MDEV-4645: Incorrect reads of frozen binlog events; FDE corrupted in relay log

  
  Currently several places use description_event->common_header_len instead of
  LOG_EVENT_MINIMAL_HEADER_LEN when parsing events with "frozen" headers (such
  as Start_event_v3 and its subclasses such as Format_description_log_event, as
  well as Rotate_event). This causes events with extra headers (which would otherwise
  be valid and those headers ignored) to be corrupted due to over-reading or skipping
  into the data portion of the log events.
  
  It is rewritten in some details patch of Jeremy Cole (See MDEV):
  - The virtual function returns length to avoid IFs (and only one call of the virtual function made)
  - Printing function avoids printing strings

mysql-test/t/mysqlbinlog.test

@@ -275,17 +275,16 @@ FLUSH LOGS;
 
 DROP TABLE t1;
 
-# We create a table, patch, and load the output into it
-# By using LINES STARTING BY '#' + SELECT WHERE a LIKE 'Query'
-# We can easily see if a 'Query' line is missing the '#' character
-# as described in the original bug
+# We create a table named "patch", and load the output into it.
+# By using LIKE, we can easily see if the output is missing the '#'
+# character, as described in the bug.
 
 --disable_query_log
 CREATE TABLE patch (a BLOB);
 --exec $MYSQL_BINLOG --hexdump --local-load=$MYSQLTEST_VARDIR/tmp/ $MYSQLD_DATADIR/master-bin.000012 > $MYSQLTEST_VARDIR/tmp/mysqlbinlog_tmp.dat
 ### Starting master-bin.000014
 eval LOAD DATA LOCAL INFILE '$MYSQLTEST_VARDIR/tmp/mysqlbinlog_tmp.dat'
-     INTO TABLE patch FIELDS TERMINATED BY '' LINES STARTING BY '#';
+     INTO TABLE patch FIELDS TERMINATED BY '';
 --remove_file $MYSQLTEST_VARDIR/tmp/mysqlbinlog_tmp.dat
 --enable_query_log
 
@@ -293,7 +292,7 @@ eval LOAD DATA LOCAL INFILE '$MYSQLTEST_VARDIR/tmp/mysqlbinlog_tmp.dat'
 --echo The bug being tested was that 'Query' lines were not preceded by '#'
 --echo If the line is in the table, it had to have been preceded by a '#'
 --echo
-SELECT COUNT(*) AS `BUG#28293_expect_2` FROM patch WHERE a LIKE '%Query%';
+SELECT COUNT(*) AS `BUG#28293_expect_2` FROM patch WHERE a LIKE '#%Query%';
 DROP TABLE patch;
 
 #
@@ -594,3 +593,12 @@ SHOW TABLES IN test;
 --exec $MYSQL_BINLOG --server-id=2 $MYSQLD_DATADIR/$master_binlog | $MYSQL
 SHOW TABLES IN test;
 eval SET GLOBAL SERVER_ID = $old_server_id;
+
+--echo #
+--echo # MDEV-4645: Incorrect reads of frozen binlog events;
+--echo # FDE corrupted in relay log
+--echo #
+--exec $MYSQL_BINLOG --hexdump std_data/mdev-4645-binlog_checksum.binlog
+--exec $MYSQL_BINLOG --hexdump std_data/mdev-4645-binlog_group_id.binlog
+--exec $MYSQL_BINLOG --hexdump std_data/mdev-4645-binlog_group_id_checksum.binlog
+--exec $MYSQL_BINLOG --hexdump std_data/mdev-4645-binlog_none.binlog

sql/log_event.h

@@ -1253,6 +1253,7 @@ class Log_event
 #endif
   virtual Log_event_type get_type_code() = 0;
   virtual bool is_valid() const = 0;
+  virtual my_off_t get_header_len(my_off_t len) { return len; }
   void set_artificial_event() { flags |= LOG_EVENT_ARTIFICIAL_F; }
   void set_relay_log_event() { flags |= LOG_EVENT_RELAY_LOG_F; }
   bool is_artificial_event() const { return flags & LOG_EVENT_ARTIFICIAL_F; }
@@ -2469,6 +2470,8 @@ class Start_log_event_v3: public Log_event
                      const Format_description_log_event* description_event);
   ~Start_log_event_v3() {}
   Log_event_type get_type_code() { return START_EVENT_V3;}
+  my_off_t get_header_len(my_off_t l __attribute__((unused)))
+  { return LOG_EVENT_MINIMAL_HEADER_LEN; }
 #ifdef MYSQL_SERVER
   bool write(IO_CACHE* file);
 #endif
@@ -2984,6 +2987,8 @@ class Rotate_log_event: public Log_event
       my_free((void*) new_log_ident);
   }
   Log_event_type get_type_code() { return ROTATE_EVENT;}
+  my_off_t get_header_len(my_off_t l __attribute__((unused)))
+  { return LOG_EVENT_MINIMAL_HEADER_LEN; }
   int get_data_size() { return  ident_len + ROTATE_HEADER_LEN;}
   bool is_valid() const { return new_log_ident != 0; }
 #ifdef MYSQL_SERVER