
+            nullability = "NOT NULL" if not RowsEvent.__is_null(bit_mask, i) else ""
+            column_definition.append(nullability)
+
+            columns.append(" ".join(column_definition))
+
+        create_query += f' ({", ".join(columns)})'
+
+        # Prepare insert_query
+        insert_query = "INSERT into test values"
+
+        values = []
+        for i in range(16):
+            values.append('0')
+
+        insert_query += f' ({",".join(values)})')
+
+        self.execute(create_query)
+        self.execute(insert_query)
+        self.execute("COMMIT")
+
+        self.assertIsInstance(self.stream.fetchone(), RotateEvent)
+        self.assertIsInstance(self.stream.fetchone(), FormatDescriptionEvent)
+        #QueryEvent for the Create Table
+        self.assertIsInstance(self.stream.fetchone(), QueryEvent)
+
+        #QueryEvent for the BEGIN
+        self.assertIsInstance(self.stream.fetchone(), QueryEvent)
+
+        event = self.stream.fetchone()
+
+        self.assertEqual(event.event_type, TABLE_MAP_EVENT)
+        self.assertEqual(event.null_bitmask, bit_mask)
+
 if __name__ == "__main__":
     unittest.main()