MDEV-16372 ER_BASE64_DECODE_ERROR upon replaying binary log via mysqlbinlog --verbose

(This commit is for 10.3 and upper branches)

In case of a pattern of non-STMT_END-marked Rows-log-event (A) followed by
a STMT_END marked one (B) mysqlbinlog mixes up the base64 encoded rows events
with their pseudo sql representation produced by the verbose option:
      BINLOG '
        base64 encoded data for A
        ### verbose section for A
        base64 encoded data for B
        ### verbose section for B
      '/*!*/;
In effect the produced BINLOG '...' query is not valid and is rejected with the error.
Examples of this way malformed BINLOG could have been found in binlog_row_annotate.result
that gets corrected with the patch.

The issue is fixed with introduction an auxiliary IO_CACHE to hold on the verbose
comments until the terminal STMT_END event is found. The new cache is emptied
out after two pre-existing ones are done at that time.
The correctly produced output now for the above case is as the following:
      BINLOG '
        base64 encoded data for A
        base64 encoded data for B
      '/*!*/;
        ### verbose section for A
        ### verbose section for B

Thanks to Alexey Midenkov for the problem recognition and attempt to tackle,
and to Venkatesh Duggirala who produced a patch for the upstream whose
idea is exploited here, as well as to MDEV-23077 reporter LukeXwang who
also contributed a piece of a patch aiming at this issue.

1 files changed, 4 insertions, 2 deletions

diff --git a/sql/log_event_old.cc b/sql/log_event_old.cc
index 8ec823d3d64..c71a1f39e28 100644
--- a/sql/log_event_old.cc
+++ b/sql/log_event_old.cc
@@ -1848,6 +1848,7 @@ bool Old_rows_log_event::print_helper(FILE *file,
 {
   IO_CACHE *const head= &print_event_info->head_cache;
   IO_CACHE *const body= &print_event_info->body_cache;
+  IO_CACHE *const tail= &print_event_info->tail_cache;
   bool do_print_encoded=
     print_event_info->base64_output_mode != BASE64_OUTPUT_DECODE_ROWS &&
     print_event_info->base64_output_mode != BASE64_OUTPUT_NEVER &&
@@ -1867,8 +1868,9 @@ bool Old_rows_log_event::print_helper(FILE *file,
   {
     if (copy_event_cache_to_file_and_reinit(head, file) ||
         copy_cache_to_file_wrapped(body, file, do_print_encoded,
-                                     print_event_info->delimiter,
-                                     print_event_info->verbose))
+                                   print_event_info->delimiter,
+                                   print_event_info->verbose) ||
+        copy_event_cache_to_file_and_reinit(tail, file))
       goto err;
   }
   return 0;