MDEV-20574 Position of events reported by mysqlbinlog is wrong with encrypted binlogs, SHOW BINLOG EVENTS reports the correct one.

Analysis

Mysqlbinlog output for encrypted binary log
#Q> insert into tab1 values (3,'row 003')
#190912 17:36:35 server id 10221  end_log_pos 980 CRC32 0x53bcb3d3  Table_map: `test`.`tab1` mapped to number 19
# at 940
#190912 17:36:35 server id 10221  end_log_pos 1026 CRC32 0xf2ae5136     Write_rows: table id 19 flags: STMT_END_F

Here we can see Table_map_log_event ends at 980 but Next event starts at 940.
And the reason for that is we do not send START_ENCRYPTION_EVENT to the slave

Solution:-
Send Start_encryption_log_event as Ignorable_log_event to slave(mysqlbinlog),
So that mysqlbinlog can update its log_pos.
Since Slave can request multiple FORMAT_DESCRIPTION_EVENT while master does not
have so We only update slave master pos when master actually have the
FORMAT_DESCRIPTION_EVENT. Similar logic should be applied for START_ENCRYPTION_EVENT.

Also added the test case when new server reads the data from old server which
does not send START_ENCRYPTION_EVENT to slave.

Master Slave Upgrade Scenario.
When Slave is updated first, Slave will have extra logic of handling
START_ENCRYPTION_EVENT But master willnot be sending START_ENCRYPTION_EVENT.
So there will be no issue.
When Master is updated first, It will send  START_ENCRYPTION_EVENT to
slave , But slave will ignore this event in queue_event.

1 files changed, 18 insertions, 16 deletions

diff --git a/sql/log_event.cc b/sql/log_event.cc
index 0e0d69b515c..66f1d6bc790 100644
--- a/sql/log_event.cc
+++ b/sql/log_event.cc
@@ -2077,6 +2077,19 @@ Log_event* Log_event::read_log_event(const char* buf, uint event_len,
          alg != BINLOG_CHECKSUM_ALG_OFF))
       event_len= event_len - BINLOG_CHECKSUM_LEN;
 
+    /*
+      Create an object of Ignorable_log_event for unrecognized sub-class.
+      So that SLAVE SQL THREAD will only update the position and continue.
+      We should look for this flag first instead of judging by event_type
+      Any event can be Ignorable_log_event if it has this flag on.
+      look into @note of Ignorable_log_event
+    */
+    if (uint2korr(buf + FLAGS_OFFSET) & LOG_EVENT_IGNORABLE_F)
+    {
+      ev= new Ignorable_log_event(buf, fdle,
+                                  get_type_str((Log_event_type) event_type));
+      goto exit;
+    }
     switch(event_type) {
     case QUERY_EVENT:
       ev  = new Query_log_event(buf, event_len, fdle, QUERY_EVENT);
@@ -2203,24 +2216,13 @@ Log_event* Log_event::read_log_event(const char* buf, uint event_len,
       ev = new Start_encryption_log_event(buf, event_len, fdle);
       break;
     default:
-      /*
-        Create an object of Ignorable_log_event for unrecognized sub-class.
-        So that SLAVE SQL THREAD will only update the position and continue.
-      */
-      if (uint2korr(buf + FLAGS_OFFSET) & LOG_EVENT_IGNORABLE_F)
-      {
-        ev= new Ignorable_log_event(buf, fdle,
-                                    get_type_str((Log_event_type) event_type));
-      }
-      else
-      {
-        DBUG_PRINT("error",("Unknown event code: %d",
-                            (uchar) buf[EVENT_TYPE_OFFSET]));
-        ev= NULL;
-        break;
-      }
+      DBUG_PRINT("error",("Unknown event code: %d",
+                          (uchar) buf[EVENT_TYPE_OFFSET]));
+      ev= NULL;
+      break;
     }
   }
+exit:
 
   if (ev)
   {