MDEV-14721 Big transaction events get lost on semisync master when

replicate_events_marked_for_skip=FILTER_ON_MASTER

When events of a big transaction are binlogged offsetting over 2GB from
the beginning of the log the semisync master's dump thread
lost such events.
The events were skipped by the Dump thread that found their skipping
status erroneously.

The current fixes make sure the skipping status is computed correctly.
The test verifies them simulating the 2GB offset.

mysql-test/suite/rpl/r/rpl_semi_sync_skip_repl.result

@@ -0,0 +1,30 @@
+include/master-slave.inc
+[connection master]
+connection master;
+call mtr.add_suppression("Timeout waiting for reply of binlog");
+SET @@GLOBAL.rpl_semi_sync_master_enabled = 1;
+SET @@GLOBAL.rpl_semi_sync_master_timeout=100;
+connection slave;
+include/stop_slave.inc
+SET @@GLOBAL.replicate_events_marked_for_skip=FILTER_ON_MASTER;
+SET @@GLOBAL. rpl_semi_sync_slave_enabled = 1;
+include/start_slave.inc
+connection master;
+CREATE TABLE t1 (a INT) ENGINE=innodb;
+SET @@GLOBAL.debug_dbug= "d,dbug_master_binlog_over_2GB";
+SET @@SESSION.skip_replication=1;
+INSERT INTO t1 SET a=1;
+SET @@SESSION.skip_replication=0;
+INSERT INTO t1 SET a=0;
+connection slave;
+connection master;
+SET @@GLOBAL.debug_dbug="";
+SET @@GLOBAL. rpl_semi_sync_master_timeout = 10000;
+SET @@GLOBAL. rpl_semi_sync_master_enabled = 0;
+connection master;
+DROP TABLE t1;
+connection slave;
+include/stop_slave.inc
+SET @@GLOBAL. rpl_semi_sync_slave_enabled = 0;
+SET @@GLOBAL.replicate_events_marked_for_skip = REPLICATE;
+include/rpl_end.inc

mysql-test/suite/rpl/t/rpl_semi_sync_skip_repl.test

@@ -0,0 +1,62 @@
+# MDEV-14721 Big transaction events get lost on semisync master when
+# replicate_events_marked_for_skip=FILTER_ON_MASTER
+#
+# When events of a big transaction are binlogged offsetting over 2GB from
+# the beginning of the log the semisync master's dump thread
+# lost such events.
+# The test verifies the fixes' correctness simulating the 2GB offset.
+
+source include/have_semisync.inc;
+source include/not_embedded.inc;
+source include/have_innodb.inc;
+source include/have_debug.inc;
+source include/master-slave.inc;
+
+--connection master
+# Suppress warnings that might be generated during the test
+call mtr.add_suppression("Timeout waiting for reply of binlog");
+
+--let $sav_enabled_master=`SELECT @@GLOBAL.rpl_semi_sync_master_enabled `
+--let $sav_timeout_master=`SELECT @@GLOBAL.rpl_semi_sync_master_timeout `
+SET @@GLOBAL.rpl_semi_sync_master_enabled = 1;
+SET @@GLOBAL.rpl_semi_sync_master_timeout=100;
+
+--connection slave
+source include/stop_slave.inc;
+--let $sav_skip_marked_slave=`SELECT @@GLOBAL.replicate_events_marked_for_skip `
+SET @@GLOBAL.replicate_events_marked_for_skip=FILTER_ON_MASTER;
+--let $sav_enabled_slave=`SELECT @@GLOBAL.rpl_semi_sync_slave_enabled `
+SET @@GLOBAL. rpl_semi_sync_slave_enabled = 1;
+
+source include/start_slave.inc;
+
+--connection master
+CREATE TABLE t1 (a INT) ENGINE=innodb;
+
+# Make the following events as if they offset over 2GB from the beginning of binlog
+SET @@GLOBAL.debug_dbug= "d,dbug_master_binlog_over_2GB";
+SET @@SESSION.skip_replication=1;
+INSERT INTO t1 SET a=1;
+SET @@SESSION.skip_replication=0;
+INSERT INTO t1 SET a=0;
+
+--sync_slave_with_master
+
+#
+# Clean up
+#
+--connection master
+SET @@GLOBAL.debug_dbug="";
+--eval SET @@GLOBAL. rpl_semi_sync_master_timeout = $sav_timeout_master
+--eval SET @@GLOBAL. rpl_semi_sync_master_enabled = $sav_enabled_master
+
+--connection master
+DROP TABLE t1;
+
+--sync_slave_with_master
+source include/stop_slave.inc;
+--eval SET @@GLOBAL. rpl_semi_sync_slave_enabled = $sav_enabled_slave
+--eval SET @@GLOBAL.replicate_events_marked_for_skip = $sav_skip_marked_slave
+
+--let $rpl_only_running_threads= 1
+--source include/rpl_end.inc

sql/log_event.cc

@@ -1711,6 +1711,8 @@ bool Log_event::write_header(ulong event_data_length)
     */
 
     log_pos= writer->pos() + data_written;
+    
+    DBUG_EXECUTE_IF("dbug_master_binlog_over_2GB", log_pos += (1ULL <<31););
   }
 
   now= get_time();                               // Query start time

sql/sql_repl.cc

@@ -1904,11 +1904,8 @@ send_event_to_slave(binlog_send_info *info, Log_event_type event_type,
   */
   if (info->thd->variables.option_bits & OPTION_SKIP_REPLICATION)
   {
-    /*
-      The first byte of the packet is a '\0' to distinguish it from an error
-      packet. So the actual event starts at offset +1.
-    */
-    uint16 event_flags= uint2korr(&((*packet)[FLAGS_OFFSET+1]));
+    uint16 event_flags= uint2korr(&((*packet)[FLAGS_OFFSET + ev_offset]));
+
     if (event_flags & LOG_EVENT_SKIP_REPLICATION_F)
       return NULL;
   }